Effect of accelerated weathering on discoloration and roughness of finished ash wood surfaces in comparison with red oak and hard maple

This study investigated the discoloration and roughening of finish and unfinished ash (Fraxinus americana), red oak (Quercus rubra), and hard maple (Acer nigrum) wood surfaces exposed to artificial weathering, with the aim of assessing the potential for ash wood for interior and exterior applications. Ash wood surfaces were treated with several coats of satin and high gloss polyurethane finishes in order to evaluate their potential for value added products from waste ash wood generated from an exotic insect (emerald ash borer) infestation. Red oak and red maple wood specimens were included in the study for comparison purposes. The weathering experiment was performed by cycles of UV light irradiation with and without water. Surface discoloration was measured according to ISO 2470 standard with a micro flash reflectometer in the CIELAB system. The surface roughness was measured with a surface profilometer and a roughening profile developed for each weathered surface. Results obtained showed that ash wood exposed to a combination of UV light and water spray had a color change pattern very similar to that of maple, and both species had a faster and higher levels of discoloration compared to red oak. However, when exposed to continuous UV radiation without water, ash had a higher level of discoloration than maple and red oak. Evaluation of changes in the roughness showed that maple had the lowest roughness after weathering, but finished ash surfaces also showed roughness characteristics similar to that of maple after 450 h exposure.     

Weathering,water absorption,and durability of silicon,acetylated, and heat‐treated wood

In this study, two colloidal dispersions of pure amorphous silicon dioxide particles, acetylated, and heat‐treated samples were tested for a possible application as a wood protection agents. The silicon, acetylated, and heat‐treated samples were exposed to an accelerated weathering experiment, and their dimensional stability was assessed. The weathering experiment comprised cycles of 2 h UV‐light irradiation followed by water spray for 18 min. The surface changes of the weathered samples were characterized by FT‐IR spectroscopy and color measurements. According to results, the silicon treatments showed lower color changes than untreated ones. However, acetylated and heat‐treated samples provided the lowest color changes. The resistance of the silicon, acetylated, and heat‐treated wood to decay was studied by means of brown and white rot fungi in laboratory decay tests. Decay test results revealed that acetylated and heat‐treated wood samples showed better decay resistance against P. placenta and C. versicolor than silicon treatments. Samples modified with silicon were exposed in above ground standard lap‐joint test in Ultuna, Sweden. The dispersions of pure amorphous silicon dioxide impregnated in wood did not significantly influence its hygroscopic and dimensional behavior. However, the silicon treatment reduced the color changes caused by weathering. The silicon impregnated samples showed a weak fungal discoloration similar to that of chromated copper arsenate impregnated controls in above ground standard lap‐joint test. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4506–4513, 2006     

Chemical characterization of Cedrus deodara wood extracts using water and molybdenum catalysts

The effect of the presence of some molybdenum catalysts on the amount of extractives in cedar wood has been studied. Autoclave treatment of cedar wood in the presence of some molybdenum catalysts can increase the amount of extracts. While autoclave treatment of cedar wood in water gave 2.85% extractives, the same treatment in the presence of H₃PMo₁₂O₄₀ gave 7.51% extractives. In the presence of silica-supported MoO₃, the amount of extractives was 5.50%. The extractives obtained using water were partially soluble in chloroform (40.7%). Only 27.6% of the extractives obtained using H₃PMo₁₂O₄₀ was soluble in the same organic solvent. When cedar was treated with silica-supported MoO₃, 56.4% of the extractives was soluble in chloroform. The extracts can be a source of fatty acids for biodiesel production and simple carbohydrates. The analysis of the chloroform-soluble fraction showed that the autoclave treatment of cedar wood gave 49.7% of a mixture of 2-hydroxy-1-(hydroxymethyl)ethyl hexadecanoate, 2-hydroxy-1-(hydroxymethyl)ethyl octadecanoate, and 2,3-dihydroxypropyl octadecanoate. The extractives obtained in the presence of the polyoxometalate molybdenum derivative gave 95% of the same esters of fatty acids, while those obtained in the presence of silica supported MoO₃ showed the presence of 93% of the same esters. Gas chromatography–mass spectrometry (GC-MS) of water-soluble fraction showed the presence of some simple carbohydrates, mainly ribose, xylose, and arabinose.     

