Abstract
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. 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. 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. 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. Here, we showed that a reversible shape-memory effect (rSME) is achievable for polyurethane water-blown semicrystalline foams. 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. 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 °C, while the melting temperature interval was around 15 K. 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%. 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 Tlow = 10 °C and Thigh = 47 °C. 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.
Highlights
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
In order to obtain a range of densities and thermal and thermomechanical properties different number average molecular weights and their combinations were used without any change of the processing conditions
In In this study, series of of semicrystalline semicrystallinewater-blown water-blown this study,wewereport reportthe thesuccessful successful synthesis synthesis of a series free-rise foams using commerciallyavailable available linear linear poly(ε-caprolactone)-diols poly(ε-caprolactone)-diols crosslinked with free-rise foams using commercially crosslinked with rSMEeffect effectisisachievable achievable for Crosslinked Poly(ε-caprolactone) (cPCL)
Summary
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. A series of studies describing polyurethane-based foams with shape-memory effect (SME) has been published [2,3,4], where, flexible when heated, the shape-memory polymer (SMP) foam can be shaped to a desired. 2016, 8, 412 geometry can be stored during a required period and the recovery of the 2 oforiginal form,Polymers the introduced shape of the SMP-foam can be triggered by regulating the ambient temperature. The shaping to shaped to a desired form, the introduced geometry can be stored during a required period and the a temporary form is commonly referred to as programming step. A SMP-foam is recovery of the original shape of the SMP-foam can be triggered by regulating the ambient heated during programming to a Tprog until foam’s softening and compressed to a temporary shape
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