Incorporation of l-lactide random copolymers with Japanese cypress oil (α-pinene) using supercritical carbon dioxide

Abstract

This study involved the incorporation of useful compounds, such as repellents and antibacterial agents, at high concentrations in L-lactide (L-LA) random copolymers. The amount of α-pinene released in gas from the copolymers was also evaluated. Outstanding controlled release properties were developed using random copolymers of L-lactide (L-LA) with γ-valerolactone (VL), ε-caprolactone (CL), tetramethylene carbonate (TEMC) (1,3-dioxepan-2-one), and 1,5-dioxepan-2-one (DXO) using tin 2-ethyl-hexanoate [Sn(oct)₂] as a catalyst at 150 °C for 24 h without solvent. Preparation of controlled release materials was accomplished using α-pinene from Japanese cypress oil and synthetic random copolymers of L-LA with cyclic monomers as base materials under supercritical carbon dioxide (scCO₂). Poly(L-LA-ran-VL), poly(L-LA-ran-CL), poly(L-LA-ran-TEMC), and poly(L-LA-ran-DXO), which have lower T_m and ΔH_m values than poly(L-LA) were used for the impregnation experiments. The oil content of the copolymers was greater than that in poly(L-LA). The content of oil into poly(L-LA-ran-TEMC) (80 : 20) was 8.1%, 2.1-fold greater than that in poly(L-LA) (Lacea H-100) (H-100), and 1.5-fold greater than that in poly(L-LA) (Lacea H-440) (H-440). Although a previous study showed that 3.2% D-limonene could be incorporated into poly(L-LA-ran-CL) (85 : 15) under the same conditions, results of this experiment showed that 5.8% and 6.6% oil could be incorporated into poly(L-LA-ran-CL) (81 : 19 or 91 : 9), respectively. Results from controlled release experiments demonstrated that the oil content in the polymer decreased upon copolymer degradation for all copolymers. In gas release tests, polymers H-440 and poly(L-LA-ran-VL) (85 : 15) released gas upon hydrolysis. Although the weight loss of H-440 was only 9% at 56 days, the calculated loss of oil in H-440 was 28%.