Properties of wheat straw particleboards bonded with different types of resin

Wheat straw particleboard bonded with a urea–formaldehyde (UF) resin, usually employed in the manufacture of wood-based particleboards, or with a resin based on epoxidised oil was manufactured using a compression molding machine. The effects of resin type on internal bond strength, flexural modulus, and thickness swelling were examined. The properties of boards using UF resins were poor. Internal bond strength and thickness swelling, linked to adhesion quality, were especially low. The high compatibility between straw particles and oil-based resin was explained in terms of straw surface free energy. In straw, this parameter exhibits a much lower polar component than wood species and leads to higher compatibility with resins based on oil than with water-soluble systems like UF.     

树脂型甲醛捕捉剂对脲醛树脂性能的影响

在实验室制备得到树脂型甲醛捕捉剂,考察了甲醛捕捉剂与不同F/U摩尔比脲醛树脂混合使用后制备得到的刨花板力学性能及甲醛释放量。研究结果表明,甲醛捕捉剂的添加能有效降低刨花板的甲醛释放量,但对混合树脂的最终力学强度性能不利。混合树脂的摩尔比F/U是决定相关刨花板力学性能及甲醛释放量的主要因素。当与摩尔比F/U=1的脲醛树脂混合使用时,添加占总施胶量5%甲醛捕捉剂的刨花板甲醛释放量可达到E1级,同时,内结合强度值满足室内级国家标准要求。与摩尔比F/U=1.2的脲醛树脂混合使用,当甲醛捕捉剂的添加量为20%时,刨花板性能达标。     

Upgrading of urea formaldehyde-bonded reed and wheat straw particleboards using silane coupling agents

Reed and wheat straw particleboards bonded with urea formaldehyde (UF) resin were manufactured from two different material configurations (i.e., fine and coarse particles). The board densities were in the range of 0.550–.90g/cm³. The effects of particle size and board density on the board properties were examined. The properties of particleboard produced from fine particles were better than those made from coarse particles. An increase in board density resulted in a corresponding improvement in the board properties. The properties of OF bonded reed and wheat straw particleboards were relatively lower than those of commercial particleboards. Three silane coupling agents were used to improve the bondability between the reed and wheat particles and OF resin. Results of this study indicate that all the board properties were improved by the addition of silane coupling agent. The degree of improvement achieved from each coupling agent was different; epoxide silane was found to be more effective for reed straw particleboard, and amino silane was better for wheat straw particleboard.     

固体核磁共振法对低甲醛释放脲醛树脂化学结构的研究

在采用液体核磁对3种低甲醛释放脲醛树脂化学构造进行分析的基础上,利用13CCP/MASNMR对脲醛树脂固化产物的化学结构进行了研究.结果表明,不同固化体系下,3种低甲醛释放脲醛树脂胶黏剂的固化历程不同,固化后树脂的结构有所差别.不添加固化剂时,脲醛树脂的固化交联反应程度低,固化产物中羟甲基含量高,甲醛释放量也随之增加.加入固化剂后,促进了羟甲基的固化交联反应,脲醛树脂固化产物中羟甲基含量普遍降低.3种固化体系下,UF-3羟甲基含量最高;在氯化铵为固化剂的条件下,UF-2羟甲基含量最低,为0.0582;不添加固化剂和复合固化体系条件下,UF-1羟甲基含量最低,分别为0.0784和0.0713.不同固化体系对不同种类脲醛树脂的固化效果不同,固化后树脂的结构不同,其力学性能和甲醛释放能力也不同.     

