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STUDY OF THE PROPERTIES OF SULFUR OBTAINED BY
DEVULCANIZATION OF AGED RUBBER WASTE
G. Tosh emi o a1, M. Tokhi o 2, R. Adilo 3
Labo a o y assis an , "Clea " LLC1
Doc o o philosophy (PhD) in echnical sciences, Chie Specialis o he Academic Ac i i y
Managemen Depa men , Ins i u e “In e na ional School o Finance Technology and Science” 2
Doc o o echnical sciences, P o esso , Depa men “Technology o high-molecula compounds
and plas ics”, Tashken Ins i u e o Chemical Technology3
h ps://doi.o g/10.5281/zenodo.17290718
Abs ac . In his s udy, he physicochemical p ope ies o ee sul u , isola ed by chemical
de ulcaniza ion o ulcanized ubbe was e, we e comp ehensi ely s udied. The de ulcaniza ion
p ocess was ca ied ou using a mix u e o FeCl3 and CH3COOH, and he e ec i eness o he
p ocess was assessed using iodome ic i a ion, IR spec oscopy, TGA/DTA, SEM-EDS, and XRD
me hods. The esul s showed ha he op imiza ion o de ulcaniza ion pa ame e s ( eac ion ime,
empe a u e, acid concen a ion) di ec ly a ec s he deg ee o C-C and C-C bond b eaking. Based
on iodome ic analysis, up o 80% o he bound sul u was con e ed o ee s a e. The esul s o
IR spec oscopy and he mog a ime ic analysis showed changes in he s uc u al and he mal
s abili y o sul u , while SEM-EDS clea ly desc ibed mo phological changes. The ob ained esul s
e ealed he possibili y o using de ulcanized sul u as an en i onmen ally sa e and p omising
aw ma e ial o indus y.
Keywo ds: de ulcaniza ion, ubbe was e, sul u , iodome ic i a ion, IR spec oscopy,
TGA/DTA, SEM-EDS, XRD, physicochemical p ope ies, en i onmen al sa e y.
In oduc ion. In ecen yea s, he issue o p ocessing ubbe was e and p oducing p oduc s
wi h high added alue has become one o he mos p essing en i onmen al and economic p oblems
on a global scale. In pa icula , ulcanized ubbe was e causes signi ican damage o he
en i onmen due o i s ine ness and e y slow decomposi ion in na u al condi ions[1][2].
The e o e, he de elopmen o e icien , en i onmen ally iendly, and cos -e ec i e echnologies
o p ocessing such was e is conside ed one o he p io i y a eas o mode n scien i ic esea ch [3].
The high mechanical s eng h o ulcanized ubbe s is de e mined by he p esence o many
co alen C-C and C-C bonds in hei s uc u e. The p ocess aimed a pu pose ully b eaking hese
bonds and es o ing he p ocessing p ope ies o ubbe is called de ulcaniza ion[4][5].
De ulcanized ubbe ma e ials a e used as a p omising aw ma e ial in he p oduc ion o polyme
composi e ma e ials (PCM) wi h high mechanical, he mal, and chemical p ope ies by
composi ion wi h polyme ma ices [6], [7].
Among he a ious de ulcaniza ion me hods, he me hod o chemical bond b eaking is o
pa icula impo ance o inc easing he p oduc i i y o C-C and C-C bonds using a mix u e o
hyd ochlo ic and ace ic acids. This me hod is ca ied ou a ela i ely low empe a u es, p ese es
he mechanical p ope ies o he es o ed elas ome , and allows o he con ol o he
physicochemical p ope ies o composi e ma e ials by op imizing he p ocess pa ame e s [8]-[10].
The pu pose o he esea ch. The main goal o his esea ch is an in-dep h analysis o he
physicochemical p ope ies o sul u , isola ed as a esul o he chemical de ulcaniza ion o aged
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ubbe was e. The main ask o his wo k is o assess he e ec i eness and selec i i y o he
p ocess, expand he possibili ies o i s indus ial and en i onmen al applica ion by de e mining he
mo phological, he mal, and chemical p ope ies o he isola ed sul u , as well as o c ea e a
scien i ic basis o he de elopmen o en i onmen ally iendly and economically iable
echnologies o p ocessing ubbe was e.
