This instrument transmits an infrared light through a sample and varies the wavelength of the light as it records how much light is absorbed at w wavelength. Your basket is empty. FTIR can identify the difference between materials, such as polypropylene and polyethylene, which 1e made of only carbon and hydrogen but have different types of bonds between the elements. Standards can be obtained from appropriate standards authorities.
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Example: metals do not absorb infrared light. FTIR is the first logical step in identifying a polymer. FTIR is also used for quality control of materials and for contamination analysis surface or internal. The resulting spectral scan absorbance or transmittance is usually specific to a general class of material.
Example: the spectral scan of Polycarbonate does not look like the scan of Nylon but all Nylon scans have unique similarities. Unknown spectral scans can be analyzed to determine the base material of the unknown by comparing their scan to spectral scans of known materials that are stored in a computer-based library.
A typical infrared scan is generated in the mid-infrared region of the light spectrum. The mid-infrared region is from to wavenumbers, which equals wavelengths of 2.
Matching the unknown infrared spectrum to known spectra can be done manually or with the help of a computerized program. Computerized spectral searches can quickly compare an unknown spectrum to a very large number of spectra located in multiple databases in a very short period of time. Computerized spectral matches to the unknown spectral scan are presented from best to worst with assigned certainty ratings.
Computer programs are very helpful for comparing unknown spectral scans to those of known materials, but computer selected matches can be misleading. A skilled FTIR analyst is needed to examine the computer selected spectral matches to ensure that sample identifications are both accurate and complete. Computer matching programs have difficulties with subtle differences that can be critically important.
Samples, which can be easily tested by reflective FTIR, include polymer pellets, parts, opaque samples, fibers, powders, wire coatings, and liquids. Materials with large quantities of carbon carbon black or carbon fiber are difficult to obtain a usable spectral scan from because carbon strongly absorbs infrared light in a broad range of frequencies.
This results in an FTIR spectrum without the minute details necessary to identify the unknown material. The better the match, the higher the certainty for a correct identification of the unknown polymer. However, an FTIR spectral scan alone should not be expected to identify the type of Nylon or Polyester, identify a Polypropylene or Acetal as a homopolymer or copolymer, or determine whether the Polyethylene is a high density or low density material.
Further identification may be aided by DSC. Further identification may be aided by an Ash Test. Quality Control: A spectral scan of a reference material can be generated and stored in a spectral library database. A stored reference scan will allow all future material scans to be compared back to the same earlier scan.
The objective is to look for material differences. Differences noted in a newly generated spectral scan could indicate a change in processing or a possible contamination problem. A computer program is used to subtract the peaks associated with the base polymer from the spectral scan and then an analysis of the remaining spectral scan is performed. The amount of contamination that can be detected depends on the spectral scans of the base polymer and the contaminant. Surface Contamination: Obvious surface contamination of polymers can be analyzed by normal reflective FTIR because the infrared beam only enters a few microns into the sample surface.
A solvent wash involves using a solvent that is nondestructive to the sample. Once the solvent is evaporated off an FTIR analysis is performed on the solvent wash residue. Standards can be obtained from appropriate standards authorities.
ASTM E1252 PDF
Purpose: Identify the primary component of a plastic, rubber, or organic material. Basic Description: This instrument transmits an infrared light through a sample and varies the wavelength of the light as it records how much light is absorbed at each wavelength. The resulting spectrum can be searched against a computerized database containing known spectra for thousands of organic materials. FTIR can identify the difference between materials, such as polypropylene and polyethylene, which are made of only carbon and hydrogen but have different types of bonds between the elements.
ASTM E1252 - FTIR ANALYSIS TESTING SERVICES
Fourier Transform Infrared Spectrometry ASTM E168, ASTM E1252