# Compostable Multilayer Films with Tailored Gas Barrier and Biodegradation

## TL;DR

This study creates compostable multilayer films using PLA and cassava starch blends, balancing gas barrier properties and biodegradation rates for sustainable packaging.

## Contribution

A novel reactive blending method is introduced to create multilayer films with tailored mechanical and biodegradation properties.

## Key findings

- Reactive blending of PLA and TPCS significantly reduced tensile strength but increased elongation at break.
- Multilayer films tripled tensile strength compared to monolayers.
- Gly-plasticized TPCS reduced oxygen permeability but increased water vapor transmission.

## Abstract

This study investigates
the barrier and biodegradation performance
of reactive blends (reactive melt mixing inside the extruder) of poly­(lactic
acid) [PLA] and thermoplastic cassava starch (TPCS). Two PLA-g-TPCS, plasticized with either glycerol (Gly) or poly­(ethylene
glycol) (PEG), were prepared by twin-screw extrusion and processed
into multilayer films through cast coextrusion. The films were characterized
to assess structural, mechanical, thermal, optical, barrier, and surface
properties, with emphasis on the effects of plasticizers. The biodegradation
of these multilayer films was evaluated over 90 days using a direct-measurement
respirometer system, tracking the evolution of CO2 in compost
under thermophilic conditions. Fourier transform infrared spectroscopy
(FTIR) analysis confirmed the successful grafting between PLA and
TPCS. Reactive blending of PLA with TPCS significantly reduced tensile
strength (TS) and Young’s modulus (YM) by over 50%, while elongation
at break (EAB) increased by 70–80%. Incorporating the PLA-g-TPCS layer into a multilayer design tripled tensile strength
and modulus compared to monolayers. TPCS enhanced chain mobility,
lowering glass transition and melting temperatures. Gly-plasticized
TPCS reduced oxygen permeability by 50%, whereas both plasticizers
increased water vapor transmission and surface hydrophilicity. The
hydrophilic TPCS accelerated abiotic degradation (hydrolysis of ester
bonds due to humidity and temperature before biodegradation) of PLA
under thermophilic conditions. Conversely, the PLA outer layers slowed
the overall biodegradation rate in multilayer films, influenced significantly
by the type of plasticizer used. Overall, PLA-g-TPCS
multilayer films combine composability (in industrial facilities and
possibly also in home composting environments) with functional performance,
offering promise for sustainable packaging.