Crystalline Cellulose Fibers Research Articles

Effect of Processing Time of Steam-Explosion for the Extraction of Cellulose Fibers from Phoenix canariensis Palm Leaves as Potential Renewable Feedstock for Materials.

This paper briefly discusses the utilization of pruning wastes as a lignocellulosic source of cellulose fibers, which could be of potential use in the development of valuable materials such as sustainable textiles and fillers for footwear components including uppers and soles. Phoenix canariensis palm leaves, one of the most common plants found in the local environment of the Alicante region (Spain), was used as a biomass raw material. Determining appropriate processing parameters and their desired range of maximum cellulose extraction states is key to improving yields. Therefore, this study aimed at determining the effect of processing conditions on cellulose extraction by optimizing the hydrothermal process, as a part of overall combined processes involving several steps. Specifically, the time of the steam-explosion stage was varied between 15 and 33 min in order to maximize the cellulose extraction yield. The composition of both the extracted fibers and the resulting by-product solutions generated during the different steps were determined by FTIR and TGA in order to analyze the effectiveness of removing hemicellulose, lignin and extractives as well as the removed substances at each stage for their further valorization. Additionally, the morphology of cellulosic fibers was evaluated by SEM and their crystallinity by XRD. Crystalline cellulose fibers were successfully extracted from pruning biomass wastes, achieving more efficient removal of hemicellulose and lignin when the hydrothermal process was assessed over 25-33 min. This resulted in finer and smoother fibers, but the crystallinity of α-cellulose decreased as the time of steam-explosion increased to 33 min. The characterization of waste solutions generated after the different extraction steps confirmed that the most effective treatments to remove lignin and hemicellulose from the cell wall are alkaline pretreatment and a hydrothermal process.

Characterization of the Putative Acylated Cellulose Synthase Operon in Komagataeibacter xylinus E25.

Bacterial cellulose is a natural polymer with an expanding array of applications. Because of this, the main cellulose producers of the Komagataeibacter genus have been extensively studied with the aim to increase its synthesis or to customize its physicochemical features. Up to now, the genetic studies in Komagataeibacter have focused on the first cellulose synthase operon (bcsI) encoding the main enzyme complex. However, the role of other accessory cellulose operons has been understudied. Here we aimed to fill this gap by performing a detailed analysis of the second cellulose synthase operon (bcsII), which is putatively linked with cellulose acylation. In this study we harnessed the genome sequence, gene expression and protein structure information of K. xylinus E25 and other Komagataeibacter species to discuss the probable features of bcsII and the biochemical function of its main protein products. The results of our study support the previous hypothesis that bcsII is involved in the synthesis of the acylated polymer and expand it by presenting the evidence that it may also function in the regulation of its attachment to the cell surface and to the crystalline cellulose fibers.

The Inducible Accumulation of Cell Wall-Bound p-Hydroxybenzoates Is Involved in the Regulation of Gravitropic Response of Poplar.

Lignin in Populus species is acylated with p-hydroxybenzoate. Monolignol p-hydroxybenzoyltransferase 1 (PHBMT1) mediates p-hydroxybenzoylation of sinapyl alcohol, eventually leading to the modification of syringyl lignin subunits. Angiosperm trees upon gravistimulation undergo the re-orientation of their growth along with the production of specialized secondary xylem, i.e., tension wood (TW), that generates tensile force to pull the inclined stem or leaning branch upward. Sporadic evidence suggests that angiosperm TW contains relatively a high percentage of syringyl lignin and lignin-bound p-hydroxybenzoate. However, whether such lignin modification plays a role in gravitropic response remains unclear. By imposing mechanical bending and/or gravitropic stimuli to the hybrid aspens in the wild type (WT), lignin p-hydroxybenzoate deficient, and p-hydroxybenzoate overproduction plants, we examined the responses of plants to gravitropic/mechanical stress and their cell wall composition changes. We revealed that mechanical bending or gravitropic stimulation not only induced the overproduction of crystalline cellulose fibers and increased the relative abundance of syringyl lignin, but also significantly induced the expression of PHBMT1 and the increased accumulation of p-hydroxybenzoates in TW. Furthermore, we found that although disturbing lignin-bound p-hydroxybenzoate accumulation in the PHBMT1 knockout and overexpression (OE) poplars did not affect the major chemical composition shifts of the cell walls in their TW as occurred in the WT plants, depletion of p-hydroxybenzoates intensified the gravitropic curving of the plantlets in response to gravistimulation, evident with the enhanced stem secant bending angle. By contrast, hyperaccumulation of p-hydroxybenzoates mitigated gravitropic response. These data suggest that PHBMT1-mediated lignin modification is involved in the regulation of poplar gravitropic response and, likely by compromising gravitropism and/or enhancing autotropism, negatively coordinates the action of TW cellulose fibers to control the poplar wood deformation and plant growth.

