Release kinetics of alpha-tocopherol and resveratrol from poly(lactic acid) and poly(lactic acid)/starch blends

The aim of this study was to investigate the use of poly(L-lactic acid) (PLLA) as active functional membranes for application in food and pharmaceutical packaging system.;PLLA films containing various concentrations of &agr;-tocopherol (&agr;-TOC) and resveratrol were fabricated, and the influence of the antioxidants on the optical, thermal, mechanical, rheological, and physical properties of PLLA films were assessed. PLLA films with added &agr;-TOC and resveratrol showed a yellowish brown color and the light transmission properties were influenced by the presence of the antioxidants. The glass transition ( Tg) and melting (Tm) temperatures were significantly reduced with the addition of antioxidants while thermal stability was enhanced. The concentrations of the two antioxidants played a critical role in the mechanical and thermo-mechanical properties of PLLA films. The melt viscosity of the PLLA films with added antioxidants was substantially higher than that of neat PLLA films. Second, maleic anhydride (MAH) was grafted onto PLLA resin in the presence of dicumyl peroxide (DCP) as a radical initiator. The effect of the MAH and DCP concentrations on the grafting and the physical and mechanical properties of PLLA films were investigated. Introduction of MAH reduced the gel content and increased grafting yield. The T g and crystallinity (Xc) significantly decreased on addition of MAH. The thermal decomposition of the PLLA films was decreased with addition of MAH while the mechanical properties were almost unchanged. Third, PLLA/starch blends were prepared by a one step reactive compatibilization process. The effect of the grafting reaction on the physical, mechanical, and morphological properties of PLLA/starch blend was assessed. Little effect of the maleation reaction on the thermal stability of the PLLA/starch blends was observed. PLLA/starch blends with grafted MAH showed significant decrease of Tg due to the plasticizing effect of MAH. Reactive compatibilization resulted in increase of storage modulus, E' of PLLA/starch blends indicating that compatibility between two phases increased by reactive compatibilizer. Good interfacial adhesion between PLLA and starch was found in the blends. Fourth, PLLA/starch blends with various concentrations of &agr;-TOC and resveratrol were fabricated, and the effects of two antioxidants on the optical (color), thermal and mechanical properties of PLLA/starch blends were assessed. PLLA/starch blend films with &agr;-TOC and resveratrol showed a yellowish color influenced by the combined effect of the white starch and brown antioxidants. The Tg and Tm were significantly reduced with the addition of antioxidants while enhanced thermal stability was observed. The release of resveratrol from PLLA and PLLA/starch blend films into ethanol followed Fickian behavior with D values between 0.073 ∼ 0.54 x 10-10 cm2·s-1, 0.90 ∼ 3.44 x 10-10 cm2·s -1, and 24.8 ∼ 74.3 x 10-10 cm2·s-1 for PLLA films; and 1.42 ∼ 6.93 x 10-10 cm2·s -1, 4.16 ∼ 22.3 x 10-10 cm 2·s-1, and 40.1 ∼ 309.0 x 10 -10 cm2·s-1 for PLLA/starch films, respectively at 13, 23, 43 °C. D values of &agr;-TOC were 0.47 ∼ 4.0 x 10-11 cm 2·s-1, 5.67 ∼ 13 x 10 -11 cm2·s-1, and 89.0 ∼ 118.0 x 10-11 cm2·s -1 for PLLA films; 0.70 ∼ 6.83 x 10-11 cm2·s-1, 4.10 ∼ 24.2 x 10-11 cm2·s-1 , and 123.0 ∼ 282.0 x 10-11 cm 2·s-1 for PLLA/starch films, respectively at 13, 23, 43 °C.