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Thermoplastic polyamide elastomer (TPAE)/calcium silicate (CaSiO3) open‐cell foam with low shrinkage and high expansion ratio was prepared by using supercritical CO2 as a blowing agent. Adding CaSiO3 led to increased melt viscoelasticity and reduced crystallinity of TPAE. The primary mechanism of CaSiO3 promoting TPAE foam to form the open‐cell structure was discussed. The interaction between CaSiO3 and TPAE is fragile, making CaSiO3 easy to fall off the cell wall and form the open‐cell structure during foaming process. The increasing CaSiO3 content leads to increased cell density and thinned cell walls, thus increasing the tensile stress on cell wall. On the other hand, the agglomeration of CaSiO3 increases particle size, making it easier to fall off from the adhesion of TPAE matrix. The two aspects work together to improve the open‐cell content of TPAE foam up to 93.28%. The open‐cell structure is conducive to increasing the gas exchange rate and significantly decreasing foam shrinkage ratio. Finally, TPAE foam with a shrinkage ratio of only 2.68% and an expansion ratio of 18.77 times was obtained. In addition, open‐cell structure improves the adsorption performance of TPAE/CaSiO3 foam by 500%. [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]

ABSTRACT A multi-functional epoxide oligomer, Joncryl ADR-4368 (ADR), is used as a modifier to prepare foamable poly(ethylene terephthalate) (PET) by reactive extrusion and compared with common tetra-functional modifier pyromellitic anhydride (PMDA) as a reference. Torque evolution reveals that ADR has a faster reaction with PET than PMDA. The reactions generate long-chain branches and gel structures, which are confirmed by rheological methods. Shear rheological studies show that PET modified with both ADR and PMDA display higher complex viscosity and lower loss tangent than unmodified sample. In particular, at a given viscosity level, ADR leads to a lower loss tangent than PMDA. Moreover, compared to PMDA, the addition of ADR results in a higher die pressure during extrusion and a more pronounced strain hardening during uniaxial elongation. These results indicate that ADR-modified PET is less viscous but more elastic than PMDA-modified PET. Owing to the higher elastic properties, ADR-modified PET presents better foaming performance in batch foaming process with CO2 as a blowing agent. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45805. [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, the foaming behavior of isotactic polypropylene (iPP) and its composites with spherical or fibrous poly(butylenes terephthalate) (PBT) using supercritical CO2 as a blowing agent were investigated. Their foaming performances were also compared in relation to the crystal morphology and rheological behavior of PP. Results demonstrate that crystal structures significantly impacted the cell structures of foams. At relatively low temperature, microcells appeared at the centers of PP spherulites where the melting started. Particularly, bi-modal cell structure formed in the foamed PP with increasing temperature. However, in the foamed PP composites with spherical or fibrous PBT, this structure almost disappeared due to the smaller PP spherulites. In foaming PP/PBT composites, the heterogeneous nucleation of spherical or fibrous PBT was effective at reducing cell size as well as improving cell density and cell uniformity. The fibrous PBT also acted as scaffolds for preserving cell shapes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41801. [ABSTRACT FROM AUTHOR]

Traditionally, in order to simplify the bubble growth process in a polymer melt, an isothermal model is typically used. In fact, the temperature of the polymer melt is changing during the foaming process. In order to accurately study the growth mechanism of bubbles in polymer melts, we build a physical and mathematical model of bubble growth in a polymer melt under nonisothermal conditions. The parameters of pressure, zero‐shear viscosity, relaxation time, Henry's constant, diffusion coefficient, and surface tension were determined. The fourth‐order Runge–Kutta method was used to solve the nonisothermal bubble model in the polymer melt. A computational program is developed to find the dimensional change during the bubble growth process, and the correctness of the model is verified. The nonisothermal growth mechanism of and factors influencing bubbles in the polymer melt are analyzed. Combined with the design of experiment (DOE) analysis method, the transfer function of the bubble radius and the maximum growth rate of bubbles with the process parameters were obtained, such as cooling rate, system pressure, and gas concentration. The results show that system pressure has the most significant effect on bubble growth. At the same time, a bubble growth prediction model is built, which can be used to predict the growth of bubbles. Through optimization analysis, it can be used to control the growth of bubbles. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47210. [ABSTRACT FROM AUTHOR]