Could you pyrolyse the composite, and use the weight loss to indicate PVA content? You may have to use the weight change starting from a temperature well above ambient, but below PVA decomposition. This would reduce interference from adsorbed water. Final temperature should be high enough to ignite all carbon residue from the polymer...this needs to be checked, but likely 450C or more.
I recommed for you to go through the content of the link below as the article contain clear and valuable princible detail about the methods to determine fiber volume fractions ,then if you have more explanations please let me know.
Dear Balaji Venkatachalam, you have to perform a TG/DTA analysis to understand the thermal properties of the sample, and you can also calculate the mass loss (%) and estimate the amount of PVA fiber (Since Aluminium oxide do not decompose or evaporate before PVA). You also should perform TG/DTA analysis of pure PVA and pure Aluminium oxide.
Another important analysis is N2 adsorption (Using BET method, or other) and porosimetry (argon, helium, mercury...), to understand the changes in the volume and estimate the occupied fiber volume.