Evaluating the durability of wood-based panels using internal bond strength results from accelerated aging treatments

In this study, the durability of wood-based panels was evaluated by comparing the internal bond (IB) strength retention after five different laboratory-based accelerated aging tests with the IB retention after 5 years of outdoor exposure in Shizuoka City. In each accelerated aging test, the IB retention of MDI-bonded panels showed high retention compared to other panels. Outdoor exposure in Shizuoka City resulted in an IB retention value for particleboard (PF) and oriented strandboard (aspen) of less than 10% after the 5-year exposure period. Medium-density fiberboards maintained their initial IB strength over the same period. Calculation of the mean IB retention for all board types allowed comparison of the severity of aging between the accelerated test methods and outdoor exposure. The ASTM six-cycle test method was the most severe among the standard treatment cycles applied.     

The aging effects of water immersion treatments in wet-bending for standardized testing of wood panels

The durability of wood-based panels is one of the most important properties when they are used in residential construction. The main objectives of this study were to investigate the quantitative relationship between the Wet-bending A test and the Wet-bending B test, examine the aging effects of the treatments specified in the wet-bending methods, and discuss the relationship between wet-bending and outdoor aging tests conducted in Shizuoka, Japan. Wet-bending tests, internal bond tests after humidity treatment, and outdoor aging tests in Shizuoka were conducted using eight types of commercial wood-based panels. A linear relationship was found between the load-carrying capacity (LCC) from the Wet-bending A test and the LCC from the Wet-bending B test. The LCC from Wet-bending B could be obtained from LCC from Wet-bending A by multiplying it by 0.9, which may be applicable as a quantitative ratio of aging effects between the two. LCC for methylenediphenyl diisocyanate-bonded panels recovered to almost 100% of the initial strength. A certain relationship was found between the LCC after Wet-bending A and the LCC after a 1-year outdoor exposure in Shizuoka. Internal bond strength showed a good correlation between the JIS-A treatment and the 1-year outdoor exposure treatment.     

室外竹质人造板耐潮湿性能研究

室外自然老化法和5种加速耐潮湿试验方法对2种竹质人造板的物理力学性能均有明显降低,试验结果表明:高温干燥和沸煮对板材性能的影响最显著,对于同一种方法处理后的试件,横向上性能降低幅度比纵向上大,静曲强度较弹性模量降低更为显著。15个月的室外自然老化法试验结果接近于6 h水煮-冰冻-干燥法的试验结果,板材性能随时间延长逐渐降低,但降低幅度逐渐变小,还需放置更长时间进行分析比较,以真正反映竹质人造板的耐潮湿性能。     

Deterioration of wood-based boards subjected to outdoor exposure in Tsukuba

Various types of wood-based boards were analyzed for deterioration after being exposed to an outdoor environment for 5 years in Tsukuba, Japan. In phenol–formaldehyde resin bonded particleboard (PB(PF)) and aspen oriented strand board (OSB(aspen)), longer exposure caused a greater reduction in the modulus of rupture and internal bond strength, an increase in the coefficients of variation, and a decrease in 95 % lower tolerance limit at the 75 % confidence level (95TL). Nail-head pull-through and lateral nail resistance were also reduced by outdoor exposure, but their coefficients of variation and 95TL were not significantly affected. In contrast, methylene diphenyl diisocyanate bonded medium density fiberboard (MDF(MDI)) only showed a slight deterioration of these properties even after 5-year exposure, and the coefficients of variation and 95TL hardly changed. After 5-year exposure, the retention of shear load in one-plane at relative displacement of 1.0 mm was high in MDF(MDI) and OSB(aspen) at 93.5 and 78.5 %, respectively, but low in PB(PF) at 41.1 %. As with PB(PF), OSB(aspen) also showed a sharp decrease in the modulus of rupture and internal bond strength, but only slightly reduced shear load in one-plane.     

室外用人造板耐老化性的评估研究进展

介绍国内外室外用人造板耐老化性的2种测定方法:室外自然老化法和室内加速老化法,分析其相关性,并重点分析室内加速老化法的主要评定指标,为今后我国室外用人造板耐老化性的评定方法研究,及相关标准体系的建设,提出建议.     

