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NOTES Stepwise Lamellar Thickening of Nylon 66 Crystal by Annealing in Glycerol INTRODUCTIONIt has been reported14 that the lamellar thickness of solution-grown crystals of several polyamides is not affected by crystallization temperatures and solvents, and that the layer thickness closely corresponds to four monomer units. Dreyfuss et a1.I.' observed, however, that under critical conditions the layer thickness doubled in a discontinuous jump on annealing.In this study, nylon 66-a typical polyamide-was annealed in the swollen state in glycerol to promote the breaking of hydrogen bonds. X-ray studies showed that the lamellar thickness increased in discontinuous steps. A corresponding stepwise increase of melting temperatures was clearly observed by differential scanning calorimetry (DSC). Moreover, new melting peaks were observed a t temperatures higher than the established melting temperature of nylon 66. They are considered to correspond closely to the melting temperatures of the crystals which are formed by the mechanism proposed by Dreyfuss and Keller.'.' EXPERIMENTALThe raw material was nylon 66 supplied by Toyo Rayon Co., Ltd. The relative viscosity a t 25°C of a 1 g h 0 0 ml solution in 98% aqueous sulfuric acid was 2.30. A 3% solution of the nylon in 60% 15 (1977) aqueous formic acid was prepared at 95°C. On cooling to room temperature, purified nylon 66 was precipitated. The precipitate was isolated, washed with water, dried under vacuum, and subjected to a pressure of 100 Kg/cm2 a t 160°C to form a disklike sheet (hereinafter, called the unannealed sample). The thin disklike sample, wrapped in a porous aluminum foil, was annealed in glycerol a t selected temperatures kept constant within fO.l°C. The sample was quenched in methanol a t room temperature and then immersed in fresh water for a few weeks to remove the solvent completely.The sample was again dried and pressed. The melting behavior was measured in a Perkin-Elmer DSC-lB differential scanning calorimeter (sample weight 3 mg) a t a heating rate of 8"C/min under a nitrogen atmosphere. The temperature scale was calibrated with tin (231.8"C) and bismuth (271°C). Small-angle x-ray scattering (SAXS) patterns were recorded photographically using nickel-filtered copper K, radiations from a Rigaku Denki RU-3 rotating anode with a pin-hole collimation system (0.5 and 0.3 mm diameter) and a specimen-to-film distance of 350 mm. The long spacing was determined from the microdensitometer trace along the same direction as the sample was pressed. RESULTS AND DISCUSSIONTypical DSC thermograms of nylon 66 samples annealed in glycerol for 24 hr at various temperatures are shown in Figure 1. The endothermic melting curve of the sample annealed a t 175°C appears as a pair of peaks (main peak or peak 1 in the figure) and it is similar to that of the unannealed ample.^ As the annealing temperature increases, the main melting peak is shifted discontinuously to higher temperatures, with the peak a t higher temperature increasing gradually in area, a t the expense o...

The static mechanical properties of nylon 66 annealed in glycerol at 201•KC for various periods molecular chains exhibit local regularities over short ranges and the disordered region caused by introduction of irregularities.

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