Cellulose diacetate-graft-poly(lactic acid)s: synthesis of wide-ranging compositions and their thermal and mechanical properties

Cellulose diacetate-graft-poly(lactic acid)s (CDA-g-PLAs) were synthesized successfully over a wide range of composition in combination of different ways of graft polymerization: a copolycondensation of lactic acid; a ring-opening copolymerization of l-lactide in dimethyl sulfoxide; and a copolymerization similar to the second, but in bulk, each initiated at residual hydroxyl positions on CDA. Differential scanning calorimetry revealed that all the copolymer products gave a single glass transition temperature Tg, which decreased sharply from 202 °C of the original CDA to ∼60 °C, close to Tg of PLA homopolymer, with an increase in molar lactyl substitution (MS) to 8 corresponding to wPLA≈67 wt% in PLA content. When the MS reached 14 (wPLA≈79 wt%) or above, PLA side-chains of the graft copolymers became crystallizable at temperatures above their respective Tgs (48–58 °C) unlike the CDA-g-PLAs of MS≤8. In tensile measurements conducted at 80–100 °C for film sheets of melt-quenched CDA-g-PLAs, it was observed that their drawability increased drastically with increasing PLA content and, at a certain wPLA of MS≥14, the elongation at rupture reached a maximum of ca. 2000%. The synergistic behaviour is discussed in correlation to the composition-dependent thermal characteristics of CDA-g-PLAs.