Weathering of chemically modified wood

The weathering characteristics and microscopic structure of unfinished acetylated and untreated radiata pine are reported. Samples were exposed outdoors over 28 weeks in Rotorua, New Zealand. Acetylated veneer had improved checking resistance when compared with untreated veneer, confirming results of a previous study on accelerated weathering of untreated and acetylated veneer. Colour changes of naturally weathered untreated and acetylated veneer were very different to that of artificially weathered veneer. Acetylated veneer was only slightly less grey than untreated veneer after 28 weeks' natural weathering.     

Natural weathering of various surface coatings on five species at four european sites

The natural weathering of surface treatments was compared at four sites and on five wood species; beech, spruce, Scots pine (sapwood), Douglas fir and dark red meranti, for 24 months. The surface treatments were: impregnating stain, film forming stain, pigmented acrylic latex paint and pigmented alkyd paint (solvent based). Despite substantial differences between the four locations, the results of the exposure differed only little. Spruce was shown to be a substantially better substrate for surface treatments than beech or Scots pine, though Douglas fir and meranti were best of all. The impregnating stain weathered uniformly, whereas the film forming stain cracked and flaked, leading to growth of blue stain fungi. Both acrylic latex and alkyd paint showed little or no damage after 2 years of weathering. The dampening effect of surface treatments on the natural changes of wood moisture content was initially quite good for the impregnating-and the film-forming stains, but both lost their efficiency after approximately 12 months. The protection conferred by acrylic latex was somewhat better, though possibly not sufficient for external joinery requiring dimensional stability. The highest level of moisture exchange damping efficiency was shown by the alkyd paint.     

The protective effect of 23 paint systems on wood against attack by decay fungi

A laboratory method was used to evaluate the protective effect of 23 different paint systems on Norway spruce wood against decay fungi. Weather-o-meter treated and non-treated paint films on wood were tested. Results were compared to those obtained on unprotected spruce wood. Finishes included in the study were primer oils, solvent-borne alkyd paints, water-borne acrylic paints, water-borne mixed alkyd/acrylic paints, alkyd emulsions and stains in different paint system combinations with one to four coats. The growth of the decay fungi of the paint films was estimated by visual inspection. After 5 months of incubation, microbial activity in the wood below the paint films was evaluated. Growth of the fungi in the wood below the paint film was measured by an indirect chemical method for estimation of microbial activity. Paint systems including a solvent-borne alkyd coat usually had a good performance when tested without prior weathering but degenerated most during the weathering process as judged from the altered water absorption and fungal growth rate. Paint systems including a treatment with a primer oil exhibited low moisture uptake also after weathering. A clear effect of fungicide additions was also seen. A water-borne penetrating oil with an acrylic top coat exhibited no visual surface attack before weathering, and low microbial activity in wood for all decay fungi before and after weathering.     

Outdoor weathering performance parameters of exterior wood coating systems on tropical hardwood substrates

Wood coating research almost exclusively focuses on softwood as substrate despite the fact that coatings applied on tropical hardwoods show a different weathering behaviour. The objective of this study was to quantify the impact of wood substrate and coating type on the weathering behaviour of finished wooden joinery in outdoor exposure using a set of statistical methods. Therefore, a broad range of white opaque paints and mid-oak semi-transparent stains were used. The coatings were industrially applied on window frames made of frequently used commercial tropical hardwood species. The general appearance of the wood/coating systems was assessed visually using a rating scale that takes into account the anatomical characteristics of hardwood. For the evaluation, a required minimum exposure time of 2.5 years outdoor weathering for joinery in vertical position and facing south-west was determined. At 30 months best performances were recorded for waterborne alkyd primers with an acrylic topcoat when dry coating film was sufficiently thick. The dry layer thickness also affected the impact of the hiding power on the performance of the wood/coating system. Within hardwood species the degradation rate of coatings on species with a fine texture was the lowest. The significant influence of the substrate’s texture on the weathering behaviour of coated hardwood stressed the need to evaluate the wood/coating system in total.     