Molecularly Imprinted Synthetic Glucosidase for the Hydrolysis of Cellulose in Aqueous and Nonaqueous Solutions

Molecular imprinting is a powerful and yet simple method to create multifunctional binding sites within a cross-linked polymer network. We report a new class of synthetic glucosidase prepared through molecular imprinting and postfunctionalization of cross-linked surfactant micelles. These catalysts are protein-sized water-soluble nanoparticles that can be modified in multiple ways. As their natural counterparts, they bind a glucose-containing oligo- or polysaccharide. They contain acidic groups near the glycosidic bond to be cleaved, with the number and distance of the acid groups tuned systematically. Hydrolysis of cellulose in a key step in biomass conversion but is hampered by the incalcitrance of the highly crystalline cellulose fibers. The synthetic glucosidases are shown to hydrolyze cellobiose and cellulose under a variety of conditions. The best catalyst, with a biomimetic double acid catalytic motif, can hydrolyze cellulose with one-fifth of the activity of commercial cellulases in aqueous buffer. As a highly cross-linked polymeric nanoparticle, the synthetic catalyst is stable at elevated temperatures in both aqueous and nonaqueous solvents. In a polar aprotic solvent/ionic liquid mixture, it hydrolyzes cellulose several times faster than commercial cellulases in aqueous buffer. When deposited on magnetic nanoparticles, it retains 75% of its activity after 10 cycles of usage.

‘Green’ composites based on liquid crystalline cellulose fibers and avocado seed starch

Fully biodegradable unidirectional green composites with excellent tensile properties were fabricated by combining one of the highest specific strength liquid crystalline cellulose (LCC) fibers as the reinforcement and microfibrillated cellulose (MFC) strengthened nonedible avocado seed starch (AVS)-based resin. MFC/AVS resin was crosslinked using 1,2,3,4-butane tetracarboxylic acid as well as plasticized using sorbitol or glycerol. Combination of alkali, mechanical and thermal treatments improved LCC fiber fracture stress from 1.5 GPa to over 1.9 GPa and Young’s modulus from 49 to 64 GPa. While the type and amount of plasticizer used changed the fracture strain of MFC/AVS resin, they also showed significant influence on the mechanical properties of the unidirectional composites. These composites prepared by hand lay-up, based on modified LCC fibers resulted in fracture stress of over 380 MPa and Young’s modulus of 19.5 GPa with less than 40% fiber content. Results suggest that there is scope to improve the properties further by using higher fiber content and automated manufacturing. These ‘green’ composites with excellent strength and stiffness may be used in many applications such as construction, automobile and others.

Advanced green composites: New directions

Green composites developed from plant based resources are meant to be naturally biodegradable. While advanced green composites with high strength and stiffness developed recently could find their way in structural applications in the future, significant scope exists to improve their properties further. This paper briefly discusses the development of advanced green composites with high strength, stiffness and toughness made using recently developed liquid crystalline cellulose (LCC) fibers. These green composites can have exceptionally high strength of over 1 GPa and Young’s modulus of over 40 GPa making them truly advanced green composites. This paper also discusses other special characteristics such as fire resistance and autonomous self-healing in green composites that can improve their durability and safety and further enhance their applicability.

