稻壳／聚乙烯复合材的自然老化与紫外光加速老化

对稻壳/聚乙烯复合材的室外自然老化情况进行1年多的观察,并对相同材料进行实验室紫外光(UV)加速老化,研究材料力学性能变化,并通过傅里叶红外波谱(FTIR)分析探讨老化机制,力争寻求二者之间的初步对应关系.自然老化试件在气温较低和日照时间较短的前5个月内(冬季)颜色基本没有变化,经历盛夏之后颜色发生显著变化,变化幅度与实验室加速老化1 500 h的结果相当.与自然老化相比,加速老化500 h后即可明显表现出各种化学特征的变化趋势,但在以后的1 500 h里没有再发生显著变化;而自然老化12个月后试材表面才有显著化学变化.老化首先使稻壳/聚乙烯复合材的颜色发生较大改变,表面化学性质变化也较早开始,但无论自然老化还是加速老化在短时间内对材料力学性能都不会产生显著影响.     

稻壳粉/聚乙烯复合材料性能的研究

采用稻壳粉对高密度聚乙烯(HDPE)进行改性,研究了稻壳粉用量对复合材料力学性能和吸水率的影响,并观察了稻壳粉在HDPE中的分散情况。结果表明:复合材料的弯曲强度随稻壳粉用量的增加先增加后下降,而拉伸强度、断裂伸长率和冲击强度则随稻壳粉用量的增加而下降;稻壳粉在HDPE中的分散不均匀,用量较大时易出现聚集现象,两相间的粘接性变差。     

热氧老化和水浸渍对木粉/HDPE和稻壳粉/HDPE两种复合材料性能的影响

木粉和稻壳粉是制备木塑复合材料(WPC)常用原料。WPC在使用过程中经常受到热和水分的影响,笔者对比研究了稻壳粉/HDPE和木粉/HDPE两种复合材料经历热氧老化和长时间水浸渍后性能的变化规律。结果表明:木粉/高密度聚乙烯(HDPE)复合材料的弯曲强度和弹性模量都大于稻壳粉/HDPE的;随着热氧老化或水浸渍处理时间的延长,复合材的挠曲性能下降,其中木粉/HDPE复合材的弹性模量下降最为迅速;复合材料表面明度值随着热处理时间的延长而减小,说明颜色变暗,稻壳粉与木粉填充的复合材之间差别不大。通过光学显微镜观察发现,HDPE与稻壳粉或木粉之间都有缝隙存在,为水分和氧气的进出提供了通道。     

高密度聚乙烯含量对木塑复合材料老化性能的影响

通过试验,分析了木塑复合材料中高密度聚乙烯含量与老化性能的关系,阐述了老化性对木塑复合材料各种性能的影响.     

UV老化后氧化铁颜料着色木纤维-HDPE复合材料的性能变化

探讨了氧化铁颜料对木纤维．高密度聚乙烯复合材耐老化性能的改善作用。采用四种常用的氧化铁颜料与木纤维、高密度聚乙烯和其他加工助剂干混,并用自行设计的双螺杆／单螺杆双阶挤出机组制造木塑复合材料。对该木塑复合材料进行人工加速紫外循环老化处理,用CIE1976L^＊a^＊b^＊表色体系和ASTMD790标准分别对老化前后的材料进行测试,结果显示加入颜料以后木塑复合材料的抗弯弹性模量没有明显的变化,但是弯曲强度都有一定程度的提高。经过2000h人工加速紫外老化以后,不论是颜色要是力学性能都发生了明显的变化。铁红和铁黑着色的试样在整个老化过程中表现较好,颜料添加量约2．28％比较适宜。     

密度对稻壳-木材复合材料性能的影响

研究测试在0．75～0．85g／cm^3的变化范围内，密度对稻壳—木材复合材料物理力学性能的影响。试验结果表明，在该密度变化范围内，密度对板的静曲强度、内结合强度及吸水厚度膨胀率等影响显著。     

