Internal-friction spectra of poly(vinyl alcohol) with various molecular masses

Abstract

Dissipative effects in poly(vinyl alcohol) films with different molecular masses and degrees of hydration have been investigated with the use of relaxation spectrometry. The mechanical-loss peaks in the internal-friction spectrum reflect two relaxation transitions (α and β peaks) and one first-order phase transition (δ peak). It has been found that a decrease in the degree of hydration and an increase in the crystallinity of poly(vinyl alcohol) substantially raises the α-transition temperature. The α peak shifts to higher temperatures as the molecular mass grows. The position of the β peak in the spectrum is independent of the molecular mass, but changes with the degree of hydration. A sharp drop of the oscillation frequency in the region of the α transition and a smooth decrease in frequency in the temperature range of the β transition have been recorded. It has been found that the shear-modulus defect determined from the frequency in the region of the α transition is independent of the molecular mass and degree of hydration of poly(vinyl alcohol).