Structure–Property Relationships of Recycled Polypropylene Modified with Functional Additives

Recycled polypropylene (rPP) often exhibits reduced mechanical performance due to degradation during repeated processing and use. In this study, inorganic fillers, nano-scale fillers, and structure-modifying additives were incorporated into rPP through melt compounding to improve its mechanical properties. The effects of additive composition on tensile properties, impact strength, crystallization behavior, and morphology were investigated. As a result, the incorporation of functional additives improved the tensile and impact properties of rPP. DSC results indicated changes in crystallization behavior depending on additive composition, whereas SEM observations revealed differences in filler dispersion and interfacial morphology. These structural changes were closely associated with the observed mechanical performance. The results demonstrate that the combined use of functional additives is an effective approach for improving the structure–property relationships of recycled polypropylene and provide insights into the design of high-performance recycled polymer materials.