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The inherently linear poly (lactic acid) suffers unsatisfying foaming behavior due to its low melt strength and poor crystallization properties. To overcome this drawback, a random terpolymer of ethylene, acrylic ester and glycidyl methacrylate (EGMA) was employed to improve the rheological behavior, crystallization properties, and foaming performance of poly (lactic acid) (PLA) through a chain extension reaction. The branched/micro-crosslinked structure formed by the chain extension reaction between EGMA and PLA effectively improved the dynamic rheological properties of PLA. As the content of EGMA increased from 0 wt% to 20 wt%, the crystal nucleation and crystal growth rate of various PLA samples have been significantly accelerated, resulting in a larger number and smaller size of spherulites, and the crystallinity of various PLA samples increased from 7.9% to 38.54%. The cell size of various PLA foams decreased from 53.5 to 22.0 μm and the cell density increased from 3.5 × 106 cells per cm3 to 2.5 × 107 cells per cm3, meanwhile, the cellular morphology of PLA foam was obviously improved. Moreover, the actual weight loss of PLA foams reached 26.1%, which is higher than the theoretical weight loss.

The effects of the cell size and distribution on the mechanical properties of polypropylene foam were simulated and analyzed by finite element modeling with ANSYS and supporting experiments. The results show that the reduced cell size and narrow size distribution have beneficial influences on both the tensile and impact strengths. Decreasing the cell size or narrowing the cell size distribution was more effective for increasing the impact strength than the tensile strength in the same case. The relationship between the mechanical properties and cell structure parameters has a good correlation with the theoretical model.

The paper uses chemical foaming method to prepare foamed polystyrene (PS) composites by a self-made visualization system. During the cell growth and deformation process, the radial response area model, the hoop tension model and cell deformation model of the resin around were established at the molecular scale, and the cell growth and deformation process of the actual injection molded and visualized expanded polystyrene (PS) composites were simulated and verified. The results show that we have established the radial response area model, the hoop tension model and cell deformation model of the surrounding resin, and the actual injection foaming process is basically consistent with the visualized simulation results of light microscope. In different foaming stages, the radial migration and circumferential stretching of the surrounding resin by the cells are different, which ultimately leads to different deformation of the cells. The growth and deformation of the cells have verified the feasibility of the radial response area model, the hoop tension model and cell deformation model during foaming process. This research work is of great significance to guide the foaming of polyolefin materials.

This paper investigates the bubble nucleation of polymer (LDPE) foams using nucleation theory and establishes a mathematical model based on in-situ observations and measurements. The effects of different foaming agent contents and shot sizes on bubble nucleation were studied in an injection foaming experiment and a new mathematical model describing the bubble nucleation kinetics was obtained based on classical nucleation theory. The model fittings were obtained for different experimental conditions. The process of foaming nucleation could be characterized intuitively through this model and can be used as a general form for other nucleation processes.

The morphology, size and surface roughness of the nucleating agent significantly affect the nucleation effect for foaming in the polymer. In this work, four nucleating agents with different morphologies, namely DE, MS, OMMT and β- CD as heterogeneous nucleation agents were selected for a polypropylene (PP) foaming injection molding process to explore nucleation mechanism. A theoretical assumption (cavity nucleation) in polymer foaming had been put forward about how to enhance the efficiency of bubble nucleation based on classical nucleation theory (CNT). Subsequently, the cavity nucleation was validated by chemical core-back injection foaming molding and in-situ visualization and elaborated by establishing a formula. Finally, designed petals shape particles as nucleating agents to further test this theory. The confirmation of this theory effectively improved the nucleation efficiency and foaming quality, which has important guiding significance to the development of lightweight products.

In this paper, the dynamic foaming process of micro-foaming polypropylene (PP) in different foaming environments in real time was obtained via a visualization device. The relationship curve between cell number (n) and foaming time (t) was plotted, and then the nucleation kinetics of foam cells was analyzed. Results showed that the formation rate of cells changed obviously with the variation of melt temperature and the content of the foaming agent. The n-t curves presented a typical “S” shape, which indicated that the appearance of the cell number increased slowly in the initial foaming period, then increased rapidly in a short time, and finally maintained a certain value. When a certain pressure was applied to the PP melt, the external force had a great influence on the n-t curve. With the increasing external force, the rate of cell formation increased rapidly, and the shape of the n-t curve changed from “S” to “semi-S” without an obvious slow increase. The investigation of the n-t relationship in the PP dynamic foaming process under different foaming environments could provide effective bases for improving the foaming quality of injection molding foaming materials.