Alfred D. French

Comparative properties of cellulose nano-crystals from native and mercerized cotton fibers

Stable aqueous suspensions of cellulose nano-crystals (CNCs) were fabricated from both native and mercerized cotton fibers by sulfuric acid hydrolysis, followed by high-pressure homogenization. Fourier transform infrared spectrometry and wide-angle X-ray diffraction data showed that the fibers had been transformed from cellulose I (native) to cellulose II (mercerized) crystal structure, and these polymorphs were retained in the nanocrystals, giving CNC-I and CNC-II. Transmission electron microscopy showed rod-like crystal morphology for both types of crystals under the given processing conditions with CNC-II having similar width but reduced length. Freeze-dried agglomerates of CNC-II had a much higher bulk density than that of CNC-I. Thermo-gravimetric analysis showed that CNC-II had better thermal stability. The storage moduli of CNC-II suspensions at all temperatures were substantially larger than those of CNC-I suspensions at the same concentration level. CNC-II suspensions and gels were more stable in response to temperature increases. Films of CNC and Poly(ethylene oxide) were tested. Both CNC-I/PEO and CNC-II/PEO composites showed increased tensile strength and elongation at break compared to pure PEO. However, composites with CNC-II had higher strength and elongation than composites with CNC-I.

Segal crystallinity index revisited by the simulation of X-ray diffraction patterns of cotton cellulose Iβ and cellulose II

The Segal method estimates the amorphous fraction of cellulose Iβ materials simply based on intensity at 18° 2θ in an X-ray diffraction pattern and was extended to cellulose II using 16° 2θ intensity. To address the dependency of Segal amorphous intensity on crystal size, cellulose polymorph, and the degree of polymorphic conversion, we simulated the diffraction patterns of cotton celluloses (Iβ and II) and compared the simulated amorphous fractions with the Segal values. The diffraction patterns of control and mercerized cottons, respectively, were simulated with perfect crystals of cellulose Iβ (1.54° FWHM) and cellulose II (2.30° FWHM) as well as 10% and 35% amorphous celluloses. Their Segal amorphous fractions were 15% and 31%, respectively. The higher Segal amorphous fraction for control cotton was attributed to the peak overlap. Although the amorphous fraction was set in the simulation, the peak overlap induced by the increase of FWHM further enhanced the Segal amorphous intensity of cellulose Iβ. For cellulose II, the effect of peak overlap was smaller; however the lower reflection of the amorphous cellulose scattering in its Segal amorphous location resulted in smaller Segal amorphous fractions. Despite this underestimation, the relatively good agreement of the Segal method with the simulation for mercerized cotton was attributed to the incomplete conversion to cellulose II. The (1-10) and (110) peaks of cellulose Iβ remained near the Segal amorphous location of cellulose II for blends of control and mercerized cotton fibers.

Characterization of cellulose II nanoparticles regenerated from 1-butyl-3-methylimidazolium chloride

Regenerated cellulose nanoparticles (RCNs) including both elongated fiber and spherical structures were prepared from microcrystalline cellulose (MCC) and cotton using 1-butyl-3-methylimidazolium chloride followed by high-pressure homogenization. The crystalline structure of RCNs was cellulose II in contrast to the cellulose I form of the starting materials. Also, the RCNs have decreased crystallinity and crystallite size. The elongated RCNs produced from cotton and MCC had average lengths of 123 ± 34 and 112 ± 42 nm, and mean widths of 12 ± 5 and 12 ± 3 nm, respectively. The average diameter of spherical RCNs from MCC was 118 ± 32nm. The dimensions of the various RCNs were all well fitted with an asymmetrical log-normal distribution function. The RCN has a two-step pyrolysis, different from raw MCC and cotton that have a one-step process.

Immobilization of lysozyme-cellulose amide-linked conjugates on cellulose I and II cotton nanocrystalline preparations

Lysozyme was attached through an amide linkage between some of the protein’s aspartate and glutamate residues to amino-glycine-cellulose, which was prepared by esterification of glycine to preparations of cotton nanocrystals. The nanocrystalline preparations were produced through acid hydrolysis and mechanical breakage of the cotton fibers from a scoured and bleached cotton fabric and a scoured and bleached, mercerized fabric, which was shown to produce cellulose I (NCI) and cellulose II (NCII) crystals respectively. A carbodiimide-activation coupling reaction was used to create the lysozyme-amino-glycine-cellulose conjugates using both NCI and NCII in a polar solvent and gave yields of covalently linked lysozyme at 604xa0mg/gram of cotton nanocrystal. The incorporation of lysozyme conjugated to the NCI and NCII preparations gave very high activity (1,500xa0U/mg cotton) when assessed using a fluorescence tag assay to measure antimicrobial activity against Micrococcus lysodeikticus. Scanning electron micrographs demonstrated an aggregation of nanoparticles corresponding to lysozyme bound on the surface of larger cotton nanocrystalline sheets. The approach of producing high enzyme activity on cotton nanocrystals is discussed in the context of selectively presenting robust hydrolase activity on nanocrystalline surfaces.

