Switching the shape of crosslinked high-density polyethylene using α-relaxation

Thermally triggerable shape memory polymers (SMPs) typically exploit the glass transition ( T g ) or melting temperature ( T m ) as switching mechanisms. Recent work on crosslinked low-density polyethylene (xLDPE) indicated that the α-relaxation of semi-crystalline thermoplastics can also act as a switch. However, since the α-relaxation of xLDPE partially overlaps with its melting range, the contribution of crystal melting could not be ruled out. To clarify this, the present study investigates crosslinked high-density polyethylene (xHDPE), whose α-relaxation temperature ( T α ) is well separated from the onset of melting. The results demonstrate that reversible switching between temporary and intermediate shapes occurs exclusively above T α and below T m , confirming that α-relaxation alone switches shape recovery without any melting. This establishes α-relaxation as a genuine switching mechanism in semi-crystalline SMPs and opens up new possibilities for the design of multi-shape memory materials. This work shows that the α-relaxation of semi-crystalline polymers serves as an additional trigger for shape memory effects. In crosslinked high-density polyethylene, reversible switching between a temporary and an intermediate shape occurs when programming is carried out above the α-relaxation temperature and below the melting temperature. The study thus confirms the fundamental suitability of α-relaxation as a switching mechanism and opens new perspectives for multi-shape memory concepts. • α-Relaxation identified as additional trigger for shape memory in crosslinked HDPE • Shape recovery occurs through solid state relaxation • Morphology rearranges reversibly during shape switching • Full shape recovery achieved after conditioning cycle • α-Relaxation enables new design route for multi-shape memory polymers