Compaction behavior of cellulose polymers

Abstract

Four cellulose polymers were investigated for their compaction behavior: Ethyl cellulose (EC), cellulose acetate (CA), cellulose acetate butyrate (CAB) and cellulose acetate propionate (CAPr). The polymer powders were compressed under pressures ranging from 7.87 MPa to 47.21 MPa. The compression behavior of the four polymers was analyzed by the Kawakita, Heckel and Cooper—Eaton methods and the compression parameters were calculated. Compared to the other polymers, CAB showed higher densification due to particle rearrangement (0.54±0.04 g ml −1). The yield pressure for rearrangement calculated from the slope of the Cooper—Eaton plot (4.76±0.59 MPa) was significantly lower for CAB than for the other polymers. The yield pressure to induce plastic deformation calculated from the slope of the Heckel plot was the lowest for CAB. In the Cooper—Eaton analysis, the calculated theoretical maximum attainable relative density at infinite pressure was larger than 1 for all the polymer powders except for EC. This suggests that compression of these polymer powders cannot be explained simply by particle rearrangement and plastic deformation. CAB compacts had superior tensile strength compared to the other polymers at similar compression pressures. At pressures above 31.48 MPa the tensile strength of compacts made from CAB and CA were comparable. At equal packing fractions, however, CA compacts had superior tensile strengths. This indicates that, even though CA is less compressible than CAB, it produces stronger compacts on compression. The polymer powder properties, determined and derived, did not predict the compression parameters very accurately when used individually. However, when several of the powder properties were combined in a multiple regression equation, acceptable correlation coefficients were obtained for the predictor equations.