Influence of temperature distribution on the foaming quality of foamed polypropylene composites

The foamed polypropylene (PP) composites were prepared by injection molding process. Fourier’s law and software were used to calculate and simulate the internal temperature distribution of PP composites, respectively, and the influence of the temperature distribution on the foaming quality of foamed PP composites was further analyzed. The result showed that the calculative and simulated results of temperature distribution in different thermal transfer directions had great reproducibility. In different isothermal planes, the temperature from the nozzle to the dynamic mold gradually decreased. The isothermal plane with a temperature of 370.36 K had a better foaming quality, average diameter of cell and cell density were 28.46 µm and 3.7 × 1010 cells·cm−3, respectively. In different regions of the same isothermal plane, the temperature gradually decreased from the center to the edge. The foaming quality in the region (c) at a temperature of 335.86 K was ideal, and the average diameter of cell and the cell density were 26.5 µm and 2.39 × 1010 cells·cm−3, respectively. This work could provide prediction for improving the foaming quality of foamed polyolefin composites.

Open-Celled Foams from Polyethersulfone/Poly(Ethylene Glycol) Blends Using Foam Extrusion

Polyethersulfone (PESU), as both a pristine polymer and a component of a blend, can be used to obtain highly porous foams through batch foaming. However, batch foaming is limited to a small scale and is a slow process. In our study, we used foam extrusion due to its capacity for large-scale continuous production and deployed carbon dioxide (CO₂) and water as physical foaming agents. PESU is a high-temperature thermoplastic polymer that requires processing temperatures of at least 320 °C. To lower the processing temperature and obtain foams with higher porosity, we produced PESU/poly(ethylene glycol) (PEG) blends using material penetration. In this way, without the use of organic solvents or a compounding extruder, a partially miscible PESU/PEG blend was prepared. The thermal and rheological properties of homopolymers and blends were characterized and the CO₂ sorption performance of selected blends was evaluated. By using these blends, we were able to significantly reduce the processing temperature required for the extrusion foaming process by approximately 100 °C without changing the duration of processing. This is a significant advancement that makes this process more energy-efficient and sustainable. Additionally, the effects of blend composition, nozzle temperature and foaming agent type were investigated, and we found that higher concentrations of PEG, lower nozzle temperatures, and a combination of CO₂ and water as the foaming agent delivered high porosity. The optimum blend process settings provided foams with a porosity of approximately 51% and an average foam cell diameter of 5 µm, which is the lowest yet reported for extruded polymer foams according to the literature.

Anisotropic solid-state PLA foaming templated by crystal phase pre-oriented with 3D printing: Cell supporting structures with directional capillary transfer function

Bones represent a superb biomaterial that combines high mechanical stiffness with nutrition delivery to its osteocyte cells through the microscopical Haversian canals and bone canaliculi. Such structure is hard to...

Recycling printed polypropylene labels and polyolefins caps as chemical foaming agent to produce foam products

Recycling printed polypropylene (PP) labels and printed polyolefins (PO) caps as a chemical foaming agent to produce foam products is studied. An experimental Taguchi L16 design with seven experimental variables involved is used: talc content and screw angular velocity, at four experimental levels; extrusion temperature profile and extruded formulations, at three levels; and, type of label washing process, the use of metal mesh and the type of label drying process, at two levels. As control variables, the morphology of the cells and the density of the foamed products are utilized. The labels/caps mixture was composed of 21% printed PP labels and 79% printed polyolefin caps. Part of the pigments from the ink labels and some polar groups of low-molecular-weight materials present in the molten polymer were partially decomposed at the PP processing temperatures, which contributes to the cell formation and growth of the extruded foams. The labels/caps mixture generated large ellipsoidal and elongated cells (740 µm) oriented in the extrusion direction because of the presence of high density polyethylene (HDPE) and EVA in the recycled PP caps and labels. The experimental factors that influenced the foam density were the screw angular velocity and temperature, and the cell morphology depended on the matrix crystallinity and melt strength.

Increasing cell density/decreasing cell size to produce microcellular and nanocellular thermoplastic foams: A review

Nowadays, polymeric foams have attracted particular attention in scientific and industrial societies due to their unique properties, such as high strength to weight ratio, excellent thermal and sound insulation, and low cost. Researchers have shown that the extraordinary properties of polymeric foams such as superior thermal insulation, can be achieved by increasing the cell density/decreasing the cell size. In this regard, firstly, the most important foaming processes, i.e. batch, extrusion, and injection molding are studied in the present research. Then, cell nucleation stage as the most crucial phenomenon for achieving high cell density/small cell size is investigated in detail. In the next step, the most important researches in the field of polymeric foams are introduced in which the largest cell densities/smallest cell sizes have been achieved. The investigations show that the most remarkable results (highest cell densities/smallest cell sizes) belong to the batch process. Also, the use of nucleating agents, increasing the solubility of blowing agent into the polymer, and the use of nanoparticles are the most efficient solutions to achieve microcellular and nanocellular structures.

Influence of molecular structure on the rheological properties and foamability of long chain branched polypropylene by “one-pot” reactive extrusion

In this work, reactive twin screw extrusion was conducted to synthesize long chain branched polypropylenes (LCB-PPs) in a “one-pot” process in which dicumyl peroxide (DCP) initiated maleic anhydride (MAH) grafting onto the linear PP, and the concomitant coupling reaction between ethylene diamine (EDA) and MAH grafted polypropylene (PP-g-MAH) proceeded in series. Fourier transfer infrared spectroscopy (FTIR) on the prepared materials confirmed the occurrence of both reactions. A series of LCB-PPs were prepared using different amounts of EDA, MAH and DCP to study their effects and determine the optimal synthesis conditions. The prepared materials were characterized by size exclusion chromatography (SEC) and rheological analysis to ascertain the polymer microstructure. The foamability of the LCB-PPs by supercritical carbon dioxide (scCO2) foaming and foam morphology were investigated. The LCB-PPs were found to have vastly improved foamability and cellular morphology. Under optimal conditions, a foam expansion ratio of over 20 was achieved.