# Toward Greener Multilayer Packaging Material Solutions Based on Microbial Protein and Polyhydroxyalkanoate

## TL;DR

Researchers developed a biodegradable, three-layer packaging material using microbial proteins and PHAs that blocks oxygen and water vapor while being recyclable or compostable.

## Contribution

A fully biobased and biodegradable multilayer packaging solution with low oxygen and water vapor permeability is introduced.

## Key findings

- Laminates achieved oxygen permeability of 2 cm3 mm/(m2 day atm) and water vapor permeability below 0.1 g mm/(m2 day).
- The multilayer films are recyclable or compostable, with potential for MP reuse as fertilizer and PHA mechanical recycling.
- The PHA layers effectively shield moisture, preserving the oxygen barrier properties of microbial protein films.

## 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 cm3 mm/(m2 day atm) and a water vapor permeability
below 0.1 g mm/(m2 day). All in all, the concept is promising
as a sustainable biobased alternative to today’s fossil-based
EVOH-laminate packaging solutions.