On gel determination in PA6-glass fiber composites

Engineering plastics are frequently reinforced but the testing procedures are in many cases significantly affected by the presence of the reinforcing agent. A method for gel content determination in PA-6/glass fiber composite crosslinked by irradiation was investigated based on extraction of the sample fraction soluble in 90% formic acid. The sample, wrapped in glass fabric, was treated under ten selected modes to optimize the analysis. Shape of the analyzed sample was shown to be important. Applying statistical tests to the results, an optimal procedure was developed that consisted of sample extraction by the solvent under mild shaking for 24 h and then removing the excessive solvent followed by drying the sample. A correction for the fraction of the glass fabric lubricant extractable by the solvent was necessary for calculation of correct results. A gel content of approximately 60 wt.% was determined with relative standard deviation less than 5%.