Research Articles

To investigate the influence of pH on the size and distribution of silver nanoparticles (Ag-NPs) as well as the antibacterial activity and catalytic performance of rice straw/silver nanocomposites (RS/Ag-NCs), Ag-NPs were synthesized on the surface of rice straw (RS) with various percentages of Ag-NPs (1.0, 5.0, 10.0, and 20.0 wt.%) under different temperatures and diverse pH values. The ultraviolet-visible spectroscopy of synthesized RS/Ag-NCs became noticeable with increased pH, and the peaks were blue-shifted to lower wavelengths. X-ray powder diffraction (PXRD) demonstrated the presence of pure Ag-NPs. Transmission electron microscopy (TEM) showed that the diameters of Ag-NPs on RS were between 7.78 and 2.84 nm at pH values of 8 to 10. The antibacterial activity of various sizes of Ag-NPs on RS was examined using Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus) based on the well diffusion technique. Higher antibacterial activity was detected as the loading percentage of RS/Ag-NCs increased and particle size decreased. The superior catalytic performance of 20.0 wt.% RS/Ag-NCs was considered in a test reaction in 4-nitrophenol (4-NP) reduction in the presence of sodium borohydride (NaBH4) in an eco-friendly solvent at ambient temperature. The results represented the high-performance catalytic activity of 20.0 wt.% RS/Ag-NCs.

Amphoteric polyacrylamide (AmPAM) is a linear water-soluble polymer that has been applied in papermaking as an agent for flocculation, retention, filtration, and dry-strength improvement. However, AmPAM with different ranges of molecular weight (MW) have different properties in these processes. In this study, a series of AmPAMs were constructed with an anionic monomer, itaconic acid (IA), a cationic monomer, methacryloxyethyl-trimethyl ammonium chloride (DMC), and a main backbone of acrylamide (AM). Four factors influencing free radical polymerization, i.e., reaction temperature, pH, initiator load, and the concentration of monomers, were systematically investigated via an orthogonal test to determine their effects on the MW of AmPAM. Spectroscopy and isoelectric point assays were used to characterize the structure of the produced AmPAM, and the MW was assessed by calculating the viscosity. The reaction temperature had the greatest influence on the MW of AmPAM, followed by the solution pH and the initiator load. To determine the dry strength of papersheets containing AmPAM, the breaking length of handsheets was assessed after adding 0.5% AmPAM (based on fiber) with different MWs. The maximum value, 4.05 km, was 15.0% higher than the control and was obtained using AmPAM with a MW of 330 kDa.

In outdoor applications, the mechanical performance of wood-plastic composites (WPCs) is affected by UV radiation, facilitating moisture intake and damaging the wood-polymer interfacial region. The purpose of this study was to evaluate the effect of moisture absorption-desorption cycles (MADCs), and the exposure to UV radiation on the interfacial shear strength (IFSS) of WPCs with 40% pinewood residue and 60% high-density polyethylene. One of the WPCs incorporated 5% coupling agent (CA) with respect to wood content. The IFSS was evaluated following the Iosipescu test method. The specimens were exposed to UV radiation using an accelerated weathering test device and subsequently subjected to four MADCs. Characterization was also performed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The absorption and desorption of moisture was slower in non-UV-irradiated WPCs, particularly in those with the CA. The UV radiation did not significantly contribute to the loss of the IFSS. Statistically, the CA had a favorable effect on the IFSS. Exposure of the samples to MADCs contributed to reduce the IFSS. The FTIR showed lignin degradation and the occurrence of hydrolysis reactions after exposure to MADCs. SEM confirmed that UV radiation did not significantly affect the IFSS.

The astronomical increase in global energy demand makes locating energy sources other than fossil fuels worthwhile. The use of tropical biomass wood waste as a renewable energy source was investigated in this study. The thermal conversion analysis of Albizia gummifera (ayinre) was carried out in a thermobalance reactor via steam gasification under varying temperature (700 to 1000 °C) and steam partial pressure (0.020 to 0.050 MPa). The experimental data was evaluated using three gas-solid reaction models. The modified volume reaction model (mVRM) gave the overall highest coefficient of determination (0.9993) and thereby the best conversion prediction. The observed char activation constant rates (from paired reaction conditions) indicated, on average, an increase in reactivity as the parameters increased. The results showed that the activation energy of the mVRM gave the lowest value (32.54 kJ/mol) compared with those of the shrinking core model (SCM) and the volume reaction model (VRM) (49.29 and 49.89 kJ/mol, respectively).

Tar and char can be regarded as unwanted byproducts during the gasification process. In this study, three types of catalyst, i.e., biomass char (bio-char), nickel supported on biomass (Ni+bio-char), and nickel supported on bio-char (bio-char+Ni), were studied to compare the catalytic effects of different preparation methods on tar model compound removal. The structural characteristics of the three catalysts were also investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) methods. The results revealed that Ni+bio-char catalyst showed much higher activity for the reformation of toluene (C7H8) as a tar model compound than the other two catalysts. Toluene could be completely converted to small gas molecules at a conversion rate of 99.92% at 800 °C, and the maximum yield of gas was 432 mL/(mL C7H8). In particular, the H2 and CH4 yields were 339 and 85 mL/(mL C7H8) at 850 °C, respectively. An N2 absorption-desorption experiment demonstrated that the specific surface area of Ni+bio-char was 32.87 times that of bio-char and 8.39 times that of bio-char+Ni. Moreover, metallic nickel (Ni0) particles could be generated in the carbon matrix of Ni+bio-char catalyst. SEM analysis confirmed that the Ni+bio-char catalyst had a more porous structure. Nickel supported on biomass might be a promising catalyst for tar reformation because of its excellent catalytic activities.

