T/73International Polymer Science and Technology, Vol. 31, No. 5, 2004

Polimery, 2004, 49, No. 2, p. 110-113

Polyurethane elastomers filled with granulated rubber

M. CzuprynskiB.Z.P.G. Stomil SA

Selected from International Polymer Science and Technology, 31, No. 4, 2003, reference PT 04/02/110; transl. serial no. 15126

Translation submitted by J.E. Baker

In concern for the environment, ways are constantly beingsought for recycling used articles made of plastics andrubber. The technologies for recycling are adapted to thetype of plastics and rubber products. Plastics wastes areusually employed, after grinding, as an addition to primarymaterial (Refs. 1-4). There are, however, considerabledifficulties in reusing rubber wastes, mainly comprising cartyres, but also other rubber wastes arising during productionof cars and during their recycling (Ref. 5). Many methodsare known for management of these wastes, for exampleincineration, pyrolysis, regeneration, gasification, andhydrogenation, but grinding is the most widely usedmethod. The latter process can give rubber granules withparticle size above 1 mm, textile wastes and wire. Thetextile cord can be removed and incinerated, and steel wirecan be sent, as scrap, to the steelworks (Ref. 6).

The granulated rubber can be reused as filler in theproduction of rubber compounds. It belongs to the groupof inert fillers, which do not cause an increase in strengthor hardness of vulcanisates. Incorporation of small amountsof granulated rubber makes it possible to maintain therequired physical-mechanical parameters of thevulcanisates (Refs. 7, 8).

Granulated rubber can be converted to reclaimed rubber,which is then used in the production of rubber compounds(Ref. 9). This makes it possible to reduce the consumption ofraw rubber, as well as the consumption of plasticisers andvulcanising agents. Reclaims are also used for the purposeof facilitating the processing of rubber compounds duringcalendering. Many methods have been developed for theregeneration of rubber made from natural rubber and fromsynthetic rubbers, such as styrene-butadiene rubber (SBR),butadiene rubber (BR), butyl rubber (isobutylene isoprenerubber, IIR), butadiene-acrylonitrile rubber (nitrile-butadienerubber, NBR) (Refs. 10-12).

The rubber granules obtained by grinding car tyresand other rubber wastes are used as filler or modifier invarious types of plastics compositions, such as polyethylene(PE) and polypropylene (PP) (Refs. 13, 14), epoxy resinsand polyurethane resins. An example is a material forfloor coverings made from epoxy resins filled withgranulated rubber, which is characterised by goodcompressive strength and wear resistance (Ref. 15).Ground rubber wastes are also used as fillers of asphaltcompositions, for use as an agent for bonding tar paperto concrete surfaces (Refs. 16, 17).

Granules from used car tyres have also foundapplication as filler for polyurethanes. Depending on thetype of raw materials used in the production ofpolyurethanes, we can obtain: linear thermoplasticpolyurethanes, polyurethane elastomers, polyurethanefoams, resins, varnishes and protective coatings, adhesivesand pourable sealing compounds, sheet coating goods,and polyureas. The extensive possibilities for usingmaterials of this type arise from their favourable properties,such as: low water absorption, good chemical resistanceto weak acids and strong bases, good abrasion resistanceand, in the case of fibres and films, high dimensionalstability (Ref. 18).

Incorporation of rubber granules with size from 1 mmto 4 mm in polyurethane with concentration of freeisocyanate groups of 30% gives a product that ischaracterised by a long storage and crosslinking time(Refs. 19, 20). Filling is also used for polyurethanescontaining from 15 to 40% of isocyanate groups modifiedby oil or water-oil dispersions (Ref. 21). These filledpolyurethanes are used for making polyurethane-rubbercompounds, of high elasticity, which makes it possible touse them as surfacing material for sports grounds andrunning tracks.

T/74 International Polymer Science and Technology, Vol. 31, No. 5, 2004

The present work describes the effect of rubber granuleswith diameter of 2 mm as filler in a polyurethane elastomerwith concentration of free isocyanate groups 12%, on themechanical properties of polyurethane-rubber compounds.

EXPERIMENTAL

Materials

Characterisation of the materials used is presented inTable 1.

Synthesis of polyurethane prepolymer

Preparation of the polyurethane-rubber compounds waspreceded by synthesis of a polyurethane prepolymercontaining free isocyanate groups in an amount of 12%.“Poles 55/20N” was placed in a glass reactor equippedwith a thermometer and stirrer, heated until it melted and,after connecting to a vacuum pump, it was submitted to adehydration process (80°C, 2.5 h, vigorous stirring).Then, after the temperature had fallen to 60°C and afterdisconnecting the vacuum pump, still stirring vigorously,decanted liquid MDI, preheated to 40°C, was added inthe amount required for obtaining the specifiedconcentration of free isocyanate groups in the prepolymer.Synthesis was carried out at 110°C under reduced pressurefor 1.5 h. The prepolymer thus obtained was conditionedfor 24 h, and then the concentration of free isocyanategroups was determined.

