What are PP granules, their advantages, applications and usage precautions?

I. The Wonderful Appearance of PP Granules

PP granules are everywhere in every corner of daily life, but we often don't notice them. When the first ray of sunlight shines into the kitchen in the morning, the plastic water cup you pick up is most likely made of PP granules; when preparing breakfast, the transparent and tough texture of the food preservation box is also derived from PP granules; when traveling, the interior parts of the car, such as the dashboard and seat backs, provide you with comfort and safety, and they are also made of PP granules. When you walk into the office, the computer shell, file box, and various stationery are all made of PP granules. Even in the hospital, some medical devices and disposable syringes cannot do without PP granules. These common items in life are all supported by the magical material PP granules, which makes people curious, what exactly is PP granules? Why can it show its prowess in so many fields? Next, let us unveil the mystery of PP granules and explore its world in depth.​

II. Basic concepts and essence of PP particles​

(I) Definition of PP particles​

PP particles, that is, polypropylene particles, are thermoplastic resins formed by polymerization of propylene monomers. From the perspective of microscopic chemical structure, polypropylene molecules are composed of a large number of repeated propylene units connected together. These units are arranged in order along the molecular chain, giving PP unique properties. The carbon atoms on the main chain of the molecule are connected to each other by covalent bonds to form a stable skeleton structure. Each carbon atom is also connected to a hydrogen atom and a methyl side chain. The presence of methyl groups causes a certain amount of steric hindrance in the molecular chain, affecting the regularity and crystallization properties of the molecular chain, and thus has an important impact on the macroscopic properties of PP, such as strength, hardness, and heat resistance. ​

In the huge family of plastics, PP particles occupy a pivotal position and are one of the four general-purpose thermoplastic resins (polyethylene, polyvinyl chloride, polypropylene, and polystyrene). Because of its series of excellent properties, such as good heat resistance, chemical stability, mechanical properties, light weight, easy processing and molding, it is widely used in various fields. From daily necessities to all aspects of industrial production, PP granule products can be seen. It is an indispensable and important material in modern industry and life. ​

(II) Production process of PP granules​

The production of PP granules starts with propylene monomers. Under the action of specific catalysts, polymerization reactions occur between propylene monomers, gradually connecting to form long-chain polypropylene molecules. These molecules gather together to form polypropylene resin. Catalysts play a vital role in this process. They can reduce the activation energy of the reaction, accelerate the polymerization rate, and also have a significant impact on the microstructure and properties of polypropylene. For example, different types of catalysts can be used to prepare polypropylene with different isotacticity and molecular weight distribution, which in turn affects the final performance of PP granules. ​

After the polypropylene resin is formed, it needs to be processed into PP granules that are convenient for subsequent processing. The common method is cutting or granulation. In actual production, there are a variety of production processes to choose from, and each process has its own unique features.​

Slurry process: This is the earliest process technology used to produce polypropylene. From the first industrial unit in 1957 to the mid-to-late 1980s, it was the main polypropylene production process for 30 years. In this process, propylene monomer is dissolved in an inert liquid solvent (such as hexane) and undergoes polymerization under the action of a catalyst. The resulting polymer is suspended in the solvent in the form of solid particles. The reaction is usually carried out in a kettle stirred reactor. After the reaction, the polypropylene particles are separated by centrifugal filtration, and then the final PP particle product is obtained by air flow boiling drying and extrusion granulation. The advantages of this process are that the production process is easy to control and the product quality is good; however, it also has obvious disadvantages. Due to the deashing and solvent recovery steps, the process is long and complicated, the device investment is large, and the energy consumption is high. With the continuous advancement of catalyst technology, the proportion of traditional slurry process in production has gradually decreased. The slurry products currently retained are mainly used in some high-value fields, such as special BOPP films, high relative molecular weight blown films, and high-strength pipes. However, in recent years, improvements have been made to this method. The use of highly active second-generation catalysts can remove the catalyst deashing step and reduce the production of random polymers, making it possible to produce homopolymers, random copolymers and impact copolymer products. ​

Bulk process: Its research and development began in the 1960s. In 1964, Dart Company in the United States built the world's first industrialized bulk polypropylene production unit using a kettle reactor. Compared with the slurry method using solvents, liquid phase bulk polymerization has many advantages. It does not use inert solvents, has a high monomer concentration in the reaction system, a fast polymerization rate, high catalyst activity, high polymerization reaction conversion rate, greater reactor time-space production capacity, low energy consumption, simple process flow, less equipment, low production cost, and less "three wastes"; it is easy to remove polymerization heat, simplify heat removal control, and increase the polymerization amount per unit reactor; it can remove low molecular weight random polymers and catalyst residues that have adverse effects on product properties, thereby obtaining high-quality products. This process can be further divided into kettle bulk method and ring tube bulk method. The kettle bulk method uses a kettle stirred reactor for polymerization reaction; the loop tube bulk method uses a loop tube reactor as the core, and has unique reaction characteristics, such as uniform distribution of reaction temperature and pressure, which can effectively improve product quality and production efficiency. At present, the bulk process occupies an important position in polypropylene production and is a widely used and relatively advanced production process. ​

Gas phase process: In this process, no solvent is introduced into the system, and propylene monomer is polymerized in the reactor in the gas phase. It has a short process, less equipment, safe production process and low production cost. The polymerization reactor mainly includes fluidized bed, vertical stirred bed and horizontal stirred bed. The typical representative of the gas phase bulk method is the Unipol gas phase process of DOW Chemical Company, which is a gas phase fluidized bed polypropylene process developed by Union Carbide Corporation (UCCP) and Shell in the 1980s. It is a fluidized bed process used in polyethylene production that was successfully transplanted to polypropylene production. The gas phase process can flexibly produce polypropylene products with different properties. By adjusting the reaction conditions and catalyst system, PP particles with different melt flow rates, molecular weight distributions and copolymer compositions can be produced to meet diverse market needs. ​

Different production processes have a significant impact on the quality of PP particles. PP particles produced by the slurry method have a relatively mild production process, high isotacticity and good crystallinity, so they have high strength and rigidity and are suitable for manufacturing products with high mechanical properties requirements, such as high-strength pipes; PP particles produced by the bulk method have advantages in production cost and production efficiency, stable product quality, and can be widely used in the production of various general plastic products; PP particles produced by the gas phase method are outstanding in the diversity of product performance and can produce products that meet different special needs, such as PP particles with high melt flow rate, which are suitable for high-speed injection molding processes, can improve production efficiency and reduce production costs.

