MICROSTRUCTURE AND HYGRO-MECHANICS PROPER TIES OF AGAR-GEL

This study concerns the measurement of the mechanical and hygroscopic properties of a biopolymer: agar gel. The morphology of the gel is sho wn by scanning electron microscopy using a freeze fracture technique. It is shown that the agar gel presents a diphasic morphology conserved during drying. The hygroscopic properties of the gel are established through the determination of the isothermal desorption. This study all ows, in particular, to define the hygroscopic domain of the material. We study then the shrinkage of agar gel during drying, throughout dete rmination of the variations of the contraction coefficient and the hyg rometric expansion coefficient, as a function of the medium humidity. Finally, the theological study of the gel is established. The experime nts consist of the measurement of the change in Young's modulus as a f unction of water content, by simple compression tests. The results are then used to determine Poisson's ratio, by measuring the propagation speed of ultrasonic waves through the gel.