Effects of cellulose, bentonite and hybrid cellulose/bentonite fillers on morphology, ambient and low temperature tensile properties of thermoplastic starch composites for refrigerated food packaging application

Abstract

Thermoplastic starch (TPS) is a biodegradable and renewable bio-based plastic which has great potential for the fabrication of edible and biodegradable film for refrigerated food packaging application. In this study, improvement in the TPS ambient and low temperature tensile properties was aimed by the incorporation of hybrid fillers. TPS composites incorporating 5wt% bentonite / cellulose (Bent/Cellulose) hybrid fillers in different ratios (100:0, 80:20, 60:40, 40:60, 20:80 and 0:100) were prepared by film casting process. Ultra-sonication process was done to improve the filler dispersion in the TPS matrix and enhance the filler-matrix molecular interactions.The morphology of the pristine and ultra-sonicated fillers was characterized while the mechanical and thermal properties of the neat TPS and TPS composites were evaluated and compared by tensile test and DSC analysis, respectively.Results indicated that the ultra-sonicated bentonite possesses more plate-like shape with delaminated and more uniform platelets as compared to the pristine bentonite.On the other hand, cellulose exhibits reduction in the fiber size (diameter and length) upon the ultra-sonication process.Changes in the morphology of both bentonite and cellulose resulted in greater filler dispersion and interactions with the TPS molecular chains due to the obtained higher filler surface area.Tensile properties of the neat TPS and TPS composites were evaluated after the samples pre-conditioned at ambient and 2°C. Ultra-sonicated fillers resulted in greater improvement in the tensile properties when the samples pre-conditioned at both ambient and 2°C.The TPS has achieved its highest tensile strength and elongation at break (ambient and 2°C) when the ultra-sonicated hybrid bent/cellulose in 80:20 ratio was added into its structure.