III. Working principle of PP particles

(I) Molding principle

During the molding process, the state change of PP particles is closely related to the dynamic behavior of the molecular structure. Take injection molding as an example. This is an important process for converting plastic particles into plastic products. In the barrel of the injection molding machine, PP particles undergo a transition from solid to viscous flow. As the barrel temperature rises, heat is gradually transferred to the PP particles, intensifying the molecular thermal motion. When the temperature reaches the melting point of PP (generally around 160-170℃), the intermolecular forces weaken, the molecular chains begin to move relatively freely, and the PP particles gradually melt into a viscous flow state. At this time, the rotation of the screw pushes the viscous flow PP forward, and under the shearing action of the screw, the material is further mixed and evenly mixed, and a certain pressure is obtained. ​

During the injection molding process, precise temperature control is crucial. If the temperature is too high, the thermal motion of the PP molecular chain is too intense, which may lead to molecular chain degradation and reduce the performance of the product, such as reduced strength and poor heat resistance; if the temperature is too low, the PP particles cannot be fully melted and have poor fluidity, which will cause injection molding difficulties and defects such as lack of material and rough surface of the product. Pressure is also a key factor affecting the quality of injection molding. Appropriate pressure can ensure that the viscous PP in the mold cavity is fully filled to form a complete product shape. Excessive pressure may cause flash and excessive internal stress in the product, while too low pressure cannot fill the cavity with materials. ​

When the viscous PP is injected into the mold cavity, the cooling system of the mold begins to work. The mold temperature is low, and heat is transferred from the PP melt to the mold, which gradually slows down the thermal motion of the PP molecules and the molecular chains begin to rearrange and crystallize. As the temperature drops further, the PP melt gradually cools and solidifies, eventually forming a plastic product with a certain shape and size. During the cooling process, the cooling rate also has a significant effect on the performance of the product. A faster cooling rate will result in a lower crystallinity of the product, and the molecular chain arrangement is not regular, resulting in poor strength and rigidity of the product, but it can improve production efficiency; a slower cooling rate is conducive to the formation of products with higher crystallinity and improve the performance of the products, but the production cycle will be extended. ​

Extrusion molding is also one of the commonly used processing methods for PP particles. In the extruder, the PP particles are also heated to a viscous flow state, and through the rotation and extrusion of the screw, they pass through a die of a specific shape to form a continuous profile, such as pipes, plates, sheets, etc. During the extrusion process, the PP molecular chain is oriented under the action of the die and arranged along the extrusion direction, thereby giving the product better mechanical properties in this direction. Calendering molding is to pass the molten PP through the gap between multiple heated rollers, so that it is extended into a thin sheet or film under the pressure and temperature of the rollers. During the calendering process, the PP molecular chain will also be oriented under the action of the rollers, and the parameters such as the temperature, speed and pressure of the rollers have an important influence on the thickness uniformity, surface quality and performance of the product.
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(II) Principles in special applications (taking pneumatic conveying as an example)​

In industrial production, the conveying of PP particles is an important link, and pneumatic conveying is a commonly used conveying method. Pneumatic conveying uses airflow as the conveying medium, generates airflow through compressed air or other gases, and makes the material particles suspended in the airflow or flow in groups along the pipeline, thereby achieving the purpose of long-distance material transportation. ​

Its working process can be divided into several key stages. The first is the feeding stage, when PP particles enter the pneumatic conveying system from storage equipment such as silos. In this process, it is necessary to ensure the uniformity and stability of the feeding to avoid excessive or insufficient feeding, which affects the conveying effect. Usually, some feeding equipment, such as rotary valves, star-shaped unloaders, etc., are used, which can accurately control the supply of PP particles so that they enter the conveying pipeline at a set rate. ​

When the PP particles enter the conveying pipeline, they begin to move under the action of the airflow. The speed and pressure of the airflow are key factors affecting the conveying effect. According to the conveying principle, when the air flow velocity reaches a certain value, it is called the suspension velocity. At this time, the PP particles can overcome their own gravity, suspend in the air flow, and flow with the air flow. In practical applications, in order to ensure that the PP particles can be smoothly conveyed, the air flow velocity is usually higher than the suspension velocity by a certain value. For example, for PP particles with smaller particle size and lighter density, the required suspension velocity is relatively low; while for PP particles with larger particle size and higher density, a higher air flow velocity is required to achieve suspension conveying. ​

During the pneumatic conveying process, there is also the situation of material group conveying. When the material concentration in the conveying pipeline is high, the PP particles may gather together to form a group and move along the pipeline under the impetus of the air flow. This conveying method is more common in some occasions with large conveying volume requirements, but it is necessary to pay attention to controlling the material concentration and air flow parameters to prevent pipeline blockage. For example, in a large plastic processing plant, when a large amount of PP particles are transported from the raw material storage area to the processing workshop, the material group conveying method may be used to improve the conveying efficiency. ​

The pneumatic conveying system is also equipped with separation and dust removal devices. When the PP particles are transported to the destination, they need to be separated from the air flow. Commonly used separation equipment includes cyclone separators and bag dust collectors. The cyclone separator uses centrifugal force to throw PP particles to the wall in the rotating airflow, thereby separating them from the airflow; the bag dust collector intercepts PP particles on the surface of the bag by filtering, and the purified gas is discharged. These separation and dust removal devices can not only ensure the effective collection of PP particles, but also reduce pollution to the environment.

IV. Excellent advantages of PP particles

(I) Physical performance advantages

Strength and hardness: Products made of PP particles are excellent in strength, stiffness and hardness, which enables them to meet strict structural requirements in many application scenarios. From a microscopic perspective, the crystal structure of PP has an important influence on its mechanical properties. In the crystallization region, the molecular chains are closely arranged to form a regular lattice structure. This orderly arrangement enhances the intermolecular forces and gives the material higher strength and hardness. For example, in the automotive industry, PP particles are widely used to manufacture bumpers, instrument panels and other components. Bumpers need to have good impact resistance to absorb and disperse energy when the vehicle collides and protect the safety of the vehicle and passengers. PP materials can meet this requirement through reasonable formula design and molding process. Its high strength and toughness make it not easy to break when hit, and can effectively play a protective role. The instrument panel needs to have a certain stiffness and hardness to ensure its shape stability and installation accuracy. These characteristics of PP materials make it an ideal choice for instrument panel manufacturing.​

In the field of construction, pipes made of PP particles also show excellent performance. PP pipes have high compressive strength and can withstand fluid transportation under a certain pressure. They are widely used in water supply and drainage systems. Their good rigidity makes them not easy to deform when buried underground, and they can work stably for a long time, providing reliable guarantee for the normal operation of buildings. ​

Heat resistance: PP particles have good heat resistance, which is one of their significant advantages compared with many other common plastics. Generally, PP plastic products can be used normally in the temperature range of 100-120℃, and can even withstand high temperatures of 150℃ for a short time without deformation. In contrast, the heat resistance of polyethylene (PE) is relatively low, and its use temperature is generally below 80℃. Above this temperature, PE products are prone to softening and deformation; the heat resistance of polyvinyl chloride (PVC) is also not ideal, usually between 60-80℃. At high temperatures, PVC will release harmful gases and its performance will be significantly reduced. ​

The heat resistance of PP particles comes from its molecular structure and crystallization characteristics. The methyl side chain in its molecular chain increases the steric hindrance between molecules, making the movement of the molecular chain relatively difficult, thereby improving the heat resistance of the material. At the same time, a higher degree of crystallinity also helps to improve the heat resistance of PP. The compact structure of the crystalline region can better resist the effects of heat, reduce the thermal movement of the molecular chain, and maintain the shape and performance of the material. In the field of kitchen supplies, tableware and cooking utensils made of PP materials can be used in high temperature environments. For example, PP lunch boxes for microwave ovens can be directly placed in microwave ovens for heating, which is convenient and fast, and will not release harmful substances due to heat, ensuring food safety and the health of users. In industrial production, PP materials are used to manufacture some equipment parts that need to operate in a higher temperature environment, such as chemical pipelines, heat exchangers, etc., which can withstand the erosion of high temperature media and ensure the smooth progress of industrial production. ​

