Sized PAN-based carbon fibers were treated with hydrochloric and nitric acids, as well as argon and oxygen cold plasmas, and the changes on their surfaces evaluated. The physicochemical properties and morphological changes were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), tensile strength tests and Raman spectroscopy. The nitric acid treatment was found to cause the most significant chemical changes on the carbon fiber surface, introducing the largest number of chemical groups and augmenting the roughness. The oxygen plasma treatments caused ablation of the carbon fiber surface, removing carbon atoms such as CO and CO 2 molecules. In addition, the argon plasma treatment eliminated defects on the fiber surface, reducing the size of critical flaws and thus increasing the fiber's tensile strength.
Poly(phenylene sulfide) (PPS) is an engineering thermoplastic polymer that presents high temperature resistance (glass transition temperature around 85 ºC and melting point at 285 ºC). These properties combined with its mechanical properties and its high chemical resistance allows its use in technological applications such as molding resins and as matrix for structural thermoplastic composites. During the manufacture of thermoplastic composites, the polymer is exposed to repeated melting, quenching and crystallization processes. The properties of semicrystalline polymers, such as PPS, depend on its crystallization behavior. This work deals with the PPS crystallization kinetics under different thermal cycles. This study was performed under isothermal conditions in a differential scanning calorimetry (DSC), coupled to Perkin Elmer crystallization software referred to as Pyris Kinetics -Crystallization. The results were correlated with microscopic analyses carried out in a polarized light microscope, equipped with a controlled heating and cooling accessory. In this case, the experimental conditions were the same adopted for the DSC analyses. From the results, parameters could be established to be used in the composite manufacture.
The use of polyamic acid (PAA) precursor as interphase in polymer composites is one of the many applications of polyimides (PIs). In this work, composites based on poly(ether-ether-ketone) (PEEK) and carbon fibers were prepared using two manufacturing techniques for thermoplastic composites: hot compression molding, and aqueous polymeric suspension prepregging using PIs as interphase. Two PAAs were synthesized and used as interphases: 3,3'-4,4'-benzophenonetetracarboxylic dianhydride/oxydianiline (BTDA/ODA) and pyromellitic dianhydride/ oxydianiline (PMDA/ODA). The PAA/PI systems were analyzed by differential scanning calorimetry (DSC), thermogravimetry (TGA), Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Results from these analyses confirmed the synthesis of these compounds. Aqueous polymeric suspension prepregging was more efficient than hot compression molding when the PMDA/ODA PAA/PI interphase was used; also, the interlaminar shear strength of composites produced using this technique was 14.5% higher than the one produced using hot compression molding.
Resumo:No presente trabalho duas técnicas de manufatura de compósitos termoplásticos estruturais são investigadas: a de moldagem por compressão a quente convencional e a de pré-impregnação via suspensão polimérica. A primeira consiste na impregnação do reforço via polímero fundido; enquanto que a segunda faz uso de suspensões poliméricas aquosas, onde a impregnação do reforço ocorre pelo contato deste com a suspensão aquosa de partículas da matriz polimérica. Esta técnica combina a matriz polimérica em pó com um outro polímero formador da suspensão, um poli(ácido âmico -PAA), sendo que os dois polímeros são simultaneamente depositados sobre o reforço, durante a impregnação. Este mesmo PAA, em uma segunda fase do processo, é convertido termicamente em uma poliimida (PI) podendo formar uma região de interfase entre o reforço e a matriz polimérica. Este trabalho tem como objetivo a síntese e a caracterização de um PAA, à base de BTDA/DDS, e a avaliação de sua influência na formação da região de interfase em compósitos de poli(sulfeto de fenileno) (PPS)/fibras de carbono. Resultados de DSC e TG mostram o sucesso da síntese do PAA e de sua conversão em PI, esta com estabilidade térmica até 396 °C. O compósito processado pela técnica de suspensão polimérica apresenta resistência ao cisalhamento interlaminar (56,3 MPa) 12,6% superior ao compósito obtido por moldagem por compressão a quente convencional (50,0 MPa). Estes resultados são confirmados por análises das superfícies de fratura, que mostram que o uso do PAA melhora a interfase do PPS/fibra de carbono. Palavras-chave: Fibra de carbono, interface/interfase, síntese, poli(ácido âmico). Optimization of the Interface/Interphase of Carbon Fiber/PPS Thermoplastic Composites using BTDA/DDS Poly(amic acid)Abstract: In the present work two different manufacturing techniques of thermoplastic composites are investigated: the conventional hot compression molding and the aqueous suspension prepregging. The first one involves the impregnation of the reinforcement with molten polymer; while the second one uses aqueous polymeric suspensions, where the reinforcement impregnation occurs by its contact with the particle aqueous suspension of a polymeric matrix. This technique combines the powder polymeric matrix with another polymer which forms the suspension, a poly(amic acid -PAA). In this technique, both polymers are deposited simultaneously on the reinforcement during the impregnation. In a second phase of the processing, the PAA is thermally converted in a polyimide (PI) that can form an interphase region between the reinforcement and the polymer matrix. The objective of this study is the synthesis and the characterization of a PAA, based on BTDA/DDS, and the evaluation of its influence on the interphase region in the poly(phenilene sulphite) (PPS)/carbon fiber composite. DSC and TG results show the success of the PAA synthesis and its conversion into PI, which exhibits thermal stability up to 396 °C. The processed composite by polymeric aqueous suspension showed interlaminar...
O objetivo do presente trabalho é apresentar a síntese de um poli (ácido âmico) (PAA) a ser utilizado como formador de interfase no processamento de compósitos termoplásticos de alto desempenho. Os materiais compósitos termoplásticos constituídos de um reforço rígido e de uma matriz dúctil têm as suas propriedades mecânicas fortemente dependentes do mecanismo de transferência de carga fibra/matriz. Por esse motivo, a região da interface/interfase nos materiais compósitos possui um papel fundamental nas propriedades finais do material. O PAA surge como uma alternativa para melhorar a adesão fibra/matriz na região interfacial em compósitos de alto desempenho, constituídos de matrizes termoplásticas, reforçadas com fibras de carbono ou vidro. O PAA é utilizado na forma de sal, na preparação de suspensões poliméricas de matrizes termoplásticas. O PAA estudado neste trabalho foi sintetizado utilizando-se os reagentes BTDA e DHPr. Em seguida, o PAA foi convertido em PI por imidização em solução. Análises por FTIR mostram o sucesso da síntese do PAA e da sua conversão em PI. As técnicas de DSC e TGA determinaram as temperaturas de transição vítrea (~213 °C) e de decomposição (~310 °C), respectivamente. Estes resultados motivam a utilização do PAA/PI como formador de interfase na obtenção de compósitos termoplásticos com temperaturas de processamento abaixo de 310 °C.
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