Novel color stabilization concepts for decorative surfaces of native dark wood and thermally modified timber

UV and visible light exposure of dark colored wood and thermally modified timber (TMT) is strongly connected with discoloration and photobleaching of the respective wood surfaces. Conventional and nanoscale UV absorbers as well as radical scavengers (HALS), mainly effective for the protection of softwood and bright hardwood, were found to be improper for the light stabilization of dark wood surfaces. In the current work discoloration mechanisms are discussed considering the role of wood extractives and the sensitivity of dark colored wood types to visible light and results are presented which were obtained by applying novel protecting systems for the light stabilization of transparently coated surfaces from dark colored wood types and TMT.     

Accelerated ultraviolet weathering of PVC/wood‐flour composites

Ultraviolet weathering performance of polyvinyl chloride (PVC) filled with different concentrations of wood flour was studied. Extruded PVC/wood‐flour composite samples were subjected to cyclic ultraviolet lamps/condensation exposures and assessed over a total of 400 and 2600 hours. Each assessment consisted of DRIFTFTIR and XPS collections, contact angle measurement, color measurement, and tensile property testing. The experimental results indicated that wood flours are effective chromophore materials since their incorporation into a rigid PVC matrix accelerated the degradation of the polymeric matrix. Photodegradation converted unfilled PVC samples to a colored material of lower extensibility. Although composite samples exhibited greater discoloration than unfilled PVC samples, they retained all their original strength and stiffness properties even after 2600 hours of cyclic UV irradiation/condensation exposures.     

A new innovative stabilization method for the protection of natural wood

The UV-light exposure of natural wood leads initially to a fast color change, and in the further stages to large chemical modifications and mechanical breakdown of the wood surface layer. Even in diffuse light exposure, prevailing in indoor conditions, the discoloration of wood is a serious esthetical drawback, for example, for furniture and parquetry.

Progress has been made with the development of new stabilizers, which offer a significant benefit compared to the currently used benzotriazole UV-absorbers. Using these new stabilizers the wood photo-protection against discoloration and the durability of clear and transparent pigmented coating systems can be significantly improved.     

Effect of grafted UV stabilizers on wood surface erosion and clear coating performance

The critical element for a durable exterior clear coating on wood is photochemical stability of the wood surface beneath the coating. If this interface is not stabilized, even a durable coating will delaminate due to photoinduced wood degradation. A new method for stabilizing the wood surface was developed and evaluated. HEBP [2-hydroxy-4-(2,3-epoxypropoxy)benzophenone] was grafted to western redcedar (Thuja plicata). HEBP contains an ultraviolet (UV) stabilizer moiety that improved the xenon are accelerated weathering performance of western redcedar (WRC). The weathering performance of the HEBP-modified WRC was compared with WRC treated with an unbound UV stabilizer of similar type and with untreated controls. The grafted stabilizer reduced the erosion rate (weathering) of unfinished WRC, and, as a pretreatment under clear finishes (spar varnish and exterior grade polyurethane), the stabilized surfaces improved coating performance and color retention.     

Influence of wood extractives on the photo‐discoloration of wood surfaces exposed to artificial weathering

Extracted and unextracted black cherry (Prunus serotina), red oak (Quercus rubra), and red pine (Pinus resinosa) wood specimens were exposed to artificial weathering, and their discoloration process was investigated to obtain basic understanding on the role of wood extractives in the weathering of hardwoods and softwoods. Color measurements were made with a spectrometer according to ISO 2470 standards, using the CIELAB system. Results obtained showed that the rate of whiteness was not significantly affected by extractives removed with organic solvents, but were significantly affected when organic solvent extraction was followed by water extraction. The total discoloration rate had the same pattern, and chromaticity coordinates were less affected by wood extractives. These results confirm the hypothesis that some extractives contained in wood act as antioxidants and are able to provide some protection to wood surfaces against weathering degradation. However, more work is needed to understand the chemistry and mechanism of action of these extractives so as to develop any practical use for this property. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 425–434, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20248     

Performance of organic nanoparticle coatings for hydrophobization of hardwood surfaces

The protection of wood surfaces against water is a primary requirement to enhance their life-time and durability. In this article, a hydrophobic surface modification of selected hardwood surfaces (including high-density (HD) and low-density (LD) samples) is presented, by coating them with waterborne imidized nanoparticles under pure conditions or with vegetable oil. The performance of both nanoparticle coatings relative to noncoated and oil-coated samples was evaluated by water contact angles, microscopy, and optical profilometry. The pure nanoparticle coatings often increase the hydrophobicity, but they do not yet form a fully protective layer due to their porous structure after drying. The nanoparticle coatings with vegetable oil form a continuous layer with a maximum contact angle of 118°. The coating formation highly depends on the wood density (and resulting surface porosity), resulting in spreading of the aqueous dispersion on HD wood and penetration on LD wood. A thin continuous nanoparticle coating with incorporated vegetable oil provides highest contact angles, as the roughness of the original wood fibers remains visible in the surface profile.     

