Packaging from Nature: Understanding the Mechanical and Molecular Properties of Cellulosic Films

Society is living through a time-critical shift towards a more sustainable and circular economy. The daunting question plagues the passions of this generation of scientists: How can we sustain and enable a developed lifestyle worldwide to our growing population with finite resources? Over the last century; synthetic plastics, derived from fossil-based resources, have dominated the field of material sciences, providing innovative and functional solutions for a wide range of applications and advancing our lifestyles immeasurably. However, due to the limited nature of this resource, coupled with the fact that many synthetic polymers are non-biodegradable, there is an imperative drive for a more sustainable alternative. In fact, we are rapidly approaching the absolute threshold of plastic consumption that our planet can sustain, with the packaging industry alone contributing over one third of global plastic production, with a staggering 141 million tons of plastic packaging destined for landfill produced annually [1]. Clearly, it is vital that this industry’s contribution to global warming and plastic pollution is addressed. As such, the food-packaging industry is seeing a resurgence in the popularity of biopolymer-based products. In particular, cellulose-based films, manufactured using the Viscose Method from sustainable forests are becoming a vital competitor to their synthetic counterparts. First commercialised in the 1930s, the Viscose Method is used to extract cellulose from wood or plant pulp and covert it to functional films that are both biodegradable and renewable. Over the years, this technology has been optimised to provide high-quality food packaging with competitive mechanical and barrier properties. One of these developments, was the addition of plasticisers in order to improve ductility, an essential property in application. The Futamura Group are the World’s largest producers of these cellulose films, and currently employ a range of softeners and additives to improve performance. With mounting pressures to reach global sustainability goals, it is important to investigate the efficacy of this softener package and ascertain how it could be altered and substituted for cheaper, greener alternatives. As such, this thesis presents findings regarding the function of a range of established and potential softeners in both commercial and lab-softened films. We investigate the fluctuations of mechanical and molecular properties of films with varying concentrations of both individual and combination softeners packages, as well as an inclusion of a hemicellulose blend. To assess mechanical performance, a combination of tensile and strain-dependent impact testing, was employed. Molecular behaviour has been hypothesised through the application of Dynamic Mechanical Thermal Analysis across a range of frequencies and temperatures to identify key molecular relaxations of cellulose molecules under the influence of various softeners. With this work, we have embarked on the beginning steps of a large scale commercial sustainability project that will see the revolution of plant-based films. This work will alleviate the limitations of relying on costly plasticisers that limit these films biodegradability, making cellulosic films the sustainable packaging of the future.