Sources of Glass Transition Temperature Variation in Poly(methyl methacrylate)/Cellulose Composites
Abstract
Variation in glass transition temperature (Tg) measured by differential scanning calorimetry (DSC) is addressed, specifically for composites of poly(methyl methacrylate) (PMMA) and freeze-dried cellulose nanocrystals; mortar-and-pestle grinding use for creating solventless PMMA/cellulose nanocomposites is evaluated. Experimentally, solvent-containing and solventless PMMA and PMMA/cellulose composite samples (prepared using mortar-and-pestle grinding, melt-pressing, and acetone addition) were tested by DSC in hermetically-sealed pans using one of two maximum first heating scan temperatures; post-DSC samples were photographed. Mortar-and-pestle-ground cellulose was imaged by Field Emission Scanning Electron Microscopy (FE-SEM). Post-DSC samples had different shapes, some corresponding to greater increases in Tg from first to second heating, associated with Tg variation. A shape classification is proposed. Second heating Tg was affected by first heating peak temperature in solvent-containing samples. FE-SEM showed only low aspect ratio microscale cellulose particles. Visual analysis of samples after DSC testing is recommended; mortar-and-pestle grinding is found unsuitable for solventless PMMA/cellulose nanocomposite preparation.