Polyvinyl chloride (PVC) is the third largest synthetic polymer plastic in the world (after polyethylene and polypropylene ), with an annual production of about 40 million tons of PVC. PVC is a polymer formed by the polymerization of vinyl chloride monomer (VCM) in the presence of initiators such as peroxides and azo compounds or under the action of light or heat according to the free radical polymerization mechanism. Vinyl chloride homopolymers and vinyl chloride copolymers are collectively referred to as vinyl chloride resins.

PVC was once the world’s most produced general-purpose plastic with a wide range of applications. PVC comes in two types: rigid (sometimes abbreviated as RPVC) and flexible. Rigid polyvinyl chloride is used in building pipes, doors and windows. It is also used to make plastic bottles, packaging, bank cards or membership cards. Adding plasticizers can make PVC softer and more flexible. It is used in pipes, cable insulation, flooring, signs, phonograph records, inflatable products and rubber substitutes.

On October 27, 2017, the World Health Organization’s International Agency for Research on Cancer published a preliminary list of carcinogens for reference, and polyvinyl chloride was included in the list of Category 3 carcinogens.

PVC is an amorphous white powder with a low degree of branching. Its glass transition temperature is 77-90°C and it starts to decompose at around 170°C. It has poor stability to light and heat. When it is above 100°C or exposed to sunlight for a long time, it will decompose to produce hydrogen chloride, and further autocatalytic decomposition will cause discoloration, and the physical and mechanical properties will also decrease rapidly. In practical applications, stabilizers must be added to improve the stability to heat and light.

The molecular weight of industrially produced PVC is generally in the range of 50,000 to 110,000, with large polydispersity. The molecular weight increases with the decrease of polymerization temperature. It has no fixed melting point. It starts to soften at 80-85°C, becomes viscoelastic at 130°C, and starts to change to viscous flow at 160-180°C. It has good mechanical properties, tensile strength of about 60 MPa, impact strength of 5-10 kJ/m2, and excellent dielectric properties. PVC is insoluble in common solvents, but it will swell in monomers and certain chlorinated hydrocarbon solvents.

Composition structure

Polyvinyl chloride is a polymer material that uses a chlorine atom to replace a hydrogen atom in polyethylene. It is an amorphous polymer with a small amount of crystalline structure. The structure of this material is as follows: -(CH2-CHCl)n-. PVC is a linear polymer in which most of the VCM monomers are connected in a head-to-tail structure. The carbon atoms are arranged in a zigzag shape, and all atoms are connected by σ bonds. All carbon atoms are sp 3 hybridized.

There are short syndiotactic stereoregular structures on the PVC molecular chain. As the polymerization temperature decreases, the syndiotactic stereoregularity increases. There are unstable structures such as head-to-head structure, branched chain, double bond, allyl chloride, tertiary chlorine in the macromolecular structure of polyvinyl chloride, which make it poor in heat deformation resistance and aging resistance. Therefore, these shortcomings can be eliminated after cross-linking.

Crosslinking is divided into radiation crosslinking and chemical crosslinking.

1. Radiation cross-linking: Use high-energy rays, generally rays generated by cobalt 60 radiation sources or electron rays generated by electron acceleration, and mainly use the latter. Then add a cross-linking aid (a monomer with two or more carbon-carbon double bond structures) for cross-linking. However, the operation is difficult and requires high equipment.
2. Chemical crosslinking: Use triazole dithioamine salt (FSH) for crosslinking. The crosslinking mechanism is that amine and thiol combine to attack the carbon-chlorine polar bond to perform a substitution reaction. After crosslinking, the product’s UV resistance, solvent resistance, temperature resistance, impact toughening and other properties will be comprehensively improved.

History

Polyvinyl chloride was discovered by V. Regno of the United States as early as 1835. When vinyl chloride is irradiated with sunlight, a white solid, namely polyvinyl chloride, is generated.

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 under sunlight. In the early 20th century, Russian chemist Ivan Ostromislensky and German chemist Fritz Klatte of the Griesheim-Elektron company simultaneously tried to use PVC for commercial purposes, but the difficulty was how to process this hard and sometimes brittle polymer.

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 BF Goodrich Company in the United States synthesized PVC and applied for a patent in the United States. Waldo Semon and BF Goodrich Company developed a method of plasticizing PVC by adding various additives in 1926, making it a more flexible and easier to process material, which soon gained widespread commercial application.

In 1914, it was discovered that organic peroxides could accelerate the polymerization of vinyl chloride. In 1931, the German French company used emulsion polymerization to achieve industrial production of polyvinyl chloride. In 1933, WL Simon proposed that high-boiling point solvents and tricresol phosphate could be heated and mixed with PVC to make soft polyvinyl chloride products, which made a real breakthrough in the practical application of PVC. British Brunner Mond Chemical Industry Company, American Union Carbide Company and Goodrich Chemical Company almost simultaneously developed the suspension polymerization of vinyl chloride and the processing and application of PVC in 1936. In order to simplify the production process and reduce energy consumption, Saint-Goban Company of France developed the bulk polymerization method in 1956. In 1983, the world’s total consumption was about 11.1 Mt and the total production capacity was about 17.6 Mt; it was the second largest plastic variety after polyethylene production, accounting for about 15% of the total plastic production. China’s self-designed PVC production unit was put into trial production at Liaoning Jinxi Chemical Plant in 1956. The 3 kt unit was officially put into industrial production in 1958, and the output reached 530.9 kt in 1984.

PVC was industrialized in the early 1930s. Since the 1930s, for a long time, the output of polyvinyl chloride has been the first in the world’s plastic consumption. In the late 1960s, polyethylene replaced polyvinyl chloride. Although polyvinyl chloride plastics have retreated to second place, their output still accounts for more than a quarter of the total plastic output.

Before the 1960s, the production of vinyl chloride monomer was mainly based on calcium carbide acetylene, because the production of calcium carbide consumes a lot of electricity and coke and is costly. After the industrialization of vinyl chloride production by ethylene oxychlorination in the early 1960s, countries turned to cheaper petroleum as raw materials. In addition, since a large part of the raw materials of polyvinyl chloride (about 57% by weight) is chlorine, which is an inevitable by-product of the alkali industry, it is not only rich in raw material sources, but also one of the very important products for the development of the chlor-alkali industry and the balance of chlorine. Therefore, although the proportion of polyvinyl chloride in plastics has declined, it still maintains a relatively high growth rate.