一种脲醛树脂胶粘剂的设计

鉴于对文献的分析和实验验证,本文提出一种脲醛树脂胶粘剂的设计原则。即:1)脲醛树脂最终摩尔比应取1.40～1.20:1,这样可以使制成的板材具有足够的胶接强度;2)为了使人造板的甲醛释放量达到10mg/100g(穿孔法)以下,树脂中的游离尿素应在10%以上;3)在脲醛树脂的分子中引入尿素的环状衍生物,如三嗪环或Uron。环状化合物含量最好在10%左右。按此原则合成了三种树脂,在试验室按标准刨花板和中密度纤维板工艺制成板材,其甲醛释放量在10mg/100g左右,板材物理力学性能均超过国家标准和企业标准。     

轻质豆秸刨花板工艺的研究

从UF胶制造轻质豆秸刨花板的初步研究,分析了板的密度、施胶量、热压时间等工艺因子对板性能的影响。试验结果表明,利用豆秸制造轻质刨花板是完全可行的,其产品主要物理力学性能为:密度0.483 g/cm 3、吸水厚度膨胀率11.2 % 、内结合强度0.303 MPa、静曲强度8.98 MPa,均达到日本JISA 5908 的技术指标。     

复合工艺对竹/塑复合刨花板性能的影响

利用聚乙烯(PE)粉末取代部分脲醛树脂(UF)胶黏剂,与竹刨花制备三层结构竹/塑复合刨花板。通过正交试验探讨PE添加量、UF施胶量、热压温度及热压时间对竹/塑复合刨花板主要物理力学性能的影响。结果表明:较优工艺组合为PE添加量6%、UF施胶量2%、热压温度205℃、热压时间12s/mm,竹/塑复合刨花板达到LY/T1842—2009《竹材刨花板》A类理化性能指标要求;2h吸水厚度膨胀率和甲醛释放量分别为2.6%和2.4mg/100g,与普通竹材刨花板对比,分别减少了54.4%和54.7%;静曲强度达到19.6MPa,提高了14.0%。采用PE粉末替代部分UF胶黏剂生产竹/塑复合刨花板可行,且具有广泛的应用前景。     

用不脱水低摩尔脲醛树脂制造低游离甲醛刨花板与中密度纤维板

试验结果表明差示扫描量热仪 (DSC)能够测得NLFS - 1型捕捉剂与甲醛反应 ,并且这种捕捉剂能够捕捉脲醛树脂胶中的大部分游离甲醛 ,其捕捉量与树脂的摩尔比或游离甲醛量有关。对于低摩尔比 ,不脱水脲醛树脂刨花板和中密度纤维板 ,仅用 5 %捕捉剂就能获得较高的捕捉能力。这些板的游离甲醛释放量均能达到欧洲E1级或国标GB -T11718- 1999A级标准。刨花板后期热处理 ,对板的内结合强度提高明显 ,但板的甲醛释放量略有增加     

Preparation and properties of waste tea leaves particleboard

Urea-formaldehyde (UF) adhesive is the main source of formaldehyde emission from UF-bonded boards. The components in waste tea leaves can react with formaldehyde to serve as a raw material in the production of low formaldehyde emission boards. In our study, waste tea leaves and UF adhesive were employed in the preparation of waste tea leaves particleboard (WTLB). An orthogonal experimental method was applied to investigate the effects of process parameters on formaldehyde emission and mechanical properties of WTLB. The results indicated that: 1) waste tea leaves had the ability to abate formaldehyde emission from boards; and 2) density of the WTLB was a significant factor affecting its modulus of rupture (MOR), modulus of elasticity (MOE) and internal bonding (IB).     

酸碱处理对制备再生桉木颗粒板的影响

废弃人造板中的胶黏剂影响人造板的回收利用。笔者利用化学法对废弃桉木颗粒板中的胶黏剂进行处理,分别探究不同浓度的硫酸、甲酸、硝酸、氢氧化钾分解废弃木颗粒板中脲醛树脂的最佳条件。结果表明,在90℃,水浴处理2 h条件下,甲酸浓度大于60%,硫酸浓度大于25%,或硝酸浓度大于25%可完全分解固化后的脲醛胶黏剂;对酸处理后的木颗粒的颜色、形貌、化学性质进行分析,甲酸对木颗粒的形态、颜色影响较小。用酸处理后制得的再生木颗粒板,力学性能相对于未经处理的再生木颗粒板得到显著提高。     

低甲醛释放量刨花板用脲醛树脂结构的研究(英文)

