Microstructural features affecting mechanical properties: Effect of processing on dispersion of carbon black (N220) nanoparticles reinforcement in poly (lactic acid)

The interrelation between microstructure and macroscopic behavior is important information, which is used to characterize generally inhomogeneity, orientations, distributions; ultimately its structure relationship with specific properties. Carbon black (N220) filled poly (lactic acid) composites were processed by using melt mixing (i.e. MMCM - Melt Mixing followed by Compression Molding) and solution mixing technique (i.e. DDCS - Dissolution Dispersion followed by Casting Sheet. Carbon black filled poly (lactic acid) composites were characterized for microscopic - structural analysis and compared with mechanical properties. Microstructural analysis on tensile fractured specimens by optical microscope and scanning electron microscope was done in order to determine the microstructural features affecting mechanical properties; transmission electron microscopy and atomic force microscopy were performed to evaluate the effect of processing techniques on the dispersion of carbon black nanoparticles reinforcement in poly (lactic acid). The analysis of the mechanical properties showed an increase up to the loading of 2-3 wt% of carbon black followed by a decrease in mechanical properties at 5 wt% and above due to microstructural changes induced by low structure carbon black in the poly (lactic acid) matrix. The dominance of filler-filler interaction beyond 2.5 wt% was clearly visible in optical, electron and atomic force microscopic studies. The appearance of smooth and rough surfaces in optical and scanning electron microscopic images, presence of agglomerated carbon black in transmission electron microscopic images and the decrease in average roughness analyzed via atomic force microscopic images indicates microstructural changes in poly (lactic acid) after addition of carbon black. The filler-filler interaction as imaged and recorded from the transmission electron images and atomic force microscopic roughness values was the cause for a decrease in mechanical properties of carbon black filled poly (lactic acid) composites at 5.0wt% and beyond.