New Stereocomplex PLA-Based Fibers: Effect of POSS on Polymer Functionalization and Properties

Abstract

In this work, a novel approach for the functionalization of electrospun stereocomplex polylactide (sc-PLA)-based fibers, prepared from solutions containing equimolar amount of high-molecular-weight poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), was developed. The method, which consists in introducing functionalized polyhedral oligomeric silsesquioxanes (POSS) into the electrospinning solutions, was carried out by employing as a solvent system a 2:1 mixture of chloroform (CHCl 3 ) and 1,1,1,3,3,3hexafluoro-2-propanol (HFIP), never applied in the production of sc-PLA fibers, which was found to promote POSS solubilization while simultaneously allowing to obtain an excellent fiber homogeneity. Indeed, the specific effect of the single components of the solvent mixture, CHCl 3 and HFIP, on fiber structuring and morphology was evaluated. Conversely to the fiber morphology, which turned out to be significantly affected by the chosen electrospinning solvent, the PLA stereocomplexation, occurring upon subsequent annealing treatment at 100 °C (as evidenced by differential scanning calorimetry (DSC) and X-ray diffraction analyses), was found to be similar for fibers prepared starting from the different types of solvent. Unlike solution casting, electrospinning allows the exclusive formation of stereocomplex crystallites, simultaneously promoting a submicrometric dispersion of the silsesquioxanes, with the consequent fiber functionalization. In our work, two different kinds of POSSone characterized by hydroxyl groups (POSS−OH) and another one functionalized with an aminobearing molecule (POSS−NH 2 )were exploited to impart hydroxyl and amino functionalities to PLA based nanofibers, while preserving the capability of the polymer system to form a pure stereocomplex on subsequent annealing. In particular, it was found that the amino groups of the sc-PLA fibers functionalized with POSS−NH 2 , promote specific interactions with a metal precursor, i.e., PdCl 2 , which, as a result of a subsequent reduction, forms metal nanoclusters homogeneously dispersed on the fiber surface. The higher thermal and chemical resistance of the sc-PLA fibers with respect to those based solely on PLLA allowed to significantly broaden the applications of the catalytic system. Indeed, the sc-PLA/Pd fibers turned out to be very active in the Heck reaction, easily recoverable and reusable for multiple catalytic cycles.

A Novel Electrostimulated Drug Delivery System Based on PLLA Composites Exploiting the Multiple Functions of Graphite Nanoplatelets

“…Figure 6B compares TGA curves of the neat PLLA with those of the systems containing graphite (PLLA_G and PLLA_G_p). As already reported for other PLA-based materials, 48 the thermal decomposition of all the analyzed samples was found to occur in one step in the temperature range between ca. 300 and 400 °C.…”

Biobased System Composed of Electrospun sc-PLA/POSS/Cyclodextrin Fibers To Remove Water Pollutants

“…As previously reported, 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 …”

“…Indeed our system, which is alternative to the conventional materials applied for environmental applications and possesses properties potentially exploitable in the field of water treatment, takes 28 Indeed, the electrospinning process turned out to allow a nanometric dispersion of the silsesquioxane [29][30][31][32] and, consequently, in the case of the exploitation of functionalized POSS, an homogenous distribution on the polymer nanofiber surface of the reactive groups, which were found to be accessible but simultaneously strongly linked to the polymer matrix. 28…”

PLA maleation: an easy and effective method to modify the properties of PLA/PCL immiscible blends

“…The presence of double/multiple melting peaks is a commonly observed phenomenon for semicrystalline polyesters, caused by the existence of melting and recrystallization processes. In the specific case of PLA, some authors have interpreted it as arising from a phase transition (from the less stable α′ form to the more perfect α polymorph, melting at higher temperature) [33,34]. Whatever mechanism is taking place during the heating scan of the PLA matrix (recrystallization or phase transition), it is clear that such behavior is influenced by the PLA-g-MA content in the blend, the reorganization phenomena becoming more evident together with the crystallization extent on increasing the amount of PLA-g-MA.…”