,

A WILEY-INTERSCIENCE PUBLICATION
John Wiley & Sons
NEW YORK CHICHESTER BRISBANE TORONTO SINGAPORE
 \,

12-57
1002 RECYCLING (PLASTICS) Vol. 19

PrfJdUCts,Report EPA 670/2-74-027, U.S. Environmental Protection Agency, Cincinnati, Ohio, 1974, Fuel Source
167 pp.
34. kl. E. Banks, \V. D. Lusk, and R. S. Ottinger, Nmc*Chemical Coriccpts for Utilization of Waste Plastics.
Report S\V-l6c, U.S. Environmental Protection Agency, \Vashirigton, D.C., 1971, 129 pp. The use of s c
35. H. Alter, Ind. Eng. Cliem. 52. 121 (1960).
”

as natural-gas ani
36. G. Scott, Resource Recovery Conseccntion 1(4), 341 (1976). most economical 11
37. Internntional Research & Technology, Recycling Plastics, A Survey nnd Asse.ssnient of Rescnrch and 90%organic mateii
Technolog\, Society of the Plastics Industry, New York, 1973, 56 pp.; *J. I,. Holman, J . B.Stephenson,
from 18.6 to 27.9,
and kl. .J. Adam, “Recycling of Plastics from Urban and Industrial Refuse” in Bureau of Aliries Report
of Investigations 795.5, U.S. Department of Interior, 1972.
tire-fired boiler w
34. J. R. Lawrence in ref. 28, pp. 50-62. and was designed
39. .J. H. Bilhrey, Jr., J. \V. Sterner, and E. C. Valdez in ref. 20. kg of steam per hi
40. G. Menges and E. Haberstroh in ref. 19, pp. 1199-1197. vestibule and t h e
flashback fires arr
I
! the necessary tun
HARVEYA L T E R
a char that increa
Chamber of Commerce of the United States j carbon-black corn
I
!
ash-removal areE
j Lucas-Goodyear 11
j and failure to c o r
Shredded tiru
fired a 15%mixtui
burned a 10% t i
problems and SUE
coal fuel. The LII
I
RUBBER i
Scrap-tire transp,
limits tire-fired bu
I or tire manufactu
I incinerator was cii
A technique for vulcanizing rubber into a useful material was developed in the today, based on ll
18OOs,and a rubber-reclaiming process based on steam pressure to devulcanize natural T h e Japanezz
rubber was developed in 1858 (1). Today, high cost silicone rubber polymers are re- process was develll
claimed in much the same way, although most synthetic polymers require complicated since 1980. The Se
reclaiming techniques. Rubber in asphalt (qv), scrap rubber as fuel, rubber pyrolysis, as oil to produce
rubber reuse, eg, tire splitting and as reefs and crash barriers, etc, and other studies waste-tire treatmi
were conducted as rubber-recycling technology advanced. However, the discovery
Pyrolysis
of plastics and oil-extended rubbers has led to a reduction in the use of rubber as a
reclaimed material except for more costly polymers, eg, silicones amdl fluorocarbons. Scrap-tire p:
It is uneconomical to pyrolyze rubber scrap because of uncompetitive costs and few I oil, and carbon-bll
product make&, especidy in the United States. In most instances, it is more expensive troleum; Carbon,,
to prepare and burn scrap rubber than to burn natural gas, fuel oil, or coal. Higher fuel conceived to d e w
costs and petroleum scarcity in Europe and other parts of the eastern hemisphere make and quality (15-
rubber reuse as 2 fuel source more economical there thaii in the United States. Rubber Chopped tires are
reuse will become more prevalent in the United States as fuel and petroleum-derivative ducing atmosphea
costs for polymers increase. Approximately 67% of the scrap rabber, primarily as tires, I
off-gases. Condeni
is used as landfill (2). Owners of landfills charge up to $3.00 per tire, and disposal costs the ceramic balls..
a t municipal landfills are ca $0.10-0.20 per tire (3-4). As the economics become more balls. The carbor
favorable, rubber reuse will gain more recognition in resource-conservation and been removed. T
-recovery activities (5-6). butylene. The oil,,
Vol. 19 RECYCLING (RUBBER) 1003