Polyvinyl chloride plastic products are widely used, but in the mid-1970s, people realized that the residual vinyl chloride monomer (VCM) in polyvinyl chloride resins and products is a serious carcinogen, which will undoubtedly affect the development of polyvinyl chloride to a certain extent. However, people have successfully reduced the residual VCM by adding spiral plate heat exchangers, so that the VCM content in the polyvinyl chloride resin will be less than 10 ppm, meeting the requirements of sanitary resin, and expanding the application range of polyvinyl chloride. It can even make the VCM content in the resin less than 5 ppm, and there is very little residual VCM after processing. It is basically harmless to the human body and can be used as food and medicine packaging and children’s toys.

PVC material in China

PVC materials with special requirements are usually imported from abroad in China, with well-known foreign companies such as United Carbide and Nordic Chemicals. With the continuous research and technological accumulation of major research institutes and production units in China, the formula design and manufacturing of PVC modified materials in China have reached the international advanced level, completely replacing imported materials from abroad, and many products have been exported abroad.

Main categories

According to different application scopes, PVC can be divided into : general-purpose PVC resin, high-polymerization PVC resin, and cross-linked PVC resin. General-purpose PVC resin is formed by the polymerization of vinyl chloride monomer under the action of an initiator; high-polymerization PVC resin refers to a resin polymerized by adding a chain extender to the polymerization system of vinyl chloride monomer; cross-linked PVC resin is a resin polymerized by adding a cross-linking agent containing diene and polyene to the polymerization system of vinyl chloride monomer.

According to the method of obtaining vinyl chloride monomer, it can be divided into calcium carbide method, ethylene method and imported (EDC, VCM) monomer method (ethylene method and imported monomer method are usually referred to as ethylene method).

According to the polymerization method, polyvinyl chloride can be divided into four categories: suspension polyvinyl chloride, emulsion polyvinyl chloride, bulk polyvinyl chloride, and solution polyvinyl chloride. Suspension polyvinyl chloride is the largest variety, accounting for about 80% of the total PVC production. Suspension polyvinyl chloride is divided into six models according to absolute viscosity: XS-1, XS-2…XS-6; XJ-1, XJ-2…, XJ-6. The meaning of each letter in the model: X-suspension method; S-loose type; J-tight type.

According to the amount of plasticizer, PVC plastics are usually divided into: non-plasticized PVC, plasticizer content is 0; rigid PVC, plasticizer content is less than 10%; semi-rigid PVC, plasticizer content is 10-30%; soft PVC, plasticizer content is 30-70%; polyvinyl chloride paste plastic, plasticizer content is more than 80%. The difference in properties between rigid PVC and soft PVC is shown in the table:

Nature	Unit	Rigid PVC	Soft PVC
Density	g/cm³	1.3–1.45	1.1–1.35
Thermal conductivity	W/(m·K)	0.14–0.28	0.14–0.17
Yield Strength	psi	4500–8700	1450–3600
	MPa	31–60	10.0–24.8
Young’s modulus	psi	490000	—
	GPa	3.4	—
Flexural Strength (Yield)	psi	10,500	—
	MPa	72	—
Compression strength	psi	9,500	—
	MPa	66	—
Coefficient of thermal expansion (linear)	mm/(mm·°C)	5×10^−5	—
Vicat softening temperature	°C	65–100	—
Resistivity^a	Ω·m	10^16	10^12 –10^15
Surface resistivitya	Ω	10^13 –10^14	10^11 –10^12

Note: a, at relative humidity of 60% and room temperature

Preparation method

Polyvinyl chloride can be made from ethylene, chlorine and a catalyst through a substitution reaction. Due to its fire and heat resistance, polyvinyl chloride is widely used in a variety of products in various industries: wire sheaths, optical fiber sheaths, shoes, handbags, bags, accessories, signs and billboards, building decoration products, furniture, ornaments, rollers, hoses, toys, door curtains, rolling doors, auxiliary medical supplies, gloves, cling film for certain foods, certain fashions, etc.

Aggregation methods

PVC is prepared by free radical addition polymerization. The polymerization methods are mainly divided into suspension polymerization, emulsion polymerization, bulk polymerization and micro-suspension polymerization. Suspension polymerization is the main method, accounting for about 80%-82% of the total PVC production, followed by emulsion polymerization, accounting for about 10%-12% of the total PVC production, and then bulk polymerization, accounting for about 8%. The particle structure obtained by the suspension method and the bulk method is similar, with an average particle size of 100~160 microns. The particle size obtained by the emulsion method and the micro-suspension method is about 0.2 microns and 1 micron. Only a small amount of polyethylene copolymers for coatings are prepared by the solution method. Pure water, liquefied VCM monomer, and dispersant are added to the reactor, and then the initiator and other additives are added. After heating to a certain temperature, the VCM monomer undergoes a free radical polymerization reaction to generate PVC particles. Continuous stirring makes the particle size uniform and the generated particles suspended in water. In addition, there is also a micro-suspension method to produce PVC paste resin, which has good product performance and paste-forming properties.

① Suspension polymerization:

The basic formula of vinyl chloride suspension polymerization is composed of vinyl chloride monomer, water, oil-soluble initiator, and dispersant, but in fact, pH regulator, molecular weight regulator (mainly for low polymerization degree varieties), anti-sticking kettle agent, defoaming agent, etc. are also added. According to the different requirements of loose and compact polyvinyl chloride, the ratio of water to monomer in the formula varies between (1.2~2):1. The process of vinyl chloride suspension polymerization is roughly as follows: water, dispersant, other additives, and initiator are added to the polymerization kettle in turn, evacuated and filled with nitrogen to remove oxygen, and then monomers are added, and the temperature is raised to the predetermined temperature for polymerization. During the polymerization process, the temperature and pressure remain constant. The pressure drops by 0.1~0.2MPa in the later stage, which is equivalent to 80%~85% conversion rate, and the polymerization is terminated. If the pressure is reduced too much, the resin will be dense. After the polymerization is completed, the monomer is recovered, the material is discharged, and the finished polyvinyl chloride resin is obtained through post-processing procedures.

