12/03/2021
By Sokny Long

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Ph.D. proposal defense by Christopher Souza on “Interfacial Rheology, Simulation, and Optimization of Bicomponent Nylon 6,6 Fibers Flame Retarded with Polyphosphonate.”

Ph.D. Candidate: Christopher G. Souza
Defense Date: Thursday, Dec. 16, 2021
Time: 1 to 2:30 p.m. EST
Location: This will be an in-person defense held in Saab ETIC 445. There will also be a virtual Zoom log-in for anyone who is interested in attending the defense and unable to attend in person. Those interested in attending should contact the student Christopher_Souza@student.uml.edu and committee advisor Stephen_Johnston@uml.edu at least 24 hours prior to the defense to request access to the meeting.

Committee Chair (Advisor): Stephen Johnston, Professor, Plastics Engineering, UMass Lowell

Committee Members

  • Akshay Kokil, Assistant Teaching Professor, Plastics Engineering, UMass Lowell
  • Jay Park, Assistant Professor, Plastics Engineering, UMass Lowell
  • Margaret Sobkowicz-Kline, Associate Professor, Plastics Engineering, UMass Lowell

Brief Abstract:

Nylon 6,6 is a commonly used polymer in melt spinning, with uses in apparel and furniture. Unfortunately, flame retarding the material has proven difficult due to environmental and health concerns, or reactivity between nylon 6,6 and the potential retardant with incompatible processing temperatures. Flame retardants can be applied as surface treatments, but this approach has limited durability. This study strives to incorporate organophosphorus flame retardants into nylon 6,6 melt spun fibers using coextrusion, which would remove additional process steps, while maintaining the ability to dye the material and preventing the loss of the desired flame-retardant properties after laundering. In this work, the examination of the interactions between a polyphosphonate flame retardant and nylon 6,6 in the melt spinning process will be examined through rheology, simulation, and final fiber optimization.

There are many issues with coextrusion of nylon 6,6 and polyphosphonate. Like other flame retardants, polyphosphonate can react with the nylon when brought into contact at melt processing temperatures, leading to the formation of gels and char, each of which can inhibit the melt spinning process. Melt flow instabilities are also concerns as each of these can prevent the continuous drawing and collection. Despite these issues, the process presents an opportunity for good control over the tensile strengths and flame retardant properties of the final fiber. By diluting the flame retardant of the coextruded fiber in a thermoplastic polyester elastomer, the chemical interaction between the flame retardant and nylon 6,6 can be inhibited, while also changing the drawing characteristics of the later to increase its orientation and thus its strength. So far, the bicomponent melt spinning process has shown promise in the creation of flame retarded bicomponent fiber, in which mutliple samples of varied diameter, skin-core ratios and core blend ratios have been produced. Characterization of these fibers has included thermal analysis, microcombustion calorimetry, tensile testing and cross section examinations. Additionally, rheological testing on the FR blend and nylon 6,6 have shown promise in examining the reactivity of the interface between the two melt phases. With these, a suite of simulations on a simplified melt-spinnerete geometry has shown the presence of a deadzone within that may lead to excessive residency times for the material.

Three studies are proposed that aim to maximize the flame retardant loading as well as the resulting fiber strength. Once completed the same methods and insights gained could be applied to other systems where additives other than the specific FR used are desired yet have similar compatibility issues in the melt spinning process. To this end, the first study will examine the rheology of the reactive interface between the nylon 6,6 and the flame retardant, along with spectroscopy to ascertain what is being created. Second, a series of simulations will be used to examine the presence of melt flow instabilities within a skin-core bicomponent melt spinning die, including the insights gained from the interfacial rheology. Finally, the effect of altering the solidification temperature of a single phase of a bicomponent fiber on the morphology and strength of the combined system will be examined.

All interested are welcome to attend in person or remotely.