Fuel Source

T h e use of scrap rubber for Euel is one of the best alternatives for reusing rubber
as natural-gas and fuel-oil costs increase. Whole tires and 2.5-cm tire”chips are the
most economical fuels because of shredding-cost savings. Tires that contain more than
90%organic materials have a heat value of ca 32.6 MJ/kg (ca 14,000 Btuhb). Coal varies I
from 18.6 to 27.9 MJ/kg (ca 8000-12,000 Btu/lb). A cyclonic, rotary-hearth, whole- I

tire-fired boiler was operated by Goodyear Tire and Rubber Co. from 1975 to 1977 I
and was designed to burn 1400 kg of automobile tires per hour, thus generating 11,300
kg of steam per hour (5,7). In the Lucas furnace, tires are conveyed into an airtight
vestibule and then onto the outer rim of a rotating hearth. The vestibule prevents
i
flashback fires and limits furnace air leaks. An air-velocity head of 5.1 cm provides
the necessary turbulence for combustion (8). Residues from the burning tires form
I
a char that increases combustible heat loss and tends to clog furnace grates, but the
carbon-black content also reduces slagging problems. Improper combustion a t the
1
ash-removal area of the furnace may prevent burning of the carbon black. T h e
Lucas-Goodyear tire-burning furnace was shut down because of mechanical problems
and failure to comply with Michigan’s air-pollution emission standards (9).
Shredded tire chips have been burned successfully in stoker-fired boilers. Uniroyal
fired a 15% mixture of tire chips with coal and both General Motors and B.F. Goodrich
burned a 10% tire-chip mixture with coal (10-12). Tire-grinding size-reduction
problems and supplier delivery costs have stymied cofiring projects based on tire and
coal fuel. T h e Lucas furnace was developed to burn tires without size reduction.
Scrap-tire transportation can cost $0.04/kgI not including grinding costs, and thus
limits tire-fired boiler facilities to areas with ample scrap-tire supplies, eg, large cities
or tire manufacturers. T h e cost of burning one metric ton of tires per hour in a tire
incinerator was ca $0.20-$0.40 per tire in 1974, which escalates to $0.35-0.70 per tire
today, based on 10% straight-line inflation (13).
T h e Japanese are using whole scrap tires to fuel portland-cement kilns. T h e
process was developed by the Bridgestone Tire Company and has grown substantially
since 1980. T h e Saitama plant of Nihon Co. Ltd. burns 140,000 tires per month as well
as oil to produce 287,000 t of cement per month. Use of tires as fuel is considered a
waste-tire treatment system (14).

Pyrolysis

Scrap-tire pyrolysis has been the subject of several research studies by rubber,
oil, and carbon-black interests throughout the world (see Rubber compounding; Pe-
troleum; Carbon, carbon black). The Tosco I1 process pyrolysis-research study was
conceived to develop process equipment and to maximize carbon-black production
and quality (15-17). T h e Tosco I1 process is shown schematically in Figure 1 (5).
Chopped tires are fed into a rotary drum with hot ceramic balls a t 480449°C in a re-
ducing atmosphere. T h e rubber pyrolyzes and forms a solid residue, an oil vapor, and
off-gases. Condensed oil separates in a fractionator, and the gas is used for fuel to heat
the ceramic balls. A trommel screen separates the fine carbon black from the ceramic
balls. T h e carbon is pelletized after steel, fiber glass, and other contaminants have
been removed. T h e off-gas is basically a combination of ethylene, propylene, and
butylene. T h e oil, which contains about 1%sulfur, can be substituted directly for fuel
 I
i
j
!
t
I Vol. la,
1004 RECYCLING (RUBBER)
i
Flue -gas W’
emissions are pyr-
wire. ’I”
t 1 . tI !
rubber
H
1
Surge Dryer/
Separator Scrubber I
N ii
tires hopper preheater the bre:,
i
of tires;
Hot within
flue gas Hot could b)
balls 0t,
‘ heater
Ball Pyrolysis
drum
pyrolys;
reactior
rate. Ru
Air t Flue surface
impairs;
this blai
Warm -ball Accumulator
Naptha
Molten-.
and qua
the moll

