Bio-Composites Consisting of Cellulose Nanofibers and Na+ Montmorillonite Clay: Morphology and Performance Property.

This paper reports the usage of cellulose nanofibers (CNFs) as a continuous nanoporous matrix and nanoclay (NC) as additive to fabricate hybrid films. CNF/Cloisite Na+ nanoclay composite films containing 10-50 wt % of NC were prepared for the study. The effects of NC incorporation and its content on mechanical, wettability and thermal degradation properties were investigated. The results showed that the film had a multilayer structure with gradually deposited CNT-NC hybrid on the filter paper Pure CNF films had higher moduli compared with those from the composite films, as the incorporation of NC decreased hydrogen bonding and networking ability of CNFs, especially at the high NC loading levels. The composite films demonstrated self-extinguishing ability when being exposed to the open flame. Composites with over 35 wt % NC did not burn because of the formation of a protective barrier containing ordered NC platelets. The addition of montmorillonite NC led to increased surface water contact angle, showing enhanced hydrophobicity of the material. During the film's thermal pyrolysis, the first process occurred between 100 and 200 °C, resulting mainly from the evaporation of absorbed water; the second, between 280 and 350 °C, indicated thermal decomposition of cellulose; and the slow third stage happened from the 350 to 600 °C, representing carbonization. The results demonstrate that the apparent activation energies for all the CNF/NC composites were higher than the pure CNF film. CNF/NC films fabricated in this process are a promising barrier material for packaging applications.

Influence of Cellulose Nanoparticles on Rheological Behavior of Oil Well Cement-Water Slurries.

Performance of hardened oil well cement (OWC) is largely determined by the rheological properties of the cement slurries. This work was carried out to investigate the effect of water- to-cement ratio (WCR) and cellulose nanoparticles (CNPs), including cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs), on rheology performance of OWC-based slurries using a Couette rotational viscometer coupled with rheological models. The yield stress and viscosity of neat OWC slurries had a decreasing trend with the increase of WCRs. The suspension became increased unstable with the increase of WCRs. The properties of CNPs, including rheological behaviors, surface properties and morphology, determine the rheological performance of CNP-OWC slurries. In comparison with CNC-OWC slurries, the gel strength, yield stress and viscosity of CNF-OWC slurries were higher as CNFs were more likely to form an entangled network. The gel strength, yield stress and viscosity of CNP-OWC slurries increased with reduced CNF size through regrinding and the proportion of CNFs in the mixture of CNFs and CNCs, respectively.

Cellulose Nanocrystals (CNCs) from Corn Stalk: Activation Energy Analysis.

Cellulose nanocrystals (CNCs) were isolated from corn stalk using sulfuric acid hydrolysis, and their morphology, chemical structure, and thermal stability properties were characterized. The CNCs had an average length of 120.2 ± 61.3 nm and diameter of 6.4 ± 3.1 nm (L/D = 18.7). The degree of crystallinity of the CNCs increased to 69.20% from the 33.20% crystallinity of raw corn stalk fiber, while the chemical structure was well kept after sulfuric acid hydrolysis. Thermal stability analysis showed that the degradation temperature of the CNCs reached 239.5 °C, which was higher than that of the raw fiber but lower than that of the extracted cellulose. The average activation energy values for the CNCs, evaluated using the Friedman, Flynn-Wall-Ozawa (F-W-O) and Coats-Redfern methods, were 312.6, 302.8, and 309 kJ·mol-1 in the conversion range of 0.1 to 0.8. The isolated CNCs had higher values of activation energy than did the purified cellulose, which was attributed to the stronger hydrogen bonds present in the crystalline domains of CNCs than in those of cellulose. These findings can help better understand the thermal properties of polymer/CNC composites.

Preparation and Properties of Electrospun Poly (Vinyl Pyrrolidone)/Cellulose Nanocrystal/Silver Nanoparticle Composite Fibers.

Poly (vinyl pyrrolidone) (PVP)/cellulose nanocrystal (CNC)/silver nanoparticle composite fibers were prepared via electrospinning using N,N'-dimethylformamide (DMF) as a solvent. Rheology, morphology, thermal properties, mechanical properties, and antimicrobial activity of nanocomposites were characterized as a function of material composition. The PVP/CNC/Ag electrospun suspensions exhibited higher conductivity and better rheological properties compared with those of the pure PVP solution. The average diameter of the PVP electrospun fibers decreased with the increase in the amount of CNCs and Ag nanoparticles. Thermal stability of electrospun composite fibers was decreased with the addition of CNCs. The CNCs help increase the composite tensile strength, while the elongation at break decreased. The composite fibers included Ag nanoparticles showed improved antimicrobial activity against both the Gram-negative bacterium Escherichia coli (E. coli) and the Gram-positive bacterium Staphylococcus aureus (S. aureus). The enhanced strength and antimicrobial performances of PVP/CNC/Ag electrospun composite fibers make the mat material an attractive candidate for application in the biomedical field.

Improvement of straw surface characteristics via thermomechanical and chemical treatments.

This study focused on effects of thermomechanical treatment, acid hydrolysis and enzymatic hydrolysis of rice straw fibre on its water resistant. Xylose and arabinose yields were 19.97% and 2.55%, respectively with thermomechanical treatment, 24.35% and 3.18% with acid hydrolysis, and 20.11% and 2.73% with enzymatic hydrolysis. The acid treatment dissolved hemicellulose significantly, leading to more fines and more voids in the surface of the rice straw fibre. The fines showed a higher water retention value (WRV) of 137.41% and exhibited higher swelling capacity. An increase in acid loading resulted in the increased WRV. The enzymatic hydrolysis increased the crystallinity of cellulose, but no significant correlation could be found between the chemical component and the water resistance of the rice straw fibre.

Evaluation of elastic modulus and hardness of crop stalks cell walls by nano-indentation.

Agricultural biomaterials such as crop stalks are natural sources of cellulosic fiber and have great potential as reinforced materials in bio-composites. In order to evaluate their potential as materials for reinforcement, the nano-mechanical properties of crop-stalk cell walls, i.e. those of cotton (Gossypium herbaceu) stalk, soybean (Glycine max) stalk, cassava (Manihot esculent) stalk, rice (Oryza sativa L.) straw, and wheat (Triticum aestivum L.) straw, were investigated by means of nano-indentation and atomic force microscopy (AFM). The elastic modulus of wheat straw was found to be 20.8 GPa, which was higher than that of the other four crops. The highest hardness was observed in cotton stalk at 0.85 GPa. The elastic moduli of the crop stalks were lower than those of most of the hardwood species, but higher than that of some softwoods and of lyocell fiber. The mean value of the hardness of the five crop stalks' cell walls was higher than those of wood or lyocell fiber.