Abstract
In the present study, agro-food waste derived rice straw (RS) was valorized into cellulose microfibers (CMFs) using a green process of combined ultrasound and heating treatments and were thereafter used to improve the physical properties of thermoplastic starch films (TPS). Mechanical defibrillation of the fibers gave rise to CMFs with cumulative frequencies of length and diameters below 200 and 5–15 µm, respectively. The resultant CMFs were successfully incorporated at, 1, 3, and 5 wt% into TPS by melt mixing and also starch was subjected to dry heating (DH) modification to yield TPS modified by dry heating (TPSDH). The resultant materials were finally shaped into films by thermo-compression and characterized. It was observed that both DH modification and fiber incorporation at 3 and 5 wt% loadings interfered with the starch gelatinization, leading to non-gelatinized starch granules in the biopolymer matrix. Thermo-compressed films prepared with both types of starches and reinforced with 3 wt% CMFs were more rigid (percentage increases of ~215% for TPS and ~207% for the TPSDH), more resistant to break (~100% for TPS and ~60% for TPSDH), but also less extensible (~53% for TPS and ~78% for TPSDH). The incorporation of CMFs into the TPS matrix at the highest contents also promoted a decrease in water vapor (~15%) and oxygen permeabilities (~30%). Finally, all the TPS composite films showed low changes in terms of optical properties and equilibrium moisture, being less soluble in water than the TPSDH films.
Highlights
Today, the proper management of agro-industrial wastes is an essential socioeconomic and environmental issue
Other studies have reported a decrease in the Oxygen permeability (OP) of starch-based films with cellulosic fractions [36,65], which are in agreement with the results reported
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Summary
The proper management of agro-industrial wastes is an essential socioeconomic and environmental issue Most of these residues or by-products, generated in large quantities globally, are currently discarded or burned in the harvest fields [1]. Cellulose and its derivatives extracted from biomass, such as cellulose microfibers (CMFs) and cellulose nanofibers, are highlighted renewable materials at the micro- and nanoscale, respectively, with low density, good compatibility, and excellent mechanical properties [12]. These lignocellulosic fractions can be used as reinforcing fillers of biopolymers in green composites for food packaging applications
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