The application of plastic modification technology is very wide, in order to reduce the cost of plastic products, improve the performance, improve the function, are inseparable from the plastic modification technology. Almost all the properties of plastics can be improved by modification methods, such as plastic appearance, transparency, density, accuracy, process ability, mechanical properties, chemical properties, electromagnetic properties, corrosion resistance, aging resistance, wear resistance, hardness, thermal properties, flame retardant, barrier and other aspects.
The most successful chemically modified product is known asABS, acrylonitrile-butadiene- styrene copolymer. In the physical modification method, a new material category has been formed, that is, reinforced composites. Due to the simple and strong applicability of physical modification methods such as filling and blending, such modification methods are widely used in China.
1. Agricultural plastic film
It is recognized from agricultural production that the use of plastic products for crop cover cultivation and irrigation is one of the effective ways to increase crop yield. Agricultural plastics in China developed from the cultivation of crops covered with plastic film. At present,China’s agricultural mulching film is not only ranked first in the world in terms of output and coverage area, but also greatly improved in quality. The film used has developed from ordinary transparent film to multi-variety and multi-functional film, such as the use of filling modified production of insulation functional film. The insulation effect is very significant.
As we know, the role of the agricultural plastic film is to provide a good thermal environment for crops, and at night due to the low outdoor temperature for the growth of crops particularly adverse, in order to improve the membrane temperature at night will prevent absorbs heat from the soil in the night far infrared mu (11 ~ 13 m) the way through the film.
According to the infrared spectrum analysis, SiO2 and other inorganic materials have a good absorption of far infrared in this band. Therefore, people often choose cheap, easy to process kaolin, mica and other fillers to add to the film, the production of thermal insulation agricultural film, so that the temperature in the plastic greenhouse at night can increase 1 ~ 2℃.
The development of degradable plastic film is another example of filling modification technology.The popularization and application of plastic film, while bringing great benefits to agricultural production, has caused great concern about the possible white pollution caused by the long-term residual of plastic film in soil.
2. Plastic products for packaging
The linear low density polyethylene (LLDPE), which appeared in the 1970s, has excellent mechanical properties such as tensile and tear resistance due to its molecular structure. However, its melt viscosity is quite high, which brings great difficulties to processing. By blending LLDPE and LDPE with the mass fraction of 10% ~ 50% under the condition of not changing the equipment, the packaging film with higher mechanical properties than LDPE can be produced without increasing the torque of the equipment.
For example, HDPE film containing up to 30% CaCO3 has been successfully used to make garbage bags.
3. Plastic products for daily use
Daily plastic products by a large number of applications are shoes, bags, furniture and so on. What be worth mentioning is the mixed artificial leather that uses high-tech production to go out, have excellent softness and air permeability, its performance, design and color can be comparable with dermal, not only satisfied the requirement of goods of shoe, case bag, promoted the development of afore-mentioned market conversely.
In the production of PVC artificial leather, CaCO3 is often used as filler, and the addition amount can be as high as 50%. In addition to CaCO3, kaolin, pulverized coal ash, glass beads can also be used as fillers. The addition of filler can not only reduce the cost, but also improve the hardness of PVC artificial leather, adjust the surface gloss.
4. Construction plastic products
Construction with plastic upper and lower conduit, gas pipe and plastic door window and all sorts of building plastic adornment material already accepted for people generally now, its potential market is very huge. Construction plastic products are mostly PVC, in order to improve the impact resistance and aging resistance of plastic door and window products, usually added in the formula 6% modifier (methacrylate vinegar – butadiene – styrene) Copolymer (MBS), chlorinated polyethylene (CPE) and 4% TiO2.
On the one hand, TiO2 can be used as pigment; on the other hand, it can enhance the performance of uv resistance and prolong the service life. Better mechanical properties can be obtained by adding about 5% CaCO3 in PVC pipe production.
5. Industrial supporting plastic products
In household appliances, electronic products, automobiles, posts and telecommunications, machinery, transportation and other industrial supporting products, plastic is widely used because of its excellent properties such as low density, friction resistance, corrosion resistance, insulation and heat insulation in these fields.
Modification technology can not only improve the performance of general plastics to the requirements of industrial plastics, but also overcome some weaknesses of engineering plastics meet stringent requirements for use. In fact, industrial plastics are one of the largest areas of plastic modification. PE and PP modified plastics are widely used in industrial accessories. The application of modified PE in communication cables and optical cables is an effective example in recent years.
We know that communication cable and optical cable materials have high requirements for material performance itself or processing performance, so this kind of materials abroad are sold in the form of special materials, and there is no special materials in China, are based on blending modification technology to produce communication cable insulation material, sheath material and cable sheath material.
They are prepared by blending and melting extrusion after selecting basic resin and modified resin and selecting necessary additives and processing AIDS. The obtained HDPE communication cable insulation material, LLDPE communication cable sheath material, MDPE communication cable insulation material, LDPE communication cable insulation material, LDPE communication cable sheath material can fully meet the cable materials required dielectric, low temperature resistance, oxidation resistance, heat resistance and other performance requirements. HDPE cable sheath material can meet the requirements of optical cable material wear resistance and environmental stress cracking.
In cable extrusion production, it can adapt to low and medium speed extrusion of 1200m/ min and high speed extrusion of 2400m/ min. PP is one of the important universal plastics, with low density, non-toxic, corrosion resistance and other advantages, the dosage is second only to PVC, PE.
However, its low temperature brittleness and high shrinkage rate and other shortcomings limit its use as industrial products, so modification technology is often used to improve its various properties, especially to improve its toughness. The modification of PP mainly includes copolymerization modification and blending modification. The modified PP can be used as the bumper of light vehicles and cars, housing of household appliances, car fans and so on.
The bumper is required to have good toughness and low temperature resistance，PP can be toughened by ethylene-propylene diene (EPDM) and polyolefin elastomer (POE). In pp-POe-talc toughening system, the impact strength can reach 300J/ m when POE content is 10%. When POE content is 15% ~ 25%, the impact strength can reach 550J/ m, which meets the requirements of bumper.
The addition of talc reduces the impact properties of the system, but its tensile strength, tensile elastic modulus and thermal deformation temperature are greatly increased. Modification technology is not only suitable for general plastics, but also for engineering plastics with special properties, and it is also a good way to improve the properties of materials.
As we know, polytetrafluoron (PTFE) has strong acid and alkali corrosion resistance, resistance to friction and environmental stress cracking and other excellent properties, but its creep, size instability, wear, coupled with the melt viscosity is large, so it cannot be used for conventional extrusion, injection processing.
By adding liquid crystal polymer (LCP), graphite modification, such as adding 10% (mass fraction) LCP PTFE-LCP alloy, compared with pure PTFE, its wear resistance improved nearly 100 times, and the material can be used as wear-resistant parts.
In addition, adding LCP into ultra-high molecular weight polyethylene (UHMMPE) and HDPE can greatly reduce the melt viscosity, so the EXTRUSION process can be used to produce UHMMPE pipe.