Influence of wood extractives on two-component polyurethane adhesive for structural hardwood bonding

ABSTRACT

When bonding wood for structural applications, the wood–adhesive bond is influenced by a variety of factors. Besides the physical and mechanical properties of wood species, their chemical composition, e.g. wood extractives, can play a role in bonding wooden surfaces. A two-component polyurethane system (2C PUR) was chosen to better adapt to the current adhesion problem. The influence of extractives on crosslinking was determined by Attenuated Total Reflection-Fourier Transform Infrared Spectrometer (ATR-FTIR) and on the rheological behavior in terms of gel point and storage modulus. Therefore, 2C PUR was mixed with 10% of eight common wood extractives separately. Furthermore, the mechanical properties of beech wood (Fagus sylvatica L.) bonded with extractive enriched adhesive were tested by means of tensile shear strength tests and evaluation of wood failure. These results of ATR-FTIR clearly show that the majority of crosslinking was terminated after 12 hr. Acetic acid and linoleic acid expedited the isocyanate conversion during the first 2.5 hr. The curing in terms of gel point and storage modulus of 2C PUR was accelerated by starch, gallic acid, linoleic acid, and acetic acid. Heptanal, pentanal, 3-carene, and limonene decelerated the curing. All extractives lowered the storage modulus determined after 12 hr. The bonding of beech wood with extractive–adhesive blends showed a slight decrease of the mechanical properties, with the exception of a marginal increase in the case of linoleic acid and pentanal.

In summary, it can be said that 2C PUR is sensitive to the influence of wood extractives and can therefore be partly held responsible for adhesion problems occurring when extractives in surface-wide and higher contents are available.     

Photostability of wood surfaces esterified by benzoyl chloride

The photostabilization of wood surfaces is desirable to enhance the life of wood under exterior use and to improve the performance of clear coatings on wood surfaces. Chemical modification of wood has been found effective in upgrading properties such as biological durability and dimensional stability and has been suggested as a potential way for inducing photostability on wood surfaces. In this study, the photostability of chemically modified wood was assessed under accelerated weathering conditions. Wood specimens of Pinus roxburghii (Chir pine) were esterified with benzoyl chloride to 19.5 wt % gain and exposed to a xenon arc light source in a Weather‐O‐Meter for different periods ranging from 0 to 500 h. The irradiated samples were analyzed for color changes and chemical changes. The analysis of color changes in wood surfaces by ultraviolet–visible irradiation was carried out with a color measuring (CIELAB) system, and chemical changes were characterized with fluorescence and Fourier transform infrared spectroscopy. The esterification of wood by benzoyl chloride suppressed the color changes (photodiscoloration) due to irradiation. Modification also reduced the lignin degradation and generation of carbonyl groups on the surface of the irradiated wood. The fluorescence emission spectra of irradiated unmodified wood showed a large reduction in intensity and a large redshift in the emission maximum, whereas modified wood showed only a small change in fluorescence intensity on irradiation. The results show that the esterification of wood with benzoyl chloride was effective for the photostabilization of the wood polymers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Effect of weathering cycle and manufacturing method on performance of wood flour and high‐density polyethylene composites

Wood–plastic lumber is promoted as a low‐maintenance high‐durability product. When exposed to accelerated weathering, however, wood–plastic composites may experience a color change and loss in mechanical properties. Differences in weathering cycle and composite surface characteristics can affect the rate and amount of change caused by weathering. In this study, 50% wood flour filled high‐density polyethylene composite samples were injection molded, extruded, or extruded and then planed to remove the manufacturing surface characteristics. Composites were exposed to two accelerated weathering cycles in a xenon arc weathering apparatus. This apparatus exposed the samples to xenon arc radiation, which is a combination of UV, visible, and IR radiation that is similar to solar radiation. Composites were exposed to radiation with or without water spray. After exposure to radiation and water spray, composites with more wood component at the surface (i.e., planed samples) experienced a larger percentage of total loss in flexural modulus of elasticity and strength after weathering compared with the other composites. Composites exposed to radiation only did not experience as much change in properties as those exposed to radiation with water spray. The results of this study demonstrate that exposing wood–plastic composites to water spray in combination with radiation is more severe than exposing wood–plastic composites to radiation only. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3131–3140, 2006     

