NMR Relaxation and Diffusion Study of Ultrasound Recycling of Polyurethanes
We have examined the effect of intense ultrasound on unfilled polyurethane foam and rubber using proton NMR transverse relaxation and pulsed-gradient diffusion studies, sol extraction, GPC characterization, and glass transition measurements. Results correlate well with ultrasound amplitude. The proton T2 relaxation at 70.5 deg. C exhibits three discrete components, due to heavily entangled sol and crosslinked network; unentangled polymeric sol plus dangling network chain ends; and oligomer remnants. Devulcanizing produces heavy sol, increases segmental mobility of all species, and generates more dangling chain ends. In foams, but not in rubber, additional light sol is generated at the expense of network. All mobilities are significantly lower than in the other rubbers we have studied, an effect unrelated to the glass transition, nearly constant at -60 deg. C. Diffusion measurements, possible only in foams, show a bimodal spectrum whose fast component slows markedly with ultrasound amplitude, attesting to the production of fragments heavier than the original oligomers, as confirmed by GPC analysis. This work is the first to study ultrasound devulcanization in industrial rubbery foams.
Isayev, Avraam, "NMR Relaxation and Diffusion Study of Ultrasound Recycling of Polyurethanes" (2004). Polymer Engineering Faculty Research. 182.