Volume 8 Issue 4

Torrefaction of sawdust has the advantages of increasing its heating value, lowering its O/C ratio, and making it more convenient to transport and crush. Torrefied sawdust has characteristics that are more similar to coal than to sawdust. The initial pyrolysis temperature and residue content of torrefied sawdust are higher than those of sawdust. With the increase of coalification degree of three different coals, the initial pyrolysis temperature and residue contents are raised. The initial pyrolysis temperatures and remaining contents of lignite, bituminous coal, and anthracite are 330, 380, and 500 °C and 61.3, 75.1, and 89.5%, respectively. The torrefied sawdust also has a synergistic effect on the conversion of anthracite and bituminous coal, but it has an inhibitory effect on lignite. The composition of gaseous products was also measured after pyrolysis. The results demonstrate that with the addition of torrefied sawdust to anthracite and bituminous coal, the gaseous products contain more combustible components, such as H2, CO, and CH4, which increase the heating value. Moreover, the effect is more obvious with the co-pyrolysis of torrefied sawdust and anthracite. However, the co-pyrolysis of torrefied sawdust and lignite leads to decreasing CO and light hydrocarbons (CnHm (n=1, 2)) in the resulting gaseous products, which has a negative effect on the quality of the gaseous products. The co-pyrolysis characteristics of torrefied sawdust with different rank coals are discussed in this paper.

Poly-epichlorohydrin-dimethylamine (p-DMA-co-ECH) was synthesized and was used to modify bleached eucalyptus kraft pulp (BEKP). The modified pulp (designated PDMAECH pulp) was characterized by zeta potential, FTIR, NMR, and SEM. Both the PDMAECH pulp and the BEKP were used as adsorbents to remove Acid Scarlet G (ASG) from aqueous solution. The effects of operational parameters on the efficiency of dye removal, including pH, adsorbent dosage, initial dye concentration, and contact time, were investigated. Results showed that modification could change the surface characteristics and effectively enhance the adsorption capacity. The optimum pH for ASG removal with the modified bleached eucalyptus kraft pulp (PDMAECH pulp) was found to be 4.0, and for BEKP it was 2.0. Under the optimized conditions, the maximum capacities for ASG adsorption were also investigated. The adsorption processes of both adsorption reactions were spontaneous and exothermic, and the adsorption capacities decreased with an increase in temperature. Freundlich and Langmuir models were used to analyze the obtained experimental data. The Langmuir model was found to be a better fit for the experimental data for both adsorbents. Kinetic studies showed that the rate of adsorption of ASG on both adsorbents obeyed a pseudo-second-order kinetics model. The desorption process for PDMAECH pulp was also explored.

Birch sawdust was extracted with a pressurized hot water (PHW) flow-through system. The pH of the extract was controlled during extraction by the addition of acetic acid/sodium acetate buffer. Three different pH levels, 4.0, 4.2, and 4.6, were used. Extraction temperatures were 160, 170, and 180 °C, with a constant 4 mL/min flow rate through the 50 mL extraction vessel. During PHW extraction with plain water, the end pH of the extract dropped from 5 to below 3. Buffers kept the pH of the extracts constant during the first 30 min of extraction. Compared to plain water, the use of buffers resulted in a lower yield of xylans during the 170 °C extraction. However, with the buffered system it was possible to obtain xylans from sawdust with a higher molar mass than plain water extraction. Acetic acid/sodium acetate buffer enabled control of the hydrolysis rate of xylans during extraction.

The process of wood drying can induce defects caused by drying stress, which limits the processing and utilization of this valuable material. Here, we investigated elastic strain, viscoelastic creep strain, and mechano-sorptive (MS) creep strain caused by shrinkage anisotropy using the image analytical method during slow conventional drying of white birch (Betula platyphylla Suk) disks. The rheological properties of wood disks with different moisture contents (MC) were analyzed together with the influences of MC and radial position on each strain. The results showed that relations between stress and strain are complex; below the fiber saturation point (FSP), the wood disk is initially subject to tangential tensile stress; with decreasing MC, the tensile stress turns into a compressive stress. MS creep strain increased with decreasing MC; however, elastic strain and viscoelastic creep strain were positively correlated with MC. Elastic strain decreased after first increasing, and then remained stable while the MS creep strain significantly increased from pith to bark, at 10% MC and 18% MC, respectively. Shrinkage anisotropy was the main reason for strain during the drying processing, and it was one of the main factors causing cracks during drying or application.

Kenaf (Hibiscus cannabinus), a fast-growing fiber crop, is a potential substitute for wood to make composition boards. This work investigated single- and three-layer kenaf core particleboards (KPBs) and kenaf core-cedar wood composite particleboard (KCPB) with polymeric methylene diphenyl diisocyanate (pMDI) and phenol formaldehyde (PF) resins. The physical and mechanical properties including bending modulus (MOE) and strength (MOR), internal bond (IB) strength, water absorption (WA), thickness swelling (TS), and linear expansion (LE) were tested following the ASTM D 1037 and ANSI A 208.1 standards. It was shown that kenaf core can be made into standard-satisfying particleboards with comparable performances to cedar-based wood panels. Three processing factors, i.e., board density, resin content, and layered construction, had significant influences on panel properties. KPBs denser than 0.70 g/cm3 and with 6% PF met with the standard specifications. The WA, TS, and LE of single-layer KPBs decreased with increased density. Three-layer KPBs showed improved MOE, MOR, and IB strengths, and effectively avoided the unbalanced structure shown in the single-layer KPBs in thickness direction. The three-layer KPBs with a 50:50 surface-to-core ratio had the best comprehensive performances. The results can be helpful for the application of kenaf residues in the wood composites industry.

