Plastic products are a general term for daily and industrial products made of plastic as the main raw material. They include products made of injection molding, vacuum forming and other processes using plastic as the raw material. Plastic is a type of synthetic polymer material with plasticity. It forms the three major synthetic materials that are indispensable in daily life with synthetic rubber and synthetic fiber. Specifically, plastic is a material that uses natural or synthetic resin as the main component, adds various additives, can be molded into a certain shape under certain temperature and pressure conditions, and maintains the same shape at room temperature.

Development History

Compared with metal, stone and wood, plastic products have the advantages of low cost and strong plasticity. They are widely used in the national economy. The plastic industry occupies an extremely important position in the world today. For many years, the production of plastic products has developed rapidly around the world. China's plastic product output has always been at the forefront of the world rankings, and the output of many plastic products has ranked first in the world. China has become a major plastic product producer in the world. From 2001 to 2010, the average annual growth rate of China's plastic product output remained above 15%, and in 2010, China's total plastic product output reached 58.3 million tons.

From the perspective of demand, China's per capita plastic consumption is still far behind that of developed countries in the world. According to statistics, the plastic-to-steel ratio, an indicator of the development level of a country's plastic industry, is only 30:70 in China, which is lower than the world average of 50:50, and is far lower than the 70:30 in developed countries such as the United States and 63:37 in Germany. In the future, with the technological progress and consumption upgrade of China's modified plastic, China's demand for plastic products is expected to maintain a growth rate of more than 10%.

Plastic products are widely used, and the huge downstream industry provides strong support for the development of China's plastic products industry. With the introduction of the "Planning Rules for the Revitalization of the Petrochemical Industry", China's plastic products industry has ushered in new development opportunities. China's plastic products market demand is mainly concentrated in agricultural plastic products, packaging plastic products, construction plastic products, industrial transportation and engineering plastic products.

Performance characteristics

Compared with other materials, plastic have the following performance characteristics:

1. Light weight

Plastic are lighter materials with a relative density ranging from 0.90 to 2.2. Obviously, can plastic float on the water? Especially foamed plastic, because of the micropores inside, the texture is lighter, and the relative density is only 0.01. This characteristic makes plastic can be used in the production of products that require weight reduction.

2. Excellent chemical stability

Most plastic have good corrosion resistance to acids, alkalis and other chemical substances. In particular, polytetrafluoroethylene (F4), commonly known as the king of plastic, has a chemical stability that is even better than gold. It will not deteriorate even if it is boiled in "aqua regia" for more than ten hours. Due to its excellent chemical stability, F4 is an ideal corrosion-resistant material. For example, F4 can be used as a material for conveying corrosive and viscous liquid pipelines.

3. Excellent electrical insulation performance

Ordinary plastic are poor conductors of electricity, and their surface resistance and volume resistance are very large, which can reach 109-1018 ohms in digital terms. The breakdown voltage is large and the dielectric loss tangent is very small. Therefore, plastic are widely used in the electronics industry and the mechanical industry. Such as plastic insulated control cables.

4. Poor conductor of heat, with sound-absorbing and shock-absorbing effects

Generally speaking, the thermal conductivity of plastic is relatively low, equivalent to 1/75-1/225 of steel, and the micropores of foam plastic.

Contains gas, and its heat insulation, sound insulation and shock resistance are better. For example, the thermal conductivity of polyvinyl chloride (PVC) is only 1/357 of steel and 1/1250 of aluminum. In terms of thermal insulation capacity, single-glass plastic windows are 40% higher than single-glass aluminum windows, and double-glass windows are 50% higher. After combining plastic windows with hollow glass, they are used in residences, office buildings, wards, and hotels, saving heating in winter and air conditioning expenses in summer, and the benefits are very obvious.

5. Wide distribution of mechanical strength and high specific strength

Some plastic are as hard as stone and steel, and some are as soft as paper and leather; from the perspective of mechanical properties such as hardness, tensile strength, elongation and impact strength of plastic, the distribution range is wide and there is a lot of room for choice. Because plastic have a small specific gravity and high strength, they have a higher specific strength. Compared with other materials, plastic also have obvious disadvantages, such as easy to burn, not as high rigidity as metals, poor aging resistance, and not heat-resistant.

