New Used Tire Recovery Process For Value-Added · PDF fileNEW USED TIRE RECOVERY PROCESS FOR VALUE-ADDED ... of the cryogenic process at liquid nitrogen ... New Used Tire Recovery

NEW USED TIRE RECOVERY PROCESS

FOR VALUE-ADDED PRODUCTS

Dr. Klementina Khait

BIRL, Industrial Research Laboratory

Northwestern University

Evanston, IL 60201-3135

ABSTRACT

The goal of this work is to demonstrate a novel pulverization process

known as solid state shear extrusion (originally developed in the former USSR)

for used tire recovery. Whole tire products and tread tires have been

successfully pulverized into fine powder of different particle sizes and size

distribution. The powder which is formed by shear deformation under pressure

coupled with an extensive cooling has unique particle shape and morphology and

is somewhat reactive.

This novel pulverization process is both technically and economically

superior to other known tire grinding processes.

INTRODUCTION

At present, scrap tires are converted into crumb rubber by either

mechanical or cryogenic size reduction technology. Because of the high cost

of the cryogenic process at liquid nitrogen temperatures, mechanical size

reduction by chopping and grinding at ambient temperature is used more often.

Tires are shredded to about 3/4-inch chips followed by a magnetic separation

of steel and removal of polyester fiber. The rubber chips are then reduced to

rough, smaller pieces by a cracker grinder or granulator in a series of

screening and re-grinding operations to achieve the desired particle size of

about 500 microns.

For the traditional rubber "reclaim," crumb rubber is mixed with water,

oil and chemicals and heated under pressure. During this process the carbon­

sulfur bonds are ruptured, and rubber becomes parti ally de-crossl inked (or

devulcanized) and capable of being shaped into slabs. These slabs are shipped

to tire manufacturers as an alternative to virgin rubber for use in tires or

other rubber products. Since reclaimed rubber has reduced elasticity, it is

currently used in only about Z percent of new tires.

The novel used tire recovery process originally was developed as a joint

effort between the Academy of Science in the former Soviet Union and Berstorff

Maschinenbau GMBH of Germany. This process, based on Solid State Shear

Extrusion (SSSE) is both technically and economically superior to all other

known processes. The SSSE process, also referred to as Elastic Deformation

Grinding (EDG), is governed by high shear and pressure. It utilizes

Berstorff's co-rotating, inter-meshing twin-screw extruder1 which converts

coarsely- shredded used tire pieces of about 1/4 inch to a small-particle­

size, high-surface, area, somewhat reactive powder. The extruder has

proprietary screw configurations and is equipped with a chiller for rapid

cooling of the powdered rubber during the pulverization process. The

resultant fine tire powder is sorted by vibration screens and is subsequently

transported by a conveyor to a sacking station.

cnUMB RUBBER

PULVERIZATION OF USED TIRES

Berstorff's pilot scale twin-screw extruder 2E-40A was used for

pulverization trials. Used-tire samples of tread rubber (TR) and whole-tire

product (WTP) were donated by Baker Rubber Inc., South Bend, IN. WTP was also

given by Tire Technology Inc., Rockton, IL, and peel rubber was provided by

Rouse Rubber Industries, Vicksburg, MS. Schematics of the SSSE (or EDG)

pulverization process is depicted on Figure 1. Crumb rubber of approximately

1/4" size was fed into the extruder with a designed screw configuration to

convert rubber int: powder of different particle size and particle size

distribution. Coarse to fine product of 5-100 mesh (4000 to 149 microns)

could be obtained in one pass through the extruder. In order to produce finer

powder of 100-200 mesh (149 to 74 microns) or smaller, two passes through the

'--. -

~---------------------------- -------------,

First Pass I

Cooting WnlOf

Second Pass

TIRE POWDER

PARTICLE SIZE RANGE

I P .... : COllrDD to

F1no

II Pa1ll8:

5· 100 40nO· ,.1"

flnD to 100. 200 149· ,.1 Ultratln. or smaller

FIG. 1. - Novel Pulverization Process: Solid State Shear

Extrusion (SSSE) or Elastic-Deformation Grinding (EDG).

extruder are needed. All tire samples contained polyester fiber which did not

affect the pulverization process. About 300 pounds D~ t1re powders o~ various

particle sizes were, produced in one and two passes through the pulverization

extruder and characterized.

