Characterization of polyamide 6 made by reactive extrusion. II. Analysis of microstructure

Abstract

SYNOPSISConsideration is given to the characterization of microstructure in polyamide 6 prepared by polymerization of e-caprolactam in a corotating twin-screw extruder. Results obtained by FTIR, WAXD, DSC, and DMTA are discussed in terms of the molecular mass of the polymer, the thermal history of the material. and the influence of residual monomer. I NTRO DUCT1 0 NA previous investigation considered the preparation of polyamide 6 (PA6) by the catalyzed anionic polymerization of t-caprolactam in a corotating twinscrew extruder.' It was shown that, using an appropriate catalyst and activator system together with an optimized screw profile and operating conditions, high polymer could be produced with an average machine residence time of about 90 s. Molecular mass and residual monomer level were strongly influenced by screw speed. Mechanical properties compared favorably with commercial PA6 made by hydrolytic polymerization, with notched Izod impact strength and elongation at break being significantly higher for material produced by reactive extrusion.This article considers the effects of processing history and material composition on microstructure of the materials produced. In this respect, previous work has established the existence of two crystalline forms of PA6, an a-phase and a thermodynamically less stable y phase, giving rise to wide angle X-ray diffraction (WAXD) peaks at 8 = 19.6" ( a l ) , 23.5O( a 2 ) , and 21.3' ( y ) , respectively.2 In addition, differential scanning calorimetry (DSC) was used to study the effects of processing conditions and recrystallization rate on the thermal properties of PA6 fibers and yarns.3 * To whom correspondence should be addressed.Journal of Applied Polymer Science, Vol. 54,899-907 (1994) EXPERIMENTALAn earlier article discussed experimental procedures used for the preparation of PA6 by anionic polymerization of t-caprolactam in a corotating intermeshing twin-screw extruder.' In the present study, consideration is given to the structural analysis of polymer prepared in this way at specified screw speeds ranging from 50 to 150 rpm, and under different conditions of melt cooling, either by rapid quenching in water at 23"C, or after allowing the 4-mm diameter polymer extrudate to cool more slowly in air to room temperature. Some samples were also made with additions of 10% by weight of sized short glass fiber reinforcement, blended with the t-caprolactam/catalyst/activator feedstock, in order to investigate possible effects from additive nucleation on the crystalline microstructure.

Numerical simulation of reactive extrusion processes of PA6

“…There are complex interactions among such phenomena as fluid flow, heat transfer and chemical reaction during the reactive extrusion process, which cause the theoretical research to be very difficult. [1][2][3][4][5][6][7][8][9][10][11] The existing theoretical investigations have been mainly confined to one-dimensional (1D) models and have generally simplified the complicated relationships among fluid flow, chemical reaction, material structures, physicochemical properties, and heat transfer.…”

“…The investigations into the polymerization of polyamide 6 (PA6) in extruders can date back to 1968; it was Illing who reported the method of the anionic polymerization of caprolactam into PA6 in twin screw extruders 1, 2. Since the 1980s, Menges, Michaeli, and Berghaus and their colleagues at the University of Aachen and the IKV Company,3–6 as well as Hornsby and Tung at the University of Brunel7 and White and Kye at the University of Akron,8–11 all applied themselves to the research of this process.…”

Anionic copolymerization of nylon 6/12: A comprehensive review

“…However, such reactions are affected not only by the type of initiation system, and active growth centers but also by the concentration of initiation system and reaction conditions which play an undeniable role in the characteristics of the final product. In other words, initiation system comprising a catalyst and an activator, and also reaction conditions have a major influence on the polymerization rate, yield, structure, and properties of the synthesized materials, which, in turn, affect the other characteristics of the final polymer [35][36][37][38][39]. The process type should also be considered carefully for the selection of a suitable initiation system [31,[35][36][37][38][39][40][41][42][43].…”

Supertough (Polyamide 6)/(acrylonitrile butadiene rubber) nano alloy through in situ polymerization of caprolactam in the presence of acrylonitrile butadiene rubber nanophase

“…Features of this method are the very fast polymerization process and the narrow molecular weight distribution [10]. Hornsby and Tung [11] showed that the impact strength and elongation-at-break values of Nylon 6 obtained by this method are higher than those of other commercial polyamides.…”