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Modified plastics refer to plastic products that are processed and modified by filling, blending, reinforcing and other methods on the basis of general plastics and engineering plastics to improve the flame retardancy, strength, impact resistance, toughness and other properties. Plastics processed by the above modification technology are called modified plastics. Generally speaking, modified plastics are better than plastics in flame retardancy, strength, impact resistance, aging resistance and other properties.
The modified plastic parts can not only achieve the strength properties of some steel materials, but also have a series of advantages such as light weight, rich colors and easy molding. Therefore, the trend of "replacing steel with plastic" has emerged in many industries, and it is almost impossible to find a material that can replace plastic products on a large scale at this stage.
Glass fiber reinforced PA was studied in the 1950s, but it was not industrialized until the 1970s. Since the development of super-tough PA66 by DuPont in the United States in 1976, major companies have developed new modified PA products. The United States, Western Europe, Japan, the Netherlands, Italy and other countries have vigorously developed reinforced PA, flame retardant PA, and filled PA, and a large number of modified PAs have been put on the market.
PA, as the largest and most important variety of engineering plastics, has a strong vitality, mainly because it can achieve high performance after modification. Secondly, the automotive, electrical, telecommunications, electronics, machinery and other industries have increasingly strong requirements for high performance of products. The rapid development of related industries has promoted the process of high performance of engineering plastics, making it play an increasingly important role.
1. The market demand for high-strength and high-rigidity nylon is increasing. New reinforcement materials such as inorganic whisker reinforcement and carbon fiber reinforced PA have become important varieties, mainly used for automotive engine parts, mechanical parts and aviation equipment parts.
2. Nylon alloying will become the mainstream of the development of modified engineering plastics. Nylon alloying is an important way to achieve high performance of nylon, and it is also the main means to manufacture special nylon materials and improve the performance of nylon. By blending other polymers, the water absorption of nylon is improved, the dimensional stability of the product is provided, as well as low-temperature brittleness, heat resistance and wear resistance. Therefore, it is suitable for different uses of vehicles.
3. The manufacturing technology and application of nano nylon have been rapidly developed. The advantages of nano nylon are that its thermal properties, mechanical properties, flame retardancy and barrier properties are higher than those of pure nylon, while the manufacturing cost is equivalent to that of back-through nylon. Therefore, it has great competitiveness.
4. The flame retardant nylon used in electronics, electrical appliances is increasing day by day, and green flame retardant nylon is increasingly valued by the market:
5. Antistatic, conductive nylon and magnetic nylon have become the process of electronic equipment and high performance.
6. The research and application of processing aids will promote the functionalization and high performance of modified nylon.
7. The application of comprehensive technology and the refinement of products are the driving force for the development of its industry.
Two: Molding
Processing characteristics:
1. Nylon is susceptible to moisture. In the atmosphere, the equilibrium water absorption rate of PA is 3.5%, PA66 is 2.5%, PA610 is 1.5%, and PA1010 is 0.8%.
The water content of nylon has a great influence on its mechanical properties. In the molten state, the presence of water will cause the hydrolysis of nylon, resulting in a decrease in molecular weight, a decrease in the mechanical properties of the product, and defects such as bubbles, silver wires and streaks on the surface of the product during molding. Therefore, it must be fully dried before molding.
2. Nylon melt has low viscosity and high fluidity, and the nozzle will produce "casting" phenomenon. It wastes raw materials and pollutes the nozzle. If a screw injection molding machine is used, the melt will flow back between the screw and the barrel wall during injection, making the injection inaccurate. Therefore, when nylon is molded in a screw injection molding machine, a check ring must be installed at the end of the screw.
3. Nylon is a crystalline polymer. The melting point is obvious and high, so nylon needs to be molded at a higher temperature. Nylon that is too molten has poor thermal stability and is easy to decompose. Therefore, the process conditions must be strictly controlled.
4 Nylon has a large molding shrinkage rate. For the manufacture of high-precision products, the mold design should determine its size based on the test, and the molding process should be strictly controlled.
Hardness refers to the ability of a material to resist other harder objects pressing into its surface.