Electrical properties and insulation: PP particles have excellent electrical properties and insulation properties, which makes them widely used in the field of electronics and electrical. Its electrical insulation performance is almost unaffected by humidity, which is particularly important in a humid environment. From the perspective of electrical properties, PP is a non-polar polymer. There are no polar groups in the molecular structure, and the electron cloud is evenly distributed. This makes the PP material almost non-polarized under the action of the electric field, so it has extremely low dielectric constant and dielectric loss factor. The dielectric constant is a parameter that measures the ability of a material to store electrical energy in an electric field. The dielectric constant of PP is generally between 2.2 and 2.6, which is much lower than many other insulating materials. This means that PP stores less electrical energy in an electric field and can effectively reduce energy loss. The dielectric loss factor reflects the energy loss caused by polarization and conductivity in the alternating electric field. The dielectric loss factor of PP is extremely small, and it can maintain good insulation performance under high-frequency electric fields. ​

In electronic equipment, PP materials are often used to manufacture electrical housings, sockets, plugs, wire and cable insulation layers and other components. Electrical housings need to have good insulation properties to prevent users from electric shock. The high insulation of PP materials can provide reliable safety protection for users. The insulation layer of wires and cables requires materials to have excellent electrical insulation and environmental resistance. PP materials can not only effectively isolate current, but also resist erosion from environmental factors such as moisture and chemicals, ensuring the long-term stable operation of wires and cables. In some fields with extremely high requirements for electrical performance, such as aerospace, electronic communications, etc., PP materials can also meet their strict requirements after special modification, providing important material support for the development of these fields.
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(II) Advantages of chemical properties

Chemical corrosion resistance: PP particles have excellent corrosion resistance to a variety of chemical substances, which makes them show unique application advantages in many fields such as chemical industry and medical treatment. In terms of chemical structure, the carbon atoms in the PP molecular chain form stable covalent bonds with hydrogen atoms and methyl groups. This chemical bond structure makes PP have strong resistance to most chemical reagents. For example, PP has good tolerance to common acid, alkali and salt solutions. In chemical production, many reaction processes involve highly corrosive chemicals. Pipes, storage tanks, reactor linings and other equipment components made of PP materials can effectively resist the erosion of these chemicals and ensure the safety and stable operation of chemical production. In the laboratory, PP reagent bottles, pipette tips, centrifuge tubes and other consumables are widely used. They can hold various chemical reagents and will not react chemically with the reagents, ensuring the accuracy of the experimental results and the safety of the experimental operation. ​

In the medical field, PP materials also play an important role. Medical devices may come into contact with various disinfectants, cleaning agents, human body fluids and other chemical substances during use. The chemical corrosion resistance of PP materials enables them to meet this use requirement of medical devices. For example, disposable syringes are usually made of PP materials. They can not only withstand the immersion disinfection of disinfectants, but also will not react chemically when in contact with human body fluids, ensuring the safety and reliability of medical devices. ​

Stability: PP particles have a high degree of chemical stability and are not easy to react chemically with other substances. This feature allows them to be stored and used for a long time. The structural stability of the PP molecular chain is the basis of its chemical stability. The chemical bonds in its molecular chain are relatively strong and not easily destroyed by external factors. In daily life, we can see many PP products, such as plastic buckets and trash cans. They are exposed to the outdoor environment for a long time, and experience the effects of natural factors such as wind, sun, and rain. They can still maintain the stability of their physical and chemical properties, and are not easy to age, deform or damage. In industrial applications, products made of PP materials can also be used for a long time in various complex chemical environments. For example, in the petrochemical industry, PP materials are used to manufacture pipelines for transporting oil, natural gas and other media. These pipelines need to operate for a long time in harsh chemical environments. The chemical stability of PP materials ensures the service life and safety of the pipelines. ​

(III) Environmental protection and sustainable advantages​

Recyclability: PP particles are a recyclable material, and their recycling is of great significance to environmental protection and sustainable development. The recycling process of PP materials is relatively simple, mainly including collection, classification, cleaning, crushing, granulation and other steps. First, collect discarded PP products through various channels, such as plastic product recycling stations, garbage sorting and recycling systems, etc. Then, the collected waste PP products are classified to remove impurities and other materials to ensure the purity of the recycled PP materials. Next, the classified PP products are cleaned to remove dirt, oil and other pollutants on the surface. The cleaned PP products are crushed into small pieces or fragments for subsequent processing. Finally, the crushed PP materials are reprocessed into PP particles through a granulator, and these recycled PP particles can be used again in the production of plastic products. ​

Recycling PP particles can not only reduce the waste of resources and reduce the demand for new raw materials, but also effectively reduce the environmental pollution caused by landfill and incineration. According to statistics, for every ton of PP particles recycled, about 1.5 tons of oil resources can be saved, while reducing a large amount of carbon dioxide emissions. In the production of plastic products, the use of recycled PP particles can reduce production costs and improve the economic benefits of enterprises. At present, with the improvement of environmental awareness and the continuous development of recycling technology, the recycling rate of PP particles is gradually increasing, and more and more companies and consumers are beginning to pay attention to the recycling of PP materials.
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Degradation characteristics: Under certain conditions, PP particles have certain degradation characteristics, which has a positive effect on reducing white pollution. Although PP is a difficult-to-degrade polymer material, by adding specific degradation agents or using special processing techniques, PP can be gradually degraded in the natural environment. For example, under the irradiation of ultraviolet rays, the molecular chain of PP materials with added photodegradants will gradually break, thereby achieving degradation; PP materials with added biodegradants can be degraded under the action of microorganisms. However, it should be noted that the degradation rate of PP is relatively slow, and the degradation process is affected by many factors, such as ambient temperature, humidity, light intensity, etc. Despite this, the degradation characteristics of PP particles under certain conditions still provide a feasible way to solve the problem of white pollution. In some occasions where the use cycle of plastic products is short and the environmental requirements are high, such as disposable tableware, agricultural mulch, etc., degradable PP materials can be used to reduce the long-term impact of discarded plastic products on the environment. With the continuous advancement and improvement of degradation technology, it is believed that PP materials will achieve greater breakthroughs in degradation performance and make greater contributions to environmental protection. ​

(IV) Cost advantage​

PP particles have significant advantages in terms of cost, thanks to its wide range of raw material sources and simple production processes. Propylene, the raw material for PP, is a common petrochemical product that can be obtained through the processing of fossil energy such as oil and natural gas. Oil and natural gas are abundant in reserves worldwide and the supply is relatively stable, which makes the source of propylene wide and the price relatively stable. Compared with some other high-performance plastics, the cost of raw materials for PP is lower. For example, the price of bisphenol A, the raw material for polycarbonate (PC), is high, and the production process is complicated, resulting in a relatively high cost of PC; while the price of paraxylene, the raw material for polyphenylene sulfide (PPS), fluctuates greatly, and the synthesis process is difficult, making the cost of PPS high.​

From the perspective of production technology, the production process of PP particles is relatively simple. Whether it is slurry method, bulk method or gas phase method, these processes have been developed to a relatively mature level, the equipment investment is relatively small, and the production process is easy to control. In contrast, the production process of some special plastics is complex, requiring special equipment and technology, and the energy consumption and raw material consumption in the production process are also high, resulting in a significant increase in their production costs. For example, the production of polyimide (PI) requires special conditions such as high temperature and high pressure, and the production equipment is expensive and the production process is complex, making the cost of PI much higher than that of PP. ​

The low cost of PP particles gives it a clear economic advantage in large-scale applications. In the plastic products market, cost is one of the important factors affecting product competitiveness. Due to the low cost of PP particles, plastic product manufacturers can reduce production costs and improve the market competitiveness of their products. In the packaging industry, packaging products such as plastic bags and plastic bottles made of PP are inexpensive and can meet the packaging needs of a large number of commodities; in the construction field, PP pipes, pipe fittings and other products have low costs and are widely used in building water supply and drainage systems, reducing the cost of construction projects. In other fields, such as household items, toys, office supplies, etc., the low cost of PP materials also makes these products highly cost-effective and popular among consumers.