Effect of extractives on the performance properties of wood flour‐polypropylene composites

In this study, the effects of extractives in wood flour on the physicomechanical properties of wood flour‐polypropylene (PP) composites have been investigated. Three different solvents, hot‐water (HW), 1% NaOH (AL), and dichloromethane (DM), were used to remove extractives in both poplar and eucalypt wood flour. The obtained results showed that mechanical properties of the composites were moderately enhanced on using extractive‐free lignocellulosic materials in both the wood types. A large increase in the strength of eucalyptus flour‐PP composites was observed upon the removal of extractives from eucalyptus flour. Unlike the mechanical properties, no improvement in the water absorption and thickness swelling was observed for any type of extracted‐free samples. The thermal degradation behavior of the composites showed that in both cases, the degradation temperatures shifted to higher values after removing the extractives. In general, the removal of AL solubles was more effective in its improvement of the physicomechanical properties than the removal of HW and DM extractives. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The impact of drying and steaming processes on surface color changes of tension and normal beech wood

Abstract

Beech wood has a high frequency of defects such as red heartwood, reaction wood (tension wood). For the experimental measurements four logs without visible defects like red heartwood, which can noticeably affects the measurements' results were qualified. The drying medium temperature in the first phase of the process before the moisture content of the specimens fell below the FSP was maintained at 45?°C. Then, the temperature was gradually increased to the maximum value 65?°C. The results showed that different initial wood moisture content does not affect to final value of tension and normal wood. The colorimetric parameter L* was much higher for tension wood. After steaming, there were greater differences in the colorimetric parameters, respectively, a* and b*. After drying the difference of all colorimetric parameters between tension and normal wood was significantly less. The color changes were only noticed in the surface layers of specimens. Differences were small, and thus, the impact of the tension wood on the color changes was not confirmed. However, since the lightness of tension wood plays a key role for its visual detection, it may be adequate to only measure the lightness parameter (L*).     

Soybean and linseed oil‐based composites reinforced with wood flour and wood fibers

Composites consisting of a conjugated linseed or soybean oil‐based thermoset reinforced with wood flour and wood fibers have been prepared by free radical polymerization. The thermoset resin consists of a copolymer of conjugated linseed oil (CLO) or conjugated soybean oil (CSO), n‐butyl methacrylate (BMA), divinylbenzene (DVB), and maleic anhydride (MA). The composites were cured at 180°C and 600 psi and postcured for 2 h at 200°C under atmospheric pressure. The effect of varying filler load, time of cure, filler particle size, origin of the fillers, and resin composition has been assessed by means of tensile tests, DMA, TGA, Soxhlet extraction followed by ¹H‐NMR spectroscopic analysis of the extracts, and DSC. The best processing conditions have been established for the pine wood flour composites. It has been observed that the addition of MA to the resin composition improves the filler‐resin interaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Alkaline extraction of xylan from wood using microwave and conventional heating

