scholarly journals Compression Molding of Thermoplastic Polyurethane Foam Sheets with Beads Expanded by Supercritical CO2 Foaming

Polymers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 656
Author(s):  
Tao Zhang ◽  
Seung-Jun Lee ◽  
Yong Hwan Yoo ◽  
Kyu-Hwan Park ◽  
Ho-Jong Kang
Keyword(s):  
Cell Size ◽  
Supercritical Co2 ◽  
Cell Structure ◽  
Thermoplastic Polyurethane ◽  
Compression Molding ◽  
Expansion Ratio ◽  
Compression Pressure ◽  
Elongation At Break ◽  
Foaming Process ◽  
Foaming Temperature

Expanded thermoplastic polyurethane (ETPU) beads were prepared by a supercritical CO2 foaming process and compression molded to manufacture foam sheets. The effect of the cell structure of the foamed beads on the properties of the foam sheets was studied. Higher foaming pressure resulted in a greater number of cells and thus, smaller cell size, while increasing the foaming temperature at a fixed pressure lowered the viscosity to result in fewer cells and a larger cell size, increasing the expansion ratio of the ETPU. Although the processing window in which the cell structure of the ETPU beads can be maintained was very limited compared to that of steam chest molding, compression molding of ETPU beads to produce foam sheets was possible by controlling the compression pressure and temperature to obtain sintering of the bead surfaces. Properties of the foam sheets are influenced by the expansion ratio of the beads and the increase in the expansion ratio increased the foam resilience, decreased the hardness, and increased the tensile strength and elongation at break.

scholarly journals Kinked Bisamides as Efficient Supramolecular Foam Cell Nucleating Agents for Low-Density Polystyrene Foams with Homogeneous Microcellular Morphology

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1094
Author(s):  
Bastian Klose ◽  
Daniel Kremer ◽  
Merve Aksit ◽  
Kasper P. van der Zwan ◽  
Klaus Kreger ◽  
...  
Keyword(s):  
Cell Size ◽  
Self Assembly ◽  
Large Scale ◽  
Elevated Temperatures ◽  
Foam Cell ◽  
Cell Structure ◽  
Expansion Ratio ◽  
Low Density ◽  
Nucleating Agents ◽  
Foam Density

Polystyrene foams have become more and more important owing to their lightweight potential and their insulation properties. Progress in this field is expected to be realized by foams featuring a microcellular morphology. However, large-scale processing of low-density foams with a closed-cell structure and volume expansion ratio of larger than 10, exhibiting a homogenous morphology with a mean cell size of approximately 10 µm, remains challenging. Here, we report on a series of 4,4′-diphenylmethane substituted bisamides, which we refer to as kinked bisamides, acting as efficient supramolecular foam cell nucleating agents for polystyrene. Self-assembly experiments from solution showed that these bisamides form supramolecular fibrillary or ribbon-like nanoobjects. These kinked bisamides can be dissolved at elevated temperatures in a large concentration range, forming dispersed nano-objects upon cooling. Batch foaming experiments using 1.0 wt.% of a selected kinked bisamide revealed that the mean cell size can be as low as 3.5 µm. To demonstrate the applicability of kinked bisamides in a high-throughput continuous foam process, we performed foam extrusion. Using 0.5 wt.% of a kinked bisamide yielded polymer foams with a foam density of 71 kg/m3 and a homogeneous microcellular morphology with cell sizes of ≈10 µm, which is two orders of magnitude lower compared to the neat polystyrene reference foam with a comparable foam density.

Effect of rare earth nucleating agent on supercritical CO2 foaming behavior of block copolymerized polypropylene

2021 ◽  
pp. 026248932110536
Author(s):  
Yun Zhang ◽  
Yadong He ◽  
Chunling Xin ◽  
Yanbin Su
Keyword(s):  
Rare Earth ◽  
Saturation Temperature ◽  
Nucleating Agent ◽  
Expansion Ratio ◽  
Good Effect ◽  
Cell Diameter ◽  
Average Cell ◽  
Foaming Process ◽  
Foaming Temperature ◽  
Crystal Content

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.

Effect of Plasticizer (DOP) on Cell Structure and Mechanical Properties of Extrusion-Foamed PVC Sheet

2015 ◽  
Vol 815 ◽  
pp. 601-606 ◽  
Author(s):  
Ming Yi Wang ◽  
Nan Qiao Zhou ◽  
Jun Hu
Keyword(s):  
Mechanical Properties ◽  
Cell Structure ◽  
Dioctyl Phthalate ◽  
Bubble Coalescence ◽  
Low Density ◽  
Foaming Agent ◽  
Elongation At Break ◽  
Foaming Process ◽  
Continuous Extrusion ◽  
Scanning Electron

Using supercritical CO2 as the foaming agent, rigid polyvinyl chloride (R-PVC) foam sheets were prepared in a continuous extrusion foaming system. The effects of dioctyl phthalate (DOP) on the rheological properties of PVC were investigated using a Brabender torque rheometer while other basic formula remained unchanged. The influences of DOP content on microstructure, mechanical properties and density of PVC micro foamed sheet were investigated with scanning electron microscopy (SEM). The results showed that the addition of DOP resulted in increased flexibility and the elongation at break of the foamed PVC sheet, while the mechanical properties of foamed PVC sheet decreased with the increase of DOP content, implying that excessive addition of DOP will cause gas escape and bubble coalescence in the foaming process. Low density PVC foam sheets with fine cell morphology were obtained when 2 phr DOP was added in PVCformula.

