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.

Evaluation of polypropylene/clay nanocomposite foamability based on their morphological and rheological aspects

2018 ◽  
Vol 54 (5) ◽  
pp. 829-850 ◽  
Author(s):  
Anindya Dutta ◽  
Sabapathy Sankarpandi ◽  
Anup K Ghosh
Keyword(s):  
Cell Density ◽  
Thermal Studies ◽  
Expansion Ratio ◽  
Clay Nanocomposites ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Transmission Electron ◽  
Polypropylene Matrix ◽  
Induced Crystallization

To identify the effect of rheological influence on the development of microstructure in polypropylene/clay nanocomposites and thereby the influence of the developed microstructure on the foamability of the nanocomposites, a set of nanocomposites was prepared and batch foamed using supercritical CO2. Polypropylene and nanoclay were selected for preparing nanocomposites. During foaming, the nanocomposites were saturated with CO2 gas for three different time periods and subsequently in-situ heating was done to achieve cell growth. The gas saturation was done at subcritical condition followed by the foaming at critical condition of CO2. Thermal studies of the composites were investigated through differential scanning calorimetry, and clay dispersion morphology was investigated and validated using wide-angle X-ray diffraction, transmission electron microscopy, and parallel plate rheology. The improvement in foam morphology (cell size and cell density) and subsequent reduction in foam density was analyzed. The fingerprint characteristics of nanocomposites have an enormous role on foam structure development. With the increase in clay loading, cell density increased; furthermore, with an increase in saturation time, there was a phenomenal decrease in expansion ratio of neat polypropylene due to CO2-induced crystallization which could be mitigated by the incorporation of nanoclay into the polypropylene matrix. Therefore, nanoclay could be exploited as the inhibitor of CO2-induced crystallization.

Expandable polystyrene without any embedded blowing agent

2020 ◽  
pp. 0021955X2094497
Author(s):  
Habib Haji Avdi ◽  
Morteza Nasiri ◽  
Mohammad Javad Tehrani ◽  
Maryam Alizadeh Aghdam ◽  
Farhang Abbasi
Keyword(s):  
Suspension Polymerization ◽  
Expansion Ratio ◽  
Scanning Calorimetry ◽  
Blowing Agents ◽  
Blowing Agent ◽  
Rate Of Polymerization ◽  
Polystyrene Matrix ◽  
Expandable Polystyrene ◽  
Before And After

In this research, in-situ suspension polymerization of styrene in the presence of graphene, without any blowing agent, was investigated. Steam used in the expansion process of graphene-filled expandable polystyrene (GEPS). The dispersed graphene nano-sheets in the polystyrene matrix may absorb water in high temperatures, which evaporates by lowering the pressure and expansion precedes. The effects of graphene type and loading and steam temperature on the expansion ratio evaluated. Scanning electron microscopy (SEM) used to reveal the cross-section morphologies before and after expansion. The effect of graphene on the polymerization kinetics evaluated by differential scanning calorimetry (DSC). The results showed that by increasing the graphene loading, the rate of polymerization decreased, and the expansion ratio increased. The highest expansion ratio of about 4.8 was for particles containing 0.4% of graphene. Therefore, it was shown that by using graphene as a dispersed phase, polystyrene particles expanded without any organic blowing agents. Here, the idea of expandable polymers without any embedded blowing agent is introduced, which eliminates the release of volatile organic compounds and makes the process environmentally friendly.

scholarly journals Tinjauan karakteristik foam plastik mikroseluler polistirena dengan penambahan aditif pada teknologi superkritis

2018 ◽  
Vol 9 (1) ◽  
pp. 33
Author(s):  
Faidliyah Nilna Minah ◽  
Firman Kurniawansyah ◽  
S Sumarno
Keyword(s):  
Carbon Dioxide ◽  
Cell Density ◽  
Supercritical Co2 ◽  
Cell Diameter ◽  
Coconut Fiber ◽  
Microcellular Foam ◽  
Fiber System ◽  
Average Cell ◽  
Blowing Agent ◽  
Scanning Electron

