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

Abstract

Highly CO 2 -philic nanoparticles, octatrimethylsiloxy polyhedral oligomeric silsesquioxanes (POSS) are used to increase the affinity of poly(methyl methacrylate) (PMMA) to CO 2 in supercritical carbon dioxide (scCO 2 ) 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 × 10 12 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). ScCO 2 processing decreased the density of the polymer by more than 50%.

Impacts of cellulose nanofibers on the morphological behavior and dynamic mechanical thermal properties of extruded polylactic acid/cellulose nanofibril nanocomposite foam

“…15 Polymer with bubbles of gas makes polymer foams which are caused by the blowing agent and classified into three categories as regular, microcellular (cell size: <10 μm and cell density: 10 9 -10 12 cells/cm 3 ), and nanocellular (cell size: <1 μm and cell density: >10 15 cells/cm 3 ). 16,17 Elements for the mercantile growth of foams contain lightness, inexpensiveness, lower thermal conductivity, a broad domain of formulations from hard foam to elastic foam, a number of different processes, simple production of various parts, absence of pressure in several production methods, the higher strength-to-mass ratio in analogy to another polymer families and great impact. [18][19][20][21] In extrusion foaming processes, due to the high pressure, the gas injected into the polymer melt dissolves.…”

Computational design of nucleating agents of poly (methyl methacrylate) microcellular foams: “savanna‐like” surface structures and their effects on foaming

“…Disks were loaded into a high‐pressure vessel with 12‐mm inside diameter and 210 mm height (inner volume 23.8 cm 3 ) and sealed tightly. After evacuation, high‐pressure CO 2 was loaded in the vessel and the vessel was heated up to 100°C, referring to previous studies on foams of PMMA or PMMA‐based composites 37–39 . The inner pressure was adjusted to be 40 MPa, the upper‐pressure limit of the apparatus, with a back‐pressure regulator.…”

“…After evacuation, high-pressure CO 2 was loaded in the vessel and the vessel was heated up to 100 C, referring to previous studies on foams of PMMA or PMMAbased composites. [37][38][39] The inner pressure was adjusted to be 40 MPa, the upper-pressure limit of the apparatus, with a back-pressure regulator. This condition was maintained for 24 h to reach saturation of CO 2.…”

Interfacial stabilizing and reinforcing effects of silsesquioxane-based hybrid Janus molecules in extrusion supercritical CO2 foaming of polypropylene

“…In literature, it has been reported that closed-cage polyhedral oligomeric silsesquioxanes (POSS) with polymer-philic groups could be well dispersed in poly(methyl methacrylate) at low POSS loadings, which reinforces the foams slightly [25]. An alternative strategy was to mix a polymer with POSS that has both polymerphilic and CO 2 -philic groups, such that the POSS could disperse well in the polymer and serve as CO 2 nucleators by either clustering to form heterogeneous nucleation sites or attracting CO 2 to nucleation sites [26][27]. Culhaciogu et al also reported that at high loadings, such POSS could also improve the solubility of CO 2 in polymers, leading to enhanced mechanical and thermal properties of the resultant foams [28].…”