PVC resin related technical indicators you must know

Bulk density and powder dry flow Bulk density refers to the apparent density under certain compression conditions, which is usually 10% to 30% larger than the apparent density, and is an index used to balance the properties of the powder. The dry flow of the resin can predict the feeding performance of the resin in the feeding hopper. The resin with large spherical particles and uniform particle size has good dry flow, so the dry flow of the suspension method and the bulk resin is good. These two indicators have a great impact on the design and operation of the large mixing system, but these two contents are not yet available in the current routine resin testing. Molecular weight distribution The molecular weight distribution of PVC resin is closely related to molding processing and product quality, and usually narrow distribution or bimodal distribution is better. Because the double bond structure and the like are mostly concentrated in the low molecular weight part. However, due to the expensive testing equipment, most manufacturers do not have such testing capabilities. Generally speaking, it is better to have a narrow molecular weight distribution in the molding process of polymers, because the processing properties and the properties of the products are relatively uniform. A distribution of fractions that is too broad indicates the presence of a certain amount of lower or higher molecular weight fractions in the polymer. The existence of the former will significantly reduce its thermal stability, heat distortion temperature, electrical insulation, mechanical strength and aging resistance; the existence of the latter will often make it difficult to plasticize uniformly under normal processing conditions, and will also cause products. The internal quality, especially the deterioration of the appearance quality, will appear unplasticized particles like fisheyes on the surface of the product when it is serious. Average particle size The average particle size and sieve residue represent the same physical properties of PVC resin, but the representation and measurement methods are different. The average particle size can be obtained by the laser particle size analyzer method, and the particle size information can be obtained by the diffraction of the particles to the laser, and the average particle size can be obtained through analysis and calculation. Original whiteness Original whiteness and aging whiteness are completely different indicators. The aging whiteness indicates the thermal stability of the resin, while the original whiteness indicates the color of the resin itself, which has almost nothing to do with thermal stability. processing does not have much guiding significance. The original whiteness has a certain relationship with the formula of the resin, the variety and purity of the raw materials. In addition, the color difference, particle concentration rate, etc. will be detected and analyzed in the bulk PVC resin. These indicators are an extension of the relevant indicators in the national standard. In fact, the core that really affects the processing of PVC resin and the performance and quality of products is the molecular structure, particle shape and composition of residual impurities of PVC resin. Due to the difficulty of routine detection of these items, they should not be used. Therefore, only through various conventional indicators, the different properties of the resin can be displayed, which is convenient for detection and utilization in actual production and processing.