Plastic is a material with high polymer as the main component. It is composed of synthetic resin and fillers, plasticizers, stabilizers, lubricants, pigments and other additives. It is in a fluid state during manufacturing and processing to facilitate modeling , It presents a solid shape when processing is completed.
The main component of plastic is synthetic resin. Resins are originally named after lipids secreted by animals and plants, such as rosin, shellac, etc. Synthetic resins (sometimes simply referred to as "resins") refer to polymers that have not been mixed with various additives. The resin accounts for about 40% to 100% of the total weight of the plastic. The basic properties of plastics are mainly determined by the properties of the resin, but additives also play an important role.
Why should plastic be modified?
The so-called "plastic modification" refers to the method of changing its original performance and improving one or more aspects by adding one or more other substances to the plastic resin, thereby achieving the purpose of expanding its scope of application. Modified plastic materials are collectively referred to as "modified plastics".
Up to now, the research and development of plastics chemical industry has synthesized thousands of polymer materials, of which only more than 100 are of industrial value. More than 90% of the resin materials commonly used in plastics are concentrated in the five general resins (PE, PP, PVC, PS, ABS) At present, it is very difficult to continue to synthesize a large number of new polymer materials, which is neither economical nor realistic.
Therefore, in-depth study of the relationship between polymer composition, structure and performance, and modification of existing plastics on this basis, to produce suitable new plastic materials, has become one of the effective ways to develop the plastics industry. The sexual plastics industry has also achieved considerable development in recent years.
Plastic modification refers to changing the properties of plastic materials in the direction expected by people through physical, chemical or both methods, or to significantly reduce costs, or to improve certain properties, or to give plastics New functions of materials. The modification process can occur during the polymerization of the synthetic resin, that is, chemical modification, such as copolymerization, grafting, crosslinking, etc., can also be conducted during the processing of the synthetic resin, that is, physical modification, such as filling, co- Mixing, enhancement, etc.
What are the methods of plastic modification?
1. Filling modification (mineral filling)
By adding inorganic mineral (organic) powder to ordinary plastics, the rigidity, hardness and heat resistance of plastic materials can be improved. There are many types of fillers and their properties are extremely complex.
The role of plastic fillers: improve plastic processing performance, improve physical and chemical properties, increase volume, and reduce costs.
Requirements for plastic additives:
(1) Chemical properties are inactive, inert, and do not react adversely with resin and other additives;
(2) Does not affect the water resistance, chemical resistance, weather resistance, heat resistance, etc. of the plastic;
(3) Does not reduce the physical properties of the plastic;
(4) Can be filled in large quantities;
(5) The relative density is small and has little effect on the density of the product.
2. Enhanced modification (glass fiber/carbon fiber)
Reinforcement measures: by adding fibrous materials such as glass fiber and carbon fiber.
Enhancement effect: it can significantly improve the rigidity, strength, hardness, and heat resistance of the material,
Adverse effects of modification: But many materials will cause poor surface and lower elongation at break.
Enhancement principle:
(1) Reinforced materials have higher strength and modulus;
(2) Resin has many inherent excellent physical and chemical (corrosion resistance, insulation, radiation resistance, instantaneous high temperature ablation resistance, etc.) and processing properties;
(3) After the resin is compounded with the reinforcing material, the reinforcing material can improve the mechanical or other properties of the resin, and the resin can play the role of bonding and transferring load to the reinforcing material, so that the reinforced plastic has excellent properties.
3. Toughening modification
Many materials are not tough enough and too brittle. By adding materials with better toughness or ultrafine inorganic materials, the toughness and low-temperature performance of the materials can be increased.
Toughening agent: In order to reduce the brittleness of the plastic after hardening, and improve its impact strength and elongation, an additive added to the resin.
Commonly used toughening agents-mostly maleic anhydride grafting compatibilizer:
Ethylene-vinyl acetate copolymer (EVA)
Polyolefin elastomer (POE)
Chlorinated Polyethylene (CPE)
Acrylonitrile-butadiene-styrene copolymer (ABS)
Styrene-butadiene thermoplastic elastomer (SBS)
EPDM (EPDM)
4. Flame retardant modification (halogen-free flame retardant)
In many industries such as electronic appliances and automobiles, materials are required to have flame retardancy, but many plastic raw materials have low flame retardancy. Improved flame retardancy can be achieved by adding flame retardants.
Flame retardants: also known as flame retardants, fire retardants or fire retardants, functional additives that impart flame retardancy to flammable polymers; most of them are VA (phosphorus), VIIA (bromine, chlorine) and Compounds of ⅢA (antimony, aluminum) elements.
Molybdenum compounds, tin compounds, and iron compounds with smoke-suppressing effects also belong to the category of flame retardants. They are mainly used for plastics with flame retardant requirements to delay or prevent the burning of plastics, especially polymer plastics. Make it longer to ignite, self-extinguishing, and difficult to ignite.
Plastic flame retardant grade: from HB, V-2, V-1, V-0, 5VB to 5VA step by step.
5. Weather resistance modification (anti-aging, anti-ultraviolet, low-temperature resistance)
Generally refers to the cold resistance of plastics at low temperatures. Due to the inherent low temperature brittleness of plastics, plastics become brittle at low temperatures. Therefore, many plastic products used in low temperature environments are generally required to have cold resistance.
