PMMA-sepiolite nanocomposites as new promising materials for the production of nanocellular polymers

Abstract

A B S T R A C TIn this work, a new system based on poly(methyl methacrylate) (PMMA) sepiolite nanocomposites that allow producing nanocellular polymers by using the gas dissolution foaming technique is described. Nanocomposites with different nanoparticle types and contents have been produced by extrusion. From these blends, cellular materials have been fabricated using the so-called gas dissolution foaming method. An extensive study of the effect of the processing parameters (saturation pressure and foaming temperature) on the cellular materials produced has been performed. Results showed that among the three sepiolites used, only those modified with a quaternary ammonium salt are suitable for being used as nucleating agents in PMMA. With these nanoparticles bimodal cellular polymers, with micro and nanometric cells, have been produced. Cell sizes in the range of 300-500 nm and cell densities of the order of 10 13 -10 14 nuclei/cm 3 have been obtained in the nanocellular region. A foaming temperature of 80°C and a wide range of saturation pressures (between 10 and 30 MPa) and low particle contents (between 0.5 and 1.5 wt%) allow obtaining these materials. Furthermore, it has been found that cell size in the nanometric population can be controlled by means of the particles content; a reduction in the cell size is obtained when the particles content increases. Finally, results indicate that an increase in the foaming temperature leads to cellular nanocomposites with lower relative densities (below 0.21) and larger cell sizes (above 450 nm).

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

“…The conclusion from the analysis of the core region is that the heterogeneous nucleation effect due to the addition of TPU is pressure-dependent. This is a surprising result, since in other heterogeneous systems such as in blends with nanoparticles [42] or with nanometric micelles, [35] the heterogeneous nucleation was proved to be predominant over a wide range of pressures. However, this is not the case for the PMMA/TPU system.…”

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

“…When adding an appropriate second phase to a pure polymer, the interfaces between the matrix and the second phase act as preferable nucleation sites, that is, the Gibbs energy barrier, which should be overcome to form a nucleus, is lower when this second phase is added [24]. To produce nanocellular polymers with this approach, nanoparticles [25][26][27] or block copolymer micelles [10,[28][29][30] can be used as the second phase. In particular, block copolymer spherical micelles with CO 2 -philic domains gather all the qualities required to act as ideal nucleants: the nucleation is favourable in the micelles, they present uniform size and surface properties, they are easily dispersible, and the number of micelles formed is usually large [31].…”

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

“…Foaming experiments were conducted using a two‐step foaming process . First, samples were put into the pressure vessel at a constant CO 2 pressure of 10 MPa and at a temperature of 25 °C for the saturation stage during 20 h, enough to achieve saturation of CO 2 in the PMMA samples . Then, the pressure was abruptly released at a pressure drop rate of 15 MPa s −1 at the first moments of the pressure drop.…”

“…In a bimodal cellular structure, the micrometric cells, though smaller in number, typically occupy a significant volume of the sample. Then, to quantify the observed bimodality, the relative volume occupied by the population of nanometric cells, V nano , is measured: where A m is the observed area occupied by the micrometric cells (cell sizes greater than 1 μm) in the SEM images and A t the total area of the image. The resulting two‐dimensional area ratio is equivalent to the three‐dimensional volume ratio given that the surfaces analysed were uniform and random, according to the Delesse principle in stereology .…”