DETERMINA
TION OF STYRENE-BUT
ADIENE AND ISOPRENE
DETERMINATIONSTYRENE-BUTADIENE
PARTICULA
ARTICULATE
MATTERTIRE TREAD RUBBERS IN PILED P
ARTICULA
TE MA
TTER

TAKASHI SAITO

Department of Chemical Technology, Kanagawa Institute of Technology, 1030, Shimoogino,

Atsugi-city, Kanagawa, 243-02 (Japan)
ABSTRACTA method of simply and quickly determining styrene-butadiene (SBR) and isoprene (NR)tire tread rubbers in piled particulate matter on a highway was investigated.
The particulate matter was analyzed with a gas chromatograph to which a Curie-point
pyrolyzer was attached. The contents of the SBR and NR tire tread rubbers in the piled
particulate matter were determined by measuring the generated amount of styrene anddipentene (l-methyl-4-isopropylcyclohexene) attributed to the respective rubber polymers
contained in the matter, and the calibration curves of the amounts of the standard tire tread
rubbers plotted against the peak areas of styrene and dipentene generated by the pyrolysis.
The pyrolysis of the rubber polymers was conducted at 590°C for 5 seconds.
The average contents of SBR tire tread rubber in piled particulate matter collected on theinside and outside of a tunnel on the highway were 0.0675-0.0920 and 0-0.0653 wt.%,
respectively, and those of NR tire tread rubber were 0.127-0.176 and 0-0.100 wt.%.

Gas chromatography; isoprene; polymers; pyrolysis; rubber, isoprene; rubber, styrene-butadiene; styrene-butadiene; tires.

INTRODUCTION

It is generally thought that tire tread rubber particles, generated when car
tires are abraded, are a latent pollutant which may tend to cause environmental contamination. Dannis has estimated that the average abrasion ratioof rubber used in one car tire was 90 mg/km [1]. The rubbers used in thetire treads of motor cars are styrene-butadiene rubber (SBR) types containing various additives and a small amount of BR, and isoprene rubber (NR)types containing additives and a small amount of SBR. The SBR are
generally used in the tire treads of passenger cars, and the NR in therelatively large-sized tires of buses, trucks, and the like. The additives
include carbon black, process oil (aromatics), and so forth, which containcarcinogenic polycyclic aromatic hydrocarbons [2-5]. In view of this, it ismore important to monitor the particles of tire tread rubbers as an environmental pollutant.
Some reports have been found on determination of tire tread rubbers
contained in piled particulate matter [6-9]. However, most of the analyticalmethods described in the reports are unsuitable for simultaneous determination of SBR and NR, because the methods employ different separation
conditions for pyrolyzates of SBR and NR which are subjected to gas
chromatographic (GC) analysis.
In this investigation, in order to achieve the simultaneous determinationof SBR and NR, we examined the selection of those pyrolyzates which areuseful as an index for the determination of the rubber polymers, and theseparation conditions for the pyrolyzates, in order that they may be subjected to GC analysis. The results of the investigation were satisfactory.
Moreover, this method was applied to the determination of the contents of
SBR and NR tire tread rubber particles in piled particulate matter collected
at the inside and outside of a tunnel on a highway roadside.

EXPERIMENTAL

Materials
The standard SBR and NR tire tread rubber samples used in the experiment were cured rubber sheets of about 2 mm thickness, which were
supplied by Yokohama Rubber Co. These rubbers were of the same type as
the rubbers used in the tire treads of general economy cars. The sheet-shaped
rubbers were ground with a grinder to provide powder for the experiment.

Apparatus and GC conditions
A Curie-point pyrolyzer (Model JHP-2, Japan Analytical Industry Co.)was coupled directly to a gas chromatograph (Model GC-8APF, Shimadzu)
equipped with a flame ionization detector, which can be equipped eitherwith a packed column or a capillary column.
For the packed column, a 3 m X 3 mm I.D. glass column containing 20%
silicone DC 710 on Diasolid M (60-80 mesh) (Gasukuro Kogyo Co.) wasused. The oven temperature was 165°C. The temperatures of injection anddetection ports were both 190 °C. The carrier gas used was nitrogen and theflow-rate was 30 ml/min.
For the capillary column, a 25 mX0.2 mm I.D. fused silica capillarycolumn coated with 5% phenylmethylsilicone (HiCap-CBP5, Shimadzu) wasused. The column temperature was increased from 60°C to 150°C at a
programme rate of 5°C/min. The temperatures of the injection and detec-

