Doctors Sandeep, Zhu, Deng, and Ragauskas are investigating a process that shows reduced energy requirements in the production of nanocellulose without sacrificing yield. Future work is planned to evaluate how pretreatment prior to mechanical fibrillation can affect fiber properties.
Different methods have been used for the production of nanocellulose for exploiting the attractive mechanical properties of cellulose I nano-elements. However, most of the methods currently in use have certain limitations. An aggressive acid hydrolysis produces nanocellulose with low yield, requires acid-resistant equipment, and presents challenges in waste stream management. The mechanical fibrillation method results in much longer and more entangled nanocellulose elements, leading to stronger networks and gels; however, the lack of feasible methods of preparation, high energy consumption, and the formation of nonhomogeneous distribution of nanocellulose geometry are the limitations of mechanical fibrillation. The use of a commercial grinder for mechanical fibrillation has a great potential for scale-up. However, the grinder treatment has to be optimized for high performance nanofibers.
In these joint studies between the U.S. Forest Service/USDA Forest Products Lab and IPST, researchers are using a commercial grinder to mechanically fibrillate bleached softwood fibers. After one hour of fibrillation, most of the fibers became nano-sized fibers. When the number of hours of fibrillation was increased from one to six hours, there was no significant change in the morphology or fibrillation of the fibers. The increase in energy consumption for mechanical fibrillation was linearly correlated to fibrillation time. The use of mild enzymatic hydrolysis before mechanical fibrillation using pure endoglucanase or multiplex enzyme as pretreatment for bleached softwood fibers before mechanical fibrillation significantly reduced energy required (20% or 30% less, respectively, when compared to mechanical fibrillation alone). Also, the results showed a high nanocellulose yield after pretreatment from endoglucanase (97% yield) and those with multiplex enzyme formulations (90% yield). This indicates that there is not much difference in the nanocellulose properties produced by these two different types of pretreatments.
Future studies will evaluate how these pretreatments followed by mechanical fibrillation affect the fiber properties compared to one which solely uses mechanical fibrillation. The results from this will help identify enzymatic pretreatments that will be helpful in lowering the processing cost for the production of high-performance nanofibers.