The challenge of antimicrobial glazed ceramic surfaces

The resistance that microorganisms develop to antibiotics is a worldwide challenge. The antimicrobial agents as disinfectants for surface treatments are widespreadly used to prevent the proliferation of microorganisms, but their use should be repeated over time to ensure a complete microbe-free surface. Surfaces with permanent antimicrobial properties suppose a recent demand in materials science for functional polymeric coatings, metals, treated wood or ceramic glazed tiles. Whereas polymeric coating has been extensively studied, the antimicrobial functionality on ceramic glazed surfaces is not completely achieved. This work reviews glazed ceramic tiles developments in antimicrobial and virucidal surfaces. The main antimicrobial physical or chemical mechanisms have been described as the base to develop active glazed surfaces. The main tests required to evaluate the antimicrobial response in glazed ceramic tiles are also summarized. The high temperature required in the ceramic processing is the key point to achieve a micro/nanostructure that potentiates the antimicrobial and virucidal response of the glazed surfaces. A discussion on recent developments as well as the main routes and challenges to obtain permanent surfaces with antimicrobial and virucidal response is provided.     

Flame retardancy afforded by polyaniline deposited on wood

Wood scantlings were coated with polyaniline (PANI) during the in situ polymerization of aniline with ammonium peroxydisulfate in an aqueous medium. The coating was made in hydrochloric or phosphoric acid solutions in both the absence and presence of stabilizers, poly(N‐vinylpyrrolidone) or colloidal silica. The PANI‐coated wood was placed in a flame or in a furnace operating at 400 or 600°C, and the decrease in the mass was determined. The wood coated with PANI was less reduced in its mass than uncoated samples and was converted to charcoal rather than to ashes. The deposition of related polymers, polypyrrole and poly(1,4‐phenylenediamine), provided similar protection against heat exposure. Fourier transform infrared and Raman spectra of the residues after the burning of PANI‐coated wood were compared. The soaking of wood in PANI colloids did not result in similar protection of wood against fire; the coating of the cellulose fibers with PANI during the polymerization was needed for the enhanced stability of wood at elevated temperatures. The concept of carbonization processes at the surface layer of PANI‐coated cellulose fibers leading to the formation of carbonaceous microtubes is offered to explain the improved stability of wood against flame and heat exposure. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 103: 24–30, 2007     

防紫外线超疏水织物涂层构筑及性能

以羟基氟硅油、季戊四醇三丙烯酸酯(PETA)为原料,制备了含双键的聚氨酯,在整理液中添加紫外线吸收剂(UVA400)和纳米二氧化硅颗粒,以提高涂层的紫外线防护效果和表面粗糙度,通过紫外光引发双键自由基聚合构筑防紫外超疏水织物涂层,并对材料进行了FTIR、SEM、疏水性及紫外线防护性能测试。结果表明:羟基氟硅油和PETA引入到了聚氨酯分子链中;织物表面具有微纳米状凸起,形成了粗糙的表面涂层。当整理液固体组分中w(SiO2)=15%,w(UVA400)=1.5%时,涂层织物的接触角为154?,滚动角为9?,紫外线防护系数(UPF)为72,紫外线A(UV-A)波段的透过率为2.96%,具有超疏水和紫外线防护性能;涂层织物经120h加速老化实验后,接触角为155?,UPF为117,UV-A波段的透过率为2.68%,具有良好的耐久性。     

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 nanodiamond surface functionalization using oleylamine on the scratch behavior of polyacrylic/nanodiamond nanocomposite

