![]() When the foam is stretched at T prog, the most structural elements should be elongated in the direction of stretching, and thereby the orientation of actuation and skeleton domains at T low should be more pronounced than in compression mode (see Figure 2). Since in foams there is no preferred direction of single elements (pores’ walls and struts) upon uniaxial compression, we hypothesize, in addition, that programming efficiency in tension mode could be higher than in the conventional compression mode. ![]() įor rSME, the programming step aims to induce the orientation of macromolecules and therefore to give a direction to actuation and skeleton domains upon cooling of the material. Detailed quantification procedures of one-way SME in compression are described. The process is repeatable however the programming step requires an external force for each shape-memory cycle (so called one-way SME). When the foam, in its temporary shape, is heated under load-free conditions above T sw, the original shape is recovered. Keeping the degree of compression, the foam is cooled down to T low so that the switching temperature T sw (namely melting T m or glass T g transition temperature) is passed and the switching segments are “frozen” in a way that the programmed shape of the foam is kept. Conventionally, a SMP-foam is heated during programming to a T prog until foam’s softening and compressed to a temporary shape. The shaping to a temporary form is commonly referred to as programming step. A series of studies describing polyurethane-based foams with shape-memory effect (SME) has been published, where, flexible when heated, the shape-memory polymer (SMP) foam can be shaped to a desired form, the introduced geometry can be stored during a required period and the recovery of the original shape of the SMP-foam can be triggered by regulating the ambient temperature. While the field of conventional PU foams has been extensively investigated and their large-scale manufacturing processes are well established, a completely new principle of foam’s operation, patented in the early 1990s, encouraged scientists for a new research aiming to integrate polyurethane foams into the field of smart materials. ![]() Other common applications include seals, packaging, shoe soiling and self-skinning articles. Polyurethane (PU) foams are widely spread in our daily life as a core part of the majority of comfort items, such as cushions or pillows. We anticipate that our experimental study opens a field of systematic investigation of rSMEs in porous polymeric materials on macro and micro scale and extend the application of water-blown polyurethane foams to, e.g., protective covers with zero thermal expansion or even cushions adjustable to a certain body shape. The composition with broad distribution of molecular weights of poly(ε-caprolactone)-diols exhibited an rSME of about 12% upon cyclic heating and cooling from T low = 10 ☌ and T high = 47 ☌. All semicrystalline foams exhibited excellent one-way SME with shape-fixity ratios slightly above 100% and shape-recovery ratios from the second cycle of 99%. Densities of synthesized foams varied from 110 to 180 kg∙m −3, while peak melting temperatures were composition-dependent and changed from 36 to 47 ☌, while the melting temperature interval was around 15 K. We selected commercially available crystallizable poly(ε-caprolactone)-diols of different molecular weight for foams synthesis, followed by investigations of morphology, thermal, thermomechanical and shape-memory properties of obtained compositions. Here, we showed that a reversible shape-memory effect (rSME) is achievable for polyurethane water-blown semicrystalline foams. However, the need to program the foams before each operation cycle could be a drawback impeding the entry of shape-memory polymeric (SMP) foams to our daily life. ![]() High expansion ratios during the shape-recovery are of special interest when big volume changes are required, for example to fill an aneurysm during micro-invasive surgery or save space during transportation. The discovery of the one-way shape-memory effect in PU foams provided a fresh impetus for extensive investigations on porous polymeric actuators over the past decades. Water-blown polyurethane (PU) foams are of enormous technological interest as they are widely applied in various fields, i.e., consumer goods, medicine, automotive or aerospace industries.
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