"plastic modification", "modified plastic" and other words are often hung in our mouth, then, what is plastic modification, what is the change?

What is plastic modification?

Plastic modification is the general purpose resin through physical, chemical, mechanical methods to improve or increase its function, In electricity, magnetism, light, heat, aging resistant, flame retardant, mechanical performance and so on to use the function of the special environment condition. From the production of raw material resin to a variety of specifications and varieties of modified plastic masterbatch, in order to reduce the cost of plastic products and improve their functionality, there are plastic modification technologies.

What are the technical methods of plastic modification?

Mention plastic modification, many people will think of filling, blending, fiber reinforcement, etc., but few people have a very comprehensive understanding of plastic modification technology. In fact, plastic modification commonly used methods are the following:

1, add modification

In the polymer (resin) to add small molecule inorganic matter or organic matter, through physical or chemical action, in order to obtain a certain expected performance of a modification method. This method is one of the earliest modification methods, its modification effect is obvious, the process is simple, the cost is low, so it is widely used. I believe that those who have done graduation projects in colleges and universities have come into contact with and understand this method.

This modification method according to the purpose of modification is divided into reducing cost (add a variety of cheap inorganic, organic fillers), improve strength (add a variety of reinforcement fibers), improve toughness (add elastomers and ultrafine fillers, etc.), improve flame retardancy (add metal oxides, metal hydroxide, inorganic phosphorus, organic halide, organophosphorus, silicone and nitride Etc.), improve the life (add a variety of antioxidants, light stabilizers, etc.), improve the processability (add plasticizers, heat stabilizers, lubricants and processing AIDS, etc.), increase the wear resistance (add graphite, MoS2, SiO2, etc.), improve the crystal structure (add nucleating agents, Specific organic carboxylic acids, sorbitol, etc.), improve antistatic and electrical conductivity (add antistatic agents and conductive agents), improve degradability (starch filling, degradation additives, etc.), improve anti-ray radiation performance, etc.

Additives commonly used in this method are: inorganic additives (fillers, enhancers, flame retardants, colorants and nucleating agents, etc.), organic additives (plasticizers, organotin stabilizers, antioxidants and organic flame retardants, degradation additives, etc.).

(2) Adding polymer material

This method has also become a blending modification, the main method is to blend one or more other resins (including plastics and rubber) in a resin, so as to change the performance of the original resin. Because the composite system modified by blending is a polymer substance, its compatibility is better than the addition of small molecules of the system, while the modification of the other properties of the original resin does not have much impact. Our common polymer alloy is the modified product of this method. Blending modification is the most effective way to develop new polymer materials, and it is also the main way to achieve high performance and refinement of existing plastic varieties.

2, shape and structure modification

This method is mainly for the plastic itself resin shape and structure to modify. The usual method is to change the crystalline state of the plastic, crosslinking, copolymerization, grafting and so on.

(1) Morphological control modification

The morphological control modification of plastics is to control the different aggregation forms of plastic products, so that it can achieve our expected performance. This method is under the action of non-external force through the adjustment of processing and forming process conditions, shape control, generally known as self-modification, of which self-enhancement is the most commonly used. Many properties of plastics can be improved through plastic shape control, such as mechanics, heat, optics and other aspects, and some aspects of the modification effect is very obvious. For example, the quality of crystallization is controlled by nucleation technology, and the high orientation is obtained by bidirectional stretching technology.

(2) Crosslinking modification

Crosslinking should be familiar, generally linear structure crosslinking network structure or three-dimensional structure. Cross-linking is triggered by external conditions, usually different forms of energy (such as light, heat, radiation, etc.). Macromolecular chains produce reactive free radicals or functional groups due to external action, thus forming new chemical bonds between macromolecular chains, so that linear structure polymers form different degrees of network structure polymers. For example the crosslinking modification of polypropylene can be improve its mechanical properties .

(3) copolymerization and graft modification

This method is mainly to add other molecular segments or functional groups to the original molecular chain. Copolymerization refers to the polymerization reaction of two or more monomers, which can expand the properties of polymers and is an important way to improve the properties and uses of polymers. For example, polystyrene and acrylonitrile copolymerization improves the weakness of polystyrene brittleness; Polyvinyl chloride and vinyl acetate copolymerization improve the plasticity of polyvinyl chloride. Chain transfer grafting, chemical grafting, radiation grafting, its modification in rigid body and elastomer applications more, such as styrene-butadiene graft copolymer to improve the impact performance of PS.

3, composite modification

Composite modification of plastics that is, two or more layers of film, sheet and other materials are composite together to form a multilayer film, sheet and other materials method by adhesive or hot melt. The composite modification of plastics is actually the extreme of the intermediate blend modification method of plastic blending, and can also be regarded as a special plastic blending modification.

