Construction of gas permeable channel in poly(l-lactic acid) membrane and its control of the micro atmosphere in okra packaging.

An atmosphere within a package affects the metabolic process of food and the microbial growth of fresh products and has a vital role in preserving food. It depends on the membrane's specific gas permeability and selectivity to generate a desirable atmosphere for storage. In this study, triblock poly(l-lactic acid‑d-ɛ-caprolactone) (PLDC) copolymers and three-arm poly(l-lactic acid-g-ɛ-caprolactone) (PLGC) star copolymers were synthesized, in which a microphase-separated morphology of sea-island structure was established in PLGC membrane as a gas "fast permeation channel" for regulating CO and O permeability and CO/O selectivity. AFM observation revealed different well-defined micro phase-separated structures of PLGC with size ranges of 200- 300 nm. Comparing PLGC membrane with PLLA, CO and O transmission rates increased by 416.9 % and 132.7 %, while HO transport rates increased by 245.6 %. Mechanical testing shows that the PLGC membrane exhibits 40.8-fold elongation at break compared to PLLA, showing excellent flexibility. Moreover, okra's equilibrium-modified atmosphere packaging was designed based on a theoretically derived model. Preservation results suggested that the PLGC packaging membrane could generate an ideal high 8.7- 9.2 % CO and low 2.3- 2.7 % O atmosphere for okra preservation, delaying the discoloring and rotting of okra.