Comparative analysis of eight common plastic modification techniques

(1) Fiber reinforcement
Long fiber reinforced thermoplastic (UCRT) is a new type of lightweight and high-strength engineering structural material, which is easy to be recycled and reused due to its light weight, low price and easy to be recycled. The use of natural fibers such as flax, sisal reinforced plastic body parts has been recognized in the automotive industry. On the one hand, natural fibers are environmentally friendly materials. On the other hand, plant fibers are 40% lighter than glass fibers, reducing vehicle weight and reducing oil consumption. The body floor is made of flax reinforced PP, the tensile strength of the material is higher than steel, the rigidity is not lower than glass fiber reinforced material, the parts are easier to be recycled. The drive shaft made of fiber reinforced plastic by GKN Technology of UK can reduce the weight by 50%-60%, the torsional resistance is 1.0 times greater than steel, and the bending rigidity is 1.5 times greater. Plastic springs can significantly reduce weight. The plate spring made of carbon fiber reinforced plastic (CFRP) is 14kg, reducing the weight by 76%. In the United States, Japan, Europe have been used in the use of plate spring, cylindrical spiral spring fiber reinforced plastic, in addition to the obvious vibration and noise reduction effect, but also to achieve the purpose of lightweight.

(2) Toughening technology
The rigidity (including strength) and toughness of polymer structural materials are the two most important performance indexes which restrict each other. Therefore, the research of strengthening and toughening at the same time is always a difficult problem in polymer materials science. Chinese Academy of Sciences institute of chemistry of polymer blend filled with a new way of enhanced toughening, which results in solving the high polymer material at the same time strengthening toughening of scientific problem for important breakthrough, the ultra high toughness successfully prepared for the first time in domestic polyolefin engineering plastics, general plastic upgrade for great variety, for further high-performance engineering plastics and engineering plastics provides a new way. The High gravity Engineering Technology Research Center of the Ministry of Education has successfully developed the national "863" project -- "Nano-cacO3 plastic toughening masterbatch and its preparation technology". This base material can make PVC toughened and modified, mainly used in the production of PVC door and window profiles, but also used in the production of PVC pipes, plates and other hard products. Look from development trend, PVC plastic door window has the potential that replaces steel window and woodiness door window greatly in the round. At present, the annual production capacity of PVC door and window profiles in China is 1 million T, and the trend is rising. The use of nano CaCO3 plastic toughened base material to produce PVC window and window profiles can not only improve the overall performance of the product, but also reduce the cost of profiles per ton by more than 100 yuan. At the same time, its application field will also be extended to PP, ABS and other plastic materials. Using nano CaCO3 to toughen PVC is a non-elastomer toughening plastic technology developed in recent years (inorganic rigid particle toughening plastic technology), which is still in the research stage in China. There are two major problems when nano CaCO3 is directly added. One is that nano particles will agglomerate in the plastic matrix, causing uneven dispersion and affecting the toughening effect. Second, because the nano CaCO3 particle is small, it is easy to produce dust and affect the environment. However, the successful development of nano-cacO3 plastic toughened masterbatch and its preparation technology effectively solved the two major problems faced in the same research field at home and abroad.

(3) Filling modification (powder filling)
Since the plastic filling modification was put into the market in the early 1980s, due to its low price, excellent product performance and the improvement of some physical properties of plastic products, it can be replaced by synthetic resin, and the production process is simple, the investment is small, has significant economic and social benefits. The surface modifiers of inorganic powder materials filled with star phase modification were from stearic acid to coupling agent, and the coupling agents were silane, titanate, aluminate, borate, phosphate and other varieties emerged. Talc is often used to fill polypropylene. The talc powder has the characteristics of flake structure, so the talc powder with fine particle size can be used as the reinforcement filler of polypropylene. In the modification system of polypropylene, adding superfine talc powder can not only improve the rigidity, surface hardness, heat resisting creep, electrical insulation and dimensional stability of polypropylene products significantly, but also improve the impact strength of polypropylene. Adding a small amount of talc powder to polypropylene can also play the role of nucleating agent and improve the crystallinity of polypropylene, thus improving the mechanical properties of polypropylene. By improving the crystallinity and refining the grains, the transparency of polypropylene is also improved. Polypropylene composites filled with 20% and 40% superfine talc can significantly improve the rigidity and creep resistance of polypropylene at room temperature and high temperature. For polyethylene blown film, super fine talcum powder filler is better than other fillers, easy to shape, good process.