4
Cas Depolyrr
cooler oil
In 11
rubber t,
Char Residue
oils are
Figure 1. Tosco I1 process. autoclaw
the heati
oil. In the Tosco 11process, higher temperatures produce more gas and less liquid. The rubber ii
pilot-plant process was designed to handle 15 t of tires per day, and generally one ton is replac
of tires produced 0.5-0.6 m3 (3-4 bbl) of oil, 1270-1540 kg of carbon black, 190-220 the tack
kg of steel, and 154-176 kg of fiber glass. The Tosco I1 project has been completed, 40 MJ/k;
but further work has halted partly because the carbon-black industry in the United (30).
States already has excess capacity. Also, the types of blacks and other related contents
in the residue from tire pyrolysis, eg, ZnO, possibly other inorganic materials, and glass In Asphai
fiber from old tires, are unpredictable. However, carbon blacks are carefully chosen
t o acRieve specific properties in compounded rubbers. Thus, the diverse and ampre- The
dictable residue mixture is useful only as a OW grade filler for mechanical goods and 58 t of rE
is uncompetitive as a carbon-black source. Approxiii
Foster Wheeler has two pyrolysis plants operating in the Federal Republic of compourr
Germany, and other European countries and Japan are pyrolyzing scrap rubber. T y - The?
iolysis is building a 136-t/$ pyrolysis plant in the United Kingdom (18), and the One conn
company will use vertical cross-flow reactors (19). Intennco in Houston has recently h. The hc:
shut down a 45-t/d scrap-tire pyrolysis pilot plant. In the Intennco process, two reactors chips to ff
in series pyrolyzed shredded tires with indirect heat a t ca 54OOC in a reducing atmo- particles
sphere. T h e process yielded ca 0.5 cubic meters (ca 3 bbl) of aromatic oil (3040% light for water.
oil) per ton of scrap rubber. Contaminants in the carbon-black char were removed by materials
several confidential processing steps (20). In the United States, tire pyrolysis has been asphalt d
studied as a method for recovering carbon black; however, production of carbon black asphalt a
from petroleum oils is less expensive, easier to control, and better in quality.
Yol. 19 RECYCLING (RUBBER) 105

Whole tires have been pyrolyzed in a semifluidized-bed reactor (21). The tires
are pyrolyzed on a tilting grate and the grate tilts to discharge the steel belt and bead
wire. This test unit has potential because whole tires are pyrolyzed, thus eliminating
rubber-grinding costs.
Nippon Zeon also had a tire-pyrolysis pilot plant. The company estimated that
the break-even cost was $0.25 per tire (22-23). A recent study indicates that pyrolysis
of tires and other polymers should be considered as a means for disposing of scrap
within environmental constraints. However, a plant processing 90,000 t/yr of scrap
could be profitable, based on reclaimed-product sales (24).
Other techniques include oxidative, steam-atmosphere (251, and molten-salt (26)
pyrolyses. Rubber pyrolysis is an exothermic reaction in a partial-air atmosphere. T h e
reaction rate and ratio of char black and oil products are controlled by the oxygen-flow
rate. Rubber pyrolysis in a steam atmosphere results in a cleaner char with a greater
surface area than char pyrolyzed in an inert atmosphere. T h e steam-pyrolyzed char
impairs the physical properties of cured rubber. Because of the greater surface area,
this black could be used for activated carbon, but production costs are prohibitive.
Molten-salt baths produce pyrolyzed char and oil products. The product characteristics
and quantities vary, depending upon the salt used. Recovery of the carbon black from
the molten salt also is a problem.