Kinetic and structural analysis of fluorescent peptides on cotton cellulose nanocrystals as elastase sensors

Human neutrophil elastase (HNE) and porcine pancreatic elastase (PPE) are serine proteases with destructive proteolytic activity. Because of this activity, there is considerable interest in elastase sensors. Herein we report the synthesis, characterization, and kinetic profiles of tri- and tetrapeptide substrates of elastase as glycine-esterified fluorescent analogs of cotton cellulose nanocrystals (CCN). The degree of substitution of peptide incorporated in CCN was 3-4 peptides per 100 anhydroglucose units. Glycine and peptide-cellulose-nanocrystals revealed crystallinity indices of 79 and 76%, respectively, and a crystallite size of 58.5 Å. A crystallite model of the peptide-cellulose conjugate is shown. The tripeptide conjugate of CCN demonstrated five-fold greater efficiency in HNE than the tripeptide in solution judged by its kcat/Km of 33,515. The sensor limits of detection at 2mg of the tri- and tetrapeptide CCN conjugates over a 10 min reaction time course were 0.03 U/mL PPE and 0.05 U/mL HNE, respectively.

Comparative physical and chemical analyses of cotton fibers from two near isogenic upland lines differing in fiber wall thickness

The thickness of cotton fiber cell walls is an important property that partially determines the economic value of cotton. To better understand the physical and chemical manifestations of the genetic variations that regulate the degree of fiber wall thickness, we used a comprehensive set of methods to compare fiber properties of the immature fiber (im) mutant, called immature because it produces thin-walled fibers, and its isogenic wild type Texas Marker-1 (TM-1) that is a standard upland cotton variety producing normal fibers with thick walls. Comprehensive structural analyses showed that im and TM-1 fibers shared a common developmental process of cell wall thickening, contrary to the previous report that the phase in the im fiber development might be retarded. No significant differences were found in cellulose content, crystallinity index, crystal size, matrix polymer composition, or in ribbon width between the isogenic fibers. In contrast, significant differences were detected in their linear density, cross-section micrographs of fibers from opened bolls, and in the lateral order between their cellulose microfibrils (CMFs). The cellulose mass in a given fiber length was lower and the CMFs were less organized in the im fibers compared with the TM-1 fibers. The presented results imply that the disruption of CMF organization or assembly in the cell walls may be associated with the immature phenotype of the im fibers.

Quantum mechanics models of the methanol dimer: OH⋯O hydrogen bonds of β-d-glucose moieties from crystallographic data

The interaction of two methanol molecules, simplified models of carbohydrates and cellulose, was examined using a variety of quantum mechanics (QM) levels of theory. Energy plots for hydrogen bonding distance (H⋯O) and angle (OH⋯O) were constructed. All but two experimental structures were located in stabilized areas on the vacuum phase energy plots. Each of the 399 models was analyzed with Baders atoms-in-molecules (AIM) theory, which showed a widespread ability by the dimer models to form OH⋯O hydrogen bonds that have bond paths and Bond Critical Points. Continuum solvation calculations suggest that a portion of the energy-stabilized structures could occur in the presence of water. A survey of the Cambridge Structural Database (CSD) for all donor-acceptor interactions in β-D-glucose moieties examined the similarities and differences among the hydroxyl groups and acetal oxygen atoms that participate in hydrogen bonds. Comparable behavior was observed for the O2H, O3H, O4H, and O6H hydroxyls, acting either as acceptors or donors. Ring O atoms showed distinct hydrogen bonding behavior that favored mid-length hydrogen bonds.

