【作者】 张涛；

【导师】 方征平；

【作者基本信息】 浙江大学 ， 高分子材料， 2013， 博士

【摘要】 天然麻类纤维,由于其具有密度低、力学性能好以及可自然降解等优势,已经在家纺和工业领域有着广泛的用途。尤其是近年来,将其作为力学增强体而制备的热固性树脂基复合材料,进一步拓展了其在航空航天、汽车、电子以及建筑等领域的应用。然而,麻类纤维的热稳定性能和阻燃性能均比较低,一直制约了其在高端领域的应用。本文基于苎麻织物特殊的化学组成和结构特点,采用层层组装的方法在其表面构建了膨胀型阻燃涂层,并将其应用于苯并嗯嗪树脂基复合材料层压板中。首先,设计并合成了含有萘基、2,2-二苯基丙烷基和新戊基三种不同主链结构的芳香二胺型苯并噁嗪树脂单体(分别简称为BAPNCP、BAPBACP和BAPNPGCP),采用傅里叶红外光谱(FT-IR)、核磁共振谱(1H NMR和13CNMR)和元素分析等方法确定了化学结构,研究了主链结构对苯并噁嗪树脂单体固化行为以及固化物阻燃性能的影响。结果表明,BAPNPGCP单体分子量在三者中是最低的,单位质量所含苯并噁嗪环的含量最高,从而其在开环固化过程中的固化焓也是最高的。有趣的是,BAPNPGCP固化物poly(BAPNPGCP)在热失重为5wt%时的温度及其在900℃时的残炭比poly(BAPBACP)的分别高出8℃和7wt%。同时,poly(BAPNPGCP)的总热释放量比poly(BAPBACP)的一半还低,表明了苯并噁嗪环含量对成碳和阻燃性能的显著影响。poly(BAPNCP)的热稳定性能和阻燃性能是三者中最高的,可能是高耐热性萘基和苯并嗯嗪环含量的协同作用。其次,利用氨基化碳纳米管(MWNT-NH2)的正电荷性和聚磷酸铵(APP)的负电荷性,通过层层组装技术在柔顺且多孔状的苎麻织物表面构建了MWNT-NH2/APP纳米阻燃涂层,并采用紫外-可见吸收光谱(UV-vis)、扫描电子显微镜(SEM)、衰减全反射傅里叶红外光谱(ATR-FTIR)和X射线能量分析光谱仪(EDX)等方法跟踪了组装过程。SEM观察显示,MWNT-NH2在苎麻织物表面任意取向,在微米尺度范围发生堆叠。ATR-FTIR和EDX分析表明,APP随组装层数的增加而逐步引入多层膜。与苎麻织物空白样相比,随着组装层数和MWNT-NH2悬浮液浓度的增加,处理后苎麻织物的热稳定性能、阻燃性能和残炭量显著提高。因此,MWNT-NH2与APP在柔顺且多孔状苎麻织物表面的结合,形成了贴体且膨胀型阻燃涂层,从而直接控制了热量传递过程以及纤维素衍生物的释放。第三,利用聚乙烯亚胺(PEI)的正电荷性和APP的负电荷性,通过层层组装技术在柔顺且多孔状的苎麻织物表面构建了自熄灭性PEI/APP多层膜,且采用ATR-FTIR、SEM、EDX和原子力显微镜(AFM)等方法跟踪了组装过程。ATR-FTIR和EDX分析表明,随着组装层数的增加,PEI和APP交替吸附于苎麻织物表面。与苎麻织物空白样相比,随着组装层数的增加,处理后苎麻织物在400～600℃温度范围的残炭显著提高,且其增加值明显高于表面涂层重量的净增值。同时,处理后样品的自熄灭能力也随着组装层数的增加而显著提高。调整PEI和APP两种聚电解质溶液的浓度搭配,很容易地控制了磷／碳(P/C)和磷／氧(P/O)比值以及涂层重量的净增值,从而有效地控制了最终苎麻织物的热稳定性和阻燃性能。最后,将纯的以及构建了MWNT-NH2/APP和PEI/APP阻燃涂层的苎麻织物作为增强体,以苯并噁嗪树脂作为基体制备了复合材料层压板(分别简称为BZ/ramie、BZ/ramie/MWNT/APP和BZ/ramie/PEI/APP),研究了阻燃整理后苎麻织物对复合材料阻燃性能和力学性能的影响。结果表明,与BZ/ramie相比,BZ/ramie/MWNT/APP和BZ/ramie/PEI/APP的热释放速率峰值和总热释放量显著降低,极限氧指数明显提高,垂直燃烧级别分别达到了V-0和V-1级。同时,在拉伸和弯曲外力作用下,阻燃涂层加强了纤维和纤维、纤维和基体之间的界面结合力,呈现出更高的强度和韧性。更多还原

