Processibility, rheology, mechanical properties, degradation, thermal and shear stability of PVC in blends with PMMA within the range where the constituents are compatible have been thoroughly investigated. Compatibility has been confirmed by different techniques such as inverse gas hromatography, DTA and viscometry, although viscometric measurements indicated some inconsistency depending on the molecular weight of PMMA. The torque-time curves obtained under different processing conditions, temperature, shear rate and blend composition, showed the addition of PMMA (up to 10 wt. %) to significantly improve the processibility of PVC. Blend's fusion time has dropped almost three times, whereas the plasticizing energy was 40% smaller compared to that of pure PVC. Also an increase in heat and shear stability was noticed. Samples of PVC/PMMA blends under steady shearing conditions at 170-200°C were studied in a capillary rheometer for rheological properties. The shear stress vs. shear rate curves follow the power law relationship with a very low flow behavior index that slightly depended upon the addition of PMMA. More pronounced changes were noticed in consistency indices. The flow curves for blends are between those of each of the pure consituents. This information about the nature of the rheological response of PVC/PMMA blends confirmed the integrity of the blend and the existence of rheological compatibility. Also the blends indicated much better mechanical and thermal properties affected positively by the blend composition but only to some extent (less than 10 wt. %) PMMA. Thermal decomposition was tested at higher temperatures (>150°C) in a nitrogen atmosphere and the evolving HC1 was detected by pH measurements. PMMA (even in small amounts) has considerably decreased the degree of degradation of PVC.
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