PVC
,聚氯乙烯
Polyvinyl chloride, abbreviated as PVC (Polyvinyl chloride) in English, is a vinyl chloride monomer (VCM) in peroxides, azo compounds and other initiators; or under the action of light and heat according to the free radical polymerization reaction mechanism Polymers formed by polymerization. Vinyl chloride homopolymer and vinyl chloride copolymer are collectively referred to as vinyl chloride resin.
PVC is a white powder with an amorphous structure. The degree of branching is small, the relative density is about 1.4, the glass transition temperature is 77~90℃, and it starts to decompose at about 170℃. The stability to light and heat is poor, above 100℃ or after a long time. Sun exposure will decompose to produce hydrogen chloride, which will further autocatalyze the decomposition, causing discoloration, and the physical and mechanical properties will also decline 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. It has a large polydispersity, and the molecular weight increases with the decrease of the polymerization temperature; it has no fixed melting point, and starts to soften at 80-85°C, and becomes viscoelastic at 130°C. , 160~180℃ begin to transform into a viscous fluid state; it has good mechanical properties, the tensile strength is about 60MPa, and the impact strength is 5-10kJ/m2; it has excellent dielectric properties.
PVC used to be the world's largest production of general-purpose plastics, and it is widely used. It is widely used in building materials, industrial products, daily necessities, floor leather, floor tiles, artificial leather, pipes, wires and cables, packaging films, bottles, foaming materials, sealing materials, fibers, etc.
Basic Information
Chinese name
Polyvinyl chloride
Foreign name
Polyvinyl chloride (PVC)
colour
Yellowish
Attributes
Translucent and shiny
structure
-(CH2-CHCl)n-
contents
1 Basic introduction
2 composition structure
3 basic classification
4Development history
5 Development prospects
6 Preparation method
7Physical and chemical properties
8 molding conditions
9Material processing
10 main uses
11 Research on new materials
12 Identification method
13 main hazards
basic introduction
PVC
PVC
Referred to as PVC, it is a thermoplastic resin polymerized by vinyl chloride under the action of an initiator. It is a homopolymer of vinyl chloride. Vinyl chloride homopolymer and vinyl chloride copolymer are collectively referred to as vinyl chloride resin. PVC is a white powder with an amorphous structure with a small degree of branching. The molecular weight of industrially produced PVC is generally in the range of 50,000 to 120,000, with a large polydispersity, and the molecular weight increases with the decrease of the polymerization temperature; it has no fixed melting point, and starts to soften at 80-85°C, and becomes viscoelastic at 130°C. , 160～180℃ begin to transform into viscous fluid state; it has good mechanical properties, the tensile strength is about 60MPa, the impact strength is 5～10kJ/m²; it has excellent dielectric properties. However, the stability to light and heat is poor. It will decompose to produce hydrogen chloride above 100℃ or after long-term sunlight exposure, and further autocatalytic decomposition will cause discoloration, and the physical and mechanical properties will also decline rapidly. It must be stabilized in practical applications. Agent to improve the stability to heat and light. PVC is very hard and has poor solubility. It can only be dissolved in a few solvents such as cyclohexanone, dichloroethane and tetrahydrofuran. It is stable to organic and inorganic acids, alkalis, and salts, and its chemical stability increases with the use of temperature. And reduce. PVC is dissolved in acetone-carbon disulfide or acetone-benzene mixed solvent and used for dry spinning or wet spinning to form fibers, called chlorinated fiber. It is flame-retardant, acid and alkali resistant, antimicrobial, abrasion resistant, and has good warmth retention and elasticity.
Composition structure
PVC structure
PVC structure
The stereoscopic structure of PVC
The stereoscopic structure of PVC
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 VCM monomers are connected in a head-to-tail structure. The carbon atoms are arranged in a zigzag pattern, and all atoms are connected by sigma bonds. All carbon atoms are sp3 hybridized.
There is a short syndiotactic structure on the PVC molecular chain. As the polymerization temperature decreases, the syndiotacticity increases. The macromolecular structure of polyvinyl chloride has the disadvantages of head structure, branched chain, double bond, allyl chloride, tertiary chlorine and other unstable structures, which make heat-resistant deformation and poor aging resistance. After pretending to be cross-linked, such shortcomings can be eliminated.
Cross-linking is divided into radiation cross-linking and chemical cross-linking.
1. Radiation crosslinking. High-energy rays are used, generally rays produced by a cobalt 60 radiation source or electron rays produced by electron acceleration, and the latter is mainly used. Add a crosslinking aid (two or more carbon-carbon double bond monomers) for crosslinking. However, the operation is difficult and requires high equipment.
2. Chemical crosslinking. Triazole dimercaptoamine salt (FSH) is used for cross-linking. The cross-linking mechanism is that the amine combines with the sulfhydryl group to attack the carbon-chlorine polar bond to perform a substitution reaction. After cross-linking, the performance of the product, such as UV resistance, solvent resistance, temperature resistance, impact toughening, etc., will be comprehensively improved.
Basic classification
According to the different application scope, PVC can be divided into: general-purpose PVC resin, high polymerization degree PVC resin, and cross-linked PVC resin. The general-purpose PVC resin is formed by the polymerization of vinyl chloride monomer under the action of an initiator; the high degree of polymerization PVC resin refers to the resin polymerized by adding a chain extender to the vinyl chloride monomer polymerization system; the cross-linked PVC resin is A resin polymerized by adding a crosslinking agent containing diene and polyene to the vinyl chloride monomer polymerization system.
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 (the ethylene method and imported monomer method are commonly 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 process polyvinyl chloride is the largest variety in output, accounting for about 80% of the total output of PVC. Suspension method PVC 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-compact type.
According to the plasticizer content, PVC plastics are often divided into: non-plasticized PVC, plasticizer content is 0; rigid PVC, plasticizer content is less than 10%; semi-rigid PVC, plasticizer content 10-30%; soft PVC, plasticizer content is 30-70%; PVC paste plastic, plasticizer content is more than 80%.