【Abstract】 As a kind of interesting natural cellulosic fibers, bast fiber shows promising applications as reinforcement of composites in many advanced fields (such as automotive, aerospace, military and construction industries, etc.) besides home textile, because of its biodegradability, low price, low density and excellent mechanical properties. However, the highly flammable nature limits its practical applications. In view of the special chemical composition and structure of ramie fabric, we have constructed intumescent flame retardant coating on ramie fabric, and then applied the flame retardant ramie fabric to prepare ramie fabric/polybenzoxazine laminates.Firstly, three kinds of novel aromatic diamine-based benzoxazines containing naphthalene, propane-2,2-diyldibenzene and neopentyl group in the backbone, respectively (designated as BAPNCP, BAPBACP and BAPNPGCP, respectively), have been synthesized and characterized. In addition, the effect of backbone structures on curing behaviors of the monomers and thermal and flammability properties of the resulting polymers were studied. The results indicated that BAPNPGCP displayed the highest enthalpy of the curing reaction associated with the ring-opening of benzoxazine, which was due to the effect of benzoxazine ring content per unit mass. Interestingly, the5wt%weight loss temperature and char residue at900℃for poly(BAPNPGCP) were8℃and7wt%higher than those of poly(BAPBACP). Meanwhile, the total heat release of poly(BAPNPGCP) was less than half that for poly(BAPBACP), indicating the substantial effect of benzoxazine ring content on flammability and char formation. Furthermore, it was found that poly(BAPNCP) gave the best thermal stability and flame retardancy, which was due to synergistic effect between naphthalene group and benzoxazine ring content.Secondly, a new flame retardant nanocoating has been constructed by the alternate adsorption of polyelectrolyte amino-functionalized multiwall carbon nanotube (MWNT-NH2) and ammonium polyphosphate (APP) onto flexible and porous ramie fabric, and the film growth was monitored by UV-visible spectrometry (UV-vis), scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and energy-dispersive X-ray analysis (EDX). SEM indicated that the adsorbed carbon nanotube coating was a randomly oriented and overlapped network structure, which is a promising candidate for flame retardancy applications. ATR-FTIR and EDX confirmed that the APP was successfully incorporated into the multilayers sequentially. Assessment of the thermal and flammability properties for the pristine and nanocoated ramie fabrics showed that the thermal stability, flame retardancy and residual char were enhanced as the concentration of MWNT-NH2suspension and number of deposition cycles increases. The enhancements are mostly attributed to the barrier effect of intumescent network structure, which is composed of MWNT-NH2and the absorbed APP.Thirdly, self-extinguishing multilayer coatings consisting of polyelectrolyte polyethylenimine (PEI) and ammonium polyphosphate (APP) have been constructed by layer-by-layer assembly technique onto flexible and porous ramie fabric, and the film growth was monitored by ATR-FTIR, SEM, EDX and Atomic force microscopy (AFM). ATR-FTIR and EDX directly confirmed that PEI and APP were successfully incorporated onto the surface of ramie fabric sequentially. Assessment of the thermal and flammability properties for the coated ramie fabrics showed that the char residue at temperature ranging from400to600℃during thermogravimetric analysis (TGA) and the self-extinguishing ability during vertical flame test were significantly enhanced as compared with the pristine sample, which showed strong dependency on the number of deposited layers, especially on the concentration collocation of both polyelectrolytes.Finally, we prepared polybenzoxazine matrix laminates reinforced with pristine and treated ramie fabrics with20bilayers of MWNT/APP or PEI/APP (designated as BZ/ramie, BZ/ramie/MWNT/APP and BZ/ramie/PEI/APP, respectively), and studied the influence of treated ramie fabric on mechanical and flame retardant properties for laminates. Compared to BZ/ramie, the total heat release and maximum peak values of BZ/ramie/MWNT/APP and BZ/ramie/PEI/APP decreased substantially, and the limiting oxygen index values were increased significantly. The burning ratings of BZ/ramie/MWNT/APP and BZ/ramie/PEI/APP during UL-94vertical flame test were V-0and V-1, respectively. Flexural and tensile tests indicated that multilayers of flame retardant coating can enhance interfacial adhesion between the matrix and reinforcement, so as to improve flexural strength, tensile strength and elongation at break.更多还原