The glass fibers (specifically in fiber-reinforced epoxy composites) at higher temperatures turn into just pure glass at higher temperatures in TGA and the weight loss just stops at a certain point (as seen in the figure). What is the exact microstructural/chemical composition change that the fibers undergo? Why don't they completely degrade like other fibers such as carbon fibers?
Glass fibers made of silicate and oxides of other alkaline ions. These inorganic compounds do not degrade below 1000oC which is the temperature you examined. The fiber does melt in the vicinity of 800oC (if you used the standard E-glass fiber), but does not evaporate. When you examine glass fiber reinforced epoxy, only the epoxy portion first degrade around 400-500oC, chars (if you examine it under nitrogen) or decomposes and evaporates (if you examine it under air). If you are interested in knowing the fiber content, you can examine the composite under air. The fiber content is the remaining weight at 800oC under air. The only errors you can expect is the very small weight reduction from the surface of the fiber (less than a few percent) due to the chemical reaction of the surface species as well as evaporation of the water around the interface.
Dear Tayyab,
The maximum temperature you used is 800C which is not even close to the melting point of glass. The degradation in your thermograph is the binding epoxy plus the oxygen-based impurities that might be attached on the surface of the glass fibres (e.g. hydroxyls).
Furthermore, you mentioned that carbon fibers completely degrade, which is not the case: carbon degrades at even higher temperatures. However, carbon can escape as CO or CO2 if there is enough oxygen or impurities on your carbon fibers. Also carbon fibres are usually coated with epoxy or vinylester (i.e. sizing agents) which also contributes to the degradation of such components.
Regards,
Orestis.
you increased the temperature to 700 ° C, which is the degradation temperature of organic matter so that it does not degrade because these fibers soften up to 1200 ° C (There is no real melting point) where it begins to degrade
Pure material represent suitable because increased obtain in impure
Regard
Hi
Actually glass fibre are made of ceramics. In general our heating scan may start from RT to maximum of 1000 0C. but glass fibre ceramics high in specific heat absorption and they need minimum of 2500 oC to undergo any change so glass fibres are remains aft TGA scan.
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