V. Instructions for use of PP granules

(I) Key points for different processing methods

Injection molding: Injection molding is one of the important methods for processing PP granules. Its process flow is relatively complex and requires strict control of each link. The first is mold design, which is the key prerequisite for injection molding. The structural design of the mold should be optimized according to the shape, size and precision requirements of the plastic product to ensure that the plastic product can be smoothly molded. For example, for plastic products with complex shapes, such as dashboards in automotive interiors, the core and cavity structures of the mold need to be carefully designed to ensure that the details of the plastic product can be clearly presented. The material selection of the mold is also crucial. Generally, high-strength and wear-resistant steels such as P20 and 718 are selected to ensure that the mold maintains good dimensional stability and surface quality during long-term injection molding production. ​

In the injection molding process, temperature control is one of the key factors affecting the quality of plastic products. The barrel temperature needs to be accurately set according to the characteristics of PP granules and the requirements of plastic products. Generally speaking, the temperature of the front section of the barrel is relatively high, which can be set at 200-230℃ to ensure that the PP particles are fully melted; the temperature of the middle section of the barrel is moderate, about 180-200℃, which is used to further plasticize the material; the temperature of the rear section of the barrel is relatively low, at 160-180℃, mainly to prevent the material from melting too early and causing uneven plasticization. The mold temperature also needs to be strictly controlled, usually between 30-80℃. Lower mold temperature can speed up the cooling speed of plastic products and improve production efficiency, but it may cause the surface quality of plastic products to deteriorate, such as defects such as flow marks and silver streaks; higher mold temperature helps to improve the surface quality of plastic products, improve the crystallinity and dimensional stability of plastic products, but it will prolong the production cycle. ​

Injection pressure is also an important parameter in injection molding. The size of injection pressure directly affects the filling effect and dimensional accuracy of plastic products. In the early stage of injection molding, in order to make the molten PP quickly fill the mold cavity, a higher injection pressure is required, generally between 80 and 150MPa; when the mold cavity is close to full, the injection pressure should be appropriately reduced to avoid problems such as flash and overflow in plastic products, and reduce the internal stress of plastic products. Holding pressure and holding time also have an important impact on the quality of plastic products. The holding pressure is generally 60%-80% of the injection pressure, and the holding time is usually between 5 and 20 seconds. The specific value needs to be adjusted according to factors such as the thickness, size and shape of the plastic product. Appropriate holding pressure and holding time can compensate for the shrinkage of plastic products during the cooling process and improve the density and dimensional accuracy of plastic products.
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The choice of injection speed also needs to be carefully considered. High-speed injection molding can improve production efficiency and reduce the molding cycle of plastic products, but it may cause defects such as weld marks and trapped air in plastic products; low-speed injection molding can improve the surface quality of plastic products and reduce the occurrence of defects, but it will reduce production efficiency. In actual production, the appropriate injection speed should be selected according to the specific situation of the plastic product, and multi-stage injection speed control can be used to optimize the molding quality of the plastic product. ​

Extrusion molding: Extrusion molding is the process of processing PP particles into continuous profiles such as pipes, plates, sheets, etc. through an extruder. In extrusion molding, the selection of equipment is crucial. Parameters such as the screw diameter, aspect ratio, and screw groove depth of the extruder will affect the material conveying, plasticization, and extrusion effects. For different product requirements, an extruder of appropriate specifications should be selected. For example, when producing large-diameter pipes, it is necessary to select an extruder with a larger screw diameter and a smaller aspect ratio to ensure sufficient extrusion volume and sufficient plasticization of the material; while when producing thin-walled plates, it is necessary to select an extruder with a smaller screw diameter and a larger aspect ratio to achieve precise extrusion control and good plate quality. ​

Screw speed is one of the key operating points in extrusion molding. The screw speed directly affects the residence time and plasticization effect of the material in the extruder. Generally speaking, the higher the screw speed, the shorter the residence time of the material in the extruder, the worse the plasticizing effect may be, but the extrusion volume will increase; the lower the screw speed, the longer the material stays in the extruder, the better the plasticizing effect, but the extrusion volume will decrease. Therefore, it is necessary to reasonably adjust the screw speed according to the characteristics of the PP particles, product requirements and the performance of the extruder to achieve the best extrusion effect. For example, for PP particles with good fluidity, the screw speed can be appropriately increased to improve production efficiency; while for PP particles with poor fluidity, the screw speed needs to be reduced to ensure that the material is fully plasticized. ​

Temperature distribution also plays an important role in extrusion molding. The barrel of the extruder is usually divided into multiple heating zones, and the temperature of each heating zone should be reasonably set according to the plasticization process of the material. Generally speaking, the temperature of the feeding section of the barrel is relatively low, about 160-180℃, which is mainly used to preheat the material; the temperature of the compression section gradually increases, between 180-200℃, to further compact and plasticize the material; the temperature of the metering section is the highest, between 200-230℃, to ensure that the material is fully melted and evenly mixed. The temperature of the die head and the die also needs to be precisely controlled, generally slightly lower than the temperature of the metering section, between 190-220℃, to ensure the dimensional accuracy and surface quality of the extruded profile. If the temperature of the die head and the die is too high, the profile will expand and become larger; if the temperature is too low, the profile surface will be rough, and even extrusion will be difficult. ​

During the extrusion molding process, the process needs to be adjusted according to different product requirements. For example, when producing pipes, the traction speed and cooling method of the extruder need to be controlled. The pulling speed should match the extrusion speed to ensure the dimensional accuracy and tensile properties of the pipe; the cooling method generally adopts water cooling or air cooling, and the cooling speed should be moderate. Too fast cooling speed will cause stress inside the pipe and affect the performance of the pipe. When producing sheets, it is necessary to pay attention to the thickness control and surface flatness of the sheet. The thickness of the sheet can be controlled by adjusting parameters such as the die gap, extrusion speed and pressure of the three-roll calender; the surface flatness of the sheet can be improved by optimizing the screw structure and heating system of the extruder and adopting a suitable die head design.
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Calendering: Calendering is the process of passing the molten PP through the gap between multiple heated rollers to extend it into a thin sheet or film. The equipment for calendering mainly includes calender, preheating device, cooling device and winding device. The calender is the core equipment, and the temperature and speed control of its rollers play a key role in the quality of calendering.
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The temperature of the calender roller needs to be strictly controlled. Generally speaking, the temperature of the first few rollers of the calender is relatively high, about 180-200℃, which is mainly used to fully melt and plasticize the PP material; the temperature of the subsequent rollers gradually decreases, between 150-180℃, and is used to cool and shape the calendered products. If the roller temperature is too high, the PP material will be over-plasticized, the mechanical properties of the calendered product will decrease, and the roller sticking phenomenon may also occur; if the roller temperature is too low, the PP material will be unevenly plasticized, and the surface of the calendered product will be rough and uneven. The temperature distribution of the roller should also be uniform, otherwise it will cause uneven thickness of the calendered product. ​

The speed control of the roller is equally important. There needs to be a certain speed difference between adjacent rollers, that is, the speed ratio, to ensure that the PP material is subjected to a certain stretching and shearing effect between the rollers, so that the calendered product has good performance and dimensional accuracy. Generally speaking, the speed ratio is controlled between 1.05-1.2, and the specific value needs to be adjusted according to the characteristics of the PP material and the requirements of the calendered product. If the speed ratio is too small, the material will not be subjected to sufficient stretching and shearing, and the strength and dimensional stability of the calendered product will be poor; if the speed ratio is too large, the internal stress of the calendered product will increase, and problems such as warping and cracking will occur easily. ​

During the calendering process, the material formula adjustment should not be ignored. In order to meet different product requirements, the formula of PP materials needs to be optimized. For example, in order to improve the transparency of the calendered product, an appropriate amount of nucleating agent can be added; in order to enhance the flexibility of the calendered product, a plasticizer can be added; in order to improve the heat resistance of the calendered product, a heat-resistant modifier can be added. In addition, according to the requirements of the calendering process, the fluidity and melt strength of the material need to be adjusted to ensure that the material can pass through the roller gap smoothly during the calendering process and form a calendered product of good quality.

