Preparation and Characterization of Regenerated Cellulose Film from a Solution in Lithium Bromide Molten Salt Hydrate.

Xueqin Zhang,Huihui Wang,Xuejun Pan,Naiyu Xiao,Chuanfu Liu

doi:10.3390/polym10060614

Abstract

In this study, the molten salt hydrate of lithium bromide (LiBr) was utilized as a non-derivatizing cellulose dissolution solvent to prepare regenerated cellulose films for kraft pulp. The effects of LiBr concentrations (60, 62, and 65 wt %) and dissolving time (from 5 to 40 min with the interval of 5 min) on the structures and the properties of the films were investigated. Fourier transform infrared (FT-IR) and cross-polarization magic-angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C NMR) characterizations verified the breakage of inter- and intra-cellulose hydrogen bonds during the regeneration, resulting in the disruption of the crystalline structure of cellulose. X-ray diffraction (XRD) data indicated that the regeneration converted the polymorphism of cellulose from I to II as well as decreased its crystallinity. Ultraviolet-visible spectra (UV-Vis) and scanning electron microscopy (SEM) analyses revealed the excellent optical transparency of the films to visible light due to the complete dissolution of cellulose fibers as well as the sufficient breaking of the inter- and intra-cellulose hydrogen bonds. In terms of tensile testing, tuning LiBr concentrations and dissolving time could increase the elongation at break and tensile strength of the films. The maximum elongation at break of 26% and tensile strength of 67 MPa were achieved when the films prepared in 65 wt % LiBr for 10 and 15 min, respectively. These results indicated the great potential of the cellulose films for packaging use.

Highlights

With the urgent demand to address the energy and environment issues that are caused by using fossil resources, there have been increasing interests in exploring biomass-based renewable and sustainable materials
Fourier transform infrared (FT-IR) was used to investigate the changes in chemical structure of cellulose during the FT-IR was to investigate the changes chemicalAs structure of Figure cellulose during the dissolution dissolution and used regeneration in lithium bromide (LiBr) molten saltinhydrate
The regenerated cellulose films were prepared from kraft pulp in LiBr molten salt hydrate under different conditions (LiBr concentrations and dissolving time)

Summary

Introduction

Cellulose-based films have drawn considerable attention for packaging, including food packaging [2,3], because of their optical transparency, tunable porous structure, and good mechanical properties [4]. The insolubility of natural cellulose in water and common organic solvents due to the highly crystalline structure makes it very challenging to prepare the films directly from celluloses [5]. Many solvent systems have been developed to negate the dissolution recalcitrance of cellulose to prepare regenerated films [4]. The solvent systems can be divided into derivatizing and non-derivatizing ones [6]. Non-derivatizing solvent systems have been extensively studied for dissolving and regenerating cellulose, as well as developing advanced and homogeneous cellulose derivatives [6]. A well-known cellulose non-derivatizing solvent system is

Methods

Results

Conclusion