【作者】 刘慧；

【导师】 方征平；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2010， 博士

【摘要】 辐照加工有着不受环境温度限制、穿透能力强和易于控制等多方面优势而广泛应用于工业、农业及医疗卫生等各个方面,已在交联线缆、橡胶硫化、泡沫塑料、表面固化、医疗用品消毒和食品辐照保藏等领域形成产业规模,并取得显著成效。在高分子科学领域中,聚烯烃在高能射线的作用下易被电离激发,生成大分子自由基,大分子自由基通过相互碰撞而引发交联反应,形成网状结构,这种交联网状结构可以有效地提高基体的力学性能。本文的主要研究内容是采用零维的富勒烯(C60)和氢氧化镁(Mg(OH)2)、一维的多壁碳纳米管(MWCNTs)、二维的有机蒙脱土(Clay)等不同维度的纳米粒子添加到高密度聚乙烯／乙烯-乙酸乙烯酯共聚物(HDPE/EVA)基体中,通过熔融共混法制备纳米复合材料,利用电子束对纳米复合材料进行辐照加工,对比研究辐照前后纳米复合材料的热学性能、燃烧性能、流变行为以及力学性能的变化,通过相关测试和表征手段证实不同纳米粒子在辐照作用下发生了结构改变,进一步揭示电子束辐照HDPE/EVA基纳米复合材料的结构与性能之间的相互关系。首先,通过熔融共混法制备了HDPE/EVA/C60纳米复合材料,考察C60对体系性能的影响。发现C60在低添加量(≤2 wt%)时即可大幅度地提高基体的热稳定性,尤其在空气中极大地推迟了基体的热氧化降解温度；在阻燃性能方面,可有效延长基体的点燃时间,显著降低基体燃烧的峰值热释放速率(PHRR),表明C60在低添加量时即可提高基体的阻燃性能。当体系辐照后,证实C60会捕捉基体辐照后产生的大分子自由基而形成“桥”连接的网络结构,这种特殊的网络结构可以使体系的热氧化降解温度、动态模量、玻璃化转变温度以及力学性能都有所提高,但辐照作用却对体系的阻燃性能有不利的影响。其次,通过熔融共混法制备了HDPE/EVA/MWCNTs纳米复合材料,考察MWCNTs对体系性能的影响。发现MWCNTs在低添加量(≤2 wt%)时也可大幅度地提高基体的热稳定性,同样在空气中极大地推迟基体的热氧化降解温度；在阻燃性能方面,虽然点燃时间有所缩短,却可以有效降低基体燃烧的PHRR值。MWCNTs被电子束辐照后,规整结构受到了一定破坏,但整体结构没有改变。辐照对体系提高热氧化降解温度起到积极的作用,辐照后基体产生交联结构同样提高了体系的动态模量、玻璃化转变温度以及力学性能。与HDPE/EVA/C60体系相似,辐照作用对基体的阻燃性能也同样产生了不利的影响。第三,通过熔融共混法制备了HDPE/EVA/Clay纳米复合材料,考察Clay对体系性能的影响。发现Clay在基体中呈现插层结构,在添加量增加时可以提高基体的热稳定性,尤其是可以极大地推迟基体的最大失重速率温度；在阻燃性能方面,Clay在低添加量时(1wt%)可延长基体的点燃时间,同时显著降低基体燃烧的PHRR值；但当添加量大于3wt%以后,PHRR值却逐渐升高。体系辐照后,Clay插层结构的层间距进一步扩大,扩大了层间距的Clay对体系阻燃性能的提高明显优于C60和MWCNTs体系。基体产生交联结构导致了体系的动态模量、玻璃化转变温度以及力学性能的提高。最后,通过熔融共混法制备了HDPE/EVA/Mg(OH)2复合材料,考察辐照剂量的改变对体系性能的影响。发现随着辐照剂量的增加,体系的交联密度不断增加,交联网络不断增强；增强的交联网络提高了基体的热稳定性,尤其是可以极大地推迟基体的最大质量损失温度；辐照作用使体系的PHRR值逐渐升高,但却可以大幅度地降低烟密度；同时,辐照对提高体系的熔融温度和熔融焓同样起到了积极的作用。更多还原

【Abstract】 Irradiation technology is widely applied to industrial, agricultural, biomedical sectors due to its overwhelming advantages such as no resistance to temperature, strong penetration power and easy control. Currently, irradiation tenchnology has become industrial development in electrical wire and cable, rubber vulcanization, foamed plastics, surface curing, medical sterilization and food irradiation. Ionized by high energy irradiation in polyolefins, macro-radiacals can combine with each other to form a crosslinking network structure which can increase the mechanical properties effectively.The present dissertation focuses on the structure and properies of HDPE/EVA nanocomposites irradiated by high energy electron beam. Effect of the irradiation on thermal and mechanical properties, combustion and rheological behaviours of irradiated HDPE/EVA nanocomposites are compared with un-irradiated ones. Four kinds of nano-fillers, C6o, MWCNTs, Clay and Mg(OH)2, are employed into the HDPE/EVA blend, and various measurements and characterization are used to confirm the structural change of the irradiated nanocomposites.Firstly, the structure and properies of irradiated HDPE/EVA/C60 nanocomposites are studied. The results show that at very low loading (≤2 wt%), C6o could remarkably improve the thermal stability, especially postpone the temperature of the maximum mass loss rate (Tmax) in air atmosphere. Meanwhile, C60 could prolong the time to ignition (tign) and dramatically reduce the peak heat release rate (PHRR), which implies that at very low loading, C60 could reduce the flammability greatly. After irradiation, it was proved that the "bridge" structure, between C60 and HDPE/EVA blend, increases the thermal oxidation degradation, storage modulus, glass transition temperature and mechanical properties. However, the flame retardancy of irradiated HDPE/EVA/C60 nanocomposites decreased.Secondly, the structure and properies of irradiated HDPE/EVA/MWCNTs nanocomposites are studied. The results show that at very low loading (≤2 wt%), MWCNTs could remarkably improve the thermal stability, especially postpone the Tmax in air atmosphere. Meanwhile, MWCNTs could dramatically reduce the values of PHRR but shorten the tign. After irradiation, the structure of MWCNTs was slightly destroyed but the contour structure kept intact. The network structure in the irradiated HDPE/EVA/MWCNTs nanocomposites increases the thermal oxidation degradation, storage modulus, glass transition temperature and mechanical properties. The flame retardancy decreased, which is similar to the results of the irradiated HDPE/EVA/C60 nanocomposites.Thirdly, the structure and properies of irradiated HDPE/EVA/Clay nanocomposites are studied. The intercalated structure was formed in HDPE/EVA/Clay nanocomposites, which could remarkably improve the thermal stability and postpone the Tmax. Meanwhile, at very low loading (1 wt%), clay could prolong the tign and dramatically reduce the values of PHRR, but when the content of clay is higher than 3 wt%, the values of PHRR increase. After irradiation, the flammability property of irradiated HDPE/EVA/Clay nanocomposites is reduced due to the increased layer space, which is different from the results of the irradiated HDPE/EVA/C60 nanocomposites and irradiated HDPE/EVA/MWCNTs nanocomposites.Finally, the properies of irradiated HDPE/EVA/Mg(OH)2 composites are studied. The degree of crosslinking network is enhanced with increasing the irradiation dose. The network structure improves the thermal stability, the temperature of melting, the heat of melting and the glass transition temperature of irradiated HDPE/EVA/Mg(OH)2 composites and does favor to the smoke suppression.更多还原