Effects of carbon fiber and glass fiber on shape memory polymers based on benzoxazine-epoxy binary systems

Abstract

Recovery stress is an important parameter of shape memory polymers. Generally, recovery stress in SMPs can be enhanced by using fiber reinforced composites with suitable reinforcing agents such as carbon fiber or glass fiber. We aim to study effects of carbon fiber and glass fiber on thermal, mechanical, and shape memory properties of benzoxazine-epoxy SMPs, particularly on recovery stress enhancement. The compositions of carbon fiber and glass fiber reinforced benzoxazine-epoxy SMPs were in a range of 30 to 50vol%. The carbon fiber and glass fiber reinforced benzoxazine-epoxy shape memory polymer was compression-molded at 170oC under a pressure of 10 MPa for 3 hours. The experimental results revealed that glass transition temperature of the composite samples increased with decreasing fiber contents. The maximum glass transition temperature of benzoxazine-epoxy SMPs was 162oC at 30vol% of the carbon fiber. In addition, storage modulus, flexural strength, and flexural modulus values of the SMP specimens increased with increasing carbon and glass fiber contents. Benzoxazine-epoxy SMPs exhibited shape fixity and shape recovery values more than 85% and 96%, respectively. The recovery time of benzoxazine-epoxy SMPs was in a range of 1.71 to 121.2 seconds. Furthermore, the carbon fiber reinforced benzoxazine-epoxy SMPs provides outstandingly high recovery stress up to 138.8 MPa at 30vol% of the carbon fiber. These results suggested potential usages of these materials in advanced applications, such as hinge or deployable structure.