Toughening of glass fiber reinforced composites with a cyclic butylene terephthalate matrix by addition of polycaprolactone

The problem of high melt viscosity of thermoplastics can be solved by using cyclic butylene terephthalate (CBT), a low viscous prepolymer that polymerizes to the thermoplastic polybutyleneterephthalate (PBT). If CBT polymerizes isothermally, big perfect crystals can grow, which induces brittleness. To solve this problem, CBT is mixed with polycaprolactone (PCL). CBT and PCL will form a copolymer, which leads to a much tougher material, both for unfilled material and for composites. The samples are tested under tensile, bending and impact loading. The increased toughness is due to the lower crystallinity, induced by the copolymerization, which is assessed by a DSC-test.