Prospects
1 Development trend of polyvinyl chloride resin industry
The consumption of polyvinyl chloride resin in China is mainly concentrated in South China and East China. The total consumption of Guangdong, Zhejiang, Fujian, Shandong and Jiangsu accounts for about 70.0% of the total consumption of the country. Among them, the market demand in Guangdong and Fujian provinces The largest volume, but insufficient production capacity, the proportion of imported PVC resin is relatively high; Jiangsu, Shandong and Zhejiang have relatively developed PVC resin processing industries, and the consumption of the three provinces accounts for about 34.0% of the total domestic consumption; North China Regional production and sales are basically balanced. With the strengthening of development efforts in the central and western regions and the construction of large-scale infrastructure, the consumption of PVC resin in the central and western regions will gradually increase.
2 Demand forecast
The polyvinyl chloride resin industry is a basic and energy-intensive industry, which is greatly affected by demand and energy prices. It is also a basic chemical raw material, so it is also very closely related to economic development. Judging from the situation in 2012, the domestic PVC resin production capacity is still declining, and the downstream demand growth is relatively slow, coupled with the obstruction of exports and the increase in imports, the overall operating rate of domestic PVC resin enterprises is not high, and the number of idle capacity is relatively high. The market price has always remained low and medium, and the price fluctuation range has been reduced. In addition, the listing of PVC resin futures has increased the uncertainty of the price fluctuation of the PVC resin market to a certain extent. my country's PVC resin industry will still be in a relatively difficult period of integration, and there will be a variety of factors that will affect the future development of my country's PVC resin.
3 Export issues
① Cost barriers
PVC is a basic chemical raw material with relatively small product differentiation. Under the domestic perfectly competitive market structure, the cost is the most important factor affecting the competitiveness of enterprises. Due to industry characteristics, raw materials and energy account for a relatively high proportion of product costs. The cost of the petroleum ethylene method is mainly affected by the price of petroleum; the production cost of the calcium carbide method is mainly affected by the cost of calcium carbide. Generally speaking, the cost of calcium carbide accounts for about 70% of the cost of PVC, and the cost of electricity accounts for about 60% of the cost of calcium carbide. Western my country has abundant power resources and relatively low electricity prices. Compared with eastern calcium carbide manufacturing enterprises, western calcium carbide manufacturing enterprises have certain advantages in terms of cost. And enterprises with resource endowment and supporting calcium carbide production will build a more solid cost barrier.
② Industrial policy barriers
In order to promote the upgrading of the industrial structure of the chlor-alkali industry and standardize the development of the industry, in accordance with the sustainable development principles of "optimizing layout, orderly development, adjusting structure, saving energy, protecting the environment, safe production, and technological progress", the National Development and Reform Commission formulated and issued the "Chlor-Alkali ( Caustic soda, polyvinyl chloride) industry access conditions", and have been implemented since December 1, 2007: In terms of industrial layout, it is required that new chlor-alkali production enterprises should be close to resource and energy sources. In principle, the eastern region will no longer except relocate enterprises. Newly built calcium carbide method PVC projects and supporting caustic soda projects; technological aspects require the construction of new, renovated and expanded calcium carbide method PVC projects must be accompanied by the construction of calcium carbide slag comprehensive utilization devices such as calcium carbide slag cement; access conditions also depend on energy consumption Indicators and environmental protection set standards for new projects. The adjustment of industrial policies has greatly raised the threshold of capital, technology, talents, and resources for the chlor-alkali industry.
③ Scale barriers
The scale of investment required to produce PVC is relatively large, the fixed cost is relatively high, and the scale benefits are relatively obvious. Large-scale enterprises are in a more advantageous position in negotiations with suppliers, which is conducive to reducing raw material costs. Companies with large production and sales have a correspondingly higher market share, have greater market influence, and are relatively easier to acquire customers. Once PVC manufacturers reach a large scale of production and sales, their marginal costs will gradually decrease and their ability to resist risks will be enhanced.
④ Capital barriers
At the same time, with the country’s increasingly strict safety and environmental protection supervision, the construction of chlor-alkali production equipment must be equipped with corresponding large-scale environmental protection equipment (for example, the calcium carbide route must be equipped with calcium carbide slag cement equipment, etc.), and the capital investment is relatively large. Most small and medium-sized enterprises generally Can't afford it.
Therefore, manufacturers investing in this industry must have strong financial strength and there are certain financial barriers.
The demand for PVC in India's domestic market has increased year by year, from more than 1.7 million tons in 2009 to more than 2.2 million tons in 2012; however, there were only five PVC manufacturers in India with a domestic production capacity of 1.25 million tons per year. India Finolex Industries is the largest producer of PVC pipes in India. Due to the imbalance between supply and demand, there is a large gap, so the average annual PVC import volume in India reaches 950,000 tons. At the same time, India's vinyl raw material gap is also increasing year by year, in 2011 it was 722,000 tons, in 2012 it was 976,000 tons, and in 2013 it will reach 1.12 million tons. According to statistics, from April to September 2012, India's PVC imports were mainly from South Korea, Taiwan, Germany, the United States, Mexico and other countries and regions. Among them, PVC imports from South Korea and Taiwan both exceeded 200,000 tons.
Rajesh Deshpande said that India's PVC downstream products are mainly PVC pipes and accessories, accounting for 43% of the country's total PVC downstream products. In the first six months of the 2012-2013 fiscal year, downstream demand increased by 20%, and imports increased by 50%. According to the development speed, by March 2013, the domestic market demand in India will reach 2.2 million tons, and the development speed of PVC pipes will also reach double digits.
As the PVC downstream consumer market expands year by year, India's PVC industry has a greater development opportunity. According to Rajesh Deshpande's forecast, the growth of the downstream consumer market for PVC products in India stems from many aspects. The government's investment in infrastructure construction has increased year by year. Statistics show that during the "Twelfth Five-Year Plan" period, the Indian government's investment in infrastructure construction will reach 890 billion US dollars; the rural infrastructure construction and development fund will increase to 3.5 billion US dollars; the rural drinking water and environmental sanitation investment budget will reach 2.5 billion US dollars; US$53 million will be invested in the construction of irrigation systems; in the Delhi-Mumbai Industrial Corridor, US$90 billion will be invested in the construction of large-scale infrastructure, of which the Japanese government sponsored US$4.5 billion.
