Up to now, there are only six types of plastics with a large number of recycling identification codes; the rest have not been recycled The plastic with the identification code is marked as No. 7 (other plastics) if it should be recycled by the government. Therefore, we will use these types of general-purpose plastics as examples to understand these plastics and examine their hazards during the manufacturing, use, and disposal stages.
PET is the English abbreviation of "polyethylene terephthalate", which is a kind of polyester. The raw material of a bottle is one of the most common plastics around our lives. Since the manufacturing process of the bottle is very similar to that of glass blowing, if the bottom of the bottle is not a straight line but a small dot, the material is likely to be PET.
When manufacturing PET, first of all, para-xylene (PX) from an aromatic hydrocarbon factory is converted into terephthalic acid, and then terephthalic acid and ethylene-derived ethylene glycol are subjected to condensation polymerization to produce PET. As mentioned above, para-xylene is toxic and inhibits the central nervous system, causing headaches, nausea, dizziness, vomiting, chest tightness, confusion, weakness in limbs, staggering and other symptoms; but its toxicity is lower than that of benzene and is internationally cancerous Research institutes (IARC) are classified as a third category of carcinogens (ie substances that lack evidence of carcinogenicity in humans).
In addition, in the polymerization reaction, heavy metal antimony must be used as a catalyst, so there will be a small amount of antimony remaining in PET, about 200-300 ppm. According to research, PET bottles will dissolve a little antimony, and may also dissolve phthalate plasticizers; when the temperature increases, or after a long time, the dissolution of these two substances will also increase. Antimony can cause headaches, dizziness, and depression. Phthalates are not PET plasticizers, so it is speculated that it may be because some PET bottles are recycled from PET contaminated with plasticizers. In addition, the antimony dissolved in the soft PET bottle is higher than that of the rigid PET bottle.
PET can be recycled. After recycling, it is usually melted and drawn into fibers to knit clothes. Therefore, when buying clothes, if it is marked with polyester fiber, it is likely to be fiber made of PET recycled materials. There are foreign countries that recycle PET bottles to make bottles, but because the molecules of PET will break due to high temperature during the recycling process (other plastics will do), the color of the recycled materials is not good (brownish yellow) Therefore, if you want to make a special bottle, you usually need to add 70% of the new material. From here we can see that recycling does not have a solution to the problem of plastic abuse, but we still have to reduce the amount at the source.
Polyethylene (PE) and polypropylene (PP) are plastics directly polymerized from ethylene/propylene. Since there is no benzene ring, no chlorine, or other functional groups such as alcohol and acid on the molecular chain, relatively speaking, The simplest and safest plastic. PE and PP are non-polar polymers, which are not compatible with phthalate plasticizers, and PE can be made into low density with many branches, low crystallinity, softness and transparency through different polymerization processes Polyethylene (LDPE), or made of high-density polyethylene (HDPE) with fewer branches, high crystallinity, harder, and opaqueness, so generally no plasticizer is added, although there are also special plasticizers, it is not universally used.
The molecular structure of PP is linear, although the methane group (CH3) on the molecular chain is non-polar, the regular or irregular distribution on the main chain will affect the crystallinity of the molecule, and thus affect its mechanical and thermodynamic properties. Generally, the crystallinity is between HDPE and LDPE, which is opaque or translucent (the degree of crystallinity will affect the transparency of the material, and the higher the crystallinity is, the more opaque), so its gas barrier is close to HDPE and higher than LDPE. Also because of the presence of methane groups on the molecular chain, PP mechanical properties (including strength and hardness) are higher than PE, and the heat resistance temperature is also higher than PE. PP heat resistance temperature is about 100℃~130℃, HDPE heat resistance temperature is about 90℃～110℃, LDPE heat resistance temperature is about 70℃～90℃.
Although in use, PE and PP seem to be safer plastics (but don’t forget that they also have additives, such as stabilizers, colorants, etc., so they are not guaranteed to be absolutely safe), in the production process, yes The environment will also have an impact. Professor Wu Kunyu of National Taiwan University once pointed out that although ethylene and propylene "are not inherently carcinogenic and lack toxicity information, past studies have confirmed that they can indeed be metabolized into ethylene oxide and propylene oxide in the body. The organization is classified as a human carcinogen, and propylene oxide is an animal carcinogen, so ethylene and propylene should basically be classified as potentially hazardous to human health." In addition, ethylene and propylene are also flammable and explosive materials, dangerous Gao, where propylene is the protagonist of the 2014 Kaohsiung gas explosion.
