Chitosan from Solid-State Fermentation of Soybean Residues By Filamentous Fungi As Biobased Paperboard Coating Additives for HVAC Applications

The HVAC (Heating, Ventilation, and Air-conditioning) industry markets phenolic resin coated-paperboard media for use in the air-cooling of agricultural livestock pens and enclosures. Phenolic resins such as phenol formaldehyde have been shown to improve dry stiffness and water resistance of paper base sheets. However, in HVAC applications where good wet strength and water absorption properties are required, phenol formaldehyde-coated paperboards unfortunately have reduced wet stiffness levels compared with uncoated paperboards, thus resulting into premature failure of the air-cooling media. Furthermore, the use of phenolic resins may reduce the recyclability or biodegradability of the used coated paperboards. Chitosan, a versatile biopolymer commonly derived from crustacean shells in seafood wastes, has found numerous applications across multiple disciplines due to its unique and interesting properties. Some of these properties include its antimicrobial quality, chelating properties, and the ability to form hydrogels, fibers, and films. Chitosan has also found potential applications in the pulp and paper industry, mainly as surface coating or sizing additive for paper and paperboard products with enhanced or functionalized properties. These properties include water resistance, air barrier, wet and/or dry strength, and antimicrobial properties. Thus, chitosan could serve as a bio-based alternative to conventional phenolic resin as paperboard coating materials. However, the current process for chitosan production involves costly, labor-intensive, and harsh chemical treatments of seafood waste and also suffers from raw material supply inconsistencies and geographical limitation. Fortunately, chitosan can also be found as cell wall components of filamentous fungi. These fungi can be grown in fermentation cultures using agricultural and food processing residues as substrates to produce high-quality chitosan continuously and sustainably, and with expectedly lower separation and recovery costs.

The current study investigated the use of soybean processing residues such as meal and hulls as substrate for the growth and chitosan production of fungi using solid-state fermentation (SSF). Selected fungal strains with documented high chitosan production capabilities were screened for direct growth and utilization of solid soybean residue fermentation substrate. Results show that three out of the six screened fungi strains exhibited expansive mycelial growth on soymeal substrate while the rest only showed liquefaction of the soymeal substrate. The fungal strains exhibiting growth on the soymeal substrate were selected for fermentation kinetics and optimization studies to determine optimal SSF conditions for growth and chitosan production. The product chitosan is intended for application as coating additives for paper-based evaporative cooling media requiring wet stiffness and water absorption/wicking characteristics. Economic analysis indicate a target chitosan yield of 20 % (w/w of substrate) in order to match the price of the conventional phenolic resin coatings of $3.00 per lb. Further cost reductions are possible with lower chitosan application weights or coating techniques for optimum wet stiffness and wicking performance. Parallel investigations were conducted using commercially available chitosan to determine the optimum levels of chitosan concentration in carrier solution, coating weight, and other coating process variables for improved coated paperboard dry and wet stiffness and water absorption/wicking. Chitosan-coated paper basesheets, along with the uncoated and phenolic resin-coated sheets were characterized and compared for Wet Taber Stiffness and Wicking Height according to the manufacturer’s methods and specifications. The target critical-to-quality (CTQ) parameters and their levels for application as cooling pads are 1600 mg wet Taber stiffness and 2 inches of wicking height over 10 minutes. The economics of paperboard coating using chitosan compared with phenolic resins based on coating amounts on weight or area basis, unit costs, and product performance will be further discussed.