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Epoxy resin is a versatile high-performance thermosetting material with attractive properties for many engineering applications. However, epoxy resins may come into contact with various chemical liquid environments while in service which can degrade their mechanical properties and deteriorate their performance. Water diffusion into epoxy resins is well-studied; however, little research has been reported on the diffusion mechanisms of other liquids/ solvents and their mixtures. Therefore, this study addresses this gap through the use of gravimetric analysis to investigate the absorption of water and various chemical liquids, and their mixtures into epoxy resin. The liquid diffusion characterizations, which include weight gain, diffusion coefficients, and edge effects have been investigated. A two-stage absorption process was observed for water, ethanol, methanol, and their mixtures. A unique three-stage diffusion process of butyl formate, decalin, and their mixtures in 977-2 epoxy resin was observed. A correction factor was used to account for the edge effects. The experimental results showed a dependency of saturation levels and diffusion coefficients on the polarity of the liquids and on the interaction level between the penetrants and the polymer. Furthermore, the absorption rate of the binary mixtures is intermediate between the rates of either penetrant. KEYWORDS edge effects, epoxy resin, liquids absorption, moisture diffusion, two-stage moisture uptake, 1 | INTRODUCTION Exposure of polymers to chemical liquids is a crucial mechanism for degradation in polymeric materials, therefore it is important to understand the diffusion mechanism and long-term effects [...]

The long-term water absorption behavior of UD and [+ or -]45 carbon fiber/977-2 epoxy composite and unreinforced 977-2 epoxy resin has been studied at different environments with various temperatures and relative humidities. Fickian behavior was noticed initially followed by a slight and continuing increase in saturation with time, a behavior that continues for at least 4 years. Fickian saturation and diffusion coefficients of all materials were derived using graphical method. Initial Fickian equilibrium moisture contents were found not to be dependent on temperature but the long-term increase in solubility increased with temperature. Absorption rates showed strong dependency on temperature and relative humidity. The activation energy values for all materials in the initial stage found to be much higher (40 kJ/mole) than the long-term stage (10 kJ/mole). [E.sub.a] values of the neat resin were observed to be slightly lower than the composites. The slow continued weight gain in the long-term absorption experiments has been seen to be coupled with an incomplete drying and a higher diffusion rate on drying and subsequent re-conditioning. The possible reasons and mechanisms for the long-term gradual increase in moisture absorption was further investigated. It was found that molecular relaxation is the most likely dominant mechanism. POLYM. ENG. SCI., 58:2175-2184, 2018., INTRODUCTIONComposite materials have been used for many years in many engineering applications due to their superior properties. Polymer composites are often used in contact with liquids and vapors, either organic [...]

Due to the increasing demands on automotive components, manufacturers are relying on injection moulding components from fibre-reinforced polymers in an attempt to increase strength to weight ratio. The use of reinforcing fibres in injection moulded components has led to component failures whereby the material strength is hampered through the formation of weldlines which are also a problem for unreinforced plastics. In this study, an industrial demonstrator component has the injection locations verified through a combination of fibre orientation tensor simulation and optical microscopy analysis of key locations on the component. Furthermore, the automotive component manufactured from 30% glass fibre–reinforced polyamide 6-6 is simulated and optimized through a Taguchi parametric study. A comparison is made between the component, as it is currently manufactured, and the optimum processing parameters determined by the study. It was found that the component can be manufactured with roughly 7.5% fewer weldlines and with a mould fill time 132 ms quicker than the current manufacturing process. [ABSTRACT FROM AUTHOR]

Water diffusion into composites in different directions was examined in this study with the aim of determining the best way of measuring diffusion coefficients and to provide values to compare with model predictions. Water absorption behavior of unreinforced epoxy resins and carbon fiber reinforced epoxy composite materials was investigated with long‐term exposure to different environmental conditions. Initial Fickian absorption was observed followed by a slower second stage that continues for at least 3.7 years. Fiber architecture was found to be an important aspect of controlling absorption, where water diffusion along fibers was observed to be about three times faster than across the fibers and about seven times faster than through the thickness. A three‐dimensional finite element computer model based on Fickian diffusion behavior was developed to predict the levels of moisture absorption under hot/humid environments. A multi‐scale modeling approach was used which allowed the results of simulations at the micro‐structural level to be used to predict the diffusivity in different directions. The modeled diffusion coefficients showed high dependency on the detailed micro‐structure. Experimental results provided a baseline for the validation of the model, and it was found that these data could be closely predicted using a reasonable micro‐structure characterization. POLYM. COMPOS., 39:E2305–E2315, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Defects in polymer composites associated with in‐service damage induced by impact and those produced by environmental degradation due moisture absorption can have a significant influence on the mechanical properties and failure modes of the structures. This study evaluates the flexural characteristics and failure modes of ±45° carbon/epoxy laminates under different conditions. The flexural strength and stiffness of these composites were inspected before and after subjecting to water absorption, drying, re‐drying and low energy impact. It was observed that both absorbed water and low energy impact caused significant deformations and fractures which drastically reduced the load carrying ability of the ±45° carbon/epoxy laminates. Re‐drying slightly improved the properties and reversed the effects of water. POLYM. COMPOS., 39:2771–2782, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]