Plastics have been widely used as food packaging due to their excellent properties and low price. Unfortunately, plastics are not biodegradable which leads to the accumulation of plastic waste in landfills. To prevent this problem in New Zealand, the development of biodegradable food packaging using cheap material as an alternative to plastic packaging is being explored. Zein, the co-product of corn oil production, can form edible film however its mechanical properties are quite poor. To improve these properties, chitosan also another bio-product of marine source, could be used as a co-polymer for zein film. Therefore, the main purpose of this project was to study the effect of blending formulation and crosslinking on the properties of zein/chitosan film. Poly(ethylene glycol)-400 (PEG-400) and tripolyphosphate (TPP) were respectively used as a plasticiser and a crosslinker. The effect of PEG-400 and TPP on the film properties and performance was assessed.
Different blending formulas using various zein/chitosan ratio ranging from 80:20 to 50:50 and PEG-400 addition ranging from 10% to 50% of the total solid (1% w/v of the total blending solution) were used. The measured properties of film forming solution and resulting film included pH, viscosity, colour, thickness, swelling index, water vapour permeability, mechanical properties, water content, water solubility and thermal stability. The film was prepared using wet casting method. Based on these results, regression modelling was used for the optimization of blending formula via desirability test to assess fitness of film on the targeted application. Afterwards, crosslinking post-processing using different doses of TPP in the soaking solution and different processing times were performed to the previously optimized film blending formula. Both swelling properties and thermal properties of crosslinked films were evaluated. It was found that the film properties of PEG-400 plasticized zein/chitosan blended film were more affected by PEG-400 content than zein-chitosan ratio while the film forming solution properties presented the reversed finding.
Based on the optimisation of the blending formula using mathematical modelling, this study showed that one of the potential applications of this film is packaging protection for fruit products. The use of tripolyphosphate (TPP) as cross-linker presents effective crosslinking performance towards this optimum blending formula for fruit protection, i.e. zein and chitosan ratio of 50:50 with 30% addition of PEG-400 of the total polymer content (1% w/v). Overall, the results in this study provide an evidence that plastic-like mechanical properties of zein/chitosan blended films with high water barrier property and higher thermal stability than low or high density polyethylene can be obtained and demonstrate high potential to use in replacing plastic film in food packaging.
