Separable, Deconstructable, Multilayer Biopolyester Films

Multilayer films can prove challenging to recycle—UMass researchers are looking for a solution.

Increasing sustainability for plastic packaging is at the forefront of many manufacturers’ minds. Multilayer films make effective food packaging, protecting contents from damage and spoilage. A drawback of these materials is that they are difficult to recycle. They are often composed of fused polymers, making sortation challenging or impossible. In plastic recycling, preserving feedstock quality is vital; the complexity of materials can impede this. Redesigning existing materials could be key for moving closer to a circular plastics economy.

You can also read: Next-Gen Packaging: Edible and Protein-Based Films.

Sustainable multilayered films must have good barrier properties and be dissolvable and degradable to eliminate waste. Researchers at UMass approached this dichotomy by sandwiching poly(vinyl alcohol) (PVOH) between two layers of biopolyester. PVOH has an excellent oxygen barrier, with properties such as O2 permeability determined by the degree of hydroxylation. Since polyesters have poor barrier properties but can be enzymatically degraded, this combination offers a solution that meets both criteria.

Optimizing the Film’s Recycling Process

Hydrolysis of acetate groups in poly(vinyl acetate) can alter the characteristics of PVOH. Thus, different grades of PVOH can have various levels of water solubility. Residual acetate groups also disrupt inter/intra-molecular hydrogen bonding, which eases dissolution. Higher water solubility means ease of dissolution at the material’s end-of-life.

Enzyme deconstruction breaks down the biopolyester outer layers of the film, and choosing the right enzyme eases this process. Researchers found that thermophilic, hydrophobic esterases, such as PETase, MHETase, and leaf-branch compost cutinase, were effective. Like PVOH, hydrolysis rate can affect biopolyesters, allowing researchers to fine-tune the material for better recyclability.

Biopolyester Films for the Future

Researchers extruded the 5-layer film, comprising of polybutylene adipate terephthalate (PBAT, biopolyester), PVOH, and a 50:50 blend of both. The gauge of this film was 3.9 mil (0.0039 inches). The researchers found that the film had a lower oxygen transmission rate (OTR) when co-extruded. Additionally, larger film particles dissolved faster than smaller particles in 70 °C water.

Redesigning valuable materials, such as multilayer films, will be vital as the plastics industry moves towards a more sustainable future. As researchers develop new materials, designing for less complexity can promote a circular economy. Additionally, focusing on issues such as limiting byproducts, toxicity, and embodied process energy can progress sustainability in manufacturing. Thinking about sustainability means considering new ways for engineering to help meet societal needs, in and outside the lab.