Development Trend

The development direction of plastic can be summarized into two aspects. One is to improve performance, that is, to modify existing varieties by various methods to improve their comprehensive performance; the other is to develop functions, that is, to develop polymer materials with physical functions such as light, electricity, and magnetism, so that plastic can have photoelectric effects, thermoelectric effects, piezoelectric effects, etc.

From the current development speed of the world's plastic industry, Germany and Sweden rank first, followed by Japan and some European countries, and the United States is slower. Foreign plastic packaging presents the following development trends:

Copolymer composite packaging film

Currently, some European and American countries have invested heavily in the development of non-polar and polar ethylene copolymers, which will greatly improve the tensile and co-extrusion properties of plastic films, and improve transparency, sealing strength, stress resistance, crack resistance, as well as enhance stability, improve molecular weight distribution and extrusion rheological properties.

Foreign experts believe that the current development focus of the world's plastic industry is on plastic modification, coating technology for plastic products, rapid biodegradation of waste plastic, and comprehensive technology for plastic recycling and reuse. For example, some European and American manufacturers use linear ethylene-¦Á-olefin copolymer and ethylene-vinyl acetate copolymer mixed material/PA bags, which are suitable for packaging ice cream, cream and other foods.

Multifunctional composite film

A large number of multifunctional composite films have been developed abroad to further refine their functions. For example: cold-resistant film can withstand low temperature environments of -18¡æ, -20¡æ, and -35¡æ; moisture-proof film made by moisture-proof treatment of PP, its series of products can be divided into several types such as moisture-proof, anti-condensation, anti-steaming and adjustable moisture; anti-corrosion film can package perishable, acidic and sweet foods; friction film has stable stacking; special PE film is chemical and corrosion resistant; odorless insect repellent is added to the anti-moth film; heat-resistant film of biaxially oriented nylon 66 replaces biaxially oriented nylon 6 to package food, and its high temperature resistance reaches 140¡æ; new special food packaging film can improve the aroma retention of food packaging; the transparency of non-crystalline nylon film is similar to glass; high shielding film can maintain the stability of color, aroma, taste, nutritional indicators and taste quality; metal protective film uses LDPE modified film to package liquid products, which can be heat-sealed in low temperature environment; PP synthetic paper is used to improve the light resistance, cold resistance, heat resistance, water resistance, moisture resistance, grease resistance, acid resistance, alkali resistance and impact resistance of the packaging.

Currently, plastic cups and composite cups (outer layer PSP, inner layer PP, lid PS) are popular abroad to package cold and hot drinks, wine, and convenience foods. France uses PE bottles to package fructose and yogurt, and Germany uses PC bottles to package milk. China uses PE bottles to package medicines, etc.

Bottom numbers

Plastic can be seen everywhere in our lives. Plastic products are made of different materials, and different materials have different applications. The numbers at the bottom of the plastic bottle represent different materials.

The number "1" represents polyethylene terephthalate, or PET. It is mainly used in mineral water bottles, carbonated and juice beverage bottles, and soy sauce and vinegar bottles. The heat-resistant temperature of PET bottles is 70 degrees Celsius. They are only suitable for warm or frozen drinks. They are easily deformed when filled with boiling water or heated, and substances harmful to the human body will also dissolve.

The number "2" represents high-density polyethylene, or HDPE. HDPE is made into composite films with other plastic and is also used in aquatic products.

The number "3" stands for polyvinyl chloride, or PVC. Because of its low price, it is also used to make intravenous infusion bags and disposable sterile infusion equipment. However, long-term use can lead to the accumulation of harmful substances such as DEHP. Therefore, from a safety perspective, the choice of non-PVC materials in the pharmaceutical industry is a future trend.

The number "4" is low-density polyethylene, or LDPE. Plastic No. 4 is used in large quantities for packaging. LDPE is mainly used to produce food cling film and plastic bags for food.

The number "5" is polypropylene, or PP. One is to make containers. PP is different from other materials. PP can be put into a plastic container in a microwave oven, and it is a reusable plastic container that can be used as a storage container for food, oils and condiments. The second is packaging film, which is unstretched and biaxially stretched. Unstretched polypropylene (CPP) is often used for the packaging of snacks, bread, fruits, etc.; biaxially oriented polypropylene (BOPP) is a flexible packaging material comparable to cellophane.

