M. A. El-Bakary

Determination of spectral dispersion curves of polypropylene fibres

A new mathematical formula is derived to determine the spectral dispersion curve of a fibre having a circular cross sectional shape. This formula depends on the principle of a variable wavelength interferometric technique taking into consideration the area under the fringe shift instead of the fringe shift itself. This method overcomes the difficulty of the presence of any irregularity of the transverse circular cross sectional shape of the fibre. Analysis of the new mathematical formula is given and applied experimentally for polypropylene fibres with draw ratio 3.5 and 4.0. Optical microscopy and optical diffraction methods are used to determine the cross sectional area of the fibres. Also, conventional VAWI and two-beam methods are applied for these fibres to confirm the results of the new analysis. Microinterferograms are given for illustration.

Detection of the variation of the optical and geometrical parameters of fibres due to the cold drawing process

A method is described to detect the variation of the refractive index profile, transverse sectional shapes, areas and mechanical properties of fibres during the cold drawing process. A rotator-mechanical drawing device is used for rotating the fibre around its longitudinal axis during the cold drawing process for the fibre from the two fixed ends. In this method, the rotator-mechanical drawing device is attached with a Pluta polarizing interference microscope for detecting the variation of the geometrical dimensions of fibres in front of the interferometer. The suggested method permits determining the refractive index profile of the drawn fibres taking into consideration the transverse sectional area and the enclosed area under the fringe shift. Nylon 6 and polypropylene fibres are used in this investigation. The optical orientation factor and orientation angle are calculated for these fibres to clarify the orientation of molecules due to the cold drawing process. Microinterferograms are given for illustration.

An interferometric method for studying the influence of temperature on the mean refractive indices and cross-sectional area of irregular fibres

An interferometric method using a double refracting polarizing interference microscope is suggested to solve the problem of determination of the mean cross-sectional area of irregular fibres. Using this method and a hot-stage device attached to the Pluta polarizing interference microscope, the influence of temperature on the refractive indices and the mean cross-sectional area of two samples of acrylic fibres (Co-polymer of acrylonitrile with another vinyl monomer and Dralon) are studied. This investigation gives information about the opto-thermal behavior of these irregular fibres. Microinterferograms are given for illustration.

Effect of annealing on the optical and mechanical properties of cold drawn polypropylene fibres

Refractive indices and birefringence changes with strain produced by different stresses in annealed and unannealed polypropylene fibres (4 :1 draw ratio, 515 tex polypropylene from Bolton, UK) were measured interferometrically. Calculations were carried out using multiple-beam Fizeau fringes in transmission to determine the Cauchys constants, dispersive coefficient and the dielectric constant at infinity. The orientation factor and orientation angle of the fibre material were calculated for different strain values. Poissons ratio and the strain optical coefficient were also determined. An empirical formula is suggested to correlate the orientation factor, orientation angle, area of cross-section and birefringence with the draw ratio, and the constants of this formula were determined. The effect of the draw ratio on the refractive index profile was studied. Microinterferograms and curves are given as illustrations.

The spectral dispersion curves of highly oriented fibres

Spectral dispersion curves of the refractive indices and birefringence of highly oriented fibres [poly(ethylene 2,6-naphthalene-dicarboxylate) (1000 denier/248 filaments, PEN-Q50M4; PEN), poly(ethylene terephthalate) (PET), Seun yarn (meta-aramid fibres, Teijin Japan; CONEX) and Technora T-240 (1000 denier/667 filaments aramid fibres, Teijin Japan; TECHNORA)] have investigated using the automatic variable-wavelength interferometric (VAWI) technique. This technique is especially recommended for measuring the refractive indices of highly oriented fibres. The polarizabilities per unit volume are calculated for these fibres and the molecular orientation function of PEN and PET are determined. Microinterferograms are given for illustration.

