Chinese name: PVC
English name: polyvinyl chloride
PVC plastic properties
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℃
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
Drying treatment: Usually no drying treatment is required.
Melting temperature: 185~205C
Mold temperature: 20~50C
Injection pressure: up to 1500bar
Holding pressure: up to 1000bar
Injection speed: In order to avoid material degradation, generally a relatively fast injection speed is used.
PVC can be divided into soft PVC and hard PVC. Among them, hard PVC accounts for about 2/3 of the market, and soft PVC accounts for 1/3. Soft PVC is generally used for the surface layer of floors, ceilings and leather. However, because soft PVC contains softeners (this is also the difference between soft PVC and hard PVC), it is easy to become brittle and difficult to preserve, so its scope of use is limited. Hard PVC does not contain softeners, so it has good flexibility, easy to form, not brittle, non-toxic and non-polluting, and has a long storage time, so it has great development and application value. Hereinafter referred to as PVC.
The essence of PVC is a vacuum blister film, which is used for surface packaging of various types of panels, so it is also called decorative film and adhesive film, which is used in many industries such as building materials, packaging, medicine and so on. Among them, the building materials industry accounts for the largest proportion, 60%,
The second is the packaging industry, as well as several other small-scale applications.
PVC plastic properties
Polyvinyl chloride resin is a thermoplastic with amorphous structure. Under ultraviolet light, hard PVC produces light blue or purple-white fluorescence, while soft PVC emits blue or blue-white fluorescence. When the temperature is 20℃, the refractive index is 1.544, the specific gravity is 1.40, and the density of products with plasticizer and filler is usually in the range of 1.15～2.00, the density of flexible PVC foam is 0.08～0.48, and the rigid foam is 0.03. ~0.08. PVC water absorption is not more than 0.5%.
The physical and mechanical properties of PVC depend on the molecular weight of the resin, the content of plasticizers and fillers. The larger the molecular weight of the resin, the higher the mechanical properties, cold resistance, and thermal stability, but the processing temperature is also high, and the molding is more difficult; the lower molecular weight is the opposite of the above. The filler content increases and the tensile strength decreases.
⒉ Thermal performance
The softening point of polyvinyl chloride resin is close to the decomposition temperature. It has begun to decompose at 140°C, and decomposes more rapidly at 170°C. In order to ensure the normal progress of the molding process, the two most important process indicators for the polyvinyl chloride resin are specified, namely the decomposition temperature and thermal stability. The so-called decomposition temperature is the temperature when a large amount of hydrogen chloride is released, and the so-called thermal stability is the time when a large amount of hydrogen chloride is not released under a certain temperature condition (usually 190°C). Polyvinyl chloride plastics will be decomposed for a long time when exposed to 100℃, unless alkaline stabilizers are added, they will decompose quickly if they exceed 180℃.
The long-term use temperature of most PVC plastic products should not exceed 55℃, but the long-term use temperature of specially formulated PVC plastics can reach 90℃. Soft PVC products will become hard at low temperatures. Polyvinyl chloride molecules contain chlorine atoms, so it and its copolymers are generally flame and flame resistant, self-extinguishing, and no dripping. A
Polyvinyl chloride resin is a relatively unstable polymer, which can also degrade under the influence of light and heat. The process is to release hydrogen chloride, and the structure changes, but to a lesser extent. At the same time, it will accelerate decomposition in the presence of mechanical force, oxygen, odor, HCl and certain active metal ions.
After the HCl is removed from the polyvinyl chloride resin, a conjugated double chain is generated on the main chain, and the color changes. As the amount of hydrogen chloride decomposition increases, the PVC resin changes from the original white to yellow, rose, red, brown or even black.
The electrical properties of PVC depend on the amount of residue in the polymer and the type and amount of various additives in the formulation. The electrical properties of PVC are also related to the situation of heating: when heating decomposes PVC, its electrical insulation is reduced due to the presence of chloride ions. If a large amount of chloride ions are generated, it cannot be neutralized by alkaline stabilizers (such as lead salts). Will cause its electrical insulation performance to decline significantly. PVC is not like non-polar polymers such as polyethylene and polypropylene, its electrical properties change with frequency and temperature, such as dielectric constant decreases with increasing frequency.
Polyvinyl chloride has excellent chemical stability and is extremely valuable as a corrosion-resistant material. PVC is stable to most inorganic acids and alkalis, and it is not dissolved when heated and is interpreted as hydrogen chloride. Azeotrope with potassium hydroxide produces a brown insoluble unsaturated product. The solubility of PVC is related to the molecular weight and polymerization method. Generally, the solubility decreases with the increase of the molecular weight of the polymer, and the emulsion resin has poorer solubility than the suspension resin. It can be dissolved in ketones (such as methylhexanone, cyclohexanone), aromatic solvents (such as toluene, xylene), dimethylformyl, tetrahydrofuran. Polyvinyl chloride resins are almost insoluble in plasticizers at room temperature, and swell significantly or even dissolve at high temperatures.
