Evaluation of crystallinity variation and phase dispersion in polymer blends and nanocomposites by Raman mapping

Raman mapping technique was used to characterize the crystallinity variations and phase distribution of individual components in polymer blends and polymer nanocomposites. The conformational changes of poly-l-lactide (PLA) and poly-ε-caprolactone (PCL) were analysed in complex structures comprising PLA₅₀PCL₅₀ binary and PLA₅₀TPS₃₀PCL₂₀ ternary blends (TPS = thermoplastic starch). The mapping images of PLA₅₀PCL₅₀ binary blend showed the existence of the PLA component in the amorphous form, whereas well-crystallized PLA was observed in the mapping images of PLA₅₀TPS₃₀PCL₂₀ ternary blend. XRD and solid-state ¹³C NMR confirmed the Raman findings on these changes of PLA crystallinity in the blends. Causes of these crystallinity changes were revealed from Raman mapping of phase dispersion of blend components which exhibited small domains of PLA phase confined in between large clusters of PCL in the binary blend, whereas an improved dispersion of both phases in the ternary blend resulted owing to the presence of TPS phase. The role of compatibilizer in the dispersion of graphene (G) filler in the polyethylene matrix was also successfully visualized using Raman mapping technique in polyethylene–graphene (PE-G) and PE-G-CPE35 nanocomposites. The dispersion of graphene was less optimum in the PE-G composites, whereas in the PE-G-CPE35 composites, the addition of compatibilizer resulted in improved filler dispersion. The findings from Raman mapping were also corroborated with the TEM analysis of the filler dispersion.