Abstract
The pressure sensitive adhesives made of natural rubber have high peel strength because the structural development of natural rubber in adhesives is supposed to occur during the peeling process. It is well known that the amorphous chains of natural rubber start to crystallize at around 400% of uniaxial strain by stretching. It has been frequently supposed that these phenomena are responsible for the increase of the peel strength and the elastic property of natural rubber, but in-situ observation of the crystallization phenomena in natural rubber adhesives during the peeling of pressure sensitive adhesion tapes has not yet been successful performed.In this paper we tried in situ observation of the strain-induced crystallization in a pressure sensilive adhesive made of natural rubber and tackifier, and succeeded to observe the crystallization behavior of natural rubber molecules in adhesives during thepeeling. The strain-induced crystallites are highly oriented and act as physical crosslinking points in the pressure sensitive adhesives during the peeling and they also bring stress uniformity in the pressure sensitive adhesives. Therefore, pressure sensitive adhesive made of natural rubber shows high peel strength without chemical crosslinking. These phenomena are supported by the X-ray diffraction pattern during peeling and the stress in the adhesive could be estimated by precious analyses of crystal deformation.
