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How does plastic raw material influence plastic extrusion tube quality?
Oct 18, 2017

The polymerization method, structure, relative molecular weight, relative molecular weight distribution of polymers and various additives have a great influence on the properties of plastic products like plastic tubes etc. 


(1) polymerization degree: the degree of polymerization refers to the number of repeating structural units contained in the resin chain. The greater the degree of polymerization, the higher the average molecular weight, tensile strength, impact toughness and stiffness increase, the mechanical properties of products are good, low temperature resistance, heat resistance and chemical resistance of product the higher. At the same time, the flowability of the melt is poor, the viscosity is high, and the forming process is difficult. Therefore, polymerization degree is an important basis for the selection of resins.


(2) apparent density: apparent density refers to the quality of resin per unit volume. The apparent density is related to the porosity of the resin particles. The porosity is high, the apparent density is low, and the amount of absorption aid is much. Otherwise, it is difficult to absorb the heat stabilizer or lubricant, so it is difficult to increase density or melt.


(3) volatile matter: volatile matter mainly refers to moisture. High water content, easy to produce bubbles during molding and processing process which leads to stress concentrate at the bubbles, which cause the mechanical properties decreased; water is too small, the processing is easy to produce static electricity, while the moisture content will affect raw materials mixing uniformity during processing.


(4) impurities: foreign impurities and their yellow spots. Impurities have great influence on the appearance of the products, and defects are formed on the surface of the product after processing. The stress is easy to be concentrated around the defect , and finally it may cause the products to crack.


(5) sieve residue: sieve residue is an index to reflect the particle size of resin. The particle size of the resin should be as narrow as possible; the particles are too fine; the free flow of the polymer and its dry mix powder is blocked; the particles are too thick; the resin is difficult to disperse and difficult to gel. The uneven size of particles also affects the distribution of additives during processing, and the uneven distribution of additives can lead to surface defects of products.


(6) the absorption amount of plasticizer: its size subjects to surface properties and particle size and distribution, the porosity of the resin particles, it influence degree of absorption lubricant or heat stabilizer when processing, absorb too much or too little has adverse effects, appearance defects in the final products, such as "fish eye", "particle bumps" and "crystal" etc..


(7) thermal decomposition: thermal decomposition temperature higher than the melting point of the resin, the resin is not easy to change color, coking in the processing of products, easy control of the processing parameters; temperature close to or below the melting point of the thermal decomposition of resin, resin easy decomposition, in the processing of products, such as color degradation, then the need for adding heat stabilizer to improve the thermal stability of the resin.

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