Oil palm mesocarp fibers (OPMFs) are left as a waste material after oil extraction. A new application of OPMF is needed to economically utilize these fibers; thus OPMFs need to be modified to render them hydrophobic. Hydrogen peroxide was used to initiate the graft copolymerization of butyl acrylate onto OPMF in aqueous solution. The duration of reaction, temperature, and amounts of butyl acrylate and initiator were optimized using response surface methodology (RSM) coupled with a four-factor central composite design (CCD). The response variable was percentage grafting (%G). A quadratic model was obtained and developed to correlate the independent variables to %G. The optimum conditions predicted through RSM were 110 min duration of reaction, 50 °C temperature, 28 mmol of monomer, and 5.99 mmol of initiator, with a %G of 116.2%. Synthesized graft copolymers were characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis. The thermal stability of OPMF improved significantly after grafting. The FTIR and SEM results showed that graft copolymerization successfully occurred onto the OPMF backbone. The tensile test results support the utilization of grafted OPMF as a potential compatibilizer.

There has been great attention focused on the effects of first and second generation biofuels on global warming. The Energy Independence and Security Act (EISA) and the Renewable Fuel Standard (RFS) have mandated production levels and performance criteria of biofuels in the United States. The thermochemical conversion of biomass to ethanol shows potential as a biofuel production pathway. The objective of this research was to examine the alcohol yields and GHG emissions from the thermochemical conversion process for six different feedstocks on a gate-to-gate basis. GHG analyses and life cycle assessments were performed for natural hardwood, loblolly pine, eucalyptus, miscanthus, corn stover, and switchgrass feedstocks using a NREL thermochemical model and SimaPro. Alcohol yield and GHG emission for the hybrid poplar baseline feedstock conversion were 105,400 L dry metric ton−1 and 2.8 kg CO2 eq. per liter, respectively. Compared with the baseline, loblolly pine produced the highest alcohol yields, an 8.5% increase, and the lowest GHG emissions per liter of ethanol, a 9.1% decrease. Corn stover, due to its high ash content, had the lowest yields and the highest GHG emissions per liter of ethanol. The results were highly sensitive to the ash and water content of the biomass, indicating that biomass properties can significantly affect the environmental impact of the thermochemical ethanol conversion process.

The interactive effect of the thermo-mechanical densification and heat treatment on the set-recovery of modified wood were investigated for optimizing the combined modification process in this study. Process parameters such as thermo-mechanical densification temperature, duration of densification, and heat treatment temperature were selected as main factors; three levels of each of these factors were chosen, and then nine experiments plus one verification experiment were conducted according to the principles of the Taguchi DoE method and the results of ANOVA analysis. It was observed that the dimensional stability of combined modified Chinese fir wood in the compression direction can be effectively improved by elevating the heat treatment temperature and densification temperature, the percentage contributions of which were 76.04% and 21.18%, respectively. Meanwhile the set-recovery had no dependence on the duration of the densification process. The value of the set-recovery in the verification experiment agreed quite well with the predictions. From an economic view, the optimal condition for the combination modification of Chinese fir wood was that of a densification temperature of 170 °C, densification duration of 10 min, and heat treatment temperature of 200 °C.

An oxygen-delignified eucalypt pulp (Eucalyptus grandis x Eucalyptus urophylla hybrid)was provided by a Brazilian pulp mill. It was treated with chlorite to remove lignin, or by a long acidolysis stage to remove most of the hexenuronic acid groups (HexA) followed by a chlorite treatment to remove the lignin. Three pulp samples were treated with increasing ozone charges (up to 2% on pulp) at high consistency and room temperature. The pulp containing no lignin but all of the HexA appeared to be the most affected by the ozone treatment. This indicated that the reaction of ozone with HexA generates radicals, which then react with cellulose, leading to depolymerization. It also indicated that lignin captures some of these radicals. ESR spectroscopy confirmed that hydroxyl radicals are formed when ozone reacts with maleic acid, which can be considered a HexA model compound. These findings open the way to the improvement of chlorine-free bleaching sequences containing ozone stages.

The effects of the amounts of flour from the red pepper (Capsicum annuum) fruit stem (RPFS), together with coupling agent (CA), on the mechanical and physical properties of polypropylene (PP)-based composites were investigated. Pellets manufactured through single screw extruders were injection molded into composite samples. Density, mechanical property, and dimensional stability of manufactured composites were determined according to ASTM standards. Results were analyzed using central composite design (CCD). Statistical analyses showed that filler loading significantly affected the density, as well as mechanical and physical properties of thermoplastic composites. Density of the composites was increased with filler loading but not affected by coupling agent amounts. In the case of mechanical properties, tensile modulus, flexural strength, and flexural modulus were improved with increasing filler loading while the tensile strengths, elongation at break, and impact strength of the samples were decreased. The tensile strength of the thermoplastic composites was positively affected by CA contents, but other mechanical properties were not affected as much. In the case of physical properties, thickness swelling and water absorption of the composites were increased with increasing weight percent of RPFS flour. However, these properties were not significantly changed by CA addition. Overall results revealed that RPFS flour could be potentially suitable raw materials for thermoplastic composites.