Characterization of corn/sugar palm fiber-reinforced corn starch biopolymer hybrid composites

Contemporary environmental concerns, such as non-biodegradable disposal materials and the growing mountain of garbage as well as the plant waste accumulation, are increasingly recognized as ecological threats. Space for landfills is limited, and additional incineration capacities require high capital investment and cause further environmental problems. All these issues forced the researchers and scientists to move toward manufacturing and developing eco-friendly engineering materials from renewable sources to replace conventional non-biodegradable materials in several applications that could preserve the green environment. Amongst these sources are corn plant and sugar palm tree, which are a vital source for many biomasses. Therefore, a series of lab experiments through a solution casting technique was carried out to prepare and characterize starch, fibers, polymers, composites, and hybrid composites in four correlated stages to achieve a hybrid composite from corn/sugar palm fiber reinforced cornstarch. The first stage was designed to study the chemical composition, physical properties, thermal stability, and surface morphology of thermoplastic corn starch and corn hull, husk, and stalk fibers, which were extracted from different corn plant parts. The obtained samples were characterized on a powder basis. The corn husk and corn starch revealed an excellent combination of properties. Cornhusk provided the highest cellulose content (45.7%) as well as the most favorable surface morphology. Corn starch revealed acceptable amylose content (24.6 g/100g) and tolerable thermal stability with an onset melting point of 161.2 ºC. Since the cellulose and starch demonstrated an excellent correlation between the function and structure of biomolecules. Hence, both corn starch and husk have the potential for use in many applications of the biomaterial.The second stage was accomplished to determine the effect of various concentrations of selected plasticizers in cornstarch-based films, to prepare a new biopolymer. The physical, morphological, thermal, and tensile properties of produced films were evaluated. The results showed that the thickness, moisture content, and water solubility increased with the addition of plasticizer concentration. Regardless of plasticizer sort, the tensile stress and modulus of plasticized films decreased as the plasticizer concentrations were raised beyond 25%. Likewise, the relative crystallinity decreased by increasing the plasticizer content from 0% to 25%, but it began to grow once the concentration increased above 25%. The fructose-plasticized films presented consistent and more coherent surfaces compared to sorbitol and urea counterparts. In summary, the plasticizer types and concentrations are significantly affected on the performance of the cornstarch-based film, especially for 25% fructose addition. In the third stage, biodegradable composite films were prepared by using different concentrations of husk fiber as a reinforcing filler to the optimum biopolymer produced from the previous stage. The findings indicated that the incorporation of husk fiber, in general, enhanced the performance of the composite films. There was a noticeable reduction in the density, moisture content of the films, and soil burial assessment showed less resistance to biodegradation. The morphological images presented a consistent structure and excellent compatibility between matrix and reinforcement, which reflected on the improved tensile strength and modulus as well as the crystallinity index. In the last stage, hybrid composites were successfully prepared by loading different concentrations of sugar palm fiber to the best composite from the previous stage. The incorporation of sugar palm fiber increased the thickness and the crystallinity index while reducing the density, moisture content, water solubility, water absorption, and water vapor permeability of the films. The tensile strength and modulus of the films were increased from 6.8 MPa to 19.05 MPa and from 61.15 MPa to 1133.47 MPa respectively for the film contains 6% sugar palm fiber, making it the most efficient reinforcing. To sum up, corn husk/sugar palm fiber reinforced cornstarch hybrid composite films as anticipated, improved the mechanical properties, and the water barrier characteristics. Thus, they are suitable for replacing conventional non-biodegradable materials in many applications.

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