Estudo da influência do condicionamento higrotérmico nas propriedades viscoelásticas de compósitos termoplásticos

Abstract

ResumoO contínuo crescimento na utilização de compósitos termoplásticos em componentes estruturais na indústria aeroespacial deve-se, primordialmente, à flexibilidade de projeto, excelência de suas propriedades mecânicas e baixa massa específica, aliadas aos elevados valores de resistência mecânica e rigidez e baixa incidência de corrosão. No entanto, componentes que requerem exigências estruturais, quando expostos a ambientes agressivos como elevada temperatura e umidade, podem ter suas propriedades mecânicas sensibilizadas por esses fatores ambientais, e devem ser cuidadosamente avaliados antes de serem colocados em serviço. Embora existam diversos trabalhos na literatura reportando este problema para compósitos estruturais, poucos estudos relacionam, de maneira sistemática, a avaliação da absorção de umidade com o comportamento viscoelástico de matrizes de PPS reforçadas com fibras de carbono, quando este compósito é utilizado em aplicações aeronáuticas. Sendo assim, o objetivo deste trabalho é avaliar a influência do condicionamento higrotérmico nas propriedades viscoelásticas de laminados PPS/fibras de carbono. Os resultados mostram que os laminados condicionados em câmara higrotérmica apresentaram absorção de umidade segundo as leis de Fick, porém, não foram observadas variações significativas na temperatura de transição vítrea quando comparado compósitos condicionados e não condicionados. Palavras-chave: compósitos termoplásticos, efeito higrotérmico, propriedades mecânicas. AbstractContinued growth in the use of thermoplastic composites for structural components in the aerospace industry due, primarily, to the design flexibility, excellent mechanical properties and low density, combined with the high values of strength and stiffness and low incidence of corrosion meeting the stringent performance requirements of these structures while in service. However, components that requires structural requirements when exposed to harsh environments such as high temperature and moisture, can have their mechanical properties reduced by these environmental factors, and should be carefully evaluated before being placed in service. Although there are several studies in the literature reporting this problem for structural composites, few studies relate in a systematic way, assessing the moisture absorption with the viscoelastic behavior of PPS matrix reinforced with carbon fibers, when the composite is used in aeronautical applications. Thus, the aim of this study is to evaluate the influence of hygrothermal conditioning on the viscoelastic properties of PPS/carbon fiber composites. The results show that the laminates conditioned in a hygrothermal chamber had moisture absorption according to Fick laws, but it was not observed a significant glass transition temperature variation when compared conditioned and not conditioned specimens.

Structure, Thermal, and Mechanical Behavior of the Polysulfone Solution Impregnated Unidirectional Carbon Fiber Yarns

“…As it was shown in [29], the moisture absorption for epoxy-based composites reinforced with both glass and carbon fabrics was nearly the same, whereas for polyphenylene sulfide-based composites, replacing the reinforcers from glass to carbon fabrics resulted in the decreases in moisture absorption magnitude from 0.2 to 0.06%. Thus, it can be concluded that the combination of polysulfones as matrix polymers with continuous carbon fibers as reinforcers provides excellent resistance to the combined effect of temperature changes and moisture absorption, which was confirmed in several experimental investigations [30][31][32]. It should be noted that the melt viscosity of the most of the high performance thermoplastics is much higher, being two to three orders of magnitude higher than thermoset polymers (in the range of 10 2 -10 4 Pa•s) [33].…”

Mechanical Performance of Carbon Fiber/Polyamide 6: Comparative Study Between Conditioning in Distilled Water with Heating and Saline Solution

“…Thus, it is essential to know the diffusion coefficient since the moisture absorbed by the polymeric composites can cause significant changes in the physico-chemical characteristics of the matrix. This behavior can reduce the mechanical strength and stiffness of the material due to the plasticization effect of the matrix, making the material more ductile, leading to the weakening of the fiber/matrix interface and, consequently, detaching the fiber/matrix interface and degrading the laminate structure 24 .…”

A review on research, application, processing, and recycling of PPS based materials

“…At the same time, Faria et al [90] evaluated the influence of hygrothermal conditioning on the viscoelastic properties of PPS/CF laminates. Plasticization of the polymer matrix is one of the most pronounced effects of moisture absorption, reducing the glass transition temperature.…”