A Comparative Study on the Characterization of Nanofibers with Cellulose I, I/II, and II Polymorphs from Wood.

Haiying Wang,Tiantian Wu,Suiyi Li,Xiaoxuan Wang,Xudong Cheng,Dagang Li

doi:10.3390/polym11010153

Haiying Wang, Tiantian Wu + Show 4 more

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https://doi.org/10.3390/polym11010153

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Journal: Polymers	Publication Date: Jan 17, 2019
Citations: 18	License type: CC BY 4.0

Affiliation: Nanjing Forestry University

Abstract

Polymorphic changes in cellulose nanofibers (CNFs) are closely related to their properties and applications, and it is of interest to investigate how polymorphic changes influence their properties. A comparative study on the properties of CNFs with cellulose I, I/II, and II polymorphs from wood was conducted herein. CNFs were obtained by chemical extraction combined with a simple and efficient mechanical treatment (one pass through a grinder). This process resulted in a relatively high yield of 80–85% after a simple grinding treatment. The polymorphic changes in the CNFs and the chemical composition, morphology, tensile performances, and thermal properties were systematically characterized and compared. The X-ray diffraction and FTIR analyses verified the existence of three types of purified pulps and CNFs with cellulose I, cellulose I/II, and cellulose II polymorphs (CNF-I, CNF-I/II, CNF-II). Morphological observations presented that these three types of CNFs all exhibited high aspect ratios and entangled structures. Tensile testing showed that the CNF films all exhibited high tensile strengths, and the fracture strains of the CNF-I/II (11.8%) and CNF-II (13.0%) films were noticeably increased compared to those of the CNF-I film (6.0%). If CNF-II is used as reinforcing material, its larger fracture strain can improve the mechanical performance of the CNF composites, such as fracture toughness and impact strength. In addition, CNF-I, CNF-I/II, and CNF-II films showed very low thermal expansion in the range 20–150 °C, with the coefficient of thermal expansion values of 9.4, 17.1, and 17.3 ppm/K, respectively. Thermogravimetric analysis (TGA) revealed that the degradation temperature of CNF-I and CNF-II was greater than that of CNF-I/II, which was likely due to increased α-cellulose content. This comparative study of the characterization of CNF-I, CNF-I/II, and CNF-II provides a theoretical basis for the application of CNFs with different polymorphs and could broaden the applications of CNFs.

Highlights

Cellulose, a linear chain of ringed glucose molecules, is the most abundant natural biopolymeric material on earth [1]
We reported an efficient method for extracting cellulose nanofibers (CNFs) with cellulose II polymorph by chemical extraction combined with a simple mechanical grinding treatment
We found that the delignification plays an important role in the polymorphic transformation from cellulose I to cellulose II during mercerization and in the subsequent fibrillation of CNF-II [19]

Summary

Introduction

A linear chain of ringed glucose molecules, is the most abundant natural biopolymeric material on earth [1]. Based on the different orientation of cellulose chains and hydrogen-bond networks, several polymorphs of crystalline cellulose (I, II, III, and IV) have been identified [2,3]. Cellulose I is referred to as native cellulose, which has two forms, including Iα and Iβ [2]. II is usually prepared from cellulose I through mercerization (alkali treatment) or regeneration (solubilization and recrystallization) [4]. The polymorphic transformation from cellulose I (parallel-chain structure) to cellulose II (antiparallel-chain structure) occurs via sodium hydroxide treatment [5]. Due to the different supermolecular structures of cellulose

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