Comprehensive Experimental Study of Mechanical Properties, Stress Relaxation, Shape Memory Performance, Thermal Analysis and Morphology of 3D/4D Printed HDPE-PETG

Abstract

This study addresses the critical limitations of 3D printing with high-density polyethylene (HDPE), such as poor printability and lack of smart functionality, by developing novel HDPE-PETG blends that simultaneously enhance printing performance and introduce 4D shape memory capabilities to HDPE. Through systematic characterization of blends containing 15, 30, and 45 wt% PETG, it was demonstrated that 30% PETG content optimally balances mechanical properties, achieving 24.5 MPa tensile strength and 87.2% elongation, and printability, with a reduction in interlayer gaps compared to 15% PETG. Meanwhile, higher PETG content (45%) achieves exceptional shape memory performance with 89.0% fixity and 75.7% recovery. Dynamic mechanical analysis reveals PETG's glass transition (80°C) as the shape memory switching temperature, with SEM confirming an immiscible two-phase morphology that synergistically combines HDPE's structural integrity with PETG's thermal responsiveness. Stress relaxation also increased with increasing PETG and the HDPE with a semi-crystalline structure improves stress relaxation resistance. These results establish HDPE-PETG as a novel material system that transforms conventional HDPE into a versatile, sustainable feedstock for advanced 3D/4D printing applications, overcoming processing challenges while adding smart functionality for the first time. Also, the results indicate excellent synergy in the blends due to the use of stress relaxation resistance, recyclability, low cost due to HDPE and excellent 3D printability, shape memory effect and mechanical properties due to PETG.