tion ports were both 190°C. The carried gas used was helium and theflow-rate was 0.87 ml/min with a splitting ratio of 1 : 60.
The peak areas of the pyrolyzates were measured by an integrator (Model
C-R3A, Shimadzu).
Procedure
For piled particulate matter samples, piled paniculate matter present on
the surface of 30 cm X 30 cm square at the side of a paved highway werecollected, and were sieved through a 28-mesh sieve so that large particles
were removed, and then dried in a desiccator. Amounts of less than 1 mg of
the dried piled particulate matter samples were weighed out with a microbalance (Mettler), and were placed directly on pyrofoil, and then subjected topyrolysis-GC analysis.
The contents of the SBR and NR tire tread rubbers were determined bypyrolyzing the piled particulate matter samples and measuring the amountsof styrene and dipentene produced, and then using the respective calibration
curve. However, the NR tire tread rubber contained a small amount of SBR
rubber from which styrene was generated. This would cause an error in themeasured content of the SBR tire tread rubber. Accordingly, firstly, theamount of dipentene generated was used to calculate the content of the NR
tire tread rubber in the sample. Then the amount of styrene attributed to the
NR tire tread rubber and contained in the sample was estimated. From theamount of styrene produced by the pyrolysis of the sample, the estimatedamount of styrene was subtracted. By using the difference between theamounts of styrene, the content of the SBR tire tread rubber in the sample
was calculated.
RESULTS AND DISCUSSION

PyrolyzatesFig. 1 shows the pyrograms of the piled paniculate matter sample which
was analyzed by pyrolysis-GC with a packed column and a capillarycolumn. The pyrolysis temperature was 590ｰC, and the time was 5 s. The
peaks of the pyrolyzates were identified by comparing the retention times ofthe standard substances.
The pyrolyzates obtained by the pyrolysis of the SBR tire tread rubber
were butadiene, styrene, benzene, etc., the main pyrolyzates being butadiene
and styrene. In the pyrograms, the styrene peak is apparently separated, butthat of butadiene is insufficiently separated, overlapping the peak of an
unknown substance. Therefore, this study employed the peak of styrene as
an index for determination of the content of SBR tire tread rubber in a piled
particulate matter sample.

On the other hand, the pyrolysis of the NR tire tread rubber gave
isoprene, a main component of the NR rubber, and dipentene, the dimer(cyclization) of isoprene [10-12]. Furthermore, the pyrolysis gave styrene,benzene, toluene, and the like which might be attributed to used SBR,
process oil and so forth. As an index for use in the determination of the NR
tire tread rubber, the dipentene peak was used, because the amount ofdipentene could be determined simultaneously with that of styrene under thesame GC conditions, and the peak of dipentene in the pyrogram was clearly
separated from other peaks.
Pyrolysis temperature
The correlation between the pyrolysis temperature and the pyrolyzates ofthe standard SBR and NR tire tread rubber samples was examined. Fig. 2
shows the results. The comparison of the yields of styrene generated bypyrolyzing the standard SBR tire tread rubber sample at six differentpyrolysis temperatures revealed that the styrene yield increased linearly withthe pyrolysis temperature; For the standard NR tire tread rubber sample,
the pyrolysis at about 450-600°C gave a maximum yield of dipentene. The
reason seems to be that, above a pyrolysis temperature of 600°C there wasan increase in the amount of the pyrolyzates such as isoprene and low
molecular weight hydrocarbons.
We selected 590°C as the most reasonable pyrolysis temperature at which
styrene and dipentene were generated at relatively high yields. Under suchconditions the yields of styrene and dipentene were about 4.5 and 6.0 wt.%
respectively.

Pyrolysis time
The effect of the pyrolysis time on the yield of styrene and dipentene was
examined next. Fig. 3 shows the correlation between the yields of styrene
and dipentene and the pyrolysis time. When the standard SBR tire tread
rubber sample was pyrolyzed at 590°C, the yield of styrene was constantwith a pyrolysis time of 4 seconds and longer. With a pyrolysis time ofshorter than 4 seconds, the yield of styrene decreased as the pyrolysis timedecreased. For the standard NR tire tread rubber sample, the same tendency
as described above was found.

