In‐situ microfibrillar PET/iPP blend via slit die extrusion, hot stretching, and quenching: Influence of hot stretch ratio on morphology, crystallization, and crystal structure of iPP at a fixed PET concentration

Abstract

The in situ microfibrillar blend of poly(ethylene terephthalate) (PET)/isotactic polypropylene (iPP) was fabricated through a slit die extrusion, hot stretch, and quenching process. The morphological observation indicates that while the unstretched blend appears to be a common incompatible morphology, the hot stretched blends present PET in situ fibers whose characteristics, such as diameter and aspect ratio, are dependent on the hot stretching ratio (HSR). When the HSR is low, the elongated dispersed phase particles are not uniform at all. As the HSR is increased to 16.1, well‐defined PET microfibers were generated in situ, whose diameter is rather uniform and is around 0.6 ∼ 0.9 μm. The presence of the PET phase shows significant nucleation ability for crystallization of iPP. Higher HSR corresponds to faster crystallization of the iPP matrix, while as HSR is high up to a certain level, its variation has little influence on the onset and maximum crystallization temperatures of the iPP matrix during cooling from melt. Optical microscopy observation reveals that transcrystalline layers form in the microfibrillar blend, in which the PET microfibers play as the center row nuclei. In the as‐stretched microfibrillar blends, small‐angle X‐ray scattering measurements show that matrix iPP lamellar crystals have the same orientation as PET lamella. The long period of lamellar crystals of iPP is not affected by the presence of PET micofibers. Wide‐angle X‐ray scattering reveals that the β phase of iPP is obtained in the as‐stretched blends, whose concentration increases with the increase of the HSR. This suggests that finer PET microfibers can promote the occurrence of the β phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4095–4106, 2004

Tuning viscoelastic and crystallization properties of polypropylene containing in-situ generated high aspect ratio polyethylene terephthalate fibrils

“…Such variation indicates that the overall isothermal crystallization rate increases with an increase in fibril content due to the heterogeneous crystal nucleation effect of the fibrils. For example, at 135 C, the t 1/2 for crystallization of PP/PET (99/1 wt%) is 490 s; however, the t 1/2 for crystallization of PP/PET (9/5 wt%) is reduced to 206 s. Previous studies have demonstrated that the presence of spherical PET domains improve the crystallization kinetics of PP by providing additional surfaces for crystal nucleation [39,40]. However, this effect is more significant with the presence of fibrillated PET domains.…”

“…However, this effect is more significant with the presence of fibrillated PET domains. The divergence of the crystallization kinetics of PP/ fibrillated-PET and PP/spherical-PET is attributed to a more favourable crystal nucleation and growth process due to the availability of more heterogeneous crystal nucleation sites [39,40]. For a given PET content, the submicron diameter of the fibrillated-PET domains offers a larger surface-to-volume ratio in comparison with spherical-PET domains (which have diameters on the micrometer scale).…”

Crystallization of oriented isotactic polypropylene (iPP) in the presence of in situ poly(ethylene terephthalate) (PET) microfibrils

“…around 133 and 125 C, respectively, see Fig. 3), due to the heterogeneous nucleation of PET microfibrils [23,24,33]. The PET microfibrils act as heterogeneous nuclei, resulting in the increased onset and maximum crystallization temperatures.…”

“…137 C, indicating that the synergistic effect of PET microfibrils on the iPP crystallization exists in the oriented iPP melt in the presence of PET microfibrils. In our previous works, it is found that the transcrystallization occurs in PET/iPP microfibrillar blend under quiescent condition [23,24], suggesting the existence of the relatively strong interaction between the surface of PET microfibrils and iPP molecules in vicinity of PET microfibrils, since it is reported that the high surface energy would be in favor of transcrystalline growth [34]. Therefore, we argued that the interaction may suppress the relaxation of shear induced nucleation precursors, and the larger oriented entities can survive and increase the onset of crystallization temperature.…”

“…It was found that the in situ poly-(ethylene terephthalate) (PET) microfibrils can act as an effective nucleating agent for iPP and PE [23,24], three origins for crystal nucleation under shear flow field exist: (a) the classical row nucleation, (b) fibril nuclei and (c) nuclei induced by fibril assistant alignment [25]. In the later work, the injection molded bars of the PET/iPP microfibrillar blends were prepared by conventional injection molding (CIM) and by shear controlled orientation injection molding (SCORIM).…”