The size of the hardness value is a conditional quantitative reflection of the hardness of the material. It is not a simple and definite physical quantity. The size of the hardness value depends not only on the material itself, but also on the test conditions and measurement methods. That is, different hardness measurement methods will produce different hardness values for the same material. Therefore, to compare the hardness between materials, the hardness values must be measured by the same measurement method to be comparable.
The following methods are commonly used to express hardness:
a. Shore hardness
b. Rockwell hardness
c. Mohs hardness
Hardness of modified plastics
Hardness of modified plastics refers to a modification method in which hard additives are added to plastics. Commonly used hardness additives are rigid inorganic fillers and fibers.
(1) Adding rigid inorganic fillers
Surface treatment to improve the hardness of plastics
The surface hardness improvement method of plastics refers to only improving the hardness of the surface of the plastic product, while the hardness of the inside of the product remains unchanged. This is a low-cost hardness improvement method.
This modification method is mainly used for shells, decorative materials, optical materials and daily necessities. This modification method mainly includes three methods: coating, plating and surface treatment.
Blending and compounding to improve the hardness of plastics
(1) Blending to improve the hardness of plastics
The method of improving plastic blending is to mix a high hardness resin with a low hardness resin to improve its overall hardness. Common blended resins include: PS, PMMA, ABS and MF, etc. The resins that need to be modified are mainly PE, PA, PTFE and PP.
(2) Compounding to improve the hardness of plastics
The method of improving the hardness of plastics by compounding is to compound a layer of high hardness resin on the surface of low hardness plastic products. This method is mainly suitable for extruded products, such as plates, sheets, films and pipes. Commonly used composite resins are PS, PMMA, ABS and MF.
1. Plastic additives 2. Dispersion state of filler materials in modified plastics and their formation The performance of filled modified plastics is closely related to the properties of the main component matrix resin and the properties, morphology, size and concentration of the filler materials. The dispersion state of the filler materials: the polymer aggregation structure and woven structure of the matrix resin: the interface structure of the filler and the resin also have a great influence. The following mainly discusses the dispersion state of the filler materials.
1. When inorganic particles are added to the polymer melt and sheared by a screw or other mechanical action, three types of inorganic particle dispersion microstructure states may be formed. 1 Inorganic particles form a second aggregation structure in the polymer. In this case, if the particle size of the inorganic particles is small enough and the interface between the particles is well bonded, the inorganic particles play a reinforcing role on the polymer like a rigid chain, and this dispersion state has a good reinforcing effect. For example, one of the important reasons why colloidal silica and carbon black have a reinforcing effect on rubber is that they form this second aggregation structure in rubber. 2. Inorganic particles exist in a random dispersion state, some aggregate into agglomerates, and some exist in individual dispersion forms. This dispersion state can neither strengthen nor toughen. Since the interaction between particles in the powder mass is very weak, it will become the weakest link in the filling material. 3. Inorganic particles are evenly and individually dispersed in the matrix resin. In this case, whether there is a good interface bonding between the particles and the matrix resin, a certain strengthening and toughening effect will be produced. In order to obtain a reinforced and toughened filled modified plastic, the third dispersion state is hoped.
2. Whether the inorganic powder filler material can be individually and evenly dispersed in the matrix resin is related to many factors. Under the condition of fixed processing conditions? It is related to the specific surface area of the inorganic particles, the surface free energy, the viscosity of the surface polar resin melt of the surface polar resin? The mutual chemical reaction between the inorganic particles and the matrix resin. From the perspective of the expected effect of filling and modification, the smaller the size of the inorganic particles, the better. However, the smaller the size, the higher the surface energy, the stronger the self-cohesion ability, and the more difficult it is to disperse evenly. Due to the surface energy and the static electricity generated by the collision and friction of high-speed movement, it condenses into powder masses. This kind of agglomerate can no longer be opened by mechanical shear force in the subsequent mixing and molding process, and it will present the second dispersion state mentioned above and become the most undesirable "white spot" in the modified plastic.
