Traditional formaldehyde-based adhesives still play a crucial role in the current market, despite increasing environmental concerns resulting from their production. The purpose of this paper was to ...evaluate the environmental impacts of formaldehyde-based adhesives, urea-formaldehyde (UF) adhesive and phenol-formaldehyde (PF) adhesives, mainly used in wood products. In this study, a functional unit of 1 kg adhesive was used. GaBi 6 software was employed to perform the life cycle assessment (LCA). Several key parameters for life cycle analysis were analyzed, such as global warming potential, acidification potential, eutrophication potential, and human health. As a result, the greenhouse gas emissions ranged from 2.04 kg CO
2
-eq./kg of UF adhesive to 2.88 kg CO
2
-eq./kg of PF adhesive. In terms of the overall environmental impacts, it was found that UF adhesive had a nearly 50% higher life cycle impact than PF adhesive. Comparing the energy consumption used in UF and PF adhesives, UF adhesive was much lower than PF adhesive. Transportation distance was determined to be a sensitive parameter with respect to global warming potential for formaldehyde-based adhesive.
Formaldehyde-based adhesives have been used for several decades due to its convenience. In this paper, we aimed to explore the economics of urea–formaldehyde (UF) adhesives that can be used in wood ...panels. Two formaldehyde production pathways: metal oxide pathway and silver pathway, were compared in this study. SuperPro Designer v9.5 software was employed to perform the techno-economic analysis (TEA). Key parameters of TEA were calculated and compared of these two pathways, including total capital investment, annual operating cost and product revenues. It was found that the unit production cost of UF adhesive made from metal oxide pathway ($0.86/kg) was less expensive than that from silver pathway ($0.99/kg), but the total capital cost was slightly higher in metal oxide pathway (40 million $) than silver pathway (38 million $). Additionally, sensitivity analysis indicated that final product yield and material costs were the most sensitive factors among all inputs.
Penetration is the ability of an adhesive to move into the voids on the surface of a substrate or into the substrate itself. The cellular nature of wood can cause significant penetration of an ...adhesive into the substrate. The objective of this work was to evaluate the influence
of the degree of condensation of urea-formaldehyde (UF) resins on the radial penetration into silver fir (Abies alba, Mill.) and hence on the distribution of resin in the wood tissue by means of microscopic determination. Three UF resins with different degrees of condensation together
with extender and hardener were used as adhesive mixes and were applied onto one of the surfaces to be bonded by hot pressing parallel to the grain direction, with Safranin added as a coloring agent. Microtome slides (20 μm thick) were cut from each joint sample, showing the bondline and
the two adherends with the resin penetrated in radial direction. The depth of adhesive penetration was determined by epi-fluorescence microscopy. The results show a significant correlation between the penetration behavior and the degree of condensation (molecular size, viscosity) of the
resins. The higher the degree of condensation, the lower is the penetration possibility, expressed as 'Average penetration' depth (AP). The portion of filled tracheids in the radial direction on both sides of the bondline ('Filled interphase region', FIR) however, did not depend statistically
on the viscosity of the resin mix.
curing kinetics of commercial urea-formaldehyde (UF) adhesive was
investigated. With this objective, the following thermal analysis methods
were utilized: differential scanning calorimetry (DSC), ...dielectric analysis
(DEA) and dynamical mechanical analysis (DMA). DSC measurements were obtained
in dynamical scanning regime with the heating rates (β) of 5; 10; 15 i
20ºC/min. Test samples consisted of pure UF adhesive, UF adhesive / wood
flour mixes and UF adhesive / wood extractives mixes of selected wood
species. Catalyst (NH4Cl) addition was 0.2% (per oven dry weight) for all
test samples. Results of peak temperature (Tp), enthalpy of reaction (ΔH),
and activation energy (Ea) were analyzed for each UF adhesive system. In
addition, the isoconverzional models of Ozawa-Flynn-Wall (OFW) and
Kissinger-Akahira-Sunose (KAS) were applied on the DSC test data. DEA tests
proceeded in the isothermal regime in the real hot pressing conditions using
veneer samples of the selected wood species as adherents. UF adhesive was
applied with the NH4Cl addition of 0.2% (per oven dry weight). Press
temperatures were 120; 140 i 160ºC. Dielectric parameters were recorded
through IDEX sensor applied on the bond line of veneer samples and connected
to LCR meter. Degree of reaction (α) was obtained on the basis of electric
conductivity. DMA rheological tests were performed in the sinusoidal shear
stress regime at the temperature of 80ºC. Test samples consisted of pure UF
adhesive and the UF adhesive / wood extractives mixes. Two separate sample
series were used, one with the NH4Cl addition of 0.2% (per oven dry weight)
and the other without catalyst addition. Gel time was determined at the
crossover of the storage modulus (G') and loss modulus (G"), resulting in the
loss factor tanδ=1. Results of DSC and DMA tests on UF adhesive / wood
extractive mixes, showed significant influence of pH value and acid buffer
capacity of selected wood species on kinetics of curing reaction. Lower
values of said chemical characteristics of a given extractive, resulted in
decrease of peak temperature and activation energy, as well as in shorter gel
time for a corresponding mixture. Both, DSC measurements of UF adhesive /
wood flour mixtures and DEA results of UF adhesive cure in the hot pressed
veneer samples, have showed significant influence of wood anatomy structure
on curing behavior of UF adhesive.
