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以热塑性树脂,如高密度聚乙烯(high density polyethylene,HDPE),聚丙烯(polypropylene,PP)等作为木材胶黏剂,利用热压-冷压串联的平压工艺制备木质原料/热塑性树脂复合材料,不仅能从根源上解决游离甲醛释放的问题,而且能为热塑性树脂的回收利用提供一条新的路径[1-3]。目前,热塑性树脂已与异氰酸酯基胶黏剂、大豆基胶黏剂等共同成为环保型木材胶黏剂的重要发展方向[4-6]。热塑性树脂在一定温度下熔融后,能与多孔性的木材单板形成胶钉结合,赋予复合材料一定的强度[7],但表面自由能低、结晶度高、与木质原料相容性差,是HDPE和PP等热塑性树脂作为胶黏剂的最大缺陷,导致复合材料的耐沸水和耐高温破坏能力较弱,应用范围受限[8-9]。通过减少木质原料表面的羟基数量,或促进木质原料与热塑性树脂发生化学交联,是提高界面相容性的根本方法[10-14]。笔者前期研究发现[15]:以乙烯基三甲氧基硅烷(A-171)和引发剂过氧化二异丙苯(DCP)为改性剂制备的硅烷化杨木单板,能够与HDPE薄膜形成优良的胶接,复合材料的胶合强度、耐水性能和耐高温能力显著增强。与传统的脲醛树脂(UF)等热固性胶黏剂不同,热塑性树脂胶黏剂具有受热软化、冷却固化的特性,其对木材的胶合是其在木材表面熔融软化、流展、渗透和冷却固化的过程。因此,对于特定的热塑性树脂胶黏剂,必须确定适当的热压温度,使胶黏剂既能在木材表面充分的流展、渗透,且不会出现因黏度过低而发生过度渗透导致胶层过薄等现象,同时能够促进硅烷化木材单板与HDPE薄膜达到充分胶合状态。本研究分析了不同的热压温度对硅烷化杨木单板/HDPE薄膜复合材料性能的影响。
Properties of silane modified poplar veneer/high density polyethylene film composites with varying pressing temperatures
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摘要: 为了研究热压温度对硅烷化杨木(107杨Populus × euramericana)单板/高密度聚乙烯(HDPE)薄膜复合材料各项性能的影响,以乙烯基三甲氧基硅烷(A-171)和过氧化二异丙苯(DCP)为杨木单板的改性剂,在不同的热压温度下(140,150,160,170 ℃)与HDPE薄膜复合制备了硅烷化杨木单板/高密度聚乙烯(HDPE)薄膜复合材料。采用万能力学试验机、动态力学分析仪(DMA)和冷场发射扫描电子显微镜(SEM)测定了不同热压温度下复合材料的物理力学性能、动态热力学性能以及胶接界面结构的变化。结果表明:热压温度为140~150 ℃时,复合材料的界面结合力较弱,胶接界面层存在明显的缝隙。当热压温度达到160 ℃时,硅烷化杨木单板与HDPE大分子自由基发生充分有效的胶合,形成能有效提高复合材料性能的胶接界面结构。当热压温度从140 ℃升高到160 ℃时,胶合强度、静曲强度(MOR)和弹性模量(MOE)分别由1.27 MPa,63.90 MPa和5 970.00 MPa增加到1.89 MPa ,72.20 MPa和6 710.00 MPa,但热压温度继续增加,胶合强度和抗弯性能均降低。当热压温度从140 ℃增加到170 ℃时,复合材料24 h吸水率(WA)和吸水厚度膨胀率(TS)分别从72.41%和4.98%降至54.22%和4.09%。复合材料的储能模量保留率E′(130 ℃)由62.31%提高到92.01%,到达tanδmax的温度点从144 ℃延后至200 ℃。复合材料的耐高温破坏能力随着热压温度增加逐渐增强。图5参15Abstract: To study the influence of hot-pressing temperatures on the performance of silane modified poplar veneer/high-density polyethylene (HDPE) film composites, silane modified poplar veneer/HDPE film composites were prepared using silane A-171 (vinyl trimethoxysilane) and dicumyl peroxide (DCP) as veneer modifiers with hot-pressing temperatures of 140, 150, 160, and 170 ℃. A mechanical testing machine, dynamic mechanical analysis (DMA), and a scanning electronic microscope (SEM) were used to test the physical-mechanical properties, thermal stability, and bonding interface structure of composites. Results showed that when hot-pressing temperatures ranged from 140 ℃ to 150 ℃, obvious gaps between silane treated poplar veneer and plastic film were present. When pressing temperature increased from 140 ℃ to 160 ℃, increased (in MPa) tensile strength (1.27 to 1.89), modulus of rupture(MOR)(63.90 to 72.20) and modulus of elasticity (MOE) (5 970.00 to 6 710.00) were noted. When pressing temperature increased from 140 ℃ to 170 ℃, water absorption (WA) decreased from 72.41% to 54.22% and thickness swelling (TS) from 4.98% to 4.09%. At 130 ℃ when DCP content rose from 0 to 0.15%, the retention rate of the storage modulus increased from 62.31% to 92.01%. This also applied to the temperature for tanδmax which lagged from 144 ℃ to 200 ℃. In conclusion, silane modified poplar veneer/HDPE film composites have better physical-mechanical properties and thermal stability at 160 ℃. Because silane treated veneer can closely entangled with HDPE radicals generated by DCP under suitable pressing temperature, which contributed to forming stronger interface structure between the two phases.[Ch, 5 fig. 15 ref.]
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https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.2016.03.016