1,324 research outputs found
Ether Bond Formation in Waste BiomassāDerived, Value-Added Technical Hardwood Kraft Lignin Using Glycolic Acid
Ether bond formation in technical hardwood kraft lignin (THKL) by crosslinking using glycolic acid was investigated for bio-adhesive applications. Industrial hardwood kraft black liquor was used to extract the THKL utilized by acidification. Chemical and thermal properties of the THKL with and without crosslinking were analyzed by Fourier transform infrared (FTIR) spectroscopy, solid-state 13C cross-polarization/magic angle spinning nuclear magnetic resonance (13C CP/MAS NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). FTIR results revealed a new peak corresponding to the ether bond and hemiacetal formation due to crosslinking at 1075 cm-1 and 1324 cm-1. 13C CP/MAS NMR spectra revealed the presence of a higher number of ether bonds due to the reduced aromatic and aliphatic hydroxyl groups in THKL and new bonds formed at 62-64 ppm and 168-191 ppm due to crosslinking. XPS results revealed that new bonds were formed between glycolic acid and THKL, leading to increased atomic oxygen percentage and carbonāoxygen bonds in crosslinked THKL detected by peak intensity changes at 287.7 and 288.8 related to OāCāO and OāC=O. Also, the oxygen content increased from 14.88% to 31.76% due to bond formation. GPC confirmed a higher molecular weight and broader molecular-weight distribution of THKL. DSC and TGA curves of crosslinked THKL revealed exothermic behavior, high thermal stability, and low thermal degradation rate. Owing to a significant amount of kraft black liquor being generated by wood pulp industries and attractive chemical properties of THKL, THKL demonstrates promise as a raw material to produce green, sustainable bio-adhesives via the crosslinking of its different hydroxyl groups using glycolic acid
Analytical Modeling of Rheological Postbuckling Behavior of Wood-Based Composite Panels Under Cyclic Hygro-Loading
This study was conducted to develop analytical models to predict postbuckling behavior of woodbased composite panels under cyclic humidity conditions. Both the Rayleigh method and von Karman theory of nonlinear plate with imperfection were used to obtain a closed form solution to the hygrobuckling and postbuckling. In addition, mechano-sorptive creep effects were also taken into account for the derivation of analytical models. The closed-form solutions derived for both isotropic and orthotropic materials showed a good agreement with the experimental results in terms of the center deformation of hardboard, especially in the case of the edge movements. The unrecovery deformation was much greater at the first cycle and then decreased as the number of cyclic hygro-loading increased
Effects of Hydrolysis on the Removal of Cured Urea-Formaldehyde Adhesive in Waste Medium-Density Fiberboard
The vast production of medium-density fiberboard (MDF) in the world is expected to generate a large quantity of waste MDF after its service life, which requires the recycling of waste MDF (wMDF). This work attempted to investigate the removal of cured urea-formaldehyde (UF) resins adhesive in wMDF using hydrolysis for a possible way of recycling wMDF. The wMDFs were fabricated with two kinds of recycled fibers (RFs): refiner recycled fibers (RRFs) and hammer mill recycled fibers (HRFs) from red and radiata pine. The wMDFs were also produced at different RFs contents, such as 0, 5, 10, 20, 30, 50, and 100%. The panels were then hydrolyzed with water and oxalic acid solution to remove the cured UF resins. The Kjeldahl method was applied to determine the nitrogen (N) content in the panel before and after hydrolysis. Regardless of the wood species and recycling process, the mass loss, pH, and formaldehyde liberation of wMDFs after hydrolysis were greater for oxalic acid than those in water, confirming a greater N content had been extracted by oxalic acid than water. The resin removal became greater as the RFs content increased. In addition, the resin removal was slightly greater in wMDFs made of HRFs than the RRFs. Moreover, red pine RFs gave higher resin removal than radiata pine. These results suggested that a proper combination of the recycling process and additives could make it possible to recycle wMDF panels in the future.Keywords: cured urea-formaldehyde, hydrolysis, medium-density fiberboard, oxalic acid, recyclin
Coulomb oscillations based on band-to-band tunneling in a degenerately doped silicon metal-oxide-semiconductor field-effect transistor
The Coulomb oscillations based on band-to-band tunneling through a valence band in silicon metal-oxide-semiconductor field-effect-transistors were discussed. It was found that the formation of tunnel barries and a quantum dot in a single-electron transistor structure originated from two p+ - p+ tunnel junctions and a p+ -doped channel with mesoscopic dimension, respectively. At liquid nitrogen temperature, the Coulomb-blockade oscillations with multiple peaks were also observed. Analysis shows that the single-electron charging effect based on band-to-band tunneling was confirmed using the electrical and thermal characterization of the quantum dots.open2
One-pot Enzymatic Synthesis of Deoxy-thymidine-diphosphate (TDP)-2-deoxy-ā-d-glucose Using Phosphomannomutase
Production of deoxy-thymidine-diphosphate (TDP)-sugars as substrates of glycosyltransferases, has been one of main hurdles for combinatorial antibiotic biosynthesis, which combines sugar moiety with aglycon of various antibiotics. Here, we report the one-pot enzymatic synthesis of TDP-2-deoxy-glucose employing high efficient TMP kinase (TMK; E.C. 2.7.2.12), acetate kinase (ACK; E.C. 2.7.1.21), and TDP-glucose synthase (TGS; E.C. 2.7.7.24) with phosphomannomutase (PMM; E.C. 5.4.2.8). In this study, replacing phosphoglucomutase (PGM; E.C. 5.4.2) by PMM from Escherichia coli gave four times higher specific activity on 2-deoxy-6-phosphate glucose, suggesting that the activity on 2-deoxy-glucose-6-phosphate was mainly affected by PMM activity, not PGM activity. Using an in vitro system starting from TMP and 2-deoxy-glucose-6-phosphate glucose, TDP-2-deoxy-glucose (63% yield) was successfully synthesized. Considering low productivity of NDP-sugars from cheap starting materials, this paper showed how production of NDP-sugars could be enhanced by controlling mutase activity
Presence of a Distinct S3 Layer in Mild Compression Wood Tracheids of Pinus radiata
A study of electron microscopic evidence for the presence of a distinct S3 layer in mild compression wood tracheids of Pinus radiata was performed. S3 layers have an important role to play in strengthening the xylem tissues in standing trees and in minimizing collapse in wood tissues. These layers are also likely to be an important factor in wood processes involving physical and chemical treatments, as well as in the biodegradation of wood
TEM Examination of Surface Characteristics of Rubberwood (Hevea brasiliensis) HTMP Fibers
A study was conducted on the surface features of rubberwood high temperature thermomechanical (HTMP) fibers. The transmission electron microscopy (TEM) was used for the characterization of the surface features. The fracture behavior of the cell walls of the fibers were also studied. It was found that the outer surface of the HTMP fiber wall was completely covered by middle lamella, whose thickness was highly variable
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