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Study On Structure And Performance Of Super Toughness Nylon11 Alloy And Mesoscopic Simulation Of Its Compatibility

Posted on:2011-02-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y X GuoFull Text:PDF
GTID:1101360308980787Subject:Military chemistry and pyrotechnics
Abstract/Summary:PDF Full Text Request
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,╬▓relaxation 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.
Keywords/Search Tags:PA11, POE, Morphology Structure, Rheological Behavior, Crystallization Kinetics, Compatibility, Mesoscopic Simulation
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