Abstract
A deep eutectic solvent (DES) composed of sulfamic acid and glycerol allowed for the sustainable preparation of cellulose nanofibrils (CNF) with simultaneous sulfation. The reaction time and the levels of sulfamic acid demonstrated that fibers could be swelled and sulfated simultaneously by a sulfamic acid-glycerol-based DES and swelling also promoted sulfation with a high degree of substitution (0.12). The DES-pretreated fibers were further nanofibrillated by a grinder producing CNF with diameters from 10 nm to 25 nm. The crystallinity ranged from 53–62%, and CNF maintained the original crystal structure. DES pretreatment facilitated cellulose nano-fibrillation and reduced the energy consumption with a maximum reduction of 35%. The films prepared from polyvinyl alcohol (PVA) and CNF showed good UV resistance ability and mechanical properties. This facile and efficient method provided a more sustainable strategy for the swelling, functionalization and nano-fibrillation of cellulose, expanding its application to UV-blocking materials and related fields.
Highlights
Cellulose nanofibrils (CNFs) are promising, high-performing materials due to their high mechanical strength and chemical versatility as well as the diversity and abundance of raw materials in which they are found [1]
The crystallinity of the original cellulose pulp, deep eutectic solvent (DES)-treated cellulose, and CNF were analyzed by wide-angle X-ray diffractometry (WAXD) using a Bruker D8 ADVANC X-ray diffraction (Bruker, Karlsruhe, Germany) using Cu K(alpha) radiation operated at 40 kV
The poplar bleached pulp was pretreated by a sulfamic acid-glycerol-based DES, the treated pulp was grinded through a supermasscollider, and sulfated CNF was obtained
Summary
Cellulose nanofibrils (CNFs) are promising, high-performing materials due to their high mechanical strength and chemical versatility as well as the diversity and abundance of raw materials in which they are found [1]. In order to avoid the side reaction, it is necessary to find a reagent to replace urea in order to prepare DES with sulfamic acid and pretreat the biomass to produce sulfated CNF. There is little information in the literature about substituting urea in sulfamic, acid-based DES for the sulfation of cellulose. As a green and sustainable organic chemical, glycerol is a colorless, odorless, nontoxic and sweet liquid with a low price (USD 2 per kilogram) [29], which does not react with cellulose It has been reported in the literature that glycerol is used as a hydrogen bond donor in DES to prepare CNF [30]; glycerol is a suitable alternative for urea in DES to sulfate CNF and reduce side reactions. PVA/CNF nanocomposites were prepared by solvent casting, whose transparency and mechanical properties were characterized
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