Nanostructure and crystallization phenomena in multilayered films of alternating iPP and PA6 semicrystalline polymers

Abstract

The present work is concerned with the study of the crystalline morphology and the nanostructure of a multilayered system of two alternating immiscible semicrystalline polymers: isotactic polypropylene (iPP) and polyamide 6 (PA6). Films with a volume ratio of 70/30 were prepared by means of layer multiplying coextrusion. Contrary to previous experiments, performed with semicrystalline/amorphous and amorphous/amorphous nanolayered systems, the studied iPP/PA6 film does not exhibit a well defined maximum in the USAXS patterns.This result accounts for an irregular layered structure, as further confirmed by means of TEM images. Nevertheless, such a layered assembly still influences the crystallization behaviour of both constituent polymers. On the one hand, the crystallization of PA6 within the multilayered material is substantially hindered as evidenced by its weak scattering intensity. Real time studies as a function of temperature undoubtedly detect the presence of a WAXS peak and a SAXS maximum associated to PA6 above the melting temperature of iPP. Room temperature AFM studies also confirm the occurrence of crystalline structures within the PA6 layers. On the other hand, SAXS and WAXS measurements at room temperature reveal the occurrence of an oriented lamellar morphology within the iPP layers bearing uniaxial symmetry around an axis perpendicular to the layers surface. Results show that the crystalline molecular chains are placed mainly parallel to the layer surfaces forming edge-on lamellae. Moreover, X-ray scattering results are in agreement with the occurrence of two populations of lamellae, both edge-on and perpendicular to each other, in agreement with the crosshatched morphology observed by AFM.

Deformation mechanisms of polypropylene/polystyrene multilayered films

“…However, as shown in literature and previous investigations, it is possible to combine semicrystalline and amorphous polymers, such as polypropylene (PP) and PS, by a multilayer coextrusion process, which creates ultrathin layers down to 10 nm in size 13, 14. Other combinations with at least one crystalline polymer have been described, too 15–18…”

Fractionated crystallization in semicrystalline polymers

“…A schematic showing the mechanism of multilayer film breakup and droplet formation during thermal treatment is shown in Figure 7, including hole formation, hole growth, droplet formation and coalescence [36]. This approach has been applied by Hiltner and Baer [53] to investigate confined crystallization or fractionated crystallization of PP [4,[37][38][39][40][41][42], PEO [43][44][45][46][47], PCL [47], HDPE [43,49], PC [50], PA6 [51], and PVDF [52], and the relevant references are summarized in Table 2. Adapted with permission from ref.…”

Improvement of Transparencies and Mechanical Properties of Poly(cyclohexylene dimethylene cyclohexanedicarboxylate) Parts Using a Compounding Nucleating Agent to Control Crystallization

“…In addition, although the MDBS particle size is on a microscale, the nanofibers formed by the self-organization of MDBS work better as an NA [36,37]. Compared to generalized nanoparticles used in polymer engineering [11,38,39], from the view of industrial production, the microscale MDBS is more easily dispersed in the matrix; nanoparticles dispersed in polymer matrices are prone to aggregation, due to their small particle sizes, large specific surface areas, and high surface energies [40,41,42,43]. Therefore, microscale MDBS is more convenient for processing and production.…”