scholarly journals Effect of Vulcanization and CO2 Plasticization on Cell Morphology of Silicone Rubber in Temperature Rise Foaming Process

Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3384
Author(s):  
Tianping Zhang ◽  
Shun Yao ◽  
Lu Wang ◽  
Weijun Zhen ◽  
Ling Zhao
Keyword(s):  
Silicone Rubber ◽  
Temperature Rise ◽  
Cell Structure ◽  
Cell Formation ◽  
Complex Viscosity ◽  
Bubble Nucleation ◽  
Sudden Increase ◽  
Co2 Diffusion ◽  
Foaming Process ◽  
Higher Temperature

Both vulcanization reaction and CO2 plasticization play key roles in the temperature rise foaming process of silicone rubber. The chosen methyl-vinyl silicone rubber system with a pre-vulcanization degree of 36% had proper crosslinked networks, which not only could ensure enough polymer matrix strength to avoid bubble rupture but also had enough dissolved CO2 content in silicone rubber for induced bubble nucleation. The CO2 diffusion and further vulcanization reaction occur simultaneously in the CO2 plasticized polymer during bubble nucleation and growth. The dissolved CO2 in the pre-vulcanized silicone rubber caused a temperature delay to start while accelerating further vulcanization reactions, but the lower viscoelasticity caused by either CO2 plasticization or fewer crosslinking networks was still the dominating factor for larger cell formation. There was a sudden increase in elastic modulus and complex viscosity for pre-vulcanized silicone rubbers at higher temperature because of the occurrence of further vulcanization, but CO2 plasticization reduced the scope of change of rheological properties, and the loss factor was close to 1 around 170 °C, which is corresponding to the optimum foaming temperature. The foamed silicone rubber had a higher cell density and smaller cell size at a higher temperature rising rate, which is due to higher CO2 supersaturation and faster vulcanization reaction. These results provide some insight into the coupling mode and effect of CO2 plasticization and vulcanization for regulating cell structure in foaming silicone rubber process.

Experimental and numerical study of the polyurethane foaming process using high-pressure CO2

2020 ◽  
pp. 0021955X2097429
Author(s):  
Dongdong Hu ◽  
Chen Zhou ◽  
Tao Liu ◽  
Yichong Chen ◽  
Zhen Liu ◽  
...  
Keyword(s):  
Numerical Study ◽  
Cell Structure ◽  
Saturation Pressure ◽  
Gas Diffusion ◽  
Bubble Nucleation ◽  
Cell Diameter ◽  
Henry's Constant ◽  
Average Cell ◽  
Foaming Process ◽  
High Pressure Co2

A simulation of simultaneous bubble nucleation and growth was performed for polyurethane/CO2 physical foaming process. The single-factor and comprehensive effects of viscoelastic properties, Henry’s constant, CO2 diffusion coefficient and surface tension on the cell morphology were numerically analyzed. The results show that the cell density of PU foam ( N0) increases and its average cell diameter ( Dv) reduces with increased Henry’s constant and slower gas diffusion. Both N0 and Dv reduces with the curing degree ( α). In addition, the effects of α and foaming conditions on the cell structure were experimentally investigated. With an increase of α at foamable range, Dv decreases continuously and N0 increases first and then declines. With increasing saturation pressure and depressurization rate or decreasing temperature, N0 increases and Dv reduces. There is an intrinsic correlation between the simulated and experimental variables, and the results of the simulation and experiment are generally consistent.

scholarly journals Effect of Low and High Viscosity Composites on Temperature Rise of Premolars Restored through the Bulk-Fill and the Incremental Layering Techniques

2020 ◽  
Vol 10 (22) ◽  
pp. 8041
Author(s):  
Roberto De Santis ◽  
Vito Gallicchio ◽  
Vincenzo Lodato ◽  
Sandro Rengo ◽  
Alessandra Valletta ◽  
...  
Keyword(s):  
Temperature Rise ◽  
High Viscosity ◽  
Single Step ◽  
Maximum Temperature ◽  
Main Concern ◽  
Light Curing ◽  
Higher Temperature ◽  
Temperature Rate ◽  
Dental Cavities ◽  
Flowable Composites

Background: Deep dental cavities can be restored through a single step according to the bulk-fill technique. Due to the great amount of resin to be cured, a main concern is the temperature rise occurring in the pulp chamber, potentially higher than that developed through the incremental layering technique. Temperature rise of bulk-fill composites have been evaluated. Methods: Bulk-fill composites, differing in material composition and viscosity, were used. Maximum temperature and temperature rate occurring in the composites were measured. Mesio-occlusal-distal cavities of human premolars were restored through the bulk-fill or the incremental layering techniques, and peak temperature and temperature rate occurring in the dentin, 1 mm below the cavity floor, were evaluated. Results: Temperature peak and temperature rise of flowable composites were significantly higher (p < 0.05) than packable composites. For both the techniques, higher temperature peaks were recorded in the dentin for flowable composites. Peak temperatures higher than 42 °C were recorded for the incremental layering technique considering flowable composites. Conclusions: For all the composites, the light curing modality of 1000 mW/cm2 for 20 s can be considered safe if the bulk-fill technique is performed. Instead, for the incremental layering technique, potentially dangerous temperature peaks have been recorded for flowable composites.