Brucite PVC is an amorphous high polymer with no obvious melting point. It has plasticity when heated to 120-150℃. Due to its poor thermal stability, a small amount of HCl is emitted at this temperature to promote its further decomposition, so it is necessary to add an alkaline stabilizer and HCl to inhibit its catalytic cracking reaction. Pure PVC is a hard product, and it needs to add an appropriate amount of plasticizer to make it soft. For different products, it needs to add additives such as ultraviolet absorbers, fillers, lubricants, pigments, mold inhibitors, etc. to improve the quality of PVC products. Use performance. Like other plastics, the performance of the resin determines the quality and processing conditions of the product. For PVC, the resin properties related to processing are: particle size, thermal stability, molecular weight, fisheye, bulk density, purity and foreign impurities, porosity. For PVC paste and paste viscosity and gelation performance, it should be determined to determine the processing conditions and product quality.
PVC plastic modification
Introducing the monomer copolymerization into the main chain of vinyl chloride, the result is a new type of polymer that includes two monomer chains. This polymer is called a copolymer. The main varieties and properties of copolymers of vinyl chloride and other monomers are as follows:
(1) Ethylene-vinyl acetate copolymer: the introduction of vinyl acetate monomer can play the role of general plasticizer, also known as "internal plasticization", which can avoid the disadvantages of general plasticizer volatilization, migration, extraction, etc., It can also reduce the melt viscosity, lower the processing temperature, and improve the processing performance. The vinyl acetate content in general copolymers is 3 to 14%. The main disadvantages of vinyl chloride-vinyl acetate copolymers are reduced tensile strength, heat distortion temperature, wear resistance, chemical stability, and thermal stability.
(2) Ethylene-vinylidene chloride copolymer: The plasticity, softening temperature, solubility, etc. and intramolecular plasticization of this copolymer are basically the same as those of vinyl chloride-vinyl acetate copolymer. Its biggest feature is its low water and gas permeability, high solubility in ketone solvents, and resistance to the dilution of aromatic hydrocarbons, so it can be effectively used in coatings. In addition, it is also used to make shrink film. Due to its poor heat resistance and light stability compared to vinyl chloride-vinyl acetate copolymers and higher monomer cost, it is not widely used in vinyl chloride-vinyl acetate applications.
(3) Ethylene-acrylate copolymer: The internal plasticization of this copolymer is equivalent to that of vinyl chloride-vinyl acetate. It has good thermal stability and can be used to manufacture hard and soft products, improving processability, impact resistance and Cold resistance, etc. It can also be used for coating, bonding, etc.
(4) Ethylene-maleate copolymer: The maleate content in this copolymer is about 15%, and the internal plasticization is similar to vinyl chloride-acrylate. Has better processing performance. The physical and mechanical properties are less reduced, and the heat resistance is higher than the general copolymer.
⑸ Ethylene-olefin copolymer: Copolymerization of olefin monomers such as ethylene and propylene can produce copolymer resins with excellent fluidity, thermal stability, impact resistance, transparency and heat resistance.
It is a simple and effective modification method to introduce heterogeneous polymer phase-polymer blending in the polyvinyl chloride phase, and has accumulated experience in actual production. Generally, when two or more different polymers are blended and melted, a mixture having the properties of these polymers can be prepared. In order to improve the flowability and impact performance of rigid polyvinyl chloride, currently commonly used blended polymers are: acrylonitrile-butadiene-styrene (ABS), which is mainly to improve the impact strength. Methyl methacrylate-butadiene-styrene (MBS), in addition to weather resistance, the remaining properties are almost ideal, especially the impact strength, as long as a small amount can be greatly improved. Chlorinated polyethylene (CPE) can improve the impact strength. If 20% is added, the impact strength can be very high. Ethylene-vinyl acetate (EVA) can increase impact strength. In order to improve the volatilization, migration and extraction of plasticizers during the use of soft polyvinyl chloride, commonly used blended polymers are: nitrile rubber (NBR), chlorinated polyethylene (CPE), vinyl chloride-acrylate , Copolymers such as dioctyl maleate, ethylene-vinyl acetate (EVA), ethylene-vinyl acetate-vinyl chloride copolymer, etc.
⒊ Graft reaction polymerization
The introduction of other monomers on the side chain of polyvinyl chloride or the introduction of vinyl chloride chains on the side chains of heterogeneous polymers is called graft polymerization.
⒋Low temperature polymerization
Changing the arrangement of the chain links within the PVC main chain, or changing the arrangement between the PVC chains, changes the polymerization method. This modification is called low-temperature polymerization.