Development of bio-composites with novel characteristics through enzymatic grafting

Enzymatic grafting of biopolymers has recently been the focus of green chemistry technologies due to the growing environmental concerns, and subsequent legal restrictions. Over the last decade, research covering various applications of enzymes like lipases and laccases has been increased rapidly, particularly in the field of polymer science, to graft multi-functional polymers. In this context, a series of bio-composites e.g. poly3-hydroxybutyrate [P(3HB)]grafted ethyl cellulose (EC) and bacterial cellulose (BC) [i.e., P(3HB)-g-EC/BC] and keratin-g-EC bio-composites were successfully synthesised by introducing enzymebased grafting where lipase and laccase were used as model bio-catalysts. Furthermore, various natural phenols e.g., caffeic acid (CA), gallic acid (GA), p-4-hydroxybenzoic acid (HBA), and thymol (T) were grafted onto the newly developed P(3HB)-EC and keratin-EC-based composites under laccase-assisted environment. Subsequently, the resulting bio-composites were removed from their respective casting surfaces under ambient environment and characterised using different analytical and imaging techniques. This project shows improvement in the thermo-mechanical properties of the biocomposites as compared to the individual components. The tensile strength, elongation at break point, and Young’s modulus values of the bio-composites reached very high levels in comparison to the films prepared with untreated P(3HB) and keratin that were too fragile to be measured for any of the above mentioned characteristics. Morphological analysis of the newly developed bio-composites surfaces through SEM showed a uniform distribution of the P(3HB) and keratin within the backbone polymer(EC). Interestingly, untreated P(3HB) was hydrophobic in nature and after lipase treatment P(3HB) and P(3HB)-EC-based graft composites attained a higher level of hydrophilicity. The phenol grafted bio-composites were critically evaluated for their antibacterial and biocompatibility features, as well as their degradability in a soil. In particular, the results of the antibacterial evaluation indicated that 20CA-g-P(3HB)-EC, 15GA-g-P(3HB)-EC, 15HBA-g-P(3HB)-EC, 15T-g-P(3HB)-EC, 15CA-g-keratin-EC, 15GAg-keratin-EC, 10HBA-g-keratin-EC and 20T-g-keratin-EC exerted strong bactericidal and bacteriostatic activity against Gram+ bacteria Bacillus subtilis NCTC 3610 and Staphylococcus aureus NCTC 6571 and Gram- bacteria Escherichia coli NCTC 10418 and Pseudomonas aeruginosa NCTC 10662 strains, respectively. This study shows further that at various phenolic concentrations the newly synthesised bio-composites remained cytocompatible with human keratinocyte-like HaCaT skin cells, as 100% cell viability was recorded after 5 days of incubation. From the degradation point of view,an increase in the degradation rate was recorded during the soil burial analyses. This study provides novel and additional knowledge that encourage greater utilisation of biopolymers in the development of bio-composites with novel and sophisticated characteristics for potential applications.

Level dc:type.qualificationlevel

PhD thesis

Grantor dc:publisher.institution

University of Westminster

Year dc:date.issued

2015

Author dc:creator

• Iqbal, H.M.N.

Identifier

oai:westminsterresearch.westminster.ac.uk:9v61y

OAI identifier oai:identifier

oai:westminsterresearch.westminster.ac.uk:9v61y