Despite the large gap between supply and demand, the Indian PVC industry faces certain challenges due to the greater competitive advantages of imported products. Rajesh Deshpande said frankly that there are still certain problems in the development of the PVC industry in India: for example, users have not yet seen the advantages of plastic pipes over traditional pipes; environmentalists and non-governmental organizations have explained the harms of plastic pipes from the perspective of environmental hazards; relevant production companies have not Pay attention to the quality control of its own products. Therefore, for the Indian PVC industry to achieve sustainable development, it must continue to develop new products and new technologies, and at the same time pay attention to the recycling and reuse of PVC products.
Although China has the world's largest PVC production capacity, due to the decline in ethylene prices, the ethylene-based PVC imports set a new record in 2009. On the other hand, China's PVC market has always been in a state of low operating rate. In the first half of 2009, China imported about 1.2 million tons of polyvinyl chloride, which is 1 million tons more than the total import volume in 2008. With the soaring price of ethylene, the competitive advantage of China's calcium carbide process PVC production has emerged. In the second half of 2009, China's PVC imports declined steadily. According to China Customs data, imports in November were only 60,646 tons.
In the first half of 2013, affected by many unfavorable factors such as overcapacity in the industry and weak downstream demand, the overall performance of the polyvinyl chloride (PVC) industry was poor, and companies were in a difficult situation. However, the performance of the PVC foreign trade market is eye-catching, and a number of data have obvious recovery adjustments compared with the same period in previous years. However, industry insiders pointed out that with the increase in the operating rate of PVC plants in the United States, my country's PVC foreign trade is expected to show a recovery growth in imports and a steady decline in exports.
According to statistics from China Chlor-Alkali Industry Association, as of the end of June 2013, the domestic production capacity of polyvinyl chloride (vague resin) was 23.92 million tons per year. Among them, in the first half of 2013, the newly added production capacity of PVC was 860,000 tons/year, with 350,000 tons/year exited, and a net increase of 510,000 tons/year, all withdrawn production capacity was calcium carbide production equipment. The overall production capacity expansion rate of the industry has slowed down significantly, but the trend of steady increase in production capacity continues.
In terms of exports, my country’s cumulative exports of PVC from January to May increased by 152.4% compared with the same period last year. From the perspective of flow, the largest export consumer market is India; the number of sources exported to Russia has slowed down, ranking second.
In addition, since the outbreak of the financial crisis, great changes have taken place in the global market and trade environment, trade protectionism in various countries has risen, and trade frictions against Chinese enterprises’ products have increased significantly.
Preparation
Polyvinyl chloride can be made by substitution reaction of ethylene, chlorine and catalyst. Due to its fire and heat resistance, polyvinyl chloride is widely used in various products in all walks of life: wire sheaths, fiber optic sheaths, shoes, handbags, bags, accessories, signs and billboards, architectural decoration supplies, furniture, ornaments , Rollers, hoses, toys (such as the famous Italian "Rody" jumping horse), door curtains, rolling doors, auxiliary medical supplies, gloves, plastic wrap for certain foods, certain fashions, etc.
Folding aggregation method
PVC is prepared by free radical addition polymerization. The polymerization methods are mainly divided into suspension polymerization, emulsion polymerization and bulk polymerization. Suspension polymerization is the main method, which accounts for about 80% of the total output of PVC. Pure water, liquefied VCM monomer, and dispersant are added to the reactor, and then initiator and other additives are added. After the temperature is raised to a certain temperature, the VCM monomer undergoes free radical polymerization to form PVC particles. Continuous stirring makes the particle size uniform and suspends the resulting particles in water. In addition, the micro-suspension method is used to produce PVC paste resin, which has good product performance and paste-forming properties.
① Suspension polymerization method makes the monomer suspended and dispersed in the water phase in the form of droplets, and the selected oil-soluble initiator is dissolved in the monomer, and the polymerization reaction proceeds in these droplets, and the heat of polymerization reaction is absorbed by water in time, To ensure that these droplets are dispersed in water as beads, suspension stabilizers, such as gelatin, polyvinyl alcohol, methyl cellulose, and hydroxyethyl cellulose, need to be added. Initiators mostly use organic peroxides and azo compounds, such as diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, diethylhexyl peroxydicarbonate, and azobisisoheptonitrile, azo Nitrogen two isobutyronitrile and so on. The polymerization is carried out in a polymerization vessel equipped with a stirrer. After polymerization, the material flows into the monomer recovery tank or stripper to recover the monomer. Then it flows into the mixing kettle, washed with water, dewatered by centrifugation, and dried to obtain the finished resin product. Vinyl chloride monomer should be removed from the resin as much as possible. For PVC used for food packaging, the free monomer content should be controlled below 1 ppm. In order to ensure that the resin with the specified molecular weight and molecular weight distribution range and prevent explosion during polymerization, the temperature and pressure of the polymerization process must be controlled. 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 resin is characterized by particle size and particle size distribution, molecular weight and molecular weight distribution, apparent density, porosity, fisheye, thermal stability, color, impurity content and powder free flowability. The polymerization reactor is the main equipment. It is made of steel reactor lining stainless steel or enamel. It is equipped with a stirrer and a heat transfer jacket to control the temperature, or an internal cooling pipe, a reflux condenser, etc. In order to reduce the production cost, the volume of the reactor has gradually developed from a few cubic meters to a dozen cubic meters to a large scale, and the maximum has reached 200 cubic meters (kettle reactor). The polymerizer should be descaled after repeated use. PVC made with polyvinyl alcohol and cellulose ethers as suspension stabilizers is generally looser, has many pores, and has a large surface area, which is easy to absorb plasticizers and plasticize.
② Emulsion polymerization method, one of the earliest industrial production methods of PVC. In emulsion polymerization, in addition to water and vinyl chloride monomers, surfactants such as sodium alkyl sulfonate are also added as emulsifiers to disperse the monomers in the water phase to form an emulsion, using water-soluble potassium persulfate or Ammonium persulfate is the initiator, and "oxidation-reduction" initiation system can also be used, and the polymerization process and suspension method are different. There are also added polyvinyl alcohol as an emulsion stabilizer, dodecyl mercaptan as a regulator, and sodium bicarbonate as a buffer. There are three polymerization methods: batch method, semi-continuous method and continuous method. The polymerized product is latex-like, the particle size of the emulsion is 0.05-2μm, and it can be directly applied or spray-dried into a powdery resin. The emulsion polymerization method has a short polymerization period and is easier to control. The obtained resin has a high molecular weight and a relatively uniform polymerization degree. It is suitable for making polyvinyl chloride paste, making artificial leather or impregnating products. The formulation of emulsion polymerization is complicated, and the product has a high impurity content.