本文通过~(13)C NMR研究了脲醛树脂合成新工艺中不同反应阶段时的脲醛树脂的化学结构。研究结果表明脲醛树脂的化学结构主要受甲醛/尿素的摩尔比,pH值、反应温度和反应时间的影响。对脲醛树脂中主要的官能团:游离甲醛、亚甲基、亚甲基醚、Uron等相互关系也进行了研究。指出了生产低甲醛释放量,高力学性能刨花板用脲醛树脂中主要官能团的最佳含量。     

改性脲醛树脂胶低密度稻壳-木材复合材料制造工艺的研究

采用异氰酸酯(ISO)改性的脲醛树脂胶制造低密度稻壳-木材复合材料。稻壳与木质刨花的混合比例为1:1,施胶量为7%,试验结果表明,异氰酸酯改性的脲醛树脂胶黏剂适用于低密度稻壳-木材复合材料,其物理力学性能明显优于使用传统的脲醛树脂胶黏剂。低密度稻壳-木材复合材料的物理力学性能随着改性剂异氰酸酯用量的增加而提高。密度是稻壳-木材复合材料物理力学性能的重要影响因素,低密度稻壳-木材复合材料的物理力学性能随着密度的增加而提高。在设定密度为0.45g/m~3和0.5g/cm~3的条件下,3:4的ISO/UF的稻壳-木材复合材料的物理力学性能均达到日本刨花板工业标准(JIS A5908)的要求。     

脲醛树脂胶稻草中密度纤维板的性能

通过用稻草代替木材制造脲醛树脂胶稻草中密度纤维板的可行性研究 ,探讨了板材密度、施胶量和防水剂等工艺因素对稻草中密度纤维板性能的影响。结果表明 :在实验室条件下 ,当板材名义密度为 0 .8g/ cm3和施胶量为 17%时 ,脲醛树脂胶稻草中纤板性能达到现行国家标准一等品的要求 ;施加 1.2 %的石蜡乳液 ,板材的耐水性亦能满足国标要求     

热压工艺对刨花板甲醛及其他有机挥发物释放总量的影响

以兴安落叶松刨花和脲醛树脂胶黏剂为原料,采用正交试验法研究热压温度、热压时间、施胶量、密度工艺因子对刨花板甲醛和其他挥发性有机化合物释放量的影响.结果表明:热压温度、热压时间、施胶量和密度4个工艺因子对刨花板甲醛的释放及其他有机挥发物的释放均影响显著;提高热压温度、延长热压时间、降低板密度能显著降低甲醛及有机挥发物的释放量;综合考虑甲醛及其他有机挥发物释放量确定优化工艺因子为热压温度180℃,热压时间37.5 s·min-1,施胶量11%,密度0.6 g·cm-3,压制出的刨花板甲醛及其他有机挥发物释放量明显下降,满足GB 18580-2001的要求.     

纳米二氧化硅/脲醛树脂性能的研究

探讨纳米SiO2 表面处理、加入方式、用量对纳米SiO2 脲醛树脂性能的影响。结果表明 :采用KH - 5 5 0硅烷偶联剂处理纳米SiO2 表面 ,用间歇式超声波震荡法将其加入脲醛树脂中 ,能有效改善树脂性能。当纳米SiO2 用量 <1 5 %时 ,用量越大 ,树脂的胶合强度越高 ,游离甲醛含量越低 ,粘度越大 ,固化时间不变。用纳米SiO2 (用量1% ) 脲醛树脂 (F U摩尔比 1 2 )压制胶合板、刨花板、中密度纤维板 ,板的各项性能指标都超过国家标准要求 ,甲醛释放量达到E1 级水平。同时 ,通过红外光谱和X射线光电子能谱初步探索了纳米SiO2 对脲醛树脂的增强机制     

Utilization of sweet sorghum bagasse and citric acid for manufacturing of particleboard II: influences of pressing temperature and time on particleboard properties

