Plastic modification is the production of large quantities of general-purpose resins from petrochemical enterprises through physical, chemical and mechanical methods to improve or increase their functionality in terms of electricity, magnetism, light, heat, ageing resistance, flame retardancy and mechanical properties for use under special environmental conditions.
Modified plastics is a wide-ranging, high-technology area of the plastics industry, and plastic modification technologies - filling, blending and reinforcement modification - are deeply embedded in the raw materials and moulding processes of almost all plastic products. From the production of raw material resins to modified plastic masterbatches from a variety of specifications and varieties, in order to reduce the cost of plastic products and improve their functionality, inseparable from the plastic modification technology.
In order to reduce costs, improve performance and meet different needs, plastics often have to be modified in order to adapt to various practical requirements. Here are a few common plastic modification techniques.
(1) Fibre reinforcement. Long fiber-reinforced thermoplastics (UCRT) is a new lightweight, high-strength engineering structural materials, because of its light weight, cheap, easy to recycle and reuse, the application in the automobile is developing rapidly. The use of natural fibres such as flax and sisal reinforced plastics for the manufacture of body parts has been recognised in the automotive industry. On the one hand, because natural fibres are environmentally friendly materials, on the other hand, plant fibres are 40% lighter than glass fibre, reducing the weight of the car can reduce fuel consumption. The use of linen-reinforced PP for the production of underbody panels, the material's tensile strength than steel to be higher, stiffness is not less than glass-fibre reinforced materials, the system is easier to recycle parts. British GKN technology company with fibre-reinforced plastic manufacturing drive shaft, weight reduction of 50%-60%, torsional resistance than steel 1.0 times greater, bending stiffness 1.5 times greater. Plastic springs provide a significant weight reduction. With carbon fibre reinforced plastic (CFRP) manufactured plate spring is 14kg, reducing weight by 76%. In the United States, Japan and Europe have used plate springs, cylindrical coil springs to achieve fiber-reinforced plastic, in addition to the obvious vibration and noise reduction effect, but also to achieve the purpose of light weight.
(2) Toughening technology. The stiffness (including strength) and toughness of polymer structural materials are two important performance indicators of mutual constraints. Therefore, the research of enhancing stiffness while enhancing toughening has been a difficult problem in polymer material science. The Institute of Chemistry, Chinese Academy of Sciences, polymer blends filled with a new way to enhance toughening, the results in solving the scientific problem of polymer materials while enhancing the toughening of an important breakthrough, the first time in China to successfully prepare ultra-high toughness polyolefin engineering plastics, for large varieties of general-purpose plastics upgrade, for engineering plastics as well as engineering plastics to provide a new way to further high performance. The Ministry of Education's Supergravity Engineering Technology Research Centre has successfully developed the "nano-CaCO3 plastic toughening masterbatch and its preparation technology", a national "863" project. This masterbatch can make PVC toughened and modified, mainly used in the production of PVC doors and windows profiles, but also in the production of other hard products such as PVC pipes and plates. From the development trend, PVC plastic doors and windows have the potential to replace steel and wooden windows and doors. At present, the annual production capacity of PVC window and door profiles in China is 1 million t, and the trend is constantly rising. The use of nano-CaCO3 plastic toughening masterbatch to produce PVC window and door profiles can not only improve the overall performance of the product, but also reduce the cost of more than 100 tons of profiles per ton. At the same time, its application areas will also be extended to PP, ABS and other plastic materials. The use of nano-CaCO3 to toughen PVC is a non-elastomeric toughening plastic technology (inorganic rigid particle toughening plastic technology) that has been developed in recent years and is still at the research stage in China. The direct addition of nano-CaCO3 will have two major problems: firstly, the nano-particles will agglomerate in the plastic matrix, so that the dispersion is not uniform, affecting the toughening effect; secondly, as the nano-CaCO3 particles are tiny, it is very easy to produce dust, affecting the environment. The successful development of nano-CaCO3 plastic toughening masterbatch and its preparation technology has effectively solved these two major problems faced in the same research field at home and abroad.
(3) Filling modification (powder filling). Plastic filling modification since the early 1980s into the market, due to its low price, excellent product performance, and improve certain physical properties of plastic products, can replace synthetic resins, and the production process is simple, small investment, with significant economic and social benefits. Week filling modified inorganic powder material surface modifier from stearic acid to coupling agent, received a certain effect, and coupling agent has silane, titanate, aluminate, borate, phosphate ester and other varieties have emerged.
