【作者】 郭云霞；

【导师】 胡国胜；

【作者基本信息】 中北大学 ， 军事化学与烟火技术， 2010， 博士

【摘要】 随着社会与科学技术的飞速发展,单一材料的性能已不能满足日趋发展的形势,高性能化、多功能化和复合化已成为材料发展的必然趋势。尼龙11相对于其它聚酰胺类材料,虽然具有吸水率低、耐油性好、耐低温、弹性记忆效应好、耐应力开裂性好、易于加工等优点。但是,纯粹的PA11的性能已不能满足各种产品对材料性能的特殊要求,且其相对较高的市场价格也限制了其应用领域的进一步拓展。因此,通过物理或化学改性的方法制备高性能和功能化PA11基合金材料的重要性越来越明显。国内外学者对尼龙改性的研究颇多,尤以尼龙6和尼龙66的改性研究为主,而尼龙11改性研究相对较少。而且参阅大量文献时发现,国外研究重点集中在尼龙11的晶体结构、晶形转变以及压电性能上；国内在上述方面也进行了不少的研究。而国内外,在尼龙11增塑、增强、增韧等方面的合金研究则都相对较少。本文在以往实验经验的基础上,仍采用弹性体增韧的思路,这样可以保证韧性大幅度提高,达到超韧化目的。另外,聚合物之间的相容性是决定共混物形态结构和性能的关键因素,因此本文除了对尼龙11超韧化及其合金的力学性能、形态结构、结晶性能、流变性能进行系统研究外,还首次通过Materials Studio软件对尼龙11共混体系的相容性进行了介观动力学模拟,进而分析了弹性体的增韧机理,并首次提出三维网络化增韧机理。本文主要从以下几个方面进行了研究：通过不同增韧剂改性PA11,研究结果表明,采用POE作为增韧剂,POE-g-MAH为相容剂,增韧效果明显,且经济适用。单纯用POE-g-MAH增韧时,其含量的增加对PA11合金冲击强度的影响不大,而当体系PA11/POE/POE-g-MAH三元共混时,体系冲击强度可提高到80kJ/m2以上,且POE/POE-g-MAH存在一个最佳比例,MAH接枝率并非越大越好；而POE-g-MAH含量的增加却能使拉伸强度呈线性下降,但MAH接枝率的多少对共混物拉伸强度的影响不大。动态力学性能研究表明,PA11中加入POE及POE-g-MAH后,复合体系的储能模量均比纯PA11的低；在共混体系中引入POE-g-MAH后,由于增加了PA11和POE两相间的界面亲和力,储能模量相对于AMO-0-30体系的要高；三元共混时,体系分子间的作用力增大,粘度增加,导致内耗明显增大；且损耗峰向高温方向移动,导致Tg升高。加入POE和POE-g-MAH可以有效降低PA11的吸水性,PAll与POE各个共混体系的p松弛峰高显著低于纯PA11的。共混物冲击断面的SEM分析结果显示,PA11仅与POE共混时,两相界面清晰,界面粘结松散,形成所谓的“海-岛”结构,为典型的两相不相容体系；而当PA11/POE-g-MAH/POE三元共混时,两相界面变得模糊,分散相颗粒细化,分散相与基体材料粘结强度高,成为典型的“海-海”结构。DSC研究结果表明,POE或POE-g-MAH的加入,起到异相成核的作用,可以提高PA11的结晶速率,降低晶体生长对时间的依赖性；相容剂POE-g-MAH的引入,使得PA11和POE的分子链发生缠结,增大了PA11体系的粘度,导致结晶速率下降,另外体系中形成的这些交联网络不易熔融,起到异相成核的作用,使得某些结晶不完善的小晶粒趋于完善,表现为低温熔融峰变小；纯PA11的成核方式只有均相成核方式,加入相容剂和弹性体后,结晶成核方式不仅存在自相成核方式,还存在异相成核方式,由于成核作用的影响,诱发其生长向高维数发展。XRD研究显示,PA11中单纯加入POE,可使复合材料的晶体结构从Y晶型转变为α晶型；而体系中加入POE-g-MAH,可以提高PA11的结晶能力,且使晶形更加完善。偏光显微成像研究发现,PA11中加入POE或POE-g-MAH后,黑十字消光现象消失,球晶尺寸明显变小,PA11球晶的生长受到破坏,生成大量的微晶和一些较大的晶粒；当体系变为三元共混时,由于POE-g-MAH使得PA11与POE的分子间的作用力增强,阻碍了PA11分子链折叠排入晶格的运动,不利于PA11球晶的生长,而只能以微晶形式存在。毛细管流变研究认为,PA11及其与POE的复合材料都属于假塑性流体,POE和POE-g-MAH的引入,增加了共混体系的非牛顿性,对剪切应力或剪切速率的敏感性较大；共混体系的粘流活化能均大于纯PA11的,说明共混体系的熔体粘度对温度的敏感性较高。采用介观动力学方法对PA11共混体系的相容性进行研究。采用珠子代替一个重复单元或分子片段,用由珠子组成的高斯链代替真实分子链,真实分子链的特性反映在珠子的性质上。模拟得到等密度图、自由能密度和有序度参数来表征共混体系的相容性。结果表明,PA11与POE共混体系中引入POE-g-MAH时,可以起到细化POE粒径的作用,同时它可以在PA11和POE之间形成连接点,使POE分子链接枝到PA11链上,进而提高了尼龙11的冲击韧性；共混体系介观模拟形貌基本上与实际共混物的断面形貌相吻合,这一事实验证了该模拟方法的合理性和可行性。弹性体增韧机理分析认为,增韧后的PA11复合材料试样由于在冲击作用下,产生大量银纹或剪切带,消耗了大量能量,从而显著提高了材料的冲击强度；分散相粒子间距的减小,使得分散相应力场逐渐增大,产生塑性变形的幅度增加,材料韧性也随之增大；三维网络状的分散相粒子,在体系中不仅起到骨架作用,而且在外力作用下,网络发生大变形,引发大量的银纹,吸收外界能量,从而起到增韧的作用。更多还原

【Abstract】 With the development of society and the improvement of science and technology, the performance of a single material has not meet the growing development of the situation. Polymer materials are developing toward the high performance, multifunctional and complex. Compared to other type of polyamide material, nylon 11 although has a lot of excellent properties, such as low water absorption, oil resistance, good resistance to low temperature, good flexible memory effect, good stress cracking resistance, easy processing and so on. However, the performance of pure PA11 has been unable to meet all kinds of products on the material properties of the special requirements, and its relatively high market price also limits its applications. Therefore, it is important that high performance and functional of PA11-base alloy materials are prepared by physical or chemical modification method.Nylon modification, especially on nylon 6 and nylon 66, has been studied in recent years. However, the