BACKGROUND: Despite the recognition that microbial biofilms play a role in environmental degradation of bioplastics, few studies investigate the relationship between bioplastic biodegradation and microbial colonisation. We have developed protocols based on a combination of confocal laser scanning microscopy and contact angle goniometry to qualitatively and quantitatively map surface changes due to biofilm formation and biopolymer degradation of solvent cast poly(3‐hydroxyalkanoate) films in an accelerated in vitro biodegradation system.RESULTS: A significant regression relationship between biofilm formation and polymer biodegradation (R2 = 0.96) was primarily conducted by cells loosely attached to the film surfaces (R2 = 0.95), rather than the strongly attached biofilm (R2 = 0.78). During biodegradation the surface rugosity of poly(3‐hydroxybutyrate) and poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] increased by factors of 1.5 and 1.76, respectively. In contrast, poly(3‐hydroxyoctanoate) films showed little microbial attachment, negligible weight loss and insignificant changes in surface rugosity.CONCLUSION: A statistically significant link is established between polymer weight loss and biofilm formation. Our results suggest that this degradation is primarily conducted by cells loosely attached to the polymer rather than those strongly attached. Biofilm formation and its type are dependent upon numerous factors; the flat undifferentiated biofilms observed in this study produce a gradual increase in surface rugosity, observed as an increase in waviness. Copyright © 2008 Society of Chemical Industry

Biopolymers derived from natural resources are potential alternatives to recalcitrant synthetic plastics; however, studies investigating the degradability of these biopolymers in natural environments are relatively few. This study compares the environmental degradation of polymers described as ‘green plastics’ in garden soil in terms of weight loss, topographical changes and biofilm attachment. Poly(3‐hydroxybutyrate) (PHB) and poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] (P(HB‐co‐8HV)), (copolymer containing 8 mol% HV) films degraded rapidly, losing 50% of their initial weight in 50 days. In contrast, after burial for 380 days, the medium chain length polyhydroxyoctanoate (PHO) lost 60% of its weight, poly(D,L‐lactide) (PDLL) 18% and poly[(D,L‐lactide)‐co‐glycolide] (PDLLG) 35%. Polystyrene (PS) and ethyl cellulose (EC) showed no significant degradation. Both weight loss and biofouling occurred in the following sequence: P(HB‐co‐8HV) = PHB > PHO > PDLLG > PDLL > PS = EC. The surface rugosity and surface areas of PHB and P(HB‐co‐8HV) increased three‐ and twofold, respectively, during degradation, indicating surface erosion. The surface rugosity of PHO increased twofold and the surface area increased by 25%. This in situ study demonstrates a quantifiable relationship between biofilm attachment, surface rugosity and polymer degradation. PHB and P(HB‐co‐8HV) showed greater biofouling and increased surface rugosity, and degraded significantly faster than the other polymers studied. Copyright © 2009 Society of Chemical Industry

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.