Volume 11 Issue 2

This study investigates the effect of modified wheat straw on the physical and mechanical properties of modified wheat straw/high-density polyethylene (MWS/HDPE) straw-plastic composites. Wheat straw fibers with particle sizes in the range of 0.25 to 0.50 mm were modified with caprolactam (CPL). A Fourier transform infrared spectroscopy (FT-IR) analysis of MWS showed that when the CPL level was 5%, the intensity of the hydroxyl (O–H) and carbonyl (C–O) absorption peaks noticeably decreased, indicating a corresponding decrease in the polarity of the fibers. A physical analysis of the wheat straw fibers indicated that after the modification, the characteristics of the fibers were closer to those of the HDPE polymer matrix, thus contributing to good compatibility and dispersion of the straw fibers within the matrix. The composites of the high-density polyethylene with modified wheat straw particles were successfully synthesized using the melt blend method. The prepared composites were characterized using scanning electron microscopy (SEM), and their mechanical properties were investigated. The MWS/HDPE composites showed superior mechanical properties because of a greater compatibility of MWS with HDPE. The modified WS fibers function as “biological steel,” reinforcing the HDPE to produce bio-composites.

Palm kernel shell (PKS) core fibers, an agricultural waste, were chemically modified using N-(3-chloro-2-hydroxypropyl) trimethylammonium chloride (CHMAC) as a quaternizing agent. The potential of quaternized palm kernel shell (QPKS) as an adsorbent for fluoride in an aqueous solution was then studied. The quaternized palm kernel shell (QPKS) core fibers were characterized using Fourier transform infrared spectroscopy (FTIR) and a scanning electron microscope (SEM). The effect of various factors on the fluoride sequestration was also investigated. The results showed that with an increase in the adsorbent amount and contact time, the efficiency of fluoride removal was improved. The maximum fluoride uptake was obtained at pH 3 and a contact time of 4 h. The adsorption behavior was further investigated using equilibrium isotherms and kinetics studies. The results from these studies fit well into Freundlich, Redlich-Peterson, and Sips isotherm’s with a coefficient of determination (R2) of 0.9716. The maximum fluoride removal was 63%. For kinetics studies, the pseudo-second order was the best fit for fluoride, with an R2 of 0.999. These results suggest that QPKS has the potential to serve as a low-cost adsorbent for fluoride removal from aqueous solutions.

The photo-stabilizing effect of post-extraction was evaluated for thermally modified wood. Extracted and non-extracted thermally modified Scots pine (Pinus sylvestris L.) samples were exposed in a xenon weather-ometer for 1008 h, and the surface color and chemical changes were characterized using a chroma meter, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). The results showed that: (1) the weight losses of thermally modified wood were higher than those of unmodified wood after extraction due to the leaching of some low molecular weight compounds that were generated during thermal modification; (2) the photodegradation of thermally modified wood during weathering was hindered by the presence of extractives; and (3) the color change during weathering was a little more severe in sapwood than in heartwood because more extractives were present in heartwood.

Citric acid is a potential binding agent for composite products that has three carboxyl groups that can be ester linked with the hydroxyl groups found in wood. The addition of sucrose provides hydroxyl groups and increases the amount of ester groups. This research investigated the bonding ability of a new adhesive composed of citric acid-sucrose for teak particleboard. Citric acid and sucrose were dissolved in water under various ratios, and the concentration of the solution was adjusted to 59 to 60 wt%.This adhesive solution was sprayed onto the particles at 10% resin content based on the weight of air-dried particles. Each mixture was then hot pressed at 180 and 200 °C for 10 min. The physical and mechanical properties of the particleboards were tested, and the results showed that increasing the pressing temperature affected the dimensional stability. However, increasing of citric acid in adhesive composition improved the dimensional stability and mechanical properties of the particleboards. The optimum properties of the board were achieved at a pressing temperature of 200 °C and addition of only 10% citric acid. The results also indicated that the peak intensity of C=O group increased with the addition of citric acid and increasing pressing temperature, indicating that ester linkage occurred. However, the addition of sucrose did not greatly affect the peak intensity of C=O group.

A novel, efficient, and direct blend of solvents, tetrabutylammonium acetate/dimethyl sulfoxide (TBAA/DMSO), was used for the dissolution and regeneration of bamboo pulp. Regenerated fibers were successfully prepared by a wet spinning process. The bamboo pulp without any pretreatment was readily soluble in the solvent under mild conditions. The dissolution process was observed using a confocal laser scanning microscope (CLSM). Rheological properties of the cellulose solutions at various concentrations were investigated. The regenerated fibers prepared by coagulation in ethanol were characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and an electronic tensile tester. The SEM images showed that the regenerated fibers possessed a smooth surface and circular cross-section, and the XRD and FT-IR results revealed that the fibers exhibited a cellulose II structure. The thermostability and mechanical properties of the fibers was also investigated.

