Characterisation and antimocrobial activity of poly(lacitc acid)/kenaf bio-composites containing a natural agent
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Abstract
The use of materials based on poly(lactic acid) (PLA) as alternatives to petroleum-based
polymers for a range of applications has increased in recent years. In the case of food packaging
in particular, PLA has experienced growth in combination with the use of a wide range of other
materials and/or additives derived from natural and renewable resources. However, the initial
costs associated with new technologies to produce PLA and/or other bio-based polymers are
typically high, so new techniques are required to reduce costs without compromising material
properties and biodegradability. Naturally sourced lignocellulose fibres such as kenaf
(Hibiscus cannabinus L.) are often used as cost-reducing fillers and/or reinforcing agent for
biopolymers such as PLA. This study explores the characteristics and antimicrobial (AM) activity of PLA and PLA/kenaf
composites incorporated with thymol, a natural bio-active AM substance/agent. The production
of PLA/kenaf composites containing thymol is intended for potential use in AM packaging
applications such as rigid and/or flexible packaging and coatings. Composites of PLA
incorporated with 5 to 40% w/w kenaf fibre loadings and thymol concentrations ranging from
5 to 30% w/w were prepared and compared with control systems containing either no kenaf or
no thymol. Kenaf fibres can be treated by alkalisation to improve compatibility with polymer
matrices. It was found that the PLA/kenaf composites containing treated kenaf possessed
significantly higher tensile strength and stiffness than composites prepared with untreated
kenaf. Micrograph images of the fracture surface revealed better adhesion between the treated
kenaf fibres and the matrix, thereby resulting in improved reinforcement of the composite.
Moreover, PLA/kenaf composites containing thymol exhibited lower tensile strength than
those without thymol, suggesting a possible plasticizing effect in the presence of the additive