Modeling of negative Poisson’s ratio (auxetic) crystalline cellulose Iβ

Energy minimizations for unstretched and stretched cellulose models using an all-atom empirical force field (Molecular Mechanics) have been performed to investigate the mechanism for auxetic (negative Poisson’s ratio) response in crystalline cellulose Iβ from kraft cooked Norway spruce. An initial investigation to identify an appropriate force field led to a study of the structure and elastic constants from models employing the CVFF force field. Negative values of on-axis Poisson’s ratios nu31 and nu13 in the x1-x3 plane containing the chain direction (x3) were realized in energy minimizations employing a stress perpendicular to the hydrogen-bonded cellobiose sheets to simulate swelling in this direction due to the kraft cooking process. Energy minimizations of structural evolution due to stretching along the x3 chain direction of the ‘swollen’ (kraft cooked) model identified chain rotation about the chain axis combined with inextensible secondary bonds as the most likely mechanism for auxetic response

Facile preparation of cellulose nanofibers prepared by TEMPO-mediated oxidation

Abstract Cellulose nanofibers (CNFs) with width of 20 nm and lengths of up to several µm were fully disintegrated from water hyacinth (Eichhornia crassipes) with aids of the 2, 2, 6, 6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation and mild-mechanical treatment. TEMPO-oxidized CNFs were characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). FTIR reveals the conversion of C-6 hydroxyl groups to sodium carboxylate groups, and lower thermal degradation was obtained from the TEMPO-oxidized CNFs in comparison to untreated cellulose fibers. The as-prepared TEMPO-oxidized CNFs might be possibly used in packaging and composite applications.</jats:p

Isolation and characterization of cellulose nanofibers (CNFs) from Macaranga hypoleuca

Abstract Macaranga hypoleuca is one of the potential native species for natural fibers consisting of long fibers. In M. hypoleuca pulp the main majority is cellulose, followed by hemicellulose and lignin. Based on these characters, it is possible to prepare cellulose nanofibers (CNFs) from M. hypoleuca pulp. In this work, CNFs were prepared by the combination of the chemical and mechanical treatments. Those were acid hydrolysis by sulfuric acid and ultrasonication machine forwarded. The aims studies observed the potential of M. hypoleuca pulp as a raw material of CNFs and characteristics of CNFs from M. hypoleuca pulp. The results showed of the CNFs had widths of 42 ± 7.27 nm and crystallinity of 76.9%. The decomposition temperature of the CNFs was of 332 °C. This could be value added to M. hypoleuca trees, and the CNFs extracted from this M. hypoleuca pulp might be useful for composite applications.</jats:p

Cross-linked nanocomposite hydrogels based on cellulose nanocrystals and PVA:mechanical properties and creep recovery

Abstract Cellulose nanocrystal (CNC) reinforced poly(vinyl alcohol) (PVA) hydrogels with a water content of ∼92% were successfully prepared with glutaraldehyde (GA) as a cross-linker. The effects of the CNC content on the thermal stability, swelling ratio and mechanical and viscoelastic properties of the cross-linked hydrogels were investigated. The compressive strength at 60% strain for the hydrogels with 1 wt% CNCs increased by 303%, from 17.5 kPa to 53 kPa. The creep results showed that the addition of CNCs decreased the creep elasticity due to molecular chain restriction. The almost complete strain recovery (∼97%) after fixed load removal for 15 min was observed from the hydrogels with CNCs, compared with 92% strain recovery of the neat cross-linked PVA hydrogels. The incorporation of CNCs did not affect the swelling ratio and thermal stability of the hydrogels. These results suggest the cross-linked CNC-PVA hydrogels have potential for use in biomedical and tissue engineering applications

Effect of sodium hydroxide on properties of shrimp-shells-extracted chitin nanofibers

Abstract Shrimp shells from seafood wastes were used as a raw material to prepare chitin nanofibers (ChNFs) by combined chemical and mechanical treatments. The extraction of chitin from shrimp shells involved multistep procedures of deproteinization, demineralization and deacetylation. The deacetylation refers to the replacement process of acetyl groups by reactive amino groups (-NH2). After that, treated chitin were fibrillated by high-speed blending to disintegrate ChNFs. In this work, we studied the effect of sodium hydroxide (NaOH) concentrations (0 - 30 %wt) on properties of ChNFs. Fourier transform infrared (FT-IR) spectra showed with increasing concentrations of NaOH, the intensity of the peak located at ∼1550 cm-1, corresponding to the presence of amide groups (-NH) on chitin molecules decreased. This was an indication of the removal of acetyl groups. The thermal stability of ChNFs was subsequently analyzed by thermogravimetric analysis (TGA). With increasing the concentrations of NaOH, the lower thermal stability of ChNFs was obtained. In addition, the morphologies of ChNFs with widths of a few nanometers were observed by a field emission scanning electron microscope (FE-SEM). The prepared ChNFs in this work could be possibly used as a reinforcing agent for composite applications.</jats:p

Aligned-porous-structured poly(vinyl alcohol) foams with cellulose nanocrystals

Abstract Poly(vinyl alcohol) (PVA) foams were prepared using a green lyophilization process without the use of foaming agents. PVA solutions with contents of CNCs (1–4 wt%) were prepared at two different freezing temperatures (−20 and −186 °C). With the addition of CNCs, moisture uptake of the CNC-PVA foams prepared at two freezing temperatures was lower than the neat PVA foams. With increasing CNC contents, no significant change of the moisture uptake could be observed for both types of the foams. Similar values of the moisture uptake could be found from both foams frozen at −20 and −186 °C. Scanning electron microscope measurements revealed the aligned-porous-structure of the foams frozen at −186 °C along with the ice growth direction while large and elongated pores were observed from the foams with the lower freezing temperature. These unique features of the foams prepared by a freeze-drying technique could be controlled by changing the freezing temperature, and these foams could be useful for specific applications such as tissue engineering scaffolds, thermal insulators or filters