Structure of heat-treated Nylon 6 and 6.6 fibers. II. Recrystallization mechanism

Abstract

The present work compared the recrystallization process of Nylon 6 with Nylon 6.6 fibers. For such a study, the fibers were submitted to different annealing conditions (slack and restrained conditions) in a wide range of temperatures. For the structural analysis, several techniques were applied, and among them, differential scanning calorimetry (DSC) was demonstrated to be a very important tool. Nylon 6 and 6.6 fibers responded differently to the applied annealings, indicating different recrystallization mechanisms. The Nylon 6 fiber presented the formation of new and very small crystallites in their interfibrillar regions for the annealings performed above 120ЊC independently of the annealing condition. In addition to their improvement in size and perfection as the annealing temperature increases, their presence favored a general recrystallization in a preferred direction, that is, of the fiber axis. The recrystallization process of the Nylon 6.6 was commanded by the disorientation process associated to the release of the hydrogen bonds. The DSC thermograms revealed two crystalline forms, that is, of the same type but with different degrees of size and perfection. At temperatures below the T g , the less perfect crystallites are converted into more perfect ones, while at temperatures above the T g , the intense movement of the chain segments favored a reversal in this process, that is, the more perfect ones are converted again to the less perfect form.

Preparação e Caracterização de Nanofibras de Nanocompósitos de Poliamida 6,6 e Argila Montmorilonita

“…Esta transição foi encontrada em poliamida 6 e 6,6 não orientados quando submetidos a condições específicas de tratamento e ocorre entre 80 e 170 °C para a poliamida 6 e entre 130 e 230 °C para a poliamida 6,6. No caso da endoterma de pré-fusão, essa ocorre devido a um processo de relaxação das mantas, e também foi observada em mantas de poliamida 6 [43] . Em relação ao terceiro processo, é sabido que a PA 6,6 é um polímero isso há maior facilidade no espalhamento dos fluídos.…”

Composites based on poly(ethylene terephthalate) fibers with polyaniline. I. Effect of the aniline monomer in the morphology of the PET substrate

“…Such behavior was not observed for the 0X fiber. More recently, 17 in a publication by one of the present authors, such an argument was demonstrated to be very helpful to explain the observed morphology changes in nylon 6.6 fibers due to heat treatments at different temperatures. Such studies were made with PET fibers 20 and with nylon 6.6 fibers.…”

“…It has been suggested in the literature 16,17,19,20 that such double melting peaks would be representative of the existence of two different crystalline forms in the fibers. Such behavior was not observed for the 0X fiber.…”

“…The equipment utilized for the sonic modulus determination was the PPM-5, from Fairway S/A. 2,5,16,17 Also, it is interesting to note that the temperatures of the premelting peaks occur in the same range of temperatures as that of the control ones. Figure 1 shows DSC thermograms of the undrawn and drawn PET fibers submitted to different conditions of aniline absorption (condition I: pure aniline; condition II: aniline plus benzoic acid).…”

“…Since the lower-temperature peak would correspond to the melting of smaller and or more imperfect crystallites, 17 our control drawn fiber would present a crystalline structure with a larger amount of small and or less perfect crystallites. Since the lower-temperature peak would correspond to the melting of smaller and or more imperfect crystallites, 17 our control drawn fiber would present a crystalline structure with a larger amount of small and or less perfect crystallites.…”