Waloryzacja produktów recyklingu opon

V alorisation o f p o st-c o n su m er tyre g ro u n d r u b b er

Wanda Parasiewicz

’1

Marek Tulik*

Rubber crumb (average particle size below 0.3 mm) was modified in va­

rious way and admixed to the virgin matrix compound. Fatigue to failure test and cut growth were chosen as main validation parameters. These are the most sensitive factors determining the influence o f rubber crumb on the properties of new rubber compounds. The best results were achieved when rubber crumb was Agnieszka Rogaczewska*, modified by addition o f functionalized rubbers such as epoxidased NR, maleini- Kinga Makuła* se^ EPDM,or carboxylated NBR. In all cases the significant improvement o f fatigue resistance was observed. It was possible to introduce up to 20% o f

modified fine powder keeping the level o f fatigue to failure comparable with matrix compound.

Key words: tyre recycling, grinded rubber, rubber crumb modification, fatigue resistance, valorisation o f recycled material

Waloryzacja produktów recyklingu opon

Miał gumowy o granulacji poniżej 0,3 mm poddano modyfikacji powierzch­

niowej różnymi metodami i dodawano do sporządzanej mieszanki gumowej.

Jako parametry do oceny skuteczności modyfikacji przyjęto właściwości zmę­

czeniowe wulkanizatów. Najlepsze rezultaty uzyskano w wyniku modyfikacji miału gumowego kauczukami funkcjo na li zo w any mi, jak np. epoksydowany NR, karb oksy low any NBR lub maleinizowany EPDM. We wszystkich przypadkach spowodowało to poprawę odporności na wielokrotne zginanie, która utrzymy­

wała się na poziomie wulkanizatów bez dodatku miału gumowego.

Słowa kluczowe: recykling opon, miał gumowy, modyfikacja miału gumo­

wego, wytrzymałość zmęczeniowa, waloryzacja produktów recyklingu opon

1. Introduction

Over a billion tyres are sold worldwide each year and subsequently just as many fall into category end of life tyres. European Landfill of the Waste Directive in­

troduces ban in landfill of used tyres (since 2003) and shredded tyres (2006). It create the challenge for pro­

ducers and users of tyres to develop efficient way of end of life tyres recovery [1]. Material recycling is the one of more preferable method of recovery of the voluble material.

The first step of tyre recycling is size reduction, usually by grinding. Rubber crumb of different size received in such kind of processes has limited area of application, because its admixing to new rubber com­

pounds results in significant drop of mechanical proper­

ties.

The main target of our work was to find such modi­

fication system of crumb rubber and rubber matrix compound, which allows obtaining new rubber mate­

rial with satisfactory properties.

The particles of crumb rubber could be modified only on their surface. Many attempts of different kind of such modification have been already performed

* Rubber Research Institute, Piastów, Poland

(1,2,3). The idea was to improve interface adhesion between crumb particles and new rubber matrix, but the main target of application of this material to new tyre compound still could not be achieved mainly, because of limited resistance to flexing. For this reason we choose fatigue to failure tests as the most appropriate way of product validation parameter. The target of our investigation was:

• to find modification systems of rubber crumb and rubber matrix compound, in order to obtain new rubber material with satisfactory properties

• to extend the application of rubber crumb by using significant amount of rubber powder in retreading compounds.

2. Materials

Comparison was made between 4 types of com­

mercially available rubber powders (table 1,2):

• made from tire treads with size range below 0.4 mm and 0.4-0.7 mm; produced by Bolechowo R.C (sample MB), and sample MK produced by Muelsner Recycling

• buffings, only fraction below 0.4 mm produced by Geyer-Hosaja R.C. (sample MGH)

• ground vulcanisates of tread compound, made in RRI Laboratory (sample FP).

TOM 10 wrzesień - październik 2006 r. ^{nr 5}

Table 1. Material description according CWA14250 [4]

Tabela 1. Charakterystyka materiałów wg CWA 14250 [4]

,

BH

mm Source Technology

Fine powder MB

MK

F

F 0 1 o TT

TT

A K

Powder MB2 F 0.4 — 0.7 TT A

Buffings MGH B p i o TT B

Grinded tread compound FP FM p 1 O 4^ Matrix Comp. Laboratory mill

Table 2. Chemical properties o f tested rubber powders Tabela 2. Właściwości chemiczne badanych miałów gumowych

