, look at the following in detail:
Lesson 1 Introduction to Polyvinyl Chloride Plastic
PVC is the acronym for polyvinyl chloride (polyvinyl chloride) plastic. This delightful plastic product is actually a polymerized substance of vinyl.
Simply put, an aqueous solution of salt undergoes chemical decomposition in the presence of an electric current. This process produces chlorine, caustic soda and hydrogen gas. Refining and cracking oil or gasoline produces ethylene. When chlorine and ethylene are mixed, vinyl dichloride is produced; vinyl dichloride, in turn, can be converted to produce chlorinated vinyl, which is the basic component of polyvinyl chloride. The polymerization process joins the chlorinated vinyl molecules together to form the PVC chain. Polyvinyl chloride produced in this way is in the form of a white powder. It cannot be used alone, but can be mixed with other components to produce many products.
Vinyl chloride was first synthesized in 1835 in the laboratory of Justus von Liebig. And polyvinyl chloride was synthesized by Baumann in 1872. But it wasn't until the 1820s that the first commercial products of polyvinyl chloride were produced in the United States, and within the next two decades large-scale production began in Europe.
PVC, with its outstanding characteristics of abundant raw materials (petroleum, limestone, coke, salt and natural gas), mature manufacturing process, low price and wide range of applications, has become the second largest general-purpose resin in the world after polyethylene resin, accounting for 29% of the world's total consumption of synthetic resins. PVC is easy to process, and can be processed by molding, laminating, injection molding, extruding, calendering, blow molding hollow and so on. Polyvinyl chloride is mainly used for the production of artificial leather, film, wire sheathing and other plastic soft products, but also the production of plates, doors and windows, pipes and valves and other plastic hard products.
Polyvinyl chloride has the advantages of flame retardant (flame retardant value of more than 40), high chemical resistance (resistant to concentrated hydrochloric acid, concentration of 90% of sulfuric acid, concentration of 60% of nitric acid and concentration of 20% of sodium hydroxide), mechanical strength and good electrical insulation. However, its heat resistance is poor, the softening point of 80 ℃, in 130 ℃ began to decompose and discoloration, and precipitation of HCI.
In fact, recounted so much, we should know is: in the provision of a lot of convenience to human beings, PVC and its most fatal shortcomings; it is the most destructive to the environment of the plastic products. PVC's production, use and processing will lead to the release of toxic chlorine. The production, use and disposal of PVC leads to the release of toxic chlorinated compounds. These toxins can easily find their way into the water, air and food chain, causing great damage to the environment. It is also said that PVC is indirectly linked to cancer, hormonal imbalances, birth defects, diabetes, neurological damage and immunosuppressive effects. Phthalates are used as softeners in toys made of PVC, and health-conscious parents have begun to worry about whether this substance is harmful to their children: since children chew and suck on their toys, what if these additives are toxic?
Why is PVC so loved and hated? In fact, the role of chlorine in polyvinyl chloride is also to make people love and hate, it turns out that most daily plastic products are carbon and hydrogen as the main constituent elements. The difference with PVC is that in addition to carbon and hydrogen, it also contains chlorine (about 57% by weight). The presence of chlorine in the molecule makes PVC particularly useful because it makes it compatible with many other substances. The chlorine content also helps to retard the combustion of PVC, and can be used as a "marker" to distinguish PVC in our automated sorting systems when recycling plastics. We can also use a variety of technologies to develop manufacturing methods for PVC that use little energy to produce the final product form. So it is the presence of the element chlorine that has enabled PVC to be used so quickly and in so many applications.
But, at the same time, we must not forget: chlorine is also known as the "deadly structural unit of PVC". It is the main culprit in the environmental pollution of PVC. In fact, it is also the basic component of many notorious toxic substances, such as CFCs (chlorofluorocarbons), dioxin pollution, PCBs (polychlorinated biphenyls) and DDT pesticides. Large quantities of chlorinated toxins invade the air, water streams, and food chain. Most of these chemicals - organochlorines - do not break down easily and remain in the environment for decades, with humans and animals unable to effectively remove it from their bodies ......, so that the danger lies in ambush.
