Influence of the viscosity of poly(methyl methacrylate) on the cellular structure of nanocellular materials

Three different grades of poly(methyl methacrylate) (PMMA) with different rheological properties are used for the production of nanocellular materials using gas dissolution foaming. The influences of both the viscosity of the different polymers and the processing parameters on the final cellular structure are studied using a wide range of saturation and foaming conditions. Foaming conditions affect similarly all cellular materials. It is found that an increase of the foaming temperature results in less dense nanocellular materials, with higher cell nucleation densities. In addition, it is demonstrated that a lower viscosity leads to cellular polymers with a lower relative density but larger cell sizes and smaller cell nucleation densities, these differences being more noticeable for the conditions in which low solubilities are reached. It is possible to produce nanocellular materials with relative densities of 0.24 combined with cell sizes of 75 nm and cell nucleation densities of 10¹⁵ nuclei cm^?3 using the PMMA with the lowest viscosity. In contrast, minimum cell sizes of around 14 nm and maximum cell nucleation densities of 3.5 × 10¹⁶ nuclei cm^?3 with relative densities of 0.4 are obtained with the most viscous one. © 2019 Society of Chemical Industry     

Nanocellular Polymers with a Gradient Cellular Structure Based on Poly(methyl methacrylate)/Thermoplastic Polyurethane Blends Produced by Gas Dissolution Foaming

Graded structures and nanocellular polymers are two examples of advanced cellular morphologies. In this work, a methodology to obtain low‐density graded nanocellular polymers based on poly(methyl methacrylate) (PMMA)/thermoplastic polyurethane (TPU) blends produced by gas dissolution foaming is reported. A systematic study of the effect of the processing condition is presented. Results show that the melt‐blending results in a solid nanostructured material formed by nanometric TPU domains. The PMMA/TPU foamed samples show a gradient cellular structure, with a homogeneous nanocellular core. In the core, the TPU domains act as nucleating sites, enhancing nucleation compared to pure PMMA and allowing the change from a microcellular to a nanocellular structure. Nonetheless, the outer region shows a gradient of cell sizes from nano‐ to micron‐sized cells. This gradient structure is attributed to a non‐constant pressure profile in the samples due to gas desorption before foaming. The nucleation in the PMMA/TPU increases as the saturation pressure increases. Regarding the effect of the foaming conditions, it is proved that it is necessary to have a fine control to avoid degeneration of the cellular materials. Graded nanocellular polymers with relative densities of 0.16–0.30 and cell sizes ranging 310–480 nm (in the nanocellular core) are obtained.     

Anisotropy in nanocellular polymers promoted by the addition of needle‐like sepiolites

This work presents a new strategy for obtaining nanocellular materials with high anisotropy ratios by means of the addition of needle‐like nanoparticles. Nanocellular polymers are of great interest due to their outstanding properties, whereas anisotropic structures allow the realization of improved thermal and mechanical properties in certain directions. Nanocomposites based on poly(methyl methacrylate) (PMMA) with nanometric sepiolites are generated by extrusion. From the extruded filaments, cellular materials are produced using a two‐step gas dissolution foaming method. The effect of adding various types and contents of sepiolites is investigated. As a result of the extrusion process, the needle‐like sepiolites are aligned in the machine direction in the solid nanocomposites. Regarding the cellular materials, the addition of sepiolites allows one to obtain anisotropic nanocellular polymers with cell sizes of 150 to 420 nm and cell nucleation densities of 10¹³–10¹⁴ nuclei cm^?3 and presenting anisotropy ratios ranging from 1.38 to 2.15, the extrusion direction being the direction of the anisotropy. To explain the appearance of anisotropy, a mechanism based on cell coalescence is proposed and discussed. In addition, it is shown that it is possible to control the anisotropy ratio of the PMMA/sepiolite nanocellular polymers by changing the amount of well‐dispersed sepiolites in the solid nanocomposites. © 2019 Society of Chemical Industry     

