Development of antibacterial hemp hurd/poly(lactic acid) biocomposite for food packaging

Development of antibacterial hemp hurd/poly(lactic acid) biocomposite for food packaging

Contemporary research in food packaging is being progressively focused on the development of biodegradable food packaging from biobased materials for exploring alternatives to traditional, non-biodegradable petroleum based plastics. Consequently, bioplastics are
increasingly gaining attention in the food packaging industry because of their potential of biodegradability and versatility in processing. The utilization of bioplastics however is limited because of their inherent shortcomings in thermal and mechanical stability. Recently, bioderived
fillers and plant fibres are being extensively used to address the thermo-mechanical stability and to lower the overall material cost in comparison to the baseline bioplastics. Incorporation of biobased fillers and functional nanoparticles to bioplastics not only offers
functionality but also enhances the cost-to-performance ratio of the biocomposites. To that end, this study focused on the development of cost effective, biodegradable, and functional food packaging material.

Poly(lactic acid) has been used in food packaging to replace conventional petroleum based plastics, because it possesses higher mechanical properties, greater versatility in process selection and it is deemed safe for use in food contact. However, apart from the high cost, a major shortcoming of poly(lactic acid) is a slow crystallization, and hence often requiring an added nucleating agent. The addition of low cost biobased filler to poly(lactic acid) not only lowers the overall material cost but also accelerates crystallization kinetics acting as a
nucleating agent.

Industrial hemp hurd is explored as a biobased filler with poly(lactic acid) for biocomposites to lower material cost and to address environmental concerns associated with plastic recycling. However, a major concern for the combination of biobased fillers with polymer matrices to
produce biocomposites is the weak fibre-matrix interfacial bonding. In recent years, several forms of glycidyl methacrylate-grafted polyolefins have been prepared through reactive extrusion or solution copolymerization to address this issue. The glycidyl methacrylate grafted copolymer is a potential compatibilizing agent for reducing the interfacial incompatibility in biocomposites. Hence, development of functional biocomposites for food packaging with poly(lactic acid) as bioplastic matrix, hemp hurd as biobased filler and glycidyl methacrylate as compatibilizer was the goal of this study.

Accordingly, a biocomposite was developed using extrusion and injection moulding utilizing hemp hurd and poly(lactic acid) with properties comparable to poly(lactic acid) with grafting based interfacial compatibilization. Interfacial compatibility between poly(lactic acid) and hemp hurd increased with grafted glycidyl methacrylate in comparison to the noncompatibilized control, as corroborated by scanning electron microscopy fractography. The
mechanical properties showed increases in the glycidyl methacrylate-grafted hemp hurd/poly(lactic acid) biocomposite, retaining 94% of the neat polymer strength, with increases in crystallinity at 20% (w/w) loading of hemp hurd. The impact strength data demonstrated that
the addition of GMA possesses the potential of improving physical and mechanical properties of HH/PLA composites. The onset of thermal decomposition of the biocomposites obtained through TGA was marginally lower than that of neat PLA.

The antibacterial property of hemp hurd is anecdotally reported, but not systematically investigated and reported. In this study, the antibacterial activity of hemp hurd against Escherichia coli was investigated. The antibacterial activity of hemp hurd inhibiting the growth
of E. coli was significant. To further increase the antibacterial efficacy of hemp hurd, silver nanoparticles was encapsulated into hemp hurd that exhibited high effectiveness. The silver nanoparticles were synthesized into the hemp hurd using a proprietary method developed in
collaboration with Ecofibre Pty Ltd.

The inclusion of glycidyl methacrylate further assisted in elastic moduli and strength increase at 10–30 wt. % fraction of silver nanoparticle-loaded hemp hurd in poly(lactic acid), with 20 wt. % hemp hurd-filled biocomposite exhibiting the highest range of properties within the
biocomposites investigated. Effective antibacterial activity was achieved with distinct decreases of 85% and 89% in bacterial growth at 0.025 wt. % and 0.05 wt. % loading of silver nanoparticle in the biocomposite. The biocomposites also maintained a safe level of heavy
metal migration at 0.20–3.08 mg/kg which meets the European Union (EU) legislation (2002/72/EC), substantially lower than the permitted value of 60 mg/kg. Overall, the properties of these developed biocomposites demonstrated discernible potential in development of food packaging applications.

Cost-benefit analysis was performed to assess the viability in commercial manufacturing for producing rigid food packaging. The biocomposite sensitivity and financial analyses provided data on the degree and magnitude of uncertainties related to investment to afford better product
design, and establish the potential of PLA-industrial hemp biocomposites for food packaging applications.

The findings of this study could create a platform upon which packaging designers, food scientists and engineers could initiate to employ biobased materials in their food packaging solutions.