Influence of Annealing on Microstructure and Mechanical Properties of Isotactic Polypropylene with β-Phase Nucleating Agent

Abstract

The microstructure and mechanical properties of β-nucleated iPP before and after being annealed at different temperatures (90-160 °C) have been analyzed. Annealing induced different degrees of variation in fracture toughness of β-nucleated iPP samples, namely, slight enhancement at relatively low annealing temperatures (<110 °C) and great improvement at moderate temperatures (120-130 °C), whereas dramatic deterioration at relatively high temperatures (>140 °C) has been observed. The variation of fracture toughness of β-nucleated iPP is observed to be dependent on the content of β-NA. Experiments, including scanning electronic microscope (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA), are performed to study the variations of microstructures as well as the toughening mechanism of the β-nucleated iPP after being annealed. The results indicate that the decreased number of chain segments in the amorphous region and the formation of microvoids, which is easily triggered by the secondary crystallization at 120-130 °C, are mainly responsible for the great improvement of toughness through promoting the lamellae to slip or elongate along the impact direction and inducing the intense plastic deformation during the fracture process.

Transcrystallization in nanofiber bundle/isotactic polypropylene composites: effect of matrix molecular weight

“…In Fig. 2d, the melting peak of PA 66 nanofiber bundles appears at 260°C, which is much higher than that of iPP melting (mainly below 175°C [30]). It implies that the PA 66 nanofiber bundle would be solid state during the process of composite preparation and erasing the thermal history at 200°C.…”

Crystallization behavior of isotactic polypropylene induced by competition action of β nucleating agent and high pressure

“…The other diffraction peaks at 2θ014.0°, 16.7°, 18.5°can be attributed to the reflection of (110), (040), and (130) planes of α-iPP, respectively. This means that although TMB-5 is an effective β-NA for iPP [19,20,23,24], it does not prevent the nucleation and growth of α-lamellae. This is very important because it possibly influences the crystallization behavior of iPP/TMB-5 sample under high pressure.…”

“…Both β-iPP and γ-iPP are thermodynamically metastable phases with heat of fusion of 168.5 [8] and 150 J/g [5], respectively, and only can be obtained under special conditions. For β-iPP, although the shear condition and temperature gradient provoke the nucleation and growth of β-iPP, addition of an active β-phase nucleating agent (β-NA) is proved to be the most efficient way to obtain iPP articles with high content of β-iPP [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. For γ-iPP, it is already known that crystallization under high pressure (>200 MPa) is the main way to achieve high content of γ-iPP [25][26][27][28] in common iPP.…”

Mechanical and thermal characteristics and morphology of polyamide 6/isotactic polypropylene blends in the presence of a β‐nucleating agent

“…22 The decreases in r Y and E f of the P1 group in Figure 1 could be interpreted by the increasing content of b crystals in iPP formed in the blends and were consistent with previously reported results. 23 Because the amino group in the b-NA may have caused some interactions with the hydroxyl group in the PA6 molecular chains, in the A1 group, the b-NA was encapsulated in the PA6 phase, and it was difficult for the nucleating agent to transfer into the iPP matrix. So, a relatively low content of b-NA in the PP matrix did not induce a large amount of b-iPP in the blends of the A1 group.…”

“…24 It is generally considered that the content of b-iPP is the main factor determining the toughness of iPP; however, recently, Luo et al 25 adopted different molten temperatures to prepare samples with constant b-NA contents and demonstrated that the paramount factor was the connection between the crystallites instead of the b-iPP content. Bai et al 23 suggested that critical and supercritical b-NA contents led to different supermolecular structures because of its various dissolutions among the iPP matrix, such as a bundlelike morphology with a high content of b-NA and a finely dispersed form at a low content.…”