Table of contents

·1 structure

·2 Properties

·2.1 Flame retardant

·2.2 Physical and chemical properties

·3 History

·4 Production and application

·5 Recovery and recycling

·6 Safety and Hazards

·7 References

·8 external links

·9 related entries

Structure

The structure of this material is as follows

Nature

Flame retardant

The biggest feature of PVC is its flame retardancy, so it is widely used in fire protection applications. However, polyvinyl chloride will release hydrogen chloride, chlorine and other toxic gases when heated above 148°C [5].

The combustion of PVC is divided into two steps. First, hydrogen chloride gas and dienes containing double bonds are decomposed by combustion at 240°C-340°C, and then carbon combustion occurs at 400-470°C [6].

Physical and chemical properties

Stable; not easy to be corroded by acid and alkali; heat-resistant than polyethylene but not as good as polypropylene. PVC is the only material among the seven major plastics that must use plasticizers, which makes its state change from soft and elastic to hard and brittle. The plasticizer is the "plasticizer" in the media reports. Since PVC can present a soft and elastic side, it can also simulate some uses of rubber or leather, such as artificial leather widely used in car interiors, disposable inspection gloves, flooring, tablecloths, and plastic shoes, because PVC is more expensive than natural rubber. And polyurethane artificial leather is much lower. However, the PVC industry usually uses acetylene.

history

In 1912, German Fritz Klatte synthesized PVC and applied for a patent in Germany, but failed to develop a suitable product before the patent expired. In 1926, Waldo Semon of B.F. Goodrich in the United States synthesized PVC and applied for a patent in the United States.

PVC was discovered twice in the 19th century, once by Henri Victor Regnault in 1835 and again by Eugen Baumann in 1872. On both occasions, the polymer appeared as a white solid in beakers of vinyl chloride placed in sunlight. In the early 20th century, Russian chemist Ivan Ostromislensky  and chemist Fritz Klatte of the German company Griesheim-Elektron simultaneously attempted to commercialize PVC, but the difficulty was how to process this hard, sometimes brittle polymer. Waldo Simon and BFGoodrich developed a method of plasticizing PVC by adding various additives in 1926, making it a more flexible and easier-to-process material, which soon became widely used commercially.

Production and use

Polyvinyl chloride can be made by substitution reaction of ethylene, chlorine and catalyst. Due to its fire resistance and heat resistance, PVC is widely used in various products in all walks of life: wire sheath, optical fiber sheath, shoes, handbags, bags, accessories, signs and billboards, building decoration products, furniture, hanging decorations , rollers, hoses, toys (such as the famous Italian "Rody" vaulting horse), cartoon figures, door curtains, rolling doors, paramedical supplies, gloves, plastic wrap for certain foods, certain fashion items, etc.

Polyvinyl chloride is polymerized from vinyl chloride monomer (VCM). Because 57% of its molecular mass is chlorine. Therefore, compared with other plastics, it consumes less petroleum in the same quality. However, because of the relative density of this plastic, it also consumes other energy in the process of generating chlorine, making it Many fields of application lose their edge.

At present, the most widely used PVC production process is the suspension polymerization production process. Add pure water, liquefied VCM monomer and dispersant into the reactor, and then add initiator and other additives. After the temperature rises to a certain temperature, the VCM monomer undergoes free radical polymerization to form PVC particles. Continuous agitation makes the particle size uniform and suspends the resulting particles in water. Because the reaction is an exothermic reaction, effective heat removal and heat exchange devices must be equipped: such as jacketed cooling water and tank top condenser. Moreover, because the density of PVC is higher than that of VCM. During the reaction process, with the continuous generation of PVC, the volume of the liquid phase in the reactor will continue to shrink, and pure water must be continuously added to maintain an appropriate pressure. At different polymerization temperatures, the degree of polymerization of PVC produced by VCM polymerization is different. Different grades (different grades of different degrees of polymerization) of PVC resin can be produced by controlling different polymerization temperatures.

The generated PVC slurry passes through a stripping tower to remove residual VCM gas (recycled in a certain proportion with fresh VCM after being recovered by the recovery system), then undergoes centrifugal dehydration, is dried in a drying bed, and is sieved before being packaged into a product. Generally, the VCM content in PVC powder after post-treatment is less than 1PPM.

The remaining polymerization processes, such as micro-suspension and emulsion polymerization, can produce PVC powder with a smaller particle size (10 microns, while the particle size of PVC powder produced by general suspension polymerization is 120-150 microns. Its characteristics and applications are also slightly different) Polymerized PVC is unmodified PVC. Before making the final product, it is generally necessary to add various additives, such as heat stabilizers, UV stabilizers, lubricants, plasticizers, processing aids, impact modifiers, heat modifiers, fillers, flame retardants, etc. Agents, insecticides, blowing agents, smoke suppressants and various pigments.

Recovery and recycling

Resource recycling: In the plastic classification mark, the PVC code is 3 (the word 3 is in the center of the three recycling arrows)

It must be listed on the bottom of the plastic body or on the packaging so that consumers and recyclers can sort properly.

Safety and hazards

Since the 1970s in the United States, it has been noticed that workers in polyvinyl chloride factories have some kind of malignant liver cancer. [7] Europe and Australia have also begun to notice several types of cancer among workers in polyvinyl chloride factories.

Its main problems are:

·PVC must have additives or plasticizers to use, most of these are harmful and may ooze or vaporize.

·Some additives can interfere with biological endocrine and affect reproductive function.

·Some additives may increase the risk of cancer.

·Incineration of waste containing PVC produces carcinogenic air pollutant Dioxin, a by-product of vinyl chloride. Dioxins are highly toxic substances that can cause cancer and other diseases, and they are also a global threat because they are widely dispersed in the environment and cannot be dissipated. Even at small exposures, dioxins are highly likely to be linked to immune system stress, fertility problems, various cancers and endocrine disorders. According to a 1994 report provided by the British firm ICI Chemicals and Polymer Products Ltd., according to a document published in 1989, these oxychlorination reactions (using solvents used for vinyl chloride and some chlorination), produce many Chlorodibenzo-p-di (PCDDs) and dibenzofurans (PCDFs) compounds.

PVC often uses dioctyl phthalate (DEHP) as a plasticizer. Because DEHP is easy to aerosolize, other vinyl products, including automotive interiors, shower curtains or flooring materials, will also release chemical gases into the air. And DEHP is also easily soluble in oily liquid. In addition, people have begun to pay attention to the safety issue of additive leakage if children chew these soft plastic toys.

PVC toys pose a great threat to the health of young children. Because young children in the oral stage will directly ingest plasticizers such as DEHP in polyvinyl chloride plastics by licking or putting toys in their mouths.

In 2008, a joint study between the United States and Canada pointed out that when five types of plastic shower curtains were tested, they released more than a hundred kinds of toxic substances within 28 days. [8][9]

In January 2006, the European Community moved out the "2005/84/EC Directive" prohibition: prohibiting the use of six types of phthalate softeners in toys. In the United States, more and more companies that manufacture PVC toys for this age group have voluntarily stopped using PVC or phthalates. The FDA recommends that manufacturers consider banning DEHP in devices for sensitive patients (such as infants under one month old), but the safety of alternative plasticizers has not been tested.

Environmentalist group Greenpeace advocates a global phase-out of PVC.