The production of PVC grew by leaps and bounds in the 1960s. As other products using industrialized chlorine were banned (e.g., polychlorinated biphenyls (PCBs), chlorofluorocarbons (CFCs), and chlorinated solvents, etc.), the chlorine industry turned to PVC to consume its extra chlorine. production of PVC gradually increased, especially in Asia and Latin America. Now more than 30% of the world's chlorine products are used to produce PVC.
Lesson 2 Applications of Polyvinyl Chloride
Polyvinyl Chloride is chemically stable, neutral, and non-toxic.PVC is both lightweight and strong, adaptable, and inexpensive, and these properties dictate a wide range of uses, including the manufacture of the most sensitive of items, such as medical devices, building materials, toys, and automotive cables.
Because PVC is easy and low-cost to manufacture, stable, and versatile, it has grown rapidly in recent years, replacing other less problematic materials such as glass, metal, paper, ceramics, and trees to a large extent, and it has hindered the use of non-chlorinated plastics.
The biggest applications for PVC are in building materials - cables, window frames, doors, walls, paneling, water and sewage pipes - and in household products - plastic flooring, plastic wallpaper, blinds and shower curtains.
PVC is also used in consumer goods, such as credit cards, records and toys; in office supplies, such as furniture, bookbinding tools, folders and pens; it is also used in the automotive industry, particularly for sealing, with a medium-sized car using about 16 kilograms of PVC. the polymer is a covering film layer against wear and tear, and is used as the main protective material to prolong the life of a car; and in hospitals it is the main material for disposables (including medical ware, blood bags, catheters, surgical gloves, cardiopulmonary access devices, pill and tablet packaging, and so on), and likewise it can be insulation for wires and cables, imitations of leather, and garden furniture.
In fact, the hazards of PCE are widespread and long-term, with potential environmental contamination throughout the life cycle of PCE plastics, from raw materials, to production, to use, to incineration, and so on.
Of all plastics, PVC plastic is the most environmentally destructive. Over its lifetime, it requires dangerous chemicals in its production, releases harmful additives, and produces toxic waste. The worrying news is that the production of PVC is increasing all over the world. This is despite the fact that safer and more viable alternatives to all PVC products exist.
The production of PVC also includes many hazards:
The production of PVC powders involves the transportation of hazardous and explosive raw materials, such as polychlorinated monomers (VCMs), and the generation of toxic wastes, particularly ethylene dichloride (EDC) tar. Tar waste contains large amounts of dioxins, which are then burned, dumped, and dispersed into the air.
Previously, these tar wastes were incinerated in oceanic incineration containers until 1991 when they were banned worldwide due to their toxic emissions affecting marine ecosystems. Now, these wastes are disposed of by incineration in land-based incinerators or by being buried deep underground.
A large number of additives are used in the production of PVC to make it suitable for a variety of different applications. Some additives are plasticizers, used to make the plastic softer, heavy metals are stabilizers or colorants, and fungicides protect other additives from fungal damage. So the production of PVC is accompanied by a lot of secondary toxic production.
The British Chemical Industries (ICI) produces large quantities of dioxins in these wastes, and Greenpeace found similar photos when it investigated the PVC industry in the United States in 1994 and 1996.
In the Netherlands, the production of polychlorinated vinyl chloride monomer (VCM) in Rotterdam produces large quantities of pollutants from dioxins. In Venice, Greenpeace analyzed sediment taken from Porto Marghera. It clearly showed that the lagoon was contaminated with dioxin pollutants from the Enichem plant, which produces VCM.In 1994, the environmental authorities in Lower Saxony, Germany, found high levels of dioxin in the sludge from the sewage treatment plant at the European Vinyl Company's PVC production site in Wilhelmshaven. Dioxins were also present in the dumps where this sludge was stored.
Consumer products, which are environmentally destructive production of PVC, also pose a risk to consumers during use. Plasticizers are not tightly bound to the plastic, but slowly leach out over time. For example, plasticizers in plastic flooring can volatilize indoors. The most common plasticizer, phthalate DEHP, is a suspected carcinogen. Phthalate softeners are global contaminants, and more than 90 percent are used in PVC plastics. Recently, many governments have banned plastic toys and teething chews that contain softeners. The reason is the risk of softeners leaking into the mouth when babies suck and chew.
