Mechanical properties of alginate gels: empirical characterisation

Abstract

The compressive engineering stress ( σ E)–strain ( ε E) relationship up to rupture of several mannuronic and guluronic alginate gels was studied by varying the alginate effective concentration ( c eff) from 0.8 to 1.7% w/w and was correlated by using the power model ( σ E= kε n E) with coefficients of determination ( r 2) greater than 0.95. Whereas the degree of concavity ( n) was about constant (2.17 ± 0.07) for all the gels examined, the rigidity constant ( k) was found to increase with alginate intrinsic viscosity [ η], guluronic residues fraction ( x G), and c eff, this constant being generally greater for the G-rich alginate gels at c eff=const. The rigidity constant, as well the rupture stress ( σ ER) and deformation work ( L ER), allowed the new indicators [ k/( c eff) 1.4, σ ER/( c eff) 1.4, and L ER/( c eff) 1.4] to be calculated and used to discriminate efficiently the gelling ability of M-rich alginates from that of G-rich ones. Stress relaxation testing yielded a constant relaxation time spectrum with dimensionless viscoelastic coefficients practically independent of c eff, the latter showing clearly that high-M alginate gels were more elastic than the high-G ones