research on the modification of nylon 11 is relatively little. Based on the extensive literature, it had been found that overseas research focused on the crystal structure, crystalline changes, and the piezoelectric properties of nylon 11. The same is true of domestic. However, at home and abroad, the study is relatively few on plasticizing, enhancement, toughening of nylon 11 alloys. In this paper, based on past experience, the elastomer was still used as toughening agent in order to guarantee substantial increase in toughness and achieve the purpose of super-toughening. In addition, the compatibility between the different phases of the polymers is the one of key factors in determining the morphology structure and performance of blend. This paper investigated the mechanical properties, morphology, crystalline properties, and rheological properties of the ultra-toughening nylon11. For the first time, the compatibility of nylon 11 blends systems in mesoscopic region was simulated using the Materials Studio software. Thus, elastomer-toughening mechanism was analyzed, and three-dimensional network toughening mechanism was first proposed.This paper studied from the following aspects.The different toughening agents were used to toughen PA11. The results indicate that when POE as a toughening agent and POE-g-MAH as compatibilizer, the toughening effect is obvious, which is affordable and economical. When simply using POE-g-MAH toughness, its content has little effect on impact strength of the PA11 alloy. When the system was composesed of PA11, POE and POE-g-MAH, impact strength of the system can increase to more than 80KJ/m2. There is an optimal ratio between POE and POE-g-MAH, and MAH grafting rate is not bigger and the better. The POE-g-MAH content increaseing linearly can decrease the tensile strength, but the amount of MAH graft ratio was little effect on tensile strength of the blends.Study on the dynamic mechanical properties indicated that the storage modulus of the composites system is higher than that of pure PA11 when POE and POE-g-MAH were added into PA11. The reason is that POE-g-MAH improves the interface affinity between two phases. And the storage modulus of the tri-blending system is higher than the AMO-0-30 system. What’s more, in the tri-blending system the intermolecular forces and viscosity are bigger than binary blends system so.that the intermolecular friction increases and the loss peaks move to high temperatures which resulting in higher Tg. POE and POE-g-MAH can effectively reduce water absorptivity of PA11,βrelaxation peak of PA11 blending with POE and POE-g-MAH is significantly lower than that of pure PA11.The SEM results of impact fracture of composites show that when PA11 was only mixed with POE, the two-phase interface is clear, and bond loosely, forming the so-called "sea-island" structure which is a typical two-phase incompatible systems. When PA11 blended with POE-g-MAH and POE, the two-phase interface is blurred, the dispersed phase is refined and the bonding strength between the dispersed phase and matrix material is higher. A typical "sea-the sea" structure has been formed.DSC results show that POE or POE-g-MAH play the role of heterogeneous nucleation, which can increase the crystallization rate of PA11 and reduce time-dependence