1 density

　　There are two ways to change the density of plastics, one is to reduce the density of plastics, the other is to increase the density of plastics, depending on the choice of terminal applications. Here mainly introduces the way to reduce the density of plastics. Reduce the density of plastic: according to the formula M= ρ v. That is to say, when the density of the material is reduced, the mass of the original product will be reduced without changing the volume of the original product. The common way to reduce the density of plastics is to add light filler or resin, but the decrease of density is small; The other is foaming technology, which has a wide range of weight loss, but is a little more difficult.

　　2 transparency

　　The transparency of plastics is related to the crystallinity of products. The transparency can be improved by controlling or changing the crystallinity and crystal structure of products (such as crystal form, spherulite content, crystal size and crystal regularity).

　　To measure the transparency of a material, many performance indicators need to be considered. Commonly used indicators are: transmittance, haze, refractive index, birefringence and dispersion. A good transparent material requires excellent and balanced performance.

　　Common methods to improve transparency include:

　　① To improve the refractive index, it is mainly to add high refractive index organic or inorganic materials that do not affect the transparency to improve the refractive index.

　　② To reduce the birefringence, we can control the orientation in the process, that is, to reduce the degree of orientation.

　　③ Adding nucleating agent is the most effective way to increase the transmittance of transparent resin. Nucleating agent is a kind of small molecular substance which can promote crystallization. It can play the role of nucleation in the resin, making the original homogeneous nucleation into heterogeneous nucleation, increasing the number of nuclei in the crystallization system, increasing the number of microcrystals and reducing the number of spherulites, so as to make the crystal size smaller and improve the transparency of the resin.

　　④ Add antifogging agent.

　　3 hardness and flexibility

　　(1) Hardness change the hardness of plastics is divided into surface hardness and overall hardness. Generally, hard additives are added to plastics, which are generally rigid inorganic fillers. Surface hardness: only improve the hardness of the appearance of plastic products, and the hardness of the internal products unchanged. Low cost, mainly used for decorative materials, daily necessities, etc. The main methods are coating, plating and surface treatment. Overall hardness: it is generally improved by blending plastics, that is, mixing high hardness resin with low hardness resin to improve its overall hardness. The common blend resins are PS, PMMA, ABS and MF, and the resins to be modified are mainly PE, PA, PTFE and PP( 2) The main function of plasticizer is to improve the processability of resin, that is to reduce the processing temperature and improve the processing fluidity. But when it is added to the relevant resin, it can also give the product flexibility. Suitable for plasticizer to improve the flexibility of the resin are: PVC, PVDC, CPE, SBS, PA, ABS, PVA and chlorinated polyether.

　　4 processing performance

　　Improving the processability of plastics is generally shown as follows: increasing the thermal decomposition temperature of resin; Reduce the melting temperature of the resin; Improve the processing fluidity of resin; The melt properties of the resin were improved. The common modification methods are adding modification, plasticizer and lubricant. Plasticizer can improve the plasticity of polymer; The function of lubricant is to reduce the friction between materials and the surface of materials and processing equipment, so as to reduce the flow resistance of melt, reduce the viscosity of melt, improve the fluidity of melt, avoid the adhesion between melt and equipment, and improve the surface finish of products.

　　5 strength

　　The reinforcement of plastics is to add reinforcing filler and fiber. Most of the conventional fillers directly added to the resin will cause the tensile strength of the plastic to decrease. However, some special fillers directly added not only do not cause the decrease of tensile strength, but also improve the tensile strength to a certain extent, which is called reinforcing fillers. The modification effect of reinforcing filler is far less than that of reinforcing fiber, which can only be used in some occasions where the strength requirement is not too high. Fiber reinforcement is the most common and effective method. Fiber reinforced material is the most important reinforced material for plastics, and its dosage can account for more than 90% of the whole reinforced material. It mainly includes fiber and whisker, including inorganic fiber (such as glass fiber, asbestos fiber, carbon fiber, whisker, quartz fiber, graphite fiber and ceramic fiber), organic fiber (such as PAN fiber, polyethylene fiber, PA fiber, PC fiber, PVC fiber and polyester fiber), and metal fiber (such as boron fiber and aluminum, titanium, calcium and other metal whiskers).

　　6 toughness

　　The toughening of plastics is usually the blending of elastomer materials to enhance the toughness of plastics. Commonly used elastomer toughening materials are: high impact resin, such as CPE, MBS, EVA, modified petroleum resin (MPR), etc; High impact rubber, such as ethylene propylene rubber (EPR), ethylene propylene diene monomer (EPDM), nitrile rubber (NBR), styrene butadiene rubber, natural rubber, cis-1,4-polybutadiene rubber, chloroprene rubber, etc.

　　7 thermal properties

　　The main thermal properties affecting the use of plastic products are heat resistance and low temperature resistance. The heat resistance temperature can be expressed as heat deformation temperature, martin heat resistance temperature and Vicat softening point; The temperature of low temperature resistance can be expressed by embrittlement temperature. In all fillers, except for organic fillers, most inorganic mineral fillers can significantly improve the heat resistance temperature of plastics. Commonly used heat-resistant fillers are: calcium carbonate, talc, wollastonite, mica, calcined clay, bauxite and asbestos. In addition, the heat resistance of plastics can be obviously improved by fiber reinforced modification, which is mainly because the heat resistance temperature of most fibers is very high, and the melting point is more than 1500 ℃. The commonly used heat-resistant fibers are asbestos fiber, glass fiber, carbon fiber, whisker, polyamide fiber and acrylic fiber.

　　8 flame retardancy

　　Most plastics are flammable, flame retardant performance is not very good, so in some formulations need to add flame retardant, flame retardant is generally can improve the ignition point of plastics, or can inhibit the spread of flame. The commonly used flame retardants are halogen flame retardant, phosphorus flame retardant, inorganic flame retardant, ammonium salt flame retardant, organosilicon flame retardant, lamellar inorganic nano material flame retardant, intumescent flame retardant, etc.