Investigation of the nanocellular foaming of polystyrene in supercritical CO2 by adding a CO2‐philic perfluorinated block copolymer

Nanocellular foaming of polystyrene (PS) and a polystyrene copolymer (PS‐b‐PFDA) with fluorinated block (1,1,2,2‐tetrahydroperfluorodecyl acrylate block, PFDA) was studied in supercritical CO₂ (scCO₂) via a one‐step foaming batch process. Atom Transfer Radical Polymerization (ATRP) was used to synthesize all the polymers. Neat PS and PS‐b‐PFDA copolymer samples were produced by extrusion and solid thick plaques were shaped in a hot‐press, and then subsequently foamed in a single‐step foaming process using scCO₂ to analyze the effect of the addition of the fluorinated block copolymer in the foaming behaviour of neat PS. Samples were saturated under high pressures of CO₂ (30 MPa) at low temperatures (e.g., 0°C) followed by a depressurization at a rate of 5 MPa/min. Foamed materials of neat PS and PS‐b‐PFDA copolymer were produced in the same conditions showing that the presence of high CO₂‐philic perfluoro blocks, in the form of submicrometric separated domains in the PS matrix, acts as nucleating agents during the foaming process. The preponderance of the fluorinated blocks in the foaming behavior is evidenced, leading to PS‐b‐PFDA nanocellular foams with cell sizes in the order of 100 nm, and bulk densities about 0.7 g/cm³. The use of fluorinated blocks improve drastically the foam morphology, leading to ultramicro cellular and possibly nanocellular foams with a great homogeneity of the porous structure directly related to the dispersion of highly CO₂‐philic fluorinated blocks in the PS matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Controlling the foam morphology of supercritical CO2-processed poly(methyl methacrylate) with CO2-philic hybrid nanoparticles

Highly CO₂-philic nanoparticles, octatrimethylsiloxy polyhedral oligomeric silsesquioxanes (POSS) are used to increase the affinity of poly(methyl methacrylate) (PMMA) to CO₂ in supercritical carbon dioxide (scCO₂) foaming, thus to improve its foaming performance and the foam morphology. PMMA and PMMA-POSS composite foams were produced based on the two-factorial design, at the upper and lower experimental conditions of pressure, temperature, processing time, and venting rate. The foams of PMMA-5% POSS composites exhibited smaller average pore sizes and higher pore densities than neat PMMA and PMMA-0.5% POSS composites. The smallest average pore diameter (0.3 μm) and the highest pore density (6.33 × 10¹² cm⁻³) were obtained with this composite processed at 35°C, 32 MPa, for 24 h and depressurized with fast-venting rate (0.4 MPa/s). ScCO₂ processing decreased the density of the polymer by more than 50%.     

Low‐Density Nanocellular Foams Produced by High‐Pressure Carbon Dioxide

A new type of nanocellular polymeric material based on PMMA and a MAM triblock copolymer is presented. The production avoids the use of physical additives and leads to completely homogeneous nanostructured polymers with a large number of CO₂ nucleation sites. The foamed materials show average cell sizes <200 nm and relative foam densities of 0.4, presenting a homogeneous cell structure. A physical effect not measured before in nanocellular materials is demonstrated, which leads to an increase of the glass transition temperature due to the confining effect of PMMA chains in the cell walls of the nanocellular foam. The effects of changing saturation pressure and MAM content in the cellular structure are described, together with three‐point bending Young's modulus measured using DMA.

