Doctor of Philosophy, University of Akron, 2007, Polymer Engineering

The effects of ultrasound on virgin gum isoprene rubber (IR) and on the devulcanization of unfilled and carbon black (CB) filled IR were studied. Ultrasonic treatment altered the structure and properties of gum IR by creating low molecular weight tails which broadened the molecular weight distribution and improved processability. Ultrasonic devulcanization of IR vulcanizates resulted in a reduction of gel fraction and crosslink density. Increasing the ultrasonic amplitude yielded a further reduction, regardless of CB loading, in the IR vulcanizates. This is contrary to the previous work on natural rubber (NR), the natural counterpart of IR which showed a minimum gel fraction and crosslink density at an intermediate ultrasonic amplitude. The devulcanization of filled IR resulted in more main chain scission than in unfilled IR due to the immobility of bound rubber at the filler surface which leads to lower properties in revulcanized rubbers than in virgin rubber. Upon blending the devulcanized IR with virgin IR, properties comparable to those of virgin rubber were obtained at certain blending ratios. A cure kinetics model with reversion adequately predicted the evolution of state of cure in curing and reversion stages under isothermal and non-isothermal conditions. The higher reversion observed in filled IR than in unfilled IR was consistent with the difference of reversion rate constant obtained in simulation. NMR proton transverse relaxation technique was unable to differentiate the contribution of short component mobility between physically entangled (heavy sol) and chemically crosslinked (gel) networks. Ultrasound severed both the chemical crosslinks and the main chain, creating dangling chain ends, with no generation of additional fragments of oligomeric species. Simulation of network structures using the Dobson-Gordon theory of network statistics indicated crosslinks were easier to break than main chains under ultrasonic exposure. Unfilled IR and NR had similar (open full item for complete abstract)

Committee: Avraam Isayev (Advisor) Subjects: Engineering, Materials Science

Master of Science in Polymer Engineering, University of Akron, 2013, Polymer Engineering

Continuous ultrasonic devulcanization of ground tire rubber (GTR) of 10 mesh and 30 mesh from Rondy Co., as well as whole truck tire rubber of 40 mesh (40TR), 140 mesh (140TR), 200 mesh (200TR), mixture of 40 and 80 meshes (84TR) and truck tire buffing rubber of 80 mesh (80BU) from Lehigh Technologies, Inc. were studied. The devulcanization process was conducted using an ultrasonic co-rotating twin-screw extruder at ultrasonic amplitudes from 5 to 13 µm and a frequency of 40 kHz. Ultrasonic power consumption and die pressure during devulcanization, curing behavior of devulcanized rubber, gel fraction and rheological properties of devulcanized and revulcanized rubbers, crosslink density and mechanical properties of revulcanized rubbers were obtained. It was found that GTR of 10 mesh devulcanized less than GTR of 30 mesh. Similarly, GTR of 40TR experienced less devulcanization than that of 84TR. This effect is attributed to a higher surface area in finer particles. Two groups of devulcanized rubbers exhibiting the smooth and rough extrudates were observed during the devulcanization of GTR of 10 and 30 meshes. The smooth extrudates were obtained at higher amplitudes due to more devulcanization. The revulcanizates of smooth extrudates had a higher elongation at break, but a lower modulus at 100% elongation and tensile strength. The devulcanized and revulcanized rubbers of 140TR were found to have a lower gel fraction than the devulcanized and revulcanized rubbers of 200TR. The elongation at break, modulus at 100% elongation and tensile strength of the revulcanized rubber of 140TR were found to be lower compared to those of the revulcanized rubber of 200TR. Gel fraction measurement indicated that the devulcanization of GTR of 30 mesh, 40TR and 200TR increased with an increase of the ultrasonic amplitude. In contrast, 84TR and 140TR exhibited less devulcanization at intermediate amplitudes due to prevailing effect of revulcanization over devulcanization. T (open full item for complete abstract)

Committee: Avraam Isayev Dr. (Advisor); Thein Kyu Dr. (Committee Member); Erol Sancaktar Dr. (Committee Member) Subjects: Polymers