When vinyl chloride is polymerized, transfer to monomer is the main chain termination mode, so that the degree of polymerization of polyvinyl chloride (600~1600) is independent of the initiator concentration and is only controlled by temperature (45~65 o C, and the temperature fluctuation needs to be controlled within 0.2~ 0.5 o C. The polymerization rate is mainly regulated by the amount of initiator. At present, the heat transfer performance of the polymerization kettle is good, and a high-activity initiator such as peroxycarbonate is mostly used, with an amount of 0.02%~0.05%. If high-activity and low-activity initiators are used in combination and the combination is proper, such as a half-life of 2h, it is expected to be close to a uniform reaction. Uniform reaction is conducive to heat transfer and temperature control. Polyvinyl chloride-vinyl chloride is a partially miscible system, forming two phases: One phase is a polyvinyl chloride rich phase swollen with vinyl chloride (about 30%), which becomes the main site of polymerization. The other phase is a monomer phase dissolved with trace amounts of polyvinyl chloride (< 0.1%), which is close to pure monomer. When the conversion rate is > 70%, the monomer phase disappears, the system pressure begins to be lower than the saturated atmospheric pressure of pure vinyl chloride, and the vinyl chloride in the polyvinyl chloride rich phase continues to polymerize. The polymerization is terminated when the conversion rate reaches 85%, so as not to affect the loose structure of the resin particles. The properties of the dispersant have a crucial effect on the morphology of polyvinyl chloride particles. When gelatin is selected, the surface tension of its aqueous solution is relatively large (68 mN·m^-1 at 25°C ), and a compact resin will be formed. When preparing loose polyvinyl chloride, the surface tension of the individual is required to be below 50 mN·m^-1. Partially hydrolyzed polyvinyl alcohol (surface tension of aqueous solution is 50~55 mN·m^-1 ) and hydroxypropyl methylcellulose (surface tension of aqueous solution is 45~50 mN·m^-1 ) are used in combination, and sometimes a third component is added. Although the preparation of composite dispersants can be partially referenced by surface tension, it still requires some experience and skills.

The specific process is as follows:

The monomer is suspended and dispersed in the water phase in the form of droplets, and the selected oil-soluble initiator is dissolved in the monomer. The polymerization reaction is carried out in these droplets, and the heat of the polymerization reaction is absorbed by water in time. In order to ensure that these droplets are dispersed in the water in the form of beads, it is necessary to add a suspension stabilizer, such as gelatin, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, etc. Initiators are mostly organic peroxides and azo compounds, such as diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, diethylhexyl peroxydicarbonate, azobisisoheptonitrile, azobisisobutyronitrile, etc. The polymerization is carried out in a polymerization kettle with an agitator. After polymerization, the material flows into a monomer recovery tank or a stripping tower to recover the monomer. Then it flows into a mixing kettle, washed with water, centrifuged and dehydrated, and dried to obtain the finished resin. Vinyl chloride monomer should be extracted from the resin as much as possible. For PVC used for food packaging, the free monomer content should be controlled below 1 ppm. During polymerization, in order to ensure that the resin with the specified molecular weight and molecular weight distribution range is obtained and to prevent explosion, the temperature and pressure of the polymerization process must be controlled well. The particle size and particle size distribution of the resin are controlled by the stirring speed and the selection and dosage of the suspension stabilizer. The quality of the resin is characterized by properties such as particle size and particle size distribution, molecular weight and molecular weight distribution, apparent density, porosity, fisheye, thermal stability, color, impurity content and free flow of powder.

The polymerization reactor is the main equipment, which is made of a steel reactor lined with stainless steel or enamel, equipped with a stirrer and a heat transfer jacket for controlling the temperature, or an internal cooling pipe, a reflux condenser, etc. In order to reduce production costs, the volume of the reactor has gradually developed from a few cubic meters and more than ten cubic meters to a large-scale one, and the maximum has reached 200 cubic meters (kettle reactor). The high heat transfer capacity of the polymerization reactor plays a role in ensuring the constant polymerization temperature, and stirring not only helps to mix materials and transfer heat, but also has a significant impact on liquid-liquid dispersion and resin particle characteristics. Heat transfer and stirring are two major engineering issues in vinyl chloride polymerization. The polymerization reactor needs to be descaled after repeated use. PVC made with polyvinyl alcohol and cellulose ethers as suspension stabilizers is generally loose, has many pores, a large surface area, and is easy to absorb plasticizers and plasticize.

② Emulsion polymerization:

One of the earliest methods for industrial production of PVC. In emulsion polymerization, in addition to water and vinyl chloride monomer, surfactants such as sodium alkyl sulfonate are added as emulsifiers to disperse the monomers in the water phase to form an emulsion. Water-soluble potassium persulfate or ammonium persulfate is used as an initiator. The “oxidation-reduction” initiation system can also be used. The polymerization process is different from the suspension method. Polyvinyl alcohol is also added as an emulsion stabilizer, dodecyl mercaptan as a regulator, and sodium bicarbonate as a buffer. There are three polymerization methods: intermittent method, semi-continuous method and continuous method. The polymerization product is latex-like, with an emulsion particle size of 0.05 to 2μm, which can be directly applied or spray-dried into a powdered resin. The polymerization cycle of the emulsion polymerization method is short and easier to control. The obtained resin has a high molecular weight and a relatively uniform degree of polymerization. It is suitable for making polyvinyl chloride paste, artificial leather or impregnated products. The formula of emulsion polymerization is complex and the product has a high impurity content.

③ Bulk polymerization method:

The polymerization device is quite special, mainly consisting of a vertical prepolymerization kettle and a horizontal polymerization kettle with a frame agitator. The particle characteristics of bulk PVC are similar to those of suspension resin, loose, but without film and more crystalline. In addition to heat dissipation and anti-sticking, bulk polymerization also needs to solve the problem of maintaining the loose structure of particles, which is usually ensured by two-stage polymerization. The first stage is prepolymerization, which is carried out in a vertical kettle. A small amount of vinyl chloride and a limited amount of high-activity initiator (such as acetyl peroxide sulfonate) are added to the kettle and prepolymerized at 50~70 o C to a conversion rate of 7%~11% to become a dead-end polymerization to prevent the conversion rate from being too high. Rapid stirring forms a loose particle skeleton. The conversion rate is estimated by the heat removed by the jacket and condenser.

Prepolymer, more monomers and another part of initiator are added to another slow-speed stirring kettle (30r/min), and the monomers continue to polymerize on the preformed particle skeleton, so that the particles grow and keep the shape unchanged. When the conversion rate reaches 70%~90%, the polymerization is terminated. The residual monomers are discharged, and the finished product is obtained by crushing and sieving. Prepolymerization only takes 1~2 hours, but polymerization takes 5~9 hours. One prepolymerization kettle can be equipped with several polymerization kettles. The particle size and shape of the resin are controlled by the stirring speed, and the reaction heat is taken out by the reflux condensation of the monomer. This method has a simple production process, good product quality and low production cost.

PVC modification method

PVC resin is a polar non-crystalline polymer with a density of 1.38 g/cm³ and a glass transition temperature of 87°C. Therefore, it has poor thermal stability and is difficult to process. It cannot be used directly and must be modified and mixed before it can be used with the addition of relevant additives and fillers. The different types and fractions of the added additives and fillers determine that the performance and requirements of the prepared PVC materials are different. We usually call it PVC formula, which is strictly speaking a PVC modified formula, and PVC can only be used after modification. This category is often classified as polymer modified materials. The modification of polymer materials mainly focuses on the research of high performance of general plastics, the transformation of single-component materials to multi-component composite materials (alloys, blends, composites), giving materials functionalization, optimizing performance and price, etc. The modification methods are mainly chemical modification, filling modification, reinforcement modification, blending modification and nano-composite modification. The basic principle of modification is to give materials functions or improve certain properties through additives.Therefore, the level of PVC formulation technology determines the level of technology and production capacity of a factory.

