Nanofoaming of PMMA using a batch CO2 process: Influence of the PMMA viscoelastic behaviour

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: Cellular Structuresupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Laguna‐Gutiérrez

et al. 2018

Polymer

“…For a value of = SD ϕ / 0.5, that is, a width of 100 nm with an average cell size of 200 nm, a difference of almost 1.5 mW/mK is predicted, that is, an increase of a 4.8% in the conductivity. Values of SD ϕ / of 0.5 and higher are usually detected in nanocellular materials [47,56,57], so this effect is important for the accurate prediction of the thermal conductivity of nanocellular polymers.…”

Section: Other Applications Of the Modelmentioning

confidence: 99%

Modeling the heat transfer by conduction of nanocellular polymers with bimodal cellular structures

Pinto

et al. 2019

Polymer

A model to predict the thermal conductivity of nanocellular polymers is presented. • This model applies to nanocellular materials with non-uniform cellular structures. • The thermal conductivity of bimodal systems with nanometric cells is predicted. • The model is validated using experimental results of real bimodal systems. • It can be also applied to nanocellular polymers with wide cell size distributions.

“…Besides, rheological properties are important in the analysis of the influence of the polymer viscosity into the nucleation and growing processes [19,44]. For these reasons, dynamic shear properties of all the nanocomposites were measured using a stress controlled rheometer, AR 2000 EX from TA Instruments.…”

Section: Dynamic Shear Propertiesmentioning

confidence: 99%

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

European Polymer Journal

Laguna‐Gutiérrez

et al. 2017

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).