(273g) Adjustable Shape Memory Effect in a New Epoxy-Based Copolymer

Shape-memory polymer(SMP) attracts strong interest in engineering applications recently. The unique characteristics of SMP lie on its capability of changing shape upon application of an external stimulus which can be water, infrared radiation, electric current, magnetic field or solution. A shape memory cycle for SMP includes two steps: one is one is programming process and the other is shape recovery process. The programming process consists of heating, deforming, and cooling the sample. After that the sample changed its shape from the permanent shape to the temporary shape. shape recovery process can be activated during heating up the pre-deformed sample above a transition temperature, and as a consequence, the recovery of the stored, permanent shape can be observed.

SMP materials can be used in many potential smart material applications such as heat-shrinking tubing, sensors, actuators, medical application and deployable space structures. All these application of SMP attributes to its unique properties: higher deformation capability, higher recoverable strain levels (~100% to ~400%), lower cost, lower weight, ease of manufacturing and great versatility.

In this paper, shape memory effect of a series of epoxy shape-memory polymers (SMP) is focused on, which can be tailored by changing crosslink density of the polymer. The networks are synthesized from epoxy resin and hardener through a copolymerization. Five types of tests were carried out, namely, FTIR (ATR), dynamic mechanical analyzer (DMA), differential scanning calorimetry (DSC), quasi-static tension test and shape memory behavior. Fundamental trends are established between the network crosslink density and glass transition temperature(Tg), strength, failure strain, elastic ratio, shape recovery ratio and shape recovery speed. Result of FTIR indicates that no change has been found in characteristic absorption for the polymers. The crosslink density was investigated by DMA, and elastic ratio studied by DMA decreases with decreasing crosslink density. Tg determined by DSC varies from 49 to 91oC for the polymers, which decreases with decreasing crosslink density. The strength varies from 47 to 68MPa with the corresponding elongation at break ranging from 2.5 to 5% for the polymers. Both shape recovery ratio and shape recovery speed are crucial to evaluate shape memory effect which is important for the application of SMP materials. Each polymer can show a 100% in shape recovery ratio when the active temperature is above Tg, Further, the network with higher crosslink density has a faster recovery speed compared to the other networks at Tg, while which vanishes gradually as activation temperature draws near to Tg +30 oC. The adjustable nature of shape memory effect in addition to corresponding mechanical properties are most important to the applications of SMP in many fields. This allows the shape-memory properties together with mechanical properties of the polymers to be optimized for a given application by adjusting the crosslink density of polymer without any new additives used.