scholarly journals Influence of Polylactide (PLA) Stereocomplexation on the Microstructure of PLA/PBS Blends and the Cell Morphology of Their Microcellular Foams

Polymers ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2362
Author(s):  
Zhiyuan Sun ◽  
Long Wang ◽  
Jinyang Zhou ◽  
Xun Fan ◽  
Hanghai Xie ◽  
...  
Keyword(s):  
Gas Adsorption ◽  
Average Cell Size ◽  
Butylene Succinate ◽  
Average Cell ◽  
Melt Strength ◽  
Biological Scaffolds ◽  
Microcellular Foams ◽  
Microcellular Foaming ◽  
Cell Nucleation ◽  
Cell Stability

Polylactide foaming materials with promising biocompatibility balance the lightweight and mechanical properties well, and thus they can be desirable candidates for biological scaffolds used in tissue engineering. However, the cells are likely to coalesce and collapse during the foaming process of polylactide (PLA) due to its intrinsic low melt strength. This work introduces a unique PLA stereocomplexation into the microcellular foaming of poly (l-lactide)/poly (butylene succinate) (PLLA/PBS) based on supercritical carbon dioxide. The rheological properties of PLA/PBS with 5 wt% or 10 wt% poly (d-lactide) (PDLA) present enhanced melt strength owing to the formation of PLA stereocomplex crystals (sc-PLA), which act as physical pseudo-cross-link points in the molten blends by virtue of the strong intermolecular interaction between PLLA and the added PDLA. Notably, the introduction of either PBS or PDLA into the PLLA matrix could enhance its crystallization, while introducing both in the blend triggers a decreasing trend in the PLA crystallinity, which it is believed occurs due to the constrained molecular chain mobility by formed sc-PLA. Nevertheless, the enhanced melt strength and decreased crystallinity of PLA/PBS/PDLA blends are favorable for the microcellular foaming behavior, which enhanced the cell stability and provided amorphous regions for gas adsorption and homogeneous nucleation of PLLA cells, respectively. Furthermore, although the microstructure of PLA/PBS presents immiscible sea-island morphology, the miscibility was improved while the PBS domains were also refined by the introduction of PDLA. Overall, with the addition of PDLA into PLA/10PBS blends, the microcellular average cell size decreased from 3.21 to 0.66 μm with highest cell density of 2.23 × 1010 cells cm−3 achieved, confirming a stable growth of cells was achieved and more cell nucleation sites were initiated on the heterogeneous interface.

Preparation and characterization of microcellular injection molded foams from high-performance blends based on PPS-modified PPBESK

2017 ◽  
Vol 30 (4) ◽  
pp. 480-488 ◽  
Author(s):  
Na Wen ◽  
Tao Liu ◽  
Bin Xiang ◽  
Yajie Lei ◽  
Shikai Luo
Keyword(s):  
Injection Molding ◽  
High Performance ◽  
Polyphenylene Sulfide ◽  
Mechanical And Thermal Properties ◽  
Melt Mixing ◽  
Average Cell Size ◽  
Average Cell ◽  
Molding Method ◽  
Microcellular Foams ◽  
Microcellular Injection Molding

Obtaining foams of poly-containing biphenyl moieties (phthalazinone ether sulfone ketone; PPBESK) by applying the microcellular injection molding method is very difficult because of the high melt viscosity of the materials used. To overcome this limitation, polyphenylene sulfide (PPS) was used to improve the rheological properties of PPBESK. PPBESK/PPS blends of different proportions were prepared using the melt mixing method. The rheological behavior, phase behavior, interfacial tension, and mechanical properties of the blends were then investigated. The results clearly indicate that PPS can improve the melt processability of PPBESK. However, due to the strong adhesion between the PPS and PPBESK phases, the introduction of PPS did not cause any loss of the mechanical and thermal properties of PPBESK. Accordingly, microcellular foams from modified PPBESK were prepared by microcellular injection molding with supercritical nitrogen as foaming agent. A closed cell microcellular morphology with an average cell size of 17.7 um and cell density of 109 cells cm−3 was obtained.

