LAUSR

Among plastic items, single‐use straws are particularly detrimental to marine ecosystems because such straws, including those made of poly(lactic acid) (PLA), are sharp and extremely slowly degradable in the ocean. While paper straws are promising alternatives, they exhibit hydration‐induced swelling even when coated with a non‐degradable plastic coating and promote effervescence (fizzing) in soft drinks owing to their surface heterogeneities. In this study, upgraded paper straw is coated with poly(butylene succinate) cellulose nanocrystal (PBS/CNC) composites. CNC increases adhesion to paper owing to their similar chemical structures, optimizes crystalline PBS spherulites through effective nucleation, and reinforces the matrix through its anisotropic and rigid features. The straws are not only anti‐fizzing when used with soft drinks owing to their homogeneous and seamless surface coatings, but also highly water‐resistant and tough owing to their watertight surfaces. All degradable components effectively decompose under aerobic composting and in the marine environment. This technology contributes to United Nations Sustainable Development Goal 14 (Life Below Water).