Bio-filler Saturation in Polypropylene Composite with Divergent Permeability and Thermal Endurance

Abstract

This study explores the structure–property relationships of polypropylene (PP) composites filled with four sustainable fillers, lignin, biochar, waste shell powder, and calcium carbonate (CaCO₃), to develop functionally enhanced, environmentally conscious materials. Each filler was incorporated at the highest loading level compatible with melt processability to maximize sustainability while preserving manufacturability. Comprehensive characterization was conducted to assess thermal, mechanical, and barrier performance, with a particular focus on gas and vapor permeability. Among all composites, the CaCO₃-filled PP exhibited a distinct selective permeability profile: an oxygen transmission rate (OTR) exceeding the measurable detection limit and a water vapor transmission rate (WVTR) comparable to neat PP. This distinct asymmetry is due to the structural heterogeneity caused by the filler at the highest content, which promotes oxygen diffusion while effectively blocking water permeation. Such selective transport behavior offers potential advantages in various applications, where oxygen exchange is needed without moisture accumulation. These results suggest that CaCO₃ not only reinforces the composite but also imparts tailored barrier functionality, which may benefit packaging systems requiring selective gas transport.