Thermal Degradation of Poly(N-vinylpyrrolidone)–Poly(vinyl alcohol) Blends

Abstract

Thermal stability and decomposition behavior of blends of poly( vinyl alcohol) (PV A) and poly(N-vinylpyrrolidone) (PVP) have been studied. Decomposition behavior of the blends was different from that of individual polymers. Addition of PVP to PV A effectively increases the initial thermal decomposition temperature and temperature corresponding to 50% decomposition. There is thus strong interaction between components. Effect of blend composition on the amount of residue remaining at various temperatures was studied. There is a linear increase in the amount of residue with increasing proportion ofPVP. Activation energy was calculated for the first degradation step using Horowitz-Metzger and Coats-Redfern Equation. Activation energies of the blends in the entire composition range are higher than the corresponding values of individual polymers.Thermal properties of polymers give valuable information regarding stiffness, toughness, stability and compatibility in blends. 1 -4 A detailed understanding of thermal degradation of polymers is important as the polymer is subjected to thermal history during manufacture and processing. Blending has great influence on the thermal stability of polymers and thermal stability of blends depends strongly on interaction between the individual polymers. 5 • 6 EXPERIMENTAL Blend films of PVP and PV A were prepared by solution casting using common solvent, distilled water. Blends of PVP/PVA in all compositions, namely 100/0, 80/20 (B2), 60/40 (B4), 50/50 (B5), 40/60 (B6), 20/80 (B8), and 0/100 were prepared by mixing the required amounts of 5% solution of PVP and PV A in correct proportions. The blend films were dried and preserved in vacuum desiccator. Clear transparent films were obtained. Thermogravimetric analysis (TGA) and Derivative Thermogravimetric analysis (DTG) of the films were carried out in Shimadzu DT -40 thermal analyzer in N 2 atmosphere at a heating rate of 1 ooc min-t. The amount of the samples taken for experiments were 5 mg. The thermograms were taken for constituent polymers and for blends of various compositions. RESULTS AND DISCUSSIONThe data obtained from thermogravimetric analysis t To whom correspondence should be addressed.are given in Figure 1. The initial thermal degradation peak temperature of PV A is about 200°C and associated mainly with dehydration accompanied by formation of volatile products. 7 In the present study, the initial degradation peak is observed at about 200°C. On blending with PVP, the degradation peak shifted to the higher temperature side. In the case of PV A, weight loss due to thermal degradation was about 73% at 400°C. But in the case of PVP, the weight loss is only about 30% at 400°C. Weight loss at 350°C for 100% PVA and Blends B8, B6, B5, B4, B2, and PVP was 51, 42, 38, 36, 30, 25, and 14.5% respectively. T 0 (Initial thermal decomposition peak temperature), and T 50 (temperature corresponding to 50% weight loss) were plotted against PVP weight percentage (Figures 2 and 3).Increase in PVP content effectively increases T 0 and T 5...

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