Surface wetting behavior of nanocellulose-based composite films

Thin nanocellulose-based composite films (approximately 25xa0μm) were made with cellulose nanocrystals (CNCs), cellulose nanofibers (CNFs), and Zn(2-methylimidazolate anion)2 (ZM) modified CNFs for potential use in energy storage devices such as battery separators. The film morphology and surface wettability were studied in comparison with a commercial Polypropylene-Polyethylene-Polypropylene (PEP) battery separator film. Five different models were used to determine the dispersive and polar components of surface free energy (SFE) for the films and wetting envelopes for various films were constructed. Varied morphology from mixed CNC and CNF composite and increased film porosity coupled with reduced O–H groups on the surface of modified CNFs led to increased surface wettability of CNC–CNF and ZM–CNF films, respectively. All cellulose-based films showed better surface wetting behavior compared with that of the PEP film. The Owens–Wendt–Rabel–Kaelble (OWRK) method was suitable for calculating SFE components of the composite films. The total SFE of the CNC–CNF and ZM–CNF films varied from 42.55 to 53.87xa0mJ/m2 in comparison with 20.19xa0mJ/m2 for the PEP film. The constructed wetting-envelopes can be used to predict the wetting behavior of different solvents on the composite films for target electrochemical applications.Graphical abstract

Comparison and validation of Fourier transform infrared spectroscopic methods for monitoring secondary cell wall cellulose from cotton fibers

The amount of secondary cell wall (SCW) cellulose in the fiber affects the quality and commercial value of cotton. Accurate assessments of SCW cellulose are essential for improving cotton fibers. Fourier transform infrared (FT-IR) spectroscopy enables distinguishing SCW from other cell wall components in a rapid and non-invasive way. Thus it has been used for monitoring SCW development in model plants. Recently, several FT-IR methods have been proposed for monitoring cotton fiber development. However, they are rarely utilized for assessing SCW cellulose from cotton fiber due to limited validation with various cotton species grown in different conditions. Thus, we compared and validated three FT-IR methods including two previously proposed methods analyzing entire spectra or specific bands as well as a new method analyzing FT-IR spectral regions corresponding to cellulose with various cotton fibers grown in planta and in vitro. Comparisons of the FT-IR methods with reference methods showed that the two FT-IR methods analyzing the entire spectra or cellulose regions by principal component analysis monitored SCW qualitatively, whereas the FT-IR method analyzing specific bands (708, 730, and 800xa0cm−1) by a simple algorithm allowed the monitoring of SCW cellulose levels quantitatively. The quantitative FT-IR method is a potential substitute for lengthy and laborious chemical assays for monitoring SCW cellulose levels from cotton fibers, and it can be used for a better understanding of cotton fiber SCW development and as a part of the quality assessment tools used to guide choices for improving fiber quality.

An Assessment of Surface Properties and Moisture Uptake of Nonwoven Fabrics from Ginning By-products

Greige (raw) cotton by-products resulting from cotton ginning and mill processes have long been bleached for use in absorbent nonwoven products. The potential to use greige cotton by-products as an economical source for absorbent nonwoven blends is explored. The nonwoven hydroentanglement of greige cotton lint with cot‐ ton gin motes and comber noils blends was analyzed for fiber surface polarity, swel‐ ling, and absorbance to assess properties with potential usefulness in absorbent nonwovens. The electrokinetic analysis of the fabric surface gives a composite picture of the relative hydrophilic/hydrophobic polarity absorbency and swelling properties. Nonwoven fabrics made with cleaned greige cotton lint separately blended with comber noils and ginning motes at 40:60 and 60:40 blend ratios demonstrated charge, swell, and percent moisture uptake profiles that are characteristic of the fabrics’ crys‐ talline/amorphous cellulosic content with some variance in swelling properties. How‐ ever, cellulose crystallite size varied. X-ray diffraction patterns of the three different cotton constituents displayed similar crystalline cellulose compositions. An electro‐ chemical double-layer analysis of charge based on a pH titration (ζplateau) was em‐ ployed to measure the relative fiber and fabric surface polarity which varied slightly between -21 and -29 mV. A relationship of fiber swelling (∆ζ) and percent moisture content is apparent when greige cotton lint and other fibers are blended. The blended nonwoven materials possess absorbent properties characterized by similar moisture uptake (7.1-9.5 %) and fiber polarity, but some variation in swelling is based on the by-product additive and its percent content. The crystallinity, electrokinetic, and wa‐ ter binding properties of the nonwoven by-product materials are discussed in the con‐ text of the molecular features water, cellulose, and greige cotton components that enhance potential uses as absorbent nonwoven end-use products.