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This work blends polydimethylsiloxane (PDMS) with poly-(lactic acid) (PLA) using polyhydroxyurethane (PHU) structures. The PHU is synthesized from mannitol biscarbonate and a short-chain PDMS-based diamine. The main objectives are, first, to explore the application of the PDMS-based PHU as an additive for PLA and, second, to enhance the flexibility and hydrophobicity of PLA for potential applications in sustainable packaging and biomedical nonwoven materials, such as face masks. PLA/PHU blends are prepared via melt-blending at various weight ratios and characterized using spectroscopic, thermal, rheological, morphological, and mechanical analyses. The blend containing 5 wt % PHU exhibits the optimal performance, with a 9-fold increase in elongation at break and an 18° increase in water contact angle compared to neat PLA, indicating improved toughness and hydrophobicity. Fourier-transform infrared spectroscopy and rheological studies confirm the presence of hydrogen bonding interactions between PLA and PHU, while differential scanning calorimetry confirms the partial miscibility of the blends. Then, electrospinning of neat PLA and the blend with 5 wt % PHU is optimized using a low-toxicity dioxane/acetone (40/60 wt/wt) solvent system. The resulting nonwoven mats exhibit similar physical properties between neat PLA and the blend, and they demonstrate higher porosity, smaller fiber and pore diameters, and superior hydrophobicity than polypropylene (PP) outer and middle face mask layers. Besides, hydrolytic degradation testing reveals accelerated degradation of PLA films with the introduction of the PHU and complete degradation of PLA mats in basic media. Finally, biofilm formation assays, using Staphylococcus aureus and Pseudomonas aeruginosa, validate the antibiofouling potential of both PLA and PLA/PHU films and mats.