The Effects of Solution Application on Some Mechanical and Physical Properties of Thermoplastic Amorphous Polymers Used in Conservation: Poly(vinyl acetate)s

Abstract

The tensile properties of solution-cast poly(vinyl acetate) (PVAC) films are determined by the thermodynamic quality of the solvents. Higher strength and lower elongation are evident in polymer films of poly(vinyl acetate) AYAT (Union Carbide) cast from a solution of acetone or an acetone/ ethanol/water mixture, while lower strength and greater elongation are evident in films cast from a solution of chloroform or toluene after drying for 180 days. Films of PVAC-AYAT cast from a toluene solution retained a significant amount (>4%) of solvent, while films cast from the other three solvents retained little solvent (>0.3%). For all polymer films, the glass transition temperature (Tg) was elevated greater than 18°C above the Tg of the bulk polymer. The differences in the tensile properties of the films with little retained solvent is explained on the basis of the thermodynamic quality of the solvents, 1.e., the physical properties of the solution-cast polymer film in the dry state may be affected by the conformation of the polymer chain in the solvent. The polymer chain of poly(vinyl acetate) is relatively extended in the “good” solvent chloroform but is more contracted in the “poorer” and more polar solvent, acetone. The effect of solvent quality on the polymer morphology in the dried film was also demonstrated with Fourier transform infrared spectroscopy (FTIR). Changes in spectral band intensity in the FTIR spectra within a series of poly(Vinyl acetate)s differing in molecular weights can be discerned when these are deposited on KBr from a chloroform solution but not when deposited from an acetone solution.