Search

The search for alternative processes and high performance materials precursors for carbon fibers, has been continuously the aim for use in the aerospace, automotive, energy and sports goods market. The reduction in the precursor production cost is then essential to allow the installation of an industrial plant to produce a general purpose carbon fiber. Polyacrylonitrile has been the main precursor for carbon fiber production. It has been produced by the wet and dry spinning process since it has been discovered in the beginning of the forties. Nowadays, the extrusion process of PAN fibers shows potential of cost reduction in relation to the wet spinning method. This innovative technology enables spinning by melting PAN polymer by using glycerin as the primary plasticizer, avoiding the use of highly toxic solvents. In the present work, PAN copolymer was copolymerized by conventional aqueous suspension. Its characterization was performed by FT-IR, GPC and DSC analysis. The fibers obtained by extrusion process were characterized by SEM, DSC/TGA analysis and kinetics of the thermal stabilization process was studied by Kissinger method. The results showed that styrene monomer was suitable for polymerization with PAN leading to a molecular weight Mn= 46,000 g/mol and Mw = 138,000 g/mol. The PAN-co-Styrene copolymer was suitable for obtaining extruded PAN fibers continuously with morphological and thermal properties having properties similar to commercial PAN fibers.

A disponibilidade de novos materiais, processos e equipamentos sempre traz perspectivas favoraveis ao mercado. A busca por processos alternativos e pela reducao do custo da obtencao de precursores de materiais de alto desempenho tem se tornado primordial para o desenvolvimento do setor industrial de produtos com valores mais acessiveis, visando suprir a demanda de fibras de carbono de uso geral em um mercado que vem apresentando continua expansao. As fibras de poliacrilonitrila (PAN) obtidas pelo processo de extrusao mostra potencial na reducao de custo como precursor de fibras de carbono, em relacao ao processo via fiacao a umido utilizado atualmente. Essa tecnologia inovadora permite a fiacao por fusao da PAN empregando a glicerina (proveniente da producao do biodiesel) como seu principal plastificante, e dispensando o emprego de solventes altamente toxicos. Assim sendo, o presente trabalho visou obter copolimeros de PAN que fossem adequados ao processo de fiacao por extrusao convencional. Para tanto, foi utilizado para a obtencao dos copolimeros de PAN o processo de polimerizacao em suspensao aquosa e a caracterizacao foi realizada por meio da tecnica de Cromatografia de Permeacao em Gel (GPC). Os resultados mostraram que a tecnica de GPC foi apropriada para determinar as propriedades moleculares dos copolimeros de PAN e que o comonomero estireno (ES) foi adequado para a polimerizacao, gerando copolimeros de PAN-co-ES com Mn > 40.000 g/mol e Mw > 130.000 g/mol. Palavras-chave: Poliacrilonitrila, processos de polimerizacao, massa molar da PAN, fibras de PAN.

Neste trabalho são apresentados resultados de análise térmica para poliacrilonitrila (PAN) plastificada com glicerina. Foram observados os efeitos da glicerina de alta pureza (glicerol) e demais aditivos à base de glicóis na fusão e degradação térmica da PAN pela técnica de DSC sob alta taxa de aquecimento (90 °C/min) e atmosfera inerte. Foi constatado que o glicerol reduziu a temperatura de fusão da PAN de 290 °C para 217 °C. Em uma etapa preliminar foi empregado o método de Kissinger para verificar o efeito da composição química da PAN sob sua degradação térmica. A energia de ativação aparente para o copolímero de PAN foi calculada em 149 kJ.mol-1. Sugeriu-se que a presença do comonômero acetato de vinila (AV) na composição química da PAN proporcionou menor entalpia de degradação (353 J.g-1) em comparação com outros comonômeros constituintes de uma PAN precursora de fibras de carbono (988 J.g-1).

Polyacrylonitrile fiber encompasses a broad range of products based on acrylonitrile (AN) which is readily copolymerized with a wide range of ethylenic unsaturated monomers giving rise to polymers with different characteristics and applications. Such products can be designed for cost-effective, flame and heat resistant solutions for the textile industry, aircraft and automotive markets. In the present work acrylonitrile was copolymerized with vinylidene chloride (VDC) by conventional suspension polymerization process via redox system, with an initial content of 10%/mass of the VDC monomer. The copolymer average molecular weight was obtained by Gel Permeation Chromatography (GPC) and by intrinsic viscosity analysis. To control the polymerization process continuously, qualitative and quantitative analysis of the chloride content in the PAN AN/VDC copolymer structure was accomplished by using X-ray fluorescence and potentiometric titration techniques. A good correlation was found between these two techniques, leading to a straightforward verification of VDC in the polymer structure. The thermal behavior of PAN AN/VDC copolymer was performed by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The results showed that VDC monomers exhibited a nearly stoichiometric reaction with acrylonitrile, copolymerizing about 90% of its initial mass. VDC changed significantly the polyacrylonitrile thermal behavior, decreasing the polymer degradation temperature by about 40-50°C.