Synthesis and mechanical performance of thermoformable cellulose fatty acid esters using natural soap.

A cellulose fatty acid ester consisting solely of natural organic compounds is synthesized by heterogeneous esterification. Solid soap, a natural product-based compound, is used as a mixed fatty acid source. The synthesized cellulose ester can be readily processed into a semi-transparent film. Mechanical properties of the cellulose ester are also investigated.

Effect of cellulose materials on the mechanochemical-assisted reaction system with oleic acid.

As the most abundant natural polymer in nature, cellulose has become the promising alternative raw material to replace fossil-based polymer. Owing to the presence of innumerable hydroxyl groups, various approaches are employed to render processability of cellulose. Herein, a sustainable esterification strategy, mechanochemical-assisted esterification, was developed to produce cellulose oleate (CO) with only a small amount of solvent. The differences in reactivity between all types of cellulose were elucidated. According to thermal stability analysis, the degradation temperature decreased after modification due to the substitution of the long oleoyl group. High degree of substitution (DS) of CO also possessed glass transition temperature (Tg) based on differential scanning calorimetry (DSC) analysis. Herewith, the processability of cellulose was introduced after modification. In this study, bamboo waste cellulose nanofiber oleate (BW CNF-OA) showed the highest DS (2.28) among the COs. Its higher surface reactivity due to the high surface aspect ratio led to a higher quantity of fatty acids attached to the cellulose. For the mechanical properties, low DS of COs exhibited higher tensile strength values. In a nutshell, this greener approach is more favorable than conventional chemical esterification in terms of reduced solvent dosage and improved sustainability.

Surface Modification of a Regenerated Cellulose Film Using Low-Pressure Plasma Treatment with Various Reactive Gases.

There is a growing interest in the fabrication of membranes and packaging materials from natural resources for a sustainable society. A regenerated cellulose (RC) film composed solely of cellulose has outstanding advantages including biodegradability, transparency, mechanical strength, and thermal stability. To expand the application of the RC film, various surface modification methods have been proposed. However, conventional chemical methods have disadvantages such as environmental burden and difficulty in controlling the reaction. In this work, low-pressure plasma treatment, a green, solvent-free, and easily controllable approach, was performed for surface modification of the RC film. The effects of three different plasma species (O2, N2, and CF4) and treatment conditions on the surface properties of RC films were investigated based on water contact angle measurements, chemical composition analysis, and surface topography. O2 and N2 plasma treatment slightly enhanced the surface wettability of RC films due to the etching by the plasma reactive species and the formation of new hydrophilic functional groups. In CF4 plasma treatments, the hydrophobic surface with a contact angle of 120.6° was obtained in a short treatment time (60 s) owing to the deposition of fluorocarbon groups on the surface. However, the treated surface in a longer reaction time resulted in increased wettability due to the diffusion and degradation of fluorine-containing bonds. The new insights could be valuable for further studies of surface modification and functionalization of RC films.

Esterification of Cellulose with Long Fatty Acid Chain through Mechanochemical Method.

Mechanochemical reaction, a green synthetic esterification route was utilized to prepare long-chain cellulose esters from microcrystalline cellulose. The influence of reaction conditions such as reaction temperature and time were elucidated. Only low dosage of oleic acid, 1-butyl-3-metylimidazolium acetate, and p-toluenesulfonyl chloride were required. The success of modification reaction was confirmed by Fourier transforms infrared spectroscopy as a new absorbance peak at 1731 cm-1 was observed, which indicated the formation of carbonyl group (C=O). Solid-state nuclear magnetic resonance was also performed to determine the structural property and degree of substitution (DS) of the cellulose oleate. Based on the results, increasing reaction temperature and reaction time promoted the esterification reaction and DS. DS values of cellulose oleates slightly decreased after 12 h reaction time. Besides, X-ray diffraction analysis showed the broadening of the diffraction peaks and thermal stability decreased after esterification. Hence, the findings suggested that grafting of oleic acid's aliphatic chain onto the cellulose backbone lowered the crystallinity and thermal stability.

The Relationship between Crystal Structure and Mechanical Performance for Fabrication of Regenerated Cellulose Film through Coagulation Conditions.

Cellulose films regenerated from aqueous alkali-urea solution possess different properties depending on coagulation conditions. However, the correlation between coagulant species and properties of regenerated cellulose (RC) films has not been clarified yet. In this study, RC films were prepared from cellulose nanofiber (CNF) and microcrystalline cellulose (MCC) under several coagulation conditions. Cellulose dissolved in aqueous LiOH-urea solution was regenerated using various solvents at ambient temperature to investigate the effects of their dielectric constant on the properties of RC film. The crystal structure, mechanical properties, and surface morphology of prepared RC films were analyzed using X-ray diffraction (XRD), tensile tester, and atomic probe microscopy (AFM), respectively. It is revealed that the preferential orientation of (110) and (020) crystal planes, which are formed by inter- and intramolecular hydrogen bonding in cellulose crystal regions, changed depending on coagulant species. Furthermore, we found out that tensile strength, elongation at break, and crystal structure properties of RC films strongly correlate to the dielectric constant of solvents used for the coagulation process. This work, therefore, would be able to provide an indicator to control the mechanical performance of RC film depending on its application and to develop detailed researches on controlling the crystal structure of cellulose.