Modificação de fibras de bagaço de cevada e uso em compósitos biodegradáveis de amido de milho produzidos por tape casting

Abstract

The use of starch to obtain biodegradable films of thermoplastic starch (TPS) presents several advantages, such as being derived from a natural, renewable, abundant, and low-cost source. However, starch films generally exhibit low tensile mechanical properties and high hydrophilicity. In this context, the study used brewer’s spent grain (BSG), considered a byproduct of the brewing industry, as reinforcement in corn starch–based composites. For this purpose, TPS composites plasticized with glycerol were developed using Farmal CS3650 corn starch, with an approximate composition of 28% amylose and 72% amylopectin. To produce the films, 10 wt% starch and 5 wt% glycerol were used, with the addition of 1 wt% barley bagasse fibers (unmodified, modified by alkaline treatment in sodium hydroxide (NaOH) solution, or carbonized at 200, 300, 400, and 500 °C). The films were produced using a microwave oven to heat the mixture, with pauses for manual stirring, and molded by tape casting, a technique that allows better thickness uniformity of the films compared to conventional casting. Tensile mechanical tests were performed, as well as Scanning Electron Microscopy (SEM) on fractured samples, Dynamic Mechanical Analysis (DMA), Thermogravimetric Analysis (TG/DTG), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), contact angle measurements, and soil biodegradation and phytotoxicity tests for possible agricultural application of the produced material. Improvements in tensile strength were observed for composites containing fibers carbonized at 400 °C (2.10 ± 0.09 MPa) and fibers modified by alkaline treatment (2.27 ± 0.16 MPa), representing increases of up to 51% compared to the TPS film without fiber incorporation (1.40 ± 0.11 MPa). Thermal analyses did not reveal significant differences in the thermal stability of the composites due to the low fiber content. The addition of modified fibers promoted a reduction in hydrophilicity and water absorption of the films. The incorporation of unmodified or alkali-treated fibers accelerated the biodegradation of the composites, whereas carbonized fibers maintained biodegradability similar to that of TPS. The produced films showed no phytotoxicity. Alkaline treatment and fiber carbonization proved to be promising strategies for obtaining composites with improved properties and sustainability. The developed composites show potential for applications in short-life biodegradable packaging and agricultural films, such as mulching and wraps for seeds and seedlings. Mechanical improvements and reduced hydrophilicity enhance the functional viability of materials developed. The use of agro-industrial waste (byproducts) and low-cost processes reinforces the sustainable character and application potential in environmentally responsible disposable products.