Development of environmentally friendly particleboard made from sweet sorghum bagasse and citric acid has recently attracted attention. In this study, we investigated the effects of pressing temperature and time on physical properties, such as dry bending (DB), internal bond strength (IB), and thickness swelling (TS) of particleboard. Wet bending (WB), screw-holding power (SH), biological durability, and formaldehyde emission of particleboard manufactured under effective pressing temperature and time were also evaluated. Particleboards bonded with phenol formaldehyde (PF) resin and polymeric 4,4′-methylenediphenyl isocyanate (pMDI) were manufactured as references. Effective pressing temperature and time were 200?°C and 10 min, respectively. It was clarified that DB, IB, and TS satisfied the type 18 requirements of the JIS A 5908 (2003), and were comparable to those of particleboard bonded with PF and pMDI. The WB and SH of particleboard did not satisfy type 18 of JIS. Particleboard manufactured under effective pressing conditions had good biological durability and low formaldehyde emission. Based on the results of infrared spectra measurement, the degree of ester linkages increased with increased pressing temperature and time.     

脲醛树脂合成工艺参数的优化

以F/U的终摩尔比、F/U的初摩尔比、缩聚阶段pH值、缩聚阶段温度为变量,UF中游离甲醛含量和羟甲基含量为考核指标来设计正交试验,优化脲醛树脂合成工艺参数。最佳工艺参数F/U的终摩尔比1.05:1、F/U的初摩尔比2.2:1、缩聚阶段pH值5.1～5.3、缩聚阶段温度88℃～90℃。其产品游离甲醛含量小于0.15%,羟甲基含量大于10.5%。     

竹材刨花板蠕变性能的研究

结构用刨花板由木质刨花和胶粘剂热压而成,属高分子材料,具有粘弹性。在负荷作用下产生弹性变形,在长期负荷下发生蠕变。试验表明,竹材制成的酚醛胶刨花板,在高湿环境下,比竹材脲醛胶刨花板有较好的抗蠕变能力;如在竹材刨花板上贴上一层竹席,则抗蠕变性能进一步提高。竹材脲醛胶刨花板比木材脲醛胶刨花板有较好的抗蠕变性能。在低湿度环境下,所有板材的蠕变性能差别较小。     

Development of high-performance UF-bonded reed and wheat straw medium-density fiberboard

Urea formaldehyde resin-bonded reed and wheat straw fiberboards were produced from the fibers made under different steam cooking conditions in refining processes at densities of 500 and 700kg/m³. The effect of steam cooking conditions on the board properties was examined. The steam pressure and cooking time for reed and wheat straws were 0.4MPa/10min and 0.4MPa/5min, respectively, and 0.6MPa/3min and 0.6MPa/10min for both straws. The effect of steam cooking treatment before the fiber refining process on the wettability and weight losses of the straws was also investigated. The results indicated that the mechanical properties and linear expansion of the straw medium-density fiberboard (MDF) were improved with increasing steam cooking pressure and time during the refining process, whereas the thickness swelling (TS) did not vary much. The wettability of the straws was improved by cooking treatment. The steam cooking conditions had little effect on the wettability of the straw surfaces. For reed and wheat straws, the weight losses increased with increasing steam pressure and cooking time. In addition, it was found that the properties of MDF were significantly higher than those of particleboard, especially the internal bond (IB), where the IB values of MDF were more than 10 times higher than those of particleboard. All the properties of the straw MDF, except the TS of wheat board, can meet the requirement of JIS fiberboard standard. The high performances of MDF could be due to the improved wettability and the removal of extractives during the refining process.     

Adhesive application method in MDI-UF particleboard manufacture

Chinese wood-based composite manufacturers are plagued with serious formaldehyde emission (F-emission) problems. In this study, we investigated the use of an emulsifiable diphenylmethane-4, 4′-diisocyanate (MDI) — urea formaldehyde (UF) mixture adhesive in particleboard manufacture, in order to decrease F-emission to below 9 mg per 100 g board. We paid close attention to the effect of NH₄Cl on MDI-UF curing and the method of adhesive application by differential scanning calorimetric (DSC) analysis and compared mechanical properties. Both results showed that the acidic agent NH₄Cl did hinder EMDI-UF curing and it also affected the adhesive application method. We are of the opinion that when EMDI and UF are mixed first, without adding NH₄Cl and then sprayed onto particles, mechanical properties will be improved and F-emissions will meet E1 grade requirements. __________ Translated from Scientia Silvae Sinicae, 2005, 41(2) [译自: 林业科学, 2005, 41(2)]