The effects of aging on the interfacial bond in paper-polypropylene-paper laminates

This study is focused on understanding the behavior of paper-polypropylene-paper (PPP) laminate aging in hot oil in the absence of voltage stress. Peel strength measurements on two laminates aged in polybutene oil at 90°C for up to 950 hours showed an initial rapid loss of strength followed by a much slower loss as a function of long times. Weibull analysis of the data obtained on unaged samples and those aged for 120 hours showed that the strength loss is consistent with one failure mechanism and the failure rate increases with applied stress. For the aged sample, Weibull analysis results are consistent with the prior loss of peel strength due to hot oil aging. Experiments on the solubility of the polybutene oil show that lamination reduces the amount of absorption in comparison to that for the unlaminated composite. Swelling measurements on both the polypropylene and paper components alone in the machine and transverse directions show that the polypropylene swells and the paper shrinks in both directions. Slight differences (less than 1%) between the amount of polypropylene swelling or paper shrinkage in the two directions is due to orientation in the machine direction for both components. Swelling measurements on the laminate show that both paper and polypropylene shrink, indicating that the paper governs the laminate swelling process. It is suggested that during the aging time, the differential swelling between the paper and polypropylene imposes a stress on the interface and is responsible for the loss of strength