# Enzymatic and environmental degradation of natural rubber–PHBV polymer blends

## TL;DR

This paper studies how natural rubber blended with PHBV degrades using enzymes and environmental factors, showing a way to create sustainable biodegradable materials.

## Contribution

The study introduces a synergistic two-step enzymatic process to degrade PHB/PHBV–NR blends and evaluates environmental degradation under realistic conditions.

## Key findings

- PHB/PHBV fractions in blends degrade efficiently with depolymerases, while natural rubber remains resistant.
- Recombinant latex-clearing protein from Streptomyces sp. K30 significantly degrades pretreated PHB–NR blends.
- Seawater and estuarine mud experiments show progressive degradation and surface erosion in PHB-rich blends.

## Abstract

Bio-based and biodegradable polymer blends are promising alternatives to conventional plastics, yet their environmental fate remains poorly understood. Here, we investigated the enzymatic and environmental degradation of natural rubber (NR) blended with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) using recombinant enzymes produced in Escherichia coli and Komagataella phaffii. Three PHB depolymerases from Pseudomonas lemoignei (PlDP), Acidovorax sp TP4 (AsDP), and Ralstonia pickettii (RpDP) were isolated and analyzed for thermal and pH stability. All depolymerases efficiently degraded the PHB/PHBV fraction in films and blends, whereas NR was largely resistant to degradation. To enhance rubber degradation, the latex-clearing protein from Streptomyces sp. K30 (Lcp_Ssp) was produced recombinantly and applied. It showed significant activity on NR substrates, including pretreated PHB–NR blends, demonstrating a synergistic two-step enzymatic process. Scanning electron microscopy and weight-loss assays confirmed selective PHB/PHBV degradation. Separate seawater pH–Stat degradation experiments under environmentally relevant conditions with four hydrolytic enzymes (protease, lipase, esterase, and PlDP), showed highest activity of PlDP on PHB/PHBV–NR blends. Additionally, incubation in estuarine mud revealed progressive surface erosion and pore formation, particularly in PHB-rich blends, highlighting the role of PHB/PHBV in facilitating overall biodegradation. This comprehensive assessment of enzymatic and environmental degradation processes of PHB/PHBV–NR composites provides information to design fully bio-based, degradable polymer materials for sustainable applications.