MANFREDI liliana Beatriz
congresos y reuniones científicas
Biodegradable polymer composites containing cellulose nanocrystals: preparation and property characterization
Conferencia; ICCS18 - 18th International Conference on Composite Structures.; 2015
Homogeneous dispersion of cellulose nanocrystals (CNC) in polymer matrices is difficult to achieve by means of traditional melt processing techniques owing to the high tendency of CNC to form aggregates. Proper dispersion and distribution of nanoparticles in the polymer matrix are the prerequisite for obtaining polymer nanocomposites with improved physical and mechanical properties. In order to increase the dispersion of cellulose nanoparticles in non-aqueous polymer solution or suspension, several strategies have been adopted including the use of surfactants and chemical modification of the particle surface. In this communication we report on the preparation, functionalisation and characterization of various nanocomposites with biodegradable polyester matrix ? such as polylactide (PLA), polyhydroxyalcanoates (PHB, PHBV) and polybutilensuccinate (PBS)- obtained by dispersion of CNC in PVAc acqueous emulsion (or PEG solution) as well as by mixing in organic solvents, followed by melt blending with bulk polyesters. Owing to the miscibility of the components and the biodegradability of their blends, the nanocomposites are expected to display a wide application potential as ecocompatible systems with tunable properties. Cellulose nanofibres were prepared by acid hydrolysis of commercial microcrystalline cellulose. CNC was functionalized with glycidyl methacrylate (CNC-GMA) and grafting percentage was determined by FT-IR analysis. The morphology of nanocellulose and composites was characterized by TEM (Philips CM12) and SEM microscopy (JEOL JSM-5600LV). AFM analysis (Agilent Technologies 5500) was carried out in contact mode in air. Thermogravimetric analysis (Q500 TA Instruments) of plain components and composites was carried out from 50 to 600 °C at 5 or 10 °C min-1 under both nitrogen and air. Differential scanning calorimetry (Perkin-Elmer Pyris Diamond DSC) was employed to study the phase transition behaviour at a heating/cooling rate of 10 °C/min. Tensile mechanical tests were performed on dumb-bell shaped specimens at room temperature by an Instron machine (model 4505) operating at a cross-head speed of 10 mm/min, according to ASTM D638. The results of morphological analyses indicated that at lower CNC content (1-3 wt%) the cellulose nanoparticles were almost homogeneously dispersed inside the polyester matrix with limited formation of agglomerates. These agglomerates increased as the CNC content increased. An improved dispersion of nanofibres into PLA matrix was obtained for nanocomposites containing either functionalized components (PLA-GMA, CNC-GMA) or nanocellulose dispersed in PVAc, as compared to unmodified PLA/CNC composites. Thermal analyses demonstrated that glass transition, melting temperature and crystallinity of PLA were affected by the PVAc amount. Nanocomposites with PVAc dispersed CNCs exhibited higher thermal resistance than other composites. The filler effectiveness (CFE) was evaluated for all samples on the basis of storage moduli: CNC-GMA and PVAc dispersed CNCs (3 wt%) resulted the most effective fillers. The results of tensile mechanical tests showed that the addition of cellulose nanofibres into PLA (or PHB) increased the elastic modulus of nanocomposites due to the higher modulus of CNC. Samples with CNC content ≥ 3 wt% did not show further improvement of elastic modulus, probably due to agglomeration phenomena of nanocrystals. The functionalization of components contributes to a significant increase of both elastic modulus and tensile strength. For the same concentration of CNC (3 wt%) the highest values of tensile parameters were recorded for PLA/PVAc/CNC composites, likely due to a better dispersion of CNC in PVAc followed by mixing with PLA (or PHB).