(II) Application fields and product examples

Packaging industry: In the packaging industry, PP particles are ubiquitous and play an indispensable and important role. Plastic bags made of PP particles have become one of the most common packaging materials in daily life and commercial activities due to their advantages of light weight, low cost and good flexibility. In supermarkets, most of the various foods and daily necessities we buy are packaged in PP plastic bags, which are not only convenient to carry, but also effectively protect the goods from the influence of the external environment. Cling film is also one of the important applications of PP particles. Its good tensile and barrier properties can tightly wrap food to prevent food from getting damp and deteriorating, and extend the shelf life of food. Whether in home kitchens or the catering industry, PP cling film has been widely used. ​

Food containers made of PP particles occupy an important position in the field of food packaging. These food containers are non-toxic, odorless, and high temperature resistant, and can be used to hold various foods, such as yogurt cups, fast food boxes, sauce bottles, etc. When heating food in a microwave oven, PP food containers can withstand high temperatures without releasing harmful substances, ensuring food safety and the health of users. At the same time, PP food containers have good transparency, allowing consumers to clearly see the food in the container, improving the display effect of the product. ​

The wide application of PP particles in the packaging industry not only improves the efficiency and quality of packaging, but also reduces packaging costs and meets the market's diversified demand for packaging materials. With the continuous improvement of environmental awareness, recyclable PP packaging materials are increasingly favored by consumers, making an important contribution to the sustainable development of the packaging industry. ​

Automobile industry: In the automotive industry, the application of PP particles has brought revolutionary changes to the lightweight and performance improvement of automobiles. Automobile interior parts made of PP particles, such as dashboards, door panels, seats, etc., not only have good aesthetics and comfort, but also can effectively reduce the weight of the car and reduce fuel consumption. As an important part of the car interior, the dashboard needs to have high strength and dimensional stability to ensure the normal installation and use of various instruments and control devices. PP materials can meet these performance requirements of dashboards by adding appropriate reinforcing agents and additives, and their good molding and processing performance makes the design of dashboards more diversified. ​

Automobile bumpers are also one of the important application areas of PP particles. When a car collides, the bumper needs to be able to absorb and disperse energy to protect the safety of the vehicle and passengers. PP materials have high toughness and impact resistance. Through reasonable formula design and molding process, bumpers with good energy absorption effect can be manufactured. Compared with traditional metal bumpers, PP bumpers are not only lighter, but also have better corrosion resistance and cost advantages. ​

Fan blades made of PP particles play an important role in the cooling system of automobile engines. Fan blades need to maintain good strength and dynamic balance performance under high-speed rotation. PP materials can meet these performance requirements of fan blades through modification methods such as fiber reinforcement. At the same time, the lightweight design of PP fan blades helps to reduce the load of the engine and improve fuel economy.​

The application of PP particles in the automotive industry not only achieves the lightweight of automobiles, reduces energy consumption and exhaust emissions, but also improves the performance and safety of automobiles, providing strong support for the development of the automotive industry. With the continuous advancement of automobile technology, the application prospects of PP particles in the automotive field will be broader. ​

Construction industry: In the construction industry, PP particles have become an ideal choice for many building materials due to their excellent performance. Pipe systems made of PP particles, such as water supply pipes, drainage pipes, floor heating pipes, etc., have the characteristics of corrosion resistance, wear resistance, high temperature resistance, and low temperature resistance, and can operate stably for a long time in various complex environments. PP water supply pipes have good hygienic properties, will not pollute water quality, and meet the standards for drinking water transportation. Its inner wall is smooth and the water flow resistance is small, which can effectively improve the water supply efficiency. PP drainage pipes have strong corrosion resistance, can resist the erosion of various chemicals in sewage, and extend the service life of the pipes. Floor heating pipes need to work for a long time in high temperature environments. The high temperature resistance of PP materials enables them to meet the requirements of floor heating systems and provide users with a comfortable heating experience.​

Waterproof materials made of PP particles also play an important role in the field of building waterproofing. PP waterproofing membranes have good water resistance, weather resistance and puncture resistance, which can effectively prevent moisture from penetrating into the interior of the building and protect the structural safety of the building. PP waterproofing membranes have been widely used in roofs, basements, bathrooms and other places prone to leakage. Compared with traditional asphalt waterproofing membranes, PP waterproofing membranes have the advantages of convenient construction and environmental protection and pollution-free. ​

Insulating materials made of PP particles are indispensable in building electrical systems. PP insulating materials have good electrical insulation and flame retardant properties, which can effectively prevent electrical accidents. PP insulating materials have been widely used in the insulation layer of wires and cables, the outer shell of switches and sockets, etc. Its good molding and processing performance makes the manufacture of insulating materials more convenient and less costly. ​

The application of PP particles in the construction industry has improved the performance and quality of building materials, extended the service life of buildings, and made important contributions to the development of the construction industry. With the continuous development of construction technology and the improvement of people's requirements for building quality, the application of PP particles in the construction field will continue to expand.​

Household items: In the field of household items, PP particles have brought great convenience and beauty to our lives. Furniture made of PP particles, such as chairs, tables, storage racks, etc., are light, strong, easy to clean, and are deeply loved by consumers. PP chairs are not only diverse in shape and can meet different home decoration styles, but also light in weight, easy to move and use. Its sturdy structure can withstand a large weight, ensuring the safety of use. PP tables have good stability and wear resistance, smooth surface, and are easy to clean. They are ideal for family dining and office. ​

Storage boxes are also one of the common applications of PP particles. PP storage boxes have a large capacity and good sealing, which can effectively store clothes, sundries, etc., and keep the home environment clean and orderly. Its lightweight material makes the storage box easy to carry and store, and it can be stacked as needed to save space. In every corner of the home, such as the bedroom, living room, kitchen, etc., PP storage boxes play an important role. ​

Toys made of PP particles are even better partners for children. PP toys are non-toxic, odorless, and resistant to falling, ensuring the safety of children's play. Its rich colors and diverse shapes can stimulate children's imagination and creativity. Whether it is plastic building blocks, toy cars or the internal fillings of plush toys, PP particles play an important role in them. ​

The application of PP particles in the field of household goods not only improves the practicality and aesthetics of household goods, but also brings more convenience and fun to our lives. With the improvement of people's living standards and the continuous improvement of home quality requirements, the application of PP particles in the field of household goods will be more extensive. ​