Talc is commonly used to fill polypropylene. Talc has a flake configuration of flake structure characteristics, so the finer particle size of talc can be used as a filler for polypropylene reinforcement. In the modified system of polypropylene, the addition of ultrafine talc masterbatch can not only significantly improve the rigidity, surface hardness, thermal creep, electrical insulation, dimensional stability, but also the impact strength of polypropylene. The addition of a small amount of talc to polypropylene can also play a nucleating agent role, improving the crystallinity of polypropylene, thus improving the mechanical properties of polypropylene, as well as improving the crystallinity of polypropylene, refining the grain, and improving the transparency of polypropylene. Polypropylene composites filled with 20% and 40% ultrafine talc are able to significantly improve the rigidity and creep resistance of polypropylene at both room and high temperatures. For polyethylene blown film, filled with ultrafine talc masterbatch is better than other fillers, easy to shape and good processability.
(4) Blending modification. Plastic blending modification refers to a resin mixed with one or more other resins (including plastics and rubber), so as to change the original resin performance of a modification method. Plastic blending modification is a common plastic modification method that goes hand in hand with the addition of modification. The difference between additive modification and plastic modification is that additive modification is the mixing of small molecules in the resin, while plastic blending modification is the mixing of polymeric substances in the resin. As the compound system of blending modification are high molecular substances, thus its compatibility is better than the additive system, and the modification of the original resin at the same time, the other properties of the impact is relatively small. Blends of plastics, also known as polymer alloys, are an effective way to develop new polymer materials and are the main way to achieve high performance and refinement of existing plastic varieties. Almost all the properties needed for plastics can be obtained by blending modifications. For example, PP has a small density, good transparency, high tensile strength, high hardness, good heat resistance and other advantages, but its poor impact performance, stress cracking resistance is not good, such as blending with HDPE, can maintain the original advantages of PP, but also make the blend has the advantages of impact resistance, stress cracking resistance and low temperature resistance.
(5) flame retardant technology. Generally speaking, polymer flame retardant technology is mainly divided into two ways: additive and reaction type, mainly additive type. In other words, a matching flame retardant is added to ordinary pellets, which are fully mixed in a mixer, and then re-granulated into a mixing device, mainly a twin-screw extruder, to prepare a flame retardant modified "flame retardant plastic". In the past ten years, the expansion type flame retardants pioneered by Professor Camino of the University of Turin, Italy, have played a great role in the flame retardant technology of PP. These PN-based flame retardants have high efficiency, high thermal and light stability, low toxicity, low smoke, low corrosion, low impact on processing and mechanical properties, and do not cause environmental pollution. Added flame retardants commonly used are decabromodiphenyl ether, octabromo ether, tetrabromobisphenol A, hexabromocyclododecane, etc., of which decabromodiphenyl ether in particular is used in large quantities. The decomposition temperature of brominated flame retardants is mostly around 200-300℃, which matches the decomposition temperature of various polymers, so they can play a flame retardant role at a good moment with the gas phase and coalescence, and the amount added is small and the flame retardant effect is good.
(6) Grafting modification. At present, graft modified plastic as a large molecule coupling agent, compatibilizer, toughening agent, etc., the application is very wide. The current common grafting monomer is maleic acid, GMA and acrylic acid, GMA and acrylic acid, there are large tendency to poly, grafting rate and grafting efficiency is low and other shortcomings, and the acrylic acid is very corrosive. The purpose of graft modification of polypropylene is to improve the adhesion or solubility of polypropylene to metals, polar plastics and inorganic fillers. The grafting monomers used are generally acrylic acid and its esters, maleic acid and its esters, maleimides, etc. The grafting methods are: (i) the solution method, where a peroxide initiator is added to the solvent for copolymerisation; (ii) the radiation method, where grafting is carried out under high-energy radiation; and (iii) the melt mixing method, where grafting is carried out in the presence of peroxide by mixing in a molten state, often in a twin-screw extruder. The properties of graft-modified polymers are related to the physical and chemical properties of the graft, as well as the content of the graft, the length of the graft chain, etc. The basic properties are similar to those of polypropylene, but the compatibility with polar polymers, inorganic materials, rubber, etc. can be greatly improved. The crystallinity and melting point of grafted PP decreases with the increase of graft content, while the transparency and low-temperature heat sealability increases.
(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 well solved. Such as in the addition of conductive media to improve the conductivity of the same time, mechanical properties will be reduced, so the development of composite conductive polymer materials are mainly focused on reducing resistivity and improve the overall material
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