Modified method for evaluating weathering intensity using outdoor exposure tests on wood-based panels

The deterioration of wood-based panels at eight sites in Japan over 7?years of outdoor exposure was investigated. In particular, the modulus of rupture (MOR) retention and internal bond strength (IB) retention after 7?years of exposure were compared among panels and sites. The deterioration of panels was greater in southern Japan than in northern Japan. The strength retentions in northern Japan decrease linearly, while those in southern Japan decreased exponentially. To quantify regional differences, deterioration rates were calculated based on three different weather conditions (precipitation, temperature, and sunlight hours), and the significance of each of these parameters on panel deterioration was determined. We found that the correlation coefficients between both IB and MOR retention and weathering intensity were the same whether we used 10-day, monthly, or daily weathering data.     

室外用木质人造板室内加速老化法研究进展

介绍了气候老化因素对室外用木质人造板老化性的影响机理, 以及各种室内加速老化法在国内外的研究应用现状; 针对现行室内加速老化方法中存在的问题, 提出改进方法, 并对系统性加速老化方法的应用前景进行探讨。     

竹纤维/聚丙烯复合材料的耐老化性能

采用挤出成型制备了竹粉增强聚丙烯复合材料,研究竹粉/聚丙烯复合材料在紫外加速老化与湿热老化后的力学性能变化与尺寸稳定性.结果表明:在紫外线加速老化200 h后,复合材料的弯曲强度与弯曲模量无显著变化,试件宽度与厚度在紫外加速老化前后也无显著改变;但湿热老化对复合材料的弯曲强度与弯曲模量有显著影响,在沸水中浸泡2h后,复...     

Evaluation of the weathering intensity of wood-based panels under outdoor exposure

In this study, the deterioration of wood-based panels at eight sites in Japan was investigated using outdoor exposure tests. In particular, the modulus of rupture (MOR) retention and internal bond strength (IB) retention after 5-year exposures were compared among panels and sites. The deterioration of panels located in southern Japan was higher than that of panels in northern Japan. To quantify the regional differences, the deterioration rates were calculated; the values showed clear regional differences. The deterioration rate for areas that receive much rain in the summer was higher than the rates for other sites. To eliminate regional differences, we carried out an analysis in terms of the “weathering intensity,” a factor which combines weather conditions (precipitation and temperature). Panels for which deterioration progressed extensively during exposure periods showed a strong correlation between strength retention and the weathering intensity. The significance of these parameters is discussed.     

Durability evaluation of particleboards by accelerated aging tests

Summary Specimens of four commercially produced particleboards were exposed to various accelerated aging treatments: 1) 6-cycle ASTM D-1037 exposure, 2) 6-cycle WCAMA exposure, 3) BS 5669 test, 4) cyclic soak-dry test, and 5) cyclic boil-dry test. Thickness swelling (TS) and internal bond strength (IB) were measured after each step of each cycle. Phenol and phenol (face)/isocyanate (core)bonded boards are more durable than urea and melamine urea bonded boards. The effect of treatment 1) is most severe on TS and IB retention, followed in order by treatments 2), 5), 4) and 3). When the value of springback reached about 35%, IB became equal to zero.     

Phenol–formaldehyde impregnation of densified wood for improved dimensional stability

To produce a highly stable wood-based product with increased mechanical properties, phenol formaldehyde (PF) resin impregnation was combined with the viscoelastic thermal compression (VTC) process. Dimensional stability and bending stiffness were evaluated. Two PF resins with weight average molecular weights of 172 and 780 were studied at three different concentrations, 5, 10 and 20%. After 24-h room temperature water soak and 2-h boil, both PF treatments at all concentration levels showed high levels of dimensional stability compared to non-impregnated VTC processed controls. The higher molecular weight PF provided greater stability with an average thickness swell value of 12% compared to 20 and 37% for the lower molecular weight PF resin treatment and control, respectively. High anti-swelling efficiency values were recorded for both low and high molecular weight resins, implying these modifications were effective at reducing the volumetric swelling which occurred in the unmodified control. PF treatments were also extremely effective at reducing irreversible swelling. The low and high molecular weight resin treatments had 1/5th and 1/7th the irreversible swelling than the unmodified VTC processed controls, respectively. All dimensional stability values improved as resin concentrations increased. Both resin types at all concentration levels reduced Young’s modulus.     