Processing technology of microcellular plastic represents development of foaming conventional plastic process. The processing of microcellular plastic has been acknowledged as eco-friendly technology because this plastic is produced by the use of benign supercritical carbon dioxide gas as blowing agent. In this work, the samples polystyrene and additive were saturated with supercritical CO2 at various saturation pressures from 10-22 MPa (at around glass transition temperature of 95 oC and 80 oC) When the saturation time was accomplished, the solution was decompressed rapidly into atmospheric pressure. The samples were placed in the vessel heated and completed by flowing of carbon dioxide as cooler gas into the vessel. The samples were characterized to observe volume expansion ratio, cell density, average cell diameter and surface fractured with Scanning Electron Microscopy. The microcellular foam of plastic product of PS system has cell diameter between 3.970-9.933 μm , cell density between 9.14x104 – 6.24x109 cell/ cm3. PS-CaCO3 system has cell diameter between 3.501-8.050 μm, cell density between 3.31x107 – 1.10x1011 cell/cm3, while PS-coconut fiber system hascell diameter between 2.520-8.414 μm, cell density between 1.50x108 -1.60x1010 cell/cm3 at various pressure.Keywords: polystyrene, microcellular foam plastic, supercritical CO2, CaCO3additive, coconut fiber additive.  AbstrakProses pembuatan plastik mikroseluler merupakan pengembangan dari proses pembuatan foam plastik konvensional. Plastik mikroseluler menggunakan fluida superkritis seperti CO2 dan N2 sebagai blowing agent yang ramah terhadap lingkungan, sehingga proses pembuatan foam plastik mikroseluler dikenal sebagai teknologi ramah lingkungan. Penelitian ini menggunakan sampel polistirena yang dicampur dengan partikel kalsium karbonat atau sabut kelapa dengan konsentrasi 5% yang diproses pada kondisi tekanan 10-22 MPa (T = 95 oC dan 80 oC). Setelah kondisi yang diinginkan tercapai dilakukan dekompresi secara mendadak menuju tekanan atmosfer, dan dilanjutkan dengan proses pemanasan, diakhiri dengan mengalirkan gas CO2 sebagai pendingin. Selanjutnya sampel dikarakterisasi untuk mengetahui rasio volume ekspansi foam, densitas sel, diameter rata-rata sel dan struktur foam yang dihasilkan dengan Scanning Electron Microscope. Pada penelitian ini didapatkan pada sistem PS Murni menghasilkan diameter sel antara 3,970-9,933 μm dan densitas sel 9,14x104 - 6,24x109 cell/cm3. Sistem PS-CaCO3 menghasilkan diameter sel antara 3,501-8,050 μm dan densitas sel 3,31x107 - 1,10x1011 cell/cm3, dan pada sistem PS-Sabut kelapa menghasilkan diameter sel antara 2,520-8,414 μm dan densitas sel 1,50x108 - 1,60x1010 cell/cm3 pada berbagai variasi tekanan.Kata kunci : polistirena, foam plastik mikroseluler, CO2 superkritis, aditif CaCO3, aditif sabut kelapa.

Migration of Nanoclay in PP/PS Blend and Effect of Its Localization on Cell Structure

2008 ◽  
Author(s):  
Jun-Feng Zhao ◽  
Han-Xiong Huang
Keyword(s):  
Shear Flow ◽  
Cell Density ◽  
Cell Structure ◽  
Cell Diameter ◽  
Foaming Agent ◽  
Nucleation Sites ◽  
The Mean ◽  
Nanoclay Content ◽  
Blend Nanocomposites ◽  
Low Shear

In this work, the migration of clay in polypropylene/polystyrene (PP/PS) blend and the effect of its final localization on cell structure of microcellular foamed blend nanocomposites were studied. To observe the clay migration, a multilayered blend, alternatively superposed PS and PP/clay films with a thickness of 0.2 mm, was subjected to low shear flow. Batch foaming was performed on obtained blend nanocomposites to study the influence of the nanoclay localization on cell structure by using CO2 as the foaming agent. When subjected to flow, most clay dispersed in PP phase migrated into PS gradually. The migration of nanoclay caused smaller mean cell diameter and higher cell density to foamed PS. With the reduction of nanoclay content in PP phase, the cell density of PP foam decreased due to the reduction of heterogeneous nucleation sites and the mean cell diameter became smaller.

Improved expansion ratio and heat resistance of microcellular poly(L-lactide) foam via in-situ formation of stereocomplex crystallites

2016 ◽  
Vol 54 (1) ◽  
pp. 103-119 ◽  
Author(s):  
Shuaiwei Xue ◽  
Pin Jia ◽  
Qian Ren ◽  
Xincai Liu ◽  
Richard E Lee ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Heat Resistance ◽  
Control Method ◽  
Cell Structure ◽  
High Heat ◽  
Expansion Ratio ◽  
Poly Lactic Acid ◽  
High Heat Resistance ◽  
Resistance Performance

