The current status of the enzyme-mediated isolation and functionalization of nanocelluloses: production, properties, techno-economics, and opportunities

The increasing interest for cellulose-based products has resulted in the development of processes for the controlled deconstruction of cellulose into cellulose nanomaterials, such as cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). These nanomaterials can significantly increase the diverse applications of cellulose by exploring their nanometric scale options and improved properties for various high-volume, low-volume, and emerging/novel applications. Among the nanocellulose production processes, the enzyme-mediated methods are environment friendly and with expected lower capital and operating expenditures compared to traditional processes. In addition, it creates the unique possibility of fine-tuning the process to tailor nanocellulose properties that are suitable for specific applications. This review comprehensively examines the application of enzymes in the isolation of nanocelluloses. To date, no enzyme preparation for application to nanocellulose production is available commercially. Therefore, a fundamental understanding of potential enzymes focusing mainly on their differentiated properties, mechanism and alterations promoted to cellulose at different levels is first provided. This is to shed light on the enzyme properties that can be exploited for application in nanocellulose isolation. Then, the current state of the stand-alone and integrated enzyme-mediated processes is reviewed as well as the properties and yield of the isolated nanocelluloses in comparison to nanocelluloses obtained by traditional processes. In addition, the potential of enzyme-mediated functionalization has been discussed as a promising method that imparts unique properties to nanocelluloses, further diversifying their market. A detailed discussion on the challenges and opportunities for the major technical and economic factors that impact nanocellulose price has been included as well.