Ascidians as a Sustainable Source of Cellulose: Physicochemical Characterization, Degradability, and Relevance for Bioplastic Applications.

Cellulose derived from ascidians (tunicates) is distinguished from plant-based counterparts by its marine origin, with high crystallinity, and complex hierarchical architecture. However, quantitative structure-property relationships governing its performance in bioplastic applications remain underexplored. Here, cellulose isolated from three ascidian species Ascidia sp. (T1), Herdmania cf. pallida (T2), and Ascidia sydneiensis (T3) was systematically characterized. X-ray diffraction reveals crystallinity indices (CrI) of 48% (T1) and 60% (T2, T3), the latter approaching values reported for highly ordered systems such as bacterial cellulose. Thermogravimetric analysis demonstrates species-dependent thermal stability, with maximum degradation temperatures of 345°C (T1) versus 400°C-401°C (T2, T3). Notably, T2 and T3 exhibit thermal behavior comparable to microcrystalline and bacterial cellulose, despite CrI values lower than those systems, indicating that hydrogen-bonding density and microfibrillar order govern thermal resilience. Scanning electron microscopy reveals distinct microfibrillar architectures, ranging from highly branched networks to compact laminar structures, which govern water interaction and mechanical response. Water absorption varies markedly by species: T1 and T3 absorb 2200-2400 wt% within 10 min, consistent with their branched, open fibrillar morphologies, whereas T2 absorbs only 1200 wt%, reflecting a compact lamellar microstructure that restricts water diffusion. Hydrolytic degradation after 28 days in neutral water remains minimal across all samples, confirming exceptional resistance to hydrolytic scission under mild conditions. Bioplastics fabricated from these celluloses exhibit tensile strengths of 1-4 MPa, directly correlating with microstructural packing. Collectively, these results establish that ascidian cellulose is the combination of thermal stability up to 400°C, tunable water affinity (1200-2400% absorption), and hydrolytic resistance (1-9% loss over 28 days) arises from species-specific interactions between crystallinity, hydrogen bonding, and microfibrillar architecture. This positions ascidian-derived cellulose as a distinct marine macromolecular scaffold for sustainable bioplastics where controlled water interaction and structural durability are required. In general, it is established the relationship between the biological origin, hierarchical structure, and macroscopic properties of tunicate cellulose, highlighting its potential as a marine-derived macromolecular building block suitable for sustainable bioplastics applications.