Cellulose Acetate Thermoplastics with High Modulus, Dimensional Stability and Anti-migration Properties by Using CA-g-PLA as Macromolecular Plasticizer

Abstract

Cellulose diacetate (CDA) can be melt-processed to produce numerous and widely-used plastic products. However, due to the high glass transition temperature (Tg) of CDA, the addition of up to 30 wt% of micromolecular plasticizers is indispensable, which significantly reduces the dimensional stability and raises safety concerns from the migration of plasticizers. In this work, a series of CDA-graft-poly(lactic acid) (CDA-g-PLA) copolymers were synthesized by ring-opening polymerization of lactide onto the hydroxyl groups of CDA. The resultant CDA-g-PLA copolymers possess adjustable degrees of substitution (DSPLA) and side chain length (DPPLA) by controlling the reaction time and feed ratio. The Tgs and thermal flow temperatures (Tfs) of CDA-g-PLA strongly depend on DPPLA, such as the Tgs decrease linearly with the increase of DPPLA. The CDA-g-PLA copolymers with the DPPLA of 3–9 can be directly processed to transparent plastics by melt processing without any external plasticizers, because of their low Tfs of 170–215 °C. More impressively, the CDA-g-PLA can act as the macromolecular plasticizer. The obtained CDA/CDA-g-PLA has higher storage modulus, flexural modulus and Young’s modulus than the commercial CDA plasticized with triethyl citrate. In addition, the CDA/CDA-g-PLA exhibits high dimensional stability and anti-migration property. During a long-term treatment at 80 °C and 60% humidity, the CDA/CDA-g-PLA can retain the initial shape. Therefore, this work not only proposes a facile method for achieving a direct thermoplastic processing of CDA, but also provides a macromolecular plasticizer for CDA to make lightweight, stable and safer biobased thermoplastics.