Meaning
Natural isotopes provide a nuclear spin that allows for detailed mapping of polymer chains. Analysis of carbon-13 nuclei via nuclear magnetic resonance spectroscopy reveals the exact sequence of monomers in a copolymer. This isotope accounts for approximately 1.1 percent of all natural carbon.
It enables a laboratory to distinguish between high density and low density polyethylene by observing the branching frequency.
Molecular Identification
Spectroscopic data provide a signature of the chemical environment for every atom in a resin sample. The presence of carbon-13 allows the identification of tacticity in polypropylene, which determines whether the methyl groups are arranged on one side or alternating sides of the backbone. Such structural detail dictates the final crystallinity and stiffness of the molded part.
Every peak in the spectrum corresponds to a specific carbon position.
Isotopic Ratio
Specific ratios between different isotopes allow for the verification of bio-based content in polymer blends. Because plants fix carbon-13 at different rates than fossil sources, the measurement of this isotope provides a way to audit sustainability claims.
Purity Verification
Detectable shifts in resonance peaks signal the presence of additives or degradation products. While carbon-13 is naturally occurring, its signals change when oxygen atoms or other functional groups attach to the chain during thermal processing. These deviations alert a processor to material oxidation that could lead to brittle failure.
Heat history leaves a trace.
