Development of a Comprehensive Durability Assessment Framework for Bio-Based Polymer Composites in Tropical Infrastructure Applications Across Nigerian Geopolitical Zones

The deployment of bio-based polymer composites in Nigerian infrastructure applications requires a comprehensive durability assessment framework that accounts for the diverse climatic, UV exposure, soil chemical, and biological environments encountered across the country's six geopolitical zones. This research develops and validates a multi-factor durability assessment framework for natural fibre-reinforced biopolymer composites, integrating accelerated laboratory testing with field exposure data from six representative sites across Nigeria spanning a five-year monitoring programme. Composites based on kenaf, sisal, and bamboo fibres in polylactic acid and polyhydroxyalkanoate matrices were fabricated and deployed at sites in Lagos, Kano, Maiduguri, Port Harcourt, Enugu, and Abuja, selected to represent the humid coastal, semi-arid, arid, equatorial, subtropical highland, and savanna climatic regimes. Mechanical property retention, moisture uptake, crystallinity evolution, and microbial colonisation were monitored annually. Accelerated laboratory protocols for UV weathering, hygrothermal aging, and soil burial were calibrated against field data to establish acceleration factors for each environmental stressor by zone. A probabilistic service life prediction model was developed using competing risks analysis and Monte Carlo simulation. Results demonstrate that geographic zone exerts a greater influence on composite durability than fibre or matrix type for most environmental stressor combinations. Maiduguri site composites showed UV-dominated degradation with 45 percent tensile strength loss after five years, while Port Harcourt composites exhibited moisture-dominated degradation at 52 percent strength reduction. The probabilistic model predicted zone-specific service lives of 4 to 18 years for the material-application combinations studied. The framework provides a standardised durability evaluation protocol and zone-specific design service life tables for natural fibre composite specification in Nigerian infrastructure projects. Keywords: bio-based composite, durability framework, tropical environment, service life prediction, geopolitical zones