Effect of Processing Parameters on Cellular Structures and Mechanical Properties of PMMA Microcellular Foams

2005 ◽  
Vol 24 (4) ◽  
pp. 177-195 ◽  
Author(s):  
Jin Fu ◽  
Choonghee Jo ◽  
Hani E. Naguib
Keyword(s):  
Mechanical Properties ◽  
Saturation Pressure ◽  
Viscoelastic Model ◽  
Batch Process ◽  
Processing Parameters ◽  
Analytical Models ◽  
Elastic Behavior ◽  
Average Cell Size ◽  
Average Cell ◽  
Microcellular Foams

In this study, the effect of processing parameters on the cellular morphologies and mechanical properties of PMMA microcellular foams is investigated. Microcellular closed cell Poly(methyl-methacrylate) (PMMA) foams were prepared using a two stage batch process method. The foam structure was controlled by altering the processing parameters such as foaming temperature, foaming time and saturation pressure. The foam morphologies were characterized in terms of the average cell size, cell density and foam density. Elastic modulus, tensile strength and elongation at break were studied as functions of the different foaming parameters. The mechanical properties were found to be greatly affected by the foaming parameters and vary with changing the cell morphologies. The experimental results were compared with existing analytical models to validate them and to predict the mechanical properties of microcellular polymeric PMMA foams prepared with different processing parameters. A constitutive equation for the nonlinear elastic behavior of polymeric microcellular foams was developed based on the Maxwell viscoelastic model. The results of this work can help designers optimize the foam processing parameters and achieve desired foam morphology and mechanical properties.

Effect of Processing Parameters on the Cellular Morphology and Mechanical Properties of Thermoplastic Polyolefin (TPO) Microcellular Foams

2006 ◽  
Author(s):  
Steven Wong ◽  
Hani E. Naguib ◽  
Chul B. Park
Keyword(s):  
Mechanical Properties ◽  
Saturation Pressure ◽  
Batch Process ◽  
Processing Parameters ◽  
Average Cell Size ◽  
Average Cell ◽  
Microcellular Foams ◽  
Closed Cell ◽  
Foaming Temperature ◽  
Thermoplastic Polyolefin

In this study, the effects of processing parameters on the cellular morphologies and mechanical properties of TPO70 (Thermoplastic Polyolefin) microcellular foams are investigated. Microcellular closed cell TPO70 foams were prepared using a two-stage batch process method. The microstructure of these foamed samples was controlled by carefully altering the processing parameters such as saturation pressure, foaming temperature and foaming time. The foam morphologies were characterized in terms of the cell density, foam density and average cell size. Elastic modulus, tensile strength, and elongation at break of the foamed TPO70 samples were measured for different cell morphologies. The findings show that the mechanical properties were significantly affected by the foaming parameters which varied with the cell morphologies. The experimental results can be used to predict the microstructure and mechanical properties of microcellular polymeric TPO70 foams prepared with different processing parameters.

scholarly journals Effect of PBAT on physical, morphological, and mechanical properties of PBS/PBAT foam

2019 ◽  
Vol 39 (1) ◽  
pp. 31-41 ◽  
Author(s):  
Aekartit Boonprasertpoh ◽  
Duanghathai Pentrakoon ◽  
Jirawut Junkasem
Keyword(s):  
Mechanical Properties ◽  
Chemical Structure ◽  
Testing Machine ◽  
Morphological Properties ◽  
Flexural Properties ◽  
Average Cell Size ◽  
Butylene Succinate ◽  
Average Cell ◽  
Universal Testing ◽  
Microscopy Techniques

This study examines the effect of poly(butylene adipate- co-terephthalate) (PBAT) content on the physical, morphological, and mechanical properties of poly(butylene succinate) (PBS)/PBAT foam. A compression molding technique was used to prepare the PBS/PBAT foam using the chemical blowing agent azodicarbonamide and the cross-linking agent dicumyl peroxide. The chemical structure and morphological properties of PBS/PBAT foam were examined via Fourier transform infrared and scanning electron microscopy techniques, respectively, whereas tensile and flexural properties were investigated using a universal testing machine. The results reveal that the incorporation of PBAT barely enhances the viscosity of the PBS/PBAT blend, producing only minor changes in the average cell size of PBS/PBAT foam. However, increasing the PBAT content contributes to a relatively significant improvement in the flexibility and toughness of PBS/PBAT foam, where a decrease in Young’s modulus and tensile strength of the PBS/PBAT foam is observed compared with those of the PBS foam. Similar behavior to the tensile results is noticed for the flexural properties of the neat and PBS/PBAT foams.

