Cellulosic nanocomposites. II. Studies by atomic force microscopy

Dissolving‐grade wood pulp fibers were partially esterified by mixed p‐toluene sulfonic/hexanoic acid anhydride in a nonswelling suspending agent. A biphasic morphology was revealed by atomic force microscopy (AFM) for the compression‐molded, partially modified pulp fibers. The AFM phase images indicated distinct periodicity on the scale of several 10's of nanometers. Surface etching with cellulolytic enzymes of the modified pulp fibers produced height images that had virtually the same periodicity. These results indicate that the modified pulp fibers are nanocomposites comprising unmodified cellulose and cellulose hexanoate. Regenerated lyocell fibers (from N,MMNO solvent) subjected to the same esterification system as applied to pulp fibers, by contrast, exhibited AFM phase images that indicated a high level of surface (skin) versus core reactivity. Modified lyocell fibers with an average diameter of about 12 μm and having an overall DS of 0.6 had surface layers that were approximately 1 μm thick. The latter represented a transitional phase in which the chemical composition and the physical properties were intermediate between a highly substituted surface (skin) and an unsubstituted core. When a compression‐molded sheet of the modified lyocell fibers was analyzed by microthermal analysis, the thermoplastic matrix on the lyocell fiber surface was revealed to have an apparent T_g of 75°C corresponding to cellulose hexanoate, whereas no significant thermal transition was determined for the (unmodified) fiber core. These results suggest that both partially modified lyocell fibers and partially modified pulp fibers are capable of producing composites with morphologies that have grossly different scales. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2254–2261, 2000     

Transparent,flexible, and high‐strength regenerated cellulose/saponite nanocomposite films with high gas barrier properties

Regenerated cellulose‐saponite nanocomposite films were prepared from LiOH/urea solutions, and exhibited high optical transparency and flexibility. The saponite platelets formed intercalated nanolayered structures in the composites. The longitudinal directions of both the cellulose II crystallites and the saponite platelets were preferentially oriented parallel to the film surface in the composites. The good nanodispersibility and high orientation of the saponite platelets in the composite films resulted in high mechanical strength, high Young's modulus, and good thermal dimensional stabilities, and gas barrier properties in the composites, compared with a reference cellulose film. Moreover, the tensile strength and Young's modulus of the composite film reached 241 MPa and 7.7 GPa, respectively, when a simple drawing process was applied to the wet composite film; this is probably owing to the improvement in the orientation of the cellulose II crystallites and saponite platelets in the composites. The composite films also showed high toughness and ductility. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3168–3174, 2013     

A novel approach for extracting cellulose nanofibers from lignocellulosic biomass by ball milling combined with chemical treatment

Cellulose nanofibers (CNFs) were isolated from kenaf fibers and wheat straw by formic acid (FA)/acetic acid (AA), peroxyformic acid (PFA)/peroxyacetic acid (PAA), hydrogen peroxide (H₂O₂) treatment; and subsequently through ball milling treatment. Characterization of extracted cellulose and cellulose nanofibers was carried out through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), and thermogravimetric analysis (TGA). TEM images showed that extracted cellulose nanofibers had diameter in the range of 8–100 nm. FTIR and XRD results implied that hemicellulose and lignin were mostly removed from lignocellulosic biomass with an increase in crystallinity, and isolation of cellulose nanofibers was successful. The TGA results showed that decomposition temperature of cellulose nanofibers increased by about 27°C when compared with that of untreated lignocellulosic biomass. No significant change was observed in the decomposition temperature of bleached celluloses after ball milling. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42990.     