③ Bulk polymerization method polymerization device is relatively special, mainly composed of a vertical pre-polymerization tank and a horizontal polymerization tank with a frame type agitator. The polymerization is carried out in two stages. The monomer and initiator are pre-polymerized in the pre-polymerization kettle for 1 hour to generate seed particles. At this time, the conversion rate reaches 8% to 10%, and then flows into the second-stage polymerization kettle, and the same amount of monomer as the pre-polymer is added. , Continue to aggregate. When the conversion rate reaches 85% to 90%, the residual monomers are discharged, and then crushed and sieved to obtain the finished product. The particle size and shape of the resin are controlled by the stirring speed, and the reaction heat is taken out by the monomer reflux and condensation. The production process of this method is simple, the product quality is good, and the production cost is low.
Folding modification method
PVC resin is a polar non-crystalline polymer, density: 1.380 g/cm3, glass transition temperature: 87°C, so it has poor thermal stability and is difficult to process. It cannot be used directly, it must be modified and compounded, and related additives and fillers can be added before it can be used. However, due to the different types and fractions of related additives and fillers added, this determines that the properties and requirements of the prepared PVC materials are different. We usually call it PVC formula, strictly speaking, it is 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 research on the high performance of general-purpose plastics, the conversion of single-component materials to multi-component composite materials (alloys, blends, and composites), functionalization of materials, and optimization of performance and price. 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 generally needs to be modified and pelletized first. After being prepared into pellets with a screw extruder unit, it will be more fully plasticized and easier to process, especially for products whose process is injection molding. Screw extruder is one of the most important equipment for plastic molding and processing. It uses external power transmission and heat transfer from external heating elements to carry out plastic solid transportation, compaction, melting, shearing, mixing, and extrusion molding. The screw extruder occupies an important position whether as a plasticizing granulating machine or a forming processing machine. Strictly speaking, PVC products with special requirements and PVC modified formulas are tailor-made according to customer requirements. There is also a copolymerization derivative in the PVC production process. Such modified varieties include vinyl chloride copolymers, polyvinyl chloride blends and chlorinated polyvinyl chloride.
Folding modified indicators
Colorability
PVC"Polyvinyl chloride has poor thermal stability and light resistance. Hydrogen chloride begins to decompose at 150°C, and adverse reactions occur with the content of plasticizer. In addition, the effect of pigments on PVC is reflected in whether the pigments react with PVC and other components that make up PVC products, as well as the migration resistance and heat resistance of the pigment itself. Certain 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 white pigments such as zinc oxide, zinc sulfide and lithopone will reduce the thermal stability of PVC resins. Certain colorants may interact with the degradation products of PVC resin. For example, ultramarine pigments are poor in acid resistance, so in the process of PVC coloring, they will interact with the hydrogen chloride generated by the decomposition of PVC and lose their proper color. Therefore, as far as PVC coloring is concerned, taking into account the characteristics of the resin and related additives used, combined with the characteristics of the pigment. The following issues should be paid attention to when choosing colorants.
1. Some metal ions in the pigment will promote the thermal oxygen decomposition of polyvinyl chloride resin as shown in Figure 1.
The measurement method is the hue change when the pigmented polyethylene is heated to 180°C. The pigment contains metal ions to accelerate the decomposition of PVC, resulting in a hue change. At the same time, it should be noted that the same addition of lake red can make PVC produce different color differences. If calcium is contained, the color difference is small; if manganese is contained, the color difference is large. This is due to the promotion of dehydrochlorination of PVC by metals such as manganese.
Sulfide colorants (such as cadmium red, yellow, etc.) are used to color PVC, and hydrogen sulfide may be liberated due to the separation of colorants. Such colorants should not be mixed with lead stabilizers to avoid the formation of black lead sulfide.
2. The influence of pigments on the electrical insulation of PVC
PVC" Polyvinyl chloride as a cable material is the same as polyethylene, and electrical properties after coloring should be considered. In particular, polyvinyl chloride itself is less insulating than polyethylene, so the influence of pigments is even greater. It shows that choosing inorganic pigments to color PVC is better for its electrical insulation than organic pigments (except for furnace black and anatase titanium dioxide).
Migration
Migration only occurs in plasticized PVC products, and when using dyes or organic pigments. The so-called migration is that the partially soluble dyes or organic pigments in the surrounding solvent penetrate into the surface of the PVC product through the plasticizer, and the dissolved dye (pigment) particles are also brought to the surface of the product, which leads to dissolution. Bleeding, solvent bleeding or blooming.
Another problem is "scaling". It means that the colorant is released from the system due to poor compatibility or incompatibility of the coloring material during coloring processing, and is deposited on the surface of the processing equipment (such as the inner wall of the extruder barrel, the inner wall of the die hole) .
Weather resistance
Refers to the ability of a pigment to withstand various climates. These include visible and ultraviolet light, moisture, temperature, atmospheric chlorination, and chemicals encountered during product use. The most important weather resistance includes colorfastness, chalking resistance and durability of physical properties. However, organic pigments are different due to their different structures. In addition, in the formulations containing white pigments, the weather resistance of the pigments will be more severely affected.
The fading, darkening or hue change of the pigment is generally caused by the reaction gene of the pigment. These reactive genes can interact with moisture or chemicals in the atmosphere-acids and alkalis. For example, cadmium yellow will fade under the action of moisture and sunlight. Lithol red has good light resistance and is suitable for most indoor applications, but it will fade severely when used outdoors with acid and alkali components.
The measuring method of dehydrochlorination is in accordance with JIS-K-6723, and the measuring temperature is 180°C. Based on the time of dechlorination of the uncolored polyvinyl chloride compound, the extension or retardation time is calculated at 5% and 10% intervals. A negative value indicates accelerated decomposition.
stability
The softening point of polyvinyl chloride resin is low, about 75-80℃, and the embrittlement temperature is lower than -50~-60℃. The long-term use temperature of most products should not exceed 55℃, and the special formula can reach 90℃. If the polyvinyl chloride resin is purely a linear structure with a head-to-sex interface, there are no branches and unsaturated bonds inside, although the C-Cl bond energy is relatively small, the stability of the polyvinyl chloride resin should be relatively high. . But even with high-purity polyvinyl chloride resin, hydrogen chloride gas will begin to escape when it is above 100°C or exposed to ultraviolet radiation for a long time. It shows 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 faster the degradation rate in the presence of oxygen or air.
