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The inherently linear polypropylene suffers unsatisfying foaming behavior due to its low melt strength. To overcome this drawback, polypropylene‐/polypropylene‐grafted glycidyl methacrylate/thermoplastic polyester elastomer (PP/PP‐g‐GMA/TPEE) blending foam is prepared by the chemical foaming method in this study. The foaming mechanism of blending was studied from the aspects of the rheological behavior and the crystallization property. The results show that TPEE disperses in the PP matrix with fine particles and forms ideal interfaces, which provide a large number of nucleation sites for the foaming process of blending, inducing heterogeneous nucleation. Both of the 15 wt% and 20 wt% TPEE‐modified PP composites show higher shear viscosity and obvious strain hardening behavior. It has been proved that the cross‐linking network structure formed by TPEE and PP‐g‐GMA reaction improves the melt strength. The cell size decreases from 37.6 to 24.8 μm, and the cell density increases from 2.9 × 106 cells/cm3 to 2.5 × 107 cells/cm3. Compared with PP composites, the foaming window of the PP/PP‐g‐GMA/TPEE composites was widened.

The branched/micro-crosslinked structure formed by chain extension reaction between EGMA and PLA improved the rheological behavior and crystallization properties of PLA, which ameliorated the foaming performance of various PLA samples.

Epoxy foams with different densities and microstructures were prepared by changing the process parameters including the foaming temperature, chemical foaming agent (CFA) content and precuring extent. The microstructure of foams reveals a smaller cell size, higher cell density, and more homogeneous distribution of cells at higher precuring extent. However, the cell size and distribution are not affected by the foaming temperature and CFA content without precuring process. In addition, the bubbles migration, which resulted in non-uniform cell density distribution, was promoted by increasing the foaming temperature and depressed by increasing the CFA content and precuring extent. The flexural properties of the non-uniform epoxy foams were also studied. Results showed that the flexural modulus was related to the cell morphology, while the flexural strength was affected by both the cell morphology and the position of the specimens during test. It was also found that the relative flexural modulus and strength exhibited a power-law dependence with respect to the relative density.

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Gel-free long-chain-branched polypropylene (LCBPP) was prepared by the melt radical branching reaction in the presence of peroxide initiator 2,5-dimethyl-2,5-di(tertbutylperoxy) hexane peroxide, zinc dimethyldithiocarbamate, and trimethylolpropane triacrylate in a torque rheometer. It could be inferred that recombination between PP chains via radical coupled reaction took place and trimethylolpropane triacrylate was grafted onto PP backbone by the torque curves and Fourier transformed infrared spectroscopy results. The presence of long chain branches (LCB) for modified PP was verified by the gel permeation chromatography measurements and vGP plots. On the other hand, it was found that the topological structure of PP chains transformed from linear form to a long star-like shape during the reaction progress, and the topological structure was directly determined by the radical reaction time. The topological structure of PP would further impact its melt behaviour. After complete melting of raw PP, "sparse and long" LCBPP firstly generated which possessed high melt strength owing to the increasing entanglement of long branching chains. And at the time corresponding to the summit of reaction peak on the torque curve, the modified LCBPP possess the highest melt strength owing to its long star topological structure. While as reaction time was prolonged, severe degradation of the LCBPPs would take place under too long mixing time and "dense and short" branches generated due to the residual radicals, with a sharp decline in melt strength. KEYWORDS long chain branched (LCB), melt performance, polypropylene (PP), rheology, topological structure 1 | INTRODUCTION Isotactic polypropylene is one of the most widely used resins owing to its desirable and beneficial advantages such as low density, high melting point, wide sources, superior mechanical properties, and chemical stability. 1,2 However, ordinary commercial polypropylene, prepared by Ziegler-Natta or metallocene catalyst, cannot be applied into some processes where entanglement properties and melt strength are dominant, such as thermoforming, extrusion foaming, and blow molding, due to its linear structure and poor melt strength. Therefore, it is essential to improve the melt strength of PP. It was reported that fraction of long-chain-branched (LCB) or crosslinked structures in PP were able to enhance the melt strength remarkably owing to the augment of the entanglements among the macromolecule chains. 3 When LCB exists, PP can obviously exhibit strain hardening behaviour in the melt state. 4,5As a simple and effective way, melt radical addition is mostly applied to fabricate long-chain-branched polypropylene (LCBPP) recently. [5][6][7] Compared with in situ polymerization in a reactor and high-energy electron irradiation method, melt radical reaction has some unique advantages such as solvent-free process, short reactive time, and low cost. Nonetheless, the preparation technology and

Microcellular foamed polymers have been widely used in the traffic field. However, it is difficult to successfully manufacture microcellular foamed products that simultaneously possess good cell morphology, small size, high cell density, and great surface quality. In this paper, polyamide 6 (PA6) injection microcellular foams were manufactured via short-shot and core-back foaming process to investigate the effect of the foaming process on cell quality and surface quality. Results showed that the core-back injection PA6 foams possessed a smaller cell size, higher cell density, lower cell deformation, and greater surface glossiness than short-shot foams. The cell density of core-back PA6 microcellular foams reached to 12.5 × 105 cell/cm3, which is almost 3.5 times greater than that of the short-shot foams when the weight reduction was 10%. The PA6 microcellular foams manufactured via the core-back foaming process had higher surface glossiness with different weight reduction, whereas the surface glossiness of short-shot microcellular foams dramatically declined with an increase in weight reduction. Hence, the core-back foaming process can be used to fabricate microcellular foamed polymers with good cell morphology, small size, high cell density, and fine surface quality under high weight reduction; this was beneficial for producing products that have good surface quality and high weight reduction and are used in automobiles, high-speed trains, and airplanes to reduce energy consumption.

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