The key parameters and production route for the easy production of highly transparent nanocellular films based on polymethylmethacrylate (PMMA) with thickness below 1 mm are herein described. The use of the gas dissolution foaming process (CO2 as physical blowing agent) with saturation pressures of 40 and 50 MPa, a saturation temperature of 0 °C and a saturation time of 2.5 h together with an adequate approach to foam the samples leads to the production of directly transparent nanocellular PMMA with relative densities in the range of 0.47–0.80 and cell sizes in the internal part of the film ranging 23–29 nm. The produced materials present maximum transparency of 61% for a thickness of 0.5 mm without any post-processing, a value comparable to the one previously obtained in the literature for nanocellular PMMA produced using a long-lasting process that included additional time-consuming post-processing of the samples. The produced cellular materials have been in-deep characterized, and the influence of several key parameters such as the solid skin thickness, transition region, and cellular structure on the final optical transmittance has been studied.
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