What changed? A comprehensive analysis of polymeric failure

It’s almost inevitable: a new supplier begins supplying the exact same part as the old supplier, and – you guessed it – the product begins to fail in the field. Manufacturers employing plastic parts routinely face the challenge of analyzing failed parts to determine the root cause and corrective actions.

Root Cause Analysis is used to identify and correct process issues

In this application note, our story follows a manufacturer of precision optical equipment that designed a plastic cover for a device with specifications for chemical composition, surface texture, color and optical transmission to ensure the correct diffuse transmission. A re-engineering project was subsequently initiated to reduce costs and make the product more competitive.  Initially, all parts supplied met the specifications and the product provided satisfactory performance, but shortly thereafter, the product began to fail critical performance tests. A Root Cause Analysis using many techniques for polymer testing was undertaken to identify and contain the issue.

The tools used to perform this analysis include infrared and Raman spectroscopy for chemical composition, UV-Visible spectroscopy for color and optical transmissivity, and thermal analysis for determination of physical properties.

It turned out that a switch of suppliers for the polycarbonate molded plastic covers led to failures of a precision optical measurement device. Ambient light leaking into the device caused erroneous measurements for low light level measurements. Diffuse transmission measurement of the parts by UV-Visible spectroscopy confirmed that the failed cover did not meet the specification for maximum transmittance. 

Follow the mystery failure analysis as this application note details the root cause analysis of the polycarbonate cover, made of an acrylonitrile butadiene styrene (PC-ABS) blend, using UV-Vis spectroscopy, thermal gravimetric analysis (TGA), infrared and FT-Raman spectroscopy.  The root cause of the failure tracked with the lower rutile content, and corrective action was implemented.