The number "6" is polystyrene, or PS. PS is mainly processed into film and foam plastic for packaging. Film is used for packaging fruits and vegetables; foam plastic is mostly used for instant noodle boxes and fast food boxes, but it is not resistant to high temperatures, so it cannot be directly heated in a microwave oven to avoid releasing toxic chemicals due to excessive temperature.

The number "7" is polycarbonate, that is, PC or other plastic. Plastic containers made of PC material may release toxic bisphenol A. The higher the temperature, the more it releases and the faster it releases. Therefore, do not heat it when using it, and do not expose it to direct sunlight.

Production method

Plastic product production generally includes plastic batching, molding, machining, joining, modification and assembly. The last four processes are carried out after the plastic has been molded into finished products or semi-finished products, also known as plastic secondary processing.

The key link of plastic processing in the production of plastic products. Plastic in various forms (powder, granules, solutions or dispersions) are made into products or blanks of the desired shape. There are more than thirty molding methods. Its selection is mainly determined by the type of plastic (thermoplastic or thermosetting), the starting form, and the shape and size of the product. Common methods for processing thermoplastic plastic include extrusion, injection molding, calendering, blow molding and thermoforming, while thermosetting plastic are generally processed by compression molding, transfer molding, and injection molding. Lamination, compression molding and thermoforming are methods of forming plastic on a plane. The above plastic processing methods can all be used for rubber processing. In addition, there are casting methods using liquid monomers or polymers as raw materials. Among these methods, extrusion and injection molding are the most commonly used and are also the most basic molding methods.

The mechanical processing of plastic products borrows the plastic processing methods of metals and wood to manufacture plastic products with very precise dimensions or small quantities. It can also be used as an auxiliary process for molding, such as sawing of extruded profiles. Because the properties of plastic are different from those of metals and wood, plastic have poor thermal conductivity, low thermal expansion coefficient and elastic modulus. When the clamp or tool is pressurized too much, it is easy to cause deformation. It is easy to melt when heated during cutting and is easy to adhere to the tool. Therefore, when plastic are machined, the tools used and the corresponding cutting speeds must adapt to the characteristics of plastic. Common machining methods include sawing, shearing, punching, turning, planing, drilling, grinding, polishing, threading, etc. In addition, plastic can also be cut, punched and welded by laser.

Plastic products production and plastic processing methods for joining plastic parts include welding and bonding. Welding methods are hot air welding using welding rods, hot melt welding using hot poles, high frequency welding, friction welding, induction welding, ultrasonic welding, etc. The bonding method can be divided into flux, resin solution and hot melt adhesive bonding according to the adhesive used.

The purpose of surface modification in the production of plastic products is to beautify the surface of plastic products, which usually includes: mechanical modification, that is, using processes such as filing, grinding, and polishing to remove burrs and burrs on the parts, and correct the size, etc.; painting, including coating the surface of the parts with paint, using solvents to brighten the surface, and covering the surface of the products with patterned films, etc.; coloring, including painting, printing and hot stamping; metal plating, including vacuum coating, electroplating, and chemical silver plating. Plastic processing hot stamping is to transfer the colored aluminum foil layer (or other patterned film layer) on the hot stamping film to the parts under heating and pressure. Many household appliances, building products, daily necessities, etc. use this method to obtain metallic luster or wood grain patterns.

The assembly of plastic products is the operation of assembling the finished plastic parts into complete products by methods such as bonding, welding, and mechanical connection. For example: plastic profiles are assembled into plastic window frames and plastic doors through steps such as sawing, welding, and drilling.

Composition

Some plastic are pure resins, such as polyethylene, polystyrene, etc., which are called single-component plastic. Some plastic contain other auxiliary materials in addition to synthetic resins, such as plasticizers, stabilizers, colorants, various fillers, etc., which are called multi-component plastic.

(I) Synthetic resin

Synthetic resin refers to a polymer compound synthesized by chemical, physical and other methods using coal, calcium carbide, petroleum, natural gas and some agricultural and sideline products as the main raw materials, firstly preparing low-molecular compounds (monomers) with certain synthetic conditions. The properties of this type of compound are similar to natural resins (such as rosin, amber, shellac, etc.), but the performance is superior to that of natural resins. For example: dentures made of synthetic resins.

The content of synthetic resin accounts for 40% to 100% of all the components of plastic, playing a bonding role. It determines the main properties of plastic, such as mechanical strength, hardness, aging resistance, elasticity, chemical stability, photoelectric properties, etc.

