Studies on Dry-Jet-Wet Spun Polyurethane Fibers. II. Effect of Polyurethane Shore Hardness on Spinnability and Fiber Properties G. V. Raghunath Reddy, B. L. Deopura, Mangala Joshi Department of Textile Technology, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India Received 23 December 2008; accepted 2 October 2009 DOI 10.1002/app.31593 Published online 10 December 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: This article reports a study on the spinn- ability of three different ester type thermoplastic polyur- ethanes (TPUs) with shore hardness 75A, 85A, 92A using the dry-jet-wet spinning method. The three grades have been analyzed by FTIR, GPC, and 1 H-NMR to establish the difference among them. FTIR indicated that all the three grades were chemically similar and GPC suggests that molecular weight increased with increase in shore hardness. Compositional analysis indicates that the hard segment content increases with increase in shore hardness. Shear viscosity of TPU dope solution increases with increase in shore hardness. Of the three different grades of TPUs studied, only the grades with shore hardness of 85A and 92A are spinnable under the experimental conditions. The fiber properties of three different grades have been compared. Fibers spun with the shore hardness of 85A have good elastomeric properties compared with the other two grades. Lab spun fibers have also been compared with the commercial spandex fibers. V C 2009 Wiley Periodi- cals, Inc. J Appl Polym Sci 116: 843–851, 2010 Key words: polyurethane; shore hardness; shear viscosity; spinnability; spandex INTRODUCTION Segmented polyurethane elastomers are linear block copolymers of A(HS)n-type (H, hard segment; S, soft segment) whose versatile physical properties are generally attributed to their microphase-separation structure. The microphase-separation structures arise due to the incompatibility of the hard segment and the soft segment. This microdomain two-phase mor- phology is responsible for the mechanical properties of these elastomers. 1 Many reports have dealt with the structure and mechanical properties of polyurethanes (PU) in terms of chemical composition, 2 morphology, 3 molecular weight, 4 hard segment content, 5,6 type of components, 7 thermal history, 8 strain rate, 9 the content of triol cross linking agent, 10 and extent of phase segregation. 11–13 Furguson and Patsovoudis 14–16 in a study, syn- thesized a series polyurethanes from adiprene L100 (a polyether based macrodiisocyanate) of molecular weight of  2000, trimethylene diamine, and 4,4 0 diphenylmethane diisocyanate (MDI). The molecular weight of the soft segment was kept constant and the size of the hard segment progres- sively increased, such that the final product in the series was not polyurethane, but a polyurea. These were wet spun into fibers and their tensile 14 and dynamic mechanical properties 15 were measured. It was found that their specific breaking stress, elongation, elastic recovery, and stress relaxation characteristics were all dependent on soft segment (polyether) concentration. A transitional region appeared at  50% soft segment/50% hard seg- ment concentration. They also observed that the polyurethane fibers spun by a polymer with 70.8% of soft segment content had best elastomeric prop- erties. 14 In another study by the same group, 16 they studied the effect of increasing molecular weight of soft segment while ensuring that the ratios of soft to hard segment content in PU remained constant. They reported similar observation in properties, although there was a slight deterioration in physical properties with higher soft segment molecular weight. They opined that the reason for best elasto- meric properties of polyurethane at soft segment content of 70.8% is that at this percentage of soft segment, the soft segment is in continuous phase and hard segment content is in the discontinuous phase and the fiber properties are primarily decided by the soft segment content. Shore hardness Type A is a measure of visco- elastic properties of rubber type elastomeric Correspondence to: M. Joshi (mangala@textile.iitd.ernet. in). Contract grant sponsor: Ministry of Human Resource and Development (MHRD) (Government of India). Journal of Applied Polymer Science, Vol. 116, 843–851 (2010) V C 2009 Wiley Periodicals, Inc.