Three alkali swelling methods were used to treat two kinds of kraft pulp fibers. The morphological and chemical properties of the treated fibers were elucidated in terms of alkali concentration, with the aim of developing bulky paper and conserving wood resources. The effects of beating before and after alkali swelling were examined. The water retention value of fibers increased when higher concentrations of NaOH were used for swelling. Alkali swelling increased fiber width, while fiber length decreased. With increasing NaOH concentration, fibers became curled or kinked; the crystalline structure changed from cellulose I to cellulose II, and the crystalline index decreased. Beating before and after the alkali swelling affected the swelling behavior of kraft pulps, but there was no distinct influence on the crystalline structure. The beating treatment before alkali swelling improved the alkali swelling of fiber. However, beating after the alkali treatment diminished the alkali swelling effects. In addition, the beating after alkali swelling straightened the curled fibers.

As a by-product generated from the processing of corn, the production in China of corncob (CC) is abundant, with up to 3.87 million tons per year. The biomass gasification industries make use of the CC residue as feedstock, but large volumes of generated corncob ash (CCA) requires daily disposal. In this study, CCA was characterized by laser particle size analyzer (LPSA), X-ray fluorescence (XRF), X-ray diffraction (XRD), thermal gravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy, and energy dispersive X-ray (SEM-EDX). XRF results showed that the CCA was rich in K, Ca, and P, indicating its potential as a soil amendment. High content of SiO2 in CCA revealed its potential as a pozzolan in blended cement concrete. XRD showed the presence of crystal phases such as potassium carbonate, sylvite, arcanite, quartz, calcite, and nitrite. SEM images revealed the high agglomeration of CCA. EDX gave evidence of the external surface of agglomerated particles coated with KCl. TG-DTA analysis indicates that decomposition of CCA has stepwise mechanism. The CCA powders through a 0.154 mm sieve showed a high specific surface area of 162.32 m2/g, average pore size of 12.17 Å with pore volume of 0.116 cm3/g. The carbon residue separated from CCA has the potential to be used as activated carbon.

The production of value-added chemicals from the bioconversion of lignocellulose biomass has been considered a promising venture. In this study, microwave, alkali-pretreated empty fruit bunch (EFB) was used as the substrate, utilizing pelletized filamentous Rhizopus oryzae NRRL 395 and cellulolytic enzymes for lactic acid production in a fed-batch simultaneous saccharification and fermentation (SSF) process. Insoluble solids generally do not affect the SSF process until a certain concentration is exceeded. To achieve a high lactic acid concentration in the broth, a high solids loading was required to allow a higher rate of glucose conversion. However, the results revealed a decrease in the final lactic acid yield when running SSF at a massive insoluble solids level. High osmotic pressure in the medium led to poor cellular performance and caused the Rhizopus oryzae pellets to break down, affecting the lactic acid production. To improve the process performance, a fed-batch operation mode was used. The fed-batch operation was shown to facilitate higher lactic acid yield, compared with the SSF batch mode. Enzyme feeding, as well as substrate feeding, was also investigated as a means of enabling a higher dry matter content, with a high glucose conversion in SSF of cellulose-rich EFB.

The dissolution of sugarcane bagasse cellulose (SBC) in zinc chloride solution was studied at elevated temperatures. Based on single factor experiments, the effects of zinc chloride mass fraction, dissolution time, temperature, and bagasse cellulose mass fraction were investigated by an orthogonal experiment, and the optimal dissolution conditions were obtained. The dissolution process of bagasse cellulose was observed under a microscope. Additionally, the original SBC and regenerated SBC were both characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Temperature was found to be the most important factor affecting dissolution time. The best dissolving process took place at 85 °C to dissolve 2% SBC in 85% zinc chloride for 210 min. It was shown that the zinc chloride was a direct solvent for SBC. After regeneration of cellulose in zinc chloride, the crystallinity of cellulose was decreased greatly, from 77% to 54%, its crystalline form was transformed from cellulose I to cellulose II, its thermal decomposition temperature was reduced, its thermal stability was slightly decreased, and its internal structure was disrupted.

The scale-up of a mechanochemical acetylation operation using 100-L ball mills was performed to produce acetylated Japanese cedar (Cryptomeria japonica) wood meal for wood-polypropylene composite (WPC) production. Finely and coarsely acetylated wood meals (AWMs) were successfully produced with approximately 21% and 19% weight percent gains (WPG), respectively, which was close to the theoretical value. The mechanical properties of WPCs showed similar, rather weak strength compared with the AWM-filled WPCs without maleic anhydride-grafted polypropylene (MAPP) as a compatibilizing agent; however, coarse AWM-filled WPCs showed similar or higher mechanical properties than untreated wood meal (UWM)-filled WPCs when MAPP was added. Clear enhancements in the dimensional stability of AWM-filled WPCs were observed, but no significant differences in dimensional stability were observed between WPCs filled with fine and coarse AWMs, even when MAPP was added. Morphological analyses of the fracture surface showed the retention of some wood cell wall structures in coarse AWM, and fine loadings of the thermoplastic into the lumen were clearly observed. These properties were not found on the fracture surface of fine AWM-filled WPCs; therefore, high polymer loadings into the retained wood structure with high interfacial adhesion by MAPP could be suggested for improving the mechanical properties of coarse AWM-filled WPCs.