Byline: Muhammad Nasir, Nasreen Fatima, Khalid Mohammed Khan and Durey Nayab Zahra
Summary: This communication describes the mechanical properties of the single yarn polyester composite (PC) of cotton fiber with special reference to the effect of unevenness in the structure of yarn. Unevenness % (U) and coefficient of variation (CV) in mass of spun yarn were measured. Scanning electron microscopy was carried out to understand the effect of unevenness on physical structure of fibers in the yarn which affect not only the mechanical properties of yarn but also the composites reinforced with them. Results also showed that decrease in 2.15 % of U in the yarn structure causes an increase of 25.18% in ultimate stress and 30.71% decrease in stiffness of composites.
Keywords: Surface unevenness; Cotton fiber yarn; Textile composites; Mechanical properties; Scanning electron microscopy
Plants fiber as reinforcing agent in the preparation of composite material, are getting more attention of the researcher due to its eco- environmental advantages over petroleum based fibers . Natural fibers like coir , bamboo , flax , kenaf , sisal  and jute  have extensively been used as reinforcing agents with comparable mechanical properties. These fibers were used in different forms such as continuous, random, oriented fibers.
Literature shows that the main focus of the researchers' world over is to improve and relate the mechanical properties of the composite to surface modification , orientation  and content of fibers . Textile yarn/fabric of different natural fibers has also been used as reinforcing agent in composites [11-12]. More recently a study was carried out to propose a model to describe the effect of yarn twist on the tensile strength of unidirectional plant fiber yarn composites .
Any plant fibers when collected are a cluster of intermingled fibers of different length and diameter with random orientation. During the formation of yarn, these fibers are opened, drafted and twisted to make them aligned along the axis of yarn. Therefore, instead of cotton fibers from the plants, use of spun yarn is a good option as reinforcing agent because of alignment of fibers and high degree of evenness which gives better tensile properties of the yarn and ultimately the composites.
Present study, according to our knowledge, is the first experimental report which quantitatively describes the effect of unevenness of reinforcing agents on mechanical properties of composites. The unevenness in yarn structure was measured by uster evenness testing system, its effect on physical structure of fibers in fiber bundle of yarn was analyzed by scanning electron microscopy and strength of composites were measured using uster Tensorapid III testing system. The average diameter of the yarn and composite were measured through SEM images to investigate and compare the mechanical properties like ultimate stress and stiffness with reference to the unevenness in the structure of yarn. The results showed an improvement in mechanical properties of yarn and composites.
Results and Discussion
Cotton fibers are present as a cluster of intermingled short and long fibers in its seed pot. The...
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