Nanocomposites with enhanced biodegradability and reduced oxygen permeability were fabricated via melt hybridization of organomodified clay and poly (lactic acid) (PLA) as well as a PLA/polycaprolactone (PCL) blend. The nanocomposite microstructure was engineered via interfacial compatibilization with maleated polypropylene (PP-g-MA). Effects of the compatibilizer structural parameters and feeding route on the dispersion state of the nanolayers and their partitioning between the PLA and PCL phases were evaluated with X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Although highly functionalized PP-g-MA with a low molecular weight was shown to be much more effective in the intercalation of PLA and the PLA/PCL blend into the clay gallery spaces, composite samples compatibilized by highmolecular-weight PP-g-MA with a lower degree of maleation exhibited lower oxygen permeability as well as a higher rate of biodegradation, which indicated the accelerating role of the dispersed nanolayers and their interfaces in the enzymatic degradation of PLA and PLA/PCL matrices. This evidenced a correlation between the nanocomposite structure and rate of biodegradation. The size of the PCL droplets in the PLA matrix was reduced by nanoclay incorporation, and this revealed that the nanolayers were preferentially wetted by PCL in the blend. However, PCL appeared as fine and elongated particles in the microstructure of the PLA/PCL/organoclay hybrids compatibilized by higher molecular weight and less functionalized PP-g-MA. All the PLA/organoclay and PLA/PCL/organoclay hybrids compatibilized with high-molecular-weight PP-g-MA displayed a higher dynamic melt viscosity with more pseudo solid-like melt rheological responses, and this indicated the formation of a strong network structure by the dispersed clay layers.
This study, for the first time investigates the applicability of basalt fiber as a reinforcing material for metal matrix composites through various experimental works for thermal stability and mechanical properties. The residual tensile strength values of basalt fibers after being exposed at different temperatures in a furnace for pre-determined times and/or after being immersed into molten aluminum for different lengths of time were evaluated. Throughout these experimental studies, a processing method for fabrication of these composites was optimized. In this method, basalt preforms were coated with a thin layer of aluminum by immersion into aluminum melt for a short period of time. These laminates were stacked in a mold and consolidated by hot pressing (300℃, 7 min and 630 MPa). The microstructural studies confirmed a good bonding between aluminum and basalt together with a reasonably uniform distribution of fibers within the matrix alloy. Scanning electron microscopy studies revealed the fractured basalt fibers in the matrix alloy as well as occasional improper infiltration of the matrix alloy into the fiber bundles. Consequently, the mechanical properties of aluminum/basalt composites were far inferior to those expected by law of mixtures predictions. However, the strength values of these newly developed metal matrix composites are still adequate for some engineering applications.
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