Polymers memory effect origin

Shrinkablefilm and tubing Cross linked semicrystalline thermoplastics display rubberlike properties at temperatures above their melting points. On deformation followed by fast cooling the polymer maintains its deformed shape. The polymer returns to its original shape when reheated. This memory effect is applied in the production of heat shrinkable films and tubing. Radiation doses of the order of 40 — 1(X) kGy are used in the production of heat shrinkable products. 

Applications of these polymers for optical resolution of racemates, for selective metal ion binding, and for stereoselective reactions are reviewed. The optimization of the polymer structure is described and the origin of the memory effect discussed. 

Shape memory effect of polylaclide/polyamide elastomer (PLA/PAE) (90/10 wt/wt) blends. (The sample can recover to original shape in 8 s and 3 s at 80 and 90°C, respectively.) (Adapted from Zhang, W., Chen, L., and Zhang, Y. 2009. Surprising shape-memory effect of polylactide resulted from toughening by polyamide elastomer. Polymer 50 1311-1315. Copyright Elsevier Ltd. Reproduced with permission)... 

Materials that show a shape-memory effect can be deformed into a temporary shape and afterwards they can recover their original shape on exposnre to an external stimulus [65,66]. Shape-memory polymers (SMPs) are stimuli-responsive smart polymers that have dual shape, which responds to application of an external stimulus. SMP is conventionally processed to receive its permanent shape. Afterward, the polymer is deformed and the intended temporary shape is fixed [67,68]. This process is called programming. These polymers basically consist of two phases, fixed points or frozen... 

Switching chains enables the shape memory effect. Below the r, s of the switch phase (light grey in Fig. 7.4) the chain movements are not allowed. If the temperature increases above the chains can move. In this state, if a stress is applied, the chains will suffer an elastic deformation, reducing the entropy of the chain conformation. Releasing the stress, the polymer is able to go back to its original conformation. 

Bending tests associated with thermal q cles are also able to characterize the shape memory effect in polymers (Knight et ah, 2009 Luo et al, 2008 Zheng et al, 2006,2008 Zhou et al, 2007). In the flexure test the measured quantity is the angle of deformation. The following coefficient is defined to quantify the ability of a material to recover its original shape ... 

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