Abstract
The study presents rheological behaviour of some solution mixtures from poly(vinyl alcohol) (PVA) and starch in water, with addition of glycerol as plasticizer and urea (nitrogen source for microorganisms). These solutions were used to obtained biodegradable films. The effect of temperature and concentration on the rheological behaviour of poly(vinyl alcohol) and starch solutions in water, was studied in the temperature range of 20-60 0C and concentration 10-20 % at different gravimetrical ratio PVA/starch (3.00, 1.66, 1.00, 0.60, 0.33). The rheological behaviour was studied to gradient of shear rate which varied between 3 and 1310 s-1. From experimental data it was established that concentrated solutions of PVA/starch blends exhibit a non-newtonian rheological behaviour of pseudoplastic type. The flow activation energies versus temperature are situated in range of 11.86-49.92 kJ/mol, while against the concentration between 1.61-4.54 kJ/mol. The consistency index increased with decrease of temperature and recording great values in the concentrated solutions case. The solutions with PVA/starch subunitar gravimetrical ratio have great values of consistency index, to compare those with supraunitar ratio. This fact shows that the starch is the polymer which confers solutions a great viscosity, but low temperatures determines even their jellification. Keywords: biodegradable materials, rheological behaviour, poly(vinyl alcohol), starch