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

Abstract

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.

Influence of temperature during overmolding on the tensile modulus of self‐reinforced poly(ethylene terephthalate) insert

“…Laminate plates were manufactured from this fabric by hot consolidation under a pressure of 1 MPa at a temperature of 215 C, which is well below the melting temperature for the HTPET fibers of 265 C. A detailed description of how the laminates were manufactured can be found elsewhere. 30 One layer of fabric results in a laminate thickness of 0.5 mm, and in this study, laminates made from one to five layers of fabric were manufactured for overmolding. Additionally, 2.6 mm thick samples are prepared where the material in the insert has been stretched 13% prior to hot consolidation as described elsewhere.…”

“…Additionally, 2.6 mm thick samples are prepared where the material in the insert has been stretched 13% prior to hot consolidation as described elsewhere. 30 Inserts for overmolding were subsequently prepared from the consolidated laminates.…”

“…One layer of fabric results in a laminate thickness of 0.5 mm, and in this study, laminates made from one to five layers of fabric were manufactured for overmolding. Additionally, 2.6 mm thick samples are prepared where the material in the insert has been stretched 13% prior to hot consolidation as described elsewhere . Inserts for overmolding were subsequently prepared from the consolidated laminates.…”

“…The sample insert is paired with a second insert so that the total thickness of the SrPET inserts is 3.6 mm. Additionally, 2.6 mm thick samples are prepared where the material in the insert has been stretched 13% prior to hot consolidation as described elsewhere . Such stretched SrPET insert has higher tensile stiffness originated from a oriented amorphous structure in the HTPET fibers .…”

“…30 Such stretched SrPET insert has higher tensile stiffness originated from a oriented amorphous structure in the HTPET fibers. 30 In previous study, it was shown how elevated temperature influence this oriented structure and reduces the tensile modulus. 26 All samples are overmolded with a PP material.…”