Generation of Porous Microcellular 85/15 poly (DL-Lactide-co-Glycolide) Foams Using Supercritical CO2 for Biomedical Applications

2000 ◽  
Author(s):  
Lakhwant Singh ◽  
Vipin Kumar ◽  
Buddy D. Ratner
Keyword(s):  
Relative Density ◽  
Cell Size ◽  
Supercritical Co2 ◽  
Biomedical Applications ◽  
Saturation Pressure ◽  
Average Cell Size ◽  
Average Cell ◽  
Blowing Agent ◽  
Quench Method

Abstract Porous 85/15 poly (DL-lactide-co-glycolide) or PLGA foams were produced by the pressure quench method using supercritical CO2 as the blowing agent. The effects of saturation pressure and temperature on average cell size and relative density of the resulting foams were studied. Porous PLGA foams were generated with relative densities ranging from 0.107 to 0.232. Foams showed evidence of interconnected cells with porosities as high as 89%. The cell size ranged from 30 to 70 microns.

Effect of Foaming Temperature Control on Cell Size and Cell Density of Microcellular Plastics

2005 ◽  
Vol 24 (2) ◽  
pp. 91-102 ◽  
Author(s):  
Hidetaka Kawashima ◽  
Minoru Shimbo
Keyword(s):  
Cell Size ◽  
Cell Density ◽  
Average Cell Size ◽  
Average Cell ◽  
Blowing Agent ◽  
Microcellular Plastics ◽  
Temperature Method ◽  
Foamed Plastics ◽  
Maximum Cell ◽  
Foaming Temperature

In this study, noticing foaming temperature as a factor, which induces thermodynamic instability for cell nucleation of Microcellular plastics, the effect of control method of foaming temperature on cell size and cell density - that is number per unit volume of foamed plastics - were investigated. Generally, foaming by using batch process is carried out as follows. First, blowing agent is soaked into plastics until saturation under high pressure and soaking temperature. After plastics were saturated with blowing agent, pressure is released rapidly and then temperature is raised to foaming temperature and cells are nucleated and grown. Finally, rapid cooling controls cell growth. In this case, two methods can be considered for the control of foaming temperature. One is the elevated temperature method in which temperature is raised to foaming temperature and cells are grown after decompression in the foaming process. The other is the constant temperature method in which the temperature is already kept at foaming temperature before decompression. That is, it is the method of performing soaking and foaming at the same temperature. Polymethylmethacrylate (PMMA) resins were foamed under foaming conditions which the same foaming magnification is produced by both methods and cell size and cell density of foamed PMMA were investigated. As results, in case of production of the foamed plastics having the same foam magnification, it turned out that cell density of foamed plastics becomes large and average cell size becomes small but the maximum cell size becomes large by the elevated temperature method. On the other hand, although the maximum cell size becomes small, average cell size becomes large by the constant temperature method.

scholarly journals The influence of cell size on the mechanical properties of nanocellular PMMA

2019 ◽  
Author(s):  
Frederik Van Loock
Keyword(s):  
Relative Density ◽  
Cell Size ◽  
Compression Tests ◽  
Single Edge ◽  
Average Cell Size ◽  
Average Cell ◽  
Edge Notch ◽  
Bend Tests ◽  
20 Nm ◽  
Single Edge Notch Bend

Solid-state foaming experiments are conducted on three grades of polymethyl methacrylate (PMMA). Nanocellular PMMA foams are manufactured with an average cell size ranging from 20 nm to 84 nm and a relative density between 0.37 and 0.5. For benchmarking purposes, additional microcellular PMMA foams with an average cell size close to 1 ìm and relative density close to that of the nanocellular foams are manufactured. Uniaxial compression tests and single edge notch bend tests are conducted on the PMMA foams. The measured Young's modulus and yield strength of the PMMA foams are independent of cell size whereas the fracture toughness of the PMMA foam increases with decreasing average cell size from the micron range to the nanometer range.

Morphological evaluation of ultralow density microcellular foamed composites developed through CO2-induced solid-state batch foaming technique utilizing water as co-blowing agent

2019 ◽  
Vol 39 (4) ◽  
pp. 141-171 ◽  
Author(s):  
Rupesh Dugad ◽  
G Radhakrishna ◽  
Abhishek Gandhi
Keyword(s):  
Solid State ◽  
Saturation Pressure ◽  
Saturation Temperature ◽  
Acrylonitrile Butadiene Styrene ◽  
Expansion Ratio ◽  
Average Cell Size ◽  
Average Cell ◽  
Maximum Expansion ◽  
Blowing Agent ◽  
Batch Foaming

In this work, microcellular acrylonitrile-butadiene-styrene foams were developed with utilization of water as a co-blowing agent and CO2 as the primary blowing agent through the solid-state batch foaming process. The effect of saturation parameters with the content of the co-blowing agent has been studied extensively for various foaming attributes. The co-blowing agent enhanced the average cell size and the expansion ratio which are useful for better thermal insulation. The maximum expansion ratio of 29.9 obtained from the effect of saturation temperature and co-blowing agent, 23.6 from the effect of saturation pressure and co-blowing agent, and 22.4 from the effect of saturation time and co-blowing agent. The co-blowing agent significantly affects the cell morphology of polymeric foam with saturation parameters.