Dynamic rheology and foaming behaviour of styrene–ethylene–butylene–styrene/ polystyrene blends

2016 ◽  
Vol 53 (4) ◽  
pp. 389-406 ◽  
Author(s):  
Ritima Banerjee ◽  
Suprakas Sinha Ray ◽  
Anup K Ghosh
Keyword(s):  
Volume Expansion ◽  
Complex Viscosity ◽  
Expansion Ratio ◽  
Dynamic Rheology ◽  
Blowing Agent ◽  
Foaming Process ◽  
Lower Volume ◽  
Foaming Temperature ◽  
And Storage ◽  
Nucleating Effect

Styrene–ethylene–butylene–styrene and its blends containing 10, 30 and 50 wt% polystyrene were subjected to batch foaming using physical blowing agent carbon dioxide. At higher foaming temperatures (80–110℃), complex viscosity ( η*) and storage modulus ( E′) were found to control the volume expansion ratio and the shrinkage of foams. For a given composition, optimal volume expansion was achieved at temperatures close to the glass transition temperature ( T g) of the polystyrene phase of that composition, indicating the presence of a complex viscosity window favourable for the foaming process. Blends with 30% and 50% polystyrene content possessed higher values of E′ and η*, and produced stable foams having higher volume expansion ratio, when foamed within their respective η* windows. At a much lower foaming temperature (35℃), polystyrene was found to have a nucleating effect. However, irrespective of rheological properties, all foams showed prominent shrinkage. A higher polystyrene content resulted in a lower volume expansion ratio, as well as shrinkage over a shorter period of time and a greater extent of shrinkage in the same time span. This can be attributed to the selective foaming of the ethylene–butylene phase, hindered by the stiff polystyrene aggregates.

scholarly journals Improving the Continuous Microcellular Extrusion Foaming Ability with Supercritical CO2 of Thermoplastic Polyether Ester Elastomer through In-Situ Fibrillation of Polytetrafluoroethylene

Polymers ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 1983 ◽  
Author(s):  
Rui Jiang ◽  
Tao Liu ◽  
Zhimei Xu ◽  
Chul B. Park ◽  
Ling Zhao
Keyword(s):  
Cell Density ◽  
Supercritical Co2 ◽  
Cell Structure ◽  
Average Diameter ◽  
Extrusion Process ◽  
Expansion Ratio ◽  
Cell Diameter ◽  
Scanning Calorimetry ◽  
Foaming Ability

In-situ fibrillated polytetrafluoroethylene (PTFE) enhanced nanocomposites were successfully prepared by mixing thermoplastic polyether ester elastomer (TPEE) and PTFE using a twin-screw extruder. Well-dispersed, long aspect ratio PTFE nanofibrils with a diameter of less than 200 nm were generated and interwoven into networks. Differential scanning calorimetry and in-situ polarized optical microscopy showed that the PTFE nanofibrils can greatly accelerate and promote crystallization of the TPEE matrix and the crystallization temperature can be increased by 6 °C. Both shearing and elongational rheometry results confirmed that the introduction of PTFE nanofibrils can significantly improve the rheological properties. The remarkable changes in the strain-hardening effect and the melt viscoelastic response, as well as the promoted crystallization, led to substantially improved foaming behavior in the continuous extrusion process using supercritical CO2 as the blowing agent. The existing PTFE nanofibrils dramatically decreased the cell diameter and increased cell density, together with a higher expansion ratio and more uniform cell structure. The sample with 5% PTFE fibrils showed the best foaming ability, with an average diameter of 10.4–14.7 μm, an expansion ratio of 9.5–12.3 and a cell density of 6.6 × 107–8.6 × 107 cells/cm3.

Microcellular Foaming of Biodegradable PLA/PPC Composite Using Supercritical CO2

2016 ◽  
Vol 861 ◽  
pp. 247-252
Author(s):  
Zhen Guo Ma ◽  
Xian Hua Lang ◽  
Peng Luo ◽  
Zhen Xiang Xin ◽  
Zhen Xiu Zhang
Keyword(s):  
Cell Structure ◽  
Saturation Pressure ◽  
Saturation Temperature ◽  
Poly Lactic Acid ◽  
Foam Density ◽  
Foaming Process ◽  
Composite Foams ◽  
Controlled Structure ◽  
Poly Propylene ◽  
Foaming Temperature