Powder and granular state is the dispersion state of filler materials with a length/diameter ratio of approximately 1. Filler materials with a larger length/diameter ratio refer to short fiber, needle, and flake fillers. There are two levels of dispersion problems for this type of material: first, uniformity of dispersion; second, orientation. Due to the obvious asymmetry of the length and diameter of this type of filler material, when it is filled with modified plastic molding products, the flow of the material will always produce different degrees of orientation distribution of the filler. There are two situations and two orientation states for its orientation. Under pressure, the material does not have a large flow state of filler material orientation. Under pressure, each filler individual moves in the direction of averaging the pressure difference of each part as much as possible, so that the maximum area receives pressure, resulting in the orientation of the filler material at right angles to the pressure direction. The orientation of the filler material on the same layer of the product is random and basically belongs to a two-dimensional orientation state.
Modified plastics are intermediate products in the petrochemical industry chain. They are mainly processed from five general-purpose plastics and five engineering plastics as plastic matrices. They have the characteristics of flame retardancy, impact resistance, high toughness, and easy processing. Modified plastics are a typical industry that benefits from technological progress and consumption upgrades. Thanks to the accelerated transfer of global home appliances, computers, power tools, and toys production capacity to China, China has become a major manufacturing country in these fields with its cost advantages in labor and other production factors, and has promoted the development of China's modified plastics industry. Consumption upgrades have brought China's automobile, construction and other industries into a period of rapid growth. As people's requirements for material performance continue to increase, China is becoming the world's largest potential market for modified plastics and the main driving force for demand growth.
China's modified plastics industry is developing rapidly, with an average annual growth rate of 20% and 15% in output and apparent consumption respectively. China's total annual demand for modified plastics is about 5 million tons, accounting for about 10% of all plastic consumption, but still far below the world average of 20%. In addition, China's per capita plastic consumption is still far behind that of developed countries in the world. As an indicator of the development level of a country's plastic industry, the ratio of plastic to steel in China is only 30:70, 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.
With the substantial improvement of people's living standards and the advancement of technical means, China's "replacing steel with plastic" and "replacing wood with plastic" will become a trend. As a sub-category of the plastic processing industry with rapid development and great development potential, the modified plastics industry is expected to maintain a growth rate of more than 10% in the next five years.
The overall development level of China's modified plastics industry is low, the production scale of enterprises in the industry is generally small, and the market situation of products also shows the characteristics of more primary products, unstable quality of intermediate products, and lack of advanced products, which is far from meeting the needs of China's economic development in the 21st century. Therefore, as an important part of the field of new chemical materials, modified plastics have also been listed as one of the key scientific and technological fields for development by the state. Since 2007, China has successively introduced various policies to promote the development of the modified plastics industry.
Modified plastics have been listed as one of the key scientific and technological fields for development by the state. Since 2007, China has successively introduced various policies to promote the development of the modified plastics industry. The automobile and home appliance industries are hot spots for the development of modified plastics, and the two account for more than 50%.
The application of plastics in the automotive industry began in the 1950s and has a history of more than 50 years. As automobiles develop towards lightweight and energy-saving directions, higher requirements are placed on materials. Since 1kg of plastic can replace 2-3kg of heavier materials such as steel, and every 10% decrease in the weight of a car can reduce fuel consumption by 6%-8%. Therefore, increasing the amount of modified plastics in automobiles can reduce the cost and weight of the entire vehicle and achieve energy-saving effects.
The market for modified plastics for home appliances in China is mainly occupied by foreign companies, and Chinese modified plastic companies only account for less than 1/3 of the market share. Since the products of Chinese companies are mostly limited to low-tech and low-standard levels, their ability to explore areas with high-performance requirements is obviously insufficient.
The downstream of modified plastics is mainly the automobile and home appliance industries, and the two account for more than 50%. Since 2008, the introduction of home appliances to the countryside, old-for-new and automobile preferential policies have greatly promoted the development of the industry. In addition, the policy orientation of energy conservation and emission reduction has also promoted automobile companies to reduce the weight of automobiles and thus achieve energy conservation and emission reduction, which has greatly promoted the development of the modified plastics industry.