Reducing the pretreatment cost of lignocellulosic biomass by utilizing alkali to alter its recalcitrant nature is an effective method for biofuel production. In this experiment, 1.5% KOH solution and its black liquor (spent liquor of KOH) (BL) were applied to pretreat corn stover (CS) at a temperature of 20 °C to enhance the digestibility for anaerobic digestion (AD). Results showed no significant difference in weighted average methane content on the basis of experimental methane and biogas yields between BL-treated and original KOH-treated CS after AD. The BL process significantly increased the overall methane yield by 52.4% compared with untreated CS (135.2 mL/gVS), whereas no significant difference between the overall methane yields of 1.5% KOH-treated and BL-treated CS was observed. In addition, the BL process significantly saved water and KOH consumption, by 56.2% and 57.4%, respectively, compared with the 1.5% KOH pretreatment. Overall methane production was well explained by the modified Gompertz model. The physiochemical changes to CS after BL pretreatment were confirmed by SEM, FTIR, and XRD analyses. Our findings collectively suggest that recycling and reuse of KOH black liquor might be an efficient method for lignocellulosic biomass treatment and have the capability to reduce input costs in future AD processes.

To improve the bonding strength between adhesive and enhance the performance of composite board made from corn stalk rinds, a method for preparing three-layer composite boards was proposed. Accordingly, corn stalk rinds with the epidermis removed, were used as the core layer, while crushed aggregates from the epidermis were used as the surface layer of the composite board. Single-factor and orthogonal experiments were conducted to analyze the effects of the sampling height of corn stalk rinds, the surface layer proportions, and the hot-pressing temperature and time on the physico-mechanical properties of composite board. The resulting composite board from corn stalk rinds showed enhanced properties, except for the internal bond strength (P < 0.01). The physical properties of the composite board were significantly improved (P < 0.01) by removing the crushed aggregates of the epidermis, forming a single layer of composite board. The optimal parameters were as follows: the sampling height below the ear part of the corn stalk rinds; 12% surface layers; 150 °C hot-pressing temperature; and 6 min time. Under these conditions, the physico-mechanical properties of the composite board met the requirement level for particleboard. This research supports the use of corn stalk rinds as composite boards.

This work describes a water repellent ultra-low density fiberboard (ULDF) prepared by chlorinated paraffin nanoemulsion (CPNE). Compared with the untreated ULDF, the contact angle of ULDF treated with 150 mL of CPNE increased from 40° to 134°, while its apparent surface free energy decreased from 24.19 mN/m to 10.06 mN/m. Moreover, the water absorbance of ULDF treated with CPNE decreased from 88.2% to 24% in the first hour. The improved hydrophobicity and hygroscopicity of ULDF was supported by the presence of a film on the surface of fibers, as observed by environmental scanning electron microscopy. The occurrence of chlorine and the chemical structure changes in ULDF before and after CPNE treatment were also confirmed by X-ray photoelectron spectroscopy analysis and Fourier transform infrared spectroscopy respectively. This ULDF with enhanced water repellency is a promising insulation material.

The dynamic viscoelasticity of full-size wood composite panels (WCPs) under the free-free vibrational state were determined by a vibration testing method. Vibration detection tests were performed on 194 pieces of three types of full-size WCPs (particleboard, medium density fiberboard, and plywood (PW)). The dynamic viscoelasticity from smaller specimens cut from the panels was measured using a cantilever beam vibration test apparatus, and the two data sets were compared. A strong linear relationship was discovered between the dynamic viscoelasticity values measured by the vibration detection test and the cantilever beam vibration test. The storage modulus values of the panels were far higher than their loss modulus values, and PW panels had the smallest value of loss modulus. For the panels tested, density had a good linear impact on storage modulus. In comparison with density, logarithmic decrement had a greater linear impact on loss modulus. This study demonstrated that the vibration test method is a valid approach for determining the dynamic viscoelasticity of full-size WCPs.

A hydrophilic wood surface was transformed to become superhydrophobic by layer-by-layer (LbL) assembly of polyelectrolyte/titanium dioxide (TiO2) nanoparticles multilayers and subsequent hydrophobic modification with 1H, 1H, 2H, 2H-perfluoroalkyltriethoxysilane (POTS). The chemical composition of the wood samples before and after treatment was characterized by energy dispersive X-ray analysis (EDXA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). These analyses showed that a high-surface-roughness film of TiO2 nanoparticles deposited by LbL became combined on the wood surface with a low-surface-energy thin layer of POTS. The microstructure and the hydrophobicity of the wood samples were analyzed by scanning electron microscope (SEM) and contact angle measurements, respectively. The morphology and the values of water contact angle (WCA) demonstrated that the reaction pH and number of self-assembled layers were the main factors affecting hydrophobic wood samples. After assembly with 5 or more multilayers, the wood surface exhibited excellent superhydrophobicity with the highest WCA of 161°.