Abstract
In this study some new concepts regarding certain aspects related to shape memory polymers are presented. A blend of polylactic acid (PLA) (80%) and polybutylene succinate (PBS) (20%) was prepared first by extrusion, then by injection molding to obtain the samples. Tensile, stress-relaxation and recovery tests were performed on these samples at 70 °C. The results indicated that the blend can only regain 24% of its initial shape. It was shown that, this partial shape memory effect could be improved by successive cycles of shape memory tests. After a fourth cycle, the blend is able to regain 82% of its shape. These original results indicated that a polymer without (or with partial) shape memory effect may be transformed into a shape memory polymer without any chemical modification. In this work, we have also shown the relationship between shape memory and property memory effect. Mono and multi-frequency DMA (dynamic mechanical analyzer) tests on virgin and 100% recovered samples of polyurethane (PU) revealed that the polymer at the end of the shape memory tests regains 100% of its initial form without regaining some of its physical properties like glass transition temperature, tensile modulus, heat expansion coefficient and free volume fraction. Shape memory (with and without stress-relaxation) tests were performed on the samples in order to show the role of residual stresses during recovery tests. On the basis of the results we have tried to show the origin of the driving force responsible for shape memory effect.
Highlights
The capability of the shape memory polymers (SMPs) to remember their initial form under the action of stimulants is attractive in engineering applications
It can be seen that the glass transition temperature (Tg) of polybutylene succinate (PBS) and polylactic acid (PLA) are respectively −38 and 58 °C and the melting point (Tm) of PLA
This study proposes certain new concepts for shape memory polymers
Summary
The capability of the shape memory polymers (SMPs) to remember their initial form under the action of stimulants is attractive in engineering applications. SMPs have a wide range of functions in the design of micro-biomedical components, medical devices, smart textiles, sensors, aerospace deployable equipment, and so on. This has resulted in a growing research interest in this field [1,2,3,4,5,6,7,8,9,10,11]. Shape memory effects (SME) can be obtained by a process cycle. In the case of heating stimuli, the process can be summarized in successive steps: heating, deformation, relaxation, fixation and recovery
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