Effects of pressure drop rate and CO2 content on the foaming behavior of newly developed high-melt-strength polypropylene in continuous extrusion

2020 ◽  
pp. 0021955X2094311
Author(s):  
Eric Kim ◽  
Mu Sung Kweon ◽  
Sandra Romero-Diez ◽  
Anvit Gupta ◽  
Xuejia Yan ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Strong Dependence ◽  
Expansion Ratio ◽  
Average Cell Size ◽  
Average Cell ◽  
Melt Strength ◽  
Pressure Drops ◽  
Foaming Behavior ◽  
Die Temperature ◽  
Drop Rate

We report systematic studies on the foamability of our novel high-melt-strength long-chain branched polypropylene under supercritical CO2. Continuous foaming experiments were conducted using a tandem extrusion system and a set of filamentary dies with similar pressure drops but different pressure drop rates. The foam expansion was controlled by varying the temperature at the die exit. Under identical CO2 loadings, the expansion ratio plotted as a function of die temperature exhibited similar shapes across multiple pressure drop rates. However, the shape of the curve varied across different amounts of CO2, under which the highest achievable expansion ratio occurred at a lower die temperature with increasing CO2 content. The cell density displayed strong dependence on both the pressure drop rate and the amount of dissolved CO2. The effect of the latter became more apparent at lower pressure drop rates. The average cell size decreased with increasing CO2 loading but generally showed weak dependence on pressure drop rate except at the highest value.

Synergetic effect of crystal nucleating agent and melt self-enhancement of isotactic polypropylene on its rheological and microcellular foaming properties

2020 ◽  
Vol 57 (1) ◽  
pp. 101-121
Author(s):  
Xiaoli Zhang ◽  
Xihuan Wang ◽  
Binbin Dong ◽  
Guoqiang Zheng ◽  
Jingbo Chen ◽  
...  
Keyword(s):  
Isotactic Polypropylene ◽  
Saturation Pressure ◽  
Synergetic Effect ◽  
Complex Viscosity ◽  
Nucleating Agent ◽  
Control Treatment ◽  
Foaming Properties ◽  
Average Cell ◽  
Microcellular Foams ◽  
Microcellular Foaming

Crystal nucleating agent Bis (3, 4- dimethylbenzylidene) sorbitol (DMDBS) was used to tune the melt strength and microcellular foaming properties of isotactic polypropylene (iPP) in this study. Rheological testing results reveal that the introduction of DMDBS could enhance the storage modulus and complex viscosity of iPP, obviously increase its crystallization onset temperature, compared to its counterparts without DMDBS. The addition of DMDBS could also significantly increase the cell nucleating ability of iPP, due to its large surface, cooperating with a thermal history control treatment. Quite fine microcellular iPP/DMDBS foams were fabricated with relatively small average cell sizes of nano to several micrometers, and cell densities up to 1011∼1012 cells/cm3, using the synergy effect of DMDBS and iPP’s melt self-enhancement. Under a comparatively low re-saturation pressure of 8 to 12 MPa, ideal microcellular foams could be generated, at a temperature zone of 158 to 162°C, which is slightly below to iPP’s original pellets nominal melting point.

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.

scholarly journals Morphological, thermal and mechanical properties of recycled HDPE foams via rotational molding

2021 ◽  
pp. 0021955X2110137
Author(s):  
Yao Dou ◽  
Denis Rodrigue
Keyword(s):  
Cell Density ◽  
Morphological Analysis ◽  
Mechanical Characterization ◽  
Gradual Increase ◽  
Thermal And Mechanical Properties ◽  
Rotational Molding ◽  
Average Cell Size ◽  
Average Cell ◽  
The Impact ◽  
Recycled Hdpe

In this study, foamed recycled high density polyethylene (rHDPE) parts were produced by rotational molding using different concentration (0 to 1% wt.) of a chemical blowing agent (CBA) based on azodicarbonamide. From the samples produced, a complete morphological, thermal and mechanical characterization was performed. The morphological analysis showed a gradual increase in the average cell size, while the cell density firstly increased and then decreased with increasing CBA content. As expected, increasing the CBA content decreased the foam density as well as the thermal conductivity. Although increasing the CBA content decreased both tensile and flexural properties, the impact strength showed a similar trend as the cell density with an optimum CBA content around 0.1% wt. Finally, neat rHDPE samples were also produced by compression molding. The results showed negligible differences between the rotomolded and compression molded properties indicating that optimal rotomolding conditions were selected. These results confirm the possibility of using 100% recycled polymers to produce rotomolded foam parts.

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.

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