Views: 3 Author: Site Editor Publish Time: 2019-09-08 Origin: Site
PVC pipe fittings and pipes have flame retardancy and are widely used for fire protection because of their flame retardancy. It also has good electrical insulation properties and can be used as low frequency insulating material, and its chemical stability is also very good. Do you know these qualities? different characteristics of PVC fittings will be detailed to you in this article.
PVC pipe fitting physical and chemical properties
Polyvinyl chloride has poor thermal stability and light resistance. Hydrogen chloride starts to decompose at 150 ° C, and an adverse reaction occurs with the amount of plasticizer. In addition, the effect of the pigment on PVC pipe fitting is reflected in whether the pigment reacts with PVC pipe fitting and other components constituting the PVC pipe fitting product, and the pigment itself is resistant to migration and heat. Some of the ingredients in the colorant may contribute to the degradation of the resin. For example, iron ions and zinc ions are catalysts for the degradation reaction of PVC resins.
Therefore, the use of iron oxide (red, yellow, brown and black) pigments or zinc oxide, zinc sulfide and lithopone white pigments reduces the thermal stability of PVC resins. Some colorants may interact with degradation products of PVC resins. For example, the ultramarine pigments have poor acid resistance, so in the process of PVC pipe fitting coloring, they will interact with the hydrogen chloride generated by the decomposition of PVC and lose the color they deserve.
Mobility occurs only in plasticized PVC articles and when dyes or organic pigments are used. The so-called migration is a partially soluble dye or organic pigment present in the surrounding solvent. The plasticizer penetrates the surface of the PVC pipe fitting product, and the dissolved dye particles are also brought to the surface of the product, thus causing bleed, solvent. Bleeding or blooming. Another problem is "fouling." It means that the coloring agent is freed from the system during the coloring process because it is poorly compatible or not compatible at all, and is deposited on the surface of the processing equipment.
Refers to the ability of pigments to withstand various climates. These include visible and ultraviolet light, moisture, temperature, atmospheric chlorination, and chemicals encountered during the use of the product. The most important weatherability, including non-fading, powdering resistance and durability of physical properties. Organic pigments are different due to their different structures. In addition, in formulations containing white pigments, the weatherability of the pigments is more severely affected.
The fading, darkening or hue change of the pigment is generally caused by the reactive gene of the pigment. These reactive genes can interact with moisture or chemicals in the atmosphere, acids and bases. For example, cadmium yellow fades under the influence of moisture and sunlight. Lissol red has good light resistance and is suitable for most indoor applications, and is severely discolored in outdoor use containing acid and alkali components.
The method for measuring dehydrochlorination was measured at a temperature of 180 ° C according to JIS-K-6723. Based on the time of dechlorination of the uncolored polyvinyl chloride compound, the elongation or retardation time is at intervals of 5% and 10%, and the negative value indicates accelerated decomposition.
The softening point of the polyvinyl chloride resin is low, about 75-80 ° C, and the embrittlement temperature is lower than -50 ~ -60 ° C. The long-term use temperature of most products should not exceed 55 ° C, and the special formula can reach 90 ° C. If the polyvinyl chloride resin is purely a head-shaped junction, it is afraid of a linear structure, and 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.
However, even if the polyvinyl chloride resin has a high purity, hydrogen chloride gas will start to escape at a temperature of 100 ° C or higher or ultraviolet radiation. It indicates that there are sharp groups or unstable structures in its molecular structure. The longer the time, the more degradation, the higher the temperature, the faster the degradation rate, and the faster the degradation in the presence of oxygen or air.
Polyvinyl chloride is a polar polymer with a high affinity for conductive substances such as water, so the resistance is smaller than that of non-polar polyolefins, but there is still a high volume of electricity and breakdown voltage. The polar group of polyvinyl chloride is directly attached to the main chain. Below the glass transition temperature, the dipole segment is restricted by the main chain atom of the frozen structure and cannot move, so it does not produce dipolarization. High frequency insulation material. When used for wire insulation, the electrical insulation of the suspension resin is 10-100 times higher than that of the floating resin. The presence of chloride ions produced by degradation reduces electrical insulation.
The natural color is yellowish translucent and shiny. Transparency is better than polyethylene, polypropylene, and is different from polystyrene. It is divided into soft and hard polyvinyl chloride according to the amount of additives. The soft products are soft and tough, and the hand feels sticky. The hardness of hard products is higher than that of low density polyethylene. Below polypropylene, whitening occurs at the bend. Stable; not easily corroded by acid or alkali; more resistant to heat.
Polyvinyl chloride has flame retardancy (flame retardancy value of 40 or more), high chemical resistance (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 was 80 ° C and decomposition began at 130 ° C. Without heating the stabilizer, the polyvinyl chloride starts to decompose at 100 ° C, and decomposes faster at 130 ° C or higher.
It is decomposed by heat to release hydrogen chloride gas (hydrogen chloride gas is a toxic gas) to discolor, from white → light yellow → red → brown → black. The ultraviolet rays and oxygen in the sunlight cause photo-oxidative decomposition of the polyvinyl chloride, thereby lowering the flexibility of the polyvinyl chloride and finally becoming brittle. It is not difficult to understand from here why some PVC pipe fitting turn yellow and become brittle after a long time.
You need to know the different properties of the PVC pipe fitting to determine if the PVC pipe fitting you choose can be placed in your subsequent use.