Resea ch objec and me hods. Vulcanized ca i es and echnical ubbe was e we e
selec ed as he objec o his s udy. These was es ha e high s eng h and decompose e y slowly
in he na u al en i onmen due o he p esence o nume ous co alen C-C and C-C bonds in hei
s uc u e [11], [12]. The e o e, du ing he p ocessing o was e, he me hod o chemical
de ulcaniza ion was used o he pu pose o selec i ely b eaking hei sul u bonds and es o ing
hei p ocessing p ope ies [13]. This me hod was ca ied ou as ollows:
Chemical de ulcaniza ion is ano he de ulcaniza ion me hod o ob aining de ulcanized
ubbe , whe e he ea men is ca ied ou using a chemical o de ulcanizing agen o b eak down
he sul ide modi ica ion ne wo k o he ubbe i e, and o en his me hod is combined wi h he
he mal and mechanical de ulcaniza ion p ocess o inc ease e iciency. In ade, hese chemicals
come om he classes o alipha ic, alkylphenol sul ides, amines, a oma ic me cap ans, zinc sal s,
di/sul ides, and unsa u a ed compounds. Since hese compounds ha e he p ope y and endency
o eac wi h adicals o med as a esul o he b eaking o bonds, hey a e o en used o p e en
he phenomenon o ecombina ion o molecules. Table 1 p esen s a lis o some chemicals s udied
as de ulcanizing agen s acco ding o he classi ica ion g oup, Figu e 1 shows he speci ic app oach
o chemically based de ulcaniza ion.
Classi ica ion o some de ulcanizing agen s
Table 1
Amine and ammonium
compounds
O ganic sul ides and
me cap ans
Sul u - ee o ganic and
ino ganic compounds
Thiolamine
Xylene hiols
Sodium dissol ed
Te a-bu yl-ammoniacina e
(II)
Diphenyl disul ide
Li hium aluminum
hyd ide
N, N-dialkyl a yl amines
Phenol sul ides
Supe c i ical CO2
Figu e 1. Chemical de ulcaniza ion scheme
The de ulcaniza ion p ocess was ca ied ou using a mix u e o hyd ochlo ic and ace ic
acids (FeCl3/Cl2 + CH3COOH). This mix u e selec i ely b eaks he S-S and C-S bonds in
ulcanized ubbe h ough he p o ona ion and oxida ion s ages, eleasing ee sul u in he o m
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o hyd ogen sul ide [14]. The isola ed H2S gas was cap u ed in a solu ion o cadmium ace a e and
sodium ace a e and quan i a i ely analyzed by iodome ic i a ion [15].
In o de o op imize he p ocess pa ame e s, he in luence o empe a u e, ime, and eagen
concen a ion was s udied sepa a ely. The esul ing sul u was in es iga ed using he ollowing
mode n analy ical me hods: Iodome ic i a ion - o de e mining he amoun o ee sul u and
assessing he e ec i eness o de ulcaniza ion [14], IR spec oscopy - o analyzing he bonds in
he molecula s uc u e o sul u [15], TGA/DTA - o de e mining he he mal s abili y and
decomposi ion empe a u e o sul u [16], SEM-EDS - o s udying he mo phology and elemen al
composi ion o pa icles [17], XRD - o analyzing he deg ee o c ys allini y and phase
composi ion [18]. The in eg a ion o hese me hods allows o a comp ehensi e assessmen o he
physicochemical p ope ies o he isola ed sul u and de e mines he possibili ies o i s indus ial
and ecological applica ion [19], [20], [21].
Resul s and analysis. As a esul o he de ulcaniza ion p ocess, he sul u bonds inside
he ubbe s uc u e - especially he C-C and C-C bonds - a e b oken, and a se ies o ee o weakly
bound sul u compounds a e o med. The quan i a i e and quali a i e cha ac e is ics o his sul u
can be de e mined, and he deg ee o hei sepa a ion o p ese a ion in he polyme ma ix can be
assessed using he ollowing analy ical me hods.
Fo his, i a ion was ca ied ou by he mos e ec i e classical me hod o de e mining he
amoun o ee sul u in he de ulcanized sample using he iodome ic i a ion me hod.
The esul s o de e mining he sul u con en in he sample be o e and a e de ulcaniza ion
using he iodome ic i a ion me hod a e p esen ed in Table 2. Ini ially, he change in he
concen a ion o sodium hiosul a e solu ion om 0.01 M o 0.005 M was s udied.
Table o he dependence o sul u con en on he amoun o sodium hiosul a e solu ion
based on iodome ic i a ion in de ulcanized ubbe samples.
