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Abstract

This study investigates the influence of mineral fillers on the hydrolytic stability and mechanical durability of polylactide (PLA) composites under accelerated aqueous ageing conditions. Composites containing halloysite nanotubes (HNT) and bentonite-based fillers (BM, BS, BSP) at 2 wt.% were prepared using a powder-coating and injection moulding approach. Accelerated hydrolytic degradation was conducted at 50 °C for up to six weeks. The degradation behaviour was evaluated through mass variation, water absorption, incubation medium analysis (pH and electrical conductivity), mechanical testing, surface observations, and contact angle measurements. The results revealed a clear filler-dependent response. Bentonite-filled composites exhibited increased water absorption and accelerated mass loss, which may be associated with the hydrophilic and layered structure of smectite clays facilitating moisture transport. In contrast, halloysite-filled composites showed comparatively reduced water uptake and improved short-term mechanical performance. Analysis of incubation media indicated decreasing pH and increasing conductivity, reflecting the formation of acidic degradation products and the release of ionic species. A qualitative correlation between moisture uptake and deterioration of mechanical properties was observed, particularly for bentonite-containing systems. Microstructural observations demonstrated the presence of surface roughening, microcracks, and heterogeneous degradation features, which may be linked to non-uniform filler dispersion and localised stress concentrations. Contact angle measurements confirmed ageing-induced surface hydrophilisation, although these results should be treated as indirect indicators of surface physicochemical changes. Overall, the results suggest that filler morphology, in combination with hydrophilicity and dispersion state, influences moisture transport and degradation behaviour in PLA composites. The findings contribute to understanding structure–property–degradation relationships in PLA-based systems and indicate that mineral filler selection may be considered as a strategy for tailoring material performance in moisture-exposed applications.

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