Depolymerized Scrap Rubber

In the depolymerized-scrap-rubber (DSR) experimental process, ground scrap-

rubber tires are used to produce a carbon-black dispersion in oil (27). Initially, aromatic
oils are blended with the tire crumb, and the mixture is heated a t 250-275°C in an
autoclave €or 12-24 h. The oil acts as a heat-transfer medium and swelling agent, and
the heat and oil cause the rubber t o depolymerize. As more DSR is produced and
rubber is added, less aromatic oil is needed, and eventually virtually 100% of the oil
is replaced by DSR. T h e DSR reduces thermal oxidation of polymers and increases
the tack of uncured rubber (28-29). Depolymerized scrap rubber has a heat value of
40 MJ/kg (17,200 Btuflb) and has been blended with No. 2 fuel oil as a fuel extender
(30).

In Asphalt

T h e United States generates ca 220 X IO6 scrap tires per year. Approximately
58 t of reclaimed rubber and 16,800 t of crumb rubber were produced in I977 (31).
Approximately 4500 t of reclaimed and crumb rubber were used in asphalt-rubber
compounds in 1980, which is less than 5% of the recycled rubber produced.
There are several methods for mixing and applying asphalt rubber to roadways.
One conventional method is to mix the rubber and asphalt a t ca 175-220°C for 1-2
h. T h e hot rubber asphalt is applied to the roadway and is covered with a layer of stone
chips to form a chip seal. The rubber crumb is usually scrap tires that are ground into
particles that are less than 2 mm in diameter. Besides chip seals, rubber asphalt is used
for waterproofing membranes, crack-and-joint sealers, hot-mix binders, and roofing
materials (see Waterproofing and water repellancy; Sealants). The rubber improves
asphalt ductility and increases the temperature at which the asphalt softens. T h e
asphalt and aggregate adhesive bond is stronger, and long- term asphalt durability
VOI..

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i'

Vol. 19 RECYCLING (RUBBER) 1007

Natural-rubber (NR) scrap is reclaimed with solvent naphthas, terpenes, di-

pentenes, and resins that swell, tackify, and aid in bond cleavage (see Rubber, natural).
Tires, mainly synthetic styrene-butadiene rubber (SBR),are less susceptible to oxi-
dation. Aryl disulfides, phenyl disulfides, high molecular weight mercaptans and other
sulfur-containing chemicals are used to swell and lubricate the rubber bonds and to
devulcanize the rubber by chemical oxidation and bond cleavage. 'I'he reclaiming oils
control the reclaimed-rubber chemical and physical properties. Oils soften the rubber
and increase the elongation. Reinforcing agents and fillers (qv), eg, carbon black,
aluminum silicate, and calcium carbonate, also control the reclaimed-rubber properties
and aid processing. Nonreinforcing fillers reduce the tack of devulcanized rubber and
make the reclaimed rubber easier to handle, and they abraid vulcanized particles
during finish milling so as to make the texture smoother. Reinforcing fillers increase
the tensile strength of the reclaimed material.
Reclaimed rubber can be used by itself in adhesives (qv) and solid-rubber-tire
compounds, or it can be blended with virgin rubber. Compounding is based on rubber
hydrocarbon content (RHC). To make a compound with 100 pt RHC, 70 pt of virgin
rubber and 60 p t of reclaim that is 50% RHC are needed. Rubber compounds with
reclaim require the same fillers, reinforcing agents, and plasticizers as the virgin
compound. However, reclaim already contains some zinc oxide and sulfur; usually 0.5
p t of zinc oxide and 2.5 pt of sulfur are used per 100 pt of reclaim.
Tires, natural-rubber tubes, and butyl tubes are the main sources of scrap and
reclaim. Specialty reclaims are made from scrap silicone, chloroprene (CR), nitrile-
butadiene (NBR), and ethylene-propylene-butadiene-ter-poiymer (EPDM) rubber
scraps. Tires, hoses, belts, molded and extruded goods, and asphalt products consume
ca 80%of the reclaim manufactured. Reclaimed rubber is used in the tire carcass and
sidewall compounds. Reclaimed natural rubber is used in cements, dispersions, and
pressure-sensitive tape, and butyl reclaim is used in tubes and inner liners for tires.
Until the 19609, reclaimed rubber was a principal raw material in many molded
and extruded rubber goods, ie, tires, rubber mats, and hard-rubber battery cases. With
the advent of vinyls and other plastics and less expensive oil-extended synthetic
polymers, reclaimed-rubber sales stabilized and then began to decrease. In 1973, oil
embargoes and the resulting increased energy costs caused the energy-intensive rub-
ber-reclaiming process costs to rise sufficiently to match virgin-polymer costs. In-
creased radial-tire production also led to the need for more crack-resistant rubber
compounds than could be provided by reclaimed-rubber compounds.

