Toughening of polymerized cyclic butylene terephthalate with carbon nanotubes for use in composites

Low viscosity cyclic butyleneterephthalate (CBT) is a promising material for thermoplastic composites, however after isothermal polymerization (to PBT) and crystallization the material is rather brittle. In the present work, high aspect ratio nanofiller, carbon nanotubes (CNTs), are added to improve ductility. The dispersion of CNTs in CBT is achieved by rotational mixing and appears optimal. Concentrations up to 0.1 wt.%CNT are added to investigate their influence on the mechanical behavior. The addition leads to an increase in stiffness, strength and energy to failure, however, the failure strain slightly decreases. Thermal measurements indicate that the CNTs have no influence on the crystallinity. However, when the mixture of CBT and CNTs is processed in fiber reinforced composites processed by vacuum infusion, the CNTs show a tendency of filtration through the fabric.