Shape memory polymer

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Shape memory polymers (FGP, English shape-memory polymers , SMP) are plastics having a shape memory effect ( English shape-memory effect ) - like shape memory alloys exhibit (FGL, English shape-memory alloy SMA) - ie at their former external shape despite seemingly able to “remember” a major transformation in the meantime . The first shape memory polymers consisted of two components. The first was an elastic polymer, a kind of "spring element", the second a hardening wax that can lock the spring element in any desired shape. For “programming” the SMP can be reshaped while it is heated and then cooled down. If the shape memory polymer is heated again, the wax becomes soft and can no longer counteract the force of the spring element. The shape memory polymer returns to its original shape. Analogous to the terminology of shape memory alloys, this behavior is called the one-way memory effect . One example is memory foam .

Shape memory polymers show decisive advantages over shape memory alloys in terms of their producibility and processability. Due to the low thermal conductivity of polymers, they have a significantly shorter switching time, but this plays a subordinate role in a large number of potential areas of application, especially in the medical field. Shape memory polymers switch in the soft state, while shape memory alloys have an increased modulus of elasticity in the high temperature phase (austenite) . In principle, shape memory polymers cannot be programmed by a restoring element via a continuously acting force. This is a decisive disadvantage for many applications. While shape memory alloys can work cyclically, for example by means of an additional return spring, FGP must be reprogrammed for each cycle. Some polymers, like shape memory alloys, also have a two-way memory effect, but this cannot be used in practice to do work. Shape memory polymers are therefore of particular interest for applications that require a one-time switch to the programmed shape.

Shape memory polymers are functional polymers .

Stimuli

In the example above, the temperature is used as a stimulus to trigger the shape memory effect. Stimuli that can induce a reset:

  • The mostly used stimulus is a heating of the FGP above a certain switching temperature. This can be the glass transition temperature or the melting temperature of the polymer.
  • On optical path can as butyl acrylate , which at their side chains on cinnamic acid groups under UV light of a certain wavelength crosslink , fix a mold. If the bond is broken by irradiation with a different wavelength, it comes to restoration and thus to the shape memory effect.
  • There are now shape memory polymers that can be reset using magnetic stimuli.

use

Shape memory polymers are the subject of intense research. Their commercial use will probably first take place in medical technology , where metallic shape memory materials already play a role today, but can also show biological side effects. The first companies are already offering such materials. In addition, it can be assumed that they will gain importance as a label technology. In the form of memory foam , the technology is used, among other things, for mattresses and headphones, which therefore adapt particularly well to the shape of the human body.

Similar materials

literature

  • Andreas Lendlein, Hongyan Jiang, Oliver Jünger, Robert Langer: Light-induced shape-memory polymers . In: Nature . tape 434 , no. 7035 , April 14, 2005, p. 879-882 , doi : 10.1038 / nature03496 .
  • Thorsten Pretsch, Melanie Ecker, Markus Schildhauer, Michael Maskos: Switchable information carriers based on shape memory polymer . In: Journal of Materials Chemistry . tape 22 , no. 16 , February 10, 2012, p. 7757-7766 , doi : 10.1039 / C2JM16204K .
  • Nikolaus Fritzsche, Thorsten Pretsch: Programming of Temperature-Memory Onsets in a Semicrystalline Polyurethane Elastomer . In: Macromolecules . tape 47 , no. 17 , July 15, 2014, p. 5952-5959 , doi : 10.1021 / ma501171p .
  • Thomas J. Reitinger: Shape-Memory Polymers (SMP) as materials of the future. (PDF) In: Inventor Activities 2005/2006. German Patent and Trademark Office , August 18, 2006, pp. 75–84 , accessed April 9, 2015 .

Individual evidence

  1. ↑ Ecker, Melanie: Development, Characterization and Durability of Switchable Information Carriers based on Shape Memory Polymers. Freie Universität Berlin, September 1, 2014, accessed on February 12, 2018 (German).