     

Foam Processing and Cellular Structure of Polycarbonate‐Based Nanocomposites

Summary: Via a batch process in an autoclave, foam processing of intercalated PC/clay nanocomposites, having different amounts of clay, has been conducted using supercritical CO₂ as a foaming agent. The cellular structures obtained from various foaming temperature‐CO₂ pressure ranges were investigated by SEM. The incorporation with nanoclay‐induced heterogeneous nucleation occurs because of a lower activation energy barrier compared with homogeneous nucleation as revealed by the characterization of the interfacial tension between bubble and matrix. The controlled structure of the PCCN foams changed from microcellular (d ? 20 µm and N_c ? 1.0 × 10⁹ cells · cm^?3) to nanocellular (d ? 600 nm and N_c ? 3.0 × 10¹³ cells · cm^?3). The mechanical properties of PCCN foams under compression test were discussed.

TEM micrograph for the structure of the cell wall foamed at 160 °C.     

Effects of processing parameters and thermal history on microcellular foaming behaviors of PEEK using supercritical CO2

In this study, we mainly investigate the solid‐state foaming of polyether ether ketone (PEEK) with different crystallinities using supercritical CO₂ as a physical blowing agent. The gaseous mass‐transfer and thermophysical behaviors were studied. By altering the parameters of the foaming process, microcellular foams with different cell morphologies were prepared. The effect of crystallization on the cell morphology was also investigated in detail. The results indicate that the crystallization restricts gas diffusion in the material, and the thermophysical behaviors of the saturated PEEK sample with low crystallinity presents two cold crystallization peaks. The cell density decreases and the cell size increases as the saturation pressure increases. The cell density of the microcellular foams prepared under 20 MPa is 1.23 × 10¹⁰ cells/cm³, which is almost 10 times compares to that under 8 MPa. The cell size increases as the foaming time extends or the foaming temperature increases. It is interesting that the cell morphology with a bimodal cell‐size distribution is generated when the samples are foamed at temperatures higher than 320°C for a sufficient time. Additionally, nanocellular foams can be obtained from a highly crystallized PEEK after the decrystallization process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42576.     

Generation of microcellular polymeric foams using supercritical carbon dioxide. I: Effect of pressure and temperature on nucleation

Supercritical carbon dioxide is known to swell and plasticize poly(methyl methacrylate), PMMA, dramatically. We have employed a pressure quench in a CO₂-swollen PMMA sample to generate a microcellular core structure encased by a nonporous skin. Further, we have demonstrated that classical nucleation theory can be used to model the effects of saturation pressure, temperature, and time on the cell density of the porous materials, provided that the effects of the CO₂-diluent on the surface tension of PMMA are adequately taken into account. This is because our system is in a homogeneous liquid state at our operating conditions because of the plasticization. Both model predictions and data indicate that cell density rises sharply at a saturation pressure of approximately 14 MPa (at 40°C), leveling out above 27 MPa. By contrast, the effect of temperature on cell density in the range 40°C to 80°C is minimal.     

A simple method for preparation of polymer microcellular foams by in situ generation of supercritical carbon dioxide from dry ice

In this work, poly(methyl methacrylate) (PMMA) and PMMA/nanoclay nanocomposite microcellular foams were successfully prepared using a simple method based on in situ generation of supercritical carbon dioxide (CO₂) from dry ice. The method was compared with conventional methods exempted from high pressure pump and a separate CO₂ tank. Effect of various processing conditions such as saturation temperature and pressure and clay concentration on cellular morphology and hardness of the prepared microcellular foams was examined. State of the clay dispersion in the prepared PMMA/clay nanocomposites was characterized using X-ray diffraction and transmission electron microscopy techniques. Field emission scanning electron microscopy was used to study cellular morphology of the prepared foams. It was observed that elevation of saturation temperature from 85 to 105 °C at constant saturation pressure increased cell density and decreased average cell size of the prepared PMMA foams. Furthermore, an increase in saturation pressure from 120 to 180 bar resulted in a reduction in average cell diameter and an increase in cell density of the prepared PMMA foams. On the basis of the gathered results, optimum conditions for preparation of PMMA microcellular foams were determined and applied for preparation of PMMA/nanoclay microcellular foams. It was shown that incorporation of clay into the polymer matrix resulted in a finer and more uniform cellular morphology in the final microcellular foams. It was also observed that incorporation of nanoclay into the prepared foams, up to 3 wt%, led to a moderate increase in the foam hardness.     

