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Investigation of polyetherimide’s thermal degradation and fabrication of thermal end-of-life sensor for fire protective clothing
- Author / Creator
- Cho, Chungyeon
Typically, protective clothing are made of materials that have a high temperature resistance, good mechanical and chemical properties. However, some high-performance textiles – including those used in protective clothing – age silently, undergoing a gradual reduction in their protective properties. In order to estimate the lifetime of protective clothing, especially for fire fighters, this dissertation proposes a non-destructive method to monitor the aging level of outer shell fabrics. It is hypothesized that an electrically conducting layer that loses its conductivity systematically under aging conditions can be used as the basis for an end-of-life-sensor for textiles. This sensor is fixed as a patch on the fire protective clothing; the mechanism of sensing is based on the loss of conductivity of a graphene layer on a high temperature resistant polymer during thermal aging. This sensor also can be used to monitor the condition of polymeric materials under extreme environments.
The first study introduced a simple method to prepare conductive tracks on a meta-aramid woven fabric using reduced graphene oxide (rGO). The simple “dip and dry coating” method was used to coat rGO on a meta-aramid fabric. While 15 iterations of rGO coating cycles were needed to completely wrap each m-aramid fiber with rGO sheets, 10 cycles were sufficient to establish electrical conductivity. This conductivity remained stable for up to 10 laboratory wash cycles. The conductivity of these rGO coated fabrics also remained stable during immersion in water. Furthermore, a fabrication protocol was developed for patterning both single- and two-sided rGO tracks on the m-aramid fabric. Assessment with a Martindale abrasion tester revealed that the single-sided rGO-track lost its conductivity after 150 abrasion cycles, whereas the two-sided rGO-tracks survived 3000 abrasion cycles. These results demonstrate that a simple rGO coating technique can be used to prepare end-of-life sensors for high-performance textiles.
In a second study, the selection of a high temperature resistant polymer for use in a thermal end-of-life sensor was performed. Polyetherimide (PEI) was chosen since it has a similar thermal degradation behavior as m-aramid fibers. This study investigated the thermal aging behavior of PEI at elevated temperatures. During thermal aging, PEI underwent a change in both its mechanical and chemical properties. Crosslinking and chain scission reactions took place in the PEI specimens, which in turn affected the ultimate tensile strength (UTS), functional groups, and glass transition (Tg) temperature. Furthermore, cracks formed on the PEI surface and propagated during aging, likely due to chain scission. The UTS was used to construct a time-temperature-superposition master curve. The activation energy corresponding to the decrease in the UTS was calculated to be 112 kJ/mol.
The third study proposed a design for a thermal aging sensor for fire protective clothing. A conducting layer was formed by laser irradiation to convert the top layer of a PEI film into graphite, creating a laser-induced-graphene (LIG) layer. The electrical conductivity of this graphitic layer decreased during aging at temperatures above the glass transition of PEI. At temperatures below PEI’s Tg, the electrical resistance of the LIG layer was observed to decrease due to contact annealing. This sensor showed a stable response over 10 heating and cooling cycles. Finally, the washing stability of this sensor was assessed over 10 washing cycles; the results suggest the need for a better encapsulation strategy.
Overall, this dissertation explores a novel non-destructive method to monitor the level of thermal aging of high performance fabrics. The washing stability of the sensor still needs to be improved but it offers a very large potential for outer shell fabrics used in fire protective clothing as the high temperature resistant polymer selected for the sensor has a similar thermal degradation behavior and activation energy as outer shell fabrics and the thermal aging monitoring only relies on the measurement of the electrical conductivity of the conductive layer.
- Graduation date
- Spring 2021
- Type of Item
- Doctor of Philosophy
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