(4) Blending modification
Plastic blending modification is a modification of a resin by adding one or more other resins (including plastics and rubber) to the resin to change the properties of the original resin. Blending modification of plastics is a common modification method which goes hand in hand with additive modification. The difference between the modification and plastic modification is that the modification is to mix small molecules into the resin, while the modification of plastic blending is to mix high molecules into the resin. Because the composites modified by blending are all polymers, its compatibility is better than that of additive system, and the modification has little influence on other properties of the original resin. The blend of plastics, also known as polymer alloy, is the most effective way to develop new polymer materials and the main way to realize high performance and fine refinement of existing plastics. Almost all the properties required by plastics can be obtained by blending modification. For example, PP has the advantages of small density, good transparency, high tensile strength, high hardness, good heat resistance, but its poor impact performance, stress cracking resistance is not good, such as mixing with HDPE, can maintain the original advantages of PP, and can make the blend with impact resistance, stress cracking resistance and low temperature resistance, etc..

(5) Flame retardant technology
Generally speaking, flame-retardant high polymer technology is mainly divided into two ways: additive type and reactive type, mainly additive type. In other words, the flame retardant plastic with flame retardant properties was prepared by adding flame retardant agent to the ordinary granule, mixing it fully in the blender, and then re-granulating it in the mixing device mainly composed of twin-screw extruder. In recent ten years, expansion flame retardants invented by Professor Camino of The University of Turin in Italy have played a great role in PP flame retardants. Such PN flame retardants have high efficiency, high thermal and light stability, low toxicity, low smoke, and low corrosion. They have little impact on processing and mechanical properties and will not cause environmental pollution. Decabromodiphenyl ether, octabromodiphenyl ether, tetrabromobisphenol A, hexabromocyclododecane are commonly used as additive flame retardants, among which decabromodiphenyl ether is the most commonly used. The decomposition temperature of brominated flame retardants is mostly at 200-300℃ on the left and right, which matches the decomposition temperature of various polymers, so it can play the role of flame retardancy simultaneously with the gas phase and condensation phase at the best moment, and the addition amount is small, and the effect of flame retardancy is good.

(6) Graft modification
At present, grafted modified plastics are widely used as macromolecular coupling agent, compatibilizer and toughening agent. Is currently the most common form of grafting monomers maleic acid 酑, GMA and acrylic acid, GMA and acrylic acid, people tend to get big, low grafting ratio and grafting efficiency of faults, and acrylic acid corrosion resistance is very strong. The purpose of graft modification of polypropylene is to improve the bonding or solubilization of polypropylene with metals, polar plastics and inorganic fillers. Grafting monomer is generally used in the acrylic acid and its esters, 酑 maleic acid and its ester, maleic imide, etc. Grafting methods include: (1) solution method, adding peroxide initiator in the solvent for copolymerization; Radiation method, grafting under high-energy rays; (3) Melting mixing method, in the presence of peroxide, in the molten state mixing, grafting, often in the twin screw extruder. The properties of grafted modified polymer materials are related to the physicochemical properties of grafted materials, the content of grafted materials, the length of graft chain, etc. Its basic nature can be similar to polypropylene, but its compatibility with polar polymer materials, inorganic materials, rubber, etc., can be greatly improved. The crystallinity and melting point of grafted PP decreased with the increase of graft content, but the transparency and low temperature thermal sealing property increased with the increase of graft content.

(7) Conductive function modification
Over the years, there have been numerous studies on composite conductive polymers, but there are still many problems that have not been solved. For example, when adding conductive medium to improve the conductivity, the mechanical properties will be reduced. Therefore, the development of composite conductive polymer materials mainly focuses on reducing the resistivity and improving the comprehensive properties of the materials. POE is a copolymer using metallocene catalyst ethylene-octene or ethylene-butene. It has the characteristics of narrow molecular weight distribution, narrow copolymer monomer distribution and long branch chain, which not only has excellent toughness, but also has good processing property. POE is used to modify polyolefin by blending, showing better toughening effect than traditional elastic body.

(8) Thermoplastic elastomer
Thermoplastic elastomer (TPE), as a brand new polymer material, has the advantages of both the repeatability of thermoplastic and the high elasticity of rubber and other physical and mechanical properties, as well as the excellent recovery and regeneration. Thermoplastic elastomers have a wide range of product adaptability. Thermoplastic elastomers exhibit many excellent properties due to their special molecular structure adjustability and controllability. With the development of new modification technology and the improvement of material properties, thermoplastic elastomers will have a wider market. At present, thermoplastic elastomer has developed to more than ten varieties, which have replaced part of natural rubber, synthetic rubber and plastics. Automotive thermoplastic elastomers are the most important applications, accounting for one third of the total, followed by construction, medical and daily life products.