Marine-Degradable Paramylon Ethers and Ether–Ester Derivatives with Tunable Thermoplasticity and Controlled Dissolution Behavior

Abstract

Paramylon, a β-1,3-glucan from Euglena gracilis, is a promising renewable feedstock for biodegradable plastics, but its dense hydrogen-bonding network limits thermoplastic processing. Methyl paramylon (PaMe), ethyl paramylon (PaEt), and paramylon methyl acetate ether–ester derivatives (PaMeAc) were synthesized across a wide range of substitution degrees (DS). Ethylation reduced the glass transition temperature (Tg) more effectively than methylation, and subsequent acetylation simultaneously raised thermal stability and lowered Tg, broadening the processing window. Plasticizer-free melt-pressing yielded transparent films with tensile strengths up to 31 MPa, surpassing values previously reported for alkyl-etherified polysaccharides. In Tokyo Bay seawater, biodegradation depended strongly on DS, and PaMeAc with low acetyl DS retained biodegradability comparable to PaMe. These results show that this DS-dependent dissolution and biodegradation behavior can be tuned through DS to suppress persistent solid fragments, providing a design platform for marine-degradable polysaccharide plastics.