Impact of Carbonaceous and Inorganic Nanomaterial Chemistry on Polymer Additive Release from Weathered Epoxy Composites

Nanomaterials (NMs) are small (< 100 nm), reactive, chemical species that can often be used as polymer fillers to improve mechanical strength and slow the degradation of polymer nanocomposites (PNCs). Polymers can undergo physical and chemical weathering which can result in increased release of polymer additives and non-polymerized monomers from the polymer matrix. This project aimed to study how NM chemistry and environmental weathering impacts the release and transformation of relevant PNC systems. Bisphenol A diglycidyl ether (BADGE) PNCs were synthesized containing titanium dioxide (TiO2), multi-walled carbon nanotubes (MWCNT), or graphene oxide (GO) NMs. These composites were subjected to either simulated or natural weathering conditions to quantify and characterize their capacity to leach endocrine-disrupting chemicals. Environmental variables, including temperature and ultra-violet (UV) light, were investigated for their impact on additive release. Fourier-transform infrared spectroscopy and Raman microscopy were used to characterize the PNCs which were leached in water for one to five days at 25, 45, or 65 degreesC. The degree of weathering also varied from no weathering, outdoor weathering, or simulated weathering using UV light. Leachates were analyzed using high-performance liquid chromatography quadrupole time-of-flight mass spectrometry to quantify release of bisphenol A (BPA), tert-butylphenol (TBP), and nonylphenol (NP). There were significant differences between NM types for PNCs weathered outdoors and leached at 25 degreesC for 24 h, however only TBP was detected in the leachate. When compared to the blank epoxy, GO PNCs leached significantly less in the UV and in May outdoor weathered experiments, MWCNT PNCs leached significantly less when weathered outdoors in May and June, and TiO2 PNCs leached significantly less when UV weathered. Each of the NMs has potential to decrease TBP release through sorption or photodegradation. The carbonaceous NMs (GO and MWCNT) may sorb TBP, inhibiting its release, while TiO2 may photodegrade TBP. The unweathered PNCs leached the most TBP, followed by UV weathered, and then outdoor weathered. A possible explanation for this is photodegradation of TBP by UV light in the UV- and outdoor-weathered experiments leading to removal of TBP prior to leaching. Future experiments should include additional sorption trials and long-term natural weathering with microplastic generation to further explore the release and degradation mechanisms.