Effect of photoageing and plasticizer content on the mechanical and adhesive properties of polyvinylbutyral
May, Raymond Jeffrey
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The objective of this study is to characterize the mechanical and adhesive properties of polyvinylbutyral and determine the effect of plasticizer content and photoageing on these properties. This data would be used to understand how the performance of laminated safety glass is related to the choice of adhesive interlayer. Samples of PVB plasticized with 0 to 40% butyl benzyl phthalate by weight were analyzed using a single strain rate tensile test, dynamic mechanical thermal analysis and a 1350 peel test. Two regimes of behavior were identified. PVB with low plasticizer contents, up to 10%, acts as a glassy polymer at room temperature. At higher plasticizer concentrations, greater than 20%, the material becomes elastomeric, with increased ductility and decreased moduli. The adhesive strength of each of the formulations was similar if compared at their respective glass transition temperatures. At room temperature, the heavily plasticized formulations had good adhesive strength whereas the less plasticized formulations readily debonded from the glass. These results suggest that PVB plasticized with between 20 and 40% plasticizer content is highly suitable as an interlayer material. UV radiation exposure was used to simulate the effect of sunlight on PVB. Forty micron thick samples were irradiated for up to 1000 hours of exposure time and analyzed using FTIR spectroscopy. It was determined that photo degradation had occurred in the form of a breakdown of the acetal ring structure in the vinyl butyral function. Similar treatment of 0.75 mm thick samples produced no major degradation in the mechanical or adhesive properties of the material. This is an unexpected result that conflicts with the obvious degradation discovered during FTIR spectroscopic testing. This is most likely due to the increased thickness of the mechanical samples and corresponding lo\ver UV dosage per polymer chain.
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