Plasticization of dialcohol cellulose and effect on the thermomechanical properties

Abstract

Cellulosic materials are considered good alternatives to conventional plastics in packaging applications, as they are renewable, bio-based and biodegradable, having good mechanical properties at relatively low densities. However, when considering production methods, cellulose has limitations. The possibility of exploiting the production methods of conventional plastics, such as melt processing, is precluded because cellulose decomposes before reaching melting. Lowering the glass transition, partial modification of cellulose pulp to dialcohol cellulose (DAC) fibres enabled a melt processability window between the glass transition and decomposition temperatures. Water was successfully used as an aid for DAC melt processing, but the final material properties are strongly influenced by the residual moisture content, which varies depending on the environmental conditions (temperature and relative humidity). This work aims to explore the addition of glycerol, a less volatile green plasticizer, to control the processability and physical properties of DAC-based materials. Materials containing different moisture and glycerol contents were melt compounded and the effect on the melt processability was evaluated by the in-line melt viscosity during the process. The effect of different initial moisture and glycerol contents on thermal decomposition, thermal transitions, thermomechanical and mechanical properties and surface morphology has been investigated. The addition of glycerol allows for improved melt processability, decreased elasticity and enhanced deformability up to a maximum glycerol content. An excess of glycerol leads instead to a neat fall in mechanical properties and thermal stability. The possibility of post-industrial mechanical recycling was also demonstrated and the effect on the thermal decomposition and mechanical properties assessed.