Weather resistance: refers to a series of aging phenomena such as fading, discoloration, cracking, chalking, and strength reduction of plastic products due to the influence of external conditions such as sunlight, temperature changes, wind and rain. Ultraviolet radiation is a key factor in promoting plastic aging.
6. Modified alloy
Plastic alloy is the use of physical blending or chemical grafting and copolymerization methods to prepare two or more materials into a high-performance, functional, and specialized new material to improve the performance of one material or have both The purpose of material properties. It can improve or enhance the performance of existing plastics and reduce costs.
General plastic alloys: such as PVC, PE, PP, PS alloys are widely used, and the production technology has been generally mastered.
Engineering plastic alloy: refers to the blend of engineering plastics (resin), mainly including the blending system with PC, PBT, PA, POM (polyoxymethylene), PPO, PTFE (polytetrafluoroethylene) and other engineering plastics as the main body, And ABS resin modified materials.
The growth rate of PC/ABS alloy usage is in the forefront of the plastics field. At present, the research of PC/ABS alloying has become a research hotspot of polymer alloys.
7. Zirconium phosphate modified plastic
1) Preparation of polypropylene PP/organic modified zirconium phosphate OZrP composite by melt blending method and its application in engineering plastics
First, octadecyl dimethyl tertiary amine (DMA) is reacted with α-zirconium phosphate to obtain organically modified zirconium phosphate (OZrP), and then OZrP is melt blended with polypropylene (PP) to prepare PP/OZrP composites . When OZrP with a mass fraction of 3% is added, the tensile strength, impact strength, and flexural strength of the PP/OZrP composite can be increased by 18. 2%, 62. 5%, and 11. 3%, respectively, compared with the pure PP material. The thermal stability is also significantly improved. This is because one end of DMA interacts with inorganic substances to form a chemical bond, and the other end of the long chain is physically entangled with the PP molecular chain to increase the tensile strength of the composite. The improved impact strength and thermal stability are due to the zirconium phosphate induced PP to produce β crystals. Secondly, the interaction between the modified PP and the zirconium phosphate layers increases the distance between the zirconium phosphate layers and better dispersion, resulting in increased bending strength. This technology helps to improve the performance of engineering plastics.
2) Polyvinyl alcohol/α-zirconium phosphate nanocomposite and its application in flame retardant materials
Polyvinyl alcohol/α-zirconium phosphate nanocomposites can be mainly used for the preparation of flame retardant materials. the way is:
① First, the reflux method is used to prepare α-zirconium phosphate.
②According to the liquid-solid ratio of 100 mL/g, take quantitative α-zirconium phosphate powder and disperse it in deionized water, add ethylamine aqueous solution dropwise under magnetic stirring at room temperature, then add quantitative diethanolamine, and ultrasonically treat to prepare ZrP-OH aqueous solution.
③Dissolve a certain amount of polyvinyl alcohol (PVA) in 90 ℃ deionized water to make a 5% solution, add a quantitative ZrP-OH aqueous solution, continue to stir for 6-10 hours, cool the solution and pour it into the mold to air dry at room temperature , A thin film of about 0.15 mm can be formed.
The addition of ZrP-OH significantly reduces the initial degradation temperature of PVA, and at the same time helps promote the carbonization reaction of PVA degradation products. This is because the polyanion generated during the degradation of ZrP-OH acts as a proton acid site to promote the shearing reaction of the PVA acid group through the Norrish II reaction. The carbonization reaction of the degradation products of PVA improves the oxidation resistance of the carbon layer, thereby improving the flame retardant performance of the composite material.
3) Polyvinyl alcohol (PVA)/oxidized starch/α-zirconium phosphate nanocomposite and its role in improving mechanical properties
Α-Zirconium phosphate was synthesized by sol-gel reflux method, organically modified with n-butylamine, and OZrP and PVA were blended to prepare PVA/α-ZrP nanocomposite. Effectively improve the mechanical properties of the composite material. When the PVA matrix contains 0.8% by mass of α-ZrP, the tensile strength and elongation at break of the composite material are increased by 17. 3% and 26. Compared with pure PVA, respectively. 6%. This is because α-ZrP hydroxyl can produce strong hydrogen bonding with starch molecular hydroxyl, which leads to improved mechanical properties. At the same time, the thermal stability is also significantly enhanced.
4) Polystyrene/organic modified zirconium phosphate composite material and its application in high temperature processing nanocomposite materials
α-Zirconium phosphate (α-ZrP) is pre-supported by methylamine (MA) to obtain MA-ZrP solution, and then the synthesized p-chloromethyl styrene (DMA-CMS) solution is added to the MA-ZrP solution and stirred at room temperature 2 d, the product is filtered, the solids are washed with distilled water to detect no chlorine, and dried in vacuum at 80 ℃ for 24 h. Finally, the composite is prepared by bulk polymerization. During the bulk polymerization, part of the styrene enters between the zirconium phosphate laminates, and a polymerization reaction occurs. The thermal stability of the product is significantly improved, the compatibility with the polymer body is better, and it can meet the requirements of high-temperature processing of nanocomposite materials.