稻壳形态对稻壳--木材复合材料性能的影响

测试了稻壳形态对稻壳-木材复合材料物理力学性能的影响。试验结果表明，以20网日、30网日和40网目的稻壳为补充材料制备的密度为0．80g／cm^3的板的物理力学性能均达到国标二级品的要求。确立20网目的稻壳适宜于稻壳-木材复合材料。     

CMC-g-PMMA改性稻壳碎料-水泥复合材料的性能

采用羧甲基纤维素与甲基丙烯酸甲酯的接枝共聚物(CMC-g-PMMA)作为改性剂对稻壳碎料进行表面处理,制成不同稻壳碎料含量的稻壳碎料-水泥复合材料(RHPC).对RHPC复合材料的密度、抗折性能、断面表面形貌、吸声性能、保温性能和燃烧性能进行测试和分析.结果表明:添加CMC-g-PMMA可大幅度提高RHPC复合材料的抗折强度和模量,当稻壳碎料含量为20%,CMC-g-PMMA添加量为1%时,抗折强度和模量分别为未添加助剂试样的2.27和2.71倍;声波频率为2 000 Hz以下,提高稻壳碎料含量后,水泥复合材料的吸声系数明显提高,1 000 Hz时,稻壳碎料含量为40%的试样的吸声系数高达0.67;制备的稻壳碎料-水泥复合材料为不燃性材料,具有良好的保温性能.     

热氧老化对稻壳粉/高密度聚乙烯复合材料抗弯强度的影响

通过对稻壳粉/高密度聚乙烯复合材料热氧老化研究,得到材料的抗弯强度随老化时间的变化规律。稻壳粉/高密度聚乙烯复合材料在65℃热氧老化条件下,0～12 h期间抗弯强度急剧下降;12～122 h期间抗弯强度呈上升趋势;122 h后抗弯强度趋于稳定。     

热压工艺对稻壳-木材复合材料性能影响的研究

研究测试了热压温度与时间对稻壳-木材复合材料物理力学性能的影响。试验结果表明，随着热压时间的延长，稻壳-木材复合材料的物理力学性能相应地提高。在140～160℃的热压温度区间表内，提高热压温度有助于提高稻壳一木材复合材料的物理力学性能；稻壳一木材复合材料适宜的热压工艺条件为30s／mm板厚的热压时间，160℃的热压温度。     

Moisture conditions in coated wood panels during 24 months natural weathering at five sites in Europe

Abstract

Wood moisture content of coated panels of Scots pine sapwood was recorded during 24 months natural weathering in Vienna by logging electric resistance and temperature near the surface. Eight coating systems with various film thicknesses were used, including three solvent borne alkyd stains, three water borne acrylic stains and two water borne acrylic paints. At five sites in Europe wood moisture content of panels coated with three solvent borne alkyd stains, a brown acrylic stain and a white opaque acrylic paint was recorded weekly by changes in panel mass. Fluctuations in wood moisture content were influenced by the film thickness, water permeability and colour of the coating systems used. Degradation phenomena led to decreasing moisture protection of less durable coating systems over time of exposure. The exposure site clearly affected wood moisture content in the panels.     

Properties of paper mill sludge-wood fiber-HDPE composites after exposure to xenon-arc weathering

We used paper mill sludge(PMS) to substitute for part of the wood fibers(WF) used to reinforce high density polyethylene(HDPE).The resulting composites were subjected to xenon-arc weathering.The composite filled with limited PMS(under 10 %) had mechanical properties and aging resistance similar to those without PMS.The composites containing more PMS faded and cracked more readily than those without PMS.Based on the carbonyl index,crystallinity,and wood index,PMS appeared to accelerate the degradation of composites during weathering.Adding PMS to WF–HDPE composites reduced the weathering resistance,and this reduction was not significant if the PMS content did not exceed 20 % of the wood fibers.Therefore,PMS could be used as a reinforcement in wood-plastic composites at levels less than20 % of the wood fiber content.     

