The Role of Structure and Interactions in Thermoplastic Starch–Nanocellulose Composites

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.

Composites of Thermoplastic Starch and Lignin-Rich Agricultural Waste for the Packaging of Fatty Foods

“…The strong hydrogen-bond network between the additives and the matrix can also be responsible for the hardening and reinforcing effect, typical of these types of additives. , In Figure d, it can be seen that the addition of WS led to a strong decay in the elongation at break of the TPS composites. This result, typically observed in other composites reinforced with lignocellulosic fillers, was attributed to the restriction of the flow and mobility of the polymer chain during the stretching generated by the incorporation of the rigid additives. ,, Noticeably, the mechanical strength of the composites developed in our work outperformed other TPS composites loaded with natural additives, such as the fibers of sisal and hemp . The reinforcement effect of the filler was in agreement with the abovementioned thermal analysis, showing slight differences between WS and HWS in both analyses.…”

“…This result could be related to the high content of lignin in the nut waste that has been demonstrated to present UV-blocking activity. , This effect is not observed in films with 1 wt % of fillers. Moreover, the incorporation of biomass results in an increase in the opacity of the composites due to the light-scattering effect. , Therefore, the lower opacity of TPS–HWS with respect to TPS–WS can be related to the decreased size of the HWS particles, their better distribution in the matrix, and compatibility with the rest of the components, as found in the morphological study (Figures S1 and ).…”

“…In this context, sustainable and biodegradable bioplastic materials derived from renewable sources have emerged as promising substitutes for conventional plastics. − However, their often-poor mechanical properties, low thermal stability, and limited processability through the most used industrial processes (e.g., injection molding and extrusion) hamper their full exploitation in various markets . Among bioplastics, the starch polymer is one of the most promising candidates to replace traditional plastics due to its thermoplastic properties when processed with a plasticizer under specific temperature and pressure conditions. , Specific plasticizers, mainly polyols, are used to disrupt the starch granules’ high crystalline structure, which limits the thermal processability of the neat biopolymer. , Starch is a natural polymer whose structure consists of long and linear chains of glucose units bonded through α-(1–4)-linkages, called amyloses, and short chains of glucose units highly branched through α-(1–6)-linkages, called amylopectins. , It occurs as densely packed semicrystalline granules found in leaves, stems, seeds, and roots of many vegetables (e.g., corn, cassava, rice, potato, wheat, etc.) where it constitutes the main energy source of plants. , The low price, availability, and good thermoprocessability of starch have promoted the use of thermoplastic starch (TPS) in multiple industrial sectors, such as food packaging, paper, and pharmaceuticals. , However, as with most polysaccharide biopolymers, starch applicability is strongly limited by its high moisture sensitivity and poor mechanical properties. , Therefore, in the past, this natural polymer has been chemically modified or combined with many different additives, such as cellulose nanocrystals, , vegetable waste particles, , and montmorillonite nanoclays, , which have been demonstrated to improve its properties and widen its functionality.…”

Effective Aging Inhibition of the Thermoplastic Corn Starch Films through the Use of Green Hybrid Filler

“…Under shearing force, high temperature, and incorporation of plasticizers, granule starch can be processed into an amorphous and homogenous material known as thermoplastic starch (TPS). Glycerol and water are the most common plasticizers as they are compatible with the starch structure and were proven in many studies [5,6]. Glycerol and water can effectively reduce the intermolecular force of granule starch and loosen up the dense packing structure.…”

The Effect of Surface Characteristics of Clays on the Properties of Starch Nanocomposites

“…Glycerol and water are usually used for this purpose, and the final thermoplastic starch (TPS) can be prepared by thermomechanical methods (extrusion, injection molding) or from solution by film casting. The main disadvantages of TPS are its hydrophilicity and inadequate mechanical properties, which can be improved by blending TPS with other polymers or fillers [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ].…”