Advanced Green composites using liquid crystalline cellulose fibers and waxy maize starch based resin

Advanced green composites have been fabricated by using modified liquid crystalline cellulose (M-LCC) fibers and micro-fibrillated cellulose (MFC) modified waxy maize starch (M-WMS) based resin. LCC fibers, as a reinforcement, were modified in terms of tensile properties by a combination of chemical and heat treatment, under a predetermined tension. The surface topography, crystallinity, molecular alignment, and mechanical properties of M-LCC fibers were investigated to determine the effects of combination modification process on the fibers. M-WMS, as a resin, was prepared by two steps. In the first step, an environment-friendly cross-linker, 1,2,3,4-butane tetracarboxylic acid (BTCA), was used to improve the water resistance and tensile properties of the resin. In the second step, ‘MFC’, as reinforcing agent, was dispersed in the cross-linked resin to obtain substantial improvements in its tensile properties. Unidirectional advanced green composites consisting of M-LCC fibers and M-WMS were fabricated using hand lay-up followed by a compression molding process. The results showed that the M-LCC fibers had strength close to 2 GPa and the composites had strength close to 800 MPa. These advanced green composites could be used in structural applications.

MARTINI coarse-grained model for crystalline cellulose microfibers.

Commercial-scale biofuel production requires a deep understanding of the structure and dynamics of its principal target: cellulose. However, an accurate description and modeling of this carbohydrate structure at the mesoscale remains elusive, particularly because of its overwhelming length scale and configurational complexity. We have derived a set of MARTINI coarse-grained force field parameters for the simulation of crystalline cellulose fibers. The model is adapted to reproduce different physicochemical and mechanical properties of native cellulose Iβ. The model is able not only to handle a transition from cellulose Iβ to another cellulose allomorph, cellulose IIII, but also to capture the physical response to temperature and mechanical bending of longer cellulose nanofibers. By developing the MARTINI model of a solid cellulose crystalline fiber from the building blocks of a soluble cellobiose coarse-grained model, we have provided a systematic way to build MARTINI models for other crystalline biopolymers.

Direct in Situ Observation of Synergism between Cellulolytic Enzymes during the Biodegradation of Crystalline Cellulose Fibers

High-resolution atomic force microscopy (AFM) was used to image the real-time in situ degradation of crystalline by three types of T. reesei cellulolytic enzymes-TrCel6A, TrCel7A, and TrCel7B-and their mixtures. TrCel6A and TrCel7A are exo-acting cellobiohydrolases processing cellulose fibers from the nonreducing and reducing ends, respectively. TrCel7B is an endoglucanase that hydrolyzes amorphous cellulose within fibers. When acting alone on native cellulose fibers, each of the three enzymes is incapable of significant degradation. However, mixtures of two enzymes exhibited synergistic effects. The degradation effects of this synergism depended on the order in which the enzymes were added. Faster hydrolysis rates were observed when TrCel7A (exo) was added to fibers pretreated first with TrCel7B (endo) than when adding the enzymes in the opposite order. Endo-acting TrCel7B removed amorphous cellulose, softened and swelled the fibers, and exposed single microfibrils, facilitating the attack by the exo-acting enzymes. AFM images revealed that exo-acting enzymes processed the TrCel7B-pretreated fibers preferentially from one specific end (reducing or nonreducing). The most efficient (almost 100%) hydrolysis was observed with the mixture of the three enzymes. In this mixture, TrCel7B softened the fiber and TrCel6A and TrCel7A were directly observed to process it from the two opposing ends. This study provides high-resolution direct visualization of the nature of the synergistic relation between T. reesei exo- and endo-acting enzymes digesting native crystalline cellulose.

Fabrication of advanced “green” composites using potassium hydroxide (KOH) treated liquid crystalline (LC) cellulose fibers

Advanced green composites having excellent strength and stiffness were fabricated using liquid crystalline (LC) cellulose fibers and soy protein isolate (SPI) resin. Further, LC cellulose fibers were treated with potassium hydroxide (KOH) to improve their tensile strength and Young’s modulus by increase the crystallinity of cellulose. The improvements were significant when the treatment was carried out while keeping the fibers under tension. The Young’s modulus (stiffness) of the LC cellulose fibers increased by about 33 % from 47.8 to 63.7 GPa and the strength increased by about 18 % from 1483 MPa to 1749 MPa. X-ray diffraction (XRD) study of the LC cellulose fibers showed over 50 % increase in crystallinity after the KOH treatment. The mechanical properties of the LC cellulose fiber-reinforced composites were also high and improved further when the KOH treated fibers were used. With 65 % fiber volume it should be possible to obtain composites with strength above 1020 MPa and modulus of over 37 GPa, making them truly advanced green composites that could be used for structural applications.