我国室外人造板标准体系的构建

总结我国主要室外人造板产品的种类、产量及分布情况,汇总我国室外人造板相关标准,并与室外人造板标准进行对比分析,指出我国现有标准设置的问题,提出我国应构建包括产品标准和性能检测方法的室外人造板独立标准体系,以促进我国室外人造板的健康快速发展。     

单板层积材的加速老化性能研究

本文对高频胶合的马尾松LVL和杨木LVL的老化性能进行了讨论,并比较了乳液酚醛树脂胶和酸固化酚醛树脂胶在BDB28和A1080加速老化后的胶合剪切强度的损失率。得出的结论如下:1)乳液酚醛树脂肢胶合的马尾松LVL,胶合剪切强度随老化时间的延长逐渐趋于稳定,最后稳定在老化前强度的70％左右;2)乳液酚醛树脂胶的老化性能比酸固化酚醛树脂胶好;3)对于乳液酚醛树脂胶马尾松LVL和酸固化酚醛树脂胶杨木LVL,可以用BDB28处理方法代替A1080加速老化方法快速测定其胶合剪切强度的损失率。     

The evaluation of long-term mechanical properties of wood-based panels by indoor exposure tests

Wood-based panels such as plywood, oriented strand board, particleboard, and medium-density fiberboard are used for roof, wall and floor sheathing materials in residential construction. However, the service life of these panels is still unknown due to the lack of long-term durability data. In this paper, test results from six different indoor exposure experiments were integrated to investigate the long-term durability of wood-based panels. The indoor exposure tests lasted for a maximum of 10 years, providing the panels with the changes in moisture content that ranged between 5 and 18%. The reduction in mechanical properties was determined to be in the range of 0–16% for the bending strength, 3–22% for the modulus of elasticity, 11–31% for the internal bond strength and 0–8% for the nail-head pull-through strength. No reduction was recognized for the lateral nail resistance. Furthermore, the concept of deterioration intensity (DI) based on the moisture content history was introduced to predict the long-term durability of the panels, and various calculation methods for DI were discussed so as to increase the correlativity of this property with the reduction in a mechanical property.     

Potential utilization of sodium fluoride (NaF) as a biocide in particleboard production

The feasibility of sodium fluoride (NaF) incorporation as a biocide in the manufacture of particleboard was examined. Laboratory-scale particleboards prepared from untreated wood particles were incorporated with NaF powder at target retentions of 1, 1.5 and 3% of the total particle weight. An in-line treatment method was used to introduce the biocide during the blending stage just before adhesive application. Standard static bending and water resistance (water absorption and thickness swelling) tests indicated that embedding of the powder biocide up to the 3% level did not cause any detrimental effects on mechanical and physical properties. The laboratory decay and termite resistance tests showed that even the lower retention levels of 1 and 1.5% NaF were enough to suppress fungal and termite activity and significantly reduce the mass loss and consumption rate values of the specimens when compared to the untreated controls. Spectrophotometric analysis of leachate waters and the mass losses of the leached specimens revealed the tendency of the NaF to be depleted from the composite specimens. Therefore, the tested biocide was found to be appropriate for interior or protected above-ground outdoor exposure conditions.     

Effects of water soaking and outdoor exposure on modulus of rupture and internal bond strength of particleboard

Phenol–formaldehyde resin-bonded particleboard (PF board) and isocyanate resin-bonded particleboard (MDI board) were soaked in water at 40, 70 and 100 °C, and the relationships between soaking conditions and board properties were analyzed. The relationships between the deterioration of board properties resulting from water soaking and those arising from outdoor exposure were also analyzed. At 100 °C, the modulus of rupture (MOR) and internal bond strength (IB) of the PF board decreased significantly within the first hour, and subsequently constant values were shown with increasing soaking time. This low constant value was defined as the lower limit. At 70 °C, both the MOR and IB decreased with increasing soaking time, and reached the lower limit. At 40 °C, however, neither decreased significantly with increasing soaking time and neither reached the lower limit. The MOR of the MDI board showed the same trend as the PF board. However, the IB of the MDI board showed a different trend to the PF board, that is, the lower limit of IB required extensive soaking, even at 100 °C. The MOR and IB of both the PF and MDI boards reached the lower limit when thickness change peaked. On the other hand, the MOR and IB for outdoor exposure were lower than those for water soaking, even at the same thickness change. The MOR and IB of water soaking decreased owing to the collapse of the bonding points caused by board swelling. On the other hand, the board properties of outdoor exposure decreased owing to the collapse of the bonding points, and biodegradation also added to the decrease.     

