INVESTIGATION OF STRUCTURAL FORMATION MECHANISMS IN HYBRID COMPOSITE MATERIALS BASED ON POLYPROPYLENE (PP) AND POLYETHYLENE (PE)

Abstract

Hybrid polyolefin composites based on polypropylene and polyethylene have attracted increasing attention
because they combine low density, melt processability, chemical resistance, recyclability, and tunable mechanical performance.
However, the structural formation of PP/PE systems remains complex because PP and PE are generally
immiscible, and their final properties are controlled by phase separation, crystallization sequence, interfacial adhesion,
and processing-induced morphology. This study investigates the structural formation mechanisms of PP/PE-based hybrid
composites containing ethylene-vinyl acetate, dioctyl terephthalate plasticizer, recycled rubber, ultra-high molecular weight
polyethylene, and a maleic-anhydride-functional compatibilizer. Six formulations were designed, including HDPE-rich,
PP-rich, UHMWPE/HDPE, PVC-reference, PP/UHMWPE, and PP/rubber-rich compositions. Melt blending and extrusion
were used as the main processing route, followed by compression molding. Differential scanning calorimetry, X-ray
diffraction, SEM/TEM microscopy, FTIR spectroscopy, rheological analysis, and mechanical testing were used to clarify
crystallization kinetics, phase morphology, interphase formation, and structure-property relationships. The results indicate
that PE-rich systems are governed by high lamellar crystallinity and ductile deformation, whereas PP-rich systems
exhibit higher stiffness but lower impact resistance. The PP/UHMWPE/EVA/rubber hybrid formulation provides the most
balanced performance trend because UHMWPE domains act as heterogeneous nucleation sites and load-bearing microphases,
while EVA and compatibilizer improve interfacial stress transfer. Avrami-based kinetic analysis suggests that
compatibilization changes nucleation from predominantly homogeneous to heterogeneous behavior, reduces spherulite
size, and increases interphase continuity. The study demonstrates that controlled phase morphology and crystallization
sequence are decisive for optimizing PP/PE hybrid composites for engineering applications.