Preparation of PVC plastic and PVC plastics processing evaluation

Date: 2012-06-24 13:10 Author: 1426 Views Views Font Size: Big Mid Tiny

In order to adapt to the needs of processing, plastics, resins and additives made of various forms of dry mixing, pellets and paste. Dryblend prepared in the laboratory, generally use the volume of 5L high-speed heating mixer or kneader, joined the resin according to the provisions of the order plus stabilizers and other additives, and mixing temperature of 100 ~ 110 ℃, discharge and cooling. Prepared in the laboratory pellets, generally dry mixing masticated on a two-roll machine, pulls the film, after cooling, crushing can be used for the experiments. Available extruder granulation. Preparation of the paste according to national standards (GB 12004.2-89).
Evaluation of pvc plastic processing, generally proceed from the thermal stability, rheology and lubricity, but different processing methods, but also may have special requirements.
First, consider the thermal stability. Evaluation of the thermal stability of PVC plastic oven test roll test and torque rheometer test. The first two are observed at fixed temperature (180 ° C) sample (solid) color with the time change (white → pale yellow → red → yellow → reddish → pink → dark red → black), in order to assess the stabilizing effect . Torque Rheometer plastic thermal stability is the change in the constant temperature (200 ° C), observations of materials in the feedstock and the rotor speed torque with time from the maximum torque to the decomposition point of time is called dynamic thermal stability time, the higher the value the better the thermal stability. Injected with a hard PVC material, the dynamic thermal stability should not be less than 16min.
Second, to consider the rheology. Many factors affecting the melt flow of PVC plastic, the shear viscosity can be said that the resin properties (molecular weight, structure and morphology), additives (stabilizers, plasticizers, lubricants and fillers, etc.) and processing conditions (temperature , time, pressure), etc. functions. Therefore, the capillary rheometer to determine the melt rheology. Different processing methods, it requires the shear rate is also different (Table 1-29), thus corresponding to the different viscosity. For the injection molding of rigid PVC, if the shear viscosity in the shear rate of 103s-1 does not exceed 1000Pa • s, the charge mode have no difficulty. For PVC extrusion, the difficulty is much smaller than the injection, but limit the rate of extrusion is the critical shear rate. Exceeds the critical shear rate, melt fracture, were measured using a rotational viscometer and extrusion rheometer (GB 12004.3-89) for paste processing. Of the paste viscosity with the shear rate increases, the display changes (Newtonian, pseudoplastic and expansion), indicative of the processing results of the formula.
Third, consider the lubricity. Method in the laboratory evaluation of lubricating a two-roll machine test, test of the extruder, Determination of capillary rheometer and torque rheometer melting tests. The test of the two-roll machine by sticky roller time the long and short to determine the internal and external lubrication. The extrusion test is screw torque, the mouth of touch pressure and extrusion amount of lubrication to determine. Capillary rheometer can determine the impact of lubricants for PVC mobility, according to the material viscosity to reduce the extent (without lubricant reference), can determine the external lubrication. Quite easy to measure the torque rheometer torque curve of the PVC plastic under the torque curve shape and its characteristic value (minimum torque and maximum torque and time) can be characterized by melting characteristics, promote melting or postpone the melt, which the judge inside and outside the lubricity. This Jizheng Xin according to the requirements of different processing methods of rigid PVC melt, with the torque curve to be characterized. For extrusion, twin screw extruder depends mainly on the outside heating the material melting, require a longer melting time; single screw extruder melt than twin-screw extruder confidential fast, but not over fast, otherwise the material in the feed zone melting, the melt has long been cut, resulting in the expected temperature rise, until the degradation. For injection molding, rapid melting of PVC, but too fast will make the material burnt, too slow (too many outside lubrication) of less than a certain gelation degree. According to the research degree of gelation, the maximum torque at (give value) up to 65% to 75%.

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