Three lines of green chemistry were combined in this study, in order to produce porous materials with pore size distributions in the micro- and nano-scales. These lines are: (i) the renewable and biodegradable sources (cellulose), (ii) ionic liquids, and (iii) supercritical fluids. By dissolving cellulose in a room temperature ionic liquid and regenerating with water or methanol we obtained cellulose hydrogels and methanogels. The liquid mixtures were separated by vacuum distillation with high yield of recovery. The obtained gels were processed by supercritical carbon dioxide to give porous materials. A novel foaming procedure was applied to hydrogels in order to obtain microporous structures of cellulose and cellulose composites, while in alcogels the supercritical point drying method resulted in nanoporous aerogels. For elucidating physicochemical aspects involved in the two processes and for characterization of the produced materials, X-ray diffraction, sorption measurements (by a modified mass loss analysis and the BET method) and scanning electron microscopy were used. The role of various process parameters on the final porous structure was investigated.

Evaluation and understanding of the thermal behavior of polymers is crucial for many applications, e.g., polymer processing at relatively high temperatures, and for evaluating polymer-polymer miscibility. In this study, the differences in the thermal behavior of poly(vinyl alcohol) (PVA) raw powder and physically crosslinked films were investigated using various methods, such as thermogravimetric analysis (TGA) and derivative TGA (DTGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Various strategies were adopted, e.g., film casting from PVA solutions in H₂O and D₂O and heating of samples at carefully selected temperatures, in order to provide insights about the structure-properties relationship. It was found that the physically crosslinked PVA film presents an increased number of hydrogen bonds and increased thermal stability/slower decomposition rate compared to the PVA raw powder. This is also depicted in the estimated values of specific heat of thermochemical transition. The first thermochemical transition (glass transition) of PVA film, as for the raw powder, overlaps with mass loss from multiple origins. Evidence for minor decomposition that occurs along with impurities removal is presented. The overlapping of various effects (softening, decomposition, and evaporation of impurities) has led to confusion and apparent consistencies, e.g., from the XRD, it is derived that the film has decreased crystallinity, and apparently this is in agreement with the lower value of heat of fusion. However, the heat of fusion in this particular case has a questionable meaning.