Electrical properties
PVC"Polyvinyl chloride is a polar polymer, and has a greater affinity for water and other conductive materials, so its resistance is lower than that of non-polar polyolefins, but it still has a higher volume cathode and breakdown voltage. The polar groups of polyvinyl chloride are directly attached to the main chain. Below the glass transition temperature, the dipolar segment is restricted by the main chain atoms of the frozen structure and cannot be moved, so it does not produce dipolarization and can be used at room temperature. Of high-frequency insulation materials. When used as wire insulation, the electrical insulation of suspension resin is 10-100 times higher than that of floating resin. The presence of chloride ions produced by degradation will reduce electrical insulation.
Physical and chemical properties
The natural color is yellowish translucent and shiny. Transparency is better than polyethylene and polypropylene, but worse than polystyrene. Depending on the amount of additives, it can be divided into soft and hard polyvinyl chloride. Soft products are flexible and tough, and feel sticky. The hardness of hard products is higher than that of low-density polyethylene. However, if it is lower than polypropylene, whitening will occur at the inflection. Stable; not easily corroded by acid and alkali; relatively resistant to heat.
Polyvinyl chloride is flame retardant (flame retardant value above 40), high chemical resistance (resistant to concentrated hydrochloric acid, 90% sulfuric acid, 60% nitric acid and 20% sodium hydroxide), mechanical strength And the advantages of good electrical insulation.
Polyvinyl chloride has poor stability to light and heat. The softening point is 80°C, and it starts to decompose at 130°C. Without heating the stabilizer, polyvinyl chloride starts to decompose at 100°C, and decomposes faster above 130°C. When heated, it decomposes and releases hydrogen chloride gas (hydrogen chloride gas is a toxic gas) to change its color from white → light yellow → red → brown → black. Ultraviolet rays and oxygen in the sun will cause the photo-oxidation and decomposition of polyvinyl chloride, which will reduce the flexibility of polyvinyl chloride and eventually become brittle. It is not difficult to understand from here why some PVC plastics will turn yellow and become brittle over time.
It has stable physicochemical properties, insoluble in water, alcohol, gasoline, low gas and water vapor leakage; it can withstand any concentration of hydrochloric acid, 90% or less sulfuric acid, 50-60% nitric acid and 20% or less at room temperature The caustic soda solution has a certain degree of chemical resistance; it is quite stable to salts, but it can be dissolved in organic solvents such as ethers, ketones, chlorinated aliphatic hydrocarbons and aromatic hydrocarbons.
Industrial polyvinyl chloride resin is mainly amorphous structure, but also contains some crystalline regions (about 5%), so polyvinyl chloride has no obvious melting point, and it starts to soften at about 80°C. The heat distortion temperature (under 1.82MPa load) is 70-71℃, under pressure at 150℃, it starts to flow and slowly releases hydrogen chloride, which causes the polyvinyl chloride to change color (from yellow to red, brown, or even black).
The weight-average relative molecular mass of industrial polyvinyl chloride is in the range of 4.8-48,000, and the corresponding number-average relative molecular mass is 2-19.5 million. The weight-average relative molecular mass of most industrial resins is between 100,000 and 200,000, and the number-average relative molecular mass is between 45,000 and 64,000. Rigid polyvinyl chloride (without plasticizer) has good mechanical strength, weather resistance and flame resistance, and can be used alone as a structural material for the manufacture of pipes, plates and injection molded products in the chemical industry. Rigid polyvinyl chloride can be used as a reinforcing material.
Material properties
Unplasticized polyvinyl chloride (PVC-U) pipe fittings for water supply
Density 1380 kg/m3
Young's modulus of elasticity (E) 2900-3400 MPa
Tensile strength (σt) 50-80 MPa
Elongation @ break 20-40%
Notch test 2-5 kJ/m2
Glass transition temperature 87℃
Melting point 212°C
Vicat B1 85℃
Thermal conductivity (λ) 0.16 W/m.K
Coefficient of thermal expansion (α) 8 10-5 /K
Heat capacity (c) 0.9 kJ/(kg·K)
Water absorption (ASTM) 0.04-0.4
Refractive index hard molded product 1.52~1.55
Price 0.5-1.25 €/kg
The biggest feature of PVC is flame retardant, so it is widely used in fire protection applications. But PVC will release hydrogen chloride and other toxic gases such as dioxins during the combustion process.
The combustion of PVC is divided into two steps. First, the hydrogen chloride gas and the diene containing double bonds are decomposed by burning at 240°C-340°C, and then carbon combustion occurs at 400-470°C.
It is one of the largest plastic products in the world. It is cheap and widely used. PVC resin is white or light yellow powder. Different additives can be added according to different purposes, and PVC plastics can present different physical and mechanical properties. Adding an appropriate amount of plasticizer to the polyvinyl chloride resin can be made into a variety of hard, soft and transparent products.
The density of pure PVC is 1.4g/cm3, and the density of PVC plastic parts added with plasticizers and fillers is generally 1.15-2.00g/cm3.
Rigid polyvinyl chloride has good tensile, flexural, compressive and impact resistance, and can be used as a structural material alone.
The flexibility, elongation at break, and cold resistance of soft PVC will increase, but the brittleness, hardness, and tensile strength will decrease.
Polyvinyl chloride has good electrical insulation properties, can be used as low-frequency insulation material, and its chemical stability is also good. Due to the poor thermal stability of polyvinyl chloride, long-term heating will cause decomposition, release HCL gas, and cause polyvinyl chloride to change color, so its application range is narrow, and the use temperature is generally between -15 and 55 ℃.