4, surface modification

Plastic surface modification refers to a class of modification methods that change the surface properties of plastic products by physical or chemical methods. Plastic surface modification is different from other modifications in two points: first, its modification is limited to the surface of the product, and its internal properties do not change; The second is that its modification is implemented after a molding process of plastic products, which belongs to secondary processing modification.

The purpose of plastic surface modification can be mainly divided into two categories: one is the modification of direct application, and the other is the modification of indirect application.

(1) Direct application of plastic surface modification Direct application 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 retardant, surface conductivity and surface barrier. In recent years, the modification of the plastic surface has been developed and applied quickly, such as in the plastic barrier modification, the surface barrier modification occupies a very important position.

(2) Indirect application of plastic surface modification Indirect application modification refers to some modifications for direct application, such as to improve the adhesion of plastics, printability and layering properties and improve the plastic surface tension modification. For example, taking plastic electroplating as an example, only abs coating fastness of non-surface treated plastic varieties can meet the requirements; Especially polyolefin plastic varieties, the coating fastness is very low, must be modified to improve the combination with the coating fastness, can be electroplating treatment.

What is the modification?

Plastic modification has its purpose, and the modification method used for each demand purpose is different. Here we introduce several commonly encountered modification needs and the modification methods used.

1, change the density of plastic

(1) Reduce the density of plastic

Say that reduce the density may be you know, but in another way you understand: make plastic lighter. The density of plastics is reduced by foaming modification, adding light filler and blending light resin three kinds. Foam molding of plastic products is the most effective way to reduce its density. The two modification methods of adding light additives and blending light resin can only reduce the density slightly, the reduction is generally only about 50%, and the lowest relative density can only reach about 0.5.

Plastic foam products have a wide range of density changes, and the minimum relative density can reach 10-3.

(2) To improve the density of plastic

To improve the density of plastic is a method to increase the relative density of the original resin, mainly to add heavy filler and blend heavy resin. Add weight filler to improve the density of plastic methods the main filler metal powder, heavy mineral filler; Blending heavy resin to improve the density of plastics, this method of improvement is relatively small, generally the highest can only reach about 50%. Mainly suitable for some light resins such as PE, PP, PS, EVA, PA1010 and PPO. Often added heavy resins are: PTFE, FEP, PPS and POM.

2, the transparency of plastics improve

About the transparency of plastics, in the previous article has been introduced, here is only a brief introduction. The principle of improving the transparency of plastics is to use the relationship between crystals and transparency. The transparency of plastic is related to the crystallinity size and crystalline structure of its products, and its transparency can be improved by controlling the different morphological structures of the products.

To measure the transparency of a material, there are many performance indicators that need to be considered. Commonly used indicators are: light transmittance, fog, refraction index, birefringence and dispersion. In the above indicators, the light transmittance and fog two indicators are mainly used to characterize the light transmittance of the material, while the refractive index, birefringence and dispersion three indicators are mainly used to characterize the light transmittance quality of the material. A good transparent material requires the above performance indicators to be excellent and balanced.

Commonly used methods to change the crystal type are:

¢Ù Control the crystal quality, such as crystal type, spherulite content, crystal size, crystal regularity control;

¢Ú Improve the refractive index, mainly by adding high refractive index organic matter or inorganic matter that does not affect the transparency to improve;

¢Û Reduce birefringence, you can control the orientation in the processing, that is, reduce the orientation and achieve the purpose of reducing birefringence.

¢Ü Add to improve the transparency of plastics, refers to the method of adding small molecular substances in transparent resin, so as to improve its transparency. The use of this method can improve the transmittance, refractive index, reduce birefringence.

¢Ý Adding nucleating agent is the most effective way to increase the light transmittance of transparent resin. Nucleating agent is a small molecule substance that can promote crystallization. It can play the role of crystal nucleus in the resin, so that the original homogeneous nucleus becomes heterogeneous nucleation, increase the number of crystal nuclei in the crystallization system, increase the number of microcrystals, reduce the number of spherulites, so that the crystal size is finer and the transparency of the resin is improved.

6 add high refractive index inorganic

7) added to reduce the birefringence of the material

today add anti mist

3, plastic hardness and flexibility improved

(1) add to improve the hardness of plastic refers to the plastic hard additive is added to a modification method. The commonly used hardness filler is rigid inorganic filler and fiber.

