ELASTIC-MODULUS OF THE CRYSTALLINE REGIONS OF CELLULOSE TRIESTERS

Elastic moduli of the crystalline regions of cellulose triesters in th e direction both parallel E(l) and perpendicular E(t) to the chain axi s are measured by x-ray diffraction. E(l) values for cellulose trieste rs are as follows: cellulose triacetate (CTA), 33.2 GPa; cellulose tri propionate (CTP), 21.6 GPa; cellulose tributyrate (CTB), 17.6 GPa; cel lulose trivalerate (CTV), 17.9 GPa. These are very small compared with that of cellulose I (134 GPa) and resemble each other despite the fac t that the skeletal structure of CTP (3(2) helix) is much different fr om those of other cellulose triesters (2-fold helix). The small E(l) v alues for cellulose triesters can be explained by both the large cross -sectional area of one molecule in the crystal lattice and the lack in intramolecular hydrogen bonds. E(t) values for cellulose triesters ar e as follows: CTA (310), 2.8 GPa; CTP (110), 1.4 GPa; (020), 2.1 GPa; (120), 2.2 GPa; CTB (110), 1.1 GPa. These are one of the smallest E(t) values already reported, and decrease with increasing the length of t he side chain. Intermolecular interaction is considered to decrease wi th the length of acyl groups. The large E(t) value in the b direction of CTP reflects the dense packing of the chains in the crystal lattice . (C) 1995 John Wiley & Sons, Inc.