Table 2
№
Ti a ion solu ion
Sul u be o e
de ulcaniza io
n (%)
Sul u a e
de ulcaniza ion
(%)
Change
(%)
1
Na₂S₂O₃, 0.005 M
2.80
0.85
69.6
2
Na₂S₂O₃, 0.01 M
2.75
0.72
73.8
3
Na₂S₂O₃, 0.01 M
2.60
0.65
75.0
4
Na₂S₂O₃, 0.01 M
2.78
0.59
78.8
Analyzing he da a in Table 1, sample No. 1 used a 0.005 M hiosul a e solu ion, and he
sul u yield was 69.6%. The emaining h ee samples we e i a ed a a concen a ion o 0.01 M,
in which he amoun o sul u eleased was highe (73.8-78.8%). This indica es ha when i a ing
wi h a low concen a ion o hiosul a e solu ion, he accu acy is low, and due o incomple e
neu aliza ion o iodine o unce ain y in he i a ion, a smalle amoun o ee sul u is eco ded.
These es s showed ha 73.8%, 75.0% and 78.8% o sul u was eleased, espec i ely.
Based on he di e ence in he p e ious amoun o S (2.60 - 2.78%) and he subsequen dec ease
in he amoun , a signi ican inc ease in he le el o eleased sul u was obse ed. These equency
es s showed a s able and eliable le el o accu acy o a 0.01 M Na2S2O3 solu ion. In pa icula ,
sample No. 4 wi h an exc e ion a e o 78.8% indica es he highes e ec i eness o
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de ulcaniza ion. When i a ing wi h 0.005 M Na2S2O3, he accu acy o sul u is lowe , since in
his case, incomple e neu aliza ion o iodine, p olonged i a ion, and indis inc colo o he
indica o a e obse ed. A 0.01 M Na2S2O3 solu ion is he mos op imal, allowing o a mo e
comple e de e mina ion o he amoun o sul u eleased, wi h no signi ican di e ence in epea ed
es s. The changes in he able di ec ly con i m he e ec i eness o he de ulcaniza ion p ocess in
b eaking sul ide bonds.
A he nex s age o ou esea ch, he in luence o changes in he concen a ion o
hyd ochlo ic acid on he amoun o sul u eleased om de ulcanized ubbe s was also s udied.
The ob ained esul s a e p esen ed in Table 3.
Table o he dependence o sul u con en on hyd ochlo ic acid concen a ion based on
iodome ic i a ion in de ulcanized ubbe samples.
Table 3
№
HCl conc.
(%)
S con en
be o e
de ulcaniza i
on (%)
S con en a e
de ulcaniza ion
(%)
Sul u con en (%)
1
5%
2.75
0.82
70.2
2
10%
2.72
0.63
76.8
3
15%
2.69
0.51
81.0
4
20%
2.66
0.47
82.3
As can be seen om Table 3 below, he o al sul u con en in he samples be o e
de ulcaniza ion was ~2.66-2.75%, which was in bound (C-S, S-S) o ms. The amoun o sul u
a e de ulcaniza ion dec eased wi h inc easing HCl concen a ion: 0.82% a 5% HCl and 0.47%
a 20% HCl. This means ha an inc ease in he amoun o HCl inc eases he a e and dep h o he
de ulcaniza ion eac ion, while he amoun o bound sul u dec eases signi ican ly. When
calcula ing he sul u yield as a pe cen age, he maximum esul was eco ded a 20% HCl
(~82.3%).
In gene al, he amoun o sul u de e mined by he iodome ic me hod in he sample be o e
de ulcaniza ion by iodome ic i a ion a e aged 2.6-2.8%. A e de ulcaniza ion, a dec ease in
sul u con en o 0.6-0.8% was obse ed. This indica es ha as a esul o he p ocess, up o 80%
o he bound sul u was b oken o and ans e ed o a ee o m. Iodome ic i a ion made i
possible o quan i a i ely assess he e ec i eness o he p ocess, and a signi ican dec ease in he
sul u con en con i med he success ul cou se o he p ocess.
A he nex s age o ou esea ch, he s uc u e o de ulcanized sul u and he s uc u e o
pu e sul u we e de e mined using he IR spec um o de e mine he p esence o absence o sul u
bonds (C-S, S-S). They mani es ed hemsel es in he spec um wi h cha ac e is ic ib a ional lines.
The IR spec a o he ubbe c umb, no ini ially de ukanized, a e shown in Fig. 2. Fig. 3 shows
he IR spec a o pu e sul u and sul u a e de ulaniza ion.
In he ini ial ( ulcanized) sample, in ense peaks we e eco ded in he ange o 500-600
cm−1 o he C-C bond and 650-700 cm−1 o he C-C bond. The IR spec a o sul u in Fig. 3
showed a signi ican dec ease in he in ensi y o hese peaks in he pos -de ulcaniza ion spec a.
Also, he appea ance o new C=C bonds o a oma ic g oups may ha e been de ec ed in he ange
o 1600-1700 cm−1. Changes in he IR spec um con i m he decomposi ion o sul u bonds and
di ec ly indica e s uc u al changes.
