In the early 1900s, Cellophane, manufactured from wood pulp, transformed the packaging industry by providing a strong, moisture proof film that proved to be an effective tool in the prevention of food waste. In modern times, the drive towards a more sustainable society is initiating a resurgence of interest in cellulose-based films as they provide a renewable and biodegradable alternative to their fossil-based counterparts. This work focuses on understanding the functionality of cellulose films, with the ultimate aim of improving their mechanical and barrier properties. Tensile tests have been used to determine that an un-softened film exhibits a Young’s Modulus of 6.7 ± 0.2 GPa with a failure strain of 0.43 ± 0.02 %. With the addition of softeners, Young’s Modulus is decreased, with values ranging between 3.0 - 4.1 ± 0.2 GPa, whilst failure is doubled to 0.75 – 0.93 ± 0.08 %. This justifies the plasticisation of these films, as a superior failure strain is vital for food packaging applications. Comparatively, films derived from an agricultural waste feedstock exhibit excellent values of Young’s Modulus and failure of 3.6 ± 0.2 GPa and 0.87 ± 0.03 % respectively, making this a viable route for enhancing the sustainability of these films. Furthermore, Dynamic Mechanical Thermal Analysis and Fast-Field-Cycling NMR have been implemented, enabling an activation energy to be determined (hypothesised to be the g process in cellulose) of ~30 kJ/mol which we hope to associate with a measured peak in the impact energy at a strain rate of 0.1 s<sup>-1</sup>. The end goal is to establish links between molecular relaxations and mechanical behaviours to provide a comprehensive picture of what drives the properties of these cellulose films and how we might modify these to optimise performance.

Understanding the links between microscopic molecular relaxations and macroscopic mechanical properties in cellulose films

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ACS Fall 2022

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