Development of malt sprout-based bioplastics via injection-moulding

Abstract

Millions of tons of malt sprouts, a low added-value by-product of the brewing industry, are produced after barley malting (germination of sprouting). Their valorisation can rise from their use for the development of bioplastics whose main source can be found in different wastes and by-products of the food industry, being an abundant, inexpensive and renewable resource available. The objective of this study is the development of bio-based, biodegradable bioplastics from malt sprout (MS), whose chemical composition accounts for great amounts of both proteins and starches. Different formulations (malt sprout/plasticizer ratios) were studied to determine the suitability of injection moulding processing, where the effect of injection pressure was evaluated. The mechanical properties of the bioplastics were evaluated by dynamic mechanical analysis (DMA) and tensile tests and some functional properties such as water uptake capacity (WUC) and soluble matter loss were also studied. Finally, the obtained properties were related to the bioplastics structure that was analysed via scanning electron microscopy. The tests carried out evidenced a clear dependence between mechanical properties and WUC of MS/plasticizer ratio and injection pressure, increasing the storage modulus (E’) from 0.94 MPa for 1:1 MS/plasticizer ratio processed at 500 bar to 1.42 and 4.30 MPa for 3:1 MS/plasticizer ratio processed at 500 and 900 bar, respectively. Moreover, the WUC increased from 232 ± 32 % for 1:1 MS/plasticizer ratio processed at 500 bar to 319 ± 33 and 412 ± 79 % for 3:1 MS/plasticizer ratio processed at 500 and 900 bar, respectively.