A facile route for the synthesis of mechanically strong MWCNTs/NDs nanobifiller filled polyacrylate composites

ABSTRACT

We present here the synthesis of novel Nano-Bifiller filled composites with extremely promising material properties. To achieve this goal, initially, poly (methyl methacrylate) (PMMA) and poly (ethylene glycol) (PEG) blend were formed. Later, the matrix was reinforced with purified carbon (P-CNT), amino modified carbon nanotube (PDA-CNT) and amino modified carbon nanotube nanodiamond (PDA-CNT-ND). In this way, three series of nanocomposites, i.e. PMMA/PEG/P-CNT, PMMA/PEG/PDA-CNT, and PMMA/PEG/PDA-CNT-ND were synthesized with varying P-CNT, PDA-CNT and PDA-CNT-ND loading (i.e., 1 wt.%, 3 wt.%, 5 wt.%, 10 wt.%, 30 wt.% and 50 wt.%) by a solution blending route. The reinforcement and loading effect of these three types of nanofillers on the matrix was studied. Studies were performed using Fourier transform infrared spectroscopy (FTIR), mechanical testing, thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM) and X-ray powder diffraction (XRD) to explore the structural, morphological, mechanical and thermal properties of nanocomposites prepared. The inter-association of poly (methyl methacrylate) and poly (ethylene glycol) (PMMA/PEG) due to hydrogen bonding and covalent attachment of matrix to the sidewalls of nanotubes was confirmed by FTIR spectra. The experimental results showed that a loading of 5 wt. % filler in matrix produced a tensile strength and modulus of 26.4 (MPa) and 1255.75 (MPa) in PMMA/PEG/P-CNT nanocomposites, while 28.8 (MPa) and 1411.04 (MPa) in PMMA/PEG/PDA-CNT nanocomposites and 29.4 (MPa) and 1419.41 (MPa) in PMMA/PEG/PDA-CNT-ND nanocomposites as compared to neat PMMA which has tensile strength and modulus of 21.79 (MPa) and 1083.84 (MPa) respectively. These results depict that bifiller nanocomposites showed better mechanical properties as compared to pristine and amine functionalized MWCNT. Scanning electron microscopy revealed granular morphology with few protruding out carbon nanotubes. Thermal stability of PMMA/PEG/PDA-CNT-ND nanocomposites was found higher than PMMA/PEG/PDA-CNT and PMMA/PEG/P-CNT nanocomposites. The T_o (369^°C) and T₁₀ (515^°C) values for PMMA/PEG/PDA-CNT-ND composites was higher than PMMA/PEG/PDA-CNT [T_o (354^°C) and T₁₀ (420^°C)] and PMMA/PEG/P-CNT composites [T_o (312^°C) and T₁₀ (390^°C)]. These results suggest that the bifiller nanocomposites were thermally more stable. The XRD spectra showed a pronounced XRD peak at 25.9^°, corresponding to (002) reflection of the nanotubes indicating that MWCNT structure was not destroyed during composite formation. The peak appeared at 75.3^° were indexed to (220) reflections due to nanodiamond structure.     

Two‐Stage Depressurization in Gas Dissolution Foaming: The Production of Nanocellular Materials Free of Defects

Nanocellular polymethylmethacrylate (PMMA) is produced through a newly proposed method, a two‐stage depressurization in the gas dissolution foaming process. This method modifies the depressurization step and allows controlling the pressure during cell growth, avoiding this way, the appearance of micrometric defects in the produced cellular materials. Three grades of PMMA, as well as different production parameters, are tested in order to study their influence on the final materials. Moreover, cellular structures are compared with those obtained with a one‐stage depressurization process. Additionally, this work analyzes the foaming mechanisms taking place during the production of nanocellular materials.     

