Audio magnetic tapes manufactured using polyester urethane are known to become nonplayable over time due to the degradation of the magnetic layer. Attempting to play degraded tapes to digitize them can cause extensive damage to the tape as well as to the play back device. For this reason, most of the magnetic tapes in cultural heritage institutions are in critical state. The purpose of our study is to preserve historical recordings in magnetic tapes by developing a nondestructive technique to determine degradation status. Our approach is to combine attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT‐IR) with chemometric techniques, especially neural networks and least absolute shrinkage and selection operator (Lasso). The model built using neural networking was able to successfully classify playable and nonplayable with 97% to 98% accuracy when similar tape brands/models were in the training and the test set. With different brands/models in the test set, neural network model performed poorly. However, Lasso showed 95.5% accuracy for similar brand/models and 80.5% accuracy for different tape brands/models. This suggests that Lasso is the better technique to determine if a tape is degraded or not.
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As magnetic audio tapes age, various chemical and physical degradation processes can affect the playability of the tapes. The extent that a tape is degraded, however, is often difficult to observe without actually playing the tape. Attempting to play an extensively degraded tape can result in damage to the tape as well as to the instrument used to play the tape. Our recent work has focused on less destructive methods for determining the degree to which a tape is degraded before playing. The development of such methods would allow conservationists to predetermine if a tape should be subjected to a restoration process such as baking and eliminate any further damage from occurring. In this study, attenuated total reflectance (ATR) Fourier transform infrared (FT‐IR) spectroscopy was used as a rapid and objective method for determining the playability of polyester‐urethane magnetic tapes. A collection of 95 tapes was used to generate chemometric models based on partial least squares discriminant analysis (PLS‐DA), support vector machine discriminant analysis (SVM‐DA), artificial neural networks (ANNs), and naïve Bayes classification (NBC). Classification accuracies for playability of greater than 90% were achieved when applying the models to a separate collection of 50 tapes.
Most magnetic audio tapes in the industry were initially made with only two layers, the base film with polyethylene terephthalate (PET) and the binder layer with polyester polyurethane (PEU). The binder layer seems to undergo degradation from hydrolysis, causing the condition “sticky shed syndrome (SSS).” Hydrolysis is a reversible reaction where atmospheric moisture reacts with weak ester bonds to form degradation products, alcohols, and carboxylic acids, which produce sticky materials, hindering the playability of tapes. Later, another layer called “back coat” was introduced to magnetic audio tapes. This layer consists of carbon black embedded in PEU or polyether polyurethane. Carbon black particles in this layer absorb water, facilitate high‐speed tape winding, and remove static electricity charges. However, due to the ability to absorb water, hydrolysis can occur in the back coat layer as well. For this reason, there is a study claiming that the back coat is responsible for the degradation of magnetic audio tapes, and by removing it, SSS can be overcome. To test the validity of the above claim, this study uses attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT‐IR) with multivariate statistics to determine the degradation of the back coat layer and compare the results with the magnetic layer of the same tape identities. Results obtained show poor predictability in the back coat test set when compared with the results collected from the magnetic side, which indicates that to determine the playability status of this specific magnetic audio tape collection, the preferred side to obtain spectra is the magnetic layer.
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