Optics and Lasers in Engineering 46 (2008) 328–335 Determining the opto-mechanical and geometrical properties of high-density polyethylene fibres M.A. El-Bakary Physics Department, Faculty of Science, Mansoura University, Mansoura 35516, Egypt Received 9 April 2007; accepted 19 November 2007 Available online 10 January 2008 Abstract A method is described to determine the opto-mechanical and geometrical properties of high-density polyethylene, HDPE, fibres at the same time for the same region from the fibre. Variations of the transverse sectional shapes, areas, optical and mechanical properties of fibres during the cold drawing process were investigated. A rotator-mechanical drawing device was used for rotating the fibre around its longitudinal axis during the cold drawing process. The Pluta polarizing two-beam interference microscope was attached with the rotator- mechanical drawing device for detecting these variations under the interferometer. The rotator-mechanical drawing device permits determining the tensile stress–strain curve, Poisson’s ratio and strain optical coefficient for HDPE fibres. Also, it permits determining the refractive index profile of the drawn fibres taking into considering the transverse sectional area and the enclosed area under the fringe shift. The optical orientation factor and orientation angle was calculated for HDPE fibre to clarify the orientation of molecules during the cold drawing process. Microinterferograms are utilized for illustrations. r 2007 Elsevier Ltd. All rights reserved. Keywords: Opto-mechanical; HDPE fibre; Transverse sectional area; Birefringence profile 1. Introduction High-density polyethylene HDPE fibre is widely used in various fields; therefore, its tensile properties have been studied extensively. The fibre structure is a semi-crystalline polymer composed of lamella crystals, which are typically arranged as spherulites when cooled from the melt [1]. The mechanical properties of this fibre leads to an increase in the understanding of the behaviour of polymeric structure potentially resulting in the development of new synthetic fibres for structural applications spun from aqueous solutions [2]. The most important mechanical property of such a fibre is its tensile stress–strain curve, since it determines the response of the fibre to deformation along the fibre axis. The stress–strain response of high perfor- mance polymer fibre [3] is controlled by the ability of molecules in the material to support the applied stress [2]. Young and Eichhorn [4] used the spectroscopic and X-ray diffraction techniques to develop the understanding of the deformation micromechanics of both synthetic and natural fibres. Kromm et al. [5] characterized the mechanical properties of ultra high molecular weight PE fibres from the tensile and creep tests on single filament. Also, investigations of the geometrical parameters of fibres are very important for textile and dying industries. The transverse sectional shape contributes to the surface appearance of the fibre. The softness of fibres is governed by the fibre thickness. Studying the variations of the transverse sectional shapes of fibres due to the variation of their mechanical drawing is very important for textile production [6]. It gives information about maximum draw ratio before the fibre structure is destroyed. Also, the geometrical parameters of fibres at different draw ratio permits specifying the suitable draw ratio value for the required application [6]. The produced optical anisotropy in fibres by mechanical drawing gives valuable information for the characteriza- tion of these fibres on the molecular level. The drawn fibres reveal the transverse birefringence gradients in optical anisotropy when both refractive indices are measured at ARTICLE IN PRESS www.elsevier.com/locate/optlaseng 0143-8166/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlaseng.2007.11.007 E-mail address: elbakary2@yahoo.com