scholarly journals Role of Wood Fibers in Tuning Dynamic Rheology, Non-Isothermal Crystallization, and Microcellular Structure of Polypropylene Foams

Materials ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 106 ◽  
Author(s):  
Yongming Song ◽  
Youyong Wang ◽  
Hao Li ◽  
Qiling Zong ◽  
Ailing Xu
Keyword(s):  
Isothermal Crystallization ◽  
Fiber Composite ◽  
Cell Structure ◽  
Wood Fiber ◽  
Crystallization Rate ◽  
Complex Viscosity ◽  
Expansion Ratio ◽  
Wood Fibers ◽  
Cell Nucleation ◽  
Composite Foams

Microcellular polypropylene (PP)/wood fiber composite foams were fabricated via batch foaming assisted by supercritical CO2 (scCO2). Effects of wood fibers on rheology, crystallization, and foaming behaviors of PP were comprehensively investigated. The obtained results showed that the incorporation of wood fibers increased the complex viscosity and the storage modulus of the PP matrix. Jeziorny’s model for non-isothermal crystallization kinetics indicated that wood fibers did not change the crystal growth. However, the crystallization rate of the PP matrix was decreased to a certain extent with increasing wood fiber loadings. The wood fiber exerts a noticeable role in improving the cell density and reducing the cell size, despite decreasing the expansion ratio. Interestingly, a “small-sized cells to large-sized cells” gradient cell structure was found around the wood fibers, implying cell nucleation was induced at the interface between wood fiber and PP matrix. When wood fiber loadings were specifically increased, a desirable microcellular structure was obtained. However, further increasing the wood fiber loadings deteriorated the cell structure. Moreover, the crystallinity of the composite foams initially decreased and then slightly increased with increasing wood fiber loadings, while the crystal size decreased.

Effect of Calcination Temperature on Metal Oxides and their Photocatalytic Activity

2015 ◽  
Vol 1107 ◽  
pp. 73-78 ◽  
Author(s):  
Renugambaal Nadarajan ◽  
Wan Azelee Wan Abu Bakar ◽  
Rusmidah Ali
Keyword(s):  
Photocatalytic Activity ◽  
Metal Oxides ◽  
Surface Area ◽  
Calcination Temperature ◽  
Sol Gel ◽  
Sudden Increase ◽  
Large Particle Size ◽  
Defect Site ◽  
Structure Surface ◽  
Higher Temperature

The effects of calcination temperature on the microstructures and photocatalytic activity of sol-gel synthesized TiO2, WO3, SnO2 and ZnO metal oxides were investigated. The synergistic effect of the phase structure, surface area, and crystallinity of the photocatalysts after calcination and on the photocatalytic activity was investigated. 1,2-dichlorobenzene (DCB) was used as a model contaminant in this study. The highest photocatalytic activity was obtained using TiO2 calcined at 900oC with large particle size, could be ascribed to the enhancement by the presence of defect site. Similarly, WO3 calcined at 900oC exhibited the best photocatalytic activity in the series of calcination temperature ranging from 400-1000oC. SnO2 calcined at 800oC showed the best photocatalytic activity while ZnO was found to give the lowest percent of DCB degradation. In this study, sudden increase in the surface area at higher temperature was correlated with the enhancement in the photocatalytic activity of each catalyst.

In-Engine Measurements of Temperature Rises in Axial Compressor Shrouded Stator Cavities

2002 ◽  
Author(s):  
Leo V. Lewis
Keyword(s):  
Temperature Rise ◽  
Mechanical Design ◽  
Rotational Velocity ◽  
Axial Compressor ◽  
Labyrinth Seals ◽  
Aerodynamic Efficiency ◽  
Axial Compressors ◽  
Higher Temperature ◽  
Mass Flows ◽  
Aero Engines

