Thermochimica Acta 453 (2007) 67–71 Short communication The way to measure quantitatively full dissolution and crystallization of polyamides in water up to 200 ◦ C and above by DSC Marjoleine G.M. Wevers a,b,c , Thijs F.J. Pijpers b , Vincent B.F. Mathot b,c,∗ a DSM Research, P.O. Box 18, 6160 MD Geleen, The Netherlands b Laboratory of Macromolecular Structural Chemistry, Division of Molecular and Nanomaterials, Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, 3001 Heverlee, Belgium c SciTe, Ridder Vosstraat 6, 6162 AX Geleen, The Netherlands Received 10 July 2006; received in revised form 24 October 2006; accepted 26 October 2006 Available online 10 November 2006 Abstract The way to measure quantitatively full dissolution and crystallization of polyamides in water up to 200 ◦ C and above by DSC is described. Stainless-steel high-pressure pans enable research on fully dissolving polyamides in water under vapor pressure. The results show clearly that polyamide 6 (PA6) is soluble in water under vapor pressure in the whole concentration range and that water acts as a crystallization and melting point suppressor. The maximum temperature depression is approximately 60 ◦ C. This depression of the transitions is independent of concentration over a large range (10–70 mass% PA6 in water). When PA6 dissolves in water during heating, the polymer often sets to the sides of the DSC sample pan. Because of this the contact between the sample and the bottom of the pan reduces during measurement and therefore DSC heating curves are frequently curved. Adding steel wool to these stainless-steel high-pressure pans improves the measurements by increasing the thermal conductivity between the sample and pan bottom, and as a result the DSC curves become less curved. The interpretation of the measurements improves and the possibility of reproducible peak area calculations also in heating comes in sight. © 2006 Elsevier B.V. All rights reserved. Keywords: Polyamide 6; Pressure; Steel wool; Water; Calorimetry; Crystallization and melting temperature depressions 1. Introduction Instead of the frequently studied uptake of limited amounts of water in polyamides [1], we investigated fully dissolving polyamides in water. To this end, we used a concept developed at DSM Research in the early nineties [2–4] (and followed recently [5]): to dissolve polyamides in water and other solvents under pressure. Such a study of crystallization and melting/dissolution of polyamides like PA6 in the presence of water has not been published in the past—except for an indication by Murthy et al. who reported a melting point depression of 20 ◦ C after annealing in water under pressure at 120 or 140 ◦ C [6]. This dissolution in water decreases the melting- and crystallization tempera- tures drastically, as will be shown further on. The resulting crystallization- and melting temperature depressions realized in ∗ Corresponding author at: SciTe, Ridder Vosstraat 6, 6162 AX Geleen, The Netherlands. Tel.: +31 46 4751326; fax: +31 84 8346102. E-mail address: vincent.mathot@scite.nl (V.B.F. Mathot). principle open new routes [2–4] to turn the negative aspect of water uptake into a positive one. As is to be expected, dissolving PA6 in water during a DSC cycle causes a shift of the molar mass distribution to lower values as discussed in Ref. [4], because of shortening of the polyamide chains by scission. However, after a cycle still a polyamide results with a fairly high molar mass. While the melting- and crystallization temperature depres- sions are observed clearly by DSC, it is also obvious that in these cases the DSC heating curves are quite often curved, while the DSC cooling curves sometimes show the same behavior, see Fig. 1. Accordingly, quantitative interpretation of the melting and crystallization curves with respect to enthalpy changes is dif- ficult, and especially crystallinity calculations in melting are not very reliable because of this curvature. Such curvature of the DSC curves occurs frequently in PA6–water systems and in polyolefin-dispersions-in-water systems [7] but sometimes it also takes place in pure PA6 [8,9]. 0040-6031/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2006.10.020