Original Contribution to the Theory of Reactive Extrusion Compatibilisation of Immiscible Polymer Blends: Kinetic Modelling, Morphology Evolution, and Property Optimisation

Reactive extrusion compatibilisation of immiscible polymer blends involves complex simultaneous phenomena of interfacial chemical reaction, morphology development under flow, and property-morphology relationships that are inadequately described by existing theoretical frameworks, particularly for processing conditions relevant to Nigerian polymer compounding operations. This research develops an original theoretical contribution to the kinetics of reactive compatibilisation, morphology evolution modelling, and the quantitative relationship between morphology and final blend properties in polypropylene/polyamide and polyethylene/natural rubber blend systems. The theoretical framework integrates interfacial reaction kinetics derived from model compound experiments with a population balance model of dispersed phase breakup and coalescence under twin-screw extruder shear and elongational flow fields. Morphology evolution was tracked along the extruder screw length by withdrawing samples through side ports at a compounding facility in Lagos State. Transmission electron microscopy and dynamic light scattering characterised dispersed phase size distribution at each sampling position. Model predictions were fitted to experimental morphology data using parameter estimation algorithms. The complete framework was validated against independent experimental blending data from published literature and from additional blend pairs including polylactic acid/polyhydroxyalkanoate. Results demonstrate that morphology reached a quasi-steady state within the first 60 percent of the reactive mixing zone length, with further length having diminishing impact on domain refinement. Interfacial reaction rate constant was the dominant parameter controlling final morphology at equivalent shear history. Property prediction from morphology using the Kerner model extended with interphase correction gave tensile modulus predictions within 8 percent of experimental values. The research provides the first mechanistic framework fully integrating reactive extrusion kinetics with morphology evolution and properties for these practically important blend systems in the Nigerian polymer compounding context. Keywords: reactive extrusion, polymer blend, compatibilisation, morphology evolution, population balance model