Poly (lactic acid) (PLA)/poly (propylene carbonate) (PPC) composite foams were microcellular foamed with CO2 through a batch foaming process. The influences of PPC contents, foaming temperature, and saturation pressure on the cell structure and foam density were investigated. The biodegradable PLA/PPC composite foam showed a controlled structure of microcellular and nanocellular. With an increase in saturation temperature and pressure, the cell size was increasing and both the cell density and foam density were decreased simultaneously.

scholarly journals Ultrahigh and Tunable Electromagnetic Interference Shielding Performance of PVDF Composite Induced by Nano-Micro Cellular Structure

Polymers ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 234
Author(s):  
Yang Yang ◽  
Shuiping Zeng ◽  
Xiping Li ◽  
Zhonglue Hu ◽  
Jiajia Zheng
Keyword(s):  
Electromagnetic Interference ◽  
Supercritical Co2 ◽  
Cell Structure ◽  
Vital Role ◽  
Compression Tests ◽  
Shielding Effectiveness ◽  
Emi Shielding ◽  
Polymer Foam ◽  
Emi Shielding Effectiveness ◽  
Foaming Process

Lightweight and efficient electromagnetic interference (EMI) shielding materials play a vital role in protecting high-precision electronic devices and human health. Porous PVDF/CNTs/urchin-like Ni composites with different cell sizes from nanoscale to microscale were fabricated through one-step supercritical carbon dioxide (CO2) foaming. The electrical conductivity and electromagnetic interference (EMI) shielding performance of the composites with different cell sizes were examined in detail. The results indicated that the nanoscale cell structure diminishes the EMI shielding performance of the composite, whereas the microscale cell structure with an appropriate size is beneficial for improving the EMI shielding performance. A maximum EMI shielding effectiveness (SE) of 43.4 dB was achieved by the composite foams which is about twice that of the solid composite. Furthermore, as the supercritical CO2 foaming process reduces the density of the composite by 25–50%, the EMI SSE (specific shielding effectiveness)/t(thickness) of the composite reaches 402 dB/(g/cm2), which is the highest value of polymer foam obtained to the best of the authors’ knowledge. Finally, compression tests were performed to show that the composites still maintained excellent mechanical properties after the supercritical CO2 foaming process.

scholarly journals Thermoplastic polyurethane foams: From autoclave batch foaming to bead foam extrusion

2020 ◽  
pp. 0021955X2091220
Author(s):  
Amin Shabani ◽  
Amir Fathi ◽  
Sebastian Erlwein ◽  
Volker Altstädt
Keyword(s):  
Cell Size ◽  
Thermoplastic Polyurethane ◽  
Polyurethane Foams ◽  
Morphological Properties ◽  
Cell Size Distribution ◽  
Foam Expansion ◽  
Foam Extrusion ◽  
Foaming Process ◽  
First Time ◽  
Batch Foaming

Two ester-based and one ether-based thermoplastic polyurethane grades have been used to produce thermoplastic polyurethane foams. The foaming process comprised pressure-induced batch foaming, foam extrusion, and bead foam extrusion by using an underwater granulator. Foam density and morphological properties, such as cell size, cell size distribution, and cell density, were measured through different analytical methods. Through autoclave batch foaming a minimum cell size of 10 µm and density of 202 kg/m3 is obtained, which is lower than the densities previously reported in the literature for thermoplastic polyurethane. Extrusion foaming however could not achieve the same range of foam expansion given that the lowest density achieved is 635 kg/m3 and a minimum cell size equal to 46 µm. The production of thermoplastic polyurethane bead foams is also reported for the first time. The minimum density of the obtained foamed beads is 306 kg/m3 and the lowest cell size is 55 µm.

Foaming behavior of microcellular poly(lactic acid)/TPU composites in supercritical CO2

2017 ◽  
Vol 31 (1) ◽  
pp. 61-78 ◽  
Author(s):  
Daifang Xu ◽  
Kejing Yu ◽  
Kun Qian ◽  
Chul B Park
Keyword(s):  
Lactic Acid ◽  
Cell Structure ◽  
Thermoplastic Polyurethane ◽  
Optical Microscope ◽  
Expansion Ratio ◽  
Poly Lactic Acid ◽  
Free Energy Barrier ◽  
Scanning Calorimetry ◽  
Melt Strength ◽  
Cell Nucleation

This article presents the effects of thermoplastic polyurethane (TPU) on the crystallization and melt strength of poly(lactic acid) (PLA) and on the enhancement of cell nucleation and expansion ratio to manufacture microcellular thermoplastic PLA foams in supercritical carbon dioxide. Addition of TPU increased the crystallinity and decreased the crystallite size as observed by differential scanning calorimetry and polarized optical microscope. The formed crystal domains worked as cross-linking points to increase the melt strength of a polymer that potentially affected the cell growth. Scanning electron microscope confirmed the immiscibility between PLA and TPU, and TPU was dispersed as islands in the PLA matrix. This phase morphology further influenced the cell structure of the PLA/TPU foams. TPU acted as a nucleating agent to enhance heterogeneous cell nucleation that is caused by the decrease in free energy barrier. Tensile stress that generated around the TPU and in some local regions surrounding the crystals and crystallization was dominant to induce cell nucleation.

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