hrvatski

Studij termooksidacijske razgradnje mješavina PVC+MMBS

The process of thermooxidative degradation of nonstabilised, stabilised and commercial poly(vinyl chloride) modified by methyl methacrylate/butadiene/styrene (PVC+MMBS) in synthetic air was investigated by means of nonisothermal and isothermal thermogravimetry. Also, the process of natural weathering of commercial PVC+MMBS blends was evaluated. Adding of a thermal stabiliser and processing aids the glass temperature of PVC, determined by DSC, lowers. In the commercial blends, partial miscibility of PVC and PMMA component of MMBS was achieved due to the longer time of homogenisation. Nonisothermal measurements were carried out in the temperature range from 50 to 6500C at heating rates of 2,5; 5; 10 and 200C/min. The kinetic parameters were determined applying Flynn-Wall-Ozawa and Kissinger’s method. The applicability of compensation parameter for comparison of different systems was discussed. Isothermal thermooxidative degradation was followed at 230, 240, 250 and 2600C during 120 minutes. In order to determine kinetic parameters several kinetic models were tested and Prout-Tompkins model was chosen. MMBS, in most cases, stabilises PVC in the blends. Applying integral and differential kinetic analysis on the thermooxidative degradation of PVC at 2300C it was found that total thermooxidative rate was successively determined by three processes: autocatalysis, phase boundary reaction and diffusion. A new method, based on mathematical criteria, was proposed for determination of transition points of one rate controlling process to another. During natural weathering chain scission of PVC occurs as well as the degradation of polybutadiene in MMBS, which causes the loss of its ability of impact strength modification.

diferencijalna pretražna kalorimetrija; kinetički modeli; kinetički parametri; kompenzacijski parametar; mješavine PVC+MMBS; mješljivost; prirodno starenje; termogravimetrija.

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