Polymer Structure
Microorganisms accumulate intracellular polyester storage compounds that can be extracted and processed into biodegradable thermoplastic barrier coatings. Extracted polyhydroxybutyrate, commonly abbreviated as PHB, functions as a fully bio-based polymer derived from bacterial fermentation of sugar or starch feedstocks. This biopolymer degrades naturally in soil and marine environments without generating persistent microplastic residues.
Barrier Performance
Application of PHB onto paperboard substrates produces water vapor and oil resistant barrier layers suitable for compostable packaging applications. Crystalline domain formation within the biopolymer matrix blocks liquid moisture penetration, protecting cellulose fibers from structural softening. Coating weight selection influences barrier effectiveness, where heavier coat weights eliminate surface pinholes across textured board surfaces.
Extrusion coating or dispersion coating methods apply the polymer directly onto unbleached kraft papers, creating repulpable materials that disintegrate during commercial composting cycles.
Processing Limit
High thermal brittleness and narrow melt processing windows complicate high speed extrusions onto paperboard stock during converting operations. Thermal degradation occurs rapidly near the melting temperature, reducing molecular weight and causing barrier pinholes during web cooling. Incorporating plasticizers or copolymerizing with hydroxyvalerate improves polymer flexibility, though additive selection must preserve final compostability certification compliance.
Performance limits apply strictly to thermal stability during converting without altering environmental breakdown kinetics.