Composition and method of preparation ofthe compounds

Polyurethane-rubber compounds with the compositionshown in Table 2 were produced in a mixer consisting ofa mixing chamber and a stirrer.

In order to produce compound P0, 1,4-butanediolwas added as chain extender to the prepolymer. Thecrosslinking time was 5 min.

The polyurethane-rubber compounds P1, P2, P3, P4and P5 were produced in the mixer by introducing,

successively, granules with diameter of 2 mm and a smallamount of liquid prepolymer, sufficient for preliminarywetting of the granules, and then adding the remainingprepolymer while stirring vigorously. The mixing time forthe polyurethane-rubber masterbatches was from 2 to 8min, depending on the amount of granules introduced. Achain extender was introduced into the masterbatchesthus prepared, and crosslinking was carried out for 20min. Finished samples of the compounds were conditionedfor 24 h prior to testing.

Specimens intended for investigations of mechanicalproperties were in the form of plates with the dimensions107x117x2 mm. They were obtained by pressing thecorresponding compounds in a hydraulic press, at 90°Cand at a pressure of 5 MPa. The pressing time was basedon observation of the crosslinking time of the unfilledpolyurethane P0 at the stipulated temperature. Specimensfor investigating hardness and elasticity were made in thesame conditions of pressing.

METHODS

Determination of the content of free isocyanategroups in the prepolymer

0.5-1 g of the prepolymer was placed in a 250-cm3

conical flask and was dissolved in 6 cm3 of 0.5 M solutionof dibutylamine in chlorobenzene. Then 30 cm3 of acetonewas added and the dibutylamine excess was titrated with

slairetamwarfotsiL.1elbaT

lairetamwaR emanlacimehC rerutcafunaM

IDM etanaycosiid-'4,4-enahtemlynehpiD ynamreG–reyaB

"N02/55seloP" )etapidaenelyhte(ogilO ASmehcaZ-akinagrOenzcimehCydalkaZzczsogdyB,skroWlacimehC

rednetxeniahC loidenatuB-4,1 ynamreG–FSAB

rebburdetalunarG)selunargretemaidmm2( – owohceloB–amuGHUPP

rebbur-enahteruylopehtfosnoitisopmoC.2elbaTsdnuopmoc

ehtfolobmySdnuopmoc

%.tw,noitisopmoC

remyloperP selunargrebbuR

0P 001 0

1P 09 01

2P 07 03

3P 05 05

4P 03 07

5P 01 09

T/75International Polymer Science and Technology, Vol. 31, No. 5, 2004

0.1 M solution of hydrochloric acid in the presence ofbromophenol blue until a yellow coloration was obtained.The content of free isocyanate groups was found from theamount of dibutylamine determined, that had reactedwith them.

Strength tests on specimens of polyurethane-rubber compounds

The following mechanical properties were tested:

– tensile strength and relative elongation at break(Ref. 22),

– abrasion resistance (Schopper-Schlobach method)(Ref. 23),

– hardness (Shore, scale A) (Ref. 24).

RESULTS AND DISCUSSION

Figure 1 shows the variation in hardness of polyurethane-rubber compounds as the amount of granulated rubber inthe polyurethane elastomer increases.

The unfilled polyurethane elastomer P0 has hardnessof 90 °Sh. Incorporation of filler in the polyurethaneelastomer in an amount of 10 wt.% does not cause achange in hardness of the compound obtained, andincreasing the amount of filler to 30 wt.% only reduces thehardness by 2% relative to the value corresponding to theunfilled polyurethane. On adding up to 50 wt.% of rubbergranules, a compound is obtained whose hardness is only10% lower. Further increase in the amount of filler causesa more marked decrease in hardness, which reaches avalue that is 33% less than the original value when thefilling with granules is 90 wt.%.

Polyurethane elastomers are characterised by hightensile strength (TSb). Figure 2 shows the results ofmeasurements of the tensile strength of the elastomer filledwith granulated rubber. The elastomer without filler (P0)is characterised by tensile strength of 15 MPa. As can beseen from Figure 2, filling of polyurethane elastomercauses a systematic decrease in tensile strength.Introduction of up to 10 wt.% of granules reduces thetensile strength of compound P1 by 10%. With up to 30wt.% of filler in the polyurethane elastomer, the compoundsobtained still retain high resistance to the action ofdestructive forces. However, use of granulated rubber inan amount of 50-90 wt.% causes a considerable decreasein tensile strength of the elastomer, which greatly limits thepossibilities for practical application of these compounds.