of crystal growth. The introduction of compatibilizer POE-g-MAH causes molecular chain entanglement of PA11 and POE, which increase the viscosity of the PA11 and decline crystallization rate. The cross-linked networks that are not melting easily play the role of heterogeneous nucleation, and make some imperfect crystallization, of small grains close to perfection which low-temperature melting peaks reduce. The nucleation of pure PA11 is only homogeneous nucleation. When the compatibility agents and elastomer are added into blend system, the crystal nucleation is not only homogeneous nucleation, but there is still heterogeneous nucleation. Due to the impact of nucleation function, its growth is induced to a higher dimension.XRD results show that the POE transforms the crystal structures of blends from y to a form when only POE introduced into PA11. However, POE-g-MAH can improve the crystallization of PA11 and make the crystal perfect.Polarized microscopic results indicate that when POE or POE-g-MAH is added into PA11, the typical Maltese cross extinction disappears and spherulite size become much smaller. The growth of PA11 spherulites is restrained and a large number of microcrystalline and some large crystal grains are generated. When the system is ternary blends, POE-g-MAH increases intermolecule force between PA11 and POE, and hinder the movement of molecular chain of PA11 folding into the lattice, which is not benefit to the growth of PA11 spherulites so that they exist in the form of microcrystalline.The research results of Capillary rheological show that PA11 and PA11/POE composite are pseudo-plastic fluid. The introduction of POE and POE-g-MAH increase their non-newtonian behaviour, and there is a larger sensitivity to shear stress or shear rate. The viscosity-flow activation energy of the blending system is larger than that of pure PA11, which indicate the melt viscosity of blending system is sensitive to temperature.The phase separation of the PA11 blend system in mesoscoopic region is simulated using MesoDyn. The thermodynamic forces are obtained by a mean-field density functional method, using Gaussian chain as a molecular model. The results demonstrate that POE-g-MAH in the blends of PA11 and POE can refine particle size of POE and generate connection point between PA11 and POE of molecular clain so that it can increase the impact toughness of PA11. Blend Morphology of mesoscopic simulation is consistent with the actual cross-section morphology of blends that verify that it is feasible and practicable for this simulation method. Elastomer toughening mechanism analysis, PA11 toughened composites under the action of impact result in a large number of crazes or shear zones which consum a lot of energy, and thus significantly improve the impact strength of the material. Dispersed phase particle spacing decrease, the force field of dispersed phase increases gradually, resulting that plastic deformation region and toughness of composites increase. In the blend system, the dispersed phase particles that is three-dimensional nectwork structure, not only play a role in skeleton, but also play a toughening role in nylon 11 which the network structure produce a large number of deformation, and trigger a large number of silver grain and absorbing external energy.更多还原