CHARACTERIZATION OF TIRE POWDER

Physical and chemical characterization of tire powder included sieve

analysis, appearance and uniformity by microscopy and acetone extraction test.

Sieve-screening analysis was performed according to Baker Rubber Inc.'s test

method using 5g of talc with 100g of pulverized tire, la-minute cycle time

with 2 rubber balls on one screen. A mechanically operated Ro-Tap Sieve

Shaker, U.S. standard sieves, and rubber balls with 1.S-inch diameter were

used. Sieve analysis results for Baker Rubber samples are presented in Tables

1-4. Samples have been taken from the top, middle and bottom of the bag

containing 20 pounds of pulverized tire rubber. As can be seen from the sieve

analysis data, the majority of particles pulverized from WTP rubber in one

pass had a mesh size larger then 35 (0.029") with slight variation from 66.8%

(top), to 64.6% (middle), and 61.2% (bottom). When WTP rubber was pulverized

the second time, the particle size of that powder was further reduced, as

expected, and ranged from 51.1% (top), to 50.3% (middle), and 49.7% (bottom).

More fine powder of 60 mesh and 80 mesh have been made in a second pass.

Similar results were obtained for the powder pulverized from tread rubber

(TR)j samples that were pulverized in one pass had a particle size larger than

35 mesh which was quite consistent throughout the bag, ranging from 65.2%

(top) to 66.2% (middle), and 65.5% (bottom). When the TR sample was

pulverized the second time, the particle size of that powder was practically

urichanged. Sieve-screening analysis of the "peel" rubber (Tables 5,6) from

Rouse Rubber Industries, Inc. pulverized with Berstorff's extruder was similar

to that of WTP and TR rubber samples from Baker Rubber, Inc.

The appearance and uniformity of tire powders was studied by scanning

electron microscopy (SEM) at 40X and 250X magnification using a Hitachi model

S-570. Micrographs of the 1/4-inch WTP and TR rubber from Baker Rubber, Inc.

before and after pulverization, as well as Baker WTP-30 and TR-30 made by

conventional grinding, are shown in Figures 1-21. The WTP and TR samples used

as a feedstock consisted of irregular rod-like or diamond-like chunks of

rubber. Particles of the WTP, TR and peel samples after pulverization had a

cauliflower-like, open morphology with large surface area. Some particles

contained embedded fibers. In comparison, the conventionally ground rubber

had particles with a flat, smooth fracture surface with a relatively small

surface area. Rubber powder made using Berstorff's first commercial-size

twin-screw extruder contained primarily cauliflower-shaped particles ranging

from 50 to 500 microns.

Acetone extraction tests on pulverized tire rubber WTP, TR and

conventionally ground tire rubber showed that pulverized samples had higher

acetone values compared to ground ones. Pulverized samples had 12.6% acetone

value versus 11.6% for ground samples and pulverized TR samples showed 14.6%

acetone value versus 11.5% for ground samples. The acetone extraction data

suggest that some devulcanization of rubber probably took place during the

pulverization process.

EVALUATION OF TIRE POWDER

Tire powder ha~ been evaluated in "soft" tread compounds. The

compounding of pulverized tire powder was performed by an outside service

laboratory, Midwest Custom Mixing Inc., North Miami, Oklahoma. Pulverized WTP

and TR samples were added to the "control" soft-tread rubber compound at 5

weight percent. Samples were mixed for 10 minutes at 1700F using a 6-inch

laboratory mill, followed by compression molding. Slabs were cured for 20

minutes at 3200 F and die-cut into test specimens. An addition of 5 weight

percent of pulverized tire rubber to the "control" soft tread compound did not

affect the 100% modulus, shore A hardness and tear die C properties of the

resultant material. However, the tensile strength of the samples containing

pulverized tire rubber decreased from 2947 psi for the "control" (no added

rubber) to 2210 psi for the sample with TR powder, and to 2080 psi for the

sample with WTP powder. Elongation decreased from 820% for the "control"

sample to 750% for TR powder, and to 740% for WTP powder. The Mooney

viscosity and curing characteristics of the "control" sample were comparable

to those of the samples containing pulverized WTP and TR powder.