Tire Retreading

About 36 X lo6 automobiie tires and 13 i:lo6 truck, bus, and off-the-road tires
were retreaded in 1974 (36), and it is doubtful that retreading has increased since then
with the increase in radial-tire sales. Retreading has been the most cost-effective al-
ternative to recycling rubber. However, worn retreaded tires usually are discarded
in a landfill. Approximately 50%of discarded tires are retreadable and only about half
of these are retreaded, since the remaining tires are not inspected before they are
discarded.
 VOl.
1008 RECYCLING (RUBBER)

Grinding

Rubber-reclaiming devulcanization, pyrolysis, rubber in asphalt, and other r e -

cycling processes generally use ground scrap-rubber tires. The tires are mechanically
ground sometimes by cryogenic or solvent swelling techniques. In one process, a polar
solvent is used to swell the rubber and then to reduce particle size by shearing (37).
In the rubber-reclaiming industry, ground tire-crumb rubber is commonly referred
to as rubber reclaim, even though the rubber has not been devulcanized.
Generally, tires are mechanically ground with a two-roll, grooved rubber mill.
T h e two-mill rolls turn at a ratio of ca 1:3, thus providing the shearing action necessary
to rip the tire apart. The rubber chunks are screened and the larger material is recycled
until the desired size is reached. Bead wire is removed by hand or with magnets. For
most applications, ie, devulcanizing, pyrolyzing, asphalt, crumb-rubber particles
smaller than 1.19 mm (16 mesh) are desired. Several milling steps are required to re- cardii
duce the rubber to this size. Tire fiber is removed in intermediate operations with $0.6((
hammer mills, reel beaters, and air tables that blow a steady stream of air across the
rubber, thus separating the fiber. The fiber is baled or is sold as landfill. Because tire fuel,,
grinding is very energy-intensive, tire slitters have been used to cut the tire initially. rubtt
Steel-belted tires usually are not mechanically ground because the steel contaminates will
the rubber.
Cryogenics (qv) in conjunction with mechanical action has been used to make BlBLll
crumb rubber. Nitrogen cools the rubber below the glass transition temperature, and
the brittle rubber is pulverized in a grinding mill. A small cryogenic system can be 1. ((
installed a t the site to recycle process scrap rubber crumb into the compound mixing 2. ll
process. Cryogenic grinding of different rubber types, related costs, and rubber- II
compound properties are well documented (37-41). Cryogenic-grinding costs are 3. 11
$0.20/kg-$0.40/kg, depending on the desired particle size and the type of rubber. !!
4. ..
Generally, harder rubber tends to grind more easily. Ground-rubber scrap can be 5.
dewlcanized, pyrolyzed, or recycled directly into the rubber compound. Ground rubber II
also has been added to plastics (42). 6.

7.
Other Uses
8.

Scrap whole tires have been used for artificial fishing reefs, oyster beds, and as
a floating breakwater. Goodyear has installed more than 2000 fishing reefs made from 9.
old tires. One of the largest reefs is made of 3 X lo6 tires and stretches ca 2.4 km off
10.
Ft. Lauderdale, Florida (43). Tires have also been used as impact absorbers around 11.
highway and bridge abutments (44). Tires are also used in playgrounds, flower planters, 12.
and shoe soles. T h e tire-splitting industry cuts tires intb pieces for gaskets, shims, dock
bumpers, shock absorbers, blasting mats, etc. Rubber is sliced from tire tread to make 13.
strips for floor mats. Approximately 3 X 106 of the estimated 200 X 106 scrap tires 14.
generated each year are reused as reefs or by tire splitters. 15..

Economic Aspects 16..