The disposal of PVC creates additional environmental problems. If incinerated, either in a fire or in an incinerator, PVC, because of its chlorine content, releases acidic gases containing dioxins.PVC is a major source of dioxins globally. If landfilled, it will eventually release additives that threaten groundwater supplies; burning PVC in landfills is also a further source of dioxins
The main additives for PVC plastics are similar to those for other plastics, mainly the following, fillers, lubricants, pigments, flame retardants, stabilizers and plasticizers. In practice, it is the stabilizers and plasticizers that are most heavily used, and which make PVC different from other plastics in terms of its characteristics. Among these additives, stabilizers and plasticizers are the main ones that pose a great danger to human health and the environment.
Stabilizers, mainly contain heavy metals such as lead and cadmium. Heavy metals are added to PVC mainly to prevent degradation of PVC due to light and heat, for example, heavy metals like lead are added to cure PVC to resist heat and keep the special properties of PVC for many years. a window frame made of PVC can be used for fifty to one hundred years without the need for paint or other processing.
If PVC waste is not disposed of properly, it can spread these harmful metals into the surrounding environment. As the problem of heavy metals has been recognized, the industry has begun to look for alternative solutions. A number of options are being investigated, which of course have implications for technology implementation and overall cost. This means that it will take some time for alternatives to finally emerge. Alternatives to cadmium are now widely used and it is no longer used as an additive in the PVC industry. As far as "lead" is concerned, there is a program to phase down the use of lead in PVC production. The industry has decided to stop using lead on a voluntary basis by 2015. Lead has been replaced by other less toxic substances, such as calcium, barium or zinc, which are clearly less toxic. Some of the alternative substances are technically less efficient, which is why it will take time to find a viable solution. pvc window and door frames are longer-lasting products that will also long contain any heavy metals added to them.
For plasticizers, the main ones are titanates. These additives provide the mechanical properties, heat resistance, color, transparency properties and elasticity that PVC needs. The most common titanates are DINP and DEHP. DINP is often used in the manufacture of toys and DEHP is mainly used for medical applications of PVC (at least in Europe). However, you will be hard pressed to find toys in Europe or the US that use these phthalates produced in these regions.
It should be added that DEHP, as the most commonly used plasticizer in the world, is recognized as having no carcinogenic effect on humans. In medical applications, for example, phthalates are the best plasticizers from the point of view of efficacy, easing the pain of patients. The only disadvantage of phthalates is that when mixing the softener with PVC, the softener breaks down slightly over time. The findings come from the leading international cancer authority, the International Agency for Research on Cancer, which is part of the World Health Organization (WHO). The following are excerpts from comments and statements from the American Association for Science and Health:
"The panel concluded that DEHP in medical devices is harmless, even to those who undergo certain medical procedures with a high degree of exposure. Such as common hemodialysis or extracorporeal membrane oxidation (ECMO). And the panel found that DEHP imparts many important physical properties to medical devices that are critical to their function. If these products were free of DEHP, they would cause harm to some people. Any alternatives to DEHP or DEHP-containing medical devices should be evaluated and must be subject to the same criteria as DEHP: 1. a description of their appropriate physical properties and function in the application of the criticized medical device; and 2. a risk assessment based on studies of toxicity to animals and humans and human exposure data.
The scientific literature on DINP is not as extensive as that on DEHP. While the results of animal toxicity testing suggest that a thorough evaluation is needed, the panel concluded that many parts of this fact have little effect on humans. Normal use of toys and DINP in toys is harmless to children. To better understand the extent of exposure to children from DINP in toys, the panel recommends an in-depth study to document: 1. the amount of time children spend in contact with toys and other objects and the behavior of children with their mouths; and 2. the rate of release of DINP under realistic conditions. Such studies will improve the accuracy of DINP exposure assessments and will also facilitate the evaluation of the effects of DINP on toys or other substances on other objects that are held in a child's mouth. Any DINP or soft toys containing DINP should be evaluated for potential risk, and this evaluation must be based on animal and human toxicity data as well as human exposure data to DINP."
The world is facing a waste crisis due to PVC. Short-term production of PVC, disposed of over several years, creates a massive PVC waste problem, especially when burned and discarded.
The average life cycle of a durable product - which makes up more than half of all PVC consumed - is about 34 years. This durable, vinyl-based plastic, which was first produced and sold in the 1960s - when the plastics boom began - is now starting to enter a period of flooding with waste. The mountains of PVC waste we now see are just the first stage of a looming crisis.