(II) Plastic additives

Plastic additives

The purpose of adding additives to plastic is mainly to improve processing performance, increase efficiency and reduce costs. Additives account for a small proportion of plastic materials, but they have a great impact on the quality of plastic products. Different types of plastic require different types and amounts of additives due to different molding processing methods and usage conditions. The main additives are as follows:

1. Plasticizers

Plasticizers can increase the softness, elongation and plasticity of plastic, reduce the flow temperature and hardness of plastic, and facilitate the molding of plastic products. Commonly used ones include phthalates, sebacates, chlorinated paraffin and camphor. The most common one we see is camphor.

2. Stabilizers

We all know that plastic products will fade, become brittle and crack under the action of light, heat and oxygen during processing, storage and use. In order to delay and prevent the occurrence of aging, stabilizers must be added. Those mainly used to prevent heat aging are called heat stabilizers; those mainly used to prevent oxidation aging are called antioxidants; those mainly used to prevent light aging are called light stabilizers, and they are collectively called stabilizers. The best plastic stabilizer today is methyl tin heat stabilizer (abbreviated as 181), which is very effective for calendering, extrusion, injection molding and blow molding of rigid polyethylene (PVC). Because of its high safety, it is particularly used in food packaging and high-definition rigid polyethylene products. At the same time, it is also widely used in plastic doors and windows, water pipes, and decorative materials to replace other highly toxic plastic heat stabilizers. It has been widely used in the United States, Europe, and Japan. In recent years, 181 methyl tin heat stabilizer has begun to be widely used in China.

3. Flame retardant

The additive that can improve the flame retardancy of plastic is called flame retardant. Most plastic containing flame retardants have self-extinguishing properties or slow burning rates. Commonly used flame retardants include antimony oxide and aluminum and boron compounds, halides and phosphates, tetrachlorophthalic anhydride, tetraphthalic anhydride, etc.

4. Antistatic agent

Antistatic agent plays a role in eliminating or reducing static electricity generated on the surface of plastic products. Most antistatic agents are electrolytes, and their compatibility with synthetic resins is limited, so they can migrate to the surface of plastic to achieve the effect of absorbing moisture and eliminating static electricity.

5. Foaming agent

Plastic foaming agent is a low-molecular organic substance that can be gasified at a certain temperature, such as dichlorodifluoromethane; or an organic compound that decomposes into gas when heated. These gases remain in the plastic matrix to form foam plastic with many fine foam structures. Commonly used ones include azo compounds, nitroso compounds, etc.

6. Colorant

Colorant is used for coloring plastic. It mainly plays a beautifying and modifying role. About 80% of plastic products are made into final products after coloring.

7. Lubricant

Lubricant is a substance added to improve the demoulding property of plastic during hot molding and improve the surface finish of the product. Commonly used lubricants include: stearic acid and its salts, paraffin, synthetic wax, etc.

8. Reinforcement materials and fillers

In many plastic, reinforcement materials and fillers account for a considerable proportion, especially reinforced plastic and calcium plastic. The main purpose is: in order to improve the strength and rigidity of plastic products, generally various fiber materials or inorganic substances are added. The most commonly used reinforcing materials are: glass fiber, asbestos, quartz, carbon black, silicate, calcium carbonate, metal oxides, etc.

Classification

There are hundreds of industrially produced plastic, of which more than 60 are commonly used. The common classification methods are as follows:

Classification by performance after heating

1. Thermosetting plastic

The characteristic of this type of plastic is that it solidifies and forms after being heated for a certain period of time or adding a curing agent at a certain temperature.

The cured plastic is hard and insoluble in any solvent, and it cannot be softened again by heating. It will decompose if the heating temperature is too high. Common thermosetting plastic include: bakelite, electric jade, decorative panels and unsaturated polyester plastic.

2. Thermoplastic plastic

The characteristic of this type of plastic is that it softens when heated and hardens when cooled. Generally, there are only physical changes during the processing process while maintaining its chemical nature. The resin of this type of plastic is mostly made by addition polymerization. Common thermoplastic include: nitrocellulose plastic, cellulose acetate plastic, polyethylene plastic, polypropylene plastic, polystyrene plastic, polyvinyl chloride plastic, etc. For example, our common mineral water bottles, plastic bags, etc.

