Plastic product is a common name for daily articles and industrial articles that are made of plastics.
What is plastic?
Plastic is a kind of moldable high molecular synthetic material. It is one of the most important synthetic materials apart from synthetic rubber and synthetic fiber. The main ingredient of plastic is natural or synthetic resin. By adding various additives to the main ingredient, a kind of material can be made under a certain temperature and press. The material can keep its shape under normal conditions. The material is what we called plastic.
Main Features of Plastic
Plastic is superior to other materials in regard of following aspects:
1. Light in weight
Plastic is light in its weight with a relative density of 0.90 to 2.2. It is obvious that plastic doesn’t float in water, especially the lighter expanded plastic with a relative density of 0.01 due the tiny holes inside. Thus, plastic can be used in producing products that are required to be light.
2. Excellent chemical stability
Most of the plastics are well performed in resisting to corrosion against acid or base. The most stable one is PTFE (F4), common known as super plastic, enjoys super stability even better than gold. It changes nothing when boiled in aqua regia. F4 is the most ideal corrosion-resistant material for its superior chemical stability. It can be used as the material of tube for transporting corrosive and adhesive liquid.
3. Excellent electrical insulation
Common plastics are bad conductor of electricity. It has great surface resistance and volume resistance, about 109-1018 ohm. Its breakdown voltage is great with small dielectric loss angle tangent value; therefore, plastics are widely used in electronics industry and mechanical industry, such as plastic insulation cable.
4. Bad conductor of heat; Noise elimination and shock absorption
Generally, plastic’s thermal conductivity is relatively low, about 1/75 to 1/225 of that of steel. As there is air in the micro holes of foam plastic, it has better performance in insulating of heat and noise as well as in absorbing shock. The thermal conductivity of PVC is about 1/357 of that of steel and about 1/1250 of that of aluminums. In regard heat insulating, a single glass-plastic window is 40% higher than single glass-aluminums window and 50% higher than double glass window. Adopting windows combining plastic frame with hollow glasses in houses, office buildings, wards and hotels, it can save cost on heat in window and air conditioner in summer.
5. Wide spread of mechanical strength and higher specific strength
Some plastics are as hard as stone, steel whereas some are as soft as paper, leather. There are many choices of plastics in regard of hardness, tensile strength, extensibility and impact resistance. Since the plastic is of small specific density and great strength, it has higher specific strength. However, plastic do has its disadvantages; for example, it is inflammable, not stronger than metals, poor age resistance and heat resistance.
Development Trend of Plastics
Plastic shall focus on two aspects in its future development; the first is to improve the existing plastics with various methods to improve their integrate performance; the second is to develop plastics with various functions, such as develop polymer material to enable plastics with photoelectric effect, thermoelectric effect, piezoelectric effect, etc.
In current plastic development, Germany and Sweden rank the top, followed by Japan and some European counties; however, The U.S.A. lags behind. The current global development trends in plastic package are:
Ⅰ. Copolymer-compound package film
At present, some European countries are investing heavily in polarity and non-polarity ethylene copolymer, which ca greatly improve the stretchability, transparency, sealing, crazing resistance, stability of plastics film.
Experts from aboard believe that the key point in current plastic industry is the technologies for plastics modification, plastic products coating, rapid biodegradation of waste plastics and recycling of plastics. For example, some plants in European countries produce a kind of bag that is used for package of ice cream or food that contains milk and fat.
Ⅱ. Multi-purpose compound film
Multi-purpose compound film has being greatly developed and classified in other countries, for example, cold-resistant film performs well at the low temperature of -18℃、-20℃、-35℃; Moisture-resistant films can be classified as wet-resistant, dew-resistant, cold-steam-resistant and water-adjustable; corrosion-resistant films ca be used for package of food that is perishable and contains much acid and sugar. Special PE film performs good in resisting chemical substances and corrosion; moth-proof film is added with insect-resist agents without abnormal taste; new package film for food performs well in preserving the taste; non-crystalline nylon film is as clear as glass; high shield film performs well in preserving and stabilizing the color, smell, taste and nutrition of food; Metal protection film, used to pack liquid products by adopting modified LDPE film, can be heat sealed; packages compounded with PP can be improved in resist light, cold, water, moisture, oil, acid, base and shock.
At present, it is so popular to pack cold, hot drinks, wines and instant food with plastic cups, compound cups (outer PSP, inner PP, cover PS). In France, PE bottles are used to pack candy, yoghurt and in Germany, PC bottles are used to pack milk. In China, we use PE bottles to pack drugs, etc.
1. It is difficult to classify the recycled plastics and doesn’t save money;
2. Plastic is easy to burn and gives out poisonous gas. For example, when polystyrene burns, it gives out toluene, which can cause blindness, and when the toluene is inhaled into our body, it may cause vomit. When PVC burns, it also gives out poisonous gas--chlorine hydride. Besides, high temperature can cause the plastics to decompose with poisonous substance, such as benzene ring.
3. Plastics are made from products refined from petroleum; the bad news is the petroleum is limit on our earth;
4. Plastics can’t be decomposed in nature;
5. Plastics are easily to age due to its poor heat resistance.
Many animals are killed by plastics because they can not be decomposed in nature. For example, monkeys, pelicans, dolphins in zoo are died from eating the indigested plastic bottles discarded by visitors. When you walk close to the beautiful and pure sea, you will find so many waste plastics products are floating on the sea. Indigested plastics are found in bowels of died seafowl.