Molding conditions
Hard pvc
Material pipe temperature: 160-190℃
Mold temperature: 40-60℃
Drying temperature: 80℃x2h
Injection pressure: 700-1500kg/c㎡
Density: 1.4g/c㎡
Molding shrinkage: 0.1-0.5%
Meat thickness: 2.0-50.mm
Water absorption (24H): 0.1-0.4%
Melting softening point: 89℃
Heat distortion temperature: 70℃
Soft pvc
Material pipe temperature: 140-170℃
Mold temperature: 40-60℃
Drying temperature: 80℃x2h
Injection pressure: 600-1500kg/c㎡
Density: 1.4g/c㎡
Molding shrinkage: 0.1-0.5%
Meat thickness: 2.0-50.mm
Water absorption (24H): 0.1-0.4%
Melting softening point: 85℃
Heat distortion temperature: 55℃
Material processing
Polyvinyl chloride plastics have different forms and great differences, as well as various processing methods, such as pressing, extrusion, injection, coating and so on. The particle size, fish eyes, bulk density, purity, foreign impurities, and porosity of polyvinyl chloride resin have an impact on processability; for paste resin, the viscosity and gelling properties of the paste should be considered.
Polyvinyl chloride is an amorphous polymer with low shrinkage. The powder should be preheated before processing to remove moisture, enhance the plasticizing effect, and prevent bubbles. Moreover, PVC is easy to decompose, especially when it comes in 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 dead ends from stagnating. The mold pouring system should be thick, the gate section should be large, the mold should be cooled, the mold temperature is 30-60 degrees, and the material temperature is 160-190.
Below the glass transition temperature (Tg, 80°C), polyvinyl chloride is glassy; at Tg→viscous flow temperature (Tf, about 160°C), it is a highly elastic rubber with plasticity; at Tf→thermal decomposition temperature (Td) It is a viscous flow state, the higher the temperature, the easier the 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. Therefore, Td is the upper limit temperature for processing and molding. Due to the great force between the polyethylene molecules, the Tf is very high, even close to the decomposition temperature, so it is necessary to add a plasticizer to reduce the Tf. On the other hand, it is also necessary to add stabilizers to increase the Td of PVC in order to be processed and formed.
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 viscous flow temperature (Tf) is the temperature at which macromolecules start to move, and is related to the molecular weight. The larger the molecular weight, the higher the Tf. Therefore, for some processing molding (such as injection molding), it is necessary to appropriately reduce the molecular weight of the resin. According to the different molecular weight, domestic suspension PVC resin is divided into 1-7 grades, the larger the serial number, the smaller the molecular weight. XJ-4 (XS-4) to XJ-7 (XS-7) resins are often used in the manufacture of hard pipes, hard boards, etc. Other resins with lower models and larger molecular weights need to be added in large amounts due to higher Tf. The agent reduces Tf, so it is often used in the manufacture of soft products. Polyvinyl chloride with an average degree of polymerization below 1000 is called low-polymerization degree polyvinyl chloride, which has good processing properties, and less plasticizers can be added during processing, so that the product will not be accelerated due to the migration of plasticizers Ageing. Polyvinyl chloride products with low degree of polymerization have good transparency and are widely used in building materials, food and pharmaceutical packaging materials and to replace organic glass products.
Polyvinyl chloride melt is a non-Newtonian pseudo-fluid. The higher the shear rate, the smaller the apparent viscosity, and the change is quite sensitive. Increasing the temperature will not reduce the viscosity much. Even if the plastic is below the decomposition temperature, it will cause heat and oxidative degradation due to the high temperature for a long time, which will affect its performance. Therefore, to improve the fluidity of PVC melt, the main consideration should be to increase the shear rate (increase the pressure). In fact, increasing the external force will help the movement of the macromolecules, so that the Tf will be reduced, and the macromolecules can flow at a lower temperature.
The main purpose
1. PVC profile
Profiles and profiles are the largest area of PVC consumption in my country, accounting for about 25% of the total PVC consumption. They are mainly used to make doors and windows and energy-saving materials, and their applications are still increasing significantly across the country. In developed countries, the market share of plastic doors and windows is also the highest, for example, Germany is 50%, France is 56%, and the United States is 45%.
2. Polyvinyl chloride pipe
Among many polyvinyl chloride products, polyvinyl chloride pipes are its second largest consumption area, accounting for about 20% of its consumption. In my country, polyvinyl chloride pipes are developed earlier than PE pipes and PP pipes, with more varieties, excellent performance, and a wide range of applications, and occupy an important position in the market.
3. Polyvinyl chloride film
The consumption of PVC in the field of PVC film ranks third, accounting for about 10%. After PVC is mixed with additives and plasticized, a three-roll or four-roll calender is used to make a transparent or colored film with a specified thickness. The film is processed in this way to become a calendered film. It can also be cut and heat-sealed to process packaging bags, raincoats, tablecloths, curtains, inflatable toys, etc. The wide transparent film can be used for greenhouses, plastic greenhouses and mulch films. The biaxially stretched film has the characteristics of heat shrinkage and can be used for shrink packaging.
4. PVC hard materials and plates
Stabilizers, lubricants and fillers are added to PVC. After mixing, the extruder can be used to extrude hard pipes, special-shaped pipes and corrugated pipes of various calibers, which can be used as sewer pipes, drinking water pipes, wire casings or staircase handrails. . The calendered sheets are overlapped and hot pressed to make hard plates of various thicknesses. The plate can be cut into the required shape, and then welded with hot air with PVC welding rod to form various chemical resistant storage tanks, air ducts and containers.
5. PVC general soft products
The extruder can be used to squeeze into hoses, cables, wires, etc.; the injection molding machine can be used with various molds to make plastic sandals, shoe soles, slippers, toys, auto parts, etc.
6. Polyvinyl chloride packaging materials
Polyvinyl chloride products are mainly used for packaging in various containers, films and rigid sheets. PVC containers mainly produce bottles of mineral water, beverages, and cosmetics, as well as packaging for refined oil. PVC film can be used to co-extrude with other polymers to produce low-cost laminates and transparent products with good barrier properties. Polyvinyl chloride film can also be used for stretch or heat shrink packaging for packaging mattresses, cloth, toys and industrial goods.
7. Polyvinyl chloride wall panels and floors
Polyvinyl chloride wall panels are mainly used to replace aluminum wall panels. Except for a part of PVC resin, the other components of PVC floor tiles are recycled materials, adhesives, fillers and other components. They are mainly used on the ground of airport terminal buildings and other hard ground.
