PRIN 2008

2010 - 2012
Title: 
Biopolyester based nanohybrid materials through reactive blending of opportunely modified polymers and inorganic substrates
Principal Investigator: 
Elisa Passaglia
Project type: 
PI.ICCOM

Abstract

The present research project concerns the preparation and the study of inorganic nano-hybrids, based on polymers, stemming from renewable resources. In particular, the attention will be focused on poly(lactic acid) (PLA), while montmorillonites, hydrotalcites (commercially available as well as modified ones), TiO2, ZnO2, and hydroxyapatites will constitute the inorganic part of the new nanohybrid materials. The preparation of nanocomposites will be based on blending techniques (i.e. reactive blending), carried out in the melt, and in situ polymerisation reactions (i.e. reactor blending). To this purpose, the unique expertise of the three UR (Florence, Palermo, Milano and CNR Pisa-Florence, CNR in the following), will offer the opportunity to develop the research on different paths. In this case commercially available montmorillonites hydrotalcites (modified or not) that will be dispersed in a PLA matrix employing a batch mixer and on the other hand they will be employed for in situ polymerization reactions. This first part of the project will provide information on the effect of the structure of the organophilic modifiers and other parameters of the process (i.e. blending-time, blending-temperature, mixing speed), applied in the preparation of hybrid materials, on the morphology and the functional properties of the obtained composites, along with the possibility of absorbing new catalysts in inorganic nano-structured matrices. The optimization of the parameters will take into account the achievement of exfoliated nanocomposites. The results obtained will provide valuable indications on the structure of the most promising modifiers to be employed in the synthetic process, evaluating also the role of hydroxylic groups and/or aromatic rings present in the modifier to obtain exfoliated structures of the fillosilicate. Furthermore, the outcome of the synthetic process employing modified PLA as well as the modified fillosilicates will be evaluated. In this context, the possibility of obtaining alternative and innovative polymer structures will be of high interest. To this purpose, both the UR of Florence and CNR will aim at the synthesis of modified PLA, employing innovative catalysts (i.e. complexes based on calix[4]arene and "salen" in combination with, Al, Ti, Zr and Hf), adding chromophore groups. In addition, post-functionalization reactions of the polymer will be carried out, upon radical and transesterification reactions. In the same direction, blends of PLA with cellulose microfibers having characteristic diameters in the range of nanometers will be studied; surface treatments will be applied to enhance the dispersion and the adhesion to the polymeric matrix. The microfibers modification treatments (developed by the unit of Milan) will use oligomeric or low mol weight reactants and transesterification reactions activated during reactive mixing. This is similar to the inorganic nanofiller modifications planned for the activities of units Firenze and CNR. The presence of microfibers will permit the modulation of the rheological and mechanical characteristics of the employed matrices. In this way, the four research units will have a wide range of products available for using them as-they-are, as additives (e.g. combatibilizers and stabilizers) or for blending purposes. The polymers will be completely characterized by classical methods (i.e. NMR, GPC, IR and DSC) along with mechanical, thermo-mechanical, rheological and morphological techniques, in order to gain the real potential application of these products. The most interesting materials are then subjected to aging tests on laboratory scale, in order to gain information on their long term stability also under UV irradiation. This kind of valuation turns out to be crucial for the application of these materials especially for packaging and tissue engineering. Afterwards, the research unit of Palermo will aim at studying the possibility of transferring the preparation of the modified materials from a laboratory to an industrial scale. To this purpose, the most promising specimen will be chosen on the basis of the results gathered by the research units. In parallel, the most interesting materials will be selected on the basis of indications, given by the other two research units, will be treated in a discontinuous extruder, in order to gain more detailed information on the effect of the different processing parameters, such as temperature, time of mixing and rotor speed on the optimal processing conditions for the extrusion, in order to obtain films by compression moulding and blowing. For sake of completeness and in order to accelerate the analyses of the materials, also statistical methods, based on a fractional or factorial design of experiments will be employed, along with statistic tools like the analysis of variance and t-test.