Ionic liquids as foaming agents of semi-crystalline natural-based polymers

In this work, the ability to foam semi-crystalline natural-based polymers by supercritical fluid technology
\nis evaluated. The application of this technique to natural polymers has been limited due to the fact that
\nthey are normally semi-crystalline polymers, which do not plasticize in the presence of carbon dioxide.
\nThis can be overcome by the use of plasticizers, such as glycerol, which is a commonly used plasticizer,
\nor ionic liquids, which have recently been proposed as plasticizing agents for different polymers.
\nFollowing the green chemistry principles, the main aim is, hereafter, the design and development of new
\n3D architectures of natural-based polymers, combining ionic liquids (IL) and supercritical fluid (SCF)
\ntechnology. A polymeric blend of starch, one of the most abundantly occurring natural polymers, and
\npoly-ε-caprolactone, a synthetic polymer, which is a biodegradable aliphatic polyester commonly used in
\nan array of biomedical applications (SPCL), was processed by supercritical fluid foaming, at different
\noperating conditions, namely pressure (10.0 up to 20.0 MPa), temperature (35 up to 60 °C) and soaking
\ntime (30 min up to 3 h). The ionic liquid tested in this work was 1-butyl-3-methylimidazolium acetate
\n([bmim]Ac). The interactions between SPCL and [bmim]Ac or glycerol were analysed by Fourier
\ntransform infrared spectroscopy, differential scanning calorimetry and by mechanical tests, using both
\ntensile and compressive modes. Morphological analysis, porosity, interconnectivity and pore size
\ndistribution of the matrixes were evaluated and the morphology was analyzed by scanning electron
\nmicroscopy and by micro-computed tomography. To our knowledge the use of ionic liquids as foaming
\nagents is reported here for the first time. The results obtained suggest that this approach can further
\npromote the development of composite polymer–IL materials, particularly for catalysis, chromatography,
\nextraction and separation purposes.