As well as investigating tensile strength, we alsoinvestigated the elongation at break (Eb). Figure 3 showsthe results of measurements of elongation at break ofpolyurethane-rubber compounds. Despite a marked dropin tensile strength with filling of polyurethane elastomerfrom 10 to 30 wt.%, compounds P1 and P2 do not exhibit

Figure 1. Effect of granulated rubber (GG) content onpolyurethane elastomer Shore hardness

Figure 2. Effect of granulated rubber (GG) content onpolyurethane elastomer tensile strength (TSb)

Figure 3. Effect of granulated rubber (GG) content onpolyurethane elastomer unit elongation at break (Eb)

a large decrease in elongation at break. The unfilledpolyurethane elastomer reaches elongation at break of270%. Addition of 30 wt.% of filler caused a decrease in

T/76 International Polymer Science and Technology, Vol. 31, No. 5, 2004

elongation by just 7%, relative to the unit elongation of theunfilled elastomer. A much larger decrease in elongationat break occurs when the polyurethane elastomer is filledto more than 30 wt.%. Compound P3 exhibits a differencein Eb value of 60%, compared with the unfilled elastomer.Further increase in filling from 70 to 90 wt.% does notcause any larger changes in the value of the elongationat break.

In addition to very good tensile strength and highelongation at break, polyurethanes are also characterisedby very good abrasion resistance. Figure 4 shows theresults of measurement of the loss of volume as a resultof abrasion of polyurethane elastomer filled withgranulated rubber. In the case of the unfilled polyurethaneelastomer P0 the loss of volume as a result of abrasionwas 0.130 cm3. Incorporation of granulated rubbercauses a decrease in abrasion resistance of polyurethane-rubber compounds. A low degree of filling from 10 to 30wt.% increases the volume losses of compounds P1 andP2 from 12 to 46% relative to unfilled polyurethane.With increase in filling to 50 wt.%, the abrasion resistanceis 90% worse than in the case of the unfilled elastomerP0. The very high degree of filling of compounds P4 andP5 (70 and 90 wt.%) caused an increase in volume lossby 130 and 161% respectively, though the results attainedcan be compared with results characterising somegeneral-purpose rubber products.

CONCLUSIONS

The following conclusions can be drawn from thetest results:

– Comparison of the results of tests on unfilled polyurethaneelastomer and the polyurethane-rubber compoundsindicates that granulated rubber is an inert filler. Itcauses a decrease in the resistance of polyurethaneelastomers to the action of external forces.

– Use of granulated rubber as filler in polyurethaneelastomers in amounts from 10 to 30 wt.% causes asmall decrease in tensile strength of the polyurethane-rubber compounds. There is also a slight decrease inelongation at break and hardness, but this does notlimit the possible applications of these elastomers.

– Increasing the amount of granulated rubber above30% causes a significant worsening of the mechanicalproperties of polyurethane-rubber compounds. Thereis then a substantial decrease in hardness, tensilestrength, elongation at break and abrasion resistance.

REFERENCES

1. M. Bielinski: Polimery, 1992, 37, 364.

2. W. Perzynski and J. Jeczalik: Polimery, 1983,28, 210.

3. A.K. Bledzki and K. Goracy: Polimery, 1992,37, 241.

4. J. Polaczek and Z. Machowska: Polimery, 1996,41, 69.

5. W. Parasiewicz and K. Kosinska: Polimery,1994, 39, 136.

6. R. Gaczynski and L. Slusarski: Polimery, 1985,30, 237.

7. M. Czuprynski, S. Zajchowski and K. Piszczek:Effect of granulated rubber wastes on theproperties of rubber compounds. Proc. IXInternational Scientific Conference “Recycling inMachine Construction” (IX-ICMR ’99), Bydgoszcz1999, p. 187-193.

8. R. Sendlewski: Polimery, 1982, 27, 113.

9. J. Magryta: Polimery, 1993, 38, 132.

10. Polish patent 102 884 (1981).

11. Polish patent 134 935 (1986).

12. Polish patent 116 793 (1982).

13. Polish patent 177 682 (1999).

14. E. Kowalska et al.: Polimery, 2003, 48, 633.

15. Polish patent 165 450 (1994).

16. Polish patent 163 603 (1994).

17. I. Gawel and L. Slusarski: Polimery, 1998, 43, 280.

18. W. Szlezinger: “Plastics”. FOSZE EducationalPublishers, Rzeszów 1998.

19. Polish patent 147 545 (1989).

20. Polish patent 150 248 (1990).

21. Polish patent 175 891 (1999).

22. PN-ISO 37: 1998.

23. PN-ISO 4649: 1999.

24. PN-ISO 48: 1998.

(Received 1.4.2003)

Figure 4. Effect of granulated rubber (GG) content onpolyurethane elastomer volume loss at abrasion