Lars Jerpdal

Influence of fibre shrinkage and stretching on the mechanical properties of self-reinforced poly(ethylene terephthalate) composite

Self-reinforced poly(ethylene terephthalate) composite laminates were manufactured from fabric using a hot press. Fabric was either allowed to shrink or exposed to stretching during different phases of the manufacturing process. Composite macrostructure, crimp, was investigated and results showed that shrinkage affects fibre crimp more than stretching does. Mechanical tests showed that shrinkage do not significantly affect mechanical properties while stretching fabric by 10% during heating results in 50% increase in tensile stiffness. The lack of correlation between crimp and mechanical properties indicates that mechanical properties for self-reinforced poly(ethylene terephthalate) composites are dominated by their microstructure, molecular orientation, which may be affected by the manufacturing process.

Influence of fibre stretching on the microstructure of self-reinforced poly(ethylene terephthalate) composite

Self-reinforced poly(ethylene terephthalate) laminates were prepared from woven fabric by compression moulding. The fabric was stretched to different degrees during heating before hot consolidation to simulate a manufacturing process where the material is stretched through forming. High tenacity poly(ethylene terephthalate) fibres with different degrees of stretching were prepared for a comparison to laminates. Tensile tests were made to characterize mechanical properties, while dynamical mechanical analysis, differential scanning calorimetry, FTIR spectroscopy and X-ray diffraction analysis were employed to study microstructural changes caused by the stretching. Tensile tests show that 13% stretching of the fabric increases the laminate tensile stiffness by 34%. However, same degree of stretching for pure fibres increases the fibre tensile stiffness by 111%. Crystallinity and molecular conformations are not influenced by stretching while shrinkage upon heating increases with degree of stretching. Shrinkage is known to be related to disorientation of non-crystalline regions whereof the conclusion from this study is that the increased tensile properties are due to orientation of the non-crystalline regions of the fibre.