PVC is usually first modified and granulated. After being prepared into particles using a screw extruder, it is more fully plasticized and easier to process, especially for products that are injection molded. The screw extruder is one of the most important equipment for plastic molding. It uses external power transmission and heat transfer from external heating elements to transport, compact, melt, shear, mix and extrude plastics. Screw extruders play an important role both as plasticizing and granulating machinery and as molding machinery. Strictly speaking, PVC products with special requirements and PVC modified formulas are tailor-made according to customer requirements. There are also copolymer derivatives produced during the PVC production process. Such modified varieties include vinyl chloride copolymers, polyvinyl chloride blends and chlorinated polyvinyl chloride, etc.

Characteristic

Colorability

Polyvinyl chloride has poor thermal stability and light resistance. It begins to decompose hydrogen chloride at 150°C, and adverse reactions occur with the amount of plasticizer. In addition, the effect of pigments on PVC is reflected in whether the pigment reacts with PVC and other components of PVC products, as well as the migration resistance and heat resistance of the pigment itself. Some components in the colorant may promote the degradation of the resin. For example, iron ions and zinc ions are catalysts for the degradation reaction of PVC resin. Therefore, the use of iron oxide (red, yellow, brown and black) pigments or zinc oxide, zinc sulfide and white pigments such as lead powder will reduce the thermal stability of PVC resin. Some colorants may react with the degradation products of PVC resin. For example, ultramarine pigments have poor acid resistance, so during the PVC coloring process, they will interact with the hydrogen chloride produced by the decomposition of PVC and lose their proper color. Therefore, in terms of PVC coloring, the characteristics of the resin and related additives used should be considered, combined with the characteristics of the pigment. When selecting colorants, the following issues should be noted.

Certain metal ions in the pigment will promote the thermal oxidative decomposition of polyvinyl chloride resin.

The determination method is to measure the hue change of polyethylene with pigment when heated to 180°C. The metal ions in the pigment accelerate the decomposition of PVC, resulting in hue change. At the same time, it should be noted that the same addition of red lake can produce different color differences in PVC. For example, if calcium is contained, the hue difference is small; if manganese is contained, the hue difference is large. This is because manganese and other metals promote the dehydrochlorination of PVC.

Sulfide colorants (such as cadmium red, etc.) are used for polyvinyl chloride coloring, and hydrogen sulfide may be released due to the decomposition of the colorant. This type of colorant should not be mixed with lead stabilizers to avoid the formation of black lead sulfide.

Effect of pigments on electrical insulation of polyvinyl chloride

As the cable material, polyvinyl chloride, like polyethylene, should also consider the electrical properties after coloring. In particular, polyvinyl chloride has a worse insulation than polyethylene, so the influence of pigments is greater. This shows that the electrical insulation of PVC is better when inorganic pigments are used than organic pigments (except furnace black and anatase titanium dioxide).

Mobility

Migration only occurs in plasticized PVC products and when dyes or organic pigments are used. Migration means that some soluble dyes or organic pigments in the surrounding solvent penetrate the surface of the PVC product through the plasticizer, and those dissolved dye (pigment) particles are also brought to the surface of the product, thus causing indirect bleeding, solvent bleeding or blooming.

Another problem is “scaling”, which means that the colorant is released from the system during the coloring process because the colorant has poor solubility or is not compatible at all, and is deposited on the surface of the processing equipment (such as the inner wall of the extruder barrel and the inner wall of the die hole).

Weather resistance

Refers to the ability of pigments to withstand various climates. These include visible and ultraviolet light, moisture, temperature, atmospheric chlorination, and chemical agents encountered during the use of the product. The most important weather resistance includes non-fading, chalking resistance, and durability of physical properties. Organic pigments have different structures and are better or worse. In addition, in formulations containing white pigments, the weather resistance of the pigment will be severely affected.

The fading, darkening or hue change of pigments is generally caused by the pigment’s reactive genes. These reactive genes can react with moisture in the atmosphere or chemical agents – acids and bases. For example, cadmium yellow will fade under the action of moisture and sunlight, while Lithol Red has good light resistance and is suitable for most indoor applications, but it fades severely when used outdoors in the presence of acid and alkali components.

The method for determining dehydrochlorination is in accordance with JIS-K-6723, and the measuring temperature is 180°C. The time for dechlorination of uncolored polyvinyl chloride composite is used as the benchmark, and the extension or delay time is measured at intervals of 5% and 10%. Negative values ​​indicate accelerated decomposition.

Stability

The softening point of polyvinyl chloride resin is low, about 75-80℃, and the brittle temperature is lower than -50~-60℃. The long-term use temperature of most products should not exceed 55℃, and special formulas can reach 90℃. If the polyvinyl chloride resin is a purely linear structure with no internal branches and unsaturated bonds, the stability of the polyvinyl chloride resin should be relatively high, although the C-Cl bond energy is relatively small. However, even polyvinyl chloride resin with very high purity will begin to emit hydrogen chloride gas when it is exposed to ultraviolet radiation for a long time at above 100℃. This indicates that there are sharp groups or unstable structures in its molecular structure. The longer the time, the more degradation, and the higher the temperature, the faster the degradation rate, and the degradation rate is even faster in the presence of oxygen or air.

Electrical properties

Polyvinyl chloride is a polar polymer with a strong affinity for conductive substances such as water. Therefore, its resistance is lower than that of non-polar polyolefins, but it still has a higher volume charge and breakdown voltage. The polar groups of polyvinyl chloride are directly attached to the main chain. Below the glass transition temperature, the dipole segments are restricted by the main chain atoms of the frozen structure and cannot move. Therefore, no dipole effect is produced, and it can be used as a high-frequency insulation material at room temperature. When used for wire insulation, the electrical insulation of the suspension resin is 10-100 times higher than that of the suspension resin. The presence of chloride ions produced by degradation will reduce the electrical insulation.

Physical and chemical properties

Polyvinyl chloride is slightly yellow and translucent, with a glossy appearance. It is more transparent than polyethylene and polypropylene, but less transparent than polystyrene. Depending on the amount of additives used, it is divided into soft and hard polyvinyl chloride. Soft products are soft and tough, and feel sticky. Hard products have a higher hardness than low-density polyethylene, but lower than polypropylene, and will whiten at the bends. It is stable; not easily corroded by acids and alkalis; and relatively resistant to heat.

