Structure of polypropylene fibres coloured with a mixture of pigments with different nucleating ability Jan Broda * Institute of Textile Engineering and Polymer Materials, University of Bielsko-Bial /a, 43-309 Bielsko-Bial /a, ul. Willowa 2, Poland Received 15 April 2003; received in revised form 28 July 2003; accepted 5 August 2003 Abstract Investigations of the structure of polypropylene fibres coloured with a mixture of quinacridone and phthalocyanine pigments were carried out. The structure of the fibres, evaluated by wide-angle X-ray scattering and small-angle X-ray scattering methods, was compared to the structure of noncoloured fibres and the fibres coloured with particular pigments. It was stated, that pigments participate in the nucleation process at low take-up velocity. In the presence of pigments, nuclei of two polymorphic forms a and b are formed. In fibres coloured with the mixture of pigments the competition between formation of the a and b nuclei occurs. The b nuclei formed on the crystals of the quinacridone pigment dominate. The high number of the b nuclei, together with the higher growth rate of the b crystals, leads to the formation of a structure containing a large amount of the b form, only slightly lower in comparison to the fibres coloured with the quinacridone pigment. At higher take-up velocities under higher molecular orientation in the cooled stream of the fibre, the very effective row nuclei are produced. In the presence of such nuclei, pigments do not participate in the nucleation process and do not affect the fibre structure. q 2003 Elsevier Ltd. All rights reserved. Keywords: Polypropylene fibre; Structure; Pigment 1. Introduction Polypropylene fibres cannot be dyed with dyestuffs and bath methods commonly applied to other fibres. Due to a nonpolar paraffinic character, their dyeing is performed during spinning in a mass colouration process [1]. For the mass colouration of the polypropylene fibres inorganic and organic pigments are applied. Among inorganic pigments titanium dioxide and carbon black, pigments commonly used for colouring to white and black colours, possess the greatest importance. To obtain colour- istic effects usually the organic pigments with sufficient heat resistance are applied. In many cases the use of a mixture of two or more different pigments is required. Pigments added to the polymer melt during extrusion participate in the crystallisation process leading to the formation of the fibres structure. The influence of pigments on the crystallisation process reflects in the fibres structure and subsequently in the fibres properties [2,3]. Several pigments reveal a good nucleating ability and accelerate the polypropylene crystallisation. Out of many pigments especially quinacridone and phthalocyanine possess high nucleating efficiency. The quinacridone pigment as well as the phthalocyanine pigment occur in a crystalline state. Several polymorphic forms of pigment crystals provide differently shaped surfaces which can match the polypropylene chains. As a result of the interaction between the polypropylene molecules and the surface of the pigment crystals two polymorphic forms of polypropylene a and b can be obtained. During crystallisation of the polypropylene melt with the addition of the mixture of the quinacridone and the phthalocyanine pigments the nuclei of both polymorphic forms of polypropylene are formed [4]. One can assume that there is a competition between the formation of both nuclei, which together with a different growth rate of the a and b crystals, leads to the formation of the structure containing a different content of both forms. The nucleating efficiency of pigments, observed during crystallisation of the quiescent melt of polypropylene, is strongly limited by the fibres formation. During the fibres formation the orientation strongly influences the polypro- pylene crystallisation and the nucleating effect of pigments 0032-3861/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2003.08.014 Polymer 44 (2003) 6943–6949 www.elsevier.com/locate/polymer * Tel.: þ48-33-82-27400; fax: þ 48-33-815-1610. E-mail address: jbroda@ath.bielsko.pl (J. Broda).