Plasticization Mechanisms in Biodegradable Polymers

Biodegradable polymers such as polylactic acid (PLA), polyhydroxyalkanoates (PHAs) and poly(ε-caprolactone) (PCL) offer sustainable alternatives to conventional plastics but often suffer from brittleness and limited chain mobility. Plasticisation is employed to tailor their mechanical and thermal properties by incorporating low-molecular-weight additives, oligomeric or polymeric plasticisers and by chemical modification. These additives disrupt intermolecular forces through hydrogen bonding, dipolar interactions or steric effects, increasing free volume and facilitating chain movement. Approaches range from blending with flexible copolymers or block copolymers, adding biobased low-density molecules such as epoxidised vegetable oils or citrate esters, to reactive mixing to graft plasticisers onto the polymer backbone or side chains. Control of compatibility and dispersion is crucial; insufficient miscibility leads to phase separation, compromising transparency, mechanical strength and barrier properties. Optimising plasticiser selection and loading can lower glass transition temperatures, enhance elongation at break and tailor crystallisation kinetics without sacrificing biodegradability. These strategies underpin applications from flexible packaging and agricultural films to bioresorbable medical devices, contributing to reduced environmental impact and fostering circular economies.

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Experimental determinations of Hansen solubility parameters for a range of biobased polyesters have provided predictive insight into plasticiser–polymer compatibility. A lignin-based plasticiser demonstrated excellent miscibility with both poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and PLA, yielding a linear decrease in glass transition temperature up to high plasticiser loadings, whereas a less-compatible adipate plasticiser induced phase separation at minimal concentrations. A comprehensive review of PLA plasticisation mechanisms categorises strategies into blending with copolymers, introduction of oligomeric and low-molecular-weight plasticisers, and reactive structural modification, concluding that copolymer additives obtained via in-situ reactive mixing offer optimal performance and processing simplicity. Development of flexible PLA films plasticised with epoxidised soybean oil methyl ester achieved elongations approaching 800 per cent, enabled low-temperature extrusion to avoid polymer degradation, and delivered enhanced thermomechanical and barrier properties with minimal plasticiser migration, extending applications in sustainable food packaging.

Plasticization Mechanisms in Biodegradable Polymers publication trend

The graph below shows the total number of articles in plasticization mechanisms in biodegradable polymers across all publications each year (not limited to Nature Index journals).

Technical terms

Glass transition temperature (Tg): The temperature at which a polymer transitions from a rigid glassy state to a more flexible rubbery state.

Free volume: The unoccupied space within a polymer matrix that permits molecular movement and influences flexibility.

Miscibility: The degree to which two components form a homogeneous phase without phase separation.

Phase separation: The formation of distinct domains within a polymer blend when components are incompatible.

Hansen solubility parameter: A numerical estimate of solvent–polymer affinity based on dispersive, polar and hydrogen-bonding forces.

Reactive mixing: A processing technique where chemical reactions occur during blending to graft or bond additives onto polymer chains.

References

1. Experimentally Determined Hansen Solubility Parameters of Biobased and Biodegradable Polyesters. ACS Sustainable Chemistry & Engineering (2024).
2. Recent Approaches to the Plasticization of Poly(lactic Acid) (PLA) (A Review). Polymers (2023).
3. Epoxidized Vegetable Oils Plasticized Poly(lactic acid) Biocomposites: Mechanical, Thermal and Morphology Properties. Molecules (2014).
4. Super Tough Polylactic Acid Plasticized with Epoxidized Soybean Oil Methyl Ester for Flexible Food Packaging. ACS Applied Polymer Materials (2021).