Dynamical rigidity of cellulose derivatives in melts

Abstract

The dynamic birefringence and viscoelasticity of cellulose acetate butyrate, CAB, were measured simultaneously at various temperatures covering a wide frequency region from the rubbery plateau to the glassy zone to discuss the viscoelastic segment size of cellulose. The complex Young's modulus was separated into two components, R and G, by using the modified stress-optical rule. Here, the R component originates from the reorientation of segments, whereas the G component originates from the glassy nature. From the limiting modulus at high frequencies for the R component, the molar mass of the viscoelastic segment was determined to be 3200 for CAB. This value is consistent with a previous result for cellulose acetate propionate, CAP, for which the molecular weight of the segment is 3800. These segment sizes for cellulose derivatives are larger than those for vinyl polymers and reflect the stiff chain structure of β-linked D-glucose units (~10 glucose units per segment). The number of segments per entanglement strand, Me/MS, was also estimated to be 4 and 5 for CAP and CAB, respectively. By assuming that the ester group works as a plasticizer for cellulose, Me/MS for cellulose in hypothetical melts was estimated to be ~2. © 2014 The Society of Polymer Science, Japan (SPSJ).