Calibration curves

It is very difficult to determine the content of SBR and NR tire tread
rubbers in piled particulate matter with high accuracy, because various
commercial tire tread rubbers with different compositions are used.
Fig. 4 demonstrates two calibration curves which show the correlation
between the amounts of the standard tire tread rubber samples and the peakareas of styrene and dipentene attributed to the respective rubber polymers.
The relation between the amounts of the standard SBR and NR tire tread
rubber samples subjected to pyrolysis-GC analysis and the yields of styrene
and dipentene attributed to the respective polymers was examined. As aresult, it was confirmed that constant yields were obtained for styrene anddipentene when the amounts of the standard SBR and NR rubber samples
were below 5 and 1 mg, respectively.
For estimation of the content of SBR in the standard NR tire treadrubbersample, this sample was pyrolyzed at 590ºC for 5 seconds. The peakarea of the resultant styrene and the above mentioned calibration curve of
SBR were used to determine the amount of SBR contained in the NR tire
tread rubber sample. The average concentration of SBR obtained by 13
repeated measurements was 6.1 wt.%.
Therefore, for determination of the content of SBR tire tread rubber in apiled particulate matter sample, 6.1 wt.% of the weight of NR tire treadrubber determined by the pyrolysis-GC analysis should be subtracted fromthe weight of the SBR tire tread rubber determined by the pyrolysis-GC
analysis.

Applications
The content of tire tread rubbers in piled particulate matter collected on
the inside, at the entrance and on the outside of a tunnel on a paved
highway of Route 246 on the roadside (Kanagawa Prefecture, Japan), wasmeasured in July, 1985 (Fig. 5). The average contents of SBR tire tread
rubber in the piled particulate matter samples taken at distances of 60 m
and 20 m inside the tunnel, at the entrance, and at 20 m and 30 m outsidewere 0.0920, 0.0675, 0.0630, 0.0554, and 0.0100 wt.%, respectively. The
average contents of NR tire tread rubber at the same sites were 0.176, 0.162,
0.148, 0.0140, and 0.0085 wt.%. The contents of SBR tire tread rubber
measured at distances of 10 m and 20 m from the entrance of the tunnel inthe direction perpendicular to the highway were 0.058 and 0.0075 wt.%,
respectively. The contents of NR tire tread rubber at the same sites were
0.082 wt.%, and a trace amount. At distances of 30 m and longer from theentrance of the tunnel, neither SBR nor NR rubber was detected. The result
suggests that the particles of SBR and NR tire tread rubbers generated byabrasion of car tires tended to accumulate to a relatively high degree on theinside of the tunnel, which was scarcely directly influenced by climate or
weather conditions outside the tunnel.
Fig. 6 shows the contents of SBR and NR tire tread rubbers collected at
different positions from the above measurement sites. The contents of SBR
tire tread rubber at the inside of the tunnel, 60 m from the entrance, at theentrance, and at 30 m from the outside of the tunnel were 0.0764, 0.105, and0.0653 wt.%, respectively. The contents of NR tire tread rubber at these sites
were 0.127, 0.100, and 0.100 wt.%. In this case, the content of SBR tire treadrubber collected at the entrance of the tunnel was highest. This wasprobably attributable to the fact that the highway is curved substantially ata right angle near the entrance, and some of the cars running along the
highway brake at that point, which results in an increase in the amount ofabrasion of the tire tread rubbers. The contents of SBR and NR tire tread
rubbers at a distance of 20 m from the entrance of the tunnel were very low;
viz. 0.0201 and 0.0116 wt.%, respectively.
Fig. 7 shows the size distribution of the SBR and NR tire tread rubber
particles contained in piled particulate matter collected at the entrance ofthe tunnel. As the particle size decreased, the contents of the SBR and NR
tire tread rubber particles increased. Accordingly, from the environmental
viewpoint, it is important to monitor the movement of small rubber particles
or dusts with a particle size below about 100 ì/m, which are readily scatteredby wind and the like.
The determination limits (signal-to-noise ratio) of this method for SBR
and NR tire tread rubbers in piled particulate matters were 12.2 and 38.6 ìgbased on 1 g of the piled particulate matter, respectively. The relative
standard deviations of the measured contents of the SBR and NR tire tread
rubbers were less than 10%.
This method is effective in approximately determining the content of SBR
and NR tire tread rubbers in piled particulate matter on highway both
simply and quickly.
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