Functional principle of shape memory polymers
The principle is based on the change of shape of a material due to temperature. To do this, the polymer is “programmed” in a first step. It is molded into an “initial” shape, then mechanically deformed under heat (T > Tg) until the desired secondary shape is obtained. Then, while maintaining the force on the material, it is cooled, storing mechanical stresses. In the next step, the material is returned to its original shape on demand by heating. In this way, it changes from a glassy to a rubbery state, releasing the stresses stored during deformation.
The temperature, beyond which the material must be chauﬀé to ﬁx the secondary form and regain the permanent form, is within the material’s glass transition range (T>Tg). PolymerExpert develops shape memory polymers with Tg that can be adjusted between -20 and +140°C. In general, the target temperature should be outside the material’s operating range to ensure product stability during application.
Properties of shape memory polymers
If we compare, alloys and shape memory polymers, the latter have many remarkable properties. The elastic deformation applied to the material can be extremely large. Thus, the conceivable shapes are very numerous and make it possible to answer a broad panel of applications. In addition, the stiffness of the material and the glass transition temperature can be adjusted.
Although shape memory polymers have many advantages, it is necessary to note that their mechanical properties are less important than shape memory alloys. Therefore, the use of shape memory composites can also be considered. Thus, the fillers will ensure strength, but also, electrical conduction in some cases.