Dimensional stability of MDF panels produced from fibres treated with maleated polypropylene wax

Medium-density fibreboard (MDF) was produced from fibres treated with maleated polypropylene wax. The objectives of this study were to improve the dimensional stability of MDF panels by this treatment; to observe the maleated polypropylene wax distribution within the MDF panels using conventional fluorescence microscopy; and to determine the effects of the treatment on the mechanical properties and vertical density profile of the panels. MDF panels were produced from two resin types (urea-formaldehyde and melamine-urea-formaldehyde) and three maleated polypropylene wax contents (0, 3 and 5%). Photomicrographs show that maleated polypropylene wax forms agglomerates within the MDF panels which is an evidence of its poor distribution in our experimental conditions. Our results show an important reduction on thickness swelling and water absorption after water soaking for panels produced from treated fibres. Linear expansion and contraction in adsorption and desorption conditions between 80 and 50% relative humidity increased following fibre treatment. However, thickness swelling and shrinkage in similar conditions showed an important reduction following fibre treatment. The fibre treatment did not have negative effects on the mechanical properties or the vertical density profile of MDF panels. The modulus of rupture and modulus of elasticity in bending were increased by the treatment independently of maleated polypropylene wax content. The internal bond strength increased following the addition of 5% maleated polypropylene wax content.     

Susceptibility of thermo-hydro-treated birch plywood to mould and blue stain fungi

In this study, mould and blue stain susceptibility, capillary water uptake (CWU) and microstructural properties of two thermo-hydro-treated (THT) birch plywood products A and B were investigated. Plywood A represented a THT industrial plywood glued with a phenol formaldehyde (PF) adhesive. Plywood B represented panels from THT veneers glued with a PF film. The THT regimes were (temperature, °C/time, min): 150/10, 150/50, 160/10 and 160/50. Both THT plywood products and untreated samples were resistant to mould and blue stain growth in 1 month of exposure in laboratory and outdoor conditions. A statistically significant correlation between fungal growth in laboratory and outdoor conditions for plywood products A and B was not found (P?>?.05). Artificial weathering of both plywood products provided adverse fungal growth results compared to the natural weathering test outdoors. The fungal growth on plywood A and B samples mutually strongly correlated (P?相似文献   

Serial exposure technique for assessing performance of wood preservatives

Summary The performance of copper-chrome-arsenate (CCA) and two quaternary ammonium compounds as wood preservatives was compared using a serial exposure technique, involving successive 10-week exposures in conventional soil jars. All preservative treatments were successful in preventing decay of Pinus radiata sapwood after the first exposure, but successive 10-week exposures clearly distinguished those treatments likely to offer long-term protection. The progressively increasing times of exposure with test fungi overcame the time lag for decay initiation in wood treated to preservative retentions above the toxic threshold established by conventional laboratory methods. Consequently, an additional and higher toxic threshold could be calculated. Examination of data from field stake tests suggested that a series of toxic thresholds established by a serial exposure technique could be related to preservative retentions which protect wood in the field from decay for increasing periods of time. Results of all tests are discussed in relation to the development of a laboratory procedure which may predict field performance of wood preservatives.     

酚醛刨花板加速老化试验的研究

刨花板的耐老化性质是它作为建筑用材的一项重要指标。本试验采用人工老化方法，讨论加速老化因素对马尾松酚醛刨花板耐老化能力的影响，并对几种加速老化方法进行分析比较。结果表明：循环数、冷冻、喷蒸、干燥等因素对老化结果有不同程度的影响；不同的加速老化试验方法对刨花板ＭＯＲ、ＩＢ和ＴＳ的影响程度也不相同；可采用热水浸泡－干燥循环法代替ＡＳＴＭＤ１０３７的６循环加速老化试验；可把沸水煮１小时方法作为工厂对产品的耐侯性质量控制法。