Porosity enhancement in β nucleated isotactic polypropylene stretched films by thermal annealing

Morphology Development, Structure and Dielectric Properties of Biaxially Oriented Polypropylene

“…For each cast film, a major melting peak characteristic to -form iPP was observed in the ~163-165 °C region (Table 2), with the high-isotacticity PP2-based cast films showing Tm ( ) higher than that of PP1. Additionally, double peaks in the form of 1 and 2 peaks were observed for the cast films below the major -melting peak at ~142 °C and ~150 °C, respectively-this result is in accordance with Offord et al [6], [10] and is typical for -form iPP crystallized both isothermally and nonisothermally below 125 °C. The double melting behavior reflects melting of the original 1-phase and subsequent recrystallization into more stable 2-phase during the DSC heating scan.…”

“…SEM-cross sectional imaging of the BOPP films, as exemplified in Figure 2c-d, revealed varying amounts of porosity and voids parallel to film surface, with the amount of voids/porosity increasing in proportion with the k of the corresponding cast film (Table 2). Mechanisms behind initial cavitation and elongation of voids by biaxial stretching in -iPP films were recently discussed by Offord et al [6], [10]similar mechanisms are likely playing a role in the void formation for the mixed / -phase iPP films studied here.…”

“…This was also confirmed by the disappearance of melting peaks in the DSC scans of the BOPP films (not shown). The observed behavior can be attributed to a strain-induced crystal transformation upon biaxial stretching of iPP cast film in a partly molten state [6], [12]. Moreover, changes in the -form diffraction peak intensities upon biaxial stretching (Figure 1b) indicate alignment of crystallites as discussed elsewhere [12], [13].…”

“…The X-ray diffraction data were treated by first subtracting amorphous halo from the diffraction profiles and then using a multi-peak fitting procedure to fit the remaining crystalline peaks. TurnerJones -form crystal index (k ), a widely used relative measure of the -crystalline content, was calculated in accordance with the literature [6]. WAXS degree of crystallinity, XWAXS, was calculated by dividing the area under the crystalline curve by the total area under the original spectrum.…”

Morphology and properties of highly filled iPP/TiO2 nanocomposites

“…The c-phase and the smetic phase form in low molecular weight or under pressure and due to quenching, respectively. However, the b-form crystal of iPP is a metastable phase which is occasionally observed as a minor crystal phase in iPP that tends to transform to a-form under mechanical to thermal stimulates [21,22,[24][25][26][27]. Although presence of the b-phase leads to lower modulus and yield strength in iPP, its excellent effects on enhancement of toughness, impact strength, and heat distortion temperature of iPP has attracted much attention from research and industrial applications [21][22][23][28][29][30].…”