Tire powder has been also evaluated in asphalt mixes by Koch Materials

Company, Asphalt Division, St. Paul, Minnesota. Various properties of

rubberized asphalt need to be considered for hot-mix applications. These

properties include viscosity at high temperature for appropriate mixing and

compacting processes, consistency at high and moderate payment-surface

temperature, elastic and elongation properties. Asphalt cement with

penetration 120-130 was used. Asphalt cement and tire powder were mixed at

400°F for 1 hour under constant stirring. The absolute viscosity of

-,

, . rubberized asphalt containing 5% of pulverized tire rubber was measured as

1990 poise at 140°F which is three times higher than that of asphalt cement

(791 poise). This suggests significant reaction occured when the pulverized

powder was added to the asphalt cement.

In addition of obtaining used tire powder with ·open" morphology and

large surface area, this novel pulverization process is more energy efficient

than existing cryogenic or ambient grinding processes. According to Berstorff

Maschinenbau, the specific energy consumption during extrusion pulverization

ranges between 0.3 and 0.9 kw/kg2 depending upon the type of rubber and

particle size desired2. Tire powder made by the SSSE technology would

facilitate recycling of used tires and increase use of this reconstituted

material.

APPLICATIONS DEVELOPMENT

In order for this novel reclamation technology to have an impact on waste

tire recovery, end-uses have to be developed. Fine, somewhat reactive powder

could find uses in a broad range of value-added products. Traditionally,

crumb rubber has been used to make floor mats, various rubber goods, adhesives

and asphalt products. Additional uses for crumb rubber include running tracks

and athletic surfaces, children's playgrounds, and garbage cans.

Due to its unique particle morphology and large surface area, tire powder

made by the SSSE process would be well-suited for use in a variety of rubber

compounds, asphalt mixes, and blends with other materials because it would

lead to faster incorporation and better dispersion of the powder in those

mixes. In addition, tire powder could be used in civil engineering

applications for crash barriers, railroad crossings, and others.

SUMMARY

A new SSSE pulverization technology for recovering used tires has been

successfully demonstrated. The particle size of the tire powder ranged from

50 to 500 microns.

It has been observed that particles of tire powder produced by the new ,

pulverization technology had cauliflower-like shapes (a large surface area) as

opposed to the irregularly shaped rod-like or diamond-like, mostly flat

particles (a small surface area) of the tire powder produced by conventional

grinding techniques. A large surface area is advantageous in such applica-

tions as asphalt mixes and blends with other materials because they will

permit faster incorporation and better dispersion of the rubber in those

mixes.

It has been also noticed that the tire powder made by the SSSE method is

somewhat reactive. The acetone extraction data suggest that some

devulcanization (un-crosslinking) took place during the pulverization process.

Initial evaluation of the tire powder in the asphalt mix showed a higher

increase in viscosity than that of the asphalt mix with conventionally ground

tire rubber, as indicated by a sedimentation test and viscosity.

The first tire recycl ing 1 ine us.ing the Berstorff equipment on a

commercial scale is now operational in Germany, with a throughput of about

1000 lbs./hr. The process is more energy efficient and requires less

maintenance than currently used batch processes involving repetitive size

reduction.

This once-through process represents a significant breakthrough in waste

tire recovery, facilitating tire recycling and increasing end-uses of

reconstituted tire rubber in value-added products.

ACKNOWLEDGEMENTS

The author is grateful for financial support provided by the Illinois

Department of Energy and Natural Resources and in-kind contribution from Baker

Rubber, Inc. Donation of rubber samples by Baker Rubber, Inc., Rouse Rubber

Industries, Inc., and Tire Technology, Inc. is greatly appreciated. The

author would like to thank Mr. Richard Kwarcinski for assistance in testing.

REFERENCES

1 G. Capelle, presented at a meeting of the Rubber division, American

Chemical Society, Detroit, MI, October 8-11, 1991.

2 R. Lipp, presented at Recycle '91, Fourth Annual International Forum and

Exposition, Davos, Switzerland, April 3-5, 1991.

T~bla 1. Slava AnAlys1# Rallules lor 3.k." Rubbar ~-rP (lse Paao)

Export=.aeal Condition: (Baker Rubber Inc. m.enod)

;. ~ .. i~ • :00 ;. ,u:alo. ,'0 I"".:::ar n1h :1ft uc lava :114. UlG !: :nn. ':1;:la :':::18.

