Journal
POLYMERS
Volume 13, Issue 18, Pages -Publisher
MDPI
DOI: 10.3390/polym13183186
Keywords
thermoplastic starch; crystalline nanocellulose; plasticizers; composite film; mechanical properties; morphology; reinforcement; competitive interactions; aging; retrogradation
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Funding
- National Scientific Research Fund of Hungary (OTKA) [K131761]
- Ministry of Human Capacities (BME FIKP-BIO)
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Composite films were fabricated with cellulose nanocrystals (CNCs) as reinforcement in thermoplastic starch (TPS) up to 50 wt%. The addition of CNCs decreased film transmittance due to increased light scattering, but enhanced strength, especially in the series with 30% sorbitol. Water vapor permeability of TPS was significantly decreased by incorporating at least 20 wt% CNCs.
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.
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