Electronics industry: In the electronics industry, PP particles have become an indispensable material in the manufacture of electronic products with their excellent performance. Electronic product shells made of PP particles, such as mobile phone shells, computer main shells, tablet computer shells, etc., not only have good appearance and texture, but also effectively protect internal electronic components. PP materials have certain strength and toughness, can withstand a certain degree of collision and extrusion, and prevent electronic components from being damaged. At the same time, its good molding and processing performance makes the design of electronic product shells more diversified, which can meet the aesthetic needs of different consumers.
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Connectors made of PP particles play an important role in connecting various electronic components in electronic devices. Connectors need to have good electrical and mechanical properties. PP materials can meet these performance requirements of connectors by adding appropriate conductive agents and reinforcing agents. Its good corrosion resistance and temperature resistance can ensure that connectors work stably in various environments and ensure the normal operation of electronic equipment. ​

Insulating materials made of PP particles are also widely used in the electronics industry. In electronic components such as circuit boards and transformers, PP insulating materials can effectively isolate current and prevent electrical accidents such as leakage and short circuit. Its good insulation and flame retardant properties provide reliable guarantees for the safe operation of electronic equipment. ​

The application of PP particles in the electronics industry not only improves the performance and quality of electronic products, but also provides strong support for the development of the electronics industry. With the continuous advancement of electronic technology and the trend of miniaturization and lightweight development of electronic products, the application prospects of PP particles in the electronics field will be broader.

VI. Precautions for the use of PP particles

(I) Precautions during processing

Temperature control: During the processing of PP particles, temperature control is like accurately controlling the rhythm of a chemical reaction, which is the core element to ensure product quality. The processing temperature of PP particles is usually between 180-260℃. However, this is not an absolutely fixed value, but will fluctuate due to the specific brand of PP particles, the type and content of additives, and the differences in processing technology and equipment. For example, for some PP particles with high melt flow rate, the processing temperature may be relatively low to avoid excessive degradation of the molecular chain at too high a temperature, affecting product performance; for PP particles containing special additives or modified, it is necessary to adjust the processing temperature appropriately according to the characteristics of the additives or modified components to ensure the effectiveness of the additives and the good compatibility of PP particles with other components. ​

The impact of excessive temperature on product quality is multifaceted and serious. When the temperature exceeds the appropriate range, the thermal motion of the PP molecular chain becomes extremely violent, and the chemical bonds between molecules may break during this high-intensity motion, resulting in the degradation of the PP molecular chain. This will not only reduce the molecular weight of the PP particles, but also change its molecular weight distribution, thereby affecting the physical properties of the product. The strength and toughness of the product will be significantly reduced, and the originally strong and durable plastic products may become fragile and brittle, unable to meet the actual use requirements. The heat resistance of the product will also be negatively affected, and deformation and softening may occur at normal use temperatures, which seriously limits the application scenarios of the product. In addition, excessively high temperatures may also trigger oxidation reactions of PP particles, accelerate the aging of materials, make the product surface yellow and brittle, and shorten the service life of the product. ​

On the contrary, too low a temperature will also bring many hidden dangers to product quality. PP particles cannot be fully melted, the fluidity of the material is extremely poor, and it is difficult to evenly fill the mold cavity or pass through the die during processing, resulting in defects such as lack of material, rough surface, and poor dimensional accuracy in the product. These defects not only affect the appearance quality of the product, but also may reduce the functionality and reliability of the product. For example, during the injection molding process, too low a temperature may cause obvious flow marks, silver threads and other defects on the surface of plastic products, affecting the aesthetics of the product; during the extrusion molding process, too low a temperature will cause the surface of profiles such as pipes and plates to be rough, the internal structure to be uneven, and its mechanical properties and performance to be reduced. ​

Avoid impurities: Keeping the production environment clean is crucial to prevent impurities from mixing into PP particles. The production workshop should be cleaned and disinfected regularly, and the floor should be kept clean and free of dust, debris and other debris. The surface of the equipment should also be wiped frequently to prevent dust and oil from adhering to the equipment and falling into the PP particles during the production process. The ventilation system should be maintained and cleaned regularly to ensure that the exhaust air does not contain impurities to prevent them from re-entering the production environment. For example, in some industries such as electronics and medical that have extremely high requirements for the purity of PP particles, production workshops usually use dust-free purification technology to strictly control the number of dust particles in the air and provide a clean environment for the production of PP particles. ​

Before using PP particles, screening of raw materials is an essential link. Vibrating screens, filters and other equipment can be used to screen PP particles to remove large impurities and foreign matter that may exist in them. Vibrating screens can separate particles and impurities that do not meet the requirements through screens with different apertures; filters can use the filtering effect of the filter to block the passage of impurities. For some special-purpose PP particles, more sophisticated screening methods, such as magnetic separation and electrostatic separation, can also be used to further remove magnetic impurities and fine metal particles. For example, when producing PP particles for manufacturing electronic component housings, magnetic separation technology can effectively remove magnetic impurities such as iron filings that may exist in the raw materials, so as to avoid these impurities from affecting the performance of electronic components. ​

Impurities mixed into PP particles will have a serious negative impact on product quality. The presence of impurities will destroy the molecular structure and uniformity of PP particles, resulting in stress concentration points inside the product. When the product is subjected to external forces, these stress concentration points are prone to cause cracks to form and expand, thereby reducing the strength and toughness of the product. Impurities may also affect the processing performance of PP particles, making the processing process unstable, resulting in problems such as clogging the mold and die, and reducing production efficiency. For example, during the injection molding process, mixed impurities may get stuck in the gap of the mold, resulting in defects such as flash and burrs on plastic products; during the extrusion molding process, impurities may clog the die, causing problems such as broken strips and uneven thickness of the extruded profile. ​

Equipment maintenance: Regular maintenance and care of processing equipment is an important guarantee to ensure the smooth processing of PP particles and stable product quality. Equipment maintenance covers many aspects, including cleaning, lubrication, inspection and replacement of wearing parts. Cleaning is the basic work of equipment maintenance. Regularly remove PP particle residues, oil stains and other impurities on the surface and inside of the equipment to prevent their accumulation from affecting the normal operation of the equipment. For example, the screw, barrel, head and die of the extruder should be thoroughly cleaned after each production to avoid the solidification of residual materials and affect the material flow and plasticization effect during the next production. ​

Lubrication is essential for the normal operation of equipment. The transmission parts, bearings, screws and other parts of the equipment need to be regularly added with appropriate lubricants to reduce friction and wear, reduce the energy consumption of the equipment, and extend the service life of the equipment. When selecting lubricants, it is necessary to make reasonable choices based on the working conditions, temperature, load and other factors of the equipment to ensure that the lubricants have good lubrication, anti-oxidation and anti-wear properties. For example, for equipment working in a high temperature environment, a high temperature resistant lubricant should be selected; for high-speed running parts, a low viscosity, high wear resistance lubricant should be selected.

Regularly checking the various parts of the equipment and timely discovering and solving potential problems are the key links in equipment maintenance. The inspection content includes the mechanical structure, electrical system, heating system, cooling system, etc. of the equipment. When checking the mechanical structure, pay attention to whether the connection of each component is firm, whether there is looseness, deformation, etc.; when checking the electrical system, check whether the wires are aging, damaged, and whether the electrical components are working properly; when checking the heating system, ensure the accuracy and reliability of components such as temperature sensors and heating rods; when checking the cooling system, check whether the cooling water pipe is blocked or leaking, and whether the cooling water pump is operating normally. For example, in the maintenance of the injection molding machine, regularly check the mechanical parts of the mold such as the opening and closing mechanism and the ejection mechanism to ensure their smooth movement; check the electrical control system of the injection molding machine to ensure the normal operation of various control buttons, relays and other components to avoid control failure. ​

Timely replacement of wearing parts is also an important part of equipment maintenance. During the long-term operation of the processing equipment, some parts will gradually lose their original performance due to wear and fatigue, such as screws, barrels, molds, filters, etc. When the wear degree of these wearing parts reaches a certain limit, they need to be replaced in time to ensure the normal operation of the equipment and the stability of product quality. For example, the screw of the extruder will gradually wear out under the long-term rotation and friction of the material, resulting in poor material transportation and plasticization effects. At this time, a new screw needs to be replaced; during the multiple opening and closing and injection processes of the injection molding machine mold, the cavity surface will be worn and strained, which will affect the dimensional accuracy and surface quality of the plastic products. Therefore, the mold needs to be repaired or replaced regularly.

