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2013-12-21 by seoer8
As we all know , the thermoplastic resin , the mechanical properties of the final product with the polymer melt during the transformation process uniformity closely related. Unlike most other thermoplastic resins , rigid PVC processing aid particles due to their inherent structure resulting that it can not be processed directly . It requires a high temperature for a long processing time, which often causes thermal degradation. PVC resin processing aids to bring a lot of benefits , mainly related to the process of the melting process and melt rheology related . Processing aids help to improve adhesion and homogeneity of the melt , enhance the melt strength, melt extensibility and melt elasticity. And the processing aid component of the additive polymer structure affects the compatibility with PVC , and change some properties, such as fluxing properties and lubricity. On the other hand , the molecular weight of the processing aid in the control of molecular weight distribution and melt rheological properties will play a key role. The most common processing aids are methyl acrylate polymer. Polymethyl methacrylate (PMMA) polymer having a class higher glass transition temperature (Tg), with the PVC material and it has excellent compatibility of these properties in favor of the local shear heat generation and delivery , thereby promotion of PVC in the melt phase melting . In addition to the melt rheology improving dispersion and improve the processing efficiency, and enhance the overall balance of various properties ( especially viscosity corresponding to a melt strength ) , which are the main objectives of processing aid and the direction of development . This trend is on the one hand requires less processing aids under the premise with the same effect can be obtained , in addition, the need for uniform color, apply a transparent material, the material also requires more readily dispersed and more uniform and transparent . An accelerated melting and melt homogeneity monitoring PVC melting process is the most common method is to use a plastic rheometer (Brabender Plasticorder) or Haake rheometer . Plasticized PVC graph shows the process of plasticizing torque corresponding time . Each stage of the melt temperature are recorded . Point "A" shows the peak of the compression , the powder is compressed to reflect the conditions and thickening . "B" represents the start point plasticize the plasticized subsequent peaks. Point "C" in a melt plasticized PVC moment . From point "A" to the time difference between "C" between the points is called a " plasticizing time ." Point "C" to the measured torque is called " plasticizing torque ." PVC at this stage does not completely melted , most of the primary particles in the melt state . Continuous plasticizing torque begins to decrease , in the point "D" is rendered almost constant torque , the torque is referred to as equilibrium torque. Characterization can be roughly balanced by the torque estimated value of the melt viscosity . While continuing to heat and shear , the "E" points , PVC chain occurs dehydrochlorination and crosslinking occurs, the torque will rise again. "A" to the time difference between the point "E" between the points is called " degradation time ." PVC formulation type , the process temperature , shear rate and load levels and other factors will strongly influence the melting curve .keywords: pvc-additive
