1,721,006 research outputs found
Analysis of the hydrolysates from cured and uncured urea-formaldehyde (UF) resins with two F/U mole ratios
No full textAbstract
Uncured and cured urea-formaldehyde (UFcured) resins prepared with formaldehyde/urea (F/U) mole ratios of 1.0 and 1.2 and at the catalyst levels of 1, 2 and 3% NH4Cl were hydrolyzed for 5, 15 and 30 min and the degradation products were evaluated using gel permeation chromatography, Fourier-transform infrared (FTIR) and liquid carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopies. The molar masses of the degradation products, their functional groups and structures were determined. An extended hydrolysis time and higher catalyst levels resulted in compounds with higher molar masses. Similar functional groups and distribution of chemical species were found by both FTIR and 13C-NMR spectroscopies in the hydrolysates of UFcured, indicating water hydrolysis of hydroxymethyl groups and then methylene linkages. Methylene linkages and mono- and tri-hydroxymethyl ureas were mainly responsible for the liberation of formaldehyde from UFcured during hydrolysis. The indicated compounds are believed to contribute to the long-term release of formaldehyde from the resins. This is the first systematic report on the composition of UFcured hydrolysates.</jats:p
Tailoring of oxidized starch's adhesion using crosslinker and adhesion promotor for the recycling of fiberboards
No full textHydrolytic Removal of Cured Urea–Formaldehyde Resins in Medium-Density Fiberboard for Recycling
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Characteristics of Eco-Friendly and Sustainable Plywood Adhesive derived from Low-Quality Cat’s Eye Damar Resin
Full text linkWood panel products mainly use formaldehyde-based adhesives that release free formaldehyde and potentially cause health problems. This study aimed to develop a free-formaldehyde adhesive from cat’s eye damar (CED) resin as an alternative adhesive for plywood production. The low-quality CED resin was used to increase the added value of the resin. The adhesive formulation consists of a ratio of 30:70 (CED:benzene) dissolved for 15 minutes at 45°C. The plywood was manufactured using glue spread rates of 200, 250, and 300 g/m2 with an addition of 10% tapioca flour and hot pressed using a pressure of 2.45 MPa at 120°C for 6 minutes. The CED-based adhesive produced has a solid content of 28.76%, a pH value of 5.93, a gel time value of 70.05 minutes, and a viscosity value of 4.02 mPa.s. Fourier-transform infrared spectroscopy analysis stretching of the C-H group, indicating an alkane compound. Plywood’s physical and mechanical properties bonded with CED-based adhesive increased with higher glue spread application. Utilizing a glue spread of 300 g/m2 could produce plywood with comparable physical and mechanical properties to the urea-formaldehyde-bonded plywood.
Keywords: cat’s eye damar, dynamic mechanical analysis, formaldehyde-free adhesive, plywood, Shorea javanic
Formaldehyde-free plywood composites bonded with polyurethane adhesive derived from lignin-polyvinyl alcohol-based polyol
No full textAbstract Polyurethane (PU) adhesive derived from lignin-based polyol can be used as a substitute for urea–formaldehyde (UF) adhesive for plywood because it can be used for exterior application, it is more environmentally friendly, and does not produce formaldehyde emissions. This research work aimed to investigate and evaluate the adhesive performance of lignin-based PU adhesive for bonding plywood, synthesized by mixing methylene diphenyl diisocyanate (MDI), polyol, polyvinyl alcohol (PVOH), and lignin, then applied to the rubberwood (Hevea brasiliensis) veneers and hot-pressed at a temperature of 120 °C and a pressure of 2.5 MPa for 4 min. The lignin yield obtained was 36.17%, moisture content 5.07 ± 0.71%, ash content 0.31 ± 0.19%, and lignin purity 95.32 ± 0.61%. The increased addition level of PVOH/lignin resulted in decreased solids content of the adhesive, while viscosity, cohesion, torque, storage modulus, loss modulus, and tan delta increased. Based on the Fourier-transform infrared spectroscopy (FTIR) analysis results, urethane bonds were identified in both the adhesive and plywood. Lignin-based PU adhesive formulas with 10%, 20%, and 30% PVOH/lignin fulfilled the minimum requirements for delamination, tensile strength, and wood failure, as specified by the Japanese Agricultural Standard (JAS) No. 233:2003. Markedly, plywood bonded lignin-based PU adhesive with 30% PVOH/lignin met the standards of JAS No. 233:2003 for exterior grade plywood
Assessment of the Mass and Surface Area of the Scots Pine (Pinus sylvestris L.) Needles
No full textThe assessment of the surface area of all leaves from a tree crown is regarded as one of the key parameters in scaling ecophysiological processes, such as growth, carbon budget, and water management. The purpose of this study was to investigate the variation of the mass and surface area of Scots pine needles, obtained from trees growing in the same habitat conditions but at different stock densities, therefore occupying different biosocial positions. The mass of needles and the leaf area index (LAI) were determined for an even-aged 33-year-old Scots pine stand located at a fresh mixed coniferous forest site in southwest Poland (50°32′ N; 17°42′ E). The needles, collected from all the sample trees, were subjected to a biometric analysis to determine the total mass of needles from each tree, the mass of 1000 needle pairs, the number of needles per crown, and the needle length distribution. Based on the actual measurements, we derived allometric equations for finding the fresh mass (FMN) and the surface area of the needles (SN), using the diameter at breast height (DBH) as an independent variable. The relationships between the mass of the needles and the DBH were significant (p < 0.0001), and so were those between the surface area of the needles and the DBH (p < 0.001). The fresh mass of needles for the tree stands varied from 6458 kg·ha−1 to 11,102 kg·ha−1. The LAI was in the range of 3.2 to 5.4 m2·m−2. The mean value of the LAI for the Scots pine stand was 4 m2·m−2. Further studies are required and more algorithms need to be developed for the quantitative assessment of the LAI in Scots pine trees, using a larger number of sample trees with more varied biometric features
Advanced Eco-Friendly Wood-Based Composites II
No full textThe ongoing twin transition of the wood-based panel industry towards a green, digital, and more resilient bioeconomy is essential for a successful transformation, with the aim of decarbonising the sector and implementing a circular development model, transforming linear industrial value chains to minimize pollution and waste generation, and providing more sustainable growth and jobs [...
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