(II) Precautions in product use

Applicable environment: PP granule products have a certain range of applicable environmental conditions. Understanding and following these conditions is essential to ensure the normal use of the product and extend its service life. In terms of temperature, under normal circumstances, the long-term use temperature range of PP granule products is -20-100℃. Within this temperature range, PP materials can maintain good physical properties and chemical stability, and the product can function normally. When the temperature is below -20℃, the flexibility of PP materials will decrease significantly, becoming hard and brittle, and easily cracked when impacted by external forces. For example, in the cold winter, if PP plastic pipes used outdoors are not properly insulated, they may crack due to low temperature, causing water leakage in the pipes. When the temperature is higher than 100℃, the crystal structure of the PP material will gradually change, the thermal motion of the molecular chain will intensify, the dimensional stability and mechanical properties of the product will be affected, and deformation and softening may occur. For example, if ordinary PP plastic tableware is placed in a high-temperature disinfection cabinet for disinfection, the temperature in the disinfection cabinet is usually high, exceeding the heat resistance limit of the PP material, and the tableware may be deformed and cannot be used normally. ​

Humidity is also one of the important factors affecting the performance of PP granule products. PP material has a certain hygroscopicity. In a high humidity environment, PP granule products may absorb moisture from the air. Excessive moisture will have a negative impact on the performance of PP materials, resulting in a decrease in the strength and toughness of the product. Moisture may also form bubbles inside the product, affecting the appearance quality and dimensional accuracy of the product. For example, PP plastic products used in a humid environment, such as plastic packaging boxes and plastic containers, may appear white on the surface, bubbling, etc. if they are exposed to high humidity air for a long time, reducing the beauty and practicality of the product. Therefore, PP granule products are suitable for use in an environment with a relative humidity of less than 80%. ​

In some special environments, such as strong ultraviolet radiation, chemical corrosion, etc., the performance of PP granule products will also be affected to varying degrees. PP plastic products used outdoors are exposed to ultraviolet rays for a long time, and the molecular chains will break and degrade, causing the products to age, discolor, and become brittle. In order to improve the weather resistance of PP products in outdoor environments, UV absorbers, antioxidants and other additives can be added to PP materials. These additives can effectively absorb ultraviolet rays, inhibit the degradation of molecular chains, and extend the service life of the products. In a chemically corrosive environment, PP granular products may react with certain chemicals, resulting in a decrease in the performance of the material. For example, PP materials have a certain tolerance to certain organic solvents, strong acids and alkalis, but if they are exposed to high concentrations of these chemicals for a long time, swelling, corrosion, etc. may still occur. Therefore, when using PP granular products, avoid contact with chemicals that may corrode them. ​

Avoid contact with special substances: During the use of PP granular products, avoid contact with some special substances that may react with them or affect their performance. Some organic solvents have a dissolving or swelling effect on PP materials, which will destroy the molecular structure of PP materials and cause product performance degradation. For example, organic solvents such as acetone, toluene, and carbon tetrachloride can cause PP materials to swell, increase their volume, and reduce their strength. If PP plastic products are exposed to these organic solvents for a long time, they may deform or crack. Therefore, when using PP granular products, avoid direct contact with these organic solvents. In chemical production, if PP containers are needed to store or transport liquid materials, make sure that the materials do not contain organic solvents that dissolve PP. Corrosive chemicals such as strong acids and strong alkalis can also damage PP granular products. Although PP materials have a certain degree of chemical corrosion resistance, their surfaces will be corroded in high-concentration strong acid and alkali environments, causing changes in the appearance and performance of the product. For example, strong acid and alkali solutions such as concentrated sulfuric acid, concentrated nitric acid, and sodium hydroxide will react chemically with PP materials, causing the surface of PP materials to become rough, lose gloss, and even have holes and cracks. In the laboratory, if PP experimental equipment is used to contain strong acid and alkali solutions, it is necessary to be extra careful to avoid corrosion to the equipment caused by leakage of the solution, and also to pay attention to protection to avoid harm to personnel. ​

In addition, some highly oxidizing substances, such as potassium permanganate and hydrogen peroxide, may also react with PP granular products. These highly oxidizing substances can oxidize the molecular chains in the PP material, causing degradation and aging, and reducing the performance of the product. When using PP granular products, avoid contact with these highly oxidizing substances. In the medical industry, some disinfectants may have strong oxidizing properties. When using medical devices made of PP materials, pay attention to choosing appropriate disinfectants and disinfect them according to the correct usage method to avoid damage to the equipment caused by the disinfectant. ​

Product life and replacement: The normal service life of PP granular products is affected by a combination of factors, including the use environment, frequency of use, load conditions, etc. Under normal use conditions, such as normal indoor temperature, normal pressure, low humidity and no contact with special chemicals, daily necessities made of PP granules, such as plastic tableware and plastic toys, can usually last for several years. Taking plastic tableware as an example, if it is used in daily household use and is careful to avoid high temperature, collision and chemical erosion, it can generally be used for 3-5 years. However, if the use environment is relatively harsh, such as in high temperature, high humidity, strong ultraviolet rays or chemical corrosion environment, the life of PP granule products will be significantly shortened. For example, PP plastic trash cans used outdoors may only have a service life of 1-2 years due to long-term exposure to sunlight, wind and rain, and erosion by chemicals in various garbage. ​

To determine whether PP granule products need to be replaced, you can observe and evaluate from multiple aspects. In terms of appearance, if the product has obvious deformation, cracking, discoloration, aging, etc., it means that its performance has been seriously affected and may need to be replaced. For example, if a PP plastic bucket is deformed, leaking, or has a yellowing and brittle surface, it should be replaced in time to ensure safe use and normal function. In terms of performance, if the strength, toughness, sealing and other properties of the product decline and cannot meet the use requirements, it is also necessary to consider replacement. For example, if a PP plastic fresh-keeping box loses its good sealing and cannot effectively preserve food, it should be replaced with a new fresh-keeping box. In addition, it can also be judged based on the use time of the product. If the product has reached or exceeded its expected service life, it is recommended to replace it even if there are no obvious problems with the appearance and performance to prevent potential safety hazards. In industrial production, for PP plastic products used in some key parts, such as chemical pipelines and reactor linings, strict replacement cycles are usually formulated to ensure the safety and stability of the production process.

