3D Printing of Hemicellulosic Biopolymers Extracted from Lignocellulosic Agricultural Wastes

Despite being one of the most abundant biopolymers found in nature after cellulose, hemicellulose is still an underutilized biopolymer. Using this abundant biopolymer in 3D printing applications has a lot of potential, but so far only minor attention has been given to hemicellulose, which includes using its derivative forms together with other polymers for 3D printing. On the other hand, cellulose, in the form of cellulose derivatives or nanocelluloses such as cellulose nanofibers and nanocrystals, receives significant attention for 3D printing applications, but it needs considerable chemical modifications and various postprinting processes. Therefore, a novel practical approach, which enables hemicellulose to be 3D printed without needing chemical modifications or blending with other polymers, might enable hemicellulose to get the attention it deserves as a widely abundant, renewable, biodegradable polymer of natural origin. In this context, hemicellulosic polymers extracted from lignocellulosic agricultural wastes (corn cobs) were 3D printed for the first time without any chemical modifications or mixing with another polymer. Successful 3D printing of hemicellulosic pastes could be achieved in a very narrow window with respect to their water content, printing temperature, and extrusion multiplier. Even the slightest variations in the water content of the pastes were found to influence the 3D printability of the polymers, which was related to the viscosity of the pastes. To demonstrate a potential biomedical application of the developed printing process, a scaffold prototype was 3D printed solely from the hemicellulosic polymers without applying any chemical modifications or using any postprinting processes

Production of hemicellulose-based biodegradable films from agricultural wastes

Owing to the increasing environmental awareness and restrictions together with the depletion of fossil-based resources, production of biodegradable films receives increasing attention to substitute at least a part of the largely consumed conventional synthetic plastics. Despite there are a variety of polymers that are used for biodegradable plastic production these alternatives are either more expensive compared to their non-biodegradable petroleum-based counterparts or obtained from sources such as corn or potatoes, which have the primary function of being nutritional substances. Thus production of low cost biodegradable plastics from non-nutritional renewable resources appears to be a major need. In this perspective, hemicellulose-based biodegradable films were produced from an agricultural waste, namely cotton stalk. The hemicellulose, xylan, is obtained from cotton stalks by alkali extraction followed by ethanol precipitation. The xylan obtained this way is a glucuronoxylan (GX). GXs are unable to form continuous films without the use of additives, especially plasticizers. However due to the extraction procedure used, which does not include any lignin removal stage before or after the extraction, continuous films of GX containing lignin were formed upon solvent casting that contained no plasticizers or other additives. This technique thus reduces the cost by removing the typical lignin removal stage making the process more environmental friendly as well. The polymer that was obtained from the extraction was dissolved in water and upon the evaporation of solvent slightly yellow transparent films were obtained with a thickness of approximately 50 μm. The films obtained this way were characterized by means of their mechanical properties. An ultimate tensile strength (UTS) value of 14 MPa with an elongation at break of 12% was obtained for the films. Films were also prepared by the addition of different plasticizers at different concentrations and these were characterized by means of the mechanical and water vapor transmission rate properties

An unconventional approach for improving the integrity and mechanical properties of xylan type hemicellulose based films

The isolation of xylans from lignocellulosic biomass via alkaline extraction typically involves a neutralization step, which results in salt formation. Usually, these salts are removed from the medium to avoid their presence within the isolated xylans and films made from these polymers. The present work shows that it is not always necessary to do so, since the presence of potassium acetate (KAcO) in the films was found to be beneficial both for the film formation and mechanical properties. While desalted xylans could only form film fragments, the presence of KAcO in the films led to intact films with increased toughness by approximately 2 to 5 fold. Increasing KAcO concentration resulted in softer films while the opposite was true for NaCl indicating that the two salts had different effects on the films, which was also verified by the differences in the cross-sectional and surface morphologies of the films containing KAcO and NaCl