The glass transition temperature (Tg) is the thermal transition at which point a polymer goes from a firm glassy state to a more pliable form. Like all polymers, the glass transition is a property which is key to understanding the characteristics and performance of cellulose. Cellulose is the world’s most abundant biopolymer and it is found in its purest form in cotton. With the support of the Cotton Research and Development Corporation (CRDC), this work was undertaken to improve the understanding of the glass transition behaviour of cotton and regenerated cellulose. This knowledge is important for identifying optimum temperature and moisture conditions to manage current post-harvest cotton processing methods, nominally ginning but also spinning mill processing, and in turn improve the productivity and performance of the Australian cotton industry. Successful measurement of a reduction in modulus in DMA; calculation of Tg at the point of freezing, using DSC to measure the colligative effect of cotton in water; and measurement of mass change with the addition of water using DVS, have all indicated that cellulose does in fact go through a glass transition, and is measureable. Considered together, the results are strongly in favour of the existence of a glass transition in cellulose.

The glass transition temperature is a fundamental property of all amorphous and semi-crystalline polymers, including cotton and other celluloses. At this temperature many properties, such as modulus, heat capacity, density, refractive index, dielectric constant, thermal expansion and rate of diffusion show a distinct change. It is thus important to be able to measure the glass transition temperature, however this has proved challenging for cotton due mainly to its high level of crystallinity. This chapter outlines the relationship between the chemical structure and the glass transition temperature of polymers in general as well as the effect of physical ageing and plasticization. Models to predict the effect of plasticization are also discussed. The moisture uptake of cotton and the attempts to measure the glass transition temperature of cotton and other celluloses, in both the dry state and as a function of moisture content, are detailed. Dry cotton is estimated to have a glass transition temperature of 220°C, with the value dropping to below zero when saturated with water. Cotton is the purest natural form of the biopolymer cellulose. It is important to understand the glass transition behaviour of cellulose and utilise this knowledge to optimise temperature and moisture levels during processing. Doing so will reduce the vulnerability of fibres to damage and improve overall fibre, yarn and fabric quality.