Although many axial compressors in large aero engines use shrouded stators to retain aerodynamic efficiency, the temperature rises generated within the stator well cavities can be detrimental to the mechanical design of the disc rim or the shroud itself. These temperature rises are poorly understood and have not been widely reported. This paper presents the temperature measurements from the HP compressor stator wells of full size development engine tests, concentrating on two particular tests for the majority of its information. It is shown how standard formulae for windage and mass flows on rotor discs and in labyrinth seals can, if suitably factored, explain the observed temperatures in the first test. Inferences are drawn regarding the windage losses in the compressor, in kW, and swirl velocities, as fractions of the disc rim rotational velocity, in the stator wells. The second test is used to demonstrate the significant further temperature rise which can be caused at the front stage of the compressor by forward leakage: further analysis shows that the temperature rise is dependent on the number of stages of axial disc rim fixings behind the first stage, and that this mechanism can produce higher temperature rises than those due to windage.

scholarly journals Thermochromic Detection of Ultrasound-Induced Nanoparticle Heating in Tissue-Mimicking Solid Gel

2020 ◽  
Author(s):  
Huiting Lin ◽  
Nelson Gee-Con Chen ◽  
Chih-Mao Huang
Keyword(s):  
Cancer Cells ◽  
Temperature Rise ◽  
Color Change ◽  
Three Dimensional ◽  
Polystyrene Nanoparticles ◽  
Ultrasound Exposure ◽  
Normal Cells ◽  
Higher Temperature ◽  
First Time ◽  
Small Nanoparticles

Abstract Background Microbubble has been extensively used for ultrasound imaging and many other applications such as ultrasound cleaning. Few studies have been reported on ultrasound interactions with small nanoparticles (< 250 nm). Due to the broad use of nanoparticles in many different fields, it is critically important to clarify whether nanoparticles can have strong interaction with ultrasound. In addition, Nanoparticle assisted ultrasound therapy has recently been found to have selective killing of cancer cells compared to normal cells. Nevertheless, the mechanism is not known. The major possible mechanisms for killing cells are cavitation and heating. In this work, a simple thermochromic method is developed to clearly indicate that the interaction of nanoparticle with ultrasound can lead to temperature rise that can lead to selective killing of cancer cells. Results Direct three-dimensional detection of ultrasonically induced heating in a nanoparticle bearing tissue-mimicking gel would provide a means to estimate their effectiveness as thermally-based sonosensitizers. Such a gel was produced through the addition of an irreversible thermochromic liquid to a well-known agarose gel during fabrication. Polystyrene nanoparticles were embedded within gels during production. The placement of gels within a temperature-controlled bath set to a temperature below the transition temperature allows for the visual detection of slight temperature increases. The modified gel material was shown to undergo color change upon heating to 54 °C from blue to white. The appearance of white color on the gel is a clear indication of nanoparticle to enhance the ultrasound energy to increase the temperature of gel. Nanoparticle presence within a solid causing increased heating upon ultrasound exposure, as detected through thermochromicity, is reported for the first time. Conclusion Even small nanoparticles can have significant interaction with ultrasound to lead to temperature rise in the medium. Therefore, the selective killing of cancer cells more than normal cell should be primarily from heating instead of cavitation since cancer cells in general cannot survive in higher temperature than normal cells. Cavitation should lead to the killing of both cancer and normal cells due to the release of a large amount of energy in the process. Direct three-dimensional detection of ultrasonically induced heating in a nanoparticle bearing tissue-mimicking gel becomes feasible.

scholarly journals Composite Foams Prepared through Hollow Glass Microspheres Assisted Bubbling

2013 ◽  
Vol 22 (1) ◽  
pp. 096369351302200
Author(s):  
Zhenguo An ◽  
Jingjie Zhang
Keyword(s):  
Heat Insulation ◽  
Cell Structure ◽  
Nucleating Agent ◽  
Glass Microspheres ◽  
Insulation Property ◽  
Hollow Glass Microspheres ◽  
Hollow Glass ◽  
Foaming Process ◽  
Composite Foams ◽  
Ammonium Hydrogen

Composite foamy structures were prepared through hollow glass microspheres (HGM) assisted bubbling of silicone rubber with ammonium hydrogen carbonate as the blowing agent. The presence of HGM not only favoured the foaming process (acted as nucleating agent for the formation of minute bubbles at the initial stage of the bubbling), but also bring heterogeneous close-cell bubbles with stable inorganic shells into the foamy structure, which played an important part in the improvement of the heat insulation property of the product. Compared to the foamy structures without HGM, The composite foamy structures possessed improved heat insulation and sound absorbing properties. This work provides an additional strategy to fabricate composite foams with tailored cell structure and properties.

Control of the cell structure of microcellular silicone rubber/nanographite foam for enhanced mechanical performance

2017 ◽  
Vol 133 ◽  
pp. 288-298 ◽  
Author(s):  
Jianwei Bai ◽  
Xia Liao ◽  
Erbo Huang ◽  
Yong Luo ◽  
Qi Yang ◽  
...  
Keyword(s):  
Silicone Rubber ◽  
Mechanical Performance ◽  
Cell Structure

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.

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