Thermal‐Insulation, Electrical, and Mechanical Properties of Highly‐Expanded PMMA/MWCNT Nanocomposite Foams Fabricated by Supercritical CO₂ Foaming

Abstract

Poly(methyl methacrylate) (PMMA) foams exhibit many advantages over the most popular polystyrene (PS) foams, which make them an ideal candidate for thermal insulation application. First, PMMA has lower carbon content, lower burning rate, smaller heat release rate, and lower smoke emission than PS. [7] So, PMMA foams need less flame retardants than PS foams when used as construction thermal insulation materials, which helps reduce the overall production costs and mitigate the greenhouse effect. Second, PMMA can strongly absorb infrared light in the wavelength range of 2.8-25 µm, [8] while PS can hardly absorb infrared light. Thus, the low-density PMMA foams are expected to block more thermal radiations than the PS foams with the same density. Third, PMMA has higher CO 2 solubility than PS because the carbonyl group in PMMA has stronger adsorption capacity for CO 2 than the benzene ring in PS. [9] The higher CO 2 solubility makes it much easier to prepare low-density PMMA foam, enhancing foam's thermal insulation. Carbon nanotubes (CNTs) with unique electrical, mechanical, and thermal properties have exhibited great value in designing electrical conductive composites, [10,11] electromagnetic interference shielding, [12,13] and energy harvesting materials. [14] These excellent properties of CNTs also make them ideal fillers to design polymer foams for some important reasons. First, CNTs are excellent heterogeneous nucleating agent to increase the cell density. Cell nucleation is more likely to occur at the interfaces between fillers and polymer matrix because of the relatively low free energy barrier for heterogeneous nucleation. [15][16][17] Due to their high aspect ratio and specific area, uniformly dispersed CNTs can offer much more interfaces as the heterogeneous nucleation sites than many other spherical (i.e., nano SiO 2 [18] ) or lamellar fillers (i.e., nano clay [19] ). Moreover, CNTs can endow the polymer foams with multifunctionality by offering the same advantages that they offer in the bulk while not decreasing foam's other properties. For example, CNTs are one kind of good wave-absorbing material that can be recognized as black bodies. In electromagnetic fields, CNTs can attenuate electromagnetic radiation by forming a conductive network (conductivity loss), [12,20] or by the polarization of CNT/polymer interfaces (dielectric loss), [21,22] or by scattering and multiple Polymer Nanocomposite Foaming behavior of poly(methyl methacrylate) (PMMA)/multi-walled carbon nanotubes (MWCNTs) nanocomposites and thermally-insulating, electrical, and mechanical properties of the nanocomposite foams are investigated. PMMA/MWCNT nanocomposites containing various amounts of MWCNTs are first prepared by combining solution and melt blending methods, and then foamed using CO 2 . The foaming temperature and MWCNT content are varied for regulating the structure of PMMA/MWCNT nanocomposite foams. The electrical conductivity measurement results show that MWCNTs have little effect on the electrical conductivity of foams with l...

FTIR in situ measurement of swelling and CO2 sorption in acrylic polymers at high CO2 pressures

“…Our study should help enhancing and optimizing conditions of nano foaming. Foams, when reducing both cell size and density at the same time, are intended to exhibit enhancement of several properties, such as high thermal insulation [25] or high performance mechanical properties [26] (damping) or else useful for filtration [13].…”

Ultrahigh and Tunable Electromagnetic Interference Shielding Performance of PVDF Composite Induced by Nano-Micro Cellular Structure

“…The supercritical fluid foaming process can greatly reduce the density of the composites and fabricate a porous structure in the polymer matrix. Therefore, this technique is highly attractive as it possesses a number of benefits such as energy saving [17,18], environmental protection [19,20], thermal insulation [21,22], and vibration and noise reduction [23]. A large number of studies have reported that the introduction of the microcellular structure is conducive in improving the EMI shielding properties of conductive polymer composites [24][25][26].…”

Effect of acetylated cellulose nanocrystals on solid‐state foaming behaviors of chain‐extended poly(butylene adipate‐co‐terephthalate)

“…Polymer foams with unprecedented thermal-insulation properties play a vital role to improve energy efficiency through achieving high-efficiency thermal insulation. [61] Meanwhile, the foams with closed cell structure also provide the certain structural rigidity to the foams comparing with the foams with opened cell structure. [62] In addition, the unsurpassed and most easily available substances for the purpose of the low thermal conductivity are various kinds of gases.…”