Eddy Current Characterization of Metal Foams

1998 ◽  
Vol 521 ◽  
Author(s):  
K. P. Dharmasena ◽  
H. N. G. Wadley
Keyword(s):  
Relative Density ◽  
Cell Size ◽  
Eddy Current ◽  
Strong Dependence ◽  
Low Frequency ◽  
Average Cell Size ◽  
Average Cell ◽  
Non Invasive ◽  
Current Path

ABSTRACTCellular materials are characterized by their relative density, pore shape and orientation, the average cell size, and the degree of pore interconnectivity which all depend upon the method and conditions used for processing. This has created an interest in non-invasive sensor techniques to characterize the foam structure. Multifrequency electrical impedance measurements were performed using an eddy current technique on open cell aluminum foam with systematically varied relative densities and pore sizes. The impedance was dominated at all frequencies by the amount of metal contained within a probed volume of foam and the tortuosity of the current path. At low frequency, the impedance data were found to be relatively insensitive to pore size variations enabling an independent measure of the relative density. At high frequency, the data indicated a strong dependence on the cell size.

scholarly journals Analysis of the Foaming Window for Thermoplastic Polyurethane with Different Hard Segment Contents

Polymers ◽  
2021 ◽  
Vol 13 (18) ◽  
pp. 3143
Author(s):  
Mercedes Santiago-Calvo ◽  
Haneen Naji ◽  
Victoria Bernardo ◽  
Judith Martín-de León ◽  
Alberto Saiani ◽  
...  
Keyword(s):  
Cell Size ◽  
Saturation Pressure ◽  
Final Conclusion ◽  
Nucleation Density ◽  
Scanning Calorimetry ◽  
Average Cell Size ◽  
Average Cell ◽  
Saturation Time ◽  
A Cell ◽  
Foaming Temperature

A series of thermoplastic polyurethanes (TPUs) with different amounts of hard segments (HS) (40, 50 and 60 wt.%) are synthesized by a pre-polymer method. These synthesized TPUs are characterized by Shore hardness, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), dynamic mechanical thermal analysis (DMTA), and rheology. Then, these materials are foamed by a one-step gas dissolution foaming process and the processing window that allows producing homogeneous foams is analyzed. The effect of foaming temperature from 140 to 180 °C on the cellular structure and on density is evaluated, fixing a saturation pressure of 20 MPa and a saturation time of 1 h. Among the TPUs studied, only that with 50 wt.% HS allows obtaining a stable foam, whose better features are reached after foaming at 170 °C. Finally, the foaming of TPU with 50 wt.% HS is optimized by varying the saturation pressure from 10 to 25 MPa at 170 °C. The optimum saturation and foaming conditions are 25 MPa and 170 °C for 1 h, which gives foams with the lowest relative density of 0.74, the smallest average cell size of 4 μm, and the higher cell nucleation density of 8.0 × 109 nuclei/cm3. As a final conclusion of this investigation, the TPU with 50 wt.% HS is the only one that can be foamed under the saturation and foaming conditions used in this study. TPU foams containing 50 wt.% HS with a cell size below 15 microns and porosity of 1.4–18.6% can be obtained using foaming temperatures from 140 to 180 °C, saturation pressure of 20 MPa, and saturation time of 1 h. Varying the saturation pressure from 10 to 25 MPa and fixing the foaming temperature of 170 °C and saturation pressure of 1 h results in TPU foams with a cell size of below 37 microns and porosity of 1.7–21.2%.

Characterization of microstructures of SAN foam core using micro-computed tomography

2021 ◽  
pp. 026248932110068
Author(s):  
Youming Chen ◽  
Raj Das ◽  
Hui Wang ◽  
Mark Battley
Keyword(s):  
Cell Wall ◽  
Cell Size ◽  
Wall Thickness ◽  
Strain Localization ◽  
Cell Wall Thickness ◽  
Micro Computed Tomography ◽  
Average Cell Size ◽  
Average Cell ◽  
3D Images ◽  
Compressive Tests

In this study, the microstructure of a SAN foam was imaged using a micro-CT scanner. Through image processing and analysis, variations in density, cell wall thickness and cell size in the foam were quantitatively explored. It is found that cells in the foam are not elongated in the thickness (or rise) direction of foam sheets, but rather equiaxed. Cell walls in the foam are significantly straight. Density, cell size and cell wall thickness all vary along the thickness direction of foam sheets. The low density in the vicinity of one face of foam sheets leads to low compressive stiffness and strength, resulting in the strain localization observed in our previous compressive tests. For M80, large open cells on the top face of foam sheets are likely to buckle in compressive tests, therefore being another potential contributor to the strain localization as well. The average cell wall thickness measured from 2D slice images is around 1.4 times that measured from 3D images, and the average cell size measured from 2D slice images is about 13.8% smaller than that measured from 3D images. The dispersions of cell wall thickness measured from 2D slice images are 1.16–1.20 times those measured from 3D images. The dispersions of cell size measured from 2D slice images are 1.12–1.36 times those measured from 3D images.

