Hot compaction of woven nylon 6,6 multifilaments

We describe a study of the hot compaction of woven nylon 6,6 multifilaments produced by a patented procedure, developed at the University of Leeds, for creating novel single-polymer composites. In this process, an assembly of oriented elements, often in the form of a woven cloth, is held under pressure and taken to a critical temperature so that a small fraction of the surface of each oriented element is melted, which on cooling recrystallizes to form the matrix of the single-polymer composite. This process is therefore a way of producing novel high-volume-fraction polymer/polymer composites in which the two phases are chemically the same material. Nylon is an obvious candidate material for this process because oriented nylon multifilaments are available on a commercial scale. The aim of this study was first to establish the conditions of temperature and pressure for the successful hot compaction of oriented nylon 6,6 fibers and second to assess the mechanical properties of the manufactured hot-compacted nylon sheets. A crucial aspect of this work, not previously examined in hot-compaction studies of other oriented polymers, was the sensitivity of the properties to absorbed water, with a significant change in the properties measured immediately after hot-compaction processing and 2 weeks later when 2% water had been absorbed by the compacted nylon sheets. As expected, the water uptake had a greater effect on those properties that depended on local chain interactions (e.g., the modulus and yield strength) and less effect on those properties that depended on the large-scale properties of the molecular network (e.g., strength). The only negative aspect of the properties of the hot-compacted nylon sheets was the elevated-temperature performance of the wet sample, with the modulus falling to a very low value at a temperature of 80 degrees C. However, apart from the elevated-temperature performance, the majority of the measured properties of the hot-compacted nylon sheets were comparable to those of hot-compacted polypropylene and poly(ethylene terephthalate). (c) 2006 Wiley Periodicals, Inc.