THE DEVULCANIZATION OF UNFILLED AND CARBON BLACK FILLED ISOPRENE RUBBER VULCANIZATES BY HIGH POWER ULTRASOUND
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 rate constant ratios of main chain scission and crosslink rupture. An increase of CB loading increased this ratio for both IR and NR with higher ratio in IR. The addition of processing oil in the filled IR compounds reduced this ratio.
School:The University of Akron
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:isoprene rubber ultrasonic devulcanization gel fraction crosslink density simulation
Date of Publication:01/01/2007