Divided by application scope

1. General plastic

This type of plastic mainly refers to a type of plastic with large output, wide application and low price. They account for about 80% of the total output of plastic. The main varieties are: polyethylene, polyvinyl chloride, polypropylene, polystyrene, phenolic and amino plastic, etc.

2. Engineering plastic

Generally refers to plastic that can be used as structural materials in engineering technology. The notable characteristics of this type of plastic are high mechanical strength, strong resistance to chemical corrosion and high temperature resistance, and can replace metals or have other special uses. The main varieties are: polyamide, polycarbonate, polyoxymethylene, polysulfone, ABS, polyphenylene ether, fluoroplastic, etc.

Classification by flammability

1. Flammable plastic

This type of plastic burns violently when exposed to open flames and is difficult to extinguish. Such as nitrocellulose plastic, etc. This type of plastic is listed as dangerous goods.

2. Combustible plastic

This type of plastic burns when exposed to open flames and has no self-extinguishing properties, but burns quickly. Such as polyethylene, polypropylene, etc.

3. Flame-retardant plastic

This type of plastic can burn in strong open flames and extinguish quickly after leaving the fire. Such as phenolic plastic, acetate plastic, polyvinyl chloride plastic, etc.

Main plastic

Polyethylene plastic

(I) Introduction

Polyethylene plastic (Polyethylene) are polymers of ethylene monomers. The raw materials for production are petroleum, coke oven gas or alcohol. Industrial polyethylene is generally produced by dehydration of ethanol, catalytic hydrogenation of acetylene or high-temperature cracking. Its trade name is abbreviated as "ethylene plastic"; the English abbreviation is PE. Due to the different densities of polyethylene, it is divided into low-density polyethylene [PE(L)], medium-density polyethylene [PE(M)] and high-density polyethylene [PE(H)].

The molecular structure of polyethylene is: (¡ªCH2Ò»CH2¡ª) n. It is a linear geometric shape. Theoretically, it has no branches and is easy to crystallize. Usually, polyethylene macromolecules are composed of crystalline regions and amorphous regions in a highly elastic state; the crystalline region gives polyethylene plastic higher hardness, strength, chemical stability, etc.; the amorphous region gives polyethylene plastic higher softness, toughness, transparency, etc. In fact, polyethylene macromolecules are not absolutely without branches. Their crystallinity is different, the density is different, and the physical and mechanical properties are also different.

(II) Polymerization method

1. Low-density polyethylene

Also known as "high-pressure soft plastic". It is made by using trace oxygen as initiator to polymerize ethylene monomer at 1200-2000 atmospheres and 100-300¡æ, with oxygen, organic peroxide or azo compound as initiator.

2. Medium-density polyethylene

Medium-density polyethylene is synthesized at 30-70 atmospheres and 100-250¡æ with chromium oxide or molybdenum oxide as catalyst. In practice, it is made by the following methods:

¢Ù It is made by blending low-density polyethylene and high-density polyethylene in a certain proportion;

¢Ú It is made by copolymerizing ethylene with a second monomer such as propylene and butene by a slurry method or a solution method;

¢Û It is made by copolymerizing ethylene with a second monomer such as vinyl acetate and acrylate by a high-pressure method, or by controlling the ethylene conversion rate at a relatively low level;

¢Ü It is made by a gas phase method.

3. High-density polyethylene

It is polymerized at 10 atmospheres and 60-80¡ãC using catalysts mainly composed of alkyl aluminum and titanium tetrachloride.

(III) Performance

Physical and mechanical properties

PE is a milky white waxy translucent material, lighter than water, odorless, tasteless and non-toxic; HDPE is soft and LDPE is hard; air permeability decreases with increasing density, and HDPE has greater air permeability to N2, O2 and CO2 than other films, but relatively low air permeability to water vapor; PE has the best low-temperature resistance among general-purpose plastic, with a brittle fracture temperature of -70¡ãC, but is not resistant to high temperatures; HDPE has better strength and hardness, but poorer impact strength, elasticity and transparency; while LDPE is the opposite.

The performance of MDPE is between the two

Chemical corrosion resistance

PE can resist general acids, alkalis and salts at room temperature, but not concentrated H2SO4 and HNO3. It can resist most organic solvents below 60¡ãC and swell in aliphatic hydrocarbons, aromatic hydrocarbons and chlorinated hydrocarbons.

Aging resistance

PE degrades slowly under the action of O2 in the air; degradation is accelerated by heat, ultraviolet rays and high-energy radiation.