Globally, there are more than 150 million tons of long-life PVC products, most of which are used in parts of buildings, that will make up the PVC waste mountain over the next few years. Depending on the products being added, this mountain will double in 2005 and the world will enter the PVC waste period and have to deal with about 300 million tons of PVC waste. In industrialized countries, the increase in the volume of PVC waste has already exceeded the production of PVC. The most concerning fact is that the PVC industry is booming in Latin America and Asia, so that the final waste mountain will be generated in these parts of the world. The large amount of PVC products that will become waste in the years to come, and the growing number of PVC production projects, also indicate that PVC phase-out is also urgently needed. This is the only way to stop a growing, dangerous and difficult to deal with waste problem.
So what are we going to do about this waste? Where is the solution? Because PVC, like most plastics, does not biodegrade quickly, there are three main options: landfill, incineration, or recycling.
Today, 2.6-2.9 million tons of PVC waste is in landfills, but only 100,000 tons is recycled and only 600,000 tons is incinerated. The European Commission will be taking steps to make landfilling less attractive (as it does not provide a final solution to the environmental problems), and incineration will not provide a final solution either. Recycling may be the most effective solution in this respect, but in the current EU countries, recycling is still at a low level, with less than 3% of the total amount recycled.
There are two types of recycling methods for PVC: mechanical recycling and feedstock recycling. The mechanical recycling process refers to the direct recycling of plastics, whereby discarded material is transformed into plastic pellets. These recycled pellets are then fed into the plastics production process to form new products. Feed recycling is particularly used for those waste materials that are not suitable for mechanical recycling. Polyvinyl chloride is broken down at high temperatures and its chemical composition is reduced. In PVC-rich feed recycling, hydrochloric acid (HCI) is the main chemical recovered, which is then reused as a raw material in the PVC production process.
In fact, currently, less than 1% of PVC is inherently recyclable. This PVC scrap product cannot be recycled to its original quality, due to the fact that PVC is required to be pure PVC to get the same quality. This product is mainly "downcycled" or used to make "inferior" products such as park benches and highway fences.
Many recycled PVC products are re-added with toxic heavy metal compounds or other stabilizers, and more often than not, dangerous compounds are added to the second product.
So is it possible that recycling is not the ultimate solution either? Of course not, but there are some interesting trends that are working in favor of generating good solutions. When we recycle plastics (not only PVC), we look for the best solution, not only from an economic point of view, but also from the point of view of the environment and the use of energy. It doesn't make sense to use a lot of energy to recycle a limited amount of plastic if using that energy to recycle the plastic has a greater impact on the environment than it does on the production of new plastic items. There are better measures that can be taken before we recycle, such as reusing the energy that was used to make the plastic. We can recycle plastics, but we don't have to do it through a descending cycle. It requires sophisticated production methods to actually recover the original product and reuse it as an equivalent item.
A plant specializing in the recycling of PVC plastics has been built in Ferrara, Italy. Recycled PVC is identical in quality to the original product. Therefore, the economic value of the products produced by this recycling also justifies the operation of the plant. This plant also presents a new perspective. When 8,500 or 9,000 tons of PVC are recycled each year, it reduces our sensitivity to changes in raw material costs. Similarly, this technology can produce PVC with extraordinary qualities, opening the door to generating new and original application methods. Meanwhile, Belgium's Charlevoix Group has invented a new way of processing PVC waste materials, known as "ethylene recycling" technology. This technology can not only process the composite PVC waste materials, but also produce high-value recycled PVC. "Vinyl Cycle" technology makes use of the characteristics of PVC (selective solubility), separate PVC materials from other materials, and produce recycled materials that can be comparable to new PVC. Recently, the group has built the first "ethylene recycling" plant in cooperation with the Italian company Ferrara, a 12 million euro plant with an annual capacity of 15,000 tons of waste cables and 10,000 tons of recycled PVC.
If we have to choose between cheap, high-performance, and environmentally friendly, healthy products, I think we will not hesitate to choose the latter, although we have not yet found a solution to the problem. Although we have not yet found a reasonable and effective solution to the toxicity of polychlorinated ethylene plastics, but scientists will eventually give mankind an answer, either to terminate the production and use of polychlorinated ethylene plastics, or the use of alternative raw materials, improve the preparation method ......, in short, mankind needs to be a healthy living environment. A definitive solution to polychlorinated ethylene