8. Polyvinyl chloride daily consumer goods
Luggage bags are traditional products made by the processing of polyvinyl chloride. Polyvinyl chloride is used to make all kinds of imitation leather, which are used in luggage and sports products such as basketball, football and rugby. It can also be used to make belts for uniforms and special protective equipment. Polyvinyl chloride fabrics for clothing are generally absorbent fabrics (without coating), such as ponchos, baby pants, imitation leather jackets and various rain boots. Polyvinyl chloride is used in many sports and entertainment products, such as toys, records, and sports goods. Polyvinyl chloride toys and sports goods have a large growth rate. They have an advantage due to their low production cost and easy molding.
9. PVC coated products
Artificial leather with a backing is made by coating PVC paste on cloth or paper, and then plasticizing it at a temperature above 100°C. It can also be formed by calendering PVC and additives into a film, and then pressing it with the substrate. Artificial leather without a substrate is directly calendered by a calender into a soft sheet of a certain thickness, and then the pattern can be pressed. Artificial leather can be used to make suitcases, purses, book covers, sofas and car cushions, etc., as well as floor leather, used as floor coverings for buildings.
10. PVC foam products
When mixing soft PVC, add an appropriate amount of foaming agent to form a sheet, which is foamed into foam plastic, which can be used as foam slippers, sandals, insoles, and shock-proof cushioning packaging materials. The extruder can also be used to form low-foamed hard PVC boards and profiles, which can replace wood and is a new type of building material.
11. PVC transparent sheet
The impact modifier and organotin stabilizer are added to PVC, and it becomes a transparent sheet after mixing, plasticizing and calendering. Thermoforming can be made into thin-walled transparent containers or used for vacuum blister packaging. It is an excellent packaging material and decorative material.
12. Other
Doors and windows are assembled with hard special-shaped materials. In some countries, it has occupied the door and window market together with wooden doors, windows, aluminum windows, etc.; wood-like materials, steel-based building materials (northern, seaside); hollow containers.
The virtual circuit is one of the services provided by the packet switching network (the other is the datagram service). Simply put, it is to establish a virtual logical connection between user hosts through the internal control mechanism of the network, and to ensure the transmission of information on it. The correctness and sequence of the packet, the establishment and removal of virtual circuits before and after communication. A permanent virtual circuit is a virtual circuit that is established when the network is initialized, and the virtual circuit is always maintained. Both X.25 network and B-ISDN provide PVC services. PVC plastic bags are generally prohibited.
New material research
At present, my country's total annual demand for modified plastics is about 5 million tons, accounting for about 10% of total plastic consumption, and its proportion is far below the world average. Compared with the developed countries in the world, my country's per capita plastic consumption still has a big gap. In order to realize the rapid and stable development of my country's modified plastics industry, innovative technology is the key to future development.
Chemical industry analysts believe that the current overall development level of my country’s modified plastics industry is not very high. The production scale of enterprises in the industry is generally small, the product market produces many primary products, the quality of intermediate products is not stable enough, and the lack of advanced products is characteristic. It is far from meeting the needs of my country's current social and economic development. As an important component in the field of new chemical materials, modified plastics have been listed as one of the key scientific and technological fields for development by the country. Since the introduction of various policies in my country, 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, and both account for more than 50%.
The application of plastics in the automotive industry has a history of more than 50 years. With the development of automobiles in the direction of light weight and energy saving, higher requirements are put forward for materials. Because 1kg of plastic can replace 2-3kg of steel and other heavier materials, and every 10% reduction in the weight of the car, fuel consumption can be reduced by 6%-8%. Therefore, increasing the amount of modified plastics used in automobiles 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. The demand for modified PP, PC alloy and modified ABS was approximately 114.63, 15.13 and 149,700 tons respectively last year. The modified plastics market for household appliances in my country is mainly occupied by foreign companies, and domestic modified plastics companies account for less than one-third of the market share. Since the products of domestic companies are mostly limited to low-tech and low-standard levels, the ability to develop fields 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, the domestic "plastics for steel" and "plastics for wood" will Become a trend. As a sub-industry with the fastest growth and great potential in the plastics processing industry, the modified plastics industry is expected to maintain a growth rate of more than 10% in my country's total market demand in the next five years. [4]
1. PVC replaces steel material with plastic
Through the research of PVC modification technology, the use of foreign advanced internal plasticization technology and additive formulas ensures the mechanical and electrical properties of PVC plastic steel, improves the flame retardant performance, and makes the product have high strength, corrosion resistance, and flame retardancy. , Good insulation performance, light weight, convenient construction and other advantages. It can completely replace steel pipes in electrical wiring systems.
2. PVC replaces wood with plastic
PVC wood-plastic composite material is a new type of composite material prepared from waste wood fiber and plastic as the main raw material, supplemented by appropriate processing aids, through a hot-pressing preparation process. Its products fully reflect the concept of recycling of renewable resources and petroleum products, and are of great significance to alleviating the current shortage of wood and petroleum resources and serious environmental pollution.
Household building materials products using PVC as the main raw material have become the second pillar of my country's plastics industry, with an average annual growth rate of more than 15%. In the next 10 years, the country is expected to increase the building area of 30 billion square meters. If these buildings achieve 50% energy saving on the existing basis, the market demand for energy-saving building materials can reach trillions of yuan, which is an indoor energy-saving decoration material. There is a huge room for development. For a long time, the building materials industry has always appeared in the image of high energy consumption and high pollution. In order to meet the requirements of the low-carbon economy, after years of research and development, household building materials companies have developed a batch of PVC high-simulation building materials that use plastic instead of wood, which have become a perfect combination of low-carbon and practical household products.
Experts in the industry pointed out that the use of plastic instead of wood for PVC building materials not only saves costs, but is also recyclable and recyclable, in line with the general trend of environmental sustainable development and circular economy.
14. Synthetic materials
Polyvinyl chloride (polyvinyl chloride), referred to as PVC, is a thermoplastic resin. Polyvinyl chloride futures are also futures varieties with polyvinyl chloride as the subject matter.
