Springer Science and Business Media LLC

Xyloglucans are the principal polysaccharides coating and crosslinking cellulose microfibrills in the majority of land plants. This review summarizes current knowledge of xyloglucan structures, solution properties, and the mechanism of interaction of xyloglucans with cellulose. This knowledge base forms the platform for new biomimetic methods of cellulose surface modification with applications within the fields of textile manufacture, papermaking, and materials science. Recent advances using the enzyme xyloglucan endo-transglycosylase (XET, EC 2.4.1.207) to introduce varied chemical functionality onto cellulose surfaces are highlighted.

Hydrothermal pre-treatments decrease lignocellulose recalcitrance against enzymatic hydrolysis by removing the majority of the hemicellulose, thus increasing cellulase accessibility. However, a small amount of the hemicellulose may remain and become adsorbed to the cellulose, leading to cellulase inhibition. Here, we produced hemicellulose bound cellulose, using glucuronoxylan and galactomannan, to simulate hydrothermally pre-treated hardwoods and softwoods, respectively, and evaluated how this can affect cellulose hydrolysis by Trichoderma reesei derived cellobiohydrolase I (Cel7A). Based on X-ray powder diffraction (XRD), histochemistry, scanning electron microscopy and Simon’s staining, hemicellulose binding onto cellulose affected the physical properties of the biomass, which subsequently affected its hydrolysis rate. As a result of hemicellulose binding onto cellulose, the adsorption of Cel7A was significantly impacted (up to 45%), leading to lowered activities (a 40% reduction), especially for glucuronoxylan. The bound hemicellulose may be released from the cellulose during agitation and hydrolysis. We therefore evaluated the effect of free hemicellulose on Cel7A. Free xylan was more inhibitory to Cel7A than free mannan, demonstrating non-competitive inhibition, while mannan exhibited uncompetitive inhibition. The recalcitrant effect of both bound and free hemicellulose could be relieved by the addition of hemicellulolytic enzymes (i.e. XT6 and Man26A) during cellulose hydrolysis. During the degradation of cellulose in “realistic” woody biomasses by Cel7A, the addition of hemicellulases led to a significant improvement in cellulose hydrolysis. This study showed that hemicellulose remains a critical factor regarding biomass recalcitrance and that the addition of hemicellulolytic activities in commercial enzyme cocktails is required (especially the mannanolytic activities lacking from most commercial enzyme cocktails), in order to realise high sugar yields at low enzyme protein loadings for low-cost biofuel production.

The aim of this study was to discern the film formation mechanism of cellulose nanoparticle suspensions (CNP suspensions) by transforming the film formation process to be a water evaporation process, investigating the fast freeze-drying morphology of CNPs, the resulting natural formation structure, and the relationship of CNPs and water molecules. It was found that an increasing aspect ratio transforms CNPs from the oriented arrangement to a distributed network. Hydrogen bonds and van der Waals forces among CNPs led to a close and interactive film formation process, contributing to various microstructures in the resultant films. High aspect ratios in CNPs hindered the formation of interaction as well as increased absorbed water on CNPs. The interaction among CNPs, and the interaction between CNPs and water molecules were reflected in shear-thinning behavior of CNP suspensions. High aspect ratio CNPs had the capacity of absorbing more immobilized water, partially leading to a higher viscosity. The microstructures of CNP films were fund to be dense without significant layers or holes and varied from the fast freeze-drying morphology, due to the continuous volume reduction in water evaporation. Overall, it is expected that discerning the film formation mechanism of CNPs provide guidance for controlling the film structure and explaining the macroscopic property of the resultant materials.

Cellulose nanopaper (CNP) made of cellulose nanofibrils has gained extensive attention in recent years for its lightweight and superior mechanical properties alongside sustainable and green attributes. The mechanical characterization studies on CNP at the moment have generally been limited to tension tests. In fact, thus far there has not been any report on crack initiation and growth behavior, especially under dynamic loading conditions. In this work, crack initiation and growth in self-assembled CNP, made from filtration of CNF suspension, are studied using a full-field optical method. Dynamic crack initiation and growth behaviors and time-resolved fracture parameters are quantified using Digital Image Correlation technique. The challenge associated with dynamic loading of a thin strip of CNP has been overcome by an acrylic holder with a wide pre-cut slot bridged by edge-cracked CNP. The ultrahigh-speed digital photography is implemented to map in-plane deformations during pre- and post-crack initiation regimes including dynamic crack growth. Under stress wave loading conditions, macroscale crack growth occurs at surprisingly high-speed (600–700 m/s) in this microscopically fibrous material. The measured displacement fields from dynamic loading conditions are analyzed to extract stress intensity factors (SIF) and energy release rate (G) histories. The results show that the SIF at crack initiation is in the range of 6–7 MPa m1/2, far superior to many engineering plastics. Furthermore, the measured values increase during crack propagation under both low- and high-strain rates, demonstrating superior fracture resistance of CNP valuable for many structural applications.