The effect of organofluorine additives on the morphology, thermal conductivity and mechanical properties of rigid polyurethane and polyisocyanurate foams

2021 ◽  
pp. 0021955X2098715
Author(s):  
Cosimo Brondi ◽  
Ernesto Di Maio ◽  
Luigi Bertucelli ◽  
Vanni Parenti ◽  
Thomas Mosciatti
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Cell Size ◽  
Flexural Properties ◽  
Anisotropy Ratio ◽  
Cell Content ◽  
Average Cell Size ◽  
Average Cell ◽  
Thermal Insulating ◽  
Liquid Type

This study investigates the effect of liquid-type organofluorine additives (OFAs) on the morphology, thermal conductivity and mechanical properties of rigid polyurethane (PU) and polyisocyanurate (PIR) foams. Foams were characterized in terms of their morphology (density, average cell size, anisotropy ratio, open cell content), thermal conductivity and compressive as well as flexural properties. Based on the results, we observed that OFAs efficiently reduced the average cell size of both PU and PIR foams, leading to improved thermal insulating and mechanical properties.

Synthesis and Characterization of Bio-Based Rigid Polyurethane Foams with Varying Amount of Blowing Agent

2019 ◽  
Vol 803 ◽  
pp. 346-350
Author(s):  
Jessalyn C. Grumo ◽  
Lady Jaharah Y. Jabber ◽  
Arnold A. Lubguban ◽  
Rey Y. Capangpangan ◽  
Arnold C. Alguno
Keyword(s):  
Polyurethane Foam ◽  
Functional Group ◽  
Polyurethane Foams ◽  
Synthesis And Characterization ◽  
Rigid Polyurethane Foam ◽  
Sem Images ◽  
Average Cell Size ◽  
Average Cell ◽  
Blowing Agent

We report on the rigid polyurethane foam (RPUF) with varying amount of blowing agent. The effects of blowing agent in the formation of polyurethane will be characterized using scanning electron microscopy (SEM) and fourier transform infrared (FTIR) spectroscopy. SEM images revealed that varying the amount of blowing agent will significantly change the surface morphology of the resulting RPUF. The average cell size of the RPUF increases with increasing amount of blowing agent. Moreover, FTIR results revealed the presence of functional group related to formation of urethane bonds such as N-H, C=O, C=N and C-O-C stretching suggesting that polyurethane foam was successfully synthesized. This simple and straightforward process of RPUF using water as blowing agent will be economical.

Growth and Cell-Size Distribution of Marine Planktonic Algae in Batch and Dialysis Cultures

1973 ◽  
Vol 30 (2) ◽  
pp. 143-155 ◽  
Author(s):  
A. Prakash ◽  
Liv Skoglund ◽  
Britt Rystad ◽  
Arne Jensen
Keyword(s):  
Size Distribution ◽  
Cell Size ◽  
Growth Cycle ◽  
Exponential Growth Phase ◽  
Average Cell Size ◽  
Cell Size Distribution ◽  
Average Cell ◽  
Planktonic Algae ◽  
Maximum Cell ◽  
Dialysis Culture

An extended exponential growth phase and a higher maximum population characterized growth of planktonic algae in a dialysis system compared with that in a batch system. Algal cells grown in a dialysis culture had higher chlorophyll content and a larger average cell size than those grown in a batch culture. In both types of culture, changes in cell-size distribution were related to the phases of the growth cycle with maximum cell-size during the stationary phase. Various interactions of the component reactions of photosynthesis leading to changes in growth pattern and cell-size distribution are discussed.

Shear Induced Low- and High-Angle Boundary Characterization Using Kikuchi Bands in Transmission Electron Microscopy

2008 ◽  
Vol 584-586 ◽  
pp. 293-299 ◽  
Author(s):  
Marcello Cabibbo
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Cell Size ◽  
Grain Structure ◽  
Structure Evolution ◽  
High Angle ◽  
Boundary Misorientation ◽  
Average Cell Size ◽  
Average Cell ◽  
Transmission Electron

Microstructure evolution with equal channel angular pressing (ECAP) using route Bc, that is a 90° axial rotation of the billet between passes, up to 8 passes, was investigated by transmission electron microscopy. The study has been focused on the induced development of boundary misorientation and spacing toward microstructure refinement. Cell (low-angle) and grain (high-angle) misorientation and spacing were determined from about 250 boundaries per pass of ECAP, systematically using whether Kikuchi patterns or Moiré fringes, these latter where possible. The average cell size and misorientation saturate within the first two passes. Misorientation and spacing of high-angle boundaries decrease with the number of passes. After 8 passes, mean cell size is ≈ 1.3 µm and the fraction of high-angle boundaries is ≈ 0.7. Differences in rate of grain structure evolution per pass are linked to differences in ability of dislocations introduced in new passes to recombine with the existing ones. As ECAP strain rises, the misorientation distribution develops strong deviations from the MacKenzie distribution for statistical grain orientation. This is interpreted as a result of the tendency to form equiaxed grains in a textured grain structure.

Sign in / Sign up

Export Citation Format

Share Document