A Tuneable Switch for Controlling Environmental Degradation of Bioplastics: Addition of Isothiazolinone to Polyhydroxyalkanoates

Abstract

Controlling the environmental degradation of polyhydroxybutyrate (PHB) and polyhydroxyvalerate (P(HB-co-HV)) bioplastics would expand the range of their potential applications. Combining PHB and P(HB-co-HV) films with the anti-fouling agent 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOI, <10% w/w) restricted microbial colonisation in soil, but did not significantly affect melting temperature or the tensile strength of films. DCOI films showed reduced biofouling and postponed the onset of weight loss by up to 100 days, a 10-fold increase compared to unmodified films where the microbial coverage was significant. In addition, the rate of PHA-DCOI weight loss, post-onset, reduced by about 150%; in contrast a recorded weight loss of only 0.05% per day for P(HB-co-HV) with a 10% DCOI loading was observed. This is in stark contrast to the unmodified PHB film, where a recorded weight loss of only 0.75% per day was made. The ‘switch’ that initiates film weight loss, and its subsequent reduced rate, depended on the DCOI loading to control biofouling. The control of biofouling and environmental degradation for these DCOI modified bioplastics increases their potential use in biodegradable applications.

Review of recent advances in the biodegradability of polyhydroxyalkanoate (PHA) bioplastics and their composites

“…For example, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOI) is an anti-fouling agent, which is known to inhibit the onset of PHB and PHBV biodegradation according to ASTM D5988. 196 The chain extender Joncryl ADR-4368-CS had a similar inhibitory effect on the onset of PHA biodegradation, despite it being reported to reduce the crystallinity of PHAs, which should improve the biodegradation 197 at loadings of 5%, the Joncryl chain extender reduced the extent of soil biodegradation from 70 to 22% in 340 days following the ASTM D5988-03 protocol. The inhibitory effect is also seen under composting conditions and marine conditions at 0.2 and 5% loadings, negatively impacting the biodegradation start time, rate and extent.…”

Organocatalyzed Synthesis and Degradation of Functionalized Poly(4-allyloxymethyl-β-propiolactone)s

“…Moreover, as estimated, the complete degradation of the films in a soil mixture at 50 °C would take approximately 453 days, assuming the zeroth-order kinetics for the degradation. For comparison, it has been previously demonstrated that the PHB films were degraded with 95% mass loss after 35 days in field soil at 28 °C with 50% moisture and 58% mass loss after 160 days in sea. , …”

Biodegradation of Polyhydroxyalkanoates in Natural Soils

“…Environmental degradation of the bioplastics samples was conducted in "mature soil" under controlled conditions (Woolnough et al, 2013).…”