You can distinguish PC/ABS by measuring the glass transition temperatures on a differential scanning calorimeter (DSC). PC/ABS will have two glass transitions (Tg), one at 85-105 deg. C for the ABS and one at 155 deg. C
for the PC. This method will not be very good for determining PC to ABS ratio.
Another method that will give a qualitative estimate of ABS content is to measure modulus vs. temp using dynamic mechanical analysis (DMA). The modulus will drop at the glass transition temperatures of ABS and PC. The plateau modulus of the material at temperatures above the Tg of ABS and below the Tg of PC will be an indicator of PC to ABS ratio. You would need standards against which to compare. GE has DMA curves for most of their PC/ABS products on their web site:
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There are numerous peaks in an FTIR spectrum of PC/ABS attributed to butadiene. Unfortunately, I do not have any reference spectra available to tell you for what peaks to look. Also, depending on the type of ABS, there can be IR peaks from the high heat additives such as alpha methyl styrene, para methyl styrene or n-phenyl maleimide. If you are seeing only PC in the IR then possibly you only have PC.
There are numerous labs that can perform DSC and FTIR (or old fashioned diffraction IR), including:
Detroit Testing Laboratory (DSC & FTIR), Warren, Michigan
Constellation Technology Corporation (DMA), Tampa, Florida
