Effect of crosslinking density on the diffusion of antioxidant in XLPE matrices

Abstract

A Fourier Transform Infrared spectrometer equipped with a microbeam accessary and a linear translation stage with a pinhole mask was used to monitor the diffusion of antioxidant in crosslinked polyethylene (XLPE) matrices crosslinked with controlled amounts of crosslinking agent. Integration of the peak area for a characteristic peak of the antioxidant at different positions along the sample indicated the changing concentration due to diffusion within 30 days. This technique allowed us to study an antioxidant with a molecular weight in the thousand range. The diffusion coefficients calculated were in the order of 10−11 – 10−10 cm2·s−1. It was observed that the diffusion constants dramatically changed with the crosslinking density.

FTIR Microspectroscopy of Polymeric Systems

“…Polymer dissolution by small molecular weight solvents has been too rapid to examine using mapping techniques and the diffusion profiles for very limited low molecular mass substances have been mapped. The diffusion of an anti-oxidant into PE was one of the first reported examples [69]. The diffusion Cryasorb UV531 in PP [70], and Bovine Serum Albumin (BSA) in amylopectin [71] has also been examined.…”

Application of Real Time Mid-Infrared FTIR Imaging to Polymeric Systems. 1. Diffusion of Liquid Crystals into Polymers

“…For transmission infrared studies of diffusion, a thin, flat sample geometry must be used. This allows a simplified form of Fick's law to be used. ,, When combined with Beer's law, the expression for the diffusion profile takes the form of eq 1, where A is the absorbance of the diffusant peak at position x along the diffusion direction, A 0 is the absorbance of pure diffusant, erfc is the complimentary error function, D is the concentration independent diffusion coefficient, and t is the diffusion time.…”