January 16, 2013
GAITHERSBURG, MD. (Jan. 16, 2:25 p.m. ET) — The National Institute of Standards and Technology (NIST) has developed an enhanced form of chemical microscopy that can reveal in detail the interaction between molecules in blended polymers. The technique could prove useful for estimating the life cycle of polyethylene water pipes and joints.
Although PE water pipes have a predicted service life of up to 100 years, current tests are unable to accurately predict service life under field conditions, particularly at fusion joints. Water pipes are predominantly made from a blend of high and linear low density PE.
NIST materials scientist Young Jong Lee says that the combination improves the toughness, strength and fracture resistance of the polymer but, until now, we did not know exactly how this interaction works.
HDPE and LLDPE are so close chemically that it has been impossible to distinguish one from the other using X-ray or scanning electron microscopy. NIST’s development, which it calls BCARS (short for Broadband Coherent Anti-Stokes Raman Scattering) uses two lasers to analyse the frequencies associated with the different vibrational modes of each molecule.
By controlling the polarization of the light, the technique provides additional details on the local crystal orientation of molecules in the polymer. The images show, for example, the formation of microscopic spherical regions of partial crystallization with the LLDPE more concentrated towards the center.
Lee said: “This is a fast, three-dimensional chemical imaging technique that’s particularly useful for studying microstructures of polymeric materials”. The group is currently using BCARS to find the correlation between microscopic structures with characteristics of deformation and thermal fusion on PE pipes.