Researchers, audio engineers, and tape users have studied polyurethane-based magnetic audio tape degradation for decades, but uncertainties remain in the understanding of physical tape degradation and how to treat degraded tapes to enable their playback. Problems of squealing and shedding in old tapes, generally termed “sticky shed syndrome”, are most frequently remedied by prolonged baking at elevated temperatures. Despite its prevalence, many audio preservationists still express uncertainty about precise baking requirements and the full long-term effects of baking. This work builds on prior knowledge of tape degradation processes by assessing degraded and non-degraded polyurethane-based test tapes available at the Center for the Library’s Analytical Scientific Samples.<br/><br/>The material-level and physicochemical properties were evaluated for a range of at-risk tapes, including major and popular tape brands, both before and after exposure to typical baking conditions. Of particular interest were sticky/non-sticky “twins” of the same tape model. Thermal analysis tools were used to examine the glass transition temperatures, polymer/lubricant crystallinity, and additive volatilization in polyurethane-based tape binders and backings. Additional measurements assessed the volatile organic compounds within the tapes using mass spectroscopy, chemical functionality using reflectance spectroscopy, and surface energy effects using water contact angle. These properties served as an indicator of the condition of the tapes’ urethane binder layer and were found to have some similarities and some unexpected differences following thermal treatment.<br/><br/>While certain models of tape are known to be particularly vulnerable to degradation, the exact condition and playback performance still varies between individual tapes. Learnings from these lab-scale experiments are now being paired with playback and on-deck evaluation of test tapes in order to provide practical guidance in persevering audio materials. In particular, these efforts aim to inform improved methods for the rapid non-destructive identification of sticky tapes.

Thermal effects on the degradation and restoration of polyurethane-based magnetic media

256th National Meeting (2018)

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