'10. !:

", , :. :! I !! , :i] '0 ... I :4.0

, .. " I !1: ? ~l!'l i ~JI

I '.a';!!:':

'1 ii •• ,a

1

Z!.i i .1 !.~ I t.: , u

I , !O&.i

I ... .;. ...

.:;a::u::aQ. I ,

I I I 1:1

I '.1 I !.' I ,.. 1 '.I I 0.' I 104.1

I "un ~!:~ I!! 150 !O J 100 J "0 J !fJO I !!O ! L;lln 911.

~~~~;a4 I iiI • .! I %5.1 I a.I I Z.: I l.S I 0.3 I D.l I O.Z /1114.,

~QU: :!'Ut ~jqDt MUi:leQ em b~...;m: j:llll(B.'u) h: nil -.'Iq:st .. ;'lot ila,jur~.

Table 2. 51 ... AIzal.yai.G ltaault.. tor 3&ur Rubbar WT.P (2nd P&lJa)

~.r1aeDcal. Condic.1.oaz (BUar )I.u1)bu Inc. mechod)

'1. ilic: ... l:C ;. IUiDia. :to ~:bar "Alls 04 u= nay. ;lUI. 1M 10 ain. :,c:lo :~::III.

'01i=': :a'UUUtd

" Sll.l

"'!sn S!:, , !S

I ' •. , _OHj:'t': ;IIU:l'ltG

" I

!O

lZ.l

'0 I .s.; 1Z.3

I ,. lO

I !5.0 I !:l.!I

I ~fJa I ~~ I ~~o I uo I 'l.?t:t

~a4.5

I :~o I Ito , !:o ! !:!o I L'ln ~.al.

15.Q I '.J I !.' I 0.' I 0.' I

I leo It .. I 1':0 I Z10 I 3.i'tn ~.al.

,. , I ' . 1;,0 I 1.0 I 0., , '.' I !O".l

~~bla J. Sleva Analysis aOGUles lar Saker Rubber :1 (lsc ?assl

~ar1l1uulcal ~nd1t1oQ: (Baker RubbaC' tn&::. ::.achod)

1. ':"li: • :00 i. :.a=i •• :to :""'::::111" :~il; :n Uc:I fHY. ;:.an. inc ... :::1-:. ::1ch ::::a.

j .••.• " . '1 l,-" I' :l.; ::iat~:l"lllC !:;1 '

~.: , ., I"" I ,.. • .• '!!:::! '1.~1:t

I ,., I!"

I !!:l 1 ?.?'In :.a I,

1 0.' I '" !C~.J

Tub 4. 5te .... ..\AD1Yliu a..ault. tor 84Jc.u !bUlbar :It (2nd. ?au)

Expa~Dtal Condit.ioa: (Baker Rubbar I~c. ~.thod)

S q. i.aic: - loa ;. sam;lia. 110 r"J:=er :Oliis :n UQ $1 ..... ~~. !lid Ie :'n. 1:7;:la :~:: ••

!oiq:t; . 'Ilia.l I 13.3 1 '.0 "aUlnoa (~l

1 "'!!n S'!:!I ! ;5' 1 ;0 !O

·.Ietqn: I .U 1 n.; I

i.o.S ilat,unllC 1~1

!'Ie. 1: ~.a=i! .. ~ :ot'::=

j "'!S;'I S'!:!I !! I ;0 !O

I .•• 13.l '''al;n; i iD.! 1 " .. ita>;:u:ta: ! ! r~l

!11.

1 " : 1 loS 1'" I'" 1,·1 ::';'.2

j l:C I ;.10 J !!l0 i Z:!!I , ~ ,'In :,1.

1 ' " I'" 1 C.l 1 a.1 ., ,., ~O4.. ~

I

I "0 I :~ I !':!I J no 1 ~. ~1:'1 :l !.

I I.' ' , , i ,.; I·· . i '.: I" .. .,. ,

I ! I I

li ,I " j

Tabla 5. Sieve AnaJysls Results far Rousa Rubber (1st pass)

.: ;. 7.ic - :Co ;. iUIDI., :to :-JImOr :&11s :Ill UCl savo :UI. tM ::: ~11. :-,-ei. ':.~=.

:~a ~~ ::0 ~. ~.-'\" :11

