Phosphonium-based layered silicate-poly(ethylene terephthalate) nanocomposites: stability, thermal and mechanical properties

PET-clay nanocomposites were prepared using alkyl quaternary ammonium and phosphonium modified clays by melt-mixing at 280°C using a micro twin screw extruder. The latter clays were prepared by synthesizing phosphonium surfactants using a simple one-step method followed by a cation exchange reaction. The onset temperature of decomposition (Tonset) for phosphonium clays (>300°C) was found to be significantly higher than that of ammonium clays (around 240°C). The clay modified with a lower concentration (0.8 meq) of phosphonium surfactant showed a higher Tonset as compared to the clay modified with a higher concentration (1.5 meq) of surfactants. Nanocomposites prepared with octadecyltriphenyl phosphonium (C18P) modified clay showed a higher extent of polymer intercalation as compared with benzyltriphenylphosphonium (BTP) and dodecyltriphenylphosphonium (C12P) modified clays. The nanocomposites prepared with ammonium clays showed a significant decrease in the molecular weight of PET during processing due to thermal degradation of ammonium surfactants. This resulted in a substantial decrease in the mechanical properties. The molecular weight of PET was not considerably reduced during processing upon addition of phosphonium clay. The nanocomposites prepared using phosphonium clays showed an improvement in thermal properties as compared with ammonium clay-based nanocomposites. Tonset increased significantly in the phosphonium clay-based nanocomposites and was higher for nanocomposites which contained clay modified with lower amount of surfactant. The tensile strength decreased slightly; however, the modulus showed a significant improvement upon addition of phosphonium clays, as compared with PET. Elongation at break decreased sharply with clay

Formation and characterization of polyurethane-vermiculite clay nanocomposite foams

Nanocomposites of rigid polyurethane foam with unmodified vermiculite clay are synthesized. The clay is dispersed either in polyol or isocyanate before blending. The viscosity of the polyol is found to increase slightly on the addition of clay up to 5 pphp (parts per hundred parts of polyol by weight). The gel time and rise time are significantly reduced by the addition of clay, indicating that the clay acts as a heterogeneous catalyst for the foaming and polymerization reactions. X-ray diffraction and transmission electron microscopy of the polyurethane composite foams indicate that the clay is partially exfoliated in the polymer matrix. The clay is found to induce gas bubble nucleation resulting in smaller cells with a narrower size distribution in the cured foam. The closed cell content of the clay nanocomposite foams increases slightly with clay concentration. The mechanical properties are found to be the best at 2.3 wt% of clay when the clay is dispersed in the isocyanate; the compressive strength and modulus normalized to a density of 40 kg/m3 are 40% and 34% higher than the foam without clay, respectively. The thermal conductivity is found to be 10% lower than the foam without clay

Emblica officinalis-loaded poly(epsilon-caprolactone) electrospun nanofiber scaffold as potential antibacterial and anticancer deployable patch

Biological functions of nanofiber scaffolds can be engineered via the incorporation of plant extracts. In the present study, Emblica officinalis (EO) (Indian Gooseberry known as amla)-loaded poly(epsilon-caprolactone) (PCL) nanofibers were prepared via the electrospinning technique. The aim was to prepare nanofiber scaffolds with antibacterial and anti-cancerous properties. The scaffolds were characterized via SEM, XRD, small-angle X-ray scattering, FTIR spectroscopy, streaming potential, DSC, water contact angle and tensile measurements. Upon the incorporation of EO, the nanofiber surface became rougher and exhibited a braid-like' morphology. This is in contrast to the pristine PCL nanofibers, which exhibited a smooth fiber surface. The average fiber diameter increased, and the water contact angle of the nanofiber scaffolds decreased with an increase in the EO content in PCL. The crystalline structure of PCL was not affected; however, its crystallization temperature increased significantly and its melting temperature increased marginally with the addition of EO. The PCL scaffold showed a negatively charged surface and its -potential increased with an increase in EO content due to the presence of various functional groups. The antibacterial studies revealed that the PCL-EO nanofiber scaffolds exhibited efficient antibacterial properties against both Gram-positive and Gram-negative bacterial strains and the zone of inhibition increased with EO content. Furthermore, cellular behavior of MCF-7 cells was studied using the MTT assay, fluorescent staining and SEM, which indicated that cell proliferation was significantly inhibited by the incorporation of EO in the scaffolds