Continuous cellulose fiber-reinforced cellulose ester composites III. Commercial matrix and fiber options

Thermoplastic composites were prepared using two continuous regenerated cellulose fiber types, rayon and lyocell, and with several different commercially-available thermoplastic cellulose esters as matrix. Matrix options included cellulose acetate propionate (CAP), and several cellulose acetate butyrates (CAB) with different butyryl content, having different molecular weights and different methods of plasticization (adipates and very low molecular weight cellulose ester fractions). Choice of cellulose ester type was generally found to have little or no effect on mechanical properties. A significant effect, however, was revealed for fiber type. The lyocell-based composites thereby were reflective of the greater stiffness of a fiber produced from anisotropic solution state. Their modulus consistently exceeded 20 GPa whereas the rayon fiber-based composites had moduli between 6 and 8 GPa. The latter, however, possessed failure strains that were 3 to 4 times greater than their stiffer counterparts. Comparable performance was achieved using unsized or sized (with a textile-type size) lyocell fibers; or by using a prepregging method involving single or double coating with a matrix solution. Cross-ply construction (3 plies) resulted in a loss of between 3 and 50% of strength and stiffness properties as compared to corresponding unidirectional composites. Fiber type, fiber content, and thermal flow characteristics seemed to be the most important parameters determining composite mechanical properties.