Natural rubber is obtained by processing natural rubber latex, a liquid colloidal suspension that rapidly gels after exudation from the tree. We prepared such gels by acidification, in a large range of particle volume fractions, and investigated their rheological properties. We show that natural rubber latex gels exhibit a unique behavior of irreversible strain hardening: when subjected to a large enough strain, the elastic modulus increases irreversibly. Hardening proceeds over a large range of deformations in such a way that the material maintains an elastic modulus close to, or slightly higher than the imposed shear stress. Local displacements inside the gel are investigated by ultrasound imaging coupled to oscillatory rheometry, together with a Fourier decomposition of the oscillatory response of the material during hardening. Our observations suggest that hardening is associated with irreversible local rearrangements of the fractal structure, which occur homogeneously throughout the sample.

天然橡胶是通过加工天然橡胶胶乳获得的，天然胶乳是一种液态胶体悬浮液，在从树上渗出后会迅速胶凝。我们通过酸化在较大的颗粒体积分数范围内制备了这种凝胶，并研究了它们的流变特性。我们表明，天然橡胶胶乳表现出不可逆的应变硬化的独特行为：当承受足够大的应变时，弹性模量不可逆地增加。硬化会在较大的变形范围内进行，以使材料保持的弹性模量接近或略高于施加的剪切应力。凝胶内部的局部位移是通过与振动流变仪耦合的超声成像以及硬化过程中材料的振动响应的傅立叶分解进行研究的。