Words such as "plastic modification" and "modified plastic" are often mentioned by us. So, what is plastic modification and what kind of properties are changed?
What is plastic modification?
Plastic modification is to improve or increase the functions of general-purpose resins through physical, chemical, and mechanical methods, and achieve use under special environmental conditions in terms of electrical, magnetic, optical, thermal, aging resistance, flame retardant, and mechanical properties. Function. 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 will exist.
What is the purpose of modification?
The purpose of plastic surface modification can be mainly divided into two categories: one is direct application modification, and the other is indirect application modification.
(1) Directly applied plastic surface modification Directly applied modification refers to some modifications that can be directly applied, specifically surface gloss, surface hardness, surface wear resistance and friction, surface anti-aging, surface flame retardancy, Surface conductivity and surface barrier, etc. This aspect of plastic surface modification has been rapidly developed and applied in recent years. For example, in plastic barrier modification, surface barrier modification occupies a very important position.
(2) Indirect application plastic surface modification Indirect application modification refers to some modifications that lay the foundation for direct application, such as improving the surface tension of plastics to improve the adhesion, printability and layering properties of plastics. modification. For example, taking plastic electroplating as an example, only ABS coating fastness can meet the requirements for plastic varieties without surface treatment; especially polyolefin plastic varieties, the coating fastness is very low, and surface modification must be carried out to improve the bonding strength with the coating. degree before electroplating can be carried out.
What properties does modification change?
Plastic modification has its purpose, and the modification methods used for each required purpose are different. Here are several commonly encountered modification requirements and the modification methods used.
Change the density of plastic
(1) Reduce plastic density
Maybe you know what it means to reduce density, but you’ll understand it another way: making plastic lighter. There are three ways to reduce the density of plastics: foaming modification, adding lightweight fillers and blending lightweight resins. Foam molding of plastic products is the most effective way to reduce their density. However, the two modification methods of adding lightweight additives and blending lightweight resins can only reduce the density slightly. The reduction is generally only about 50%, and the minimum relative density can only reach about 0.5. The density of plastic foam products varies over a wide range, with the lowest relative density reaching 10-3.
(2) Increase plastic density
Increasing the density of plastic is a method to increase the relative density of the original resin, mainly by adding heavy fillers and blending heavy resins. The main methods of adding heavy fillers to increase the density of plastics include metal powder and heavy mineral fillers; blending heavy resins to increase the density of plastics has a relatively small improvement, generally only reaching a maximum of about 50%. Mainly suitable for some light resins such as PE, PP, PS, EVA, PA1010 and PPO. Heavy resins that are often added include: PTFE, FEP, PPS and POM, etc.
Improved transparency of plastics
The transparency of plastics has been introduced in previous articles, so I will only briefly introduce it here. The principle of improving the transparency of plastics is to exploit the relationship between crystals and transparency. The transparency of plastics is related to the crystallinity and crystal structure of its products. By controlling the different morphological structures of the products, its transparency can be improved.
To measure the transparency of a material, there are many performance indicators that need to be considered. Commonly used indicators include: transmittance, haze, refractive index, birefringence and dispersion, etc. Among the above indicators, the two indicators of light transmittance and haze mainly characterize the light transmittance of the material, while the three indicators of refractive index, birefringence and dispersion are mainly used to characterize the light transmission quality of the material. A good transparent material requires the above performance indicators to be excellent and balanced.
The common methods of changing the crystal type are:
① Control the crystal quality, such as crystal type, spherulite content, crystal size and crystal regularity;
② Improve the refractive index mainly by adding high refractive index organic or inorganic substances that do not affect the transparency;
③Reducing birefringence can reduce birefringence by controlling the orientation in processing, that is, reducing the orientation degree.
④Add to improve the transparency of plastic, refers to the addition of small molecules in the transparent resin, so as to improve its transparency method. This method can improve the light transmittance, refractive index, and reduce the birefringence.
⑤ Adding a nucleating agent is the most effective way to increase the light transmittance of the transparent resin. Nucleating agents are small molecular substances that can promote crystallization. It can play the role of crystal core in the resin, so that the original homogeneous nucleation into heterogeneous nucleation, increase the number of crystal cores in the crystallization system, increase the number of microcrystals, reduce the number of spherulites, so that the size of the crystal becomes fine, improve the transparency of the resin.
⑥ Add high refractive index inorganic
⑦ add can reduce birefringence substance
Improvements in plastic hardness and flexibility
(1) The hardness of adding improved plastic refers to a modification method of adding hard additives to plastic. The common hardness filling agent is rigid inorganic filler and fiber.
(2) The surface hardness of plastic refers to only improve the hardness of the appearance of plastic products, while the internal hardness of the products remains the same. This is a low-cost method for hardness improvement. This modification method is mainly used for shell, decorative materials, optical materials and daily necessities. This modification method mainly includes three methods: coating, coating and surface treatment.