: •• IO'n; 1 :a . .! J Z~ • .i j 3.; i .:;etitnltG II I I' i ''':~

, ! • .t. i

J..; : ~ . .: I Z.J ~-:J.i

I !

!"'un 5:!;v l !! : ~o r ~o :::0 i !.to ' !~O I !!o ! ~. '1" ~Ii.

/ ...... I :a.l I za.~ /, .. !l.l "., i J.' I Z - ::l.-' 1.tllnN : !

I ., ':1 , ,

~'n 51:1 115 I 50 r!1I I 100 I l.tO I 200 I !~II I :J.?ln ; ~JI.

~r" /57.3 / za.; /'.' / J..J /'.' /'.' i 1.J / z.. / 111>.1

Talli. 6. SI ... AooIys1. _Its far·-' _ (2nd P""

E.:r:=er1..u.1 CGad1t1=: {BUr R!Ii88er IDC- aardrei}

5 g. ToI.lc • llJO g. ussla. no r"IltICa" bails em oadl sitv. :JB .... 10 .nd. C)'Clo t1 ...

"'" s , . .. ..... !III

l ~sn s1ZI' J 25 I ., I" I !DO I ". I ZOO ! no' ! !.Ptn : 3&1.

WeUPlt /7 •.• Ila.1 / s.; /1.' /1., / a •• i a.: / a., ) 1114.6 ~.Ulned '":1 I

!fa. 2: 5&l1li1. ~ 1II1ddh

: ~ ,if:.. i:!S I so J so ! 100 '!'O J 200 ! nil r !.?tn ; 3 .. 1.

~~:od /.18.5 Ill .. j S..J 11.. j 1.5 I D.S / D.a 10•1 i ID4.5

~tJ. !: SUDiI ~ ,ot::::m

! We,n !:~=!I I " J 50 : so ::D '''' I Z,. , nc i Lilln ' lli.

I-.,qnt I ;'7. " i li.3 Is.,; , 1.& I 1.5 I a.' I a.! i D.! :0&.0 ! I

~.tllnCtC ,

! i I I , .. , I

-, Baker RubD~r, ~nc.

TR ~II T=ead RubDI::!::

Baker Rubber, Inc.

?IGC?ES 1- 3 TR USED AS ~ F~~DSTOC~

Baker aubber, Inc. TR !"T=aad Rubber

FIGURES 4-6 WTP USED AS A FEEDSTOCK

Baker Rubber, Inc. WT!' J;" ftlnol e Tire ?roduct WTP !" Whole Tire Product

FIGURES 7-8 CONVENTIONALLY GROUND TIRE RUBBER

'-'b

3ak~r -!\U~:'<::=,

tR ." Ir~aci :!:nc. :tubb,,=

Baker Rubber, Inc. WTP 1"\,1,0 1e Tire ProdUi

Baker Rubber, Inc. \;IP-30

Baker Rubber, Inc. WTP-30

Baker Rubber, Inc. TR-30 mesh Tread Rubber

FIGl:RES 9-11 CONVENTIONALLY GROc~D TIRE RUBBER

Baker Rubber, Inc. TR-30 mesh Tread Rubber

Baker Rubber, Inc. TR-30 mesh Tread RuDbe.

Sake!:' '.-':1 .~ .L_

FIGURES 12-13 weP PULVERIZED I~ ONE ?AS3

~ubber, rIfe. Iso Pass

FIGURES 14-15

3aker 3.uoaer, Inc~ WTP 1st Pass

WTP PULVERIZED I~ TWO PASSES Eaker Rubber, Inc. "iF 2nd Pass

Baker Rubber, Inc. WTF 2nd Pass

Baker Rubber, Inc. TR 1st Pass

Baker Rubber, Inc. TR 2nd Pass

-.

FIGURES 16-18 TR PULVERIZED IN ONE PASS

Baker Rubber, Inc. TR 1st Pass

FIGURES 19-21 TR PULVERIZED IN TWO PASSES

Baker Rubber, Inc. TR 2nd Pass

Baker ~ubber, Inc. TR 150 Pass

Baker Rubber, Inc. rR 2nd Pass