Batch foaming of carboxylated multiwalled carbon nanotube/poly(ether imide) nanocomposites: The influence of the carbon nanotube aspect ratio on the cellular morphology

A series of microcellular poly(ether imide) (PEI) foams and nanocellular carboxylated multiwalled carbon nanotube (MWCNT‐COOH)/PEI foams were prepared by the batch foaming method. MWCNT‐COOHs with different aspect ratios were introduced into the PEI matrix as heterogeneous nucleation agents to improve the cell morphology of the microcellular PEI foams. The effect of the aspect ratio of the MWCNT‐COOHs on the cellular morphology, and gas diffusion is discussed. The results show that with the addition of MWCNT‐COOH, the sorption curve showed a slight reduction of carbon dioxide solubility, but the gas diffusion rate could be improved. The proper aspect ratio of MWCNT‐COOH could improve the cellular morphology under the same foaming conditions, in which m‐MWCNT‐COOH (aspect ratio ≈ 1333) was the best heterogeneous nucleation agent. When the foaming temperature was 170°C, the cell size and cell density of nanocellular m‐MWCNT‐COOH reduced to 180 nm and increased to 1.58 × 10¹³ cells/cm³, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42325.     

An Innovative Approach to the Synthesis of PMMA/PEG/Nanobifiller Filled Nanocomposites with Enhanced Mechanical and Thermal Properties

A facile route was adopted to blend the matrix. The PMMA/PEG blend was reinforced with three types of nanofillers, i.e., pristine MWCNT (P-CNT), amine functionalized MWCNT (PDA-EA-CNT) and nanobifiller i.e. nanodiamond functional MWCNT (PDA-EA-CNT-ND) to yield three different types of nanocomposites i.e. PMMA/PEG/P-CNT, PMMA/PEG/PDA-EA-CNT and PMMA/PEG/PDA-EA-CNT-ND. These nanocomposites were reinforced with nanofiller loading (1 wt. %, 3 wt. %, 5 wt. %, 10 wt. %, 30 wt. % and 50 wt. %) by solution casting method. Structure of composite and nanofillers was confirmed by FTIR. FESEM imaging revealed that nanocomposites have micro porous morphology. At high magnification, distribution of functionalized CNT/ND appears to be protruding out of the polymeric matrix. The TGA result suggests that the thermal stability of the nanocomposites was enhanced in comparison to PMMA due to grafting of filler molecules with PMMA/PEG macromolecules. The DTG results showed that the bifiller nanocomposites (PMMA/PEG/PDA-EA-CNT-ND) exhibited improved thermal stability with T_max (431^°C) as compared to P-CNT and amine functionalized CNT (PMMA/PEG/PDA-EA-CNT) with T_max of 395^°C and 418^°C respectively. XRD results showed fine interaction between filler and the polymeric matrix. As the filler loading was increased the composites showed pronounced XRD peak at 25.9^°, corresponding to (002) reflection of nanotubes. Significant improvement in the mechanical properties of composites was recorded with the reinforcement of fillers as compared to the neat matrix. The most significant improvement in tensile strength and elastic modulus was observed for the bifiller nanocomposites with 5 wt. % PDA-EA-CNT-ND. They showed a tensile strength and elastic modulus of 29.9 MPa and 1474.31 MPa respectively as compared to amine functionalized CNT with tensile strength (25.7) and elastic modulus (1466.99 MPa)and P-CNT with tensile strength(25 MPa) and elastic modulus (1155.75 MPa).     

