Dimensional stability of melt blown PET nonwovens

This research attempted to develop melt blown poly(ethylene terephthalate),PET nonwovens that maintained their dimensional stability at temperatures above the glass transition (i.e. 80°C and above). The high degree of shrinkage of PET fibers on exposure to heat is due to the relaxation of oriented rigid amorphous segments present within the fibers. The shrinkage can be controlled by engineering fibers that contain tie or reinforcing elements between the molecules. The overall crystallization rate and crystallinity can be increased by incorporating nucleating agents during melt blowing where the stress levels are low for any on-line crystallization to occur. Sodiumbenzoate, liquid crystalline polyester (LCP) and ionomer were used as nucleating/reinforcing agents to engineer melt blown PET fibers. Poly(ethyleneterephthalate) without any additive was also melt blown under different process conditions to study the effect of process variables on the crystallinity of the fibers. The Melt blown samples were then analyzed for their structure and properties through various techniques and it was concluded that by having tie elements or crystallites in theas-produced fibers, the shrinkage of melt blown PET fibers can be controlled to less than 10% even at 190 °C. A three-phase fiber model was used to explain the shrinkage mechanism of the fibers. The fractions of different structural entities present in the fibers determine their shrinkage behavior. The fibers made from PET and sodium benzoate were smaller in diameter and better in mechanical properties compared to those from PET and liquid crystalline polyester. The addition of sodium benzoate toPET/LCP blends resulted in smaller diameter fibers with good dimensional stability.However, the resultant mechanical properties were poor. It was also observed that ingeniously selecting the process conditions one can control the shrinkage behavior of melt blown fibers with a limited processing range of variables.