Discipline: Nanoscience or Materials Science
Subcategory: Materials Science
Obed Tetteh - Southern University and A&M College
Co-Author(s): Patrick Mensah, Southern University and A&M College, Baton Rouge, LAGuoqiang Li, Lousiana State University, LA
Smart materials, when employed in the fabrication of multifunctional composites, endow the whole structure with new functionalities other than the conventional structural properties. Shape memory polymers (SMPs), a class of smart materials, can change their shape and stiffness in response to a particular stimulus such as temperature, pH, and others. Shape memory vitrimers possess both vitrimer-like and shape memory properties, and it is, therefore, important to characterize their thermomechanical behavior before their use as matrix materials for structural composites such as sandwich structures, and laminates. In this work, we report a thermosetting shape memory vitrimer (SMV) prepared by crosslinking diglycidyl 1,2-cyclohexanedicarboxylate (DCN) and branched polyethylenimine (PEI) in a non-stoichiometric ratio of 2:1 and cured at 100 °C for 2 h and at 150 °C for another 2 h. The thermal properties, compressive behavior, and shape memory behavior of the SMV were all studied. The glass transition temperature (Tg) of the SMV was found to be higher (86.5 °C) than the one synthesized from the 1:1 mixing ratio (41.5 °C), and thus, the proportion of the monomers plays a huge role on the vitrimer’s Tg. Furthermore, at temperatures below 170 °C, the SMV demonstrated greater thermal stability, with a mass loss of 8.3% at 170 °C. The vitrimer was also subjected to uniaxial compression tests to determine its mechanical properties at both 25 °C (up to 50% strain) and 100 °C. The vitrimer had a higher compressive strength at 25 °C (~187 MPa) compared to the one obtained at 100 °C (13.2 MPa). The low compressive strength at 100 °C was due to the dynamic covalent bonds in the rubbery state, requiring lower stress to deform it. It is worth noting at 100 °C, that the vitrimer failed at 35% strain in the rubbery state, with a failure stress of 1.31 MPa. Furthermore, the vitrimer exhibited excellent shape memory properties with a shape recovery ratio and a shape fixity ratio of 98% and 52%, respectively. It must be noted that the shape fixity ratio can be further increased by increasing the stress relaxation time during the hot programming cycle. Based on the results, this vitrimer is a good matrix material and will be used as a matrix material for the fabrication of sandwich structures.
Funder Acknowledgement(s): The researchers are grateful for the financial support provided by the National Science Foundation under grant number HRN 1736136.
Faculty Advisor: Professor Guoqiang Li, email@example.com
Role: Experimental work