Effect of simulated rainfall and weathering on release of preservative elements from CCA treated wood

The release of arsenic from wood pressure-treated with chromated copper arsenate (CCA) can be decreased by application of wood finishes, but little is known about the types of finishes that are best suited for this purpose. This study evaluated the effects of finish water repellent content and ultraviolet (UV) radiation on the release of arsenic, copper, and chromium from CCA-treated wood exposed to simulated rainfall. Deck boards treated with CCA were either left unfinished or dipped in a finish prepared with 1%, 3%, or 5% water repellent. All specimens were exposed to leaching from simulated rainfall, and a subset of specimens was also exposed to UV radiation. The rainfall was collected and analyzed for total elemental arsenic, copper, and chromium. The water repellent significantly decreased the amounts of these elements in the runoff, but for the short duration of this study there was no difference among the three water repellent concentrations. It is possible that water repellent content would have a greater effect over a longer exposure period. Exposure to UV radiation caused a significant increase in leaching from both finished and unfinished specimens. This effect may be a result of increased surface area during weathering as well as loss of fibers caused by UV-induced surface erosion.     

Use of iron oxides to influence the weathering characteristics of wood surfaces: a systematic survey of particle size,crystal shape and concentration

Iron oxide pigments may be an alternative treatment for limiting weathering of wood surfaces instead of stains or clear coatings. An earlier study suggested the ability of iron oxides to protect against discoloration varied with particle size. In this study, iron oxides with different crystal shapes and particle sizes were investigated along with a carbon black pigment. Loblolly pine (Pinus taeda L.) samples were impregnated with water borne iron oxide dispersions, exposed to predetermined amounts of solar radiation in the high desert of Eastern Oregon, and then evaluated for discoloration, checking and changes in chemical composition. The results from this observational study suggest that much higher levels of iron oxide are required than previously thought to prevent discoloration and limit lignin degradation. Large particle sizes led to greater opacity and provided greater protection, but no iron oxide protected as well as carbon black. The findings also suggested that iron oxides had no effect on checking, indicating that the mechanisms of discoloration and checking were not directly related.     

Application of copper monoethanolamine solutions as primers for semitransparent exterior wood stains

The effects of copper monoethanolamine (CuA) treatment of wood surfaces on the surface weathering and durability of a semitransparent penetrating stain were compared with those of chromic acid (CrA) treatment which is known as a photoprotective primer, using artificial weathering trials. Chemical changes in chemically treated and untreated wood surfaces during artificial weathering were investigated using Fourier transform infrared (FTIR) spectroscopy. Surface roughness, water contact angle measurements and scanning electron microscopy observations were performed to assess stain durability. Results of FTIR analyses indicated that lignin losses following CuA and CrA treatment were less than those of the untreated wood surfaces during the initial stage of artificial weathering. CuA pretreatment prior to staining also retarded the increase in the average surface roughness compared with that observed for the CrA-pretreated surface and untreated control (only stained) during artificial weathering. Furthermore, CuA pretreatment retarded the decrease in the contact angle compared with that observed for the untreated control, although the use of a highly concentrated CuA solution led to a decrease in the water repellency of the stained wood surface. These results indicated that CuA solution could be used for the pretreatment of wood surfaces to enhance the durability of semitransparent penetrating stains, as long as excessive CuA concentrations are avoided.     

乙酰化处理对甲壳胺医用敷料性能的影响

甲壳胺纤维与乙酸酐反应时,通过控制乙酸酐与甲壳胺纤维之间的比例,可以得到不同乙酰度的甲壳胺纤维。研究用乙酸酐改性后甲壳胺纤维及医用敷料的吸湿性能、抗菌性能和拉伸强度。实验结果表明:甲壳胺的乙酰度对敷料的性能有明显的影响;部分乙酰化后的甲壳胺纤维在与水接触后可以把大量的水分吸收进纤维中,使部分乙酰化医用敷料的吸湿性能比未处理的医用敷料有明显的改善;部分乙酰化样品的湿强度和抗菌性能比未处理的样品有所下降。     

Effect of low and high acetylation degree in the morphological, physicochemical and structural characteristics of barley starch

Barley starch was acetylated at two levels (low degree: LD (0.9), and high degree: HD (2.7)) substitution and the morphological, physicochemical and structural of the resultant acetylated barley starch were determined. The acetylated barley starches presented the signal at 1226 cm⁻¹ that corresponds to the C-O stretching of acetyl groups. The morphological study showed fusion of starch granules in the acetylated starch with HD. This effect was evident in the pasting test, because the viscoamylograph profile of HD starch showed the absence in peak viscosity, viscosity breakdown and viscosity setback. The peak gelatinization was similar for native and LD and decrease in the HD acetylated starch. The gelatinization enthalpy value showed difference among the samples, indicating that the loss of the ordered double helices more than the crystallinity loss was higher in the HD acetylated barley starch. In the retrogradation test, acetylation affected both retrogradation and enthalpy value, because acetylated barley starch with HD substitution at three storage days had 3.2 j/g and with LD 4.8 j/g. The molecular weight and z-average radius of gyration values decreased due to the acetylation process, indicating depolymerization of starch components as it was evidenced by the increase in short chains level in the acetylated samples.     