X‐ray diffraction methods in the study of the effect of microwave heating on the transformation of cellulose I into cellulose II during mercerization

X‐ray diffraction (XRD) techniques were used in the study of the effect of microwave (MW) heating on the structural properties of cotton celluloses I and II and on the mercerization mechanism of cotton fibers. Samples of celluloses I and II were MW heated at 900 W for different times ranging from 10 to 40 min. The obtained data revealed that MW heating of cellulose II in opened glass tubes produces no significant effects on the resolution of its XRD patterns, whereas the most evident effects occur when cotton fibers (cellulose I) are heated in opened tubes at 900 W for 10 and 20 min. Also, mixtures of cotton fibers and aqueous solution of NaOH with different concentrations were exposed to MW radiation for different times and different powers. It was found that MW heating has no considerable effects on the mechanism of transformation of cellulose I into cellulose II during mercerization. On the other hand, MW heating of cotton fibers during mercerization reduces the values of concentration of NaOH in the aqueous solution and the time of treatment that are needed for the complete transformation of cellulose lattice type I into cellulose lattice type II without any heating. Also it was found that the magnitude of reductions depends on the applied power. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Fibrous long‐chain organic acid cellulose esters and their characterization by diffuse reflectance FTIR spectroscopy,solid‐state CP/MAS 13C‐NMR,and X‐ray diffraction

Unsaturated and saturated organic acids with 11 and 18 carbon atoms, respectively, were used in a heterogeneous esterification reaction in the pyridine/toluene sulfonyl chloride system to prepare fibrous cellulose esters with different degrees of substitution. Highly bleached sulfite cellulose fibers were esterified during a 1‐ or 2‐h reaction time with the following organic acids: undecylenic acid, undecanoic acid, oleic acid, and stearic acid. In all cases, the heterogeneous esterification yielded partially substituted cellulose esters retaining their fibrous structure. The substitution reaction was confirmed by diffuse reflectance infrared spectroscopy and the chemical structures of cellulose esters were identified by solid‐state CP/MAS ¹³C‐NMR (75.3 MHz). X‐ray diffraction analyses showed broadening of the diffraction peaks with a higher degree of substitution of cellulose esters, which suggests structural changes within the cellulose fibers. Because the broadening peaks of X‐ray spectra or the unassigned C‐4 region of substituted cellulose chains in NMR spectra do not allow the calculation of dimensional changes of cellulose crystallites in cellulose esters, the lateral dimensions of crystallites in only cellulose fibers were calculated. The value derived from NMR (4.6 nm) differs by about 11% when compared with the value calculated from X‐ray diffraction data (4.1 nm). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1354–1365, 2000     

Preparation and characterization of modified starch‐based plastic film reinforced with short pulp fiber. I. Structural properties

Native corn starch‐ and hydroxypropylated starch (HPS‐) based plastic films were prepared using the short pulp fiber as the reinforcement and the glycerol as the plasticizer. Starch (or HPS) films showed different X‐ray diffraction patterns with the A‐type of native corn starch powder. The crystallinity of films increased with pulp content, but decreased with glycerol content and degree of substitution by hydroxypropylation. Also, the intensity of peaks at 2θ = 15.3 and 17.3° decreased with glycerol content and degree of substitution. The water uptake of films as a function of the relative humidity decreased with pulp content and degree of substitution by hydroxypropylation, but increased with glycerol content. Differential scanning calorimetry (DSC) thermograms showed that the glass transition temperature of films decreased and the endothermic peaks at the melting temperature broadened due to the plasticizing effect and the decrease of the crystallinity, which were caused by the addition of glycerol and the hydroxypropylation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2100–2107, 2003     

Hemodialysis membrane prepared from cellulose/N‐methylmorpholine‐N‐oxide solution. I. Effect of membrane preparation conditions on its permeation characteristics

Flat hemodialysis membranes were prepared from cellulose/N‐methylmorpholine‐N‐oxide (NMMO) solutions (dope) with different cellulose concentrations (6–8 wt %) by using a phase‐inversion method. The coagulant used was NMMO aqueous solution, of which the NMMO concentration and its temperature were varied in the range of 0 to 50 wt % and 5 to 60°C, respectively. The effects of these preparation conditions on the permeation characteristics, the ultrafiltration rate (UFR) of pure water, and sieving coefficient (SC) of dextran, were investigated. The decrease in cellulose concentration of the dope and the increases in both temperature and NMMO concentration of the coagulant gave a membrane with high UFR. Concerning the SC, the increase of the cellulose concentration and the decreases in both temperature and NMMO concentration gave a good result. Consequently, the membrane having the preferable UFR and SC as a hemodialysis membrane was obtained when the 8 wt % cellulose dope was coagulated in water at 5°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2302–2307, 2002