Volume 11 Issue 4

Due to stress concentration at the edges, fiber-fiber bonds under load are known to fail gradually inwards from the edges. In this paper, we propose a failure mechanism for fiber-fiber joints under load, based on the peak stresses occurring at the bond edges. We have modeled the mechanical testing of individual fiber-fiber joints using a finite element method (FEM) framework. The model is based on experimental results of fiber-fiber joint strength tests designed to induce each of the three modes in fracture mechanics: opening, sliding, and tearing. A parametric study of the peak load at the edges of the fibers was carried out in order to identify a failure mechanism. The peak stresses were not directly taken from the FEM models, as these values are highly discretization-dependent. Instead, the peak stresses were estimated from resultant forces and moments in the bond and an idealized geometry of the bonding region. The literature has, up to now, focused on shear load as a failure mechanism for fiber-fiber bonds. However, our findings indicate that pulp fiber joints are sensitive to normal stresses and insensitive to shear stresses. Hence, we suggest utilizing failure criteria related to normal stress in future work.

Effect of lignocellulosic medium supplemented with selected easily-metabolised carbon sources on microbial xylanase production was assessed. A newly isolated oil-palm-waste-domesticated bio-agent-producing fungus, identified based on rRNA analysis as T. asperellum USM SD4 was used as a representative organism. The potential of T. asperellum for enhanced xylanase production was evaluated by the statistical optimization of important cultural parameters via response surface methodology (RSM). T. asperellum showed optimum xylanase activity at pH 7; temperature 27 °C; moisture content 4 mL growth medium (gm): 1 gram dried substrate (gds) and inoculum size 2 x 106 spores/mL. Xylanase activity (2,337 IU/gds) attained in this study was far higher than ever reported for T. asperellum. Using the set of optimum conditions, the mixture of supplementary sugars to the lignocellulosic medium initiated xylanase repression in a concentration-independent manner. However, the degree of repression depended on the nature and type of respectively added sugar. The repressive effect exerted by monosaccharides (xylose, glucose, and fructose) was greater than exerted by either of dimeric (cellobiose and sucrose) or polymeric (xylan) sugars. Of all added substrates, xylan exerted the least repressive effect. Using xylose as a representative sugar, mechanism of xylanase repression was decisively explained and supported with experimental data.

Prehydrolysis is an important step in the kraft-based dissolving process for pulp production, as it helps remove as much hemicellulose as possible from cellulose fibers before the material is subjected to the main delignification operation, i.e., pulping. In this paper, a novel process concept was proposed by adding different dosages of boric acid (BA) based on the oven dry weight of Whangee, a genus of bamboo, in the prehydrolysis stage. The final yields of the prehydrolysis stage obviously increased and ferric ion contents in the hydrolyzed Whangee largely decreased with the addition of BA. Additionally, the highest α-cellulose retention occurred at a BA dosage of 0.5%. The results of acetic acid percent in the total sugars and furfural percent in xylose of the PHL showed that the addition of BA had an important impact on the structure of hemicelluloses in Whangee. Mass balance analysis of the PHL and Whangee indicated that the partly acid-insoluble lignin in Whangee was likely converted into acid-soluble lignin in the PHL.

The block shear strength of Norway spruce (Picea abies (L.) Karst.) glulam joints was tested under low temperatures. Glulam samples were glued with the three of the most common outdoor structural adhesives. The cold temperatures tested were 20, −20, −30, −40, −50, and −60 °C. Within the temperature test range, the block shear strength of the glulam joints was resistant to the effect of temperature. As the temperature decreased, the joints’ block shear strength did not show any significant change. In most cases, phenol-resorcinol-formaldehyde (PRF) adhesive yielded the strongest block shear strength, while melamine-formaldehyde (MF) adhesive yielded the weakest block shear strength. Melamine-urea-formaldehyde (MUF) adhesive yielded similar results to those of MF adhesives for all temperatures tested. The block shear strengths of the glulam joints with PRF, MUF, and MF adhesives were not sensitive to temperature change. The results indicated that PRF, MUF, and MF adhesives are stable for outdoor structural engineered wood construction in cold climates. The results also suggest that the SS-EN 14080 (2013) standard for the block shear method may not be the proper standard for testing differences in shear strength at different temperatures. The EN 302-1 (2011) standard could be more suitable for this purpose.

Print mottle is problematic in the print and paper industry. In this report, a mathematical evaluation model of print mottle was generated after analyzing several methods. The print mottle images can be evaluated by the model based on the theory of wavelet image denoising analyses that use the wavelet multi-scale fast algorithm. The model was then applied to analyze print mottle on four business papers (inkjet papers, newsprint papers, art papers, and double-coated offset printing papers). The correlation between the results of this method and the human visual evaluation system (HVS) was calculated and evaluated. Experimental results showed that the model predictions agreed with HVS results. The correlation between the printed newsprint papers and the eight different wavelet base functions was over 0.76 (such as haar, sym4, bior3.7, etc.) and decomposed at the first, second, and third levels. The results of the three other papers were better matched with the analysis by human eyes, but the correlation of the art paper and visual model were not as strong as the others. The optimal parameters for the print mottle model were presented in the four kinds of papers presented.

A prospective binder composed of a microbial polysaccharide levan present in the culture fluid was obtained. The synthesis of levan was carried out by an Azotobacter vinelandii bacteria strain using molasses, distillery stillage, and milk whey as the nutrient medium. The maximum amount of levan produced in these experiments was 14.5 g/L. Composite materials were obtained based on wood waste and biological binder. Depending on the pressing behaviour, materials were obtained within a density range of 1083 to 1443 kg/m3 and a tensile strength of 7.2 to 32.4 MPa. Water absorption and thickness swelling were 7.2% and 14.9%, respectively. During hot pressing, the resulting materials changed in their attenuated total reflection-frustrated total reflection (ATR-FTR) spectra at frequencies of 930, 1000, and 1750 cm-1, indicating the occurrence of chemical and structural changes in individual components of the lignocellulosic raw materials and changes in the composition of biological binding agent. Analysis of the physico-mechanical properties and other results of the composite materials using scanning electron microscopy (SEM) and X-ray microtomography suggested that composite materials based on the microbial polysaccharide levan-containing binder are advanced, new, and eco-friendly substances.

The isolation of lignin is of great importance to understand its structural characteristics. A lithium chloride/dimethyl sulfoxide (LiCl/DMSO) solvent system has been developed for the dissolution of lignocellulose and for the isolation of lignin for this purpose. In this work, ball-milled wheat leaf (sheath included) was dissolved in the LiCl/DMSO solvent system and then regenerated in water. Two lignin preparations, cellulolytic enzyme lignin from the ball-milled leaf (CEL) and from the regenerated leaf (RCEL), were obtained through a cellulolytic enzyme lignin procedure. The RCEL and CEL were comparatively investigated by the use of wet chemistry and spectroscopic methods. The results indicate that the effects of ball milling and regeneration on the aromatic structure and β-O-4’ linkages of lignin were not significant. The RCEL had a higher isolation yield and purity, but a similar structure with the corresponding CEL. The RCEL can be used for structural analysis.