Crack formation due to weathering of radial and tangential sections of pine and spruce

Abstract

The development of cracks and changes in appearance have been investigated on radial and tangential sections of pine (Pinus sylvestris L.) and spruce (Picea abies Karst.) after exposure outdoors for 61 months. The degradation of the sections has also been studied at the micro-level. The annual ring orientation was the most important factor affecting crack development on weathering. After 61 months of outdoor exposure, the tangential sections of spruce had 1.7–2.2 times greater mean total crack length per area unit than the corresponding radial sections. In pine, the total crack length per area unit on the tangential sections was 2.2–2.6 times greater than that on the radial sections. Tangential and radial sections show the same colour change as a result of weathering. Tangential sections have more and deeper cracks than radial surfaces. The cracks on the tangential sections occur frequently in both earlywood and latewood. On radial sections, cracks occur primarily at the annual ring borders, but to a certain extent also in the earlywood. Decomposition of the cell wall takes place in both radial and tangential cell walls, and cracks tend to follow the fibril orientation in the S2-layer of the cell wall. The radial cell wall of the earlywood has a large number of pits which are degraded at an early stage.     

Crack formation due to weathering of radial and tangential sections of pine and spruce

The development of cracks and changes in appearance have been investigated on radial and tangential sections of pine (Pinus sylvestris L.) and spruce (Picea abies Karst.) after exposure outdoors for 61 months. The degradation of the sections has also been studied at the micro-level. The annual ring orientation was the most important factor affecting crack development on weathering. After 61 months of outdoor exposure, the tangential sections of spruce had 1.7-2.2 times greater mean total crack length per area unit than the corresponding radial sections. In pine, the total crack length per area unit on the tangential sections was 2.2-2.6 times greater than that on the radial sections. Tangential and radial sections show the same colour change as a result of weathering. Tangential sections have more and deeper cracks than radial surfaces. The cracks on the tangential sections occur frequently in both earlywood and latewood. On radial sections, cracks occur primarily at the annual ring borders, but to a certain extent also in the earlywood. Decomposition of the cell wall takes place in both radial and tangential cell walls, and cracks tend to follow the fibril orientation in the S2-layer of the cell wall. The radial cell wall of the earlywood has a large number of pits which are degraded at an early stage.     

Changes in surface properties of tropical wood species exposed to the Indonesian climate in relation to mold colonies

Changes in mold populations and genera on the exposed surfaces of tropical hardwoods — albizia (Paraserianthes falcata), kapur (Dryobalanop lanceolata), mahoni (Switenia macrophylla), nangka (Artocarpus heterophyllus), puspa (Schima wallchii) — were investigated. The wood specimens were exposed to the Indonesian climate for 32 weeks. Properties including mass loss, wettability, mold growth (colony-forming units), and mold genera were evaluated. The change in properties after exposure was significantly affected by the wood species, but there was no clear relation between mass loss and the initial chemical components or between wettability and wood density. The number of mold populations was different by exposure period and wood species, but there was no significant effect of climate conditions, such as rainfall and ultraviolet radiation. Of the genera identified,Aureobasidium, Cladosporium, andPenicillium were dominant molds on the exposed wood surfaces.     

Analysis of Markov model on predicting wood composite weathering

Summary This paper evaluated the wood composite weathering over time step by Markov theory. By the null hypothesis (H₀), the panel weathering under the long-term outdoor exposure was determined to be a Markov process. The transition matrix which derived from the practical data can be calculated by program Markov and thus the future outcome of wood composite weathering can be forecasted. Also, the utility of the Markov model was successfully testified from the example of 3-year natural aging waferboard in Ottawa, Saskatoon, Fredericton areas.     