Polyvinyl chloride has the advantages of flame retardancy (flame retardancy value of 40 or more), high chemical resistance (resistance to concentrated hydrochloric acid, 90% sulfuric acid, 60% nitric acid and 20% sodium hydroxide), good mechanical strength and electrical insulation.

Polyvinyl chloride has poor stability to light and heat. The softening point is 80℃, and it starts to decompose at 130℃. Without heating stabilizer, polyvinyl chloride starts to decompose at 100℃, and decomposes faster above 130℃. When heated, it releases hydrogen chloride gas (hydrogen chloride gas is toxic) and changes color from white to light yellow to red to brown to black. Ultraviolet rays and oxygen in sunlight can cause polyvinyl chloride to undergo photo-oxidative decomposition, thereby reducing the flexibility of polyvinyl chloride and finally making it brittle. This is why some PVC plastics turn yellow and brittle over time.

It has stable physical and chemical properties, is insoluble in water, alcohol, and gasoline, and has low gas and water vapor permeability. At room temperature, it can withstand any concentration of hydrochloric acid, sulfuric acid below 90%, nitric acid at 50-60%, and caustic soda solution below 20%, and has a certain resistance to chemical corrosion. It is quite stable to salts, but can be dissolved in organic solvents such as ether, ketones, chlorinated aliphatic hydrocarbons and aromatic hydrocarbons.

Industrial polyvinyl chloride resin is mainly an amorphous structure, but it also contains some crystalline areas (about 5%), so polyvinyl chloride has no obvious melting point. It begins to soften at about 80°C and has a heat deformation temperature (under a load of 1.82MPa) of 70-71°C. It begins to flow at 150°C under pressure and begins to slowly release hydrogen chloride, causing the polyvinyl chloride to change color (from yellow to red, brown, or even black).

The weight average molecular weight of industrial polyvinyl chloride is in the range of 48000-48000, and the corresponding number average molecular weight is 20000-19500. The weight average molecular weight of most industrial resins is 100000-200000, and the number average molecular weight is 45500-64000. Rigid polyvinyl chloride (without plasticizer) has good mechanical strength, weather resistance and flame retardancy. It can be used alone as a structural material and applied to the manufacture of pipes, plates and injection molded products in the chemical industry. Rigid polyvinyl chloride can be used as a reinforcement material.

Density: 1380 kg/m³

Young’s elastic modulus (E): 2900-3400MPa

Tensile strength (σt): 50-80MPa

Elongation at break: 20-40%

Glass transition temperature: 87℃

Melting point: 212℃

Softening temperature: 85℃

Thermal conductivity (λ): 0.16 W/(m·K)

Thermal expansion coefficient (α): 8×10^-5/K

Heat capacity (c): 0.9kJ/(kg·K)

Water absorption (ASTM): 0.04-0.4

Refractive index: 1.52~1.55

The biggest feature of polyvinyl chloride is that it is flame retardant, so it is widely used in fire protection applications. However, polyvinyl chloride releases hydrogen chloride and other toxic gases such as dioxins during combustion.

The combustion of polyvinyl chloride is divided into two steps. First, it burns and decomposes hydrogen chloride gas and dienes containing double bonds at 240℃-340℃, and then carbon combustion occurs at 400-470℃.

It is one of the world’s largest plastic products, cheap and widely used. Polyvinyl chloride resin is white or light yellow powder. Different additives can be added according to different uses, and polyvinyl chloride plastic can present different physical and mechanical properties. Adding an appropriate amount of plasticizer to polyvinyl chloride resin can make a variety of hard, soft and transparent products.

The density of pure polyvinyl chloride is 1.4 g/cm³, and the density of polyvinyl chloride plastic parts with plasticizers and fillers added is generally 1.15-2.00 g/cm³.

Rigid polyvinyl chloride has good tensile, bending, compressive and impact resistance and can be used alone as a structural material.

The softness, elongation at break, and cold resistance of soft polyvinyl chloride will increase, but its brittleness, hardness, and tensile strength will decrease.

Polyvinyl chloride has good electrical insulation properties and can be used as a low-frequency insulation material. It also has good chemical stability. However, due to its poor thermal stability, long-term heating will lead to decomposition, release of HCL gas, and discoloration of polyvinyl chloride. Therefore, its application range is relatively narrow, and the operating temperature is generally between -15 and 55°C.

The conversion between PVC hardness value Pa (Pa) and Shore hardness is as follows:

Pa	Shore Hardness
45	89±2, 87~91A
50	86±2, 84~88A
55	83±2, 81~85A
60	80±2,78~82A
65	78±2, 76~80A
70	75±2，73~77A
75	72±2, 70~74A
80	69±2，67~71A

PVC hardness comparison table
Pascal hardness	Thickness	Shore hardness test value	Average hardness value
30P	6mm	93-96 °	94.5 °
35P	6mm	87-93 °	90°
38P	6mm	89-90 °	89.5 °
40P	6mm	88-90 °	89°
45P	6mm	84-90 °	85°
50P	6mm	82-83 °	82.5 °
55P	6mm	70-80 °	79°
60P	6mm	74-76 °	75°
65P	6mm	73-75 °	74°
70P	6mm	72-74 °	73°
75P	6mm	70-70.5 °	70°
80P	6mm	67-68 °	67.5 °
85P	6mm	64-66 °	65°
90P	6mm	63-64 °	63.5 °
95P	6mm	58-60 °	59°
100P	6mm	57-59 °	58°
110P	6mm	54-56 °	55°

Another hardness comparison chart
Pa	Shore Hardness
30	95±2
45	90±2
50	88±2
60	84±2
70	80±2
80	76±2
90	72±2
95	68±2
105	64±2
Note: Shore hardness value is 15 seconds reading

Molding conditions

Rigid PVC

Pipe temperature: 160-190℃

Mold temperature: 40-60℃

Drying temperature: 80℃×2h

Injection pressure: 700-1500 kg/cm²

Density: 1.4g/cm³

Molding shrinkage: 0.1-0.5%

Thickness: 2.0-50.mm

Water absorption (24 h): 0.1-0.4%

Melting softening point: 89℃

Heat deformation temperature: 70℃

Soft PVC

Pipe temperature: 140-170℃

Mold temperature: 40-60℃

Drying temperature: 80℃×2h

Injection pressure: 600-1500kg/cm²

Density: 1.4g/cm³

Molding shrinkage: 0.1-0.5%

Thickness: 2.0-50.mm

Water absorption (24h): 0.1-0.4%

Melting softening point: 85℃

Heat deformation temperature: 55℃

Material Processing

PVC plastics have different forms and are processed in a variety of ways, including pressing, extrusion, injection, coating, etc. The particle size, fisheye, bulk density, purity, foreign impurities, and porosity of PVC resins all have an impact on processability; paste resins should consider the viscosity and gelling properties of the paste.

