Plastic Material Identification with Raman Spectroscopy

Plastic material identification (including raw material and additives composition) is a key quality control requirement in the plastics industry. Current quality systems for material ID tracking are mostly based on paper trails and time-consuming, destructive laboratory tests such as differential scanning calorimetry. Non-destructive techniques such as Raman spectroscopy offer an attractive alternative, especially if the testing instrument is hand-held and can be carried to the point of test.

Recently a major recall by one of Detroit’s top three automakers was avoided with use of DeltaNu’s hand-held material analyzer. The resin manufacturer had erroneously shipped a batch of material that did not meet the OEM’s specification to the injection molder. The injection molder in turn promptly transformed the raw material into components and shipped them to the car manufacturer.

By the time the resin manufacturer realized that a mistake had been made, the components had already been installed on the automakers’ final product and the units were already sitting on the finished goods lot, waiting to be shipped to dealers. The paper trail proved to be inadequate to understand which cars had been fitted with the wrong type of material.

Upon realizing this, the resin manufacturer turned to DeltaNu for a nondestructive way to identify the cars that needed to be retrofitted with the correct components. Using DeltaNu’s technology, the resin manufacturer was able to pinpoint one by one which specific cars on the OEM lot required to be pulled back to the rework station, thus saving the automaker from reworking the whole lot or worse, issuing a recall after shipping cars with the wrong material.

Raman spectroscopy provides a method to measure the molecular composition of a sample. The Raman process measures the energy lost by light when it interacts with causes individual molecules in the sample to vibrate. The energy of the vibrations is dependent on the bond energy and the mass of the atoms associated with the bond. This leads to unique Raman spectra for every type of molecule. In other words, each substance has a different, unique Raman “fingerprint”, which can be measured and compared to a stored sample substance “fingerprint library”, thus identifying the substance. Raman spectroscopy is an ideal tool for material identification in plastics due to its unique advantages over other analytical techniques. It is a nondestructive and non-contacting method of obtaining the fingerprint spectrum of materials, requiring no special sample preparation. Raman can analyze samples via sample plastic bags, glass vials, and in aqueous solution. It does not require a large amount of a sample to do the analysis; the sample can be as small as 1–2 µm across. A short amount of measuring time, normally a few seconds, is required to obtain a Raman spectrum.

DeltaNu has developed a hand-held, lightweight material ID instrument that can store more than 500 libraries to compare against. It is operated with one hand and via a simple user menu. The resulting data is stored on a removable memory card which can be used to transfer the test results to a PC for further analysis with DeltaNu’s NuSpec suite.

For further information contact: ReporteR@deltanu.com or visit these websites (www.deltanu.com | www.intevac.com)