17..
Roughly 75% of the discarded tires are disposed of in landfills; 20% are retreaded; 18,.
191
and 5%are reclaimed, burned for fuel, split, etc. Tire- disposal costs are $0.10-$3.00 20,
per tire. Cost for incineration without heat recovery is $0.35-$0.70 per tire. Dis-
 --
Vol. 19 RECYCLING (RUBBER) 1009

Table 1. Cornparalive Fuel Costs

Source $/GJ
coal (at %4/t)b 158
oil (No. 6 fuel oil a t $0.195/Lc)h 4.66
natural gas (at $70/101 m3 d ) b 1.89
rubber
whole tire (at $O.Ofi/kg) 2.03
ground (at $0.20/kg) 6.77
To convert $/GJ to $/IO6 Btu, multiply by 1.054.
* Ref. 35.
To convert L to gal, divide by 3.785.
To convert m1 to ft3, multiply by 35.31.

carded-tire transportation can cost $0.04/kg, and size reduction can cost $0.20/kg-
$0.60/kg.
Probably the best alternative for rubber recycling on a large scale would be as
fuel, although the fuel-cost increments for natural gas and coal are lower than scrap
rubber. Costs of various fuels are compared in Table 1. As fuel costs escalate, there
will be more incentive to use scrap tires for fuel.

BIBLIOGRAPHY

1. C.Crane, R. A. Elefritz, E. L. Kay, a n d J. R. Layman, Rubber Chem. Technol. 51,577 (1978).

2. R. H. Snyder, V. R. Vincent, and F. C. Querry, paper presented at the National Tire Disposal S y m -
posium, J u n e 1977, Washington, D.C.
3. Personal communication with A-1 Refuse Service, Crow and Sons Sanitary Landfill and Pit, Estes’
Service Co., a n d West Side Sanitary Landfill, Sept. 3, 1981.
4. Personal communication with t h e cities of Fort Worth, Arlington, and Dallas, Texas, Sept. 3, 1981.
5. L.L.Gaines and A. M. Wolsky, Energy Conservation Through Alternatiue Uses A N L I C N S V - 5 , Ar-
gonne National Laboratory, Dec. 1979.
6. W. J. Markiewicz and M. J . Granksy, Solid Waste Management Series SW-22, U S . Department of
Health, Education, and Welfare, PB203619, 1972.
7. E. R. Moats, Resource Recou. Conseru. 1(3),315 (1976).
8. M.Weintraub, A. A. Orning, and C. H. Schwartz, Experimental Studies of Incineration in a Cylindrical
Combustion Chamber, U.S. Bureau of Mines RI 6908, U.S. Department of the Interior, Washington,
D.C., 1967.
9. Anonymous; and personal conversation with D.Kennedy, Dyna Electronics C o p , McLean, Va., Dec.
1981 a n d Jan. 1982.
10. R. Niles, Uniroyal, Inc., O x f o ~ det.,
, personal communication, J u n e 1981.
11. F. Querry, Paper presented a t National Tire Disposal S y m p o s i u m , J u n e 1977, Washington, D.C.
12. R. H. Taggart, Shredded Tires as Auxiliary Fuel, General Motors Report, March, 1975 and personal
communication with Warren Underwood (GM), J a n . 1982.
13. C.C. Humpstone, E. Ayres, S. G. Keahey, and T. Schell, Internat Res Technol. PB234602 (1974).
14. A Unique and Eflective Waste Tire Treatment Process, J a p a n External T r a d e Organization (Jetro),
Jan. 1980, pp. 32-35.
15. B. L. Schulman and P. A. White, Pyrolysis of Scrap Tires Using the Tosco I1 Process--Progress Report,
rept. ACS S y m p . Ser. 76 (1978).
16. C. E. Haberman. paper presented at Rubber Division ACS Symposium, May, 1977, Chicago, 111.
17. Chem. Eng 52 (Aug. 2,1976).
18. Personal communication with Paul White, Tosco Co., Los Angeles, Calif., Dec. 21, 1981.
19. R.Fletcher and H. T. Wilson, Resource Recou Conseru 5(4), 333 (1981).
20. J. E. Lunde, private conversation on July 22, 1981.
1010 RECYCLING (RUBBER)

