Self-Healable Polymer: Effect of Ionic Content and Neutralization of Poly(Ethylene Co-Methacrylic Acid)

Abstract

Self-healing is the ability of a material to regain its performance after damage. Self-healing polymers are an important advancement as they improve the service life, reduce wastage, and decrease the environmental impact of polymer-based applications without the need for replacement or human intervention. Poly(ethylene-co-methacrylic acid) (PEMAA) exhibits a self-healing response at high impact during projectile testing. In this study, the effects of the ionic content (Li, Na, Zn, Mg) and neutralization percentage (13 to 78% ) of 15 PEMAA copolymers were studied on their thermal-mechanical properties, and self-healing response. This study expands the current understanding of the self-healing mechanism since previous studies only tested the self-healing response of PEMAA neutralized by Na. Dog-bone, film, and rectangular samples were prepared via injection molding for various characterization tests. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and tensile testing were used to study the thermal-mechanical properties of PEMAA copolymers that may affect the healing response. The prepared films were shot by an air rifle from a distance of 1m and the self-healing responses were evaluated by observing the puncture sites using Scanning Electron Microscopy (SEM) and the healing efficiency was quantitatively measured using the water leakage test. Five different self-healing responses were observed and correlated to ionic content and neutralization. The DMA tests showed that PEMAA copolymers with the presence of ionic aggregate clusters corresponded with higher healing efficiency during projectile testing. Tensile testing showed that by increasing the neutralization percentage, the tensile strength and modulus of the samples increased and their self-healability generally increased. Among the investigated samples, the copolymer with 50% neutralization by Li salt showed the highest healing efficiency. The healing efficiency increased up to 100% with an increase in neutralization up to ~50% demonstrating the neutralization level required for successful self-healing. Overall, the mechanical properties affected by ionic content and neutralization were shown to have a direct impact on the self-healing efficiency of PEMAA copolymers.