PVC (Polyvinyl Chloride) is the most harmful plastic to the environment and health of all general-purpose plastics, because its production process and waste combustion will produce the dioxin of the century, and its monomer vinyl chloride manufacturing process will involve many toxic substances, Including its raw material chlorine gas is a nerve poison, intermediate 1,2-dichloroethane (EDC) is a possible carcinogen, and vinyl chloride monomer (VCM) itself is a human first-level carcinogen that can cause liver cancer. In addition, because PVC has good compatibility with many types of plasticizers, a large number of plasticizers can be added to achieve the purpose of softening. Although it is easy to process, it poses a great risk to users because it is most commonly used for plasticizing PVC The type of agent is phthalate ester, which is a toxic substance that can interfere with hormones and is very easy to dissolve. Furthermore, PVC will add heavy metal stabilizers containing lead, cadmium, tin, or zinc, and the risks cannot be ignored. Therefore, this kind of plastic should not only be reduced, but also eliminated and rejected.
PS is the English abbreviation for polystyrene, and its foaming material is commonly known as Styrofoam. As with PP, the regularity of the benzene ring on the PS in the main chain will affect its crystallinity, but commercial PS are all random and non-crystalline PS. Its texture is hard and brittle, colorless and transparent, and good coloring. And it can be copolymerized with other rubber-type polymer materials to produce products with better mechanical properties, such as copolymerization with polybutadiene rubber to form impact-resistant polystyrene. After PS foaming, the volume expands many times, the molecular distance is pulled apart by the gas, and many voids are generated, so it is not only low in density and light in weight but also has the effects of heat insulation, sound insulation, sound absorption, anti-collision, etc. It is not only commonly used in food containers Or industrial product packaging, often used in building materials.
Although PS is widely used, the risk of pollution in its production process cannot be ignored. The raw material benzene is a human carcinogen. The ethylbenzene that becomes ethylene after reaction with ethylene, and then the styrene monomer produced by dehydrogenation are all possible carcinogens; these benzene-containing volatile organic compounds may all come from the gap of pipeline equipment Zhongyi spread out and spread around the petrochemical industrial park, threatening the health of workers and surrounding residents.
When used, PS will dissolve styrene and its oligomers. Although the dissolution amount at room temperature is still low, as the temperature increases, the risk of dissolution of these toxic substances can not be ignored, so it is not recommended to use Styrofoam To serve hot food (such as instant noodle bowls). In addition, if the contact time with food or beverage is long, the dissolution of these substances will also increase.
After the PS is discarded, if it is not handled properly, it will cause great harm to the environment. For example, when it is sent to an incinerator for combustion and the combustion is incomplete, polycyclic aromatic hydrocarbons (collectively referred to as hydrocarbons containing multiple benzene rings, many of which are carcinogens or possible carcinogens), such as foam materials Styrofoam is littered in the environment. Due to its large molecular gap, the degree of entanglement is lower than that of other plastics. It is more likely to be broken into plastic fragments due to external collision or sunlight, which is difficult to clean up. Toxic substances (other types of plastics will have similar problems, except that they become plastic fragments at a slower rate). In addition, PS falling into the sea will continue to dissolve styrene and its oligomers, polluting beaches and oceans.
PS is recyclable, and there are recycling pipes in Taiwan. Just like PET and other plastics, the molecular chain will be broken and deteriorated when recycling and melting, and the recycled materials may be contaminated by other impurities, and the color will be poor, so its recycled materials Commonly used on TV or screen enclosures.
When PS is used in building insulation or electronic products, flame retardants may be added due to regulations requiring fire protection. Currently, the most commonly used is brominated flame retardants, which are usually toxic substances that are persistent and interfere with hormones. , Of which several (tetrabromodiphenyl ether, pentabromodiphenyl ether, hexabromodiphenyl ether, heptabromodiphenyl ether, octabromodiphenyl ether, and hexabromobiphenyl) have been banned by the Stockholm Convention. Plastics containing brominated flame retardants will still burn in case of fire, but they burn a little slower, but they will produce more toxic bromide dioxin. To solve this problem, you must first review the rationality of the regulations. For example, when PS or other plastics are used in building materials, as long as they are designed or used away from the fire source, why do they require fire resistance? In addition, it is necessary to look for safer and harmless flame retardants to replace brominated flame retardants.
