Effect of the molecular weights on the optical and mechanical properties of poly(vinyl alcohol) films

Pure Poly(vinylacohol) (PVA) films with molecular weights (5000, 17 000, 72 000, 125 000 gm/mol) were prepared by a casting technique. The thickness of the prepared films was 0.21 mm. Optical absorption and mechanical properties were measured. The UV-Vis-NIR absorption spectra gave the same band positions but the absorption intensity varies in a reverse trend with increasing molecular weight. The dependence of the absorption coefficient, alpha, on the photon energy, hv, has been determined and the band tails and energy gaps were calculated. It was found that the band tail increases, while the optical gaps, Young's modulus and the strength at the break for PVA films decrease as the molecular weight is increased. (C) 2002 Elsevier Science Ltd. All rights reserved.