Structure-Process-Property Relationships in Elastic Nonwovens Made From Multi-Block Elastomers

Abstract

Melt-blown webs from ester and ether thermoplastic polyurethanes (TPU) and polyether-block-amide (PEBA) elastomers were produced at different die-to-collector distances (DCD) to study the correlation between polymer type, process conditions and web properties. Air temperature and velocity profiles were measured and modeled to correlate fiber formation to melt-blowing conditions. Isothermal crystallization kinetics was measured by DSC, and analyzed by traditional Avrami and model proposed by Kurajica. Web tensile properties were explained in terms of crystallization kinetics along with air temperature profile.

Crystallization kinetic parameters derived from both models exhibited similar temperature, polymer type and hardness dependence. The air flow field from simulations showed good agreement with experimental profiles and enabled modeling of fiber formation in melt-blowing. Both air temperature and velocities dropped significantly even at the die tip and continued to fall rapidly until reaching a plateau. The crystallization onset temperatures were found to fall within DCD region of rapid air velocity and temperature drop. This suggests that polymers already started to crystallize before collector, the extent of which depends on crystallization kinetics.

Web strength behavior was highly dependent on DCD and polymer hardness. By mapping crystallization behavior onto air temperature profile, polymer crystallization kinetics was observed to have a profound effect on web strength. This was clearly demonstrated in PEBA series, in particular with the hardest grade, P55 which produced the lowest web strength mainly due to its significantly higher crystallization rate. It is concluded that web tensile behavior is strongly dependent on degree of fiber solidification achieved within the web, which is determined by crystallization kinetics and distances traveled between die and collector. Moreover, polymer extrusion and air temperatures as well as air velocity are critical in determining the amount of time it takes for polymer melt to travel the distance from the die to collector and the temperature that fibers have upon reaching collector.