This study aims to investigate the effect of microwave heating versus conventional heating for the alkaline hydrolysis of xylan from birch wood to understand the effect of the heating process on the dissolution of wood, the yield of xylan, and the degree of polymerization of the isolated xylan. The results indicate that the rate of wood dissolution is significantly higher (0.020/s) during microwave extraction than the conventional extraction (0.001/s). Wood solubilization, after an initial rapid removal of damaged fibers, is linear with time for both conventional and microwave extraction, with microwave showing a rate 20 times faster. The yield of xylan reaches a limit of about 60% for both processes but then declines slowly as thermal degradation become significant. Microwave heating provides 60% yield in 1/10th the time of the conventional process. This is found to be associated with the rapid temperature rise, and also with local “hot spots” generated during microwave treatment. The results indicated that xylan degradation was significant above 95°C. The nature of the isolated xylan was different for the two heating methods: the xylan isolated using microwave extraction for 20 min exhibits higher molecular weight (i.e., a greater degree of polymerization, about 150) than the xylan isolated using conventional extraction for the same duration (degree of polymerization, about 124) demonstrating the effectiveness of microwave heating for extraction of xylan from wood. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41330.     

Characterization of the ageing process of one-component polyurethane moisture curing wood adhesive

The aging resistance of five different one-component polyurethane (1C-PUR) adhesives with different mechanical properties has been investigated. The glue layer has been modeled as a superposition of three different layers representing the pure adhesive layer, the interaction layer between the wood and the adhesive and the plain wood layer. The modification of the mechanical properties of each layer was studied with a specific specimen for each layer. Also, a comparative analysis between natural and artificial weathering was conducted. The artificial weathering consists of a cyclic hydro-thermic treatment (treatment A5 according to DIN EN 302-1). The influence of a long time (5 months) mid-range temperature (70 °C) treatment was tested. Additionally, Fourier transform infrared spectroscopy (FTIR) analyses were conducted to determine the hypothetical chemical modification of the bond line. Generally, the strength properties of the samples decreased with the duration of the artificial weathering. However, significant differences were observed between the adhesive of the same system, especially during the temperature treatment. Furthermore, no relevant chemical degradation of the bond line was measured after 5 years of natural weathering (tested from 10 mm thick glued samples). The chosen method found that in the majority of cases, the wood is the weak layer in the bond line. Therefore, for moisture and temperature solicitation, there are no reasons to doubt the durability of the 1C-PUR glue layer for long term use. Nevertheless, further investigations are needed to better characterize the life expectancy of the wood and adhesive interface layer and to establish the influence of parameters, such as UV-radiation, wood extractives and moisture-induced stress, on the life expectancy of the bond line.     

Toughening of wood particle composites—Effects of sisal fibers

Sisal fibers were added to wood particle composites to enhance their toughness. The selected matrix was a commercial styrene diluted unsaturated polyester thermoset resin. Fracture tests were carried out using single‐edge notched beam geometries. Stiffness, strength, critical stress intensity factor K_IQ, and work of fracture W_f of notched specimens were determined. The incorporation of sisal fibers into wood particle composites significantly changed the fracture mode of the resulting hybrid composite. For the neat matrix and the wood particle composites, once the maximum load was reached, the crack propagated in a catastrophic way. For hybrid composites, fiber bridging and pull‐out were the mechanisms causing increased crack growth resistance. Addition of a 7% wt of sisal fibers almost doubled the K_IQ value of a composite containing 12% wt of woodflour. Moreover, the W_f increased almost 10‐fold, for the same sample. In general, the two composite toughness parameters K_IQ and W_f increased when the fraction of sisal fibers was increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1982–1987, 2006     

Wood plastic composites by melt impregnation: Polymer retention and hardness

Wood plastic composites were prepared through impregnation of solid wood with polyethylene. The effects of impregnation parameters on polymer retention and hardness were investigated. A screening strategy of 16‐run resolution IV design for seven factors at two levels was adopted. The seven factors were: ratio of maleated polyethylene in formulations, ratio of polyethylenes with different molecular weights, four process factors (vacuum, pressure, time, and temperature), and wood species (red maple and aspen). Polymer retention (PR) and Brinell hardness (H_B) were investigated and discussed on the basis of the impregnation parameters. The present work showed that process parameters (pressure and temperature), polymer impregnants (different molecular weight polyethylenes), and wood species contributed significantly to PR and H_B. Increasing pressure and temperature resulted in a higher PR and H_B, whereas increasing the molecular weight of polyethylene and switching wood species from aspen to red maple gave a lower PR and H_B. This study was aimed at understanding how impregnation parameters affect the final properties of wood plastic composites and developing an optimal fabrication process for wood plastic composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1672–1680, 2006     