Catalysis using gold nanoparticles decorated on nanocrystalline cellulose

A novel nanocomposite was prepared by deposition of carbonate-stabilized Au nanoparticles (AuNPs) onto the surface of poly(diallyldimethyl ammonium chloride) (PDDA)-coated carboxylated nanocrystalline cellulose (NCC). The hybrid material possessed AuNPs (1.45% by weight) with an average diameter of 2.95 ± 0.06 nm. The catalytic activity of AuNP/PDDA/NCC for reducing 4-nitrophenol to 4-aminophenol was compared to other Au-supported composites. An activation energy of 69.2 kJ mol(-1) was obtained for the reaction. Indeed, the reaction rate constant k of (5.1 ± 0.2) × 10(-3) s(-1) was comparable to the benchmark literature value obtained using AuNPs (<5 nm in diameter) decorated on a network of crystalline cellulose fibers. Our strategy promotes the use of natural resources to prepare reusable hybrid inorganic-organic materials for important reactions with facilitated product isolation/purification.

Deconstructing recalcitrant Miscanthus with alkaline peroxide and electrolyzed water

A two-stage pretreatment method was proposed and tested for deconstruction of recalcitrant Miscanthus. During a 1st pretreatment at 50 °C, 1.0–4.0% alkaline peroxide solutions were used to partially remove hemicellulose and lignin. The remaining solids were subjected to a 2nd pretreatment at 121 °C with electrolyzed water. Using 15 filter paper units of cellulase per gram cellulose, a digestibility of 95% was achieved by the two-stage method, which was higher than 81% obtained from a 1% H 2SO 4 pretreatment (200 °C, 8 min). A mass balance for the two-stage process showed that 63% hemicellulose and 64% lignin were removed from the Miscanthus samples after the 1st pretreatment. The Scanning Electron Microscopy images and Fourier Transform Infrared Spectroscopy spectra revealed that after the 1st pretreatment, crystalline cellulose fibers were partially exposed and the linkages between residual lignin and hemicellulose disappeared. After the 2nd pretreatment, cellulose fibers were completely exposed even with cracks developed.

Advanced 'green' composites

Fully biodegradable high strength composites or 'advanced green composites' were fabricated using yearly renewable soy protein based resins and high strength liquid crystalline cellulose fibers. For comparison, E-glass and aramid (Kevlar®) fiber reinforced composites were also prepared using the same modified soy protein resins. The modification of soy protein included forming an interpenetrating network-like (IPN-like) resin with mechanical properties comparable to commonly used epoxy resins. The IPN-like soy protein based resin was further reinforced using nano-clay and microfibrillated cellulose. Fiber/resin interfacial shear strength was characterized using microbond method. Tensile and flexural properties of the composites were characterized as per ASTM standards. A comparison of the tensile and flexural properties of the high strength composites made using the three fibers is presented. The results suggest that these green composites have excellent mechanical properties and can be considered for use in primary structural applications. Although significant additional research is needed in this area, it is clear that advanced green composites will some day replace today's advanced composites made using petroleum based fibers and resins. At the end of their life, the fully sustainable 'advanced green composites' can be easily disposed of or composted without harming the environment, in fact, helping it.

Large-scale production of cellulose-binding domains. Adsorption studies using CBD-FITC conjugates

A method for the gram-scale production of cellulose-binding domains (CBD) through the proteolytic digestion of a commercial enzymatic preparation (Celluclast) was developed. The CBD obtained, isolated from Trichoderma reesei cellobiohydrolase I, is highly pure and heavily glycosylated. The purified peptide has a molecular weight of 8.43 kDa, comprising the binding module, a part of the linker, and about 30% glycosidic moiety. Its properties may thus be different from recombinant ones expressed in bacteria. CBDfluorescein isothiocyanate conjugates were used to study the CBD-cellulose interaction. The presence of fluorescent peptides adsorbed on crystalline and amorphous cellulose fibers suggests that amorphous regions have a higher concentration of binding sites. The adsorption is reversible, but desorption is a very slow process. Abbreviations: CBHI – Cellobiohydrolase I; CBHII – Cellobiohydrolase II; CBD – Cellulose-binding domain; CBDCBHI, CBDCBHII – Cellulose-binding domain of cellobiohydrolase I and II, respectively; FITC – Fluorescein isothiocyanate