(2) The surface hardness improvement method of plastic refers to only improving the hardness of the surface of plastic products, and the hardness of the internal product is unchanged. This is a low-cost hardness improvement method. 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 blended and composite improved plastics: ¢Ù The plastic blending improved method is to mix high hardness resin in low hardness resin ¡ù¡ù to improve its overall hardness. Common blend resins are: PS, PMMA, ABS and MF, etc., need to modify the resin mainly PE class, PA, PTFE and PP. ¢Ú The method of improving the hardness of plastic composite is to compound a layer of 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. The commonly used composite resins are PS, PMMA, ABS and MF.

(4) Add plasticizer to improve the flexibility of plastics: the main role of plasticizer is to improve the processability of resin, that is, reduce the processing temperature and improve the processing fluidity. However, it is added to the related resin, and can also give the product flexibility. Suitable for plasticizers to improve the flexibility of the resin are: pvc, PVDC, CPE, SBS, PA, ABS, PVA and chlorinated polyethers.

4, plastic processing performance improvement

Plastic processing process is from plastic raw materials (resin + additives) into a certain strength of the product process. Thermoplastic resin and thermosetting resin the changes in the processing process are different. Improving the processing properties of plastics mainly focuses on: increasing the thermal decomposition temperature of the resin; Reduce the melting temperature of the resin; Improve the processing flow of resin; And improve the melt properties of the resin. Common modification methods are additive modification, adding plasticizers and lubricants. Plasticizer can improve polymer plasticity; The role of lubricant is to reduce the friction between the materials and the surface of the materials and processing equipment, reduce the flow resistance of the melt from the surface, reduce the viscosity of the melt, improve the fluidity of the melt, avoid the adhesion of the melt and the equipment, improve the finish of the surface of the product.

5, the enhancement of plastics

The enhancement of plastics is generally to add reinforcing fillers and fibers. Most of the conventional fillers are added directly to the resin, which will cause the tensile strength of the plastic to decrease. But some special fillers that go through the surface for a while or are directly added not only do not cause a decline in tensile strength, but will improve the tensile strength to a certain extent, we call this kind of filler as a reinforcement filler. The reinforcement modification of the reinforcement fill is far less than that of the reinforcement fiber, and can only be used for some occasions where the strength requirements are not too high. Plastic fiber reinforcement method is the most commonly used and effective reinforcement method. Fiber reinforcement materials are the most important reinforcement materials for plastics, and their dosage can account for more than 90% of the entire reinforcement materials. Reinforcement fiber materials include fiber and whisker two categories, the specific varieties are mainly: Inorganic (such as glass fiber, asbestos fiber, carbon fiber, whisker, quartz fiber, graphite fiber and ceramic fiber, etc.), organic (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.).

6, the toughening of plastics

The toughening of plastics 1Generally blend elastomer materials, commonly used elastomer toughening materials are: high impact resin, such as CPE, MBS, ACR, SBS, ABS, EVA, modified petroleum resin (MPR); High impact rubber, such as ethylene propylene rubber (EPR), ethylene propylene diene rubber (EPDM), nitrile rubber (NBR), styrene butadiene rubber, natural rubber, butadiene rubber, butyl rubber, neoprene rubber, polyisobutene and butadiene rubber, etc.

7, the thermal properties of plastics and flame retardant performance improvement

The thermal properties of plastic products are mainly heat resistant temperature and low temperature. Heat resistance temperature can be mainly used in heat deformation temperature, Martin heat resistance temperature and Vica softening point; And the low temperature temperature can generally be expressed by embrittlement temperature. In all fillers, in addition to organic fillers, most inorganic mineral fillers can significantly improve the heat resistance temperature of plastics. Commonly used heat-resistant fillers are: calcium carbonate, talc powder, wollastonite, mica, calcined clay, bauxite and asbestos. For example, the maximum use temperature of mica can reach 1000 degrees Celsius, which is the most effective heat-resistant modified filler. In addition, the reinforced plastic changes the heat resistance effect is better than the filling, mainly because the heat resistance of most fibers is very high, and the melting point is more than 1500 degrees Celsius. Commonly used heat resistant fibers are mainly: asbestos fiber, glass fiber, carbon fiber, whisker, polyamide fiber and acrylic fiber.

The flame retardancy of most plastics is not very good, and flame retardants need to be added to the plastic formula. Flame retardants, which are a class of additives that can prevent plastics from igniting or inhibit the spread of flames. In addition, it is necessary to add smoke suppressants.

8, plastic cost reduction

Reduce the cost of plastics has been the pursuit of manufacturers, so some modification methods will be used to reduce costs. The main methods are to add fillers, blend cheap resin and so on. Of course, it is hoped that the supplier can reduce the cost without forgetting the need for performance.

plastic modification is nothing more than the above content, the specific actual modification process is very complex, on the one hand is the cost benefit limitation, on the other hand is the customer demand, need a variety of modification methods to achieve.

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