Crystallinity of Polyamide-6 Matrix in Glass Fibre/Polyamide-6 Composites Manufactured from Hybrid Yarns

Ring twisting gives the strength properties of yarn like friction spinning. Two multifilaments arranged in parallel and slightly twisted together form a loose structure with a slightly mixed arrangement of fibres. The structure of pneumatic textured yarn obtained by means of a stream of compressed air has a greatly mixed arrangement of fibres. Multifilaments are connected over their length by shifting filament fibres and forming loop struc tures in the yarn surface. In the hybrid yarn composites obtained, the matrix comes from a semi-crystalline polymer. The mechanical properties of the composites are influenced by, among other aspects, the crystalline structure of the matrix [5]. With the increasing degree of crystallinity, the tensile strength, the stiffness, the modulus of resilience, the hardness of the polymer increase and the impact strength decreases [6]. The formation of the crystalline structure of the matrix depends on the applied melting temperature, the time it is maintained at this temperature, and the rate of cooling [7]. The same conditions were used for each kind of composite. Different yarns were used. In this work, the crystallinity of the polymer matrix was studied by DSC (Differential Scanning Calorimetry) and X-ray spectroscopy. The influence of the yarn structure, and consequently the arrangement of the fibres in the composite on the microstructure, was determined. The degree of crystallinity of the polyamide matrix in composites from hybrid yarns manufactured by three different systems were estimated.