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Figu e 2. IR spec a o ubbe c umb be o e eac ion
Figu e 3. IR spec a o pu e sul u
Figu e 4. IR spec um o sul u isola ed om de ulcanized ubbe c umbs
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Con inuing ou esea ch, he na u e o he loss o sul u componen s unde he in luence o
hea was s udied using he mog a ime ic analysis. The mal s abili y was analyzed by di e en ial-
he mal and he mog a ime ic me hods on he DTG-60 Shimadzu de ice o Japan in an a gon
medium. Acco ding o he analysis esul s, sul u e apo a ed in he ange o 200-400°C. The
ob ained esul can be seen in Figu e 5.
Figu e 5. TGA analysis by sul u con en
Be o e de ulcaniza ion, up o ~5% o he mass loss in he sample was due o sul u . In he
sample a e de ulcaniza ion, his indica o dec eased o ~1.2-1.5%. This esul also shows ha a
la ge pa o he sul u was eleased om he s uc u e as a esul o de ulcaniza ion. Wi h he help
o TGA, he change in sul u ela i e o empe a u e was de e mined, and his analysis con i med
he iodome ic esul s on a he mal basis.
Based on he esul s o SEM (Scanne Elec on Mic oscopy) and EDS (Ene gy-Dispe si e
Spec oscopy), he changes in he mic os uc u e and sul u dis ibu ion o ulcanized and
de ulcanized ubbe we e compa ed as ollows:
1. Non-de ulcanized ubbe (s a ing posi ion):
SEM image: Sul u -con aining agg ega es (whi e spo s) a e clea ly isible on he ubbe
su ace. These agg ega es we e une enly dis ibu ed, indica ing he accumula ion o sul u du ing
he ulcaniza ion p ocess.
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EDS analysis: The sul u concen a ion is 2.4%, which co esponds o he addi ional
amoun o sul u in ol ed in ulcaniza ion.
2. De ulcanized ubbe :
SEM image: inc eased po osi y ( oids) on he su ace, which is a esul o he elease o
sul u du ing de ulcaniza ion and he des uc ion o polyme ne wo ks. The sul u s ains ha e
signi ican ly dec eased, con i ming he b eakdown o chemical bonds.
EDS analysis: Sul u con en dec eased o 0.7%, which showed a dec ease o
app oxima ely 71%.
SEM images clea ly showed he disappea ance o sul u agg ega es on he su ace o
de ulcanized ubbe and he po osi y o he s uc u e. EDS da a con i med a quan i a i e educ ion
in sul u con en , which indica es he e ec i eness o he de ulcaniza ion p ocess. The esul s
p o ed ha he de ulcaniza ion p ocess plays an impo an ole in emo ing sul u om ubbe
and changing i s physicochemical p ope ies.
Conclusion. In his s udy, he p ocess o chemical de ulcaniza ion o ulcanized ubbe
was e was s udied, and as a esul , he physicochemical p ope ies o he isola ed ee sul u we e
comp ehensi ely analyzed. I was es ablished ha he de ulcaniza ion me hod based on a mix u e
o FeCl3 and CH3COOH selec i ely b eaks C-C and C-C bonds, ensu ing e ec i e sepa a ion o
sul u .
The quan i a i e composi ion, he mal s abili y, deg ee o c ys allini y, and mo phology o
he ob ained sul u we e assessed using mode n analy ical me hods, such as iodome ic i a ion,
IR spec oscopy, TGA/DTA, SEM-EDS, and XRD. The esul s showed ha he op imiza ion o
de ulcaniza ion pa ame e s ( empe a u e, eagen concen a ion, ime) di ec ly a ec s he deg ee
o sul u elease and allows o a signi ican imp o emen in i s quali y indica o s.
The analysis has p o en ha he isola ed sul u can be a p omising aw ma e ial o
p ocessing in a ious indus ies, in pa icula , in ag icul u e, ubbe echnologies, and
en i onmen al p o ec ion p ocesses. The e o e, his esea ch c ea es an impo an scien i ic basis
o he de elopmen o en i onmen ally iendly and cos -e ec i e echnologies o he p ocessing
o ubbe was e.
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13. Q. Zhao, H. Li, and Z. Xu, “Chemical de ulcaniza ion o was e ubbe powde using FeCl₃
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p ocess,” Polyme Recycling, ol. 2, no. 1, pp. 37–47, 1996.
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managemen in he Eu opean Union: A e iew,” Was e Managemen , ol. 32, no. 10, pp.
1742–1751, 2012.