Assessing biodegradability and mechanical,thermal, and morphological properties of an acrylic acid‐modified poly(3‐hydroxybutyric acid)/wood flours biocomposite

A poly(3‐hydroxybutyric acid) and wood flours (PHB/wood flours) composite and an acrylic acid‐grafted PHB/wood flours composite were characterized and their properties were examined and compared. Mechanical properties of PHB became significantly worse when it was blended with wood flours, due to the poor compatibility between the two phases. Much better dispersion and homogeneity of wood flours in the polymer matrix was obtained when PHB‐g‐acrylic acid (AA) was used in place of PHB in the composite. Improved mechanical and thermal properties of the PHB‐g‐AA/wood flours composite, notably an increase in tensile strength at breakpoint, evidenced its superiority to the PHB/wood flours composite. Furthermore, PHB‐g‐AA/wood flours composites were more easily processed because of their lower melt viscosity. Under soil and enzymatic environments, weight loss data indicated that both composites were more biodegradable with higher wood flours content. A reduction in tensile strength at break after exposure to soil and enzymatic environments was also observed in both blends, especially at high wood flours content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3565–3574, 2006     

Combustion properties of Brazilian natural wood species

This paper investigates the combustion characteristics of 12 wood species natural to Brazil. A mass loss cone calorimeter was used to obtain the properties associated with (i) heat release rate (HRR), peak HRR, and total heat released; (ii) total mass loss and mass loss rate; (iii) average effective heat of combustion; and (iv) time to ignition, time of pyrolysis and temperature of ignition. The samples used in this work were as follows: (i) prepared in accordance to ISO 5660‐1:2002; (ii) oven dried; (iii) irradiated with a constant heat flux of 50 kW/m²; and (iv) exhibit wood fiber orientation in a plane orthogonal to the flux incidence. Finally, the paper explores the possibility of linking the obtained combustion properties with the density and classes of selected wood species. Copyright © 2014 John Wiley & Sons, Ltd.     

Use of nanoparticles for controlled release of biocides in solid wood

The fungicides tebuconazole and chlorothalonil were successfully incorporated into polymeric nanoparticles with median particle diameters of 100–250 nm. Polyvinylpyridine (PVPy) and polyvinylpyridine‐co‐styrene (10% styrene and 30% styrene) were employed as the polymer matrix. The size of the nanoparticle increased with increased styrene content. The biocide also affected particle size, with chlorothalonil consistently yielding larger nanoparticles than tebuconazole. The release of the biocides from the polymeric nanoparticles was studied by suspending them in water. The release rate of both tebuconazole and chlorothalonil decreased with increased styrene content in the matrix, and chlorothalonil consistently released more slowly from the polymeric nanoparticles than did tebuconazole. It was found that biocides were successfully introduced into solid wood by incorporating them within polymeric nanoparticles, suspending the nanoparticles in water, and using the suspension to treat the wood with conventional pressure treatments. Once in the wood, the polymer matrix serves as a reservoir for the biocide and controls its release rate into the wood. Southern pine sapwood samples were treated with biocide‐containing nanoparticles suspended in water, then exposed to the wood decay fungus Gloeophyllum trabeum using a simple wafer test. Samples exhibited fungal resistance at appropriate levels of biocide incorporation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 458–465, 2001     

Surface properties of tannin-impregnated and varnished beech wood after exposure to accelerated weathering

The aim of this study was to determine selected surface properties of varnished beech wood impregnated with natural extracts after exposure to accelerated weathering. Beech wood samples were impregnated with aqueous solutions of 5 and 10% mimosa (Acacia mollissima) and quebracho (Shinopsis lorentzii) tannins. After weathering, colour changes (ΔL*, Δa*, Δb*, and ΔE*) in addition to scratch resistance and surface hardness values were calculated and evaluated. As a result of the weathering process, greater colour changes (ΔE*) were detected in the beech wood samples impregnated with tannins compared with the unimpregnated control samples. The least colour change occurred in the Tanalith-E-impregnated samples. Total colour change was adversely affected with tannin impregnation after the weathering processes. In terms of surface hardness and scratch resistance, the highest values were observed in the mimosa-solution-impregnated and control samples. Furthermore, it was found that scratch resistance and hardness values tended to increase during the first period of weathering and decreased thereafter. Regarding surface properties, the best results were obtained when polyurethane varnish was employed compared with the other varnish types.     

