I have a component made up of Nylon and carbon fibre and it is moulded.
Can someome please explain how to evaluate the quantitative percentage of carbon fibre present in this composite. I know the base material is Nylon and it is a carbon fibre reinforced polymer. I wanted to measure the exact percentage.
If you measure the density of the composite by immersing the sample in water and calculate it by Archimedes principle you will be able to know empirically the weight percentage of the carbon and Nylon as long as you know their individual densities.
If you measure the density of the composite by immersing the sample in water and calculate it by Archimedes principle you will be able to know empirically the weight percentage of the carbon and Nylon as long as you know their individual densities.
We would digest the component in hot sulphuric acid (be very careful) Once the fibres are floating around, add hydrogen peroxide slowly dropwise to hot mixture. Be very careful! Peroxide will oxidise carbonise nylon. When solution is clear filter through glass crucible! Weigh back.
@abrie myburgh thank you very much for the reply. Can you update me what are the quantities involved for the same any ASTM this links back to?
I did this long ago in the Aerospace workplace. Our common friend Mr.Google should help you with this. There is a sulphuric/nitric digestion also out there, but we went the Sulphuric/peroxide route.
Thermal Gravimetric Analysis (TGA) is a very suitable method for this type of problems.
There are two ways to suggest. One is to determine the density of the composite, based on the table data of the density of nylon and carbon fibers, determine their ratio. Another is to burn out the nylon in the oven at a temperature of up to 200-250 degrees and weigh the fiber that has gone away. And there and there remains the problem of porosity
Petr , this is what TGA does - it burns a sample in very controlled way. The advantages of TGA methods include: small samples, easy preparation, no aggressive wet chemistry involving strong acids and oxidizers. It is also reasonably quick. Ramping T to 600 C at 5C/min will take just a couple hours. This is much faster than traditional gravimetric methods where bringing crucibles to constant weight would take multiple hours.
TGA and ashes (burn the sample) methods are adequate to determine fiber content, however, if you have a non homogeneous fiber dispersión in the sample, when you take a sample in "mg" for TGA is posible a not correct determination. I suggest both techniques.
Quantitative metallography, which is relatively simple for such a material, will enables you to determine the fibers as well as the porosity contents. The rest is the volume fraction of the matrix.
In case of carbon fiber – Nylon composite it is difficult to evaluate the percent of each constituent based on the density calculation since the difference between the density of carbon fiber and nylon is around 6% which is practically within the calculation and measurements errors but it is feasible to solve based on the mechanical properties like tensile stress or modules of elasticity as there is wide gap between these values.
Best regards
TGA seems to work best here. Most nylons form no or little char when pyrolyzed under nitrogen, enabling thus a quantitative analysis of the composite's constituents. Run a TGA experiment at max. 20'C/min under pure nitrogen flow up to 650'C followed by switching the purge gas atmosphere to air or oxygen and combusting the carbon fibers isothermally at 650'C or at a temperature ramp to 1000'C. If residual ash is present, adjust your calculations accordingly.
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