Crystallization Behavior Of Polyamide-6 Research Articles

Reactive Compatibilization of Polyamide 6/Olefin Block Copolymer Blends: Phase Morphology, Rheological Behavior, Thermal Behavior, and Mechanical Properties.

In this study, the morphology, rheological behavior, thermal behavior, and mechanical properties of a polyamide 6 (PA6) and olefin block copolymer (OBC) blend compatibilized with maleic anhydride-grafted polyethylene-octene copolymer (POE-g-MAH) were investigated. The morphological observations showed that the addition of POE-g-MAH enhanced the OBC particle dispersion in the PA6 matrix, suggesting a better interfacial compatibility between the pure PA6 and OBC. The results of the Fourier transform infrared (FTIR) spectroscopy analysis and the Molau test confirmed the compatibilization reactions between POE-g-MAH and PA6. The rheological test revealed that the melt viscosity, storage modulus (G’), and loss modulus (G”) of the compatibilized PA6/OBC blends at low frequency were increased with the increasing POE-g-MAH content. The thermal analysis indicated that the addition of OBC had little effect on the crystallization behavior of PA6, while the incorporation of POE-g-MAH at high content (7 wt%) in the PA6/OBC blend restricted the crystallization of PA6. In addition, the compatibilized blends exhibited a significant enhancement in impact strength compared to the uncompatibilized PA6/OBC blend, in which the highest value of impact strength obtained at a POE-g-MAH content of 7 wt% was about 194% higher than that of pure PA6 under our experimental conditions.

Crystallization behavior of polyamide 6 confined in a strip-like rubbery phase

A purified xLDPE/LDPE-g-PB-g-PA6/PA6 blend with polyamide 6 (PA6) confined in a rubbery polybutadiene (PB) phase is prepared via extracting the unreacted LDPE and PA6 from a blend of PB-g-MAH functionalized LDPE (LDPE-g-PB-g-MAH) and PA6 50/50 wt/wt by using selective solvents of LDPE and PA6, respectively. The term xLDPE represents a partially crosslinked LDPE phase that cannot be dissolved by its selective solvent of toluene. The structure and crystallization behavior of PA6 in a xLDPE/LDPE-g-PB-g-PA6/PA6 blend containing 14% of PA6 by weight are studied using transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). Strip-like rather than droplet-in-matrix morphologies are found. Strip-like PA6 domains are located inside the strip-like rubbery PB phase, where LDPE is the matrix. The thickness of the strips composed of both the PB and PA6 phases are about 50–70 nm, in which the PA6 strips are ∼20 nm thick. The slow nucleation rate of the confined PA6 results in the decrease of both its melting temperature and crystallinity when it is subjected to multiple heating–cooling scans at the rate of 10 °C min−1. The crystallinity obtained by the DSC test decreases to zero after 5 heating–cooling cycles. This is because the crystallization rate of the PA6 in the purified xLDPE/LDPE-g-PB-g-PA6/PA6 blend is too slow to be detected when it is cooled from the melt with a cooling rate of 10 °C min−1. Crystallization still can take place when the temperature is higher than the glass transition temperature of PA6. The crystallinity of the PA6 will increase with an increase in annealing time under suitable annealing temperatures. The crystallization of LDPE has no effect on the crystallization of the PA6 phase because of the rubbery PB layer located between them. This work will be a guide for researchers to produce polymer blends with not only a controllable phase structure, but also with a suitable crystallinity.

PA6 and Kevlar fiber reinforced isotactic polypropylene: Structure, mechanical properties and crystallization and melting behavior

To improve the thermal and mechanical properties of isotactic polypropylene (iPP), iPP/Kevlar fiber (KF)/polyamide 6 (PA6) composites were prepared via the melt-extrusion method on twin-screw extruder. Kevlar fiber was modified with caprolactam using toluenediisocyanate (TDI) as bridge. The microstructure of modified KF was successfully characterized by Fourier transform infrared (FT-IR), X-ray photoelectron spectrometer (XPS) and scanning electron microscopy (SEM), the results showed that KF was bonded with caprolactam and became coarser. Then the modified KF was introduced into iPP, the composites have better mechanical and thermal properties, implying that modification of KF was helpful to improve the interfacial interaction of iPP/KF/PA6 composites. Besides, the crystallization curves indicated that crystallization behavior of PA6 in the composites was homogeneous and fractional. Furthermore, compatibilizer content played an important role in the mechanical and thermal properties of composites.

Effect of clay addition on the morphology and thermal behavior of polyamide 6

AbstractThe nanostructure, morphology, and thermal properties of polyamide 6 (PA6)/clay nanocomposites were studied with X‐ray scattering, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The wide‐angle X‐ray diffraction (WAXD) and TEM results indicate that the nanoclay platelets were exfoliated throughout the PA6 matrix. The crystallization behavior of PA6 was significantly influenced by the addition of clay to the polymer matrix. A clay‐induced crystal transformation from the α phase to the γ phase for PA6 was confirmed by WAXD and DSC; that is, the formation of γ‐form crystals was strongly enhanced by the presence of clay. With various clay concentrations, the degree of crystallinity and crystalline morphology (e.g., spherulite size, lamellar thickness, and long period) of PA6 and the nanocomposites changed dramatically, as evidenced by TEM and small‐angle X‐ray scattering results. The thermal behavior of the nanocomposites was investigated with DSC and compared with that of neat PA6. The possible origins of a new clay‐induced endothermic peak at high temperature are discussed, and a model is proposed to explain the complex melting behavior of the PA6/clay nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1191–1199, 2007

Effects of spacing between the exfoliated clay platelets on the crystallization behavior of polyamide‐6 in polyamide‐6/clay nanocomposites

AbstractExfoliated polyamide‐6 (PA6)/organoclay nanocomposite films with planar‐oriented clay platelets were prepared by the simple hot pressing of melt‐extruded nanocomposite pellets. The average distance between the neighboring clay platelets was controlled by changes in the clay loading content in the nanocomposites. The effects of the clay platelet spacing on the crystallization behavior of PA6 were investigated with transmission electron microscopy and wide‐angle X‐ray diffraction. The crystal lamellae were found to be mainly perpendicular to the clay surface for the nanocomposites with large spacing between the clay sheets at low clay loading contents. This perpendicular orientation morphology was attributed to the strong interactions between the PA6 molecular chain and the clay surface. In contrast, the crystal lamellae were found to be parallel to the clay surface when the spacing between the neighboring clay platelets was less than 30 nm. It was concluded that the confinement crystallization of PA6 within the nanoscale channels formed by clay sheets resulted in this parallel orientation texture. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 284–290, 2006