0s

i

MB

_ _ _

MB-2

---.—

M6H FP 1 Method

Acetone extract, % 9.8 5.9 9.8 10.5 10.5 ASTM D 297-1993

Ash, % 8.9 7.8 8.9 5.8 6.3 ISO 247-1996

Sulfur content, % 2.1 2.3 2.1 2.2 2.4 ASTM D297-1993

Rubber, % NR/SBR/BR 57 57 57 52 53 IS0/DIS 99924-1

Carbon black, % 28 30 28 29.5 32 TGA

Specific surface m2/g 0.30 0.19 0.44 0.52 0.32 BET IS05794-1

Particle size distribution determined by light microscope-Multiscan study [5]

Piet. 1. Light microscopy picture x50, o f MB sample (ambient, below 0.4 mm embedded in EPDM)

Fot. 1. Obraz mikroskopowy miału gumowego MB (frakcja poniżej 0,4 mm) osadzonego w EPDM, uzyska­

ny za pomocą mikroskopu optycznego, powiększenie 50 x

--- ►

Fig. 1. Particle size distribution, o f sample MB (am­

bient, below 0.4 mm, embedded in EPDM) [5]

Rys. 1. Rozkład wielkości cząstek miału MB-1 obliczo­

ny na podstawie badań mikroskopowych miału gumo­

wego osadzonego w EPDM

Piet. 2. Light microscopy picture x50, o f sample MK (cryogenic, below 0.4 mm, embedded in EPDM) Fot. 2. Obraz mikroskopowy miału gumowego MK (frakcja poniżej 0,4 mm) osadzonego w EPDM. Mikro­

skop optyczny, powiększenie 50 x

Stcwfont&ity nr 5 wrzesień - październik 2006 r. TOM 10

Fig. 2. Particle size distribution, sample MK (cryo­

genic, below 0.4 mm embedded in EPDM)

Rys. 2. Rozkład wielkości cząstek miału MK obliczony na podstawie badań mikroskopowych miału gumowego osadzonego w EPDM

Piet. 3. Light microscopy picture, o f sample FP x50 (below 0.4 mm, embedded in EPDM)

Fot. 3. Obraz mikroskopowy miału gumowego FP (frakcja poniżej 0,4 mm) osadzonego w EPDM; mikro­

skop optyczny, powiększenie 50 x

Fig. 3. Particle size distribution, sample FP (below 0.4 mm embedded in EPDM)

Rys. 3/ Rozkład wielkości cząstek miału FP obliczony na podstawie badań mikroskopowych miału gumowego osadzonego w EPDM

Piet. 4. Light microscopy picture x50, o f sample MGH (below 0.4 mm embedded in EPDM)

Fot. 4. Obraz mikroskopowy miału gumowego MGH (frakcja poniżej 0,4 mm) osadzonego w EPDM; mikro­

skop optyczny, powiększenie 50 x

Fig. 4. Particle size distribution, sample MGH (buffing, below 0.4 mm embedded in EPDM)

Rys. 4. Rozkład wielkości cząstek miału MGH obliczo­

ny na podstawie badań mikroskopowych miału gumo­

wego osadzonego w EPDM

3. Experimental

Applied testing method for evaluation of the pro­

perties of rubber compounds containing rubber powder.

All test have been performed according ISO standards listed in table 3.

Table 3. Testing methods o f physical properties o f rub­

ber compounds

Tabela 3. Metody badań właściwości fizycznych mie­

szanek i wulkanizatów

P ropertie s determ ined Name of standard

Mooney viscosity ML(1+4)100 PN-ISO 289-1:1998 Monsanto ODR AM, dNm PN-IS0-3417:1994 T90, min

T2, min

Tensile strength (TS), MPa PN-ISO 37:1998 Elongation at break (Eb), %

TOM 10 wrzesień - październik 2006 r. nr 5

Hardness (H), ShA PN-ISO 868;1998 Abrasion resistance by rotating

cylindrical drum device, mm3 / 4 0 m ISO 4649:2002 Fatigue to failure ISO 6394: 1998 De Mattia flex life IS0-132:2000

The influence of particle size on the properties of rubber com­

pounds with admixed rubber powder

To evaluate the influence of rubber powder particle size on properties of vulcanizates MB granulate was divided on three fractions by sieving:

MB < 0.4 mm (compound SI); MB - 0.4-0.7 mm (compound S2); MB >0.7 mm (compound S3)

Rubber powder was then added to tyre tread com­

pounds in quantity of 20%.

The result of testing of mechanical properties in comparison with matrix compound (SO) are presented in fig. 5 and 6.

