Volume 11 Issue 3

A simple but effective method of fabricating superhydrophobic paper with excellent moisture resistance was developed by precipitating carnauba wax onto the surface of cellulose fibers using a phase separation method. Response surface methodology (RSM) was used to optimize the effects of the preparation variables on the water contact angle (WCA) of the paper surface. The four independent variables were carnauba wax concentration, immersion time, coagulation bath ratio (water/ethanol), and coagulation bath time. The optimal treatment conditions were as follows: wax concentration, 3.78% (wax/chloroform, w/v); immersion time, 1.46 h; coagulation bath ratio, 13/87 (water/ethanol, v/v); and coagulation bath time, 2.63 h. Under these conditions, the experimental WCA reached 152.7°, which agreed closely with the predicted value of 154.1°. The surface morphology of the superhydrophobic paper was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the images showed that cluster-like carnauba wax aggregation completely covered the fiber surface, resulting in increased roughness. Moreover, the moisture resistance of the obtained superhydrophobic paper was evaluated. The results demonstrated that under high relative humidity conditions, the moisture resistance of the superhydrophobic paper significantly improved, and its tensile strength remained high.

Bio-based organic acids are an eco-friendly alternative to petroleum-derived products. In this work, the production of organic chemicals was investigated for the first time in the Cosenzaea myxofaciens species using hydrolysed lignocellulosic biomass from Arundo donax. The strain C. myxofaciens BPM1, isolated from bovine rumen, was able to produce a high amount of lactic acid, followed by acetic and succinic acids in synthetic substrate in microaerophilic and anaerobic conditions. When hydrolysed lignocellulosic biomass from Arundo donax supplemented with several nitrogen sources was used as substrate in separate hydrolysis and fermentation in anaerobic conditions, a significant increase in organic acids was recovered, reaching values up to 12.13 ± 0.17, 1.68 ± 0.1, and 5.23 ± 0.04 g L-1 of lactate, succinate, and acetate, respectively. Moreover, the strain C. myxofaciens BPM1 was capable of synthesizing a small amount of ethanol, with a resulting concentration ranging from 0.67 ± 0.05 to 1.46 ± 0.03 g L-1. This work shows that the strain C. myxofaciens BPM1 is a potential source of interesting bio-based chemicals for a wide range of industrial applications. In addition, the inexpensive fermentation process using A. donax hydrolysate and corn steep liquor as carbon and nitrogen sources could be suitable for economical and efficient production of succinic acid in industrial processes.

Previous studies have shown favourable properties for papaya bast fibres, with a Young’s modulus of up to 10 GPa and a tensile strength of up to 100 MPa. Because the fibres remain as residues on papaya plantations across the tropics in large quantities, their use in the making of green composites would seem to be worthy of consideration. This study aims to show that such composites can have very suitable mechanical properties, comparable to or even better than the common wood plastic composites (WPCs), and as such, represent a promising raw material for composites and a low-cost alternative to wood.

The chemical and structural properties of kenaf fibers that were treated at different steam pressures during the steam explosion process were investigated. With increased steam pressure, a higher percentage of cellulose and acid-insoluble lignin and a lower content of hemicellulose and pectin were obtained. This result was further confirmed by Fourier transform infrared (FTIR) spectroscopy. X-ray diffraction (XRD) studies revealed that the steam-exploded kenaf fibers were more crystalline than the raw kenaf fibers, and that excessive steam pressure above 3 MPa damaged the cellulose crystalline structure. Scanning electron microscopy (SEM) analysis showed a change in the surface morphology of the treated kenaf fibers. The lower content of gums and the effective defibrillation of steam-exploded kenaf fibers demonstrated the potential of steam explosion treatment in applications of kenaf fibers.

Mechanical properties of wood were evaluated using nondestructive test methods. The tests were conducted using the stress wave timing and resistance drilling machine, while static mechanical tests were conducted by an Instron universal testing machine. Both nondestructive and static mechanical tests were performed on wood specimens for Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) and elm (Ulmus rubra). There were strong linear correlations between density (ρ) and resistance amplitude (F), static modulus of elasticity (MOE) and dynamic modulus of elasticity (ED), modulus of rupture (MOR) and ED, and ultimate compressive strength (UCS) and ED. Additionally, an algorithm of the reliability index was developed with the first-order second-moment method. The reliability analysis indicated that the reliability index increased with the decreased design value for both Chinese fir and elm, but it increased as the live-to-dead load ratio (ρ) increased. To achieve the reliability index requirements of the Chinese national code, the MOR design value should be set to 12.6 and 21.7 MPa, while the UCS design value should be set to 10.2 and 13.4 MPa for Chinese fir and elm, respectively.