Addition of hard particles such as nanodiamonds to polymers to improve their physical and mechanical properties is very common. However, nanodiamonds are usually hydrophilic so their tendency to form agglomerates in a polymeric matrix is quite strong. In this study, the effect of nanodiamond surface modification on its uniform dispersion in a polymeric matrix such as polyacrylic-base polymer clear coat was investigated. For this purpose, detonation nanodiamond (DND) with an average particle diameter of 4–6 nm was used. To improve dispersion of as-received DND (AR-DND) in the polymeric matrix, the surfaces of the particles were modified by heat treatment (oxidation) in air and followed by functionalization using oleylamine (OLA) as surfactant. So, nanocomposites with different contents of AR-DND, HT-DND and OLA treated HT- DND (OLA-HT-DND) particles were produced. Their characterizations were investigated by employing many analytical methods such as: Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermo-gravimetry analysis (TGA). Scratch resistance test and study of coating surfaces, using scanning tunneling microscopy (STM), were carried out on the polymeric nanocomposites. The results showed that the surface-functionalized nanodiamonds are highly dispersive and stable in the polymeric matrix. In addition, scratch resistance was increased with the addition of nanoparticles.     

Photoactive antimicrobial agents/polyurethane finished leather

To prepare antimicrobial coating on leather surfaces with high potency against microbes, photoactive agents such as benzophenone (BP) and rose bengal (RB) were incorporated into polyurethane‐based coating solutions, respectively, and then the BP or RB containing solutions were applied onto surfaces of leather by a painting method. The photoactive antimicrobial agents treated leather samples were characterized by FTIR, SEM, and antimicrobial tests. The treated‐leather samples demonstrated excellent antibacterial activity under fluorescent light as well as UVA light and also the antimicrobial ability showed the effective durability to abrasion and daylight. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Corrosion protection performance of nanocomposite coatings under static,UV, and dynamic conditions

Silicone-modified epoxy polymeric matrix was successfully fabricated and reinforced with 1–2 wt% SiO₂, TiO₂, and TiSiO₄ nanoparticles. Fourier-transform infrared spectroscopy, contact angle measurements, differential scanning calorimetry, and field-emission scanning electron microscopy together with energy-dispersive X-ray spectroscopy were employed to investigate different characteristics of the prepared coatings. To simulate operating conditions, all samples were characterized via electrochemical impedance spectroscopy (EIS) after being subjected to different conditions. Corrosion under static conditions, in which the samples were exposed to a static electrolyte without further change in other parameters, was investigated. Furthermore, to study the effects of ultraviolet (UV) radiation in accelerating the degradation of the coatings, samples were characterized after being subjected to UV while immersed statically in the electrolyte. Additionally, the corrosion protection performance was investigated after subjecting the coated substrates to dynamic conditions involving continuous movement of the sample in the electrolyte, simulating continuous wear of the coated surfaces. Compared with the static condition, the EIS results revealed the vital role of the silicone resin and nanoparticles in improving the stability of the coating film against corrosion degradation in the presence of UV radiation, while poor performance in dynamic condition was recorded for all the coating systems.     

Enhancing exterior durability of jack pine by photo-stabilization of acrylic polyurethane coating using bark extract. Part 1: Effect of UV on color change and ATR–FT-IR analysis

Heat-treated wood is a value-added product but its exposure to various environmental factors leads to discoloration of wood surface due to the photochemical reactions. Discoloration has become an important economic problem for wood industries since product specifications are now more demanding. In addition, stricter environmental legislations necessitate the development of environmentally friendly transparent coatings with minimal use of chemicals which balances aesthetic and protection. In this study, the acrylic polyurethane coating was improved with the addition of natural antioxidant (bark extract) and lignin stabilizer alone or in combination to enhance the resistance of this coating to different weathering factors. An accelerated aging test was conducted with the aim of comparing the acrylic polyurethane coatings containing different additives with the commercially available pigmented solvent borne coating used by industry and organic UV absorbers. The modifications in chemical structure of coatings were characterized by ATR–FT-IR analysis. The color change data showed that the coating containing bark extract was the most effective and performed better than the industrial coating. However, the visual assessment showed that the coating containing bark extract and lignin stabilizer had the best performance. FT-IR analyses suggested that the chain scission reaction took place throughout the weathering but its effect was not significant for any of the coatings.     

Surface Activation and Adhesion Properties of Wood-Fiber Reinforced Thermoplastic Composites

Four surface activation methods were evaluated on a series of wood-fiber reinforced thermoplastic composites (WPCs) as a means to improve the adhesion of a water-based acrylic coating. Treatments with chromic acid and oxygen plasma performed best, increasing the acrylic coating peel load to WPCs by 170 and 122%, respectively, and yielding adhesion levels equivalent to or higher than those obtained on wood. The benzophenone/ultraviolet and flame treatments also improved the coating adhesion by 100 and 64%, respectively, but did not reach the adhesion levels achieved on wood. For both the chromic acid and oxygen plasma treatments, the WPC formulation impacted the treatment efficacy. Profilometry and scanning electron microscopy (SEM) showed that the chromic acid treatment acted mainly by roughening WPC surfaces. While surface oxidation was not evident from attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), the improved wettability of WPCs with water suggested that the oxygen plasma treatment oxidized WPCs.     

