Research Articles

The aim of this study was to evaluate effects of chemical pretreatment and storage on non-wood pulping and on pulp quality. The processes studied were hot water treatment followed by alkaline peroxide bleaching or soda cooking. The results showed that it is possible to store wheat straw outside for at least one year without significant changes in the raw material chemical composition and without adverse effects on the resulting pulp quality. The results are significant to the industry using non-woods to ensure the availability and the quality of the raw-material throughout the year in spite of the short harvesting time.

Pitch-related deposition has been a significant issue in paper mills that produce wood-containing paper grades. A component analysis showed that a mill deposit sample was a mixture of wood resin, fiber, metal cations, and other inorganics. Based on the differential scanning calorimeter (DSC) method, some critical parameters, including pH, metal cations, and their interactions, on the thermal stability of pitch-related deposits were studied. The valency of metal cations determined the ability of capturing pitch the formation of deposits. Trivalent Al3+ or Fe3+ ions had much stronger effects than divalent Ca2+, Mg2+, or Mn2+. It was also found that a higher pH and trivalent Al3+ or Fe3+ increased the thermal stability of deposits formed in colloidal pitch solutions.

Changes in the chemical structure of hornbeam and uludag fir woods during thermal treatment were investigated at three temperatures (170, 190, and 210 oC) and three durations (4, 8, and 12 hours). After thermal treatment, the extents of degradation in the chemical structure of the samples were determined, and the effects on the chemical composition of hornbeam wood and uludag fir wood were investigated. The data obtained were analyzed using variance analysis, and Tukey’s test was used to determine the changes in the chemical structure of uludag fir and hornbeam woods. The results showed that heating wood permanently changes several of its chemical structures and that the changes are mainly caused by thermal degradation of wood polymers. It was found that decreasing of the cellulose and holocelluloses ratio had a favorable effect on the interaction of the wood with moisture. According to the obtained results, hornbeam wood is affected more than uludag fir wood. For each wood, the maximum decreases of holocellulose and α-cellulose were found at 210oC for 12 hours, and the maximum increase of lignin occurred at the same treatment combination.

A centrifugal method has been modified and applied to the assessment of water retention value (WRV) in cellulosic materials. Microcrystalline cellulose (MCC), small particles/fibrils isolated from MCC using high-pressure homogenizer, and pulp fibers saturated in water were centrifuged at different speeds and times with filter paper and/or a membrane acting as the filter in the WRV measurement setup. As centrifugal speed, time, and filter pore-size increased, lower WRVs were obtained. Smaller MCC particles/fibrils retained more water than the as-received MCC and pulp fibers. The results are useful for WRV measurements of cellulosic materials, especially for microfibrillated cellulose and small cellulosic fibrils.

A convenient and efficient application of heterogeneous La-containing SBA-15 systems for the microwave assisted oxidation of a lignin model phenolic monomer, 4-hydroxy-1-phenylpropane, is reported. Low-cost and environmentally friendly H2O2 was used as the oxygen atom donor. The catalyst was prepared by immobilizing lanthanum species on the periodic mesoporous channels of siliceous SBA-15. Powder X-ray diffraction data and ICP-AES revealed that the host retains its hexagonal mesoporous structure after immobilization and most of the lanthanum species are better dispersed in the calcined materials. The surface area and pore size of La/SBA-15 was considerably decreased, indicating the intrapore confinement of the Lanthanum species. The activity of the La/SBA-15 was investigated in the oxidation of 4-hydroxy-1-phenylpropane in the presence of hydrogen peroxide as oxidant. 70.5% conversion of 4-hydroxy-1-phenylpropane was obtained after 30 min of reaction under 200W microwave irradiation, compared to a poor 28.1% degradation after 24h under conventional heating. The possibility of recycling the catalyst was studied.

Electroless nickel deposition was carried out on Fraxinus mandshurica veneers for EMI shielding under a new activation process. In the process, Pd(II) was ed on the surface of veneers modified with γ-aminopropyltrihydroxysilane (APTHS) obtained from the hydrolysis of γ-aminopropyltriethoxysilane (APTES). After the reduction, electroless plating was successfully initiated, and Ni-P coating was deposited on the veneers. The activation process and resulting coating were characterized by XPS, SEM-EDS, and XRD. The metal deposition, surface , and electromagnetic shielding effectiveness were measured. XPS analysis proved that Pd(II) was bonded to the amino group of APTHS and reduced to Pd(0). The coating was continuous, uniform, and compact. It consisted of 97.4 wt% nickel and 2.6 wt% phosphorus. XRD analysis showed that the coating was crystalline, which was related to the low phosphorus content. The plated Fraxinus mandshurica veneers exhibit good electro-conductivity with surface resistivity of 0.21Ω·cm-2 and higher electromagnetic shielding effectiveness of over 50dB in frequencies from 10 MHz to 1.5 GHz.