Polyvinyl chloride is an amorphous polymer with a small shrinkage rate. The powder should be preheated before processing to remove moisture, enhance the plasticizing effect, and prevent bubbles. Moreover, PVC is very easy to decompose, especially when it comes into contact with steel and copper at high temperatures (decomposition temperature 200 degrees). The molding temperature range is small, and the material temperature must be strictly controlled. When using a screw injection machine and a straight-through nozzle, the aperture should be large to prevent material stagnation in dead corners. The mold casting system should be coarse, the gate section should be large, the mold should be cooled, the mold temperature should be 30-60℃, and the material temperature should be 160-190℃.

Below the glass transition temperature (Tg, 80℃), polyvinyl chloride is in a glassy state; from Tg to the viscous flow temperature (Tf, about 160℃), it is in a highly elastic rubber state with plasticity; from Tf to the thermal decomposition temperature (Td ), it is in a viscous flow state, and the higher the temperature, the easier it is to flow. When the temperature exceeds Td, PVC decomposes a large amount of hydrogen chloride (HCl), and the material loses its chemical stability and physical properties, so Td is the upper limit temperature for processing and molding. Due to the strong intermolecular force of polyethylene, Tf is very high, even close to the decomposition temperature, so plasticizers need to be added to reduce Tf. On the other hand, stabilizers also need to be added to increase the Td of PVC before processing and molding can be carried out.

The glass transition temperature (Tg ) is only related to the molecular chain segment structure and has little to do with the molecular weight, while the viscosity flow temperature (Tf ) is the temperature at which the macromolecules begin to move and is related to the molecular weight. The larger the molecular weight, the higher the T f. Therefore, for some processing and molding (such as injection molding), it is necessary to appropriately reduce the molecular weight of the resin. According to the size of the molecular weight, the suspended polyvinyl chloride resin produced in China is divided into grades 1-7. The larger the serial number, the smaller the molecular weight. XJ-4 (XS-4) to XJ-7 (XS-7) resins are often used to make hard pipes, hard boards, etc. Other types are lower. Resins with larger molecular weights need to add a large amount of plasticizers to reduce T f because of their higher T f, so they are often used to make soft products. Polyvinyl chloride with an average degree of polymerization below 1000 is called low-polymerization polyvinyl chloride, which has better processing performance. Less plasticizer can be added during the processing, so that the product will not accelerate aging due to the migration of plasticizers. Low-polymerization polyvinyl chloride products have good transparency and are widely used in building materials, food and drug packaging materials, and to replace organic glass products.

Polyvinyl chloride melt is a non-Newtonian pseudo-fluid. The greater the shear rate, the smaller the apparent viscosity, and the change is quite sensitive. When the temperature rises, the viscosity does not decrease much. Even if the plastic is below the decomposition temperature, it will be thermally and oxidatively degraded due to being at a high temperature for a long time, which will affect its performance. Therefore, improving the fluidity of polyvinyl chloride melt should mainly consider increasing the shear rate (increasing the pressure). In fact, increasing the external force helps the movement of macromolecules, reduces Tf, and macromolecules can flow at a lower temperature.

Main Applications

Vinyl chloride profiles

Profiles and special-shaped materials are the largest consumption areas of PVC in china, accounting for about 25% of the total consumption of PVC. They are mainly used to make doors and windows and energy-saving materials. Their application volume is still growing significantly in china. In developed countries, the market share of plastic doors and windows is also the highest, such as 50% in Germany, 56% in France, and 45% in the United States.

PVC pipe

Among the numerous PVC products, PVC pipes are the second largest consumer, accounting for about 20% of its consumption. In china, PVC pipes were developed earlier than PE pipes and PP pipes, with a wide variety, excellent performance, and a wide range of uses, occupying an important position in the market.

Polyvinyl chloride film

The consumption of PVC in the PVC film field ranks third, accounting for about 10%. After PVC is mixed with additives and plasticized, it is made into a transparent or colored film of a specified thickness using a three-roller or four-roller calender. The film processed in this way becomes a calendered film. It can also be processed into packaging bags, raincoats, tablecloths, curtains, inflatable toys, etc. by cutting and heat sealing. Wide transparent films can be used for greenhouses, plastic greenhouses and ground films. The biaxially stretched film has the property of shrinking due to heat, and can be used for shrink packaging.

PVC hardwood and sheets

Stabilizers, lubricants and fillers are added to PVC. After mixing, the PVC can be extruded into hard pipes, special-shaped pipes and corrugated pipes of various calibers using an extruder, which can be used as sewer pipes, drinking water pipes, wire casings or stair handrails. The rolled sheets can be overlapped and hot-pressed to make hard plates of various thicknesses. The plates can be cut into the required shapes and then welded with hot air using PVC welding rods into various chemical-resistant storage tanks, air ducts and containers.

PVC general soft products

The extruder can be used to extrude hoses, cables, wires, etc.; the injection molding machine can be used with various molds to make plastic sandals, soles, slippers, toys, auto parts, etc.

PVC packaging materials

Polyvinyl chloride products are mainly used for packaging of various containers, films and hard sheets. PVC containers are mainly used to produce mineral water, beverages, cosmetic bottles, and are also used for packaging refined oils. PVC film can be used to co-extrude with other polymers to produce low-cost laminated products, as well as transparent products with good barrier properties. Polyvinyl chloride film can also be used for stretch or heat shrink packaging, used to package mattresses, cloth, toys and industrial goods.

PVC siding and flooring

PVC siding is mainly used to replace aluminum siding. In addition to a portion of PVC resin, the remaining components of PVC floor tiles are recycled materials, adhesives, fillers and other components. They are mainly used on the hard floors of airport terminals and other places.

PVC daily consumer products

Luggage bags are traditional products made from PVC. PVC is used to make various imitation leathers for luggage bags, sports products such as basketballs, footballs and rugby. It can also be used to make belts for uniforms and special protective equipment. PVC fabrics for clothing are generally absorbent fabrics (no coating required), such as raincoats, baby pants, imitation leather jackets and various rain boots. PVC is used in many sports and entertainment products, such as toys, records and sports equipment. PVC toys and sports equipment have a large growth rate, because of its low production cost and easy molding and have an advantage.

PVC coated products

Artificial leather with a backing is made by applying PVC paste on cloth or paper and then plasticizing it at above 100°C. It can also be made by first rolling PVC and additives into a film and then pressing it with a backing. Artificial leather without a backing is directly rolled into a soft sheet of a certain thickness by a calender and then pressed with a pattern. Artificial leather can be used to make suitcases, bags, book covers, sofa and car seat cushions, etc., as well as floor leather, which is used as a floor covering material for buildings.