Fig. 6. Fatigue to failure (ISO 6394) o f rubber com­

pounds containing ^{2 0} wt % o f different particle size rubber powder: SO - no powder added; SI - MB<0.4 mm admixed; S2 - admixed MB 0.4-0.7 mm; S3 - ad­

mixed MB>0.7 mm (100% - elongation, 2 Hz fre­

quency)

Rys. 6. Odporność na wielokrotne zginanie (wg ISO 6394) mieszanek zawierających 20% wag. miału gumo­

wego o różnej wielkości cząstek: S0 - bez dodatku miału; SI - z dodatkiem miału MB<0,4 mm; S2 - z do­

datkiem miału MB 0,4-0,7 mm; S3 - z dodatkiem miału MB>0,7 mm

Fig. 5. Tensile strength o f rubber compounds contain­

ing 20 wt % o f different particle size rubber powder: SO - no powder added; SI - MB<0.4 mm admixed; S2 - admixed MB 0.4-0.7 mm; S3 - admixed MB>0.7 mm Rys. 5. Wytrzymałość na rozciąganie mieszanek zawie­

rających ^{2 0}% wag. miału gumowego o różnej wielkości cząstek: S⁰ - bez dodatku miału; SI - z dodatkiem miału MB<0,4 mm; S 2 - z dodatkiem miału MB 0.4-0.7 mm; S3 - z dodatkiem miału MB>0.7 mm

As it is shown the higher loses of flex resistance and lower tensile strength were indicated when larger particle size powder was used. The results confirm that for appli­

cation to the rubber compounds and for further modifica­

tions powder of lower particles size should be used.

Surface treatment

The following options of surface treatment of rub­

ber powder were applied:

Wet method

• Oxidation in perhydrol (50 wt.% dispersion of rub­

ber powder/ 72 hrs). After drying, the sample was mixed in Brabender Plasticorder with octade- canole. It was expected that some hydroxyl group could appear on the surface of rubber particles ready for reaction with octadecanol. In our earlier work [6] we have found that ocadecanol easy mi­

grate in rubber compound so it could be good com- patibilizer for powder particles and rubber matrix.

• Water dispersion of rubber powder was heated dur­

ing one hour, then methacrylates together with di- cumyl peroxide (DCPO) and ferric sulphate were added to the reaction mixture. Two types of methacrylates were used: 2-hydroxyethyl metha­

crylate and dimethylaminoethyl methacrylate.

[7,8]

Dry mixing method

• Mixing of rubber powder with addition of a modi­

fier in Brabender Plasticorder, temp.l50°C

• mixing of rubber powder with addition of a modi­

fier in a laboratory mixer, temp.l20°C

P rop erties of rubber com­

pounds containing modified rubber powders

Modified rubber powder was evaluated in rubber compounds based on a typical SBR formulation (SBR - 100; N-330 - 50; aromatic oil - 12; ZnO - 1; stearic acid - 1; TMQ - 1; CBS - 1.4 ; sulfur -1 .8 ; phr).

Result of tests, for compounds contained 20 wt. % of rubber powder are shown in fig.7-10.

StoA tw ienty nr 5 wrzesień - październik 2006 r. TOM 10

Fig. 7. Tensile strength o f rubber compounds contain­

ing ^{2 0} wt. % o f rubber powder treated with perhydrol and/or octadecanol: SO - matrix compound; MO - con­

taining 20 wt. % o f not modified powder; M2 - contain­

ing 2 0 wt. % o f powder treated by perhydrol and oc­

tadecanol; M3 - containing 20 wt. % o f powder treated by octadecanol only

Rys. 7. Wytrzymałość na rozciąganie mieszanek zawie­

rających 2 0% wag. miału gumowego modyfikowanego perhydrolem i/lub oktadekanolem: MO - mieszanka bez dodatku miału; M2 - zawierająca 20 wag. miału pod­

danego działaniu perhydrolu i oktadekanolu; M3 - za­

wierająca 2 0 wag. miału poddanego działaniu okta­

dekanolu

Fig. 9. Tensile strength o f rubber compounds contain­

ing ^{2 0} wt. % o f rubber powder treated with methacry­

lates: SBR - matrix compound; SBR-0 contained not modified rubber powder; SBR-H contained rubber powder treated with 2-hydroxyethyl methacrylate;

SBR-D contained rubber powder treated with dimethyl- aminoethyl methacrylate

Rys. 9. Wytrzymałość na rozciąganie mieszanek zawie­

rających 2 0% wag. miału gumowego modyfikowanego metakryłanami: SBR - mieszanka bez dodatku miału;

SBR-0 mieszanka z dodatkiem miału niepoddanego mo­

dyfikacji; SBR-H mieszanka z dodatkiem miału podda­

nego m odyfikacji metakrylanem 2-hydroxyetylu;