Plastics: polyethylene; polyvinyl chloride; polystyrene; polyvinyl alcohol; polypropylene; polyacrylic acid; polybutene; polyisobutylene; polysulfone; polyoxymethylene; polyamide; polycarbonate; polylactic acid; polytetrafluoroethylene ; Polyethylene terephthalate; Epoxy resin; Phenolic resin; Polyurethane
Synthetic rubber: butadiene rubber; styrene butadiene rubber; nitrile rubber; neoprene
Synthetic fiber: polypropylene; polyester; nylon; acrylic; spandex; vinylon; nylon; dacron; keflon
Identification method
Conventional identification methods for PVC are generally summarized into the following three categories, namely:
(1) Identification of combustion method:
Softening or melting temperature range: 75~90°C;
Burning situation: self-extinguishing after being ignited;
Burning flame status: yellow up and green with smoke; after leaving the fire: extinguished after leaving the fire; smell: pungent sour.
This method is the easiest and most direct, and is generally preferred.
(2) Identification of solvent treatment:
Solvent: tetrahydrofuran, cyclohexanone, ketone, dimethylformamide;
Non-solvents: methanol, acetone, heptane.
By adding the suspected PVC plastic to the above solvent, observe the dissolution of the plastic to determine whether it is PVC. After the solvent is heated, the dissolving effect will be more obvious.
(3) Proportion method:
The specific gravity of PVC is 1.35~1.45, generally around 1.38. The difference in specific gravity or the method of determining specific gravity can be used to distinguish PVC from other plastics. But because PVC can add plasticizers, modifiers and fillers to make the PVC become very different in specific gravity, the difference in softness and hardness is very large, and at the same time, due to the addition of some ingredients, many properties of PVC plastic will be changed, resulting in Our commonly used identification methods are not effective, and even the phenomenon has changed, making it impossible to make accurate judgments. For example, in terms of density, plasticized polyvinyl chloride (containing about 40% plasticizer) is 1.19~1.35; while PVC hard products have increased to 1.38~1.50. If it is a highly filled PVC product, the density sometimes exceeds 2.
In addition, it can also be determined by measuring whether the material contains chlorine, but because vinyl chloride copolymers, neoprene rubber, polyvinylidene chloride, chlorinated polyvinyl chloride, etc. all contain a relatively high proportion of chlorine, they must be colored by pyridine. Reaction to identify. Note that before the test, the sample must be extracted with ether to remove the plasticizer. Test method: Dissolve the sample taken from ether with benzene in tetrahydrofuran, filter out the insoluble components, add methanol to make it precipitate, and extract the sample before 75 Below the degree of dryness. Do not need 1ml of pyridine to react with a small amount of dried sample. After a few minutes, add 2 drops of 5% sodium hydroxide methanol solution (1g sodium hydroxide dissolved in 20ml methanol), and immediately observe the color, 5min And observe again after 1h. Different chlorine-containing plastics can be identified based on the color.
In daily life, PVC and PE plastic film (bag) need to be distinguished with more contact. Simple method:
⑴Touch method
It feels lubricious to the touch, and the surface looks like a layer of wax (chemically called wax feel). This is a non-toxic polyethylene film bag, while the PVC film feels a little sticky.
⑵Dithering method
When shaking with hands, the sound is crisp, and the thing that floats easily is a polyethylene film bag. And the low sound of shaking with hands is a polyvinyl chloride film bag.
⑶ Combustion method
In case of fire, it is flammable, the flame is yellow, and there is paraffin-like oil dripping when burning, and there is gas when the candle is burning. It is a non-toxic polyethylene film bag. If it is not easy to burn, it will be extinguished after leaving the fire, the flame will be green, and it will be a polyvinyl chloride film bag.
⑷ Immersion method
The plastic bag is immersed in water and pressed into the water by hand, the surface is polyethylene, and the one that sinks to the bottom is polyvinyl chloride (the density of polyethylene is less than that of water, and the density of polyvinyl chloride is greater than that of water; at room temperature, they are about 0.92g/cm3 and 1.4g/cm3).
You can also take a piece of copper wire and burn it in the fire to make it red. Then, the copper wire is brought into contact with the plastic film used for the test to cause a chemical change, and then the copper wire dipped in the plastic component is put back into the flame. At this time, you need to observe carefully. If there is a colorful and dazzling green flame, it means that this plastic material contains chlorine and belongs to the polyvinyl chloride material.
Main hazard
Polyvinyl chloride is also a kind of plastic that is often used. It is a resin composed of polyvinyl chloride resin, plasticizer and anti-aging agent, and it is not toxic. However, the main auxiliary materials such as plasticizers and antioxidants are toxic. The plasticizers in daily PVC plastics mainly use dibutyl terephthalate and dioctyl phthalate. These chemicals All are toxic, and lead stearate, the antioxidant of polyvinyl chloride, is also toxic. Lead is precipitated when PVC products containing lead salt antioxidants come into contact with ethanol, ether and other solvents. Lead-containing PVC is used for food packaging and encounters with fried dough sticks, fried cakes, fried fish, cooked meat products, cakes and snacks, which will cause lead molecules to diffuse into the grease, so PVC plastic bags cannot be used Contain food, especially food containing oil. In addition, polyvinyl chloride plastic products will slowly decompose hydrogen chloride gas at a higher temperature, such as about 50°C, which is harmful to the human body. Therefore, polyvinyl chloride products are not suitable for food packaging.
Since most disposable medical device products use medical grade polyvinyl chloride (PVC) or polycarbonate (PC), the thermal decomposition products in the PVC processing process are corrosive to steel, and PC has high hardness and high viscosity. Therefore, 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 chromium plating on the barrel screw or use stainless steel as the material to make the machine screw to meet the above special requirements. In addition, in order to prevent the thermal decomposition of the PVC during the process of generating gas, it is required to aluminize the surface of the movable template, and also to aluminize the outer sheet metal or use stainless steel to make the sheet metal. The sheet metal joints are sealed with non-toxic silica gel. In order to prevent the gas generated during the plastic processing from escaping outside (the gas generated during the plastic processing can be collected through special equipment and then purified before being discharged into the atmosphere).
PVC is the main source of dioxins. Dioxin (TCDD), the deadliest substance in the dioxins family, is a well-known carcinogen, hormone decomposer, and a toxic compound, which has great harm to humans and animals. Dioxins are produced when PVC is produced, recycled, and destroyed in incinerators, or when PVC products are accidentally burned, such as when buried in garbage.
