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A new method (common mode subtraction) for strain measurement in the tensile testing of filamentous materials is presented. In this method, crosshead displacements were divided into the specimen extension and the specimen extension error, the latter is associated with the testing system (machine frame, load-cell, load-string, and grips) and force, but assumed to be independent of the gage length. Common mode tension tests for steel and nylon tire cords at different gage lengths with two types of grips were performed at first. The test results showed an obvious existence of the specimen extension error, which leads to a dependence of the engineering strain on the gage length. The specimen extension error was found to be indeed independent of the gage length and increase with force nonlinearly. Then subtractions between any two of the obtained force–crosshead displacement curves were carried out to remove the specimen extension error, and then the actual force–strain curves (linear for steel cord and nonlinear for nylon cord) were obtained. Finally, comparisons between the common mode subtraction method and other methods, which were reported to be able to correct the specimen extension error, were made. The comparison revealed the relative stiffness is the key, that is, when the specimen is “weak” in relation to the testing system, the grip is the main source of error, but if the specimen is much “stronger,” the influence of the system compliance will become significant. The comparison also showed the common mode subtraction method is clearer and more general in theory, as well as more applicable and efficient in practice.

Antibacterial and pH-responsive composite films for active food packaging were fabricated based on polyvinyl alcohol (PVA), cassava starch, ethyl lauroyl arginate (LAE), and mulberry anthocyanin. With the incorporation of LAE and mulberry anthocyanin, the PVA/starch blend films exhibited a less compact and more heterogeneous surface structure. The tensile strength and elongation at break of the active films were not significantly affected when the mulberry anthocyanin content was less than 20%. Moreover, the incorporation of mulberry anthocyanin effectively improved the UV barrier property of the blend films. Notably, while mulberry anthocyanin showed obvious color changes in buffer solutions with different pH values, the changes were indistinguishable for the PVA/starch/mulberry anthocyanin films. By contrast, the color changes of the PVA/starch/LAE/mulberry anthocyanin films were more noticeable, indicating the addition of LAE increased the pH sensitivity of the blend films. Furthermore, the PVA/starch/LAE/mulberry anthocyanin films efficiently inhibited the growth of both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) due to the strong antibacterial activity of LAE. According to the spoilage test, the active films containing 5% mulberry anthocyanin and 5% LAE effectively indicated and slowed down the spoilage process of dairy milk. Our results demonstrate that PVA/starch/LAE/mulberry anthocyanin films have high potential as bioactive packaging materials applied in the food industry.

Undesired surface wrinkling is a persistent issue far from being settled. Here, we report a simple light-assisted strategy to prevent surface wrinkling on azobenzene-containing polyblend films, which is based on...