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Polylactic acid (PLA) fibers are receiving growing interest as one of the recent innovative materials being developed for various applications. The inherent biodegradability of PLA makes it highly attractive for the biomedical and health care sectors. PLA fibers need to be partially and/or highly oriented to allow high performance and readiness for a wide range of manufacturability. In this study, the structure and properties of PLA fibers, manufactured at different spinning speeds, were studied. Laser diffractometry, polarized light microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used to determine the diameter, birefringence, molecular orientation, enthalpy and degree of crystallinity of as-spun and drawn PLA fibers. The results of DSC and XRD showed that the degree of crystallinity of the PLA fibers is significantly improved for the drawn PLA fibers compared to the as-spun fibers and leveled off in the case of changing the take-up speeds of drawn fibers.

The main goal of this work study is to study the influence of mechanical cold drawing and drawing velocity on the molecular orientation and physical structure parameters of isotactic polypropylene, iPP, fibers. A Video Opto-Mechanical device (VOM) attached with automatic multiple-beam interferometric technique was used to cold draw iPP fibers at different draw ratio and drawing velocity. The molecular structure of iPP fiber was characterized by measuring the refractive indices, birefringence, optical orientation function, orientation angle, the percentage of the volume fraction of amorphous and crystalline regions, density and the mean square density fluctuation. The obtained microinterferograms of multiple beam interference fringes were enhanced and the noises were removed by using Fourier transform method. The obtained contour lines were analyzed via a software program for fiber refractive index determination. The results show that the drawing velocity has a less effect than the draw ratio on the molecular structure of iPP fiber. The contour lines of microinterferograms are given for illustration.

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Pluta microscope used to throw light on the effect of heat treatment time on the different properties of poly (ethylene terephthalate) PET fibers. PET fibers were annealed at times ranged from 5 to 30 min at different temperatures (150, 170, 190, 210°C) using two different processes (fast cooling and slow cooling processes) in air. The refractive indices, the shrinkage, orientation factor and crystallinity of PET fibers were determined for different annealing temperature during the short time treatment. The shrinkage percentage and degree of crystallinity increased with increasing the temperature and time of annealing. Microinterferograms are given for illustration.

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.

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