Pressure Decay Studies and Error Analysis of Diffusivity and Solubility of Atmospheric Gases in Polyvinylbutyral
Laminated safety glass, used for architectural purposes as well as in the automotive industry for a vehicle's windshield, is produced using polyvinylbutyral (PVB). This polymer, when used in a plasticized state, posses a number of optical and adhesive properties important in these applications. DuPont manufactures safety glass primarily for automobile windshields. In the production of safety glass, the PVB is sandwiched between two sheets of glass and is processed at high pressures (15 bars). Under such conditions, the possibility exists for gases to diffuse into the PVB. When the Safety glass is removed from this high pressure, it is possible that the dissolved gases will not be able to escape the sandwich created by the glass and will form air pockets within the safety glass. These bubbles form unwanted defects in the safety glass. Thus, there is interest in studying the adsorption of atmospheric gases in PVB at the high pressures and temperatures the polymer encounters during processing.
The pressure-decay technique has several advantages that make it an ideal method to study the gas-PVB systems of interest. This approach enables one to obtain both diffusivity and solubility coefficients in a single experiment. Furthermore, the apparatus is designed for use at high pressures similar to the conditions under which safety glass is processed. Other methods of studying polymer-gas systems, such as chromatographic approaches, are not generally designed to withstand these pressures. Due to the low solubility and weight of the gases of interest, experiments utilizing an increase in the weight of a polymer sample also would be expected to yield poor results. The pressure-decay technique, which records the pressure change as gas absorbs or desorbs from the polymer into a constant volume, constant temperature chamber, is not directly related to weight change of the sample.