Degradation of nano-ZnO particles filled styrene-based and epoxy-based SMPs under UVA exposure

Styrene-based and epoxy-based SMPs (SSMPs and EPSMPs) filled with different contents of nano-ZnO particles were fabricated, their decolouration, UVR absorbabilities, surface hardness, dynamic mechanical properties and shape memory effects under UVA degradation test were then investigated. Experimental results showed that all samples subjected to the UVA degradation were yellowish with different degree. By adding 2 wt.% of nano-ZnO particles, all SMPs achieved full UVR blockage. 2 and 4 wt.% nano-ZnO/SSMP and 5 and 7 wt.% nano-ZnO/EPSMP could maintain their surface hardness at moderate level after the UVA degradation. Storage modulus of 4 wt.% nano-ZnO/SSMP and EPSMP before and after UVA degradation obtained satisfactory results compared with their pure forms. It was proven that shape recovery ratio was not affected by nano-ZnO particles inside SMPs. Treated EPSMPs could obtain 100% shape recovery. However, UVA degradation was proven to have effects on the shape memory effect in SSMPs. UVA-degraded SSMPs had better recovery than non-UVA-degraded SSMPs, this could be explained by the degraded surface which was changed to be hardened. 4 wt.% of nano-ZnO particles filled into SSMP and EPSMP could maintain a similar full recovery time before and after UVA degradation and could significantly reduce the recovery reaction time.