Temperature influence and CO2 transport in foaming processes of poly(methyl methacrylate)–block copolymer nanocellular and microcellular foams

Fabricated by high-pressure or supercritical CO₂ gas dissolution foaming process, nanocellular and microcellular polymer foams based on poly(methyl methacrylate) (PMMA homopolymer) present a controlled nucleation mechanism by the addition of a methylmethacrylate–butylacrylate–methylmethacrylate block copolymer (MAM), leading to defined nanocellular morphologies templated by the nanostructuration of PMMA/MAM precursor blends. Influence of the CO₂ saturation temperature on the foaming mechanism and on the foam structure has been studied in 90/10 PMMA/MAM blends and also in the neat (amorphous) PMMA or (nanostructured) MAM polymers, in order to understand the role of the MAM nanostructuration in the cell growth and coalescence phenomena. CO₂ uptake and desorption measurements on series of block copolymer/homopolymer blend samples show a competitive behavior of the soft, rubbery, and CO₂-philic block of PBA (poly(butyl acrylate)) domains: fast desorption kinetics but higher initial saturation. This competition nevertheless is strongly influenced by the type of dispersion of PBA (e.g. micellar or lamellar) and a very consequent influence on foaming.CO₂ sorption and desorption were characterized in order to provide a better understanding of the role of the block copolymer on the foaming stages. Poly(butyl acrylate) blocks are shown to have a faster CO₂ diffusion rate than poly(methyl methacrylate) but are more CO₂-philic. Thus gas saturation and cell nucleation (heterogeneous) are more affected by the PBA block while cell coalescence is more affected by the PMMA phases (in the copolymer blocks + in the matrix).     

High‐Temperature Flexural Strength and Thermal Stability of Near Zero Expanding doped Aluminum Titanate Ceramics for Diesel Particulate Filters Applications

A substantial increase in sinterability, high‐temperature flexural strength, thermal stability in combination with an average thermal expansion of 0.42 × 10^?6/^°C (30–1000°C) is achieved through magnesium silicate (Mg₃Si₄O₁₀(OH)₂) doping of Aluminum Titanate (Al₂TiO₅) ceramics. Doped specimens exhibited the sintered density of 99% of theoretical density at 1550°C and a maximum enhancement of 169.23% (70 MPa) in flexural strength at 1200°C as compared with 26 MPa measured at 30°C. Enhancement of flexural strength at elevated temperature can be attributed to the increasing extent of thermally activated crack blunting with increasing temperature, which is further evident from the dilatometric hysteresis curve recorded for these samples. XRD investigations of undoped (Al₂TiO₅, AT) samples annealed at 1100°C for 5 and 10 h have shown clear evidence of decomposition to precursor oxides by 7% and 21.13%, respectively. However, the samples of magnesium silicate–doped Al₂TiO₅ (TAT) under identical conditions have shown no sign of decomposition, indicating significantly high thermal stability. TAT formulations were also extrusion processed to investigate the suitability of forming cellular honeycomb structures. TAT formulation with superior thermo‐mechanical properties and excellent adaptability for extrusion processing can be explored for the development of next generation diesel particulate filters (DPF).     

Reaction,densification, and mechanical properties of Ti2AlCx ceramics at low applied pressure and temperature

Ti₂AlC_x ceramic was produced by reactive hot pressing (RHP) of Ti:Al:C powder mixtures with a molar ratio of 2:1:1–.5 at 10–20 MPa, 1200–1300°C for 60 min. X-ray diffraction analysis confirmed the Ti₂AlC with TiC, Ti₃Al as minor phases in samples produced at 10–20 MPa, 1200°C. The samples RHPed at 10 MPa, 1300°C exhibited ≥95 vol.% Ti₂AlC with TiC as a minor phase. The density of samples increased from 3.69 to 4.04 g/cm³ at 10 MPa, 1200°C, whereas an increase of pressure to 20 MPa resulted from 3.84 to 4.07 g/cm³ (2:1:1 to 2:1:.5). The samples made at 10 MPa, 1300°C exhibited a density from 3.95 to 4.07 g/cm³. Reaction and densification were studied for 2Ti–Al–.67C composition at 10 MPa, 700–1300°C for 5 min showed the formation of Ti–Al intermetallic and TiC phases up to 900°C with Ti, Al, and carbon. The appearance of the Ti₂AlC phase was ≥1000°C; further, as the temperature increased, Ti₂AlC peak intensity was raised, and other phase intensities were reduced. The sample made at 700°C showed a density of 2.87 g/cm³, whereas at 1300°C it exhibited 3.98 g/cm³; further, soaking for 60 min resulted in a density of 4.07 g/cm³. Microhardness and flexural strength of Ti₂AlC_0.8 sample were 5.81 ± .21 GPa and 445 ± 35 MPa.     

