Melt-processed cast films of calcite reinforced starch/guar-gum biopolymer composites for packaging applications

Abstract

Starch has tricky material properties, and it is difficult to process using conventional melt processing methods. This hinders its commercialization in packaging. In this study, a melt-processed stable composite film was fabricated in a twin-screw extruder using plasticized starch and guar gum reinforced with varying proportions of calcite. The developed composite films were subsequently characterized using different morphological, compositional, thermal and mechanical analytical techniques. The formulations with 2 wt.% and 3 wt.% calcite yielded the best results for mechanical properties (Tensile Strength: ~ 19.3 MPa and ~ 23.3 MPa; Elongation at break: ~ 43% and ~ 37.2%, respectively) and water contact angle (~ 87.3° and 97.5° respectively). Additionally, it exhibited decreased water-induced swelling and reduced water vapour transmission. Calcite particles were found to be evenly dispersed throughout the matrix. By establishing an intertwined network structure through intercalation, calcite hindered the retrogradation of starch and hence reduced the crystalline behaviour of starch. Thus, the resulting material had better mechanical properties than pure starch-based films. The presence of guar-gum in the formulation improved the elongation behaviour as well as the processability. The properties of the films developed in the study were observed to be competitive with other commercially available biodegradable polymers and the findings create optimism for rapid translation of the technology in scaled-up operations towards efficient production of commercial starch-based films.

Graphical abstract