SBR-D z dodatkiem miału poddanego modyfikacji metakrylanem dimetyloaminoetylu

Fig. 8. Fatigue to failure (IS06394) o f rubber com­

pounds containing ^{2 0} wt. % o f rubber powder treated with perhydrol and/or octadecanol: SO - matrix com­

pound; MO - containing 20 wt. % o f not modified pow­

der; M2 - containing 20 wt. % o f powder treated by perhydrol and octadecanol; M3 - containing 20 wt. % o f powder treated by octadecanol only (^{1 0 0}% - elonga­

tion, 2 Hz frequency)

Rys. 8. Odporność na wielokrotne zginanie (wg ISO 6394) mieszanek zawierających 20% wag. miału gumo­

wego modyfikowanego perhydrolem i/lub oktadeka­

nolem: MO - mieszanka bez dodatku miału;M2 - zawie­

rająca ^{2 0} wag. miału poddanego działaniu perhydrolu i oktadekanolu; M3 - zawierająca 20 wag. miału pod­

danego działaniu oktadekanolu (^{1 0 0}% wydłużenia, częstotliwość 2 Hz)

The data in fig.7 and fig.8 refers to compounds contained: rubber powder treated with octadecanol M 2(q+e)? after oxidation; M3(+£)treated only with oc- tadecanol? in com parison with original compound (SBR) and compound with not modified rubber powder (M l).

Extremely good results of „fatigue to faille” test have been received for sample M(q+E)> which run al­

most 2 times longer than original SBR compound. Sig­

nificant improvement, specially in comparison with not modified powder, was found in the case of application sample M(+e) treated only with octadecanol without oxidation.Tensile strength in all compounds with rub­

ber powder is lower, but for compounds with modified powder the results are better.

In fig.9 and fig. 10 the properties of compounds with 10 wt % of rubber powder modified with 2-hy- droxyethyl methacrylate (SBR-H) and dimethylami- noethyl methacrylate (SBR-D) are presented. There is not any positive influence on tensile strength, but flex resistance measured as De Mattia flex life (ISO-132) is better for compound containing the modified powder then not modified (SBR-0).

Application of modified powder to retreading compounds

This part of our investigation we start with tread compound produced by one of Polish manufacturer of

TOM 10 wrzesień - październik 2006 r. SCa&twteM/ nr 5

Fig. 10. De Mattia flex life (ISO-132) o f rubber com­

pounds containing 2 0 wt. % o f rubber powder treated with methacrylates: SBR - matrix compound; SBR-0 contained not modified rubber powder; SBR-H con­

tained rubber powder treated with 2-hydroxyethyl methacrylate; SBR-D contained rubber powder treated with dimethylaminoethyl methacrylate

Rys.10. Odporność na wielokrotne zginanie na apara­

cie De Mattia mieszanek zawierających 20% wag.

miału gumowego modyfikowane go metakry łanami:

SBR - mieszanka bez dodatku miału; SBR-0 mieszanka z dodatkiem miału nie poddanego modyfikacji; SBR-H mieszanka z dodatkiem miału poddanego modyfikacji metakrylanem 2-hydroksyetylu; SBR-D z dodatkiem miału poddanego modyfikacji metakrylanem dimetylo- aminoetylu

tread compounds for retreading, for sale to SME’s re- treaders.

At the first stage of our experiments rubber powder (FM) was prepared from the same compound.

The idea was to assure the best test repeatability. To obtain the powder, the compound was vulcanised, ground on laboratory mill, polished in Condux labora­

tory granulator, then sieved. Only the fraction below 0.4 mm was used for the next steps.

Table 4. Properties o f tread compounds contained dif­

ferent quantity o f FP

Tabela 4. Właściwości mieszanek bieżnikowych z do­

datkiem różnych ilości miału FM

Property/compound S-0 TIO T20 T30 Mooney viscosity

ML(1+4)100 48 57 65 69

Monsanto ODR AM,

160°C, dNm 65 67 67 64

T90, min 10 9 8 8

T2, min 3 4 4 4

TS, MPa 20 17 16 15

Eb, % 365 391 423 376

H, ShA 62 64 65 58

Abrasion resistance, mm3 110 108 110 105

It was expected that addition of the same material to matrix compound could not deteriorate the proper­

ties. To check this point the compounds with different quantity of not modified FM have been made. The properties of compounds with 10 (T10), 20 (T20) and 30 (T30) wt. % of added FM in comparison to original compound (TO) are shown in table 3.

