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Gen­er­al-pur­pose rub­bers:
The group of gen­er­al-pur­pose rubbers

17.02.2023   | Thomas Wutke

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Gen­er­al-pur­pose rub­bers are rub­ber grades that are suit­able for most appli­ca­tion sce­nar­ios in tech­nol­o­gy and indus­try. They lack the indi­vid­ual strengths of spe­cial­ty and high-per­for­mance rub­bers. How­ev­er, they offer the typ­i­cal mate­r­i­al prop­er­ties of elas­tomers at a favor­able price.

Glob­al­ly, gen­er­al-pur­pose rub­bers account for the largest vol­ume share in rub­ber pro­duc­tion (approx. 82 per­cent). When­ev­er a low-cost, heavy-duty elas­tomer prod­uct is to be man­u­fac­tured, they are the first choice.

The most com­mon rub­bers in this cat­e­go­ry include:

Nat­ur­al rub­ber (NR)

Nat­ur­al rub­ber forms the basis for around 40 per­cent of the rub­ber goods pro­duced world­wide. It is obtained from the sap of the “Hevea Brasilien­sis” rub­ber tree, whose main cul­ti­va­tion areas are in South­east Asia. Unlike syn­thet­ic rub­ber, nat­ur­al rub­ber is a regen­er­a­tive raw mate­r­i­al. This sus­tain­abil­i­ty aspect and the low price make NR an impor­tant cor­ner­stone of rub­ber production.

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Orig­i­nal­ly, nat­ur­al rub­ber was the only raw mate­r­i­al for rub­ber pro­duc­tion. There­fore, for a long time it was sim­ply referred to as rub­ber. How­ev­er, this has changed with the devel­op­ment of syn­thet­ic rub­bers. The term now cov­ers all elas­tic poly­mers from which rub­ber is made. 

The mechan­i­cal prop­er­ties of nat­ur­al rub­ber are excel­lent. It has very good elas­tic­i­ty, high tear resis­tance, excel­lent elon­ga­tion and ten­sile strength, and low com­pres­sion set.

NR is resis­tant to water and dilute acids and alka­lis, but should not come into con­tact with sol­vents, oils, greas­es, lubri­cants, gaso­line or water vapor. The aging behav­ior of NR to ozone, (UV) light and weath­er­ing is to be clas­si­fied as mod­er­ate to poor.

Due to its low heat build-up under dynam­ic load and its high ten­sile strength, the main area of appli­ca­tion for nat­ur­al rub­ber is tire con­struc­tion. It is also used in auto­mo­tive and mechan­i­cal engi­neer­ing, for exam­ple for (vibra­tion) dampers or as a bear­ing and cou­pling ele­ment for mov­ing parts. High-puri­ty NR vari­ants are fre­quent­ly processed in the food and med­ical sectors .

Rub­ber har­vest from a rub­ber tree

Styrene buta­di­ene rub­ber (SBR)

Styrene-buta­di­ene rub­ber was devel­oped at the begin­ning of the 20th cen­tu­ry. The aim was to devel­op a low-cost alter­na­tive to the (then) expen­sive nat­ur­al rub­ber and to reduce depen­dence on raw mate­r­i­al imports from South­east Asia. Its start­ing raw mate­ri­als, styrene and buta­di­ene, can be obtained inex­pen­sive­ly from crude oil and nat­ur­al gas, enabling low-cost pro­duc­tion. In terms of quan­ti­ty, styrene-buta­di­ene rub­ber is the most com­mon­ly pro­duced syn­thet­ic rubber.

SBR shows mod­er­ate to good resis­tance to dilute acids and alka­lis, polar sol­vents and water vapor. How­ev­er, it is not resis­tant to non-polar and aro­mat­ic sol­vents, oils, greas­es, lubri­cants and gaso­line. Its aging behav­ior with respect to ozone, (UV) light and weath­er­ing is poor to moderate.

The mechan­i­cal prop­er­ties of SBR are com­pa­ra­ble to those of NR. Tear resis­tance, rebound resilience, abra­sion resis­tance and com­pres­sion set are at a high lev­el. The same applies to wet slip behav­ior. Tear resis­tance is excel­lent if the mate­r­i­al is reinforced.

Styrene-buta­di­ene rub­ber is used pri­mar­i­ly in tire con­struc­tion due to its good wet slip prop­er­ties and low abra­sion. Oth­er appli­ca­tions include engine sus­pen­sions, spring ele­ments, bear­ings, con­vey­or belts and hard-wear­ing floor coverings.

Tires made of SBR for agri­cul­tur­al technology

Buta­di­ene rub­ber (BR)

Buta­di­ene rub­ber, like styrene-buta­di­ene rub­ber, orig­i­nat­ed in the ear­ly 20th cen­tu­ry from the inten­tion to replace nat­ur­al rub­ber with a cheap, read­i­ly avail­able alter­na­tive. Unlike SBR, how­ev­er, BR is almost nev­er used in its pure form. As a rule, it serves as a blend­ing com­po­nent to improve the mechan­i­cal prop­er­ties of oth­er types of rub­ber.

BR exhibits mod­er­ate to good resis­tance to polar sol­vents and dilute acids and alka­lis. It is also char­ac­ter­ized by high rebound resilience, very good abra­sion resis­tance and low heat­ing under dynam­ic loads.

How­ev­er, buta­di­ene rub­ber is not resis­tant to non-polar and aro­mat­ic sol­vents, oils, greas­es, lubri­cants and gaso­line. Its aging tol­er­ance to (UV) light, ozone and weath­er­ing is also poor to mod­er­ate. The same applies to ten­sile strength, elon­ga­tion at break and tear resistance.

Pure BR com­pounds are dif­fi­cult to process. They have to be blend­ed with high pro­por­tions of fillers and/or plas­ti­ciz­ers. In prac­tice, there­fore, they play only a minor role.

Instead, the major­i­ty of BR pro­duc­tion goes to the tire indus­try as a blend­ing com­po­nent. The addi­tion to nat­ur­al rub­ber or styrene-buta­di­ene rub­ber improves their abra­sion and rolling resis­tance as well as elas­tic­i­ty. Oth­er appli­ca­tions for BR-rein­forced elas­tomers include con­vey­or belts, shoe soles, roll cov­ers and bear­ing elements.

NR
SBR
BR
Dilut­ed acids
Mod­er­ate
Mod­er­ate
Mod­er­ate
Mod­er­ate
Mod­er­ate
Mod­er­ate
Mod­er­ate
Hot water
Mod­er­ate
Good
Mod­er­ate
Polar sol­vents
Bad
Mod­er­ate
Mod­er­ate
Non-polar sol­vents
Bad
Bad
Bad
Aro­mat­ic solvents
Bad
Bad
Bad
Min­er­al oils and greases
Bad
Bad
Bad
Gaso­line
Bad
Bad
Bad
Ozone
Bad
Bad
Bad
(UV) light
Bad
Bad
Bad
Weath­er effects
Bad
Bad
Bad

Resis­tance of gen­er­al-pur­pose rubbers

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Autor: Thomas Wutke

Thomas Wutke has been man­ag­ing the Jäger site in Frank­furt am Main since 2020 and was pre­vi­ous­ly respon­si­ble for anoth­er site. He has more than 35 years of expe­ri­ence in sales (KAM/B2B) of rub­ber and plas­tics as well as in project man­age­ment and appli­ca­tion development.

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