Flame retardant nylon 6 nanocomposite fibers : processing and characterization
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One type of engineering thermoplastic polymers that has significant commercial application is nylon. However, flammability and melt dripping is a major problem for polymers like nylon 6 because it can cause fire to spread to other flammable objects and escalate the fire in a short amount of time. Although high performance inherently flame-retardant (FR) fibers have been discovered and various durable FR finishes for nylon have been developed, cost-effective flame retardant nylon and nylon blend fabrics remain a challenge. The goal of this research is to develop non-drip inherently FR nylon 6 fibers as a cost-effective alternative for use in high volume FR fabrics. In this dissertation, a cost effective alternative of producing non-drip inherently flame retardant nylon 6 fibers with balanced performances was developed based on polymer nanocomposite systems incorporating intumescent FR and nanoclay additives. Nanoclay was added to the system to reduce FR particle loading and capitalize on the synergistic effect between nanoclay and intumescent additives. Adequate dispersion of the additives with exfoliation of the nanoclay platelets was observed using TEM and XRD. Injection molding was used as a tool for screening the performance of the nanocomposite formulations in bulk form before the fiber spinning process. Results of injection molded FR PA6 nanocomposites suggest that although a good FR performance could be achieved, mechanical properties, especially ductility, were significantly compromised. To solve this problem, rubber toughening was achieved using a thermoplastic elastomer with significant success in recovering material ductility without compromising FR performance. Ultra-sonication of the FR additives prior the fiber spinning could effectively reduce the FR particle size distribution. Single fiber tensile tests show that PA6/FR/elastomer/nanoclay formulation is able to improve both the tenacity and elongation at break from the original PA6/FR system. Moreover, flammability tests suggest that the nanocomposite FR fibers have significantly lower heat release properties and are able to retain a fibrous shape after combustion indicating the non-dripping property. Therefore, our experiments have yielded improved non-drip FR properties in PA6 through the infusion of nanoclay and non-halogenated intumescent particles (FR) via co-rotating twin-screw extrusion. One major implication of these results is that with the new non-drip FR nylon 6 fiber, it would be possible to achieve blends with higher nylon content than customary and not compromise the FR performance of the fabric, thus providing a cost effective solution for high-volume applications.