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Light stability of polypropylene

by:CSSSLD     2021-01-23
Slow cooling can obtain higher crystallinity, generated by the crystal is stable, internal stress is lesser, but the products of the molding shrinkage ratio is larger, transparency, and toughness. And injection molding processing PE, PP, bibulous rate is small, generally does not need to dry before molding processing, printing performance of products is poor, can take when printing surface decoration of corona treatment, etc. Other properties of PP and PE is extremely similar, as both are polar polymer, it has excellent electrical insulation materials, and PP can be used at higher temperatures.

PP light stability is poor polymer varieties, outdoor use must join stabilizing additives. In order to improve the light stability of PP and PE and the thermal oxidation resistance, the most commonly used method is to add antioxidant and light stabilizer. PP and PE, it has excellent chemical stability, but because there are tertiary carbon atoms in the molecular structure of PP, more easily by oxidation erosion. Under 100 ℃, the majority of inorganic acid, alkali, salt solution of PP without damage, such as PP for concentrated phosphoric acid, 40% hydrochloric acid, sulfuric acid and their salt solution at 100 ℃ is stable, but for the strong oxidizing acid is not stable. On hypochlorite and hydrogen peroxide, only in the concentrations of minor and low temperature stability.

processing conditions for PP has a great influence on the crystallinity and crystal morphology, crystal also influence on the performance of the products in the end. Often the PP crystallization rate when temperature in 120 - Between 142 ℃. Of crystallinity of PP melt quenching is low, the products have good transparency, industry commonly used this is highly transparent PP film. On the other hand, due to rapid cooling macromolecular chain too late movement and the adjustment is frozen, products tend to produce internal stress.

non-polar organic solvents to dissolve PP swelling or easily, but can only make its mild swelling at room temperature, as the temperature increases, the swelling degree increases, for the majority of polar organic solvent, PP is stable, such as alcohols, phenols, aldehydes, ketones, and most of the carboxylic acid is not easy to make its swelling, but aromatics and chlorinated hydrocarbons in above 80 ℃ for which he has dissolved, esters and ethers on it also has some erosion.

the melt viscosity of PP is lower than HDPE, good liquidity, thus forming good performance. Processing can improve the shear rate and temperature in the increase of melt flow rate, especially in order to improve the shear rate is significant. Due to PP is higher than the melting point of PE and its forming temperature is higher, also is in commonly 180 - Between 280 ℃ and should not be more than its decomposition temperature. PP is sensitive to the role of oxygen at high temperature, has a tendency to high temperature oxidation in the forming process.

light stability refers to the plastic material under the sunlight or ultraviolet light, resistance to fade, black or degradation. Because of the polyolefin plastic in synthesis, processing and use easy introduction of catalyst particles, hydrogen peroxide, hydroxyl and double bond, and poor light stability, PP. As in the 150 ℃ by 0. 5 - 3. 5 h or outdoors insolate 12 DPP would be brittle, placed indoors 4 months is bad.

PP of high temperature oxidation rate is 30 times of PE. Therefore, we should try to avoid its melt is exposed to air or reduce the time it is exposed to air, because the fever high temperature oxidation phenomenon will reduce the mechanical strength of plastic products processing, if stretch forming is difficult to control of the drawing process. Also should pay attention to avoid the PP melt contact with copper, copper can accelerate the oxidation degradation rate of PP. Processing or use in contact with the copper copper inhibitors may be added, such as aromatic amine, grass amide compounds.

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