Determining the optical properties of highly oriented fibres using a multiple-beam technique

Mathematical formulae are modified for the shape of multiple-beam Fizeau fringes in transmission to determine the mean refractive indices and birefringence of highly oriented fibres. These modified mathematical formulae are applied with the multiple-beam interference method to determine the optical anisotropy of polypropylene fibre with a draw ratio of 3.5. The refractive indices and birefringence results are compared with those obtained using the conventional method and are found to be in good agreement. The new method is also applied for (poly(ethylene 2,6-naphthalene-dicarboxylate), 1000 denier/248 filaments, PEN-Q50M4 (PEN) and poly(ethylene terephthalate) 1000 denier/250 filaments, PET-BHT, highly oriented yarn, Teijin, Japan (PET)) highly oriented fibres. Illustrations are given through microinterferograms.

Opto-thermal properties of fibres: 3-effect of anisotropic optical parameters in polypropylene fibres as a function of annealing process

Abstract This study deals with the changes in the optical properties of polypropylene fibres (4:1 draw ratio 515 tex polypropylene, Bolton, UK) due to the effect of thermal annealing on its structural characteristics. Changes in the structure of annealed polypropylene fibres at a constant time of 2 h and different temperatures (60–140 °C) were studied interferometrically. The diffraction of a He-Ne laser beam was used to measure the dimensional parameters transverse sectional shape and the area of the polypropylene fibres sections. An optical microscope was used to confirm the geometrical parameters of the cross-sections. The diffraction technique was utilized to study the effect of annealing on swelling factors of these fibres for some different liquids at room temperature 19 ± 1 °C. Two methods were applied for the measurement of the refractive indices and birefringence of the polypropylene annealed and unannealed fibres. The first was concerned with the application of the Becke-line method for determining the refractive indices and the birefringence of the skin layer. The second method used multiple-beam Fizeau fringes in transmission to observe the changes in the values of the refractive indices due to the annealing process in the skin and core layers. Also, the mean refractive indices and their profiles were determined, taking the refraction and different temperatures into consideration. The resulting data were used to calculate the polarizabilities per unit volume and the isotropic refractive index.

Interferometric determination of regular and/or irregular transverse sectional shape of homogeneous fibres

A method is suggested to determine the regular and/or irregular transverse sectional shape and area of homogeneous fibres. This method depends on double-beam interferometry using a Pluta polarizing interference microscope attached to a fibre rotator device. The transverse sectional shapes of the fibres tested are determined by measuring the thickness profiles and varying the angle of rotation for these fibres. The transverse sectional shapes and areas of (polypropylene 4:1 draw ratio 515 tex polypropylene, Bolton, UK), nylon 6 regular fibres and two samples of acrylic fibres with irregular transverse sectional shape are determined using the suggested method. Also, an optical microscope is used to obtain the cross sectional shapes of bundles of these fibres to confirm the results of this method. The mean refractive indices of the fibres used are determined using the measured values of the mean transverse sectional area. Experimental microinterferograms, obtained by varying the angle of rotation, are used to map the cross sectional shape of these fibres and are utilized for illustrations.

Variable wavelength microinterferometry applied for irregular fibres

A method is suggested to determine the spectral dispersion curves of the refractive indices of irregular fibres. This suggested method depends on variable wavelength microinterferometry, taking into consideration the enclosed area under the fringe shift. Also, this method solves the problem of determining the transverse-sectional area of these fibres. The mathematical analysis of the method is given. A Pluta double-refracting polarizing interference microscope is used jointly with the suggested method to determine the spectral dispersion curves of the refractive indices of two samples of acrylic fibres (denier 2 and Dralon). Microinterferograms are given for illustration.

Interferometric detection of structure deformation due to cold drawing of polypropylene fibres at high draw ratios

A stress–strain device was attached to a two-beam polarizing interference microscope to investigate the structure deformation associated with fibre cold drawing. A polypropylene fibre was stretched at high draw ratios, D>6, and the interference patterns were automatically digitized and stored in computer storage media. The microinterferograms show that there are two different mechanisms that occur when the fibre is stretched, depending on whether with fast or slow drawing. In case of slow drawing, smooth deformation was detected, and in case of fast drawing, microcrack deformation was presented. The refractive indices and birefringence of the fibre were measured as a function of draw ratio. The refractive index profiles using fringe image analysis were calculated in cases of fast and slow drawing. The two-beam interferometric technique is a good technique to investigate and detect microcrack deformation across the diameter of a fibre. Microinterferograms are given for illustrations.