The influence of the cooling rate on the crystallization is investigated for the Cyclic butylene terephthalate (CBT) material after polymerization to thermoplastic polybutyleneterephthalate (PBT).
From the results it is clear that a faster cooling leads to less perfect crystallization. This influence on the crystallization is linked to the mechanical properties of composites with this matrix material.
A non-isothermal production is possible with CBT. Therefore two different production techniques are developed which make it possible to produce composite plates.
The first method is the prepreg method in which rovings are used, and the second method is the film stacking method. This last method is used when fabrics are used as reinforcement.
For the non-isothermal production two different cooling rates after complete polymerization are used: a slow cooling rate and quenching. From three point bending tests an increase in toughness can be observed after quenching.
The fracture toughness Mode II test even indicate a twice as high crack propagation energy for the quenched samples compared to the slowly cooled samples.
The explanation for the higher toughness after quenching can be found in the crystal perfection. The slowly cooled as well as the quenched composites contain about the same amount of crystals, but in the case of the quenched samples the crystals contain a lot more defects.
These defects are in fact some amorphous material present in between the crystals. Therefore a higher amount of defects will give a higher toughness.
J. Baets (1), J. Devaux (2), I. Verpoest (1)
1) Katholieke Universiteit Leuven, Department Metallurgy and Materials Engineering, Heverlee, Belgium
2) Unité de chimie et de physique des hauts polymères, Belgium