21. W. Kaminsky, Resource Recov. Conseru. 5(3), 205 (1980); \V. Kaminsky, W. blenzel, and H. Sin,l,
Cortseru. Recycl. 1(1), 91 (1976); W. Kaminsky and H. Sinn, Kunsloffe 68(5), 14 (1978); H. Sinn, i y ,
Kaminsky. and J. Janning, AtigPui. Chem. I n t . Ed Engl. 15,669 (1976).
22. Personal communication with Dr. hl, hlatsuo, Nippoll Zeon of America, New Y o r k , Dec. 21, lysl.
23. Y. Saeki and G. Suzuki, Rubber Age 108,33 (Feb. 1976).
24. G. P. Bracker, Conseru. Recycl. J(3). 161 (1981).
25. d. A. Beckman, G . Crane, R. A. Elefritz, E. L. Kay, and J . R. Laman, paper presentcd a t the /Votio,tcr/
Tire Disposal Symposium, dune 14-15, 1977, Washington, D.C.
26. J . W. Larsen and B. Chang, Rubber Cliem. Technol. 49, 1120 (1976).
27. G. Crane and E. L. Kay, paper presented a t Rubber Division, ACS Symposium, Oct. 1974, Philadelphin,
Pa.
28. G. Crane, J. W. Fieldhouse, and E. I,. Kay, Rubber Chem. Technol. 48,62 (1975).
29. G. Crane, E. L. Kay, and L. B. it'akefield, J . Elastomers Plast. 7, 372 (1975).
30. G. Crane and E. L. Kay, Rubber Chem. Technol. 18, SO (1975).
31. Industrial Recovered Materials Utilization Targets /or t h e Rubber Industry, prepared f o r U.S. DOE,
Assistant Secretary for Conservation and Solar Energy, Office of Industrial Programs, by Hittinan
Associates, Inc., 1980.
32. Data Collection arid Analysis Pertinent to the PA's Decelopment o/ Guidelines for Procurement o/
Highway Construction Products Containing Recovered Afaterials, Draft, Vol. 1, Issues and Technical
Summary, EPA Contract 68-01-6014, by Franklin Associates, Ltd., and Valley Forge Laboratory, Inc.,
July 6, 1981.
33. J. P. Paul, Chemtech 9, 104 (Feb. 1979).
34. D. S. le Beau, Rubber Chem. Technol. 40,217 (1967).
35. Chem. Week, 35 (May 23, 1979).
36. W..J. Sears, p a p e r presented a t E P A conference, Apr. 2, 1975. Copies available from the Rubber
Manufacturers Association, 1901 Pennsylvania Avenue, NW, Washington, D.C., 20006.
37. W.0. Murtland, Elastomerics 110,26 (Mar. 1978).
38. L. J. Ricci, Chem. Eng., (July 4, 1977).
39. W. 0. Murtland, Elastomerics 109(12), 39 (1977).
40. D. J. Zolin, N. B. Frable, a n d J. F. Gintilcore, p a p e r presented at the 112th Meeting of ACS Rubber
Division, Cleveland, Ohio, Oct. 4-7, 1977.
41. M. C. Kazarnowicz, E. C. Osmundson, .J. F. Boyle, and R. W.Savage in ref. 40.
42. D. Tuchman and S. L. Rosen in ref. 40.
43. Rubber World 67 (Oct. 1978).
44. E. R. Moats, paper presented a t the National Tire Disposal Symposium, June 14-15,1977, Washington,
D.C.
45. U S . DOE, Energy Information Administration, National Energy Information Center, Washington,
D.C., December 21, 1981.

General References

Refs. 7, 19, and 21 are general references.

W. J . Search and T.E. Ctvatnicek, "Resource Recovery Systems for Nonrecappable Rubber Tires," Resource
Recou. Conseru. 2(2), 159 (1976).

J O H N ]PAWL
Pedco Environmental, Inc.

RECYCLING, WATER. See Water, reuse.

REFRACTION. See Analytical methods.

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