(3) the hardness of mixing and composite improvement plastic: ① plastic mixing improvement method is in the low hardness resin mixed high hardness resin, in order to improve its overall hardness. Common blend resins are: PS, PMMA, ABS and MF, etc., and the resins to be modified are mainly PE, PA, PTFE and PP.② The method of improving the hardness of plastic composite is to compound a layer of high hardness resin on the surface of low hardness plastic products. This method is mainly suitable for extrusion products, such as plate, plate, film and pipe materials. The common composite resins are PS, PMMA, ABS and MF.
(4) Add plasticizer to improve the flexibility of plastic: the main role of plasticizer is to improve the processability of resin, that is, to reduce the processing temperature, improve the processing fluidity. But it is added to the relevant resin, can also give the product flexibility. Resins suitable for improving the flexibility of plasticizer are: PVC, PVDC, CPE,
The COC polycarbonate industrial chain
SBS, PA, ABS, PVA and chlorinated polyether, etc.
Improved processing properties of plastics
The processing of plastics is the process of turning plastic raw materials (resin + additives) into products with a certain strength. Thermoplastic resins and thermosetting resins undergo different changes during processing. Improving the processing performance of plastics mainly focuses on: increasing the thermal decomposition temperature of the resin; reducing the melting temperature of the resin; improving the processing fluidity of the resin; and improving the melt characteristics of the resin. Commonly used modification methods are addition modification, adding plasticizers and lubricants. Plasticizers can improve the plasticity of polymers; the function of lubricants is to reduce the friction between materials and the surfaces of materials and processing equipment, thereby reducing the flow resistance of the melt, reducing the viscosity of the melt, improving the fluidity of the melt, and avoiding The adhesion between the melt and the equipment improves the smoothness of the product surface, etc.
Plastic Reinforcement
Plastic reinforcement is generally added with reinforcing filler and fiber. Most conventional fillers will add directly to the resin, which will cause the tensile strength of the plastic to decrease. However, some special fillers taken alone or directly added on the surface will not cause the decline of tensile strength, but will improve the tensile strength to a certain extent, we call this kind of filler reinforcement filler. The enhanced modification of the reinforcement fill is far less than the reinforced fiber, and can only be used in some occasions where the strength requirements are not too high. Plastic added fiber enhancement method is the most commonly used and effective enhancement method. Enhreinforced fiber material is the most important reinforced material for plastics, and its amount can account for more than 90% of the whole reinforced material. Enhance with fiber materials including fiber and whisker, specific varieties mainly include: inorganic class (such as glass fiber, asbestos fiber, carbon fiber, whisker, quartz fiber, graphite fiber and ceramic fiber, etc.), organic class (such as PAN fiber, polyethylene fiber, PA fiber, PC fiber, PVC fiber and polyester fiber, etc.), metal (such as boron fiber and aluminum, titanium, calcium and other metal whisker, etc.)
Toughening of plastics
The toughening of plastics is generally blended elastomer materials. Commonly used elastomer toughening materials include: high impact resins, such as CPE, MBS, ACR, SBS, ABS, EVA, modified petroleum resin (MPR), etc.; high impact resistance Rubber, such as ethylene-propylene rubber (EPR), ethylene-propylene diene rubber (EPDM), nitrile rubber (NBR), styrene-butadiene rubber, natural rubber, butadiene rubber, chloroprene rubber, polyisobutylene and butadiene rubber, etc.
Improvement of thermal properties and flame retardant properties of plastics
The thermal properties affecting the use of plastic products are mainly heat resistance temperature and low temperature temperature. Heat resistance temperature can be expressed by thermal deformation temperature, Martin heat resistance temperature and Vika softening point; and low temperature resistance temperature 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 plastic. Commonly used heat-resistant fillers are: calcium carbonate, talc powder, wollastonite, mica, calcined clay, bauxite and asbestos, etc. For example, mica maximum temperature up to 1000 degrees Celsius, is the most effective heat resistant filler. In addition, the enhancement of plastic heat resistance is better than filling, mainly because the heat resistance temperature of most fibers is very high, the melting point is more than 1500 degrees Celsius. Commonly used heat resistant fiber mainly include: asbestos fiber, glass fiber, carbon fiber, whisker, polyamide fiber and acrylic fiber.
Most plastics are not very good flame retardant, plastic formula needs to add flame retardant. Flame retardants are a class of additives that prevent plastic from igniting or inhibiting the spread of flames. In addition, also need to add smoke suppressor to assist.
Plastic cost reduction
Reducing the cost of plastics has always been the pursuit of manufacturers, so some modification methods will be used to reduce costs. The main methods include adding fillers, blending cheap resins, etc. Of course, we hope that suppliers can reduce costs while not forgetting performance needs.
The modification of plastics is nothing more than the above. The specific actual modification process is very complicated. On the one hand, it is due to cost and benefit constraints, and on the other hand, it is customer demand, which requires a variety of modification methods to be realized together.
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