Dual-shape memory effect in radiation crosslinked thermoplastic blends: fabrication, optimization and mechanisms

Recently, as an important class of mechanically active smart materials, thermoplastic dual-shape memory polymers (SMPs) have attracted notable attention and can be fabricated in many different manufacturing techniques. Here in this paper, we present experimental results, demonstrating a cost-effective manufacturing technique to enable thermoplastic SMPs with enhanced properties for a wide variety of applications. Thermoplastic SMPs based on low density polyethylene (LDPE) and polypropylene (PP) with various compositions were prepared by melt compounding, followed by a post-processing of e-beam irradiation at 5, 10, 15, 25, 50 and 100 kGy. SEM, DSC, tensile test, rheological properties measurement, sol/gel analysis and shape memory test were performed sequentially to investigate the relationship between the phase morphologies, the content fluctuations, the e-beam irradiation and the shape memory performances. In addition, we also optimized the fabrication process and studied mechanisms of shape memory performances. It was found that the melting point associated to the LDPE soft phase T-m,T-LDPE is almost independent of the content fluctuations. At the same time the mechanical properties (determined at 25 degrees C) and rheological properties (measured at 180 degrees C) can be varied systematically by controlling the structure and radiation dose. More importantly, the results also revealed that (1) irradiated LDPE-rich blends were more suitable and effective than both irradiated PP-rich and nonirradiated blends to be dual-SMPs with advantageous shape memory properties, and (2) increased radiation dose could give rise to enhanced shape recovery capacity without significantly weakening the shape fixity.