At present, plastics marked with No. 7 recycling identification code are seen on the market, the most common ones are PC and PLA. PC is short for polycarbonate. It is a colorless, transparent (no crystal), heat-resistant, impact-resistant thermoplastic plastic, with properties close to PMMA (polymethyl methacrylate; commonly used in signboards), but it has better impact resistance and processing performance and has a higher refractive index. Additives are required to have UL94 V-0 flame retardant properties. Commonly used in electronic structural parts, electrical machinery housings, lighting parts, etc., it is the main material of optical discs, which was later applied to milk bottles, water bottles, and other uses, and caused doubts. Because the PC monomer bisphenol A may dissolve during use, especially when the PC bottle or water bottle is used longer, or when the bottle body is cleaned with an alkaline cleaner, the more easily it dissolves. Bisphenol A is a toxic substance. It is estrogen-like hormone interferon that affects the brain development and behavior of fetuses and young children, affects thyroid hormones, and interferes with the dopamine activation system, resulting in hyperactivity and insufficient attention. It is easy to abuse drugs. May cause breast cancer. Therefore, many countries in Canada and the European Union have banned the use of PCs for feeding bottles.
In addition to the risk of being used in food containers, the manufacturing risks of PCs are also very high. PC is formed by the polymerization of bisphenol A and phosgene. Both monomers are toxic. The toxicity of bisphenol A is as mentioned above, and phosgene is a very dangerous colorless highly toxic gas: inhalation can be fatal, and the odor (hay smell) at the lethal concentration is still not enough to be alert; it is very strong at high concentration Suffocating smell. Exposure to phosgene will slowly decompose into hydrochloric acid and carbon dioxide, so 3-5ppm exposure will produce irritation, causing conjunctivitis, rhinitis, pharyngitis, tracheitis, tearing, blepharospasm, conjunctival redness and upper respiratory tract irritation; high dose exposure May cause lung toxicity. Clinical symptoms may be delayed 24-72 hours, including choking, chest tightness, difficulty breathing, pulmonary edema, cough, foamy bloody sputum, nausea, and anxiety. Severe pulmonary edema can be complicated by heart failure. Short-term exposure greater than 25ppm may be dangerous, and greater than 50 ppm may cause death. Pure phosgene gas is not corrosive to carbon steel; if it interacts with steam, it will produce carbon dioxide and hydrogen chloride, which will be corrosive, and liquid phosgene will corrode some plastics, rubbers, and coatings.
In addition, benzene-containing bisphenol A is not only a bad thing in itself, but one of its raw materials, phenol, and the most source of benzene is also toxic. Phenol is a solid crystal at room temperature, with a melting point of 41 °C and a boiling point of 181 °C. When heated, it will volatilize to produce toxic and flammable vapors. The gas mixed with air is explosive; chronic exposure can damage the central nervous system, liver, and kidneys; acute exposure ( Through skin contact or swallowing) can be fatal. Contact can cause severe burns to the skin or eyes.
PLA is another type of plastic often labeled No. 7, and its Chinese name is polylactic acid. PLA is a kind of biodegradable plastic. The glass transition temperature Tg is about 58 ~ 60 ℃, which is higher in biodegradable materials, but the heat resistance and material strength are still insufficient, and the processing is difficult. Therefore, the application is limited. In the early days, it was used in medicine, surgical sutures, and bone nails, but now it has been widely used in some common items, such as packaging bags and textile fibers.
PLA raw material sources include corn, sugar beet, wheat, sweet potato, and other starch or sugar, or corn hay, straw, rice straw, bagasse, and other lignocellulose agricultural waste. Although the raw materials are derived from plants and are biodegradable, they are often regarded as a safe alternative material to replace ordinary plastics; however, it will have other environmental concerns, including competing for land with food and still being used when planting its raw crops When it comes to pesticides and fertilizers, it is still inseparable from petroleum. In addition, although it is said to be biodegradable, it will not decompose in the general atmospheric environment or storage conditions. Only when there is sufficient moisture (relative humidity above 90%), sufficient oxygen (in the non-closed environment), appropriate The decomposition reaction will be carried out quickly under the environment with all conditions such as temperature (58~70℃). Therefore, if the PLA is buried, or will fall into the environment, it will exist for a long time.
Although PLA can also be recycled, if it is mixed with other plastics, it will affect the quality of its recycled materials. And this is not a rare phenomenon when the current classification of the people is not reliable and the subsequent detailed classification of the cleaning team is not complete. Therefore, to avoid the problems caused by the abuse of plastics, it is best to reduce the amount at the source, rather than just looking for safer alternative materials without changing the habits of the abused substances.