Biodegradable multilayer barrier films based on alginate/polyethyleneimine and biaxially oriented poly(lactic acid)

A layer-by-layer (LBL) approach was used to assemble alternating layers of sodium alginate (ALG)/polyethyleneimine (PEI) on biaxially oriented poly(lactic acid) (BOPLA) films in order to produce bio-based all-polymer thin films with low gas permeability. Increasing the depositing of ALG and PEI from 0 to 30 layers results in large thickness variations (from 0 to 3.92 μm). After 30 ALG/PEI layers are deposited, the resulting assembly has an OTR of 1.22 cm3/(m2 day atm). When multiplied by thickness, the resulting oxygen permeability (OP) is found to be less than 3.8 × 10−17 cm3 cm/cm2 s Pa, which is almost 3 orders of magnitude lower than that of uncoated BOPLA film (1.8 × 10−14 cm3 cm/cm2 s Pa). At the same time, the resulting multilayer-coated BOPLA films maintain high optical clarity and tensile properties. This unique barrier thin film has become a promising alternative to non-biodegradable synthetic food packaging materials.