U okviru ove doktorske disertacije istražen je uticaj drvnih vrsta bukve, jele
i topole, na kinetiku očvršćavanja komercijalnog urea-formaldehidnog (UF)
adheziva, namenjenog za proizvodnju ploča iverica. U tom cilju primenjene su
metode diferencijalne skenirajuće kalorimetrije (DSC), dielektrične analize
(DEA) i dinamičko mehaničke analize (DMA). DSC ispitivanja obavljena su u
dinamičkom režimu, pri brzinama zagrevanja (β) od 5; 10; 15 i 20ºC/min.
Ispitivane uzorke činili su čist UF adheziv, smeše UF adheziva sa drvnim
brašnom i smeše UF adheziva sa ekstraktivima ispitivanih vrsta drveta.
Dodatak katalizatora (NH4Cl) iznosio je 0,2%, mereno na suvu supstancu
adheziva, za sve ispitivane uzorke. Rezultati merenja predstavljeni su
vrednostima temperature maksimuma reakcije (Tp), entalpijom reakcije (ΔH),
kao i energijom aktivacije (Ea). Takođe, na rezultatima DSC merenja
primenjeni su izokonverzioni modeli Ozawa-Flynn-Wall (OFW) i
Kissinger-Akahira-Sunose (KAS). DEA ispitivanja obavljena su u izotermalnom
režimu i u uslovima vrelog presovanja furnirskih uzoraka ispitivanih drvnih
vrsta, slepljenih UF adhezivom sa dodatkom NH4Cl od 0,2%, mereno na suvu
supstancu adheziva. Temperature presovanja iznosile su 120; 140 i 160ºC.
Očitavanje dielektričnih parametara obavljeno je pomoću IDEX senzora
postavljenog na liniji lepljenja i povezanog sa instrumentom za merenje
impendanse. Vrednosti stepena reakcije (α), dobijene su na osnovu promene
električne provodljivosti. DMA ispitivanja obavljena su pri konstantnom
oscilatornom režimu naprezanja na smicanje i pri temperaturi od 80ºC.
Ispitivane uzorke predstavljali su čist UF adheziv i smeše UF adheziva sa
ekstraktivima ispitivanih vrsta drveta. Posebne serije ispitivanja obavljene
su sa dodatkom NH4Cl od 0,2%, mereno na suvu supstancu adheziva, kao i bez
dodatka katalizatora. Vreme želiranja ispitivanih uzoraka određeno je
presekom kriva modula sačuvane energije (G') i modula izgubljene energije
(G"), odnosno za vrednost faktora gubitka tanδ=1. Ispitivanjem UF adheziva u
smeši sa drvnim ekstraktivima, pomoću DSC i DMA metoda, utvrđeno je da pH
vrednost i kiseli puferni kapacitet ispitivanih drvnih vrsta značajno utiču
na kinetiku reakcije očvršćavanja. Niže vrednosti pomenutih hemijskih
karakteristika ekstraktiva uticale su na smanjenje temperature maksimuma
reakcije i energije aktivacije, kao i na kraće vreme želiranja odgovarajuće
ispitivane smeše. Rezultati ispitivanja UF adheziva u smeši sa drvnim
brašnom, pomoću DSC metode, kao i rezultati ispitivanja dielektričnih
parametara očvršćavanja UF adheziva pri vrelom presovanju furnirskih uzoraka,
pokazali su značajan uticaj anatomske građe ispitivanih drvnih vrsta na tok
očvršćavanja UF adheziva.
This study addresses the optimization of the nanolignin preparation method from the areca leaf sheath (ALS) by a mechanical process using a high shear homogenizer at 13,000–16,000 rpm for 1–4 h and ...its application in enhancing the performance of ultralow molar ratio urea-formaldehyde (UF) adhesive. Response surface methodology (RSM) with a central composite design (CCD) model was used to determine the optimum nanolignin preparation method. The mathematical model obtained was quadratic for the particle size response and linear for the zeta potential response. Under the optimum conditions, a speed of 16,000 rpm for 4 h resulted in a particle size of 227.7 nm and a zeta potential of −18.57 mV with a high desirability value of 0.970. FE-SEM revealed that the characteristic changes of lignin to nanolignin occur from an irregular or nonuniform shape to an oval shape with uniform particles. Nanolignin was introduced during the addition reaction of UF resin synthesis. UF modified with nanolignin (UF-NL) was analyzed for its adhesive characteristics, functional groups, crystallinity, and thermomechanical properties. The UF-NL adhesive had a slightly greater solid content (73.23 %) than the UF adhesive, a gelation time of 4.10 min, and a viscosity of 1066 mPa.s. The UF-NL adhesive had similar functional groups as the UF adhesive, with a lower crystallinity of 59.73 %. Compared with the control plywood which has a tensile shear strength value of 0.79 MPa, the plywood bonded with UF-NL had a greater tensile shear strength of 1.07 MPa, with a lower formaldehyde emission of 0.065 mg/L.
•Nano lignin of ALS was prepared mechanically by high shear homogenizer.•RSM was used as nano lignin optimization with particle size and zeta potential as response.•The optimum of nano lignin production was at 16,000 rpm for 4 h.•Nano lignin was applied to in situ modify the low molar ratio UF adhesive.•Modified UF has higher solid content, lower crystallinity, for higher mechanical properties.
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