Pyrolysis characteristics of corn stalk hemicellulose were investigated in a tubular reactor at different temperatures, with focus mainly on the releasing profiles and forming behaviors of pyrolysis products (gas, char, and tar). The products obtained were further identified using various approaches (including GC, SEM, and GC-MS) to understand the influence of temperature on product properties and compositions. It was found that the devolatilization of hemicellulose mainly occurred at low temperatures (<500°C), and produced large amounts of tar. A higher reactor temperature was conducive to the yield of gas products, accompanied by a reduction of tar because of the secondary cracking of volatiles. The gas components mainly consisted of CO2, CO, H2, and CH4, together with trace C2H4 and C2H6. The CO2 evolved easily and reached a relatively large yield of 129.2ml/g at 550°C, while CO and H2 were mainly released at higher temperatures (700-900°C). The tar was mainly composed of a range of oxygenated compounds, including ketones, furans, carboxylic acids, and alcohols, and their contents were influenced by the final temperature. An in-depth analysis of the properties of the products generated at different temperatures is favorable for a better understanding of the mechanism of hemicellulose pyrolysis.

Wheat straw (Triticum aestivum L.) and oat straw (Avena sativa L.) were subjected to acid and alkaline pre-treatments partly in combination with hydrogen peroxide. The aim was to remove lignin and increase the accessibility of the polysaccharides to enzymatic digestion. Accessibility was evaluated by digestion with a cell wall degrading enzyme complex to yield reducing sugars that may serve as precursor substrates for biofuels or building block chemicals. Changes in lignin, hemicelluloses, as well as amorphous, semi-crystalline, and crystalline regions of cellulose moieties of pretreated straw were efficiently characterized by Fourier transform near-infrared (FT-NIR) reflectance spectroscopy. These alterations of the chemical structure of straw after different pre-treatment methods were powerfully differentiated by principal component analysis (PCA). Characteristics of the different samples owing to the different pre-treatment methods could be clustered from the PCA loadings spectra.

Wheat straw (Triticum aestivum L.) and oat straw (Avena sativa L.) were chemically pretreated at different severities with the purpose of delignification, which in turn leads to a better accessibility of plant cell wall polysaccharides for further biotechnological conversion. Key parameters of these samples, i.e. weight loss, residual lignin content, and hydrolysable sugars serving as precursors for biofuel production were monitored by wet-chemistry analyses. Fourier transform near infrared (FT-NIR) spectra were correlated to these data by means of partial least-squares (PLS) regression. Weight loss (4.0 – 33.5%) of the wheat straw could be predicted (RMSEP = 3.5%, R²test = 0.75) from the entire FT-NIR spectra (10000 – 4000 cm-1). Residual lignin content (7.9 – 20.7%, RMSEP = 0.9%, R²test = 0.94) and amount of reducing sugars based on pretreated wheat straw (128 – 1000 mg g-1, RMSEP = 83 mg g-1, R²test = 0.89) were powerfully evaluated between 6900 and 5510 cm-1, a spectral region where polysaccharides and lignin absorb. All these parameters could be equally predicted with even higher accuracy from pre-treated oat straw samples. Furthermore, some important parameters for anaerobic conversion of wheat straw to biogas – biogas production, total solids, and volatile solids content – could be estimated.

Effects of injection temperature on thermal degradation and porosity of the bagasse/polypropylene injection molding composites were studied. Above 185 ºC, incomplete filling occurred. The incomplete filling increased with increase of injection temperature. It was found that the gas generated by thermal degradation of bagasse fibers was so accumulated in the injection cylinder that the injected composites ended up with incomplete filling. A modified injection method with the venting of gas increased the complete filling percentage. Mechanical properties decreased with increase of injection temperature from 165 ºC to 260 ºC. This was due to increase of porosity and fiber shortening. The calculated flexural modulus, which incorporated the effect of porosity and fiber length, agreed well with the experimental results. Composites with maleic acid anhydride grafted polypropylene (MAPP) were also investigated. Flexural strength and impact strength were improved by 45% and 35%, respectively, by addition of 20wt% MAPP. In the MAPP composites, fiber breakages at their roots were observed in the fracture surface after an impact test, while pulled-off fibers were observed in those without MAPP.