Abstract
Plasticized microbial (single cell) proteins (MPs) can be used to produce ductile and flexible plastic films with good oxygen barrier properties. However, as with other hydrogen-bond-forming oxygen barrier materials, like ethylene-vinyl alcohol copolymer (EVOH), they need to be protected from moisture because moisture decreases the oxygen barrier properties. Here, we solved the problem by producing three-layer laminate films that are fully biobased and biodegradable. Two different MP films (originating from a mixed microbial culture and Delftia tsuruhatensis biomass) were sandwiched between two different moisture-shielding polyhydroxyalkanoate (PHA) films (a poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) and a poly-(3-hydroxybutyrate-co-3-hydroxyhexanoate) material). The low-temperature melting features of the PHAs made them suitable for lamination through hot-pressing with the MPs. Liquid-water-resistant and UV-blocking laminates could be obtained, where the individual layers were also possible to delaminate as a possible recycling solution, where the MP layer could potentially be used as a fertilizer and the PHA mechanically recycled into similar or other products or composted. The laminates showed, in the best cases, an oxygen permeability of 2 cm(3) mm/(m(2) day atm) and a water vapor permeability below 0.1 g mm/(m(2) day). All in all, the concept is promising as a sustainable biobased alternative to today's fossil-based EVOH-laminate packaging solutions.