It was found that admixing even the same material in form of vulcanised powder influenced the properties of final product. This effect is stronger when higher quantity of FP was added. For further tests 20 wt.% of the admix was chosen.

Treatment of FP powder

•Modification by TOR

Vestenamer 8012 was homogenized with 37.5 phr of aromatic oil in elevated temperature to obtain ho­

mogenous solution which was added to FM in a Bra- bender Plasticorder and mixed 10 min in 150°C. The same procedure was repeated in laboratory mixer and then for further operating atl00°C during 10 min.

• Modification by functionalized rubbers: ENR (epoxidised NR with 25 wt. % of epoxy group), car- boxylated NBR (Krynac X I.46), commercially avail­

able EPDM grafted by maleic anhydride (Royaltuf 485) Rubbers have been added to FM and mixed in labora­

tory mixer atl20°C for 10 min.

Modified powder have been added to tread com­

pounds in quantity of 20 wt. %.

The results of tests in comparison with original compound (SO) and reference compound containing not modified powder are presented in tables 4, and fig. 11.

One can find that modification of rubber powder by functionalised rubbers results in significant improve­

ment of flex resistance of vulcanizates containing modified FM. De Mattia flex life and fatigue to failure reach the level of original tread compound.

S& zdtw t& iy nr 5 wrzesień - październik 2006 r. TOM 10

Fig. 11 .D e Mattia Flex Life (ISO-132) (S-0 original compound; R-0 compound containing not modified FM; R-l compound containing FM modified by TOR;

R-2 compound containing FM modified by ENR; R-3 compound containing FM modified by XNBR; R-4 com­

pound containing FM modified by M-EPDM

Rys. 11. Odporność na wielokrotne zginanie za pomocą aparatu De Mattia (ISO-132) mieszanek zawierających

2 0% wag. miału gumowego modyfikowanego kauczu­

kami funkcjonalizowanymi

Table 5. The influence o f modified FM on properties o f tread compounds contained ^{2 0} wt. % o f rubber powder (S-0 original compound, R-0 compound containg not modified FM, R-lcompound containing FM modified by TOR, R-2 compound containing FM modified by ENR; R-3 compound containing FM modified by XNBR; R-4 compound containing FM modified by M-EPDM)

Tabela 5. Wptyw modyfikacji miału FP na właściwości mieszanek bieżnikowych z dodatkiem 2 0% wag. miału

Com pound

S-0 R-C R 4 R-2 R-3 R4

Modifier n.a. TOR EN R XN BR M -E P D M

ML(1+4)100 48 65 56 63 65 67

AM,dNm 65 67 65 63 63 70

T90, min 10 8 7 8 7 9

T2, min 3 4 4 4 4 3

TS, MPa 17,5 16.0 16,4 16,9 16,8 18,1

Eb, % 365 423 317 423 411 374

H, ShA 62 65 64 63 58 66

Abrasion, mm3 110 105 94 88 74 66

4. Comments & Conclu­

sions

• The main problem limiting the application of rub­

ber powder for tyre compounds is significant loss of fatigue resistance.

• Even a fine rubber powder, prepared from the same rubber compound, adversely effects the original compound.

• It was shown that modification of rubber powder could be achieved even by its co-mixing with rub­

bers containing functional groups

• The positive results obtained by addition of ENR, M-EPDM, XNBR, and TOR suggest the possibility of increasing bond strength between rubber powder particles and rubber matrix by means of easy adapted, simple method.

• However, because of different structure of the ap­

plied polymers the nature of these interactions is complex.

• Further investigation of these complex interactions should help to find new solutions for valorisation of tyre recycling material

• Very good flex resistance was achieved by surface modification of rubber powder with octadecanol.

Two different mechanisms are possible: estrifica- tion of hydroxyl group on the surface of oxidised powder particles and improvement of compatibi­

lity between FP and matrix compound.

• The results of our investigation show the possibi­

lity to introduce up 20 wt% of rubber powder to retreading compounds without significant loss of flex resistance. This is a promising way of increas­

ing the application of rubber powder originating from end-of-life tyres. Nevertheless the investiga­

tion with application of commercial rubber powder are to be continued and further testing of other im­

portant properties influencing performance of tyres will be conducted.

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The research presented in this article have been performed in frame o f research project 4 TO E 033 24 financed by Ministry o f Science and Higher Education

Badania przeprowadzono w ramach projektu badawczego 4 TO E 033, finansowanego przez MNiSW

TOM 10 wrzesień - październik 2006 r. SfaA tw t& ity nr 5