VII. Development prospects and trends of PP particles

(I) Direction of technological innovation

In terms of modification technology, improving the impact resistance of PP particles is an important research direction. Traditional PP materials have poor impact resistance in low temperature environments and are prone to brittle fracture, which limits their application in some fields that require high material toughness. In order to solve this problem, researchers have modified PP by adding rubber toughening agents, nanoparticles, etc. For example, rubber toughening agents such as ethylene-propylene rubber (EPR) and ethylene-octene copolymer (POE) are blended with PP. Rubber particles can act as stress concentration points in the PP matrix. When the material is impacted, the rubber particles can induce silver streaks and shear bands, absorb impact energy, and thus improve the impact resistance of PP. Nanoparticles are also widely used in the modification of PP due to their unique size effect and surface effect. Nanoparticles such as nano calcium carbonate and nano montmorillonite can be evenly dispersed in the PP matrix and form a strong interaction with the PP molecular chain, which can not only improve the impact resistance of PP, but also improve its strength, rigidity and other properties.
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Improving the low-temperature performance of PP particles is also a key focus of modification technology. Through copolymerization modification, the introduction of other monomers to copolymerize with propylene can destroy the regularity of the PP molecular chain and reduce its crystallinity, thereby improving the flexibility and impact resistance of PP at low temperatures. For example, by using the method of ethylene-propylene random copolymerization, the introduction of ethylene monomer into the PP molecular chain can reduce the glass transition temperature of PP and improve its low-temperature performance. In terms of production process optimization, the research and development and application of new catalysts are the key to improving the performance and production efficiency of PP particles. At present, Ziegler-Natta catalysts and metallocene catalysts are commonly used catalyst systems in PP production. Ziegler-Natta catalysts have the advantages of high activity and low production cost, but there are problems such as uneven catalytic active centers and wide product molecular weight distribution. Metallocene catalysts have the advantages of high catalytic activity, single active center, and precise control of the molecular structure and performance of polymers, and can produce PP products with narrow molecular weight distribution and high stereoregularity. In the future, as the requirements for catalyst performance continue to increase, researchers will focus on developing new catalysts that are more efficient, environmentally friendly, and highly selective to further improve the performance and production efficiency of PP particles. ​

(II) Market demand forecast​

From the perspective of industry development trends, with the continuous development of the global economy and the improvement of people's living standards, the demand for plastic products in various industries continues to grow, which will directly drive the increase in market demand for PP particles. In the packaging industry, with the vigorous development of e-commerce, the demand for PP particles in express packaging, food packaging and other fields has shown a rapid growth trend. According to relevant market research institutions, in the next few years, the global packaging industry's demand for PP particles will grow at an annual rate of 5%-8%. In the automotive industry, in order to meet the requirements of energy conservation, emission reduction and fuel economy, lightweighting of automobiles has become an inevitable trend of development. As a lightweight and high-strength material, PP particles will be more and more widely used in automotive parts. It is expected that in the next 5-10 years, the demand for PP particles in the automotive industry will maintain a high growth rate. ​

The emergence of emerging application fields has also brought new opportunities to the PP particle market. With the popularization of 5G communication technology and the rapid development of the Internet of Things, the demand for high-performance plastics in the electronics and electrical industry is growing. After modification, PP particles have good electrical insulation properties, dimensional stability and processing properties, and can be used to manufacture 5G base station equipment, electronic component housings, smart home appliance parts and other products. In the medical field, as people pay more attention to medical health, the demand for PP particles in industries such as medical devices and medical packaging is also gradually increasing. Especially in the field of disposable medical devices, PP particles have become an ideal material choice with their advantages of non-toxicity, odorlessness, easy processing and low cost. ​

Based on the above industry development and the emergence of emerging application fields, it is expected that the market size of PP particles will continue to expand in the future. Globally, the Asia-Pacific region is the largest consumer market for PP particles. With the rapid development of emerging economies such as China and India, its market demand will maintain a strong growth trend. At the same time, the demand for PP particles in Europe and North America will also maintain steady growth, mainly due to its continued development in high-end manufacturing and emerging technology fields. According to market research institutions, by 2030, the global PP particle market size is expected to reach more than US$100 billion, with an annual compound growth rate of 6%-8%. ​

(III) Outlook on the impact on sustainable development​

In terms of environmental protection, PP particles have the characteristics of recyclability, which makes them have important potential in sustainable development. With the continuous improvement of environmental awareness and the increasingly stringent environmental regulations, the recycling rate of PP particles will be further improved. In the future, researchers will focus on developing more efficient recycling technologies and equipment to improve the quality and performance of recycled PP particles, so that they can better replace virgin PP particles and be applied in more fields. For example, by improving the recycling process, impurities and pollutants in the recycled PP particles can be removed to improve their purity and stability; advanced modification technology can be used to improve the performance of recycled PP particles to meet the requirements of high-end products. ​

Developing more environmentally friendly production processes is also an important direction for the sustainable development of the PP particle industry. At present, some PP particle manufacturers have begun to adopt green chemical processes to reduce energy consumption and waste emissions in the production process. For example, new catalysts and reaction systems are used to reduce the temperature and pressure of polymerization reactions and reduce energy consumption; solvent-free or low-solvent production processes are developed to reduce the use of organic solvents and reduce environmental pollution. In the future, with the continuous advancement of science and technology, more environmentally friendly production processes will be applied to the production of PP particles to further reduce their impact on the environment. ​

Under the background of sustainable development, the PP particle industry will also strengthen cooperation with upstream and downstream industries to form a complete circular economy industry chain. Upstream companies will provide more environmentally friendly and sustainable raw materials, and downstream companies will optimize product design and usage methods to extend the service life of products and reduce waste generation. At the same time, the industry will strengthen the publicity and promotion of PP particle recycling, enhance consumers' environmental awareness, and promote the sustainable development of PP particles.

VIII. Conclusion: The infinite possibilities of PP granules

PP granules, a seemingly ordinary material, actually contain huge energy. Starting from its basic concept and essence, we have a deep understanding of its unique chemical structure as a polypropylene thermoplastic resin and the process of manufacturing through various production processes. In terms of working principle, whether it is injection molding, extrusion or calendering molding, it shows the wonderful transformation of PP granules in different application scenarios. The principle in special applications such as pneumatic conveying also reflects its important role in industrial production.

The advantages of PP granules are even more remarkable. In terms of physical properties, its strength, hardness, heat resistance, electrical properties and insulation are excellent, enabling it to meet the strict requirements of many fields; in terms of chemical properties, chemical corrosion resistance and stability provide guarantees for its application in complex chemical environments; environmental protection and sustainability advantages, such as recyclability and degradation characteristics under specific conditions, make it in line with the pursuit of environmentally friendly materials in modern society; cost advantages make it unparalleled in large-scale applications.​

In the instructions for use, we elaborated on the key points of different processing methods, as well as the wide application in packaging, automobiles, construction, household goods, electronics and other fields, which let us see the close connection between PP particles and our lives. However, during use, whether it is temperature control during processing, avoiding impurities and equipment maintenance, or the applicable environment during product use, avoiding contact with special substances, and paying attention to product life and replacement, we need to pay strict attention to ensure the quality and performance of PP particle products. ​

Looking to the future, PP particles continue to explore in the direction of technological innovation, the development of modification technology will further enhance its performance, and the research and development of new catalysts will also promote the optimization of production processes. In terms of market demand, with the development of various industries and the emergence of emerging application fields, the market size of PP particles is expected to continue to expand. On the road to sustainable development, PP particles will make greater contributions to environmental protection with their recyclable characteristics and the development of environmentally friendly production processes. ​
PP particles play an indispensable role in modern industry and daily life, and its story continues to be written. In the future, with the continuous advancement of science and technology and people's increasing requirements for material performance, PP particles will usher in a more brilliant development and bring more convenience and surprises to our lives. It is like a master key that opens the door to innovation in countless fields. Let us look forward to it creating more infinite possibilities in the future.