With the substantial improvement of people's living standards and the advancement of technical means, it will become a trend for China to replace steel and wood with plastic.
Modified plastics are a plastic industry field with a wide range of involvement, high technological content and the ability to create huge economic benefits. And plastic modification technology - filling, blending and reinforcement modification is deeply involved in the raw materials and molding processes of almost all plastic products. From the production of raw resin to modified plastic masterbatch of various specifications and varieties, in order to reduce the cost of plastic products and improve their functionality, plastic modification technology is indispensable.
Ordinary plastics often have their own characteristics and defects. Modified plastics are to change the properties of plastics. The basic technologies include:
1. Reinforcement: Blend glass fiber and other materials with plastics to increase the mechanical strength of plastics.
2. Filling: Blend fillers such as minerals with plastics to change the shrinkage, hardness, strength and other properties of plastics.
3. Toughening: Add toughening agents to ordinary plastics to improve the toughness of plastics. The toughened and modified products are: rail gaskets.
4. Flame retardant: Adding flame retardants to ordinary plastic resins can make plastics have flame retardant properties. Flame retardants can be one or a composite system of several flame retardants, such as bromine + antimony system, phosphorus system, nitrogen system, silicon system, and other inorganic flame retardant systems.
5. Cold resistance: Increase the strength and toughness of plastics at low temperatures. The inherent low-temperature brittleness of general plastics at low temperatures limits their application in low-temperature environments. It is necessary to add some low-temperature toughening agents to change the brittleness of plastics at low temperatures. For example, plastic parts such as automobile bumpers are generally required to be cold-resistant.
Modified plastics are being used in more and more downstream fields with their superior cost-effectiveness. It can be said that modified plastics have become a consumption trend, and this trend implies the following five factors:
High performance: Modified plastics not only have the advantages of traditional plastics, such as low density and corrosion resistance, but also have well improved physical and mechanical properties, such as high strength, high toughness, high impact resistance, wear resistance and shock resistance. In addition, the improvement of the comprehensive performance of plastics provides a basis for its wide application in downstream fields.
Low cost: Compared with other materials, plastics have lower costs due to their high production efficiency and low density. The cost of plastics per unit volume is only about one-tenth of that of metals.
Government policy: China has implemented the "3C" compulsory certification system, which has strictly regulated the safety performance of products in the catalog, thereby promoting the widespread application of flame-retardant plastics in home appliances, IT, communications and other fields.
Consumption upgrade: With the improvement of living standards, people have begun to pursue more excellent product performance, requiring home appliances and other products to be more beautiful, safe and durable, thus putting forward higher requirements for the upstream plastic industry, requiring it to have better processing performance, mechanical properties, durability and safety.
Technical factors: More than 1,000 polymers have been discovered in the world, but only dozens of them are truly valuable for application. The development of new polymers not only requires huge investment, but also has unclear application prospects; on the contrary, modification technology can not only improve the performance of existing polymers to meet the needs of the industry, but also reduce the cost of some high-priced engineering plastics, becoming an effective way to develop the plastics industry.
The main types of modified plastic products are flame-retardant resins, reinforced and toughened resins, plastic alloys, functional masterbatches, etc.
Chart shows the main subdivision categories, consumer groups and market applications of modified plastics
1. Flame retardant resins
Flame retardant resins are mainly divided into flame retardant high impact polystyrene resins, flame retardant polypropylene resins, flame retardant ABS resins, etc. The above products are divided into different flame retardant specifications such as UL94 V0, UL94 V1, UL94 V2 and UL94 HB according to the flame retardant level. Compared with ordinary plastics, flame retardant plastic products can greatly reduce the risk of fire in the event of short circuit, overload, flooding, etc.
The main consumer groups of flame retardant resin products are: TV manufacturers, computer manufacturers, office appliances (printers, copiers, fax machines, etc.) companies, lighting companies, electrical companies, audio factories, etc. Mainly used to manufacture the shells, internal parts, peripheral equipment (connectors, distribution boards, plugs) of various products.
2. Reinforced and toughened resins
Reinforced and toughened resins are mainly divided into weather-resistant toughened PP special materials, glass fiber reinforced thermoplastics and other products.