It is critical to broaden the applications of poly(L-lactic acid) foams by improving heat resistance properties. The stereocomplex crystallites that are formed by melt blending of poly(L-lactic acid)/polylactide possess high melting point of about 220℃ and thus exhibit high heat resistance; therefore, the introduction of stereocomplex crystallites tends to improve the thermal stability of poly(lactic acid) foam. Unfortunately, using the solid-state foaming method, it was found that the expansion ratio of the obtained poly(lactic acid) foams was compromised with the value of 1.7 times once the stereocomplex crystallites were formed during the sample saturation stage. In this study, by applying a high compression molding temperature of 230℃, the as-prepared poly(L-lactic acid) and poly(L-lactic acid)/polylactide blends were amorphous. After being CO2 saturated at a mild condition, the specimens were foamed at 90–160℃. The wide-angle X-ray diffraction profiles presented that the stereocomplex crystallites and PLA homocrystals were in-situ generated during the foaming process. It is observed that the in-situ formed stereocomplex crystallites could act as the physical cross-linking agent to stabilize the nucleated bubbles and suppress cell coalescence, resulting in the increased expansion ratio (with value of about 23.6–25.6 times) and cell density, especially at high foaming temperatures and extended foaming time. Furthermore, the in-situ formed stereocomplex crystallites during the foaming increased the heat resistance performance of poly(L-lactic acid) foams. This novel crystallization control method helps us to find a balance point in preparing poly(L-lactic acid) foam with high expansion ratio, well-defined cell structure and high heat resistance performance.

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.

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.

Cell structure properties during in situ creep experiments in the H.V.E.M.

1978 ◽  
Vol 36 (1) ◽  
pp. 574-575
Author(s):  
D. Caillard ◽  
J.L. Martin
Keyword(s):  
Tensile Axis ◽  
Cell Structure ◽  
Image Intensifier ◽  
Foil Thickness ◽  
Average Cell Size ◽  
Average Cell ◽  
Voltage Electron ◽  
Steady Stage ◽  
Stationary Creep

The behaviour of the dislocation substructure during the steady stage regime of creep, as well as its contribution to the creep rate, are poorly known. In particular, the stability of the subboundaries has been questioned recently, on the basis of experimental observations |1||2| and theoretical estimates |1||3|. In situ deformation experiments in the high voltage electron microscope are well adapted to the direct observation of this behaviour. We report here recent results on dislocation and subboundary properties during stationary creep of an aluminium polycristal at 200°C.During a macroscopic creep test at 200°C, a cell substructure is developed with an average cell size of a few microns. Microsamples are cut out of these specimens |4| with the same tensile axis, and then further deformed in the microscope at the same temperature and stain rate. At 1 MeV, one or a few cells can be observed in the foil thickness |5|. Low electron fluxes and an image intensifier were used to reduce radiation damage effects.

Injectable in-situ Forming Depot Of Doxycycline Hyclate/α-Cyclodextrin Complex using PLGA for Periodontitis Treatment: Preparation, Charac-terization, and In-Vitro Evaluation

2020 ◽  
Vol 17 ◽  
Author(s):  
Elham Khodaverdi ◽  
Farhad Eisvand ◽  
Mohammad Sina Nezami ◽  
Seyedeh Nesa Rezaeian Shiadeh ◽  
Hossein Kamali ◽  
...  
Keyword(s):  
Complex Form ◽  
Docking Studies ◽  
Morphological Properties ◽  
Burst Release ◽  
Cyclodextrin Complex ◽  
Doxycycline Hyclate ◽  
Scanning Calorimetry ◽  
In Situ Forming

Background:: Doxycycline (DOX) is used in treating a bacterial infection, especially for periodontitis treatment. Objective: To reduce irritation of DOX for subgingival administration and increase the chemical stability and against enzy-matic, the complex of α-cyclodextrin with DOX was prepared and loaded into injectable in situ forming implant based on PLGA. Methods:: FTIR, molecular docking studies, X-ray diffraction, and differential scanning calorimetry was performed to char-acterize the DOX/α-cyclodextrin complex. Finally, the in-vitro drug release and modeling, morphological properties, and cellular cytotoxic effects were also evaluated. Results:: The stability of DOX was improved with complex than pure DOX. The main advantage of the complex is the al-most complete release (96.31 ± 2.56 %) of the drug within 14 days of the implant, whereas in the formulation containing the pure DOX and the physical mixture the DOX with α-cyclodextrin release is reached to 70.18 ± 3.61 % and 77.03 ± 3.56 %, respectively. This trend is due to elevate of DOX stability in the DOX/ α-cyclodextrin complex form within PLGA implant that confirmed by the results of stability. Conclusion:: Our results were indicative that the formulation containing DOX/α-cyclodextrin complex was biocompatible and sustained-release with minimum initial burst release.

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