Abstract
A hot stage attached with a two-beam interference (Pluta) microscope was used to apply a heating-cooling cycle (HCC) on low-density polyethylene fibres (LDPE). The variation of the refractive indices (n vertical bar and n perpendicular to) with the temperature was carried out during the heating and cooling of the LDPE fibres. The activation energy (Ea) and thermooptic coefficient (dn/dT) were calculated for the investigated LDPE fibres. The spectral dispersion curves, percent crystallinity and orientation function were determined for the treated LDPE fibres. It was found that the HCC for LDPE fibre implies: a reversible behaviour of both optical and structural properties against temperature and an improvement in the fibre crystallinity.