Zirconium diboride laminates for improved damage tolerance at elevated temperatures

The mechanical response was studied for dense laminates containing layers of ZrB₂ (~145 µm) and graphite—10 vol% ZrB₂ (~20 µm). Individual layers were formulated by mixing starting powders with thermoplastic polymers and pressing into sheets. Laminates were produced by stacking and warm pressing the sheets, debinding, and hot pressing at 2050°C, 32 MPa, in Ar. The laminates were fractured at temperatures up to 2000°C in Ar. Laminates exhibited room temperature flexure strength of 260 MPa, increasing to 300 MPa at 1600°C, and then decreasing to 160 MPa at 2000°C. Inelastic work of fracture was 0.6 kJ/m² at room temperature, reached a maximum of 1.3 kJ/m² at 1400°C, and reverted to linear elastic failure at 2000°C. During fracture, cracks were deflected at the interfaces between the strong ZrB₂ layers and the relatively weak C-ZrB₂ layers, which led to an increased inelastic work of fracture by more than an order of magnitude compared to conventional ZrB₂ ceramics. This study demonstrated that laminate architectures are a promising approach for improving the damage tolerance of ZrB₂-based ceramics at elevated temperatures.     

Supercritical CO2-assisted extrusion foaming: A suitable process to produce very lightweight acrylic polymer micro foams

A strategy of CO₂-assisted extrusion foaming of PMMA-based materials was established to minimize both foam density and porosities dimension. First a highly CO₂-philic block copolymer (MAM: PMMA-PBA-PMMA) was added in PMMA in order to improve CO₂ saturation before foaming. Then the extruding conditions were optimized to maximize CO₂ uptake and prevent coalescence. The extruding temperature reduction led to an increase of pressure in the barrel, favorable to cell size reduction. With the combination of material formulation and extruding strategy, very lightweight homogeneous foams with small porosities have been produced. Lightest PMMA micro foams (ρ = 0.06 g cm⁻³) are demonstrated with 7 wt% CO₂ at 130°C and lightest blend micro foams (ρ = 0.04 g cm⁻³) are obtained at lower temperature (110°C, 7.7 wt% CO₂). If MAM allows a reduction of T^foaming, it also allows a much better cell homogeneity, an increase in cell density (e.g., from 3.6 10⁷ cells cm⁻³ to 2 to 6 10⁸ cells cm⁻³) and an overall decrease in cell size (from 100 to 40 μm). These acrylic foams produced through scCO₂-assisted extrusion has a much lower density than those ever produced in batch (ρ ≥ 0.2 g cm⁻³).     

Applying cold sintering process to a proton electrolyte material: CsH2PO4

The Cold Sintering Process (CSP) was applied to CsH₂PO₄, a proton conducting electrolyte. The powders were sintered between 120 °C and 200 °C under 300 MPa for 1 h and the ceramics investigated for their respective structure-property-process relations. The microstructure development of the CsH₂PO₄ materials was characterized for grain size, and dihedral angle distributions for a variety of the CSP processing conditions. The electrical properties of the cold sintered CsH₂PO₄ were characterized through electrochemical impedance spectroscopy over a temperature range between 120 °C and 200 °C. The data suggests that the proton conductivity is 2.30 × 10⁻⁴ Scm^-1 at 200 °C with good repeatability during cycled measurements.