People tend to call some plastic varieties with large output, low price, wide range of uses and wide influence as general plastics. Its connotation often changes with the times and the development of science and technology. Important general plastics include polyethylene, polypropylene, polyvinyl chloride, polystyrene and other varieties.
Important general purpose plastics
General plastics mainly include polyethylene, polypropylene, polyvinyl chloride, polystyrene, ABS (acrylic-butadiene-styrene), polymethylmethacrylate and amino plastics, etc., and their output accounts for 1% of the entire plastic output. More than 90%, so it is also called bulk plastic variety.
Polyethylene (PE)
Polyethylene is the most produced variety in the plastics industry. Polyethylene is an opaque or translucent, light-weight crystalline plastic with excellent low-temperature resistance (the lowest operating temperature can reach -70 ~ -100℃), good electrical insulation and chemical stability, and can withstand most acids and alkalis. Resistant to erosion, but not heat. Polyethylene is suitable for processing by injection molding, blow molding, extrusion and other methods. According to different densities, PE can be divided into: low-density polyethylene LDPE; high-density polyethylene HDPE; linear low-density polyethylene LLDPE.
Polypropylene (PP)
Polypropylene is a thermoplastic obtained by polymerizing propylene. It is usually a colorless, translucent solid, odorless and non-toxic, with a density of 0.90 ~ 0.919 g/cubic centimeter. It is the lightest general-purpose plastic and its outstanding advantage is its ability to survive in water. It has better cooking resistance, corrosion resistance, strength, rigidity and transparency than polyethylene. The disadvantage is that it has poor low-temperature impact resistance and is easy to age, but it can be improved by modification and adding additives respectively.
Polypropylene is widely used due to its low price, good comprehensive properties and easy processing. Especially in recent years, the rapid development of polypropylene resin modification technology has made its use increasingly widespread. Ordinary polypropylene can be used to expand its scope of use through chemical and physical modification methods such as copolymerization modification, cross-linking modification, and graft modification, and its performance is comparable to engineering plastics.
Polypropylene can be made into furniture, tableware, kitchen utensils, basins, buckets, toys, etc.; it can be made into various agricultural tools, fishing nets, mushroom culture bottles, etc.; it can be made into many parts of cars, such as steering wheels, dashboards, bumpers, etc. etc.; can be made into TV sets, radio cassettes, washing machine barrels, etc.; can be made into flat yarns and woven into woven bags, made into packing tapes, and various films can also be produced for heavy packaging bags (such as grain, sugar, salt, chemical fertilizers), synthetic resin packaging), made into cigarette filters; it can be made into industrial fabrics, carpets, clothing fabrics and decorative fabrics. In particular, polypropylene geotextiles are widely used in highway and reservoir construction, and play an important role in improving project quality; It can be made into disposable syringes, surgical clothing, personal hygiene products, etc.; polypropylene material has better printing performance and can print particularly bright and brightly colored patterns.
Polyvinyl chloride (PVC)
Polyvinyl chloride is a plastic obtained by polymerizing vinyl chloride. By adding plasticizers, its hardness can be greatly changed. Hard products and soft products made from it have a wide range of uses. PVC is widely used in films in China, such as agricultural shed films, plastic sheets, shed cloths, and packaging materials. It can be used in large quantities to make pipes, sheets, and special-shaped materials, and is used in the construction industry, such as PVC doors and windows, and water pipes. etc.; PVC transparent sheets are used for food packaging; PVC is used for artificial leather to make luggage, sofas and other furniture; used for foam products, such as sports shoes, car seat cushions, floor leather, wallpaper, etc.; it is mainly used to make sheaths for wires and cables material.
Polystyrene (PS)
Polystyrene can be divided into general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), and expandable polystyrene (EPS).
GPPS is odorless, tasteless, non-toxic, hard, has good transparency, good dimensional stability, excellent electrical insulation, radiation resistance, good colorability, high stiffness and surface hardness, brittleness, low heat resistance, and poor sunlight resistance, has average chemical resistance and can be dissolved in a variety of solvents. It is mainly used for daily crystals, stationery, lamps, indoor and outdoor decorations, cosmetic containers, fruit trays, instrument casings, seed covers and food packaging, etc.
HIPS has good stiffness, colorability, and impact resistance. Its tensile strength, hardness, light resistance, and gloss are not as good as GPPS. Its transparency is greatly reduced, and its weather resistance is poor. It is mainly used for packaging materials, such as food, cosmetics, daily necessities, mechanical instruments and stationery packaging; it can also be used for household appliances, such as casings of household appliances and instruments, electrical accessories, buttons, auto parts, medical equipment accessories, cultural and sports supplies, and office supplies, various decorative parts, lighting equipment, furniture, toys, etc.
EPS, also known as expanded polystyrene material, is produced by suspension polymerization of styrene with the participation of foaming agents. The blowing agent is added before polymerization or penetrated into the polystyrene beads under heating and pressure. This material can be further processed into foam plastics, which have good cushioning, shockproof, heat insulation, and sound insulation properties. It is mainly used in packaging materials and construction fields.
Aminoplastic
Aminoplastics are plastics produced by the polycondensation reaction of raw materials with amino functional groups (urea, melamine, aniline) and aldehydes (mainly formaldehyde). It mainly includes urea-formaldehyde, melamine-formaldehyde, aniline-formaldehyde, and urea, melamine and formaldehyde co-condensation resins. Amino resin can be made into plastic powder, reinforced plastic for compression molding, injection molding, transfer molding, or laminated plastic. These products can be widely used in electrical parts, daily necessities, tableware, etc.
Advantages and Disadvantages
Plastic has the following advantages and disadvantages compared with materials such as wood, metal, cement, and glass.
