This Small Business Innovation Research Phase I project relates to the application of a surface modification to ground tire rubber (GTR) particles, enabling use of GTR as an additive to asphalt for roofing shingles, and improving its use in paving. This additive replaces the costly all-polymer additives currently used, while making use of an otherwise waste commodity. Existing processes degrade the GTR, consume excessive energy, are high-cost, and decrease the elasticity of the GTR if devulcanization occurs. Altogether, this makes the final product unsuitable for use in roofing shingles, and reduces its performance in paving asphalt. The objective of this research is to develop alternative approaches to the current technology. The intellectual merit of this proposal arises from the research related to polymer surface modification of GTR particles via a combination click chemistry and atom transfer radical polymerization (ATRP), with a polymer having considerable temperature resistance. The anticipated results and advantages include: simplification of the surface coating process, reduced degradation of the GTR particles in an asphalt compound, optimization of the viscoelastic properties of the rubber-asphalt mixture, shortening of the mixing period, reduction of the cost and energy, and improved dispersion and compatibility of rubber particles within the asphalt.
The broader impact/commercial potential of this project will stem from the successful development of a low cost, high quality, thermally stable asphalt additive with high dispersibility. It will be based on surface modified Ground Tire Rubber (GTR), enabling the development of flexible, durable, high-quality roofing materials, and enhanced paving asphalt. The polymer coated GTR particles provide the advantages of a polymer additive, but using far less polymer. Commercial polymers alone have been incorporated into mixtures of asphalt for roofing and pavement, but at high cost, with current market prices of $1.50 to $1.80 per pound. In contrast, the addition of GTR particles would cost only $0.25 per pound. The initial estimated cost to surface modify the GTR particles with a polymer coating has been calculated to be ~30% above material cost. The incorporation of surface-coated GTR particles into the roofing mixture reduces the production cost up to ~20% by reducing and/or substituting the amount of expensive polymer additives currently used. The precursor materials are commercially available at low cost. Aside from enhanced performance, and low cost, using GTR particles will provide an environmental benefit, allowing reuse of tire rubber waste typically disposed in landfills, and substantially reduces use of a nonrenewable resource.
". It shows significant progress in development of a surface modification for ground tire rubber that now allows its use as a more cost effective modifier for asphalt binders, and possibly support reuse in industrial rubber applications. Background and Need High quality asphalt binders for shingles and roads require modification. Polymers are thus added to improve rheological and viscoelastic properties. Styrene-butadiene-styrene (SBS) is the most prevalent additive. Although SBS provides beneficial stability characteristics, it is a costly component in a very cost sensitive industry -- petroleum modified asphalt (PMA) suppliers desire to have it at least partially replaced [2]. Use of Tire Rubber Tire rubber is a possible substitute for SBS, as it consists of cross-linked synthetic and natural rubbers. Tire rubber is also a waste commodity that occupies valuable landfill space [3], and certain agencies already mandate its use in asphalt for paving, regardless of cost. Tire rubber has already been used to a limited extent, but with limited success and at an even higher cost per ton over SBS, because of the added processing and energy to blend it into asphalt. It must be reduced to a very fine, micronized form to obtain properties comparable to SBS in asphalt [4] and achieve compatibility. The cost to reduce it to that form prevent it from serving as a viable alternative to SBS. Ground tire rubber (GTR) is a low cost intermediate size particle between micronized rubber powder (MRP) and the larger crumb rubber (CR). However, GTR cannot be added to asphalt without some modification, as the particles readily settle in the mixture. A modified GTR with low cost and potential for excellent phase stability would therefore be the most suitable material for an asphalt modifier [5]. Polymeric Designs' Coated Tire Rubber PD therefore developed a novel coating and process for application to the surface of the GTR particles. PD’s approach improves the GTR-Asphalt surface interaction by chemically bonding the phases -- from the rubber, to the coating, to the asphalt. Electron Microscope Images of PD's Coated Tire Rubber Uncoated GTR, and GTR coated by PD’s methods with 5% and 10% loadings were examined using scanning electron microscopy (SEM). Both showed complete coating at light and heavy loadings. SEM images at 250X magnification show only a very slight difference between the non-coated GTR in Fig. 3(a), and GTR coated with 5% PD coating in Fig. 3(b). GTR coated with 10% PD coating in Fig. 3(c) shows a very smooth coated surface, and that the whole surface of the particle is covered evenly and completely. Figures 4 through 6 show a progression of surface detail as revealed with increased magnification. Figure 4(a) reveals uncoated GTR particles with very small rubber particles, which can also be seen in greater detail in Figures 5(a) - 6(a). Figures 5(b) and 6(b) shows that a layer of PD's coating has covered the entire surface of the GTR particle, but it is thinner comparison to 10% PD coating of 5(c) and 6(c). Normal 0 false false false EN-US X-NONE X-NONE Fig. 5b and 5c show that the GTR coating has an even coverage on the particles, and the coat covers inside the voids as well. Physical coating was successful, as shown by SEM images indicating coating thickness increased with increased loading from 5 - 10%. The granularity of surface features reduces with increased loading. Test Results Asphalt was modified with PD's coated GTR by simple mixing, then analyzed using four major ASTM standard tests for PMA: separation, penetration, viscosity, and softening point. Primary focus was placed on separation testing, because settling of GTR during storage is a major industrial problem. PD’s coated GTR/asphalt mixtures were tested against SBS and uncoated GTR mixtures for its ASTM performance characteristics. The enhanced interface between the GTR and asphalt provides improved particle-particle interaction that greatly increases dispersion. The net effect is better suspension of each particle in the heated asphalt mixture, and a reduction of separation to a level well within acceptable limits. Conclusion At a minimum, this result supports economic viability for use of tire rubber modified in accordance with Polymeric Designs' proprietary process where tire rubber is mandated for use in asphalt. The results indicate stability for storage and transport. Futher research would determine the extent to which it can replace costly SBS as the modifier, and improve viscoelatic performance for binder performance. Normal 0 false false false EN-US X-NONE X-NONE Fig. 5b and 5c show that the GTR coating has an even coverage on the particles, and the coat covers inside the voids as well.