Furnierverarbeitung in der Türen-, Paneel- und Möbelindustrie

True wood vencers are nowadays gaining increasing importance in varous fields of wood industry. The processing of veneers with suitable machinery is of special interest for the manufacture of doors and panels, as well as for furniture. This paper describes the preparation of veneers by smoothing (“ironing”) by means of special hot presses and trimming by vencer seissors. Further attention is given to three veneer jointing procedures at present in use: the respective equipment, its functions and capacities, are described. With respect to costs the three systems are compared and, finally, evaluated.     

Effect of profiling and preservative treatments on the weathering characteristics of Southern pine deck boards

In this study, Southern pine (Pinus sp.) deck boards were machined to flat (control) and ribbed surface profiles. The specimens were treated with aqueous formulations of 4,5-dichloro-2-N-octyl-4-isothiazolin-3-one (EL2) and amine copper azole (CA-C) using a vacuum/pressure method. Boards were exposed to accelerated weathering for 576 h (24 days). The results showed all of the preservative-treated ribbed decking samples had a lower average number of checks compared to end matched flat samples. Checks were also shorter and narrower in the profiled deck boards than in the unprofiled specimens. Furthermore, the lowest amount of checking, cupping, twist and bowing was observed for specimens profiled and treated with the EL2.     

皮革透水汽性能的研究

从透水汽性能方面研究了未涂饰皮革、聚氨酯涂饰皮革、贴膜皮革和合成革的物质传递性能。研究结果表明 :涂饰对皮革的透水汽性能影响很大 ,未涂饰皮革的透水汽性能远远优于涂饰皮革、贴膜皮革和合成革。还分析了皮革的透水汽机理。未经过涂饰的皮革的透水汽作用是水分子在蒸汽压力作用下 ,在皮革微孔内的迁移和胶原上亲水性基团运动对水分子的传递的加合。而涂饰后的皮革、贴膜皮革和合成革的透水汽作用则只是水分子在蒸汽压力作用下在皮革微孔内迁移的结果。要提高成品皮革的透水汽性能 ,应该从如何提高皮革的孔隙率和皮革及涂饰剂的亲水性基团数目方面进行研究     

魔芋葡甘露聚糖的凝胶化特性

用测定动态粘弹性的方法探讨了碱存在下天然及乙酰化魔芋葡甘露聚糖(KGM)的凝胶化动力学特性。通过固有粘度和光散射的测定决定了KGM样品的分子量和其他分子参数。研究使用的KGM样品经乙酰化处理后发现其已被降解,但经乙酰化后的KGM的分子量与乙酰化度几乎不相关, 约为天然KGM分子量的1/2。当碱凝固剂(Na2CO3)的浓度为固定值时,观察到了凝胶化时间随KGM浓度的增大和温度的升高而缩短,但随乙酰化度的增加而变长的倾向。乙酰化处理后的KGM的脱乙酰基反应和后续的凝胶化过程比天然KGM缓慢,但能形成更有弹性的凝胶。以上现象表明,乙酰基团的存在对KGM的凝胶化过程起着极其重要的作用。在较为缓慢的凝胶化过程中,能够形成数量更多且分布均匀的凝胶网络结点,从而得到更具弹性的凝胶。     

皮革透气性能的研究

从透气性方面研究了皮革的物质传递性能及其影响因素。采用了未经涂饰的皮革、经过聚丙烯酸树脂涂饰剂涂饰 1次和 2次的皮革以及合成革 ,研究了它们对空气的透过速率与空气压差之间的关系。结果为 :这些材料的透气速率与其空气压差之间呈现良好的线性关系 ,说明其透气过程是空气在压差作用下于皮革内外侧发生传递的过程。未涂饰皮革具有良好的透气性 ,涂饰使皮革的透气性能大大降低。在如何提高皮革涂层的透气性方面应该加强研究 ,以保证在赋予皮革其它性能的前提下不至于降低其透气性     