1) Weather-resistant toughened PP special materials. Weather-resistant toughened PP special materials are a new polypropylene material with the characteristics of engineering plastics. They have the advantages of good low-temperature toughness, small molding shrinkage, high rigidity, and strong weather resistance. They are mainly used in outdoor environments that require resistance to weather and ultraviolet rays. Its main consumer groups include home appliance companies, auto parts companies, etc.
2) Glass fiber reinforced thermoplastics. Glass fiber reinforced thermoplastics products mainly include glass fiber reinforced AS/ABS, glass fiber reinforced PP, glass fiber reinforced nylon, glass fiber reinforced PBT/PET, glass fiber reinforced PC, glass fiber reinforced PPE/PPS and other products. Its main consumer groups include computer accessories companies, mechanical parts companies, power tool companies, lighting companies, etc.
3. Plastic alloys
Plastic alloys are mainly divided into PC alloy products, PVC alloy products and polyester alloy products.
PC alloy products have the characteristics of high impact strength, creep resistance, heat resistance, low water absorption, non-toxicity and excellent dielectric properties. They are mainly used in automobile instrument panels, computers and office automation equipment, power tool housings, cellular phones, etc. The main consumer groups of PC alloys are: electrical enterprises, computer manufacturing enterprises, office appliances (printers, copiers, fax machines, etc.) enterprises, auto parts factories, etc.
PVC/ABS alloy is produced with PVC and ABS as the matrix, and a variety of modifiers such as toughening agents, lubricants, stabilizers, flame retardants, etc. are added. It has excellent mechanical properties, weather resistance, processing rheological properties, good surface gloss of the products, good injection molding and extrusion effects, and is an alloy material with extremely excellent cost performance. PVC/ABS alloy can replace flame-retardant and weather-resistant ABS, PC, etc., and is widely used in home appliance housings, electrical switches, meter housings, lighting materials, communication networks, building materials, etc.
Polyester alloy has excellent mechanical properties (fatigue resistance), dimensional stability, chemical resistance, and environmental stress cracking resistance, and is mainly used in the fields of automobiles, home appliances, power tools, etc.
4. Functional masterbatch
Functional masterbatch mainly refers to high-impact polystyrene toughened flame retardant masterbatch. The masterbatch is mixed with HIPS (high-impact polystyrene resin) in a certain ratio (1:2~1:30) and the injection molded products can meet the different flame retardant requirements of UL94, IEC-65 and GB8898 standards for electrical and electronic products. At the same time, it can also improve the toughness, processing fluidity and demoulding properties of HIPS resin, give HIPS resin color, reduce production costs and improve product quality.
The main consumer groups of high-impact polystyrene toughened flame retardant masterbatch are TV manufacturers, audio factories, etc., and it is mainly used to manufacture the shells of electronic and electrical products.
1. Reinforcement technology
Fiber reinforcement is an important method for plastic modification. Both magnesium salt whiskers and glass fibers can effectively improve the comprehensive properties of polypropylene. Polypropylene reinforced with glass fiber has the advantages of low density, low price and recyclability. It is gradually replacing engineering plastics and metals in the application of automobile dashboards, automobile bodies and chassis parts: Compared with glass fibers, molded products of magnesium salt whiskers have higher precision, dimensional stability and surface finish, and are suitable for the preparation of various complex-shaped parts, lightweight and high-strength flame-retardant parts and electronic and electrical parts. As a modifier, magnesium salt whiskers can greatly improve the strength, stiffness, impact resistance and flame retardancy of polypropylene. Therefore, the application of magnesium salt whiskers and glass fibers in polypropylene modification has received more and more attention.
2. Toughening technology
Mineral reinforcement and toughening is one of the most common modification methods. The minerals added to the polypropylene raw materials are usually calcium carbonate, talcum powder, wollastonite, glass microbeads, mica powder, etc. These minerals can not only improve the mechanical properties and impact toughness of polypropylene materials to a certain extent, reduce the molding shrinkage of polypropylene materials to enhance their dimensional stability, but also greatly reduce the cost of polypropylene materials due to the huge difference in cost between minerals and polypropylene matrix.