Surface Activation and Adhesion Properties of Wood-Fiber Reinforced Thermoplastic Composites

Four surface activation methods were evaluated on a series of wood-fiber reinforced thermoplastic composites (WPCs) as a means to improve the adhesion of a water-based acrylic coating. Treatments with chromic acid and oxygen plasma performed best, increasing the acrylic coating peel load to WPCs by 170 and 122%, respectively, and yielding adhesion levels equivalent to or higher than those obtained on wood. The benzophenone/ultraviolet and flame treatments also improved the coating adhesion by 100 and 64%, respectively, but did not reach the adhesion levels achieved on wood. For both the chromic acid and oxygen plasma treatments, the WPC formulation impacted the treatment efficacy. Profilometry and scanning electron microscopy (SEM) showed that the chromic acid treatment acted mainly by roughening WPC surfaces. While surface oxidation was not evident from attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), the improved wettability of WPCs with water suggested that the oxygen plasma treatment oxidized WPCs.     

Natural fiber composites of high‐temperature thermoplastic polymers: Effects of coupling agents

Our earlier paper (Jana, S.C.; Prieto, A. J Appl Polym Sci 2002, 86, 2159) on the development of natural fiber composites of high‐performance thermoplastic polymers described a new methodology for the manufacturing of composite materials of a high‐temperature thermoplastic polymer, poly(phenylene ether) (PPE) and wood flour, a cellulosic natural filler. A thermosetting epoxy, used as a reactive solvent, reduced the processing temperature of PPE/epoxy blends to well below the decomposition temperature of natural fillers. In addition, the epoxy component, upon polymerization, formed coating layers around the filler particles to provide resistance against moisture diffusion and attacks by acids and alkali. This article describes the results of an investigation on two outstanding issues: (1) the influence of cellulosic wood particles and coupling agents on the speed of epoxy curing and reaction‐induced phase separation and (2) the effects of coupling agents on the morphology of crosslinked epoxy at the surfaces of natural fillers and mechanical properties of the composites. It was found that wood particles expedited epoxy curing in the composites; the extent of epoxy curing, however, was reduced in the presence of coupling agents. Also, the coupling agents promoted complete coverage of wood flour particles by polymerized epoxy, although the mechanical properties deteriorated over systems without coupling agents. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2168–2173, 2002     

Effect of titania and zinc oxide particles on acrylic polyurethane coating performance

The outer environment, especially UV portion of solar radiation and water (in the form of moisture or rain) has an adverse effect on the surface appearance of heat-treated wood. Exposure to UV triggers the chain scission reactions which change the intrinsic properties of heat-treated wood and discoloration of wood surface. Repeated temperature and humidity variations cause swelling and shrinking of wood surface, which consequently create cracks and fissures exposing wood's sub superficial layers to atmospheric agents. Therefore, wood industries move towards the development of coatings in order to protect the heat-treated wood while retaining wood's natural look. Water based acrylic polyurethane coatings are highly efficient, non toxic and durable coatings with upgraded film properties. In this study, an attempt is made to improve the performance of these coatings by incorporating natural antioxidant (bark extract) and inorganic UV absorbers (nano and micro titania and nano zinc oxide) into the coatings. The main objectives of this study are to investigate the wetting and penetration characteristic of these new coatings on the wood surface and to study coating thickness variation with weathering time. The Sessile-drop method and fluorescence microscope are used for this investigation. The wettability of different coatings applied to heat-treated jack pine early wood and late wood is compared. The results show that there is a significant difference between the contact angle of early wood and late wood for acrylic polyurethane coating containing titania micro particles. The contact angle between water and coated wood surface reveals that the degree of orientation of the coating materials increases as the weathering time increases. The penetration characteristics of all the four coatings are found to be very poor. In addition, the relationship between the coating thickness and the UV exposure time is studied for four water based acrylic polyurethane coatings with different additives. It is found that the coating thickness decreases with increasing weathering time and a tissue deformation beneath the coating surface takes place during weathering.     

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