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High melt strength polypropylene (HMS‐PP)/propylene‐based elastomer (PBE) microcellular foams were prepared by the extrusion foam method. The fundamental mechanism of PBE improving the foaming properties of HMS‐PP was investigated. PBE 6102, with a low melt flow rate and high ethylene content, enables HMS‐PP/PBE blends to form a microphase‐separated structure and maintain good melt strength and pronounced strain hardening, which would promote cell nucleation and hold cell structure at relatively high temperatures. Furthermore, PBE 6102 postpones HMS‐PP crystallization and decreases the optimum foaming temperature, which helps balance melt elasticity and viscosity near the foaming window to avoid cell rupturing and merging. The introduction of PBE 6102 does not reduce the crystallization rate of HMS‐PP nor the crystallinity of the foamed samples, fixing the cell structure to prevent collapse during the cell solidification stage. Microcellular HMS‐PP/PBE 6102 foams with a high expansion ratio, small cell size, and large cell count were successfully fabricated. [ABSTRACT FROM AUTHOR]

The rare earth nucleating agent was used to modify block copolymerized polypropylene (PPB) in foaming process. The results show that the crystallization of PPB and the melting temperature of β-crystal increased gradually with increased β-crystal nucleating agent content. The total crystallinity decreased with amount of addition increasing, and the relative content of β-crystal increased first and then decreased. When β-crystal nucleating agent content was 0.4 wt%, the relative β-crystal content reached the maximum value of 95.27%, and the final crystal grain refinement significantly. The addition of rare earth β-crystal nucleating agent has a good effect on improving the uniformity of foam cells. Under the same content of β-crystal nucleating agent and pressure, the average cell diameter and expansion ratio increased with the saturation temperature increasing. After the foaming temperature reaches 155°C, the expansion ratio began to decrease, which was also consistent with the changed trend of relative β-crystal content. At the same content of temperature and relative β-crystal, as the foaming pressure increased, the cell diameter decreased gradually, and the expansion ratio increased first, and then decreased. [ABSTRACT FROM AUTHOR]

The thermal performance and rheological properties of PE-HDs were measured by DSC and Hakke rotational rheometer, and then its foaming properties were investigated through the batch foaming experiments. The result indicated that there was a significant effect on the foaming performance of PE-HD from its crystallization rate and viscoelastic properties. The rheological properties and molecular weight distribution of HDPE6098 were found to be suitable for the foaming process along with its fast crystallization rate. These advantages could help to obtain an expansion ratio of 17.69 times and a cell density of 1.30 x 106 cell/cm³ for the foamed PE-HD samples. However, HDPE7000F was found to have a broad high molecular-weight range and high modulus, leading to a limitation in cell growth during foaming and a poor foamed product. [ABSTRACT FROM AUTHOR]

ABSTRACT Polypropylene (PP) foams with double crystal melting peak structure were prepared using supercritical CO2 as blowing agent. Such structure was induced by the β-nucleating agent (NA) and dissolved CO2 in a lab-scale autoclave system. From the dynamic rheological behaviors, one can see that long chain branching polypropylene (LCBPP) possess better melt elasticity than linear polypropylene (LPP). In order to improve the foamability, LPP was blended with LCBPP. The results of differential scanning calorimeter and wide-angle X-ray diffraction indicated that NA was helpful for the introduction of β-crystal in LPP, but not for LCBPP and PP blends. Therefore, the foamability and the content of β-crystal of various PP foams can be effectively controlled by adjusting the ratio of LPP and LCBPP. Meanwhile, both the cooling rate and the content of NA affected the formation of β-crystal in various PP samples. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46007. [ABSTRACT FROM AUTHOR]

Continuous fibre-reinforced thermoplastic composites based on semi-crystalline thermoplastic matrices, such as PA, and PP, have been most commonly used for thermoplastic automated tape placement (ATP). However, the fluidity of the matrix and rapid cooling rate also result in some intractable defects owing to the high peak temperatures of the nip point and compaction pressures of the roller, such as warpage, matrix squeeze-out, and fibre or ply waviness. Hence, a method for controlling the substrate temperature to achieve isothermal crystallisation in the ATP process was proposed, and the effect of isothermal temperatures on the structure and performance of the laminates was studied. The results revealed that the optimised process not only reduced the defects but also ensured the bonding strength and improved mechanical properties at a low peak temperature of the nip point. • An in-situ solidification approach for thermoplastic composites integrates isothermal crystallisation and ATP process. • Modifying the performance of ATP parts using low-cost thermoplastic composites with semicrystalline matrices. • Reducing defects such as matrix squeeze-out, in-plane and out-of-plane waviness, and warpages. • Improving the bonding strength and overall bending properties. [ABSTRACT FROM AUTHOR]