The nanoscale hygromechanical behavior of lignin is presented in this work. Three atomic force microscopy experimental methods were used to correlate moisture sorption of lignin to its mechanical behavior. First, sorption isotherms were established using cantilever mass sensing and subsequently predicted using the Guggenheim–Anderson–de Boer model. The sorption isotherms of lignin particles followed a repeatable and cyclic trend reaching a maximum moisture content of ≈ 17% at ≈ 79% relative humidity (RH). Second, 3D nanomechanical contrast images were obtained using contact resonance force microscopy (CR-FM) to observe the hygromechanical response of lignin over three RH cycles. Finally, force volume mapping and the Hertz model were used to compute the elastic modulus of lignin as a function of moisture content. As RH increased, CR-FM measurements revealed initial topographical heterogeneity, as well as notable surface softening, especially in initially smooth domains. The average elastic modulus of the smooth domain decreased from 9.0 to 4.3 to 2.4 GPa as the moisture content increased from 0.024 to 9.1 to 17.3%, respectively. Cyclic measurements confirm that the elastic modulus of lignin rebounds upon moisture desorption.

With ever increasing environmental awareness, renewable raw materials for textile and composite industry have become an important alternative to reduce the use of petroleum-based non-biodegradable fibers in various applications such as marine, automotive, sports and aerospace. Therefore, it is highly critical to understand the chemistry, structure, and properties of novel plant fibers. Natural fibers have been used for various purposes since ancient times. Numerous research and review papers were published on harvesting, production, properties and potential applications of conventional natural fibers. Sustainability, renewability, and recyclability issues increased the use of novel natural fibers globally. New applications such as natural fiber reinforced biodegradable composites also increased the importance of investigations on new natural fibers. This review paper considers extraction methods, fiber structure, chemical, physical and mechanical properties of novel cellulosic fibers. Fiber chemical constituents, functional groups, and surface hydrophilicity were discussed in terms of chemical properties. Physical properties of the cellulosic fibers such as density, crystallinity, maximum thermal degradation, mechanical performance and surface morphology were also discussed. Additionally, mechanical performance of new plant fibers was performed by comparing between some properties of common and recently characterized cellulosic fibers. The brief information about life-cycle assessment, sustainability, recycling, and biocomposite application of the novel plant fibers is also presented. According to the best our knowledge on literature review, this review may be unique to provide detailed information about recently characterized cellulosic fibers. This survey will be helpful to researchers who have interest in novel ligno-cellulosic fibers and fiber reinforced composites.

This research was conducted to determine the combined effects of different cellulolytic pretreatments (cellulase vs. mixed enzymes) and extraction methods (water vs. deep eutectic solvent, DES) on the yield, chemical and functional properties of polysaccharide (PS) from sugarcane leaves (SCLs). The DESs used were choline chloride-1,4-butanediol (DESB) and choline chloride-urea (DESU). The SCLs were initially enzyme-pretreated, followed by extraction using water and DES respectively. The produced crude polysaccharide extracts (CPSs) were characterized via FTIR, total phenolics, DPPH free radical scavenging activity and in vitro simulated gastrointestinal analysis. The results indicated that cellulolytic pretreatment improved the PS yield by 14–16%, but reduced the solubility, DPPH activity and gastrointestinal digestibility of CPS. DES-CPSs possessed higher solubility and DPPH activity than water-CPSs. FTIR analysis unveiled that lignin–carbohydrate-complex was likely the component that restricted the solubility and probably the digestibility of water-CPSs. This study concluded that pretreatment and extraction procedures distinctively affected the chemical characteristics, and subsequently the functional properties of CPS.

There has always been an interest in the professional communities of libraries, archives and conservation science to find ways of estimating the rate of degradation of paper under archival conservation conditions. Previously we reported a number of considerations for developing a kinetic degradation model based on Whatman no.1 paper. In the present research, this model was extended to 10 different papers and validated. Various physical and chemical properties of acidic, neutral, and alkaline papers were measured, such as the degree of polymerization (DP), tensile strength, equilibrium moisture content, and pH, as well as alkaline fillers content when applicable. The activation energy (Ea) based on DP of cellulose and zero-span tensile strength were determined. Ea and pH had the most significant influence on the simulated decay of paper. Papers with a high Ea (> 120 kJ mol−1), alkaline such as those containing at least 2% CaCO3, and acidic—but good printing quality papers made of bleached chemical pulp– were found the most durable in ambient conditions. Papers with a lower Ea (< 110 kJ mol−1) such as lignocellulosic papers containing significant amount of mechanical pulp were much less stable over time. Whatman filter papers, used as models of pure cellulosic papers, were found to have low Ea despite the good quality cotton fibers. A generic isoperm equation based on Ea was developed to predict the changes in the state of papers under various climatic conditions, and was applicable independently of the pH of the paper. The model developed allows a better quantification of the deterioration rate of printing papers such as those that are currently, and will be in the future, found in our archival collections.