The hot-air/hot-steam process was used for the first time as a combined pre-pressing and pre-heating system for the production of medium-density fiberboards (MDF) at the pilot scale. Pre-heating systems are designed to pre-heat fiber mats before pressing by hot-presses. Using such techniques, pressing times are reduced significantly and the board properties are influenced positively; both are essential for effective MDF production. In recent years, industry has searched for alternatives to petrochemical binders. Primarily, MDF are bonded by urea-formaldehyde (UF) resins in Europe. To replace UF resins, a laccase-mediator-system (LMS) was used to activate the wood fibers’ self-cohesion. It was found that the internal bond strength (IB) and thickness swelling (TS) were noticeably improved by applying the hot-air/hot-steam process before final hot-pressing for both LMS and 10% UF binding systems. Simultaneously, the total pressing time could be reduced by 25% when combining the hot-air/hot-steam process with hot-pressing.

As wood shrinks during the drying process, various stresses may develop and cause surface and internal checking. The aim of this study was to systematically investigate the effect of the drying temperature, relative humidity, and specimen thickness on the contraction stress in elm wood (Ulmus pumila L.) specimens during drying. The contraction stress was used as an indirect indicator of drying stresses. A measurement system was developed in-house and used to simultaneously and continuously obtain the required measurements during drying, which were then used to determine the moisture content, amount of shrinkage, and contraction stress of the wood specimens. In the process of drying, the contraction stress was initially negative with a decrease in the moisture content and an increase in the shrinkage. Then the contraction stress increased gradually and eventually stabilized upon reaching the maximum. The results also showed that as the temperature increased, the moisture content decreased, the shrinkage decreased, the maximum contraction stress decreased, and the contraction stress reached a maximum in a shorter amount of time.

Palm kernel shell (PKS) was incorporated with polylactic acid (PLA) using a solution casting method to produce PLA/PKS biocomposite films. The effects of filler content and butyl methacrylate on the mechanical properties, morphological properties, and thermal properties of PLA/PKS biocomposite films were studied. The addition of PKS into the PLA matrix decreased the tensile strength and elongation at break of PLA/PKS biocomposite films with increasing filler content. In contrast, the modulus of elasticity of the biocomposite films increased. The use of butyl methacrylate as a chemical modification for PKS enhanced the interfacial adhesion and wettability of PKS inside the PLA matrix. This effect was confirmed by the increase in tensile strength, modulus of elasticity, and thermal stability of the biocomposite films. Moreover, scanning electron microscopy showed that there was better interfacial interaction between the filler and the PLA matrix.

Physical, mechanical, and morphological properties of a clay dispersed styrene-co-glycidal methacrylate (ST-co-GMA) impregnated wood polymer nanocomposite (WPNC) were evaluated. The WPNC was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), 3-point bending, free-vibration testing, and X-ray diffraction (XRD) measurements. The FT-IR results showed that the absorbance at 1730 cm−1 was increased for ST-co-GMA-clay-WPNC compared with other nanocomposites and the raw material. The XRD results revealed that crystallinity index and d-spacing were increased compared to raw wood. The SEM results showed that ST-co-GMA-clay-WPNC had a smoother surface than other nanocomposites and raw wood. The modulus of elasticity (MOE), modulus of rupture (MOR), and dynamic Young’s moduli (Ed) of WPNCs were considerably increased compared to wood polymer composites (WPCs) and raw wood. The raw wood exhibited a higher water uptake (WU) than WPNCs and WPCs.

Specimens taken from Pinus nigra Arnold were subject to surfacing techniques by being cut with a circular saw, planed with a thickness machine, and sanded with a calibrating sanding machine (with P80 grit sandpaper). First, their surface roughness values were measured; then, the specimens were processed in the machines in a radial and tangential process. Afterwards, the change in shear strength (adhesiveness resistance) was analyzed as a result of bonding with various adhesive types (PVAc, PU) and pressure applications (0.45 N/mm² or 0.9 N/mm²). Approximately 600 specimens were prepared with the purpose of identifying the effect of variables on the bonding performance, and they were subjected to shear testing. The greatest shear strength achieved for both the tangential and radial surfaces in terms of cutting was observed in specimens processed in the thickness machine, on which polyvinyl acetate adhesive and 0.9 N/mm². pressure were applied. Specimens bonded with polyvinyl acetate adhesive displayed higher shear strength in general in comparison to those bonded with polyurethane for both tangential and radial surfaces.