The role of wood extractives in structural hardwood bonding and their influence on different adhesive systems

Bonding of hardwood for structural applications is a complex process. Various factors influence the bond performance and the interface area is considered the most crucial part. The chemical composition of the interface, e.g. wood extractives, is expected to influence the bonding of hardwoods. The subject of this study was to determine the influence of seven model substances that represent common wood extractives on different adhesive systems namely one-component polyurethane, two-component polyurethane, melamine urea formaldehyde and phenol resorcinol formaldehyde. The influence of the model substances on the cross-linking behavior of the adhesives was determined by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and on the rheological properties in terms of gel point and storage modulus. In addition, model substances characteristic for selected wood extractives were applied to the surface of European beech wood [Fagus sylvatica L.] before bonding and consequently tested in tensile shear mode according to EN 302-1. The ATR-FTIR spectra showed an influence of some substances on the crosslinking for all adhesive systems. Further, the curing process was mostly accelerated for phenol resorcinol formaldehyde, while melamine urea formaldehyde and polyurethane showed a less negative change in rheological behavior. The mechanical strength of beech wood bonds at room climate indicated only minor influence of model substances, but samples tested in wet conditions demonstrated a significant effect on some adhesive systems. It was concluded, that polyurethane adhesives degrade by acid substances and melamine urea formaldehyde by starch and gallic acid. Phenol resorcinol formaldehyde system was influenced negatively by starch and acids.     

Compression,cleavage, and shear resistance of composite construction materials produced from softwoods and hardwoods

The process of manufacturing laminated wood board is an effective technique for reducing or eliminating the negative properties of solid wood materials and for obtaining high‐performance materials. More economical composite laminated materials, which use different types of wood together and have the strength suitable for the purpose, can be produced with this technique. In the present study, composite laminated specimens containing beech (Fagus orientalis Lipsky), a type of hardwood, and poplar (Populus nigra), a softwood, were produced with layers of two thicknesses: 4 and 5 mm. Poly(vinyl acetate) (PVAc) and polyurethane (PU) glues were used in gluing. The results of the tests were compared with those for the solid wood specimens, and it was found that new composite building materials with high mechanical strength and lower cost could be produced for the construction materials sector in Turkey instead of solid wood. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3673–3678, 2006     

Synthesis and cure kinetics of liquefied wood/phenol/formaldehyde resins

Wood liquefaction was conducted at a 2/1 phenol/wood ratio in two different reactors: (1) an atmospheric three‐necked flask reactor and (2) a sealed Parr reactor. The liquefied wood mixture (liquefied wood, unreacted phenol, and wood residue) was further condensed with formaldehyde under acidic conditions to synthesize two novolac‐type liquefied wood/phenol/formaldehyde (LWPF) resins: LWPF1 (the atmospheric reactor) and LWPF2 (the sealed reactor). The LWPF1 resin had a higher solid content and higher molecular weight than the LWPF2 resin. The cure kinetic mechanisms of the LWPF resins were investigated with dynamic and isothermal differential scanning calorimetry (DSC). The isothermal DSC data indicated that the cure reactions of both resins followed an autocatalytic mechanism. The activation energies of the liquefied wood resins were close to that of a reported lignin–phenol–formaldehyde resin but were higher than that of a typical phenol formaldehyde resin. The two liquefied wood resins followed similar cure kinetics; however, the LWPF1 resin had a higher activation energy for rate constant k₁ and a lower activation energy for rate constant k₂ than LWPF2. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008