Abstract
This review summarizes the preparation methods of cellulose nanofibrils (CNFs) and the progress in the research pertaining to their surface modification. Moreover, the preparation and surface modification of nanocellulose were comprehensively introduced based on the existing literature. The review focuses on the mechanical treatment of cellulose, the surface modification of fibrillated fibers during pretreatment, the surface modification of nanocellulose and the modification of CNFs and their functional application. In the past five years, research on cellulose nanofibrils has progressed with developments in nanomaterials research technology. The number of papers on nanocellulose alone has increased by six times. However, owing to its high energy consumption, high cost and challenging industrial production, the applications of nanocellulose remain limited. In addition, although nanofibrils exhibit strong biocompatibility and barrier and mechanical properties, their high hydrophilicity limits their practical application. Current research on cellulose nanofibrils has mainly focused on the industrial production of CNFs, their pretreatment and functional modification and their compatibility with other biomass materials. In the future, with the rapid development of modern science and technology, the demand for biodegradable biomass materials will continue to increase. Furthermore, research on bio-based nanomaterials is expected to advance in the direction of functionalization and popularization.
Highlights
As the most abundant natural polymer on earth, cellulose occupies 40–50% of the earth’s total biomass reserves
This review introduces the preparation processes involved in cellulose nanofibrils (CNFs) pretreatment processes, where the main preparation process focused on is mechanical force and summarizes the most common raw fiber materials
This method requires the cellulose to be made into a solution, a tiny jet of cellulose is ejected from the needle-shaped injection port under a strong electric field environment to form a Taylor cone and as the solution evaporates, nanocellulose is formed at the tail of the Taylor cone [126]
Summary
As the most abundant natural polymer on earth, cellulose occupies 40–50% of the earth’s total biomass reserves. (iii) Chemical modification of cellulose surface hydroxyl groups, the element make it easier to separate the fibers [19,20,21]. CNFs, by introducing functional groups or polymer molecules to the CNFs surfaces by chemical grafting or physical adsorption, introducing brand-new functions such as semiconductor electrical properties, ultra-high mechanical strength and excellent hydrophobicity. This review introduces the preparation processes involved in CNFs pretreatment processes, where the main preparation process focused on is mechanical force and summarizes the most common raw fiber materials. We consider the influence of different raw fiber material composition and characteristics, compare pretreatment methods for CNFs polymerization, crystallinity (CI) and functional features and examine the industrial capacity of cellulose in this detailed report
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