(Also see Veriflex® in our portfolio.)
What is Shape Memory Polymer?
Shape memory polymer (SMP) has only been around for a couple of decades. It has applications from deploying objects in space to manufacturing dynamic molds.
Unlike shape memory alloys, SMP exhibits a radical change from a normal rigid polymer to a very stretchy elastic and back on command, a change which can be repeated without degradation of the material. The "memory," or recovery, quality comes from the stored mechanical energy attained during the reconfiguration and cooling of the material.
Above its transition temperature, SMP goes from a rigid, plastic state to a flexible, elastic state. When cooled, it becomes rigid again and can be constrained in its new shape configuration. Shape memory characteristics can be engineered into most polymers. Some of CRG's current SMP formulations are based on styrene acrylate, cyanate ester, and epoxy polymer systems.
There are many activation methods for thermally responsive SMP:
- Resistive heating
- Embedded heaters (for example, stretchy heaters, nichrome wires)
- Contact heating (MRE heaters)
- Induction heating
- Dielectic heating
- Microwave heating
- Infrared radiant heating
Some of these methods may be enabled by fillers such as conductive fillers, CNT, CNF, iron and ferrite.
A polymer engineered with shape memory characteristics provides a unique set of material qualities and capabilities that enhance the traits inherent in the polymer system itself. SMP changes between rigid and elastic states by way of thermal stimuli. The change takes place at what is referred to as the glass transition temperature (Tg). SMP can be formulated with a Tg that matches an application need. Current SMP systems have been demonstrated with Tgs from –30°C to 260°C (–22°F to 500°F).
Above its transition temperature, which can be custom-engineered, SMP goes from a rigid, plastic state to a flexible, elastic state. When cooled below that temperature, it becomes rigid again, with high specific strength. The SMP can be manipulated and cooled into a variety of new shapes; when heated above its transition temperature, it will return to its "memorized" shape.
Shape memory polymers are characterized by triggering segments that have a specific Tg. At a temperature above Tg, the material can be easily deformed. The deformed shape will be maintained when the material is cooled below the Tg. The material will "remember" or return to its original shape when it is heated to a temperature above the Tg again. The material should be manipulated in its fully elastic state and not in the temperature transition range.
While in its elastic state, SMP will recover its cast, or cured, shape if left unrestrained. Otherwise, it may be reconfigured or manipulated into other shapes, tolerating up to 200% elongation. SMP heated above its transition temperature can be stretched, folded, rolled, twisted, or bent. At any point, the SMP can be cooled to maintain its altered shape indefinitely, until once again it is brought above its transition temperature. Above its transition temperature, SMP recovers its "memorized" shape very quickly.
SMP is not simply an elastomer, nor simply a plastic. It exhibits characteristics of both materials, depending on its temperature. While rigid, it demonstrates the strength-to-weight ratio of a rigid polymer. While pliable, it has the flexibility of a high-quality, dynamic elastomer. While elastic, SMP can be manipulated in many ways. It can be reshaped many times without losing material integrity.
SMP can be cast and cured into any "memorized" shape, from a thick sheet to a concave dish, to a complicated open honeycomb network. SMP can also be used as a coating on another material. This versatility makes SMP ideal for applications such as dynamic configurable parts, deployable components, and inexpensive, reusable custom molds.
Shape memory polymer (SMP) resin is an integral component of a shape memory composite system. A shape memory composite acquires some SMP characteristics, making it a unique material for use in dynamic structures and other applications requiring both load strength and "shape-shifting" flexibility.
Under thermal controls, shape memory composites can be temporarily softened, reshaped, and rapidly hardened to function as structures in a variety of configurations. An example of a use for this versatility is the capability for space-efficient stowing and then later deployment to the operational shape. The composites can be fabricated with nearly any fiber type, and creative reinforcements permit dramatic shape changes in functional structures. Shape memory composites are also machinable.
Applications include lightweight, rigid deployable structures (an alternative or enhancement to current inflatable structures), rapid manufacturing, and dynamic reinforcement.