Mineral-reinforced toughened polypropylene is the most widely used of all modified polypropylene materials in household appliances. At present, the inner drums of pulsator washing machines and drum washing machines generally use mineral-reinforced toughened polypropylene materials to replace the early stainless steel inner drums. After being reinforced and toughened by minerals, polypropylene materials can overcome their original problems such as insufficient strength, poor glossiness, and excessive shrinkage. At present, in addition to being used to make the inner drum of washing machines, this modified polypropylene is also used to make parts such as pulsators and clothing ports. Haier Group alone uses about 1,700 tons of it each year (each washing machine inner drum weighs about 2kg). The mineral addition amount of this material is as high as 40%, its tensile strength is 33Mpa, its elongation at break can reach more than 90%, and its notched impact strength is about 10KJ/m2.
Many parts of microwave ovens are also made of mineral-reinforced toughened polypropylene materials. Due to the addition of minerals, the heat resistance temperature of polypropylene material can be further improved on the basis of its own high heat resistance temperature, so as to meet the high temperature requirements of microwave ovens. For example, the sealing strip of microwave oven door, the horn of microwave oven speaker, the horn bracket, etc. all adopt this modified polypropylene material. The shelves on the refrigerator are now basically made of mineral-reinforced and toughened polypropylene material. Since it can be integrally injection molded with the glass panel, it has well solved the problem of water seepage of the original ABS material panel.
Three, filling modification
New high-filled glass fiber modified plastic, which can overcome the defects of conventional glass fiber reinforced thermoplastic plastics. The matrix of this material is high-temperature thermoplastic plastics such as liquid crystal polymer, polyether sulfone, polyether imide and polyphenylene sulfide. When the glass fiber filling amount is 80%, the modified material can still maintain good processability. The parts produced with the new material have good characteristics of wear resistance and temperature change resistance. This new material can bond with plastics and metals and is suitable for surface molding equipment processing. Potential applications include automotive and fuel system components, bearings, electronic components, anti-scratch housings, etc. The additional benefits of this glass reinforcement are good flame retardancy, recyclability, high heat resistance and dimensional stability.
Fourth, blending and plastic alloy technology
Plastic blending modification refers to a modification method that changes the properties of the original resin by adding one or more other resins (including plastics and rubbers) to a resin. Fluoroplastic alloy is made by using China's existing ultra-high molecular weight polytetrafluoroethylene (FER) as the main raw material, directly blending with tetrafluoroethylene and fillers, and using physical methods. The performance of this material exceeds that of polytetrafluoroethylene, which is recognized as the "king of plastics" in the world.
V. Flame retardant technology
The flame retardant technology of polymers is currently mainly based on additive bromine flame retardants, and commonly used ones include decabromodiphenyl ether, octabromoether, tetrabromobisphenol A, hexabromocyclododecane, etc., among which decabromodiphenyl is used in the largest amount. Brominated epoxy resin has excellent melt flow rate, high flame retardant efficiency, excellent thermal stability and light stability, and can make the flame-retarded material have good physical and mechanical properties and no frost. Therefore, it is widely used in engineering plastics such as PBT, PET, ABS, nylon 66, and thermoplastics such as PC/ABS plastic alloys.
Other varieties in the flame retardant family include phosphorus, triazine, silicon, expansion, inorganic, etc. These flame retardants play their own unique flame retardant effects in various fields of use. Among phosphorus flame retardants, organic phosphorus varieties are mostly in oily liquid form, which is not easy to add during polymer processing. They are generally used in polyurethane foam, transformer oil, cellulose resin, natural and synthetic rubber. The red phosphorus in the inorganic phosphorus system is a pure flame retardant element with good flame retardant effect, but it has bright color, so its application is partially limited. The application of red phosphorus should pay attention to micronization and surface coating, so that it has good dispersion in polymers, good compatibility with polymers, not easy to migrate, and can maintain the flame retardant properties of polymers for a long time.
Sixth, Nanocomposite Technology
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