Melting point of pvc plastic pipe
Melting point of pvc plastic pipe is a complex concept because PVC is an amorphous plastic with no fixed melting point. However, the melting temperature range of PVC plastic is usually between 185 and 205 degrees Celsius. This temperature range refers to the temperature interval required for PVC plastic to change from solid to liquid. In practical applications, the heat resistance of PVC pipe is also affected by its formulation and processing technology, so its long-term use temperature should not exceed 55°C, while the long-term use temperature of specially formulated PVC plastic can reach 90°C
PVC plastic characteristics
1. Physical properties
Polyvinyl chloride resin is a thermoplastic with an amorphous structure. Under ultraviolet light, hard PVC produces light blue or purple-white fluorescence, and 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 product density with plasticizers and fillers is usually in the range of 1.15~2.00, the density of soft PVC foam is 0.08~0.48, and the rigid foam is 0.03~0.08. The water absorption rate of PVC is not more than 0.5%.
The physical and mechanical properties of PVC depend on the molecular weight of the resin, and the content of plasticizer and filler. 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 difficult; Low molecular weight is the opposite of the above. The tensile strength decreases with the increase of filler content.
2. thermal performance
The softening point of polyvinyl chloride resin is close to the decomposition temperature. It has begun to decompose at 140 ° C, and the decomposition is more rapid at 170 ° C. In order to ensure the normal process of molding, two of the most important process indicators for polyvinyl chloride resin are specified, namely, 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 are exposed to 100 ° C for a long time, unless an alkaline stabilizer is added, it will also decompose, and if it exceeds 180 ° C, it will decompose rapidly.
The long-term use temperature of most PVC plastic products should not exceed 55 ° C, but the long-term use temperature of special formula PVC plastic can reach 90 ° C. Soft PVC products will harden at low temperatures. Polyvinyl chloride molecules contain chlorine atoms, so it and its copolymer are generally flame resistant, with self-extinguishing, and no dripping.
3. Stability
Polyvinyl chloride resin is a more unstable polymer that, under the action of light and heat will also degrade, the process is to release hydrogen chloride, the structure of the change, but the degree is relatively light. At the same time, decomposition is accelerated in the presence of mechanical forces, oxygen, odor, HCl, and certain active metal ions.
After removing HCl from the polyvinyl chloride resin, conjugated double chains are produced on the main chain, and the color will also change. As the amount of hydrogen chloride decomposition increases, the polyvinyl chloride resin changes from the original white to yellow, rose, red, brown, and black.
4. Electrical properties
The electrical properties of PVC depend on the amount of residues in the polymer and the type and amount of various additives in the formula. The electrical properties of PVC are also related to the heating conditions: 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 that cannot be neutralized by alkaline stabilizers (such as lead salts), its electrical insulation performance will be significantly reduced. Unlike non-polar polymers such as polyethylene and polypropylene, PVC’s electrical properties change with frequency and temperature, such as the dielectric constant decreases with increasing frequency.
5. Chemical properties
Polyvinyl chloride has very good chemical stability and is very valuable as an anti-corrosion material.
PVC is stable to most inorganic acids and alkalis. It does not dissolve when heated and decomposes to release hydrogen chloride. A brown, insoluble unsaturated product is obtained by azeotropy with potassium hydroxide. The solubility of PVC is related to the molecular weight and the polymerization method. Generally speaking, the solubility decreases with the increase of the molecular weight of the polymer, and the solubility of the emulsion resin is worse than that of the suspension resin. It can be dissolved in ketones (such as methyl hexyl ketone, and cyclohexanone), aromatic solvents (such as toluene, and xylene), dimethyl formyl, and tetrahydrofuran. At room temperature, polyvinyl chloride resin is almost insoluble in plasticizers, and it swells significantly at high temperatures and even dissolves.
6. Processing properties
PVC is an amorphous polymer with no obvious melting point. It is plastic when heated to 120~150℃. Because it has poor thermal stability and contains a small amount of HCl released at this temperature, which promotes its further decomposition, it is necessary to add alkaline stabilizers and HCl to inhibit its catalytic cracking reaction. Pure PVC is a hard product, and it is necessary to add an appropriate amount of plasticizer to make it soft. For different products, additives such as ultraviolet absorbers, fillers, lubricants, pigments, mildew inhibitors, etc. are also needed to improve the performance of PVC products. Like other plastics, the performance of the resin determines the quality of the product and the processing conditions. For PVC, the resin properties related to processing include particle size, thermal stability, molecular weight, fish eyes, bulk density, purity and foreign impurities, and porosity. For PVC paste, the viscosity and gelling properties of the paste should be measured to facilitate the control of processing conditions and product quality.