PVC foam products

When mixing soft PVC, add an appropriate amount of foaming agent to make sheets, which are foamed and molded into foam plastics, which can be used as foam slippers, sandals, insoles, and shock-proof and cushioning packaging materials. It can also be made into low-foaming hard PVC sheets and profiles by extruders, which can replace wood and is a new type of building material.

PVC transparent sheet

Impact modifiers and organotin stabilizers are added to PVC, which is mixed, plasticized and calendered to become transparent sheets. It can be made into thin-walled transparent containers or used for vacuum blister packaging by thermoforming, and is an excellent packaging material and decorative material.

other

Doors and windows are assembled from hard special-shaped materials. In some countries, they have occupied the door and window market together with wooden doors and windows, aluminum windows, etc.; imitation wood materials, steel-substitute building materials (in the north, on the coast); hollow containers.

Virtual circuit is one of the services provided by packet switching network (the other is datagram service). Simply put, it is to establish a virtual logical connection between user hosts through the control mechanism within the network, and ensure the correctness and order of the packets transmitted on it. The establishment and removal of virtual circuits must be carried out before and after communication. Permanent virtual circuit is a virtual circuit established when the network is initialized, and the virtual circuit is always maintained. X.25 network and B-ISDN both provide PVC service. PVC plastic bags are generally prohibited.

New material research

At present, the total annual demand for modified plastics in china is about 5 million tons, accounting for about 10% of the total plastic consumption, which is far lower than the world average. There is still a big gap between chinese per capita plastic consumption and that of developed countries in the world. In order to achieve the rapid and stable development of china’s modified plastics industry, innovative technology is the key to future development.

Chemical industry analysts believe that the overall development level of chinese modified plastics industry is not very high at present. The production scale of enterprises in the industry is generally small. There are many primary products on the market, the quality of intermediate products is not stable enough, and there is a lack of advanced products. It is far from meeting the needs of chinese current social and economic development. As an important part of the field of new chemical materials, modified plastics have been listed as one of the key scientific and technological fields for development by china. Since the introduction of various policies in china, the development of the modified plastics industry will be further promoted. The automobile and home appliance industries are hot spots for the development of modified plastics, accounting for more than 50% of the total.

Plastics have been used in the automotive industry for more than 50 years. As cars move toward lightweight and energy-saving, higher requirements are placed on materials. Since 1 kg of plastic can replace 2-3 kg of heavier materials such as steel, and every 10% decrease in the car’s own weight can reduce fuel consumption by 6%-8%. Therefore, increasing the amount of modified plastics in cars can reduce the cost and weight of the entire vehicle and achieve energy-saving effects. The amount of different plastics used in passenger cars and commercial vehicles is also different. Last year, the demand for modified PP, PC alloys and modified ABS was approximately 1.1463 million, 151,300 and 149,700 tons respectively. The market for modified plastics for home appliances in china is mainly occupied by foreign companies, and domestic modified plastic companies account for less than 1/3 of the market share. Since the products of domestic companies are mostly limited to low-tech and low-standard levels, their ability to explore areas with high-performance requirements is obviously insufficient.

According to the “2009-2012 China Modified Plastics Industry Market Analysis and Investment Value Research Report”, with the substantial improvement of people’s living standards and the improvement of technical means, “replacing steel with plastics” and “replacing wood with plastics” will become a trend in China. As a sub-industry with the fastest development and great development potential in the plastic processing industry, the modified plastics industry is expected to maintain a growth rate of more than 10% in the total market demand in china in the next five years.

PVC replaces steel with plastic

Through the research on PVC modification technology, the use of advanced internal plasticization technology and additive formula, the mechanical and electrical properties of PVC plastic steel are guaranteed, the flame retardant performance is improved, and the product has the advantages of high strength, corrosion resistance, flame retardancy, good insulation performance, light weight, and convenient construction. It can completely replace steel pipes in electrical wiring systems.

PVC replaces wood with plastic

PVC wood-plastic composite material is a new type of composite material made from waste wood fiber and plastic as the main raw materials, supplemented by appropriate processing aids, and prepared by hot pressing. Its products fully embody the concept of recycling renewable resources and petroleum products, and are of great significance in alleviating the current problems of shortage of wood and petroleum resources and serious environmental pollution.

Home building materials products with PVC as the main raw material have become the second largest pillar of china’s plastics industry, with an average annual growth rate of more than 15%. In the next 10 years, the country is expected to add 30 billion square meters of housing construction area. If these buildings can achieve 50% energy saving on the existing basis, the market demand for energy-saving building materials can reach tens of trillions of yuan, which provides huge space for the development of indoor energy-saving decorative materials. For a long time, the building materials industry has been characterized by high energy consumption and high pollution. In order to adapt to the requirements of a low-carbon economy, home building materials companies have developed a batch of PVC high-simulation building materials that use plastic instead of wood after years of research and development, which have become home products that perfectly combine low carbon and practicality.

Industry experts point out that PVC building materials that replace wood with plastic not only save costs, but are also recyclable and in line with the general trend of environmental sustainable development and circular economy.

Identification method

Conventional identification methods for PVC are generally classified into the following three categories, namely:

Combustion Identification

Softening or melting temperature range: 75~90℃;

Combustion conditions: self-extinguishing after ignition;

Burning flame state: yellow on top, green on bottom with smoke; Situation after leaving the fire: extinguished; Smell: pungent sour smell.

This method is the simplest and most direct and is generally the first choice.

Solvent treatment identification

Solvents: tetrahydrofuran, cyclohexanone, dimethylformamide;

Non-solvents: methanol, acetone, heptane.

By adding the suspected PVC plastic to the above solvents and observing the dissolution of the plastic, you can determine whether it is PVC. The dissolution effect will be more obvious after the solvent is heated.

Gravity method

The specific gravity of PVC is 1.35~1.45, generally around 1.38. Polyvinyl chloride and other plastics can be distinguished by the difference in specific gravity or the method of measuring specific gravity. However, since PVC can be made to have a large difference in specific gravity and hardness by adding plasticizers, modifiers and fillers, and many properties of PVC plastics will also change due to the addition of some ingredients, our commonly used identification methods are not effective, and even the phenomenon changes, making it impossible to make an accurate judgment. For example: in terms of density, plasticized polyvinyl chloride (containing about 40% plasticizer) is 1.19~1.35; while PVC hard products are increased to 1.38~1.50. If it is a highly filled PVC product, the density may sometimes exceed 2.

