Reclamation and recycling of waste rubber

The pyrolysis of scrap automotive tyres

Rubber (cis-1,4-polyisoprene) is one of the most important polymers naturally produced by plants because it is a strategic raw material used in more than 40,000 products, including more than 400 medical devices. The sole commercial source, at present, is natural rubber harvested from the Brazilian rubber tree, Hevea brasiliensis. Primarily due to its molecular structure and high molecular weight (>1 million daltons) this rubber has high performance properties that cannot easily be mimicked by artificially produced polymers, such as those derived from, e.g., bacterial poly-hydroxy-alkanoates (PHAs). These high performance properties include resilience, elasticity, abrasion resistance, efficient heat dispersion (minimizing heat build-up under friction), and impact resistance. Medical rubber gloves need to fit well, be break-resistant, allow the wearer to retain fine tactile sensation, and provide an effective barrier against pathogens. The sum of all these characteristics cannot yet be achieved using synthetic gloves. The lack of biodiversity in natural rubber production renders continuity of supply insecure, because of the risk of crop failure, diminishing acreage, and other disadvantages outlined below. A search for alternative sources of natural rubber production has already resulted in a large number of interesting plants and prospects for immediate industrial exploitation of guayule (Parthenium argentatum) as a source of high quality latex. Metabolic engineering will permit the production of new crops designed to accumulate new types of valued isoprenoid metabolites, such as rubber and carotenoids, and new combinations extractable from the same crop. Currently, experiments are underway to genetically improve guayule rubber production strains in both quantitative and qualitative respects. Since the choice for gene activities to be introduced or changed is under debate, we have set up a complementary approach to guayule with yeast species, which may more quickly show the applicability and relevance of genes selected. Although economic considerations may prevent commercial exploitation of new rubber-producing microorganisms, transgenic yeasts and bacteria may yield intermediate or alternative (poly-)isoprenes suitable for specific applications.

Alternative sources of natural rubber.

Characterization and potential applications of pyrolytic char from ablative pyrolysis of used tires

Science and technology of rubber reclamation with special attention to NR-based waste latex products

Rubber, hydrocarbons, i.e., resins, and other useful by-products are extracted from shrubs such as guayule and guayule-like shrubs by a procedure wherein the shrub, after being comminuted, is processed in an aqueous and/or a non-aqueous system. An optional water treatment step can be used to remove water solubles and/or facilitate processing and achieve increased yield of desired by-products.

Process for extracting rubber and by-products from guayule and guayule-like shrubs

The smoke inhibitory activity of hydrated fillers in SBR is centered primarily in condensed-phase processes and is analogous to the generally accepted mechanism of flame retardation by the hydrates. Dissipation of heat, which disfavors pyrolysis and favors competing crosslinking reactions is probably involved. These reactions should occur chiefly among polybutadiene segments of the polymers. In addition, the smoke-suppressant efficiency of hydrated fillers should depend upon the crosslinking efficiency of the rubber. Finally, although smoke generation in latex rubber goods presents a challenge, substantial practical reductions in visible smoke can be achieved through the selection of proper hydrated fillers.

Mechanism of Smoke Inhibition by Hydrated Fillers

Our overall objective in presenting this review is to call attention to the very complicated nature of the entire disposal problem. The whole field of scrap-tire disposal is full of alternatives, compromises, legislation, and conflicting reports on technological success. We will present a brief historical section explaining why the disposal of scrap-tires is now a problem (challenge) and the events that lead to it. Statistics on the annual volume of scrap-rubber generated and the volume disposed of by major processes will be reviewed. Existing and proposed legislation will be presented, and the probable impact on the rubber industry discussed. We will state what we believe to be the characteristics of an ideal solution. The technical aspects of scrap-tire disposal will not be neglected. The physical, thermal, and chemical values of a scrap-tire will be presented as a basis of defining potential uses for scrap-tires. The existing and proposed uses of scrap-tires as well as processes for disposal a...

Scrap Tire Disposal

Many procedures and processes for the disposal of scrap tires are available Because of the complexity of the whole disposal problem—eg, collection logistics, availability and location o

Scrap Tire Disposal Procedures

Tackifying agents for rubber comprising at least one chemically or physically treated guayule resin fraction are disclosed. Physical treatments include vacuum deoiling, steam stripping deoiling, hexane deoiling, while chemical treatments include formaldehyde reaction, phenol/formaldehyde reaction, urea formaldehyde reaction, acid reaction and sulphur reaction. Untreated guayule resin fractions can also be used. Vulcanized and unvulcanized rubber compositions containing guayule resin derived tackifying agents as well as articles made therefrom are also disclosed.

Edward L. Kay

Papers

Process for extracting rubber and by-products from guayule and guayule-like shrubs

Mechanism of Smoke Inhibition by Hydrated Fillers

Scrap Tire Disposal

Scrap Tire Disposal Procedures

Rubber additives derived from guayule resins and compositions containing them