Advantages: (1) Easy to form, high degree of design freedom; (2) Easy to color; (3) Specific strength is greater than metal; (4) Specific gravity is lighter; (5) Easy to modify, easy to obtain required properties; (6) ) Good electrical insulation; (7) Good water resistance and no rust; (8) Good chemical resistance; (9) Production consumes less energy than metal; (10) As long as waste plastics are treated well, it is good for the environment Causes less damage and pollution than other materials.
Disadvantages: (1) Poor weather resistance, especially poor UV resistance, and easy to age under UV light; (2) Easy to generate static electricity; (3) Large thermal expansion coefficient, poor dimensional stability; (4) Low surface hardness, easy to produce scratches Damage; (5) Poor durability and poor resistance to environmental stress cracking.
However, with the continuous development and progress of blending technology and the achievements in high-performance general-purpose polymers, some of its shortcomings have gradually been improved, broadening the application fields of general-purpose plastics, and making plastics more and more important in the national economy. important.
Uses
Plastics have excellent properties, come in many varieties, and are widely used. It can replace the three traditional materials of metal materials, cellulose materials and silicate materials, and is the most powerful competitor of traditional materials. General-purpose plastics have been widely used in various sectors such as agriculture, light industry, textiles, electronic appliances, machinery, building materials, packaging and transportation, profoundly affecting the development of industrial and agricultural production and scientific and technological progress. In social development and national economic construction, people’s material All aspects such as improving cultural and living standards play an extremely important role.
The uses of general plastics can involve the following aspects:
- Agriculture: various agricultural films, sheets, irrigation pipes, sprinkler pipes, fishing nets, breeding boxes, and floating materials.
- Industry: Due to the electrical insulation of plastics, plastics have been widely used as insulation materials and packaging materials in the electrical industry; parts and casings in the electronics and instrumentation industries; transmission gears, bearings, etc. in the machinery industry; Various anti-corrosion containers, pipes, tanks, tanks, etc. in the chemical industry.
- Construction industry: Use plastic to replace traditional materials such as wood and metal to produce plastic doors, windows, ceilings, floor leather, water pipes and pipe fittings, gas pipes and pipe fittings, etc.
- Packaging industry: various woven bags, packaging films, composite films, hollow containers, turnover boxes, corrugated boxes, packing tapes, foam plastics, etc.
- Daily necessities: various plastic toys, toothbrushes, soap boxes, raincoats, tableware, utensils, slippers, etc.
- Medical and equipment industry: various artificial organs, medical infusion bags, disposable injection supplies, and degradable medical materials.
- Electrical appliance industry: insulation, heat preservation, anti-corrosion and moisture-proof casings of various office appliances and household appliances, corrosion-resistant and precision military parts, etc.
In addition to the wide range of applications of general-purpose plastics in the above fields, some general-purpose plastics have expanded their application fields through modification and are widely used as structural materials in cutting-edge national defense industries, transportation and aviation industries.
Development status
Since the outbreak of the global financial crisis in 2008, the China’s plastics processing industry has been severely hit. The demand for the five major general plastics has declined for the first time based on years of growth. In 2009, with the implementation of various economic stimulus policies, China’s economy took the lead in recovering, downstream operating rates increased, demand for the five major plastic general materials increased, and inventories returned to normal values, thus increasing the apparent demand for synthetic resins. In 2009, the apparent consumption of China’s five major general plastics increased significantly to 46.26 million tons, with the growth rate rising from the average growth rate of 9.4% from 2002 to 2007 to 21%. Among them, the apparent consumption of polyethylene was approximately 15.11 million tons, a year-on-year increase of 31%; the apparent consumption of polypropylene was approximately 12.52 million tons, a year-on-year increase of 21.7%. Affected by the international financial crisis, the prices of the five major general plastics plummeted in the second half of 2008, falling as much as 60.6% to mid-2003 levels. In 2009, although the price of synthetic resin rebounded slowly, it was still low. As a result, the output of China’s five major general plastics increased by approximately 8.1% year-on-year, which was lower than the increase in production capacity. In the first half of 2010, China’s five major general plastics markets generally showed a volatile downward trend. This was due to excessive imports in the first quarter and the smooth commissioning of large China’s installations in Fujian, Tianjin, Panjin, Zhenhai and other places in the first half of the year, which resulted in a concentrated release of China’s supply. The market is a buyer’s market. In the second half of the year, the China’s plastics market generally showed a trend of consolidating at a high level after oscillating upwards. Since mid-July, driven by the overall improvement of the financial market, the China’s plastics market has rapidly picked up. Early trade and downstream factories have actively covered their positions, and the market has an obvious reluctance to sell, the China’s plastics market has risen across the board. Near the end of the year, traders and downstream factories are operating cautiously. The market has insufficient momentum to chase the rise and kill the fall, and the overall trend is small fluctuations.
The improvement of technological innovation capabilities will promote the development of the general plastics manufacturing industry, and technological innovation and institutional management innovation will greatly stimulate market vitality; the transformation of state-owned joint-stock systems, the rise of the private economy, and the adjustment of new capital operations and resource allocation will form the driving force for enterprise development. The role of China’s demand in plastics economic growth is increasing, creating new market space for the development of China’s general plastics; the country’s decision on agricultural development, strategies such as strengthening the urbanization process, revitalizing the old industrial base in the Northeast, and developing the western region, have promoted the plastics industry With the strategic shift of the entire industry, it will gradually develop from the two delta regions to the central region in the future, and at the same time realize regional strategic transformation; with the acceleration of the construction of new socialist countryside and the urbanization process, the increase in China’s urbanization rate will have a negative impact on The rapid growth in demand for a series of plastic products such as plastic pipes, special profiles, artificial leather, and synthetic leather has promoted the development of general plastics.
