Plasticization of poly (L-lactide) bioplastic films with poly (propylene glycol)-b-oligo (-caprolactone)

Liquid -caprolactone (CL) oligomers were synthesized by a ring-opening reaction of CL using a propylene glycol (PPG) as the initiator for use as new plasticizers of poly (L-lactide) (PLA) films. PPG-CL oligomers containing two (PPG-2CL) and four (PPG-4CL) units of CL at both PPG end-chains were prepared. The PLA/oligomer blend films were prepared by solution blending before film casting. The tiny pools of the liquid plasticizer droplets were observed throughout the PLA film matrices, which indicated that a phase separation had occurred. The sizes of the plasticizer droplets increased as did the plasticizer blend ratio. The phase separations were in the order of PPG>PPG-4CL>PPG-2CL. The plasticizer blending slightly decreased the glass transition and crystallization temperatures of the PLA films. The crystallinities of the PLA films increased with the PPG-CL blend ratio but did not increase with the PPG. The PPG-CL blending improved the flexibility of the PLA films more than the PPG blending. The PPG-CL oligomers could be used as novel plasticizers for PLA films.