Insulation properties

The dielectric constant is small.

Poor bonding, printing and coloring properties.

(IV) Combustion characteristics

It is flammable and continues to burn after leaving the fire, and emits the same smell as paraffin burning; when burning, the tip of the flame is yellow and the bottom is blue; there is little smoke; it melts, burns and drips while burning.

(V) Applications

Low-density polyethylene has a wide range of applications. It can be used to produce films and hollow containers by extrusion blow molding, pipes by extrusion, composite films by extrusion calendering and with kraft paper as the base, and various daily necessities such as baby bottles, soap boxes, toys, cups, plastic flowers, etc. by injection.

Medium-density polyethylene is mainly used to make various bottle products, hollow products, cable products, and films for high-speed automatic packaging.

High-density polyethylene plastic has high strength and good wear resistance, so it is mainly used to make ropes, strapping tapes, etc., and can also be used to make boxes, barrels, thermos shells, etc.

Polypropylene plastic

(I) Introduction

Polypropylene plastic (Polypropylene) is made by polymerizing propylene under the action of methyl aluminum and titanium trichloride catalysts at 20 atmospheres and 50¡ãC with gasoline as solvent. Its trade name is referred to as "propylene plastic", and its English abbreviation is: PP.

(II) Identification characteristics

When not colored, it is milky white and translucent, soft; the relative density is less than that of water, and it can float on the horizontal surface; it does not soften significantly in boiling water, does not deform, and the softening temperature is 110¡æ; it feels smooth to the touch, but not greasy, and has a hard and tough texture. When the strip is stretched, it breaks brittlely.

(III) Combustion characteristics

It is flammable and can continue to burn after being removed from the fire, with a special smell escaping; the tip of the flame is yellow, with little smoke, and it burns, melts, and drips.

(IV) Structure and properties

CH3

The structural formula of polypropylene is: [¡ªCH2¡ªCH¡ª] n, which is a linear macromolecule, but the methyl side chains of polypropylene have three different arrangements, which makes it have a high degree of crystallinity. Due to the influence of the methyl side chain, the properties of polypropylene and polyethylene plastic are different, mainly in the following aspects:

1. Better chemical stability than polyethylene

Except for fuming nitric acid and fuming sulfuric acid, it has good resistance to other chemical corrosion. In the laboratory, 80% sulfuric acid and concentrated hydrochloric acid can reach 100¡ãC without destroying polypropylene.

2. Outstanding heat resistance

It can be used for a long time at 100-120¡ãC; but the impact strength decreases sharply at low temperatures, and the impact strength at 0¡ãC is half of that at 20¡ãC.

3. Lower air permeability and water permeability than polyethylene.

4. Better rigidity and tensile strength than polyethylene.

5. Directional stretching

The strength in the tensile direction is improved, the bending resistance is good, the flexibility is increased, and the bent part does not turn white after being folded and bent 1 million times.

6. Poor aging resistance compared to polyethylene

Polypropylene has methyl tertiary carbon atoms in its long chain, which is unstable. During use, it is strictly prohibited to prevent long-term contact with copper to produce "copper damage".

(V) Modification

Polypropylene plastic has certain disadvantages in its performance, such as poor cold resistance, low impact strength, poor aging resistance, etc. In order to overcome these disadvantages, modification measures are often used.

1. Copolymerization modification

Copolymerization with monomers such as vinyl chloride and acrylic acid can improve the cold resistance, flammability, and molding fluidity of polypropylene.

2. Blending modification

Blending with other thermoplastic and elastomers to prepare blends can improve the cold resistance of polypropylene.

3. Filling-reinforcement modification

Adding filling materials and reinforcing materials can improve the rigidity of polypropylene at high temperatures and reduce molding shrinkage.

4. Stretching modification

Stretching can orient the molecules and improve the mechanical strength. For example, the strength of polypropylene can be increased by 3 times after biaxial stretching.

5. Cross-linking modification

The linear structure of polypropylene is cross-linked into a network structure, which can improve heat resistance and mechanical strength.

(VI) Application

Polypropylene plastic are mainly used for films, pipes, bottles, etc. Due to its high softening point when heated, it can be used to make tableware such as bowls, basins, cups, etc.; sterilization containers for medical equipment; daily necessities such as buckets and thermos shells; pencil cases, instrument boxes, etc.; electrical insulation materials and low-foam

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