Judith Martín-de León *, Victoria Bernardo and Miguel Ángel Rodríguez-Pérez
Cellular Laboratory (CellMat), Universidad de Valladolid, Valladolid 47011, Spain; vbernardo@fmc.uva.es (V.B.); marrod@fmc.uva.es (M.Á.R.-P.) Correspondence: jmadeleon@fmc.uva.es; Tel.: +34-983-184-035
Academic Editor: Michael D. Guiver
Received: 13 May 2016; Accepted: 11 July 2016; Published: 18 July 2016
Abstract: This paper describes the processing conditions needed to produce low density nanocellular
polymers based on polymethylmethacrylate (PMMA) with relative densities between 0.45 and 0.25,
cell sizes between 200 and 250 nm and cell densities higher than 1014 cells/cm3. To produce these
nanocellular polymers, the foaming parameters of the gas dissolution foaming technique using CO2
as blowing agent have been optimized. Taking into account previous works, the amount of CO2
uptake was maintained constant (31% by weight) for all the materials. Foaming parameters were
modified between 40 C and 110 C for the foaming temperature and from 1 to 5 min for the foaming
time. Foaming temperatures in the range of 80 to 100 C and foaming times of 2 min allow for
production of nanocellular polymers with relative densities as low as 0.25. Cellular structure has
been studied in-depth to obtain the processing-cellular structure relationship. In addition, it has
been proved that the glass transition temperature depends on the cellular structure. This effect is
associated with a confinement of the polymer in the cell walls, and is one of the key reasons for the
improved properties of nanocellular polymers.
Keywords: nanocellular polymer; nanocellular foam; gas dissolution foaming; confinement; PMMA