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عنوان فارسی مقاله:
خواص مکانیکی بهبود یافته الیاف کامپوزیتی پلی آمید حاوی آمینه عاملدار نانو لوله های کربنی
عنوان انگلیسی مقاله:
Enhanced mechanical properties of polyimide composite fibers containing amino functionalized carbon nanotubes
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Aromatic polyimide fiber (PI) has been recognized as one of the most important high-performance polymeric fibers with superior performances such as excellent thermal stability, good chemical resistance, radiation shielding capability and so on [1e3]. In order to expand the application of the PI fibers, mechanical properties and other performance need to be improved. Generally, there are two approaches to improve the mechanical properties of PI fibers: to structurally modify the aromatic PIs and to fabricate PI-based composites with reinforcements. For the structure modification, such as introducing rigid heterocyclic units to the polymer backbones, several researchers have made great efforts. Sukhanova et al. fabricated a series of high performance PI fibers containing the rigid aromatic diamine 2,5-bis(4-aminophenyl)-primidine (PRM) with a tensile strength and modulus of 3.0 and 130 GPa, respectively [4]. Niu and the co-workers introduced the rigid monomer 2-(4- aminophenyl)-6-amino-4(3H)-quinazolinone (AAQ) into the PI chains and the strength and modulus of the fibers were up to 2.8 GPa and 115 GPa, respectively [5]. Even though the mechanical properties of the PI fibers have been improved by introducing rigid heterocyclic units into the polymer chains, concomitantly, shortcomings are still followed: these monomers currently are not widely available or highly expensive. PI fiber reinforcement using a nanofiller is another promising way to improve the tensile properties as well as expand their applications [6e8]. In recent years, more and more nanomaterials with remarkable properties have been introduced into polymer matrices to modify the inadequacies of the materials to meet the stringent requirements under some special circumstances [9e12]. Among these candidates, carbon nanotubes (CNTs) have gained intensive attention as one of the most promising reinforcement nanomaterials due to their extraordinary mechanical properties, high aspect ratio and excellent thermal stability [13e15]. Introducing CNTs into polymeric fi- bers has been widely utilized and investigated over the past decades [16]. However, the tensile strength and modulus of these composite fibers just reached a small fraction of the theoretical value, and some polymer/CNTs systems even showed decreased tendency of mechanical properties when incorporating CNTs into the polymer matrix [17,18], which were mainly attributed to the dispersion difficulties and poor interaction between the polymer matrix and CNTs. Therefore, a key issue for raising the reinforcement of nanofillers includes improving both the homogeneous dispersion and interfacial interaction between the polymer and CNTs. Recently, great efforts have been focused on applying the approach of surface modification of CNTs to improve the compatibility between the matrix and the nanofillers. Hu et al. found that the incorporation of CNT-COOH into the poly (p-phenylene benzobisoxazole) (PBO) matrix by one-pot in situ polycondensation increased the tensile strength and modulus of PBO fiber from 2.2 to 2.7 GPa and from 64.8 to 89.4 GPa [19]. Sainsbury et al. functionalized MWCNTs with poly (p-phenylene terephthalamide) (PPTA) oligomer units, which facilitates the integration of the PPTAMWCNTs within the PPTA matrix [20]. In this work, the asymmetric heterocyclic diamine 2-(4- aminophenyl)-5-aminobenzimidazole (BIA) and the rigid-rod dianhydride 3,30 ,4,40 -biphenyltetracarboxylic (BPDA) were selected to synthesize the PI. Meanwhile, amino-functionalized MWCNTs as reinforcement fillers were introduced into PI matrix expecting enhancing the fibers' mechanical and other performances. In general, properties of polymeric fibers mainly depend on the aggregation structure and intermolecular interactions [5,21,22]. The orientation of the molecule chains as well as the formation of the interfacial interactions can be affected by the incorporated CNTs, especially when forming extra interactions or covalent bonds between polymer matrix and functional groups on the surfaces of the CNTs, thus leading to the changes of the performances of the fibers [15,17,23]. However, until now, less systematic studies have focused on investigating the interactions between CNTs and PI chains, polymer chains orientation as well as the semicrystalline structure of PI/CNTs composite fibers. Herein, we report a new effective protocol to prepare PI/CNTs composites on the basis of NH2- MWCNTs/NMP suspensions by in situ polymerization to improve the solubility, dispersivity and interfacial interactions of CNTs in the PI matrix. A series of PI/NH2-MWCNTs composite fibers were prepared by wet-spinning process and post heat-drawing treatment. Intricate interactions between CNTs and PI as well as the evolution of the aggregation structure of the composite fibers were investigated intensively and correlated to the mechanical and other performances of the prepared composite fibers.
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کلمات کلیدی:
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