Abstract
Short fiber reinforced polymers are widely used in the construction of electronic housings, where they are often exposed to harsh environmental conditions. The main purpose of this work is the in-depth study and characterization of the water uptake behavior of PBT-GF30 (polybutylene terephthalate with 30% of short glass fiber)as well as its consequent effect on the mechanical properties of the material. Further analysis was conducted to determine at which temperature range PBT-GF30 starts experiencing chemical changes. The influence of testing procedures and conditions on the evaluation of these effects was analyzed, also drawing comparisons with previous studies. The water absorption behavior was studied through gravimetric tests at 35, 70, and 130 °C. Fiber-free PBT was also studied at 35 °C for comparison purposes. The effect of water and temperature on the mechanical properties was analyzed through bulk tensile tests. The material was tested for the three temperatures in the as-supplied state (without drying or aging). Afterwards, PBT-GF30 was tested at room temperature following water immersion at the three temperatures. Chemical changes in the material were also analyzed through Fourier-transform infrared spectroscopy (FTIR). It was concluded that the water diffusion behavior is Fickian and that PBT absorbs more water than PBT-GF30 but at a slightly higher rate. However, temperature was found to have a more significant influence on the rate of water diffusion of PBT-GF30 than fiber content did. Temperature has a significant influence on the mechanical properties of the material. Humidity contributes to a slight drop in stiffness and strength, not showing a clear dependence on water uptake. This decrease in mechanical properties occurs due to the relaxation of the polymeric chain promoted by water ingress. Between 80 and 85 °C, after water immersion, the FTIR profile of the material changes, which suggests chemical changes in the PBT. The water absorption was simulated through heat transfer analogy with good results. From the developed numerical simulation, the minimum plate size to maintain the water ingress unidirectional was 30 mm, which was validated experimentally.
Highlights
Composite materials, and especially fiber-reinforced polymers (FRP), have been increasingly representing a low-weight alternative to conventional materials such as steel, as they present high specific properties such as stiffness and strength [1,2]
FRP can even be subjected to severe environmental conditions when they are used in infrastructures immersed in water such as fixed or floating composite bumper systems, for instance in bridges or in structures to support solar panels in water [4]
Moisture generally promotes degradation of the polymer, which can happen even when subjected to usual atmospheric humidity [6,7]; it is crucial to understand how the properties of composite materials change when exposed to water
Summary
Especially fiber-reinforced polymers (FRP), have been increasingly representing a low-weight alternative to conventional materials such as steel, as they present high specific properties such as stiffness and strength [1,2]. The moisture uptake of PBT and its glass fiber composites, with different volume fractions of fibers, was shown to follow the Fick’s law for water absorption regardless of the temperature of the water where the material is immersed [30]. Ishak et al [21] studied the effect of moisture aging on fiber-free PBT and PBT with 10% short glass fiber in volume at two different levels of relative humidity, 81.2 and. For high temperature (90 ◦ C), the toughness of the material decreases significantly At this higher temperature, fiber-free PBT and PBT with 18% short glass fiber were analyzed through the determination of the pH and FTIR profile of the water where it has been immersed. The mechanical performance of the bulk tensile tests was simulated to complement the experimental results
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