Penetration of water-borne alkyd emulsions and solvent-borne alkyds into wood

The ability of water-borne alkyd emulsions and solvent-borne alkyds to penetrate into sapwood of pine and spruce is demonstrated with autoradiography and SEM-EDXA. Application of test alkyds on to tangential surfaces shows that penetration occurs mainly through the radial rays. Only a few outer longitudinal tracheids are penetrated. Water-borne alkyd emulsions and solvent-borne alkyds have similar penetration patterns and seem to penetrate to the same extent. Penetration is reduced by factors such as increasing alkyd viscosity and pigmentation.     

衬砌台车门架支撑点的布置分析

为了取代传统平面受力状态下分析门架支撑点布置的局限性,考虑三维衬砌台车结构,利用有限元优化方法对衬砌台车门架支撑点的布置进行了优化分析.结果表明,衬砌台车门架支撑点布置的合理性对衬砌结构性能的提高非常重要.在优化的基础上选择了一组参数,经过强度和刚度校核得到了衬砌台车门架支撑点的最佳布置.     

Artificial weathering of wood surfaces modified by melamine formaldehyde resins

Spruce and poplar samples were treated with different melamine formaldehyde resins. A long term artificial weathering experiment was performed in order to clarify the resistance to weathering regarding wood colour and surface hardness. The increase in hardness due to melamine treatment was well preserved after simulated long term weathering. The treated samples also showed advantages compared to untreated reference samples regarding discolouration and crack formation. Low molar mass and low degree of methylolation of the melamine resin used was found to be favourable for a successful treatment.     

Pre-service adhesion of coating systems based on alkyd primer applied to light organic solvent preservative (LOSP) treated radiata pine sapwood boards

3 or higher. Paint film thickness values for the acrylic undercoat layer were always lower than values expected from manufacturers' coverage recommendations while values for the alkyd undercoat were always higher. Presence of LOSP solvent at time of paint application increased alkyd undercoat thickness and decreased acrylic undercoat thickness when these were applied over alkyd primer. Observed adhesion failure patterns may have been caused by a combination of paint thickness variability, and the softening of alkyd paint under acrylic layers. Although adhesion failure decreased with time, it was still observed at the end of the 92-day period.

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Crack formation in unfinished siding of aspen (Populus tremula L.) and Norway spruce (Picea abies (L.) Karst.) during accelerated weathering

Crack formation is a serious defect that may reduce the lifetime of unfinished wood in service. An accelerated weathering test was carried out to study crack formation of solid wood board specimens of aspen (Populus tremula L.) and Norway spruce (Picea abies (L.) Karst.). The influence of the boards' distance from the pith was also studied. The aspen specimens developed a higher number of cracks than the spruce specimens. However, these cracks were shorter and less injurious than those propagating in spruce wood. It is concluded that a solid wood siding of aspen will show at least as good a performance as spruce regarding crack injuries. For both aspen and spruce, boards taken from near the pith had a lower proportion of long cracks than boards taken further out. This supports the rule that boards with a high proportion of annual rings perpendicular to the surface (the boards near to the pith) have a higher resistance to crack formation than boards with a high proportion of horizontal annual rings.     

Characteristics of acetylated and enzyme-modified potato and sweet potato flours

The properties of modified potato and sweet potato flours have been determined by incorporating acetyl groups (acetylation) and by treating with glucoamylase (enzymatic modification). Fractionation studies on Sepharose CL-2B showed that the content of high molecular weight fraction decreased, with a proportionate increase in the lower molecular weight carbohydrate fraction, whereas FT-IR indicated changes in crystallinity of the modified starches. The data showed that the degradation of starch is dependent on the type of modification which, in turn, determined its crystallinity and digestibility. The swelling power and solubility patterns of modified flours indicated a greater degree of associative forces in the starch granules. Scanning electron microscopy revealed indentation on acetylated starch granules, and the granules appeared as bunches/clusters, whereas surface erosion was observed in the enzyme-treated samples. The presence of substituent groups in acetylated flour influenced digestibility inversely, whereas improved digestibility was observed in enzyme-modified samples.