Color concentrates or master batches are used to pigment polymer formulations. These master batches contain a high concentration of colorant and other additives in a polymer matrix which is then diluted or “let down” with virgin resin during injection molding of the desired part. When there is a change of colorant master batch vendors, injection molders and/or their clients need to conduct a comparative analysis in order to verify that the change provides a similar chemical composition and does not adversely affect the molding process or the part.
In the current example, the client desired to determine whether two master batches were equivalent.
The analysis of the two ‘as received’ master batch pellets was simply done by visual inspection and solvent extraction to remove the polycarbonate resin followed by Fourier transform infrared spectroscopy (FTIR) analysis of the insoluble fraction which is mainly the inorganic/organometallic colorant.
FTIR spectra of both ‘as received’ master batch samples indicate the polymer matrix is consistent with bisphenol-A polycarbonate. There was no indication of the colorants. Based on the identification of the polymer, methylene chloride was selected to dissolve the polycarbonate resin and separate it from the inorganic colorant components.
Visual inspection of the two samples in methylene chloride before/after centrifuging and after filtration show significant differences in the colors of the insoluble/soluble fractions and settling tendency of the two samples.
The IR spectra of the two dried solvents isolated after centrifuging (red traces) are compared in the Figure.
The two IR spectra are very different.
While the Master Batch B sample IR spectrum exhibited residual polycarbonate, it had only end absorbance (TiO2 ?) in the IR spectrum.
The IR spectrum of the Master Batch A exhibited absorbance bands suggestive of aluminosilicate, TiO2 and a secondary amide.
Conclusion and Benefit to the Customer
Within a short period of time using common sense and FTIR spectroscopy, ANALYZE was able to determine that the master batches from the two vendors were not equivalent and could not be used in the same medical device.