In addition, it can also be determined by determining whether the material contains chlorine, but because vinyl chloride copolymers, chloroprene rubber, polyvinylidene chloride, chlorinated polyvinyl chloride, etc. all contain a high proportion of chlorine, they must also be identified through pyridine color reaction. Note that before the test, the sample must be extracted with ether to remove the plasticizer. The test method is: dissolve the sample taken with ether benzene in tetrahydrofuran, filter out the insoluble components, add methanol to precipitate it, and dry it below 75 degrees after extraction. A small amount of dried sample does not need to react with 1 mL of pyridine. After a few minutes, add 2 to 3 drops of 5% sodium hydroxide methanol solution (1g sodium hydroxide is dissolved in 20 mL methanol), observe the color immediately, and observe it again after 5 minutes and 1 hour respectively. Different chlorine-containing plastics can be identified based on color.

In daily life, we are more exposed to PVC and PE plastic films (bags) that need to be distinguished. Here is a simple method:

1. Touch method

It feels lubricated to the touch, and the surface is like coated with a layer of wax (chemically called wax feeling). This is a non-toxic polyethylene film bag, while the polyvinyl chloride film feels a little sticky.

2. Dithering method

If you shake it with your hand, it will make a crisp sound and lightly float, which is a polyethylene film bag. If you shake it with your hand, it will make a deep sound, which is a polyvinyl chloride film bag.

3. Combustion method

If it is flammable when in contact with fire, the flame is yellow, paraffin-like oil drips when burning, and there is candle burning gas, it is a non-toxic polyethylene film bag. If it is not easy to burn, it will go out when away from the fire, and the flame is green, it is a polyvinyl chloride film bag.

4. Immersion method

Immerse a plastic bag in water and press it into the water with your hand. The one that floats to the surface is polyethylene, and the one that sinks to the bottom is polyvinyl chloride (the density of polyethylene is lower than that of water, and the density of polyvinyl chloride is higher than that of water; at room temperature, they are approximately 0.92 g/cm³ and 1.4 g/cm³ respectively).

You can also take a copper wire and burn it in fire until it turns red, then put it in contact with the test plastic film to produce a chemical change, and then put the copper wire dipped in the plastic component back into the flame. At this time, you need to observe carefully. If a colorful and dazzling green flame appears, it means that this plastic material contains chlorine and belongs to the polyvinyl chloride material.

Health and Safety

Degradation

Aspergillus fumigatus can degrade plasticized polyvinyl chloride. Phanerochaete chrysosporium was grown on PVC in mineral salts agar. Ascomyces chrysosporium, Aspergillus niger, Aspergillus niger and Aspergillus sidovi were able to effectively degrade PVC.

Plasticizers

Phthalates are commonly added to plastics as plasticizers. Phthalates are designed not to covalently bind to the polymer matrix and are therefore highly susceptible to leaching. Phthalates are found in high concentrations in plastics. For example, phthalates can be present in IV bags at up to 40% by weight and in medical tubing at up to 80% by weight. Vinyl products, which are found everywhere including toys, car interiors, shower curtains and flooring, initially released chemical fumes into the air.

The hazards of lead

Lead was often added to polyvinyl chloride in the past to improve its processability and stability, but it has been shown that lead can leach into drinking water from PVC pipes.

Lead stearate, an antioxidant for polyvinyl chloride, is toxic. Lead salt antioxidant polyvinyl chloride (PVC) products will precipitate lead when in contact with ethanol, ether and other solvents. When polyvinyl chloride containing lead salt is used as food packaging and meets fried dough sticks, fried cakes, fried fish, cooked meat products, cakes and snacks, lead molecules will diffuse into the oil, so polyvinyl chloride plastic bags cannot be used to hold food, especially oil-containing foods. In addition, polyvinyl chloride plastic products will slowly decompose hydrogen chloride gas at higher temperatures, such as around 50°C. This gas is harmful to the human body, so polyvinyl chloride products are not suitable for food packaging.

Vinyl chloride monomer

In the early 1970s, the carcinogenicity of vinyl chloride (commonly known as vinyl chloride monomer or VCM) was linked to cancers in workers in the polyvinyl chloride industry. Specifically, workers in the polymerization department of a BF Goodrich plant near Louisville, Kentucky, were diagnosed with hemangiosarcoma of the liver, also known as angiosarcoma, a rare disease. Since then, studies of polyvinyl chloride workers in Australia, Italy, Germany, and the United Kingdom have all linked certain types of occupational cancer to exposure to vinyl chloride, and it has become accepted that vinyl chloride monomer is a carcinogen.

Dioxins (TCDD)

TCDD, the most deadly substance in the dioxin family, is a well-known carcinogen, hormone decomposer and toxic compound that is very harmful to humans and animals. The HCl produced by polyvinyl chloride when it burns is almost proportional to its chlorine content. Studies have shown that the chlorine in the emitted dioxins does not come from the HCl in the flue gas. Instead, most dioxins are produced in the solidified phase by the reaction of inorganic chlorides with the graphite structure in the carbon ash particles. Copper is a catalyst for these reactions.

Studies of household waste incineration have shown that dioxin production increases with increasing concentrations of PVC. Landfill fires may be a greater source of dioxins in the environment. An international survey of studies consistently found that areas affected by open waste burning have higher dioxin concentrations, and one study that investigated homologue patterns found that the samples with the highest dioxin concentrations were “typical of PVC pyrolysis”.

The second largest source of dioxins is medical and municipal waste incinerators. Various studies have been conducted with conflicting results. For example, one study of commercial-scale incinerators showed no relationship between the amount of polyvinyl chloride in the waste and dioxin emissions. Other studies have shown a clear correlation between dioxin formation and the amount of chloride present and have suggested that polyvinyl chloride is an important factor in the formation of dioxins and PCBs in incinerators.

Other

Since most disposable medical devices use medical grade polyvinyl chloride (PVC) or polycarbonate (PC), and the thermal decomposition products during the processing of PVC are highly corrosive to steel, while PC is hard and sticky, the material requirements for the plasticized parts must be corrosion-resistant, wear-resistant and have high polishing performance. Most medical injection molding machines use hard chrome plating on the barrel screw or stainless steel as the material to make the machine screw to meet the above special requirements. In addition, in order to prevent the generation of gas during the thermal decomposition of PVC during the processing, it is required to plate aluminum on the surface of the moving and fixed templates, and the outer sheet metal is also plated with aluminum or made of stainless steel. The sheet metal joints are sealed with non-toxic silicone to prevent the gas generated during the plastic processing from escaping to the outside (the gas generated during the plastic processing can be collected by special equipment and then purified before being discharged into the atmosphere).

Recycling

Polyvinyl chloride (PVC) is recyclable and its resin identification code is “3”.