Consolidation and relaxation behavior of continuous strand random glass mats with thermoplastic binders

• DOI: 10.1002/pc.10633
• Publication Date: 2004-04-15T18:14:07Z
• Authors: J. C. Knight; D. Backes; K. Jayaraman
• Keywords: 02 engineering and technology; 0210 nano-technology

AbstractThe consolidation and relaxation characteristics of glass mat reinforcements with a thermoplastic polyester binder have been studied. Attention has been given to the effect of preforming conditions on binder flow around the fibers, and on the rearrangement of fiber tows making up the preform. An instrumented hydraulic press was used to compress stacks of glass mat over a wide range of temperatures (51.7 to 176.7°C) and a range of platen closing speeds (0.02 to 2.00 mm/s). Scanning electron microscopy was used to examine the fiber tows after deformation. Individual fiber tows were observed to flatten during compression, more so at higher temperatures and slower closing speeds. The scanning electron micrographs also reveal changes in binder distribution around the fiber tows that are closely related to the degree of flattening of the fiber tows. This is because small gaps are opened up within the tow as it is flattened. Flow of binder along such gaps is predominantly due to the squeezing force, with only a minor contribution from capillary forces. The redistribution of binder then facilitates further compaction. The extent of binder redistribution is also governed by the binder viscosity, which was found to be a strong function of strain rate and temperature. The shear thinning viscosity of the binder leads to greater compressibility at the highest closing speed of 2 mm/s, although the compressibility of the mats was lower at moderately higher closing speeds. The compressibility was also higher at higher temperatures as expected. The loft was greater for stacks pressed at higher temperatures; this is a consequence of the lower binder viscosity at higher temperatures allowing more rearrangement of the tows. There was no loss of binder from the stacks in these runs.