Abstract
Composite films were fabricated by using cellulose nanocrystals (CNCs) as reinforcement up to 50 wt% in thermoplastic starch (TPS). Structure and interactions were modified by using different types (glycerol and sorbitol) and different amounts (30 and 40%) of plasticizers. The structure of the composites was characterized by visible spectroscopy, Haze index measurements, and scanning electron microscopy. Tensile properties were determined by tensile testing, and the effect of CNC content on vapor permeability was investigated. Although all composite films are transparent and can hardly be distinguished by human eyes, the addition of CNCs somewhat decreases the transmittance of the films. This can be related to the increased light scattering of the films, which is caused by the aggregation of nanocrystals, leading to the formation of micron-sized particles. Nevertheless, strength is enhanced by CNCs, mostly in the composite series prepared with 30% sorbitol. Additionally, the relatively high water vapor permeability of TPS is considerably decreased by the incorporation of at least 20 wt% CNCs. Reinforcement is determined mostly by the competitive interactions among starch, nanocellulose, and plasticizer molecules. The aging of the films is caused by the additional water uptake from the atmosphere and the retrogradation of starch.
Highlights
IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
Granules are destroyed while applying plasticizers and specific conditions, resulting in thermoplastic starch (TPS) showing a hydrophilic character and inadequate mechanical properties [1,2,3]
Structure and interactions were modified with glycerol or sorbitol as a plasticizer at a 30 or 40% concentration on a starch basis
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Starch is a semicrystalline biopolymer that is readily available, inexpensive, and biodegradable. Despite being one of the most promising biopolymers, granular starch shows limited processability that makes the use of plasticizers necessary. Granules are destroyed while applying plasticizers and specific conditions, resulting in thermoplastic starch (TPS) showing a hydrophilic character and inadequate mechanical properties [1,2,3]
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