Highly stretchable curdlan hydrogels and mechanically strong stretched-dried-gel-films obtained by strain-induced crystallization

Highly-stretchable self-standing curdlan (1,3-β-d-glucan) hydrogels were prepared via chemical cross-linking using various cross-linkers, including ethylene glycol diglycidyl ether, 1,4-butandiol diglycidyl ether, and 1,6-hexanediol diglycidyl ether. Tensile testing of the curdlan hydrogels revealed that the hydrogels had good elongation properties with 600%–900% elongation strain from their original length regardless of the cross-linker length. Stretched-dried-gel films were prepared by stretching of the hydrogels and subsequent drying. The tensile strength and Young's modulus of the stretched-dried-gel-films were 117–148 MPa and 1.6 GPa, respectively, and these values were markedly improved compared with the non-stretched films. X-ray measurements revealed that the stretched dried-gel films had oriented crystalline domains with an 80% of degree of orientation. These results indicate that the curdlan molecular chains were oriented and crystallized during the process of stretching and drying of the hydrogels. As a result, the stretched-dried-films showed a high tensile strength owing to strain-induced crystallization.