Nanoporous PMMA: A novel system with different acoustic properties

León

Laguna‐Gutiérrez

et al. 2018

Polymer

Nanostructured polymer blends with CO2-philic domains can be used to produce nanocellular materials with controlled nucleation. It is well known that this nanostructuration can be induced by the addition of a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM) to a poly(methyl methacrylate) (PMMA) matrix. However, the effect of the block copolymer molecular weight on the production of nanocellular materials is still unknown. In this work, this effect is analysed by using three types of MAM triblock copolymers with different molecular weights, and a fixed blend ratio of 90 wt% PMMA and 10 wt% of MAM. Blends were produced by extrusion. As a result of the extrusion process, a non-equilibrium nanostructuration takes place in the blends, and the micelle density increases as MAM molecular weight increases. Micelle formation is proposed to occur as result of two mechanisms: dispersion, controlled by the extrusion parameters and the relative viscosities of the polymers, and self-assembly of MAM molecules in the dispersed domains. On the other hand, in the nanocellular materials produced with these blends, cell size decreases from 200 to 120 nm as MAM molecular weight increases. Cell growth is suggested to be controlled by the intermicelle distance and limited by the cell wall thickness. Furthermore, a theoretical explanation of the mechanisms underlying the limited expansion of PMMA/MAM systems is proposed and discussed.

Section: Nanostructuration Of the Blendsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Understanding the role of MAM molecular weight in the production of PMMA/MAM nanocellular polymers

León

Laguna‐Gutiérrez

et al. 2018

Polymer

“…[21,22] Further, it is possible to produce semi-transparent nanocellular polymers, [23,24] among other interesting properties and applications. [25][26][27] The challenge in the production of these systems is currently in the reduction of the density while keeping the cell size in the nanometric range.…”

Section: Introductionmentioning

confidence: 99%

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

León

Sánchez-Calderón

et al. 2019

Macro Materials & Eng

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.

“…This effect happens when the pore size values become comparable to the mean free path of the air molecules (about 70 nm under standard conditions), decreasing significantly the air thermal conductivity inside the pores [14]. Finally, previous works also found a modification of the dielectric and acoustic properties of PMMA foams when the pore size decreases from the micro to the nanometric range [10,11], as well as an increase of the polymer matrix Tg associated to the molecular confinement of the PMMA chains in the thin pore walls (with a thickness below 100e150 nm) [12,13].…”

Section: Introductionmentioning

confidence: 83%

Nanoporous PMMA foams with templated pore size obtained by localized in situ synthesis of nanoparticles and CO2 foaming

Pinto

Morselli

et al. 2017

Polymer

a b s t r a c tPolymer foams with controlled and templated pore size have been obtained for the first time by CO 2 gas dissolution foaming from poly(methyl methacrylate) (PMMA) films. This kind of materials, with a variable porous structure, mimic some high-performance natural materials and could present significant interest in many applications. However, up to now their controlled fabrication has not been successfully achieved. Herein, we present a method to achieve a fine control in the production of such materials. Thermal in situ synthesis of ZnO nanoparticles from Zn(OAc) 2 was proposed to obtain PMMA nanocomposites, in which the ZnO nanoparticles induce heterogeneous nucleation that leads to formation of pores with size below the micron, upon CO 2 foaming. Starting from templated solid PMMA samples with well-differentiated regions, presenting or not ZnO nanoparticles, it was possible to obtain PMMA-based foams with well-defined areas of different pore sizes.