Polyurethane Rubber modification

Keywords surface-modification, polyurethane, rubber particles, composites, adhesion, filler, compatibility, coefficient of friction, peel tests, tear resistance. 

Acidification of chloramine T with sulfuric acid produces the formation of dichloramine T (DCT) and hypochlorous acid (HCIO), species which react with C=C bonds of the butadiene units. The effectiveness of the treatment is ascribed to the introduction of chlorine and oxygen moieties on the mbber surface. A decrease in the pH of the chloramine T aqueous solutions produced more extended surface modifications and improved adhesion properties in the joints produced with waterborne polyurethane adhesive (Figure 27.9). The adhesive strength obtained is slightly lower than that obtained for the rubber treated with 3 wt% TCI/MEK, and its increases as the pH of the chloramine T solution decreases (Figure 27.9). A cohesive failure in the rubber is generally obtained. 

Femandez-Garcfa J.C., Orgiles-Barcelo, and A.C., Martm-Martmez J.M., 1991, Halogenation of styrene-butadiene rubber to improve its adhesion to polyurethanes, J. Adhes. Sci Technol, 5, 1065-1080. Oldfield D. and Symes T.E.F., 1983, Surface modification of elastomers for bonding, J. Adhes., 16, 77-96. Pastor-Bias M.M., Ferrandiz-Gomez T.P., and Martm-Martmez J.M., 2000, Chlorination of vulcanized styrene-butadiene rubber using solutions of trichloroisocyanuric acid in different solvents, J. Adhes. Sci. Technol, 14, 561-581. 

For instance, the modification of silicone rubbers, poly-(tetrafluoroethylene), polyethylene, and segmented polyurethanes by ionic attachment of heparin was shown to result in a decrease of platelet adhesion onto these polymers71 74 75. A similar... 

A new approach to modification of thermosetting epoxy or polyurethane systems (Plastics Technology, p. 14 (April 1994)) involves surface modified rubber or UHMW-PE particles. These particles after reaction with Cl, 0 or F allows for improved properties (toughness, tear resistance, abrasion resistance, modified coefficient of friction) in the noted thermosets. 

Interest continues in the binding of heparin to polymers in an attempt to produce non-thrombogenic surfaces. This has been the aim in the use of glutaralde-hyde-protein complexes as coatings for latex rubber and polyurethanes. Glutaraldehyde has also been used to bind antibodies to partially hydrolysed polyamide surfaces for enzyme-linked radioassay techniques. One of the few examples of direct polymerization (as opposed to surface modification) in an attempt to produce polymers having improved compatibility involves the use of 2-methacryloyloxyethylphosphoryl choline in the formation of homopolymers and copolymers with methyl methacrylate. An isocyanato-urethane methacrylate has been synthesized from 2-hydroxyethyl methacrylate in connection with dental materials research in which the preparation of poly functional monomers for improvement of interfacial bonding with tooth tissue is a topic of some interest. 

This entry describes the technology of surface-modification of rubber particles, characterizes the properties of some rubber/polyurethane composites, discusses processing considerations, and reviews applications that have been developed to date. 

With a patented [1], proprietary surface modification, rubber particles are rendered compatible with polyurethanes. One surface modification is a controlled oxidation of the outermost molecules on each rubber particle. The treatment chemistry involves the reaction of halogen- and oxygen-containing gases with the rubber backbone to form pendant polar functional groups. Figure 1. In fact, the rubber surface becomes so hydrophilic that the treated particles are readily wetted by water. 

Surface modification also enables excellent interfacial bonding between the rubber particles and the polyurethane. The effectiveness of this surface modification in facilitating adhesion is demonstrated by comparing the bond strength of strips of rubber with polyurethane cast on them. In T-peel tests, it was found that where polyurethane was cast onto untreated strips of rubber, the bond strength was 5N/cm. In analogous... 

Manufacture of rubber/polyurethane composites with higher levels of rubber particles generally requires more drastic modifications to the molding process and equipment. This is because incorporation of rubber particles in polyol or prepolymer causes an increase in viscosity. These thicker slurries are more difficult to pump and to deaerate. 

Styrene-butadiene-styrene (SBS) block copolymers are adequate raw materials to produce thermoplastic rubber (TR) soles. SBS contains butadiene domains — soft and elastic and styrene domains - hard and tough. Because the styrene domains act as cross-linking agents in the SBS structure, vulcanization is not necessary to provide dimensional stability. TR rubber soles generally contain polystyrene (to impart hardness), plasticizers, fillers, and antioxidants processing oils can also be added. TR rubber soles have a low surface energy, so to reach proper adhesion to polyurethane adhesive a surface modification is needed. Special adhesives have been developed to avoid surface preparation but they have poor creep resistance. 

SBR rubbers can be treated with concentrated sulfuric acid to improve adhesion to polyurethane (Cepeda-Jimenez et al. 2000). The treatment is not restricted to the surface but also produces a bulk modification of the rubber because a decrease in the tensile strength and the elongation at break are found. If the SBR rubber contains paraffin wax, the treatment with sulfuric acid promotes its migration to the surface and thus solvent wiping with petroleum ether should be applied. 

---