Influence of specimen size during accelerated weathering of wood-based structural panels

ABSTRACT

Wood structural panels are commonly subjected to short-term accelerated weathering (AW) procedures to determine relative moisture durability for quality control and product development purposes. The panel edges contribute heavily to moisture uptake since edges represent the least resistant pathway for moisture intrusion. In full-size panels, the edge area to total surface area ratio is small, and moisture intrusion is primarily limited to panel faces. When small specimens are used, such as those in AW procedures, the ratio of edge area to total surface area increases and moisture intrusion at the edges may dominate, which is referred to as the edge effect. The purpose of this study was to determine if physical and mechanical properties of oriented strand board (OSB) and plywood after AW are influenced by specimen size. Specimen width was varied while thickness and length remained constant to understand if edge effects were present in small specimens with different edge area to total surface area ratios. Three AW procedures were evaluated to determine if the effect of specimen size depends on weathering method. No clear effect of specimen size on physical and mechanical properties of either composite type was found. Differences in flexural properties between specimen widths were observed for unweathered OSB, but similar property retention between specimen widths after AW indicated the same trend as the unweathered control. Plywood results were influenced by natural defects, resulting in high variability and absence of statistically significant differences. Lateral nail resistance connection properties of both OSB and plywood were highly variable for all treatment groups and were unaffected by weathering.     

Natural weathering of Scots pine (Pinus sylvestris L.) wood treated with epoxidized linseed oil and methyltriethoxysilane

In this study, the effect of natural weathering on the performance of Scots pine sapwood treated with epoxidized linseed oil (ELO) and methyltriethoxysilane (MTES) was investigated by measuring water uptake, colour, check propagation and chemical changes. Boards were impregnated in a pilot-scale autoclave under various conditions. After the treatments, pairs of samples were cut from the treated boards and exposed at 45° angle facing south for a long-term test of natural weathering above ground in Uppsala (Sweden). The effect of solar radiation and humidity on the colour changes, water uptake, check propagation and chemical alterations was assessed during 20 months of exposure. The obtained results can serve as indication for the viability of the treatments. Samples impregnated with low retentions of ELO showed similar performance regarding check propagation and moisture uptake as samples with higher retentions. No significant difference between these samples was found regarding colour change which is mainly caused by blue stain fungi on the surface. In opposite, samples treated with MTES exhibited no consistent water uptake and check propagation unproportioned to the applied retentions. The spectra of ELO- and MTES-treated wood after weathering showed a significant decrease of the peak at 1510 cm^?1 indicating delignification of wood surface caused by weathering.     

针状木纤维/HDPE复合材料的力学性能

采用一步法连续挤出技术将杨木针状纤维与高密度聚乙烯(HDPE)进行熔融复合制备木塑复合材料(NF-WPC).用正交试验法分析纤维尺寸、纤维添加量、偶联剂含量和润滑剂含量4个因子对NF-WPC力学性能影响的显著性;用扫描电子显微镜观察分析NF-WPC中木纤维与HDPE的界面结合状况;提出优化的工艺配方并与相同木材含量的木粉/HDPE复合材料进行对比研究.结果表明:针状木纤维的含量对NF_WPC冲击强度影响显著,对弯曲性能和拉伸性能的影响高度显著;偶联剂马来酸酐接枝聚乙烯(MAPE)的添加量对NF_WPC的拉伸强度、断裂伸长率和冲击强度影响显著;在本文的试验范围内,木纤维尺寸和润滑剂石蜡的含量对NF-WPC力学性能的影响不显著.确定的优化工艺配方为:木纤维长度为3～4mm、长径比为8～11,木纤维含量60%,MAPE含量4%,石蜡含量0.3%;采用优化工艺制备的NF_WPC的弯曲强度、弯曲模量、拉伸强度、拉伸模量和冲击强度分别为58.7 MPa、3.0 GPa、39.6 MPa、4.0 GPa和12.7 kJ·m-2.除冲击韧性略低外,用优化工艺配方制备的NF_WPC其他力学性能均高于用同比例木粉制备的木塑复合材料.