SIMULTANEOUS DETERMINA
TION OF NA
TURAL ANDSIMULT
DETERMINATION
NATURAL
STYRENE-BUT
ADIENE RUBBER TIRE TREAD P
ARTICLES INSTYRENE-BUTADIENE
PARTICLES
ATMOSPHERIC DUSTS BY PYROLYSIS-GAS CHROMATOGRAPHYPYROLYSIS-GAS
CHROMATOGRAPHY
YONG-KEUN LEE * and MAN GOO KIM *Department of Chemistry, College of Science, Yonsei University, Seoul 120-749 (Korea)
KYU-JA WHANG
Department of Manufacturing Pharmacy, College of Pharmacy, Sookmyung Women’s University, Seoul 140-132 (Korea)(Received August 26th, 1988; accepted November 16th, 1988)
ABSTRACTA method for simultaneous determination of natural rubber (NR) and styrene-butadiene
rubber (SBR) tire tread particles in atmospheric dust is described. Particulate rubbers are
pyrolyzed at 740°C for five seconds in a Curie-point pyrolyzer. The resulting pyrolyzates areseparated and detected by a gas chromatograph equipped with dual flame ionization
detectors. Among several pyrolysis products, isoprene and styrene are chosen as indicator
compounds for NR and SBR, respectively. The method is applied to a suite of atmospheric
dust samples collected in Seoul, Korea by an Andersen sampler and some analytical results
are presented.
Atmospheric dust; gas chromatography; natural rubber; polymers; pyrolysis;
styrene-butadiene rubber; tire tread.

INTRODUCTION
Pyrolysis-gas chromatography (Py-GC) has been successfully applied tothe characterization o[ rubber components for many years [1-4]. Since
Thompson et al. [5] reported evidence of tire-wear debris in the sweepingsfrom tunnel and parking garages, several workers [6-8] have reported
various analytical methods for determination of rubber particles in atmo-spheric dusts. The amount of rubber loss from automobile tires has been
also estimated from the number of registered vehicles and tire sales to beabout 90 mg/km due to vehicle motion [9]. According to Pierson andBrachaczek [10] and Brown et al. [11], less than 5% of the total tire wear
becomes airborne, but this amount is equivalent to 20% of the total airborne
particulate matter exhausted from internal combustion engines burning
regular gasoline.
Penetration and deposition of the airborne particulates in man’s respiratory tract is a subject of aerodynamics [12]. The toxicity of a particulate
pollutant is thus determined not only by its concentration and chemicalcomposition, but also by the particle size of the pollutant.
This paper presents details of an analytical procedure for the simultaneous determination of natural rubber (NR) and styrene-butadiene rubber(SBR) tire tread particles in atmospheric dusts by Py-GC. The performanceof the procedure and its application to a suite of urban atmospheric dust
samples are discussed. In addition, the measured concentrations of total
rubber particles and those particles which are small enough to penetrate into
the alveoli are presented.

EXPERIMENTAL

Atmospheric dust sampling
Atmospheric dust samples were collected from the street in front ofYonsei University Campus, Seoul, Korea using an Andersen sampler(Kanomax, Model 3351) which was run for 10 days for each sample. We
chose polyester filters (diameter: 80 mm; thickness: 0.075 mm) whichenabled us to remove the dusts from the filter easily and thus reduce therelative error when weighing the samples. The collected airborne dust waskept in a desiccator for at least two days, where relative humidity wasmaintained at 50% using calcium chloride solution. In order to remove
organic contaminants originating from asphalt particles or vehicle exhaust,
the samples were rinsed with benzene-ethanol (4 : 1, v/v) in an ultrasonicbath for 30 seconds. After being dried at room temperature, the samples
were weighed on a semi-microbalance (Mettler Model HK60).
Analytical standards of NR and SBR tire tread rubbers were preparedfollowing the recipes which are given in Table 1.

Pyrolysis-gas chromatographic conditions
A Curie-point pyrolyzer (Japan Analytical Industries, Model JHP-2) wasdirectly coupled to a gas chromatograph (Hitachi Model 163) equipped withdual flame ionization detectors. Atmospheric dust samples (0.5-1.0 mg)

were pyrolyzed at 740 °C for five seconds. The temperatures of the pyrolyzer
unit and the tube connecting pyrolyzer and gas chromatograph were maintained at 100°C and 200°C, respectively. The analytical column was astainless steel tube (6 m X 3 mm I.D.) which was packed with 15% Apiezon
grease L supported on 60-80 mesh Uniport B.
The column temperature was maintained at 55ｰC for the first sevenminutes and programmed to increase at a ramp rate of 20°C/min up to160°C. The nitrogen carrier gas flow-rate was 20 ml/min (Table 2).

RESULT AND DISCUSSION

Column selection
The column was selected in such a way that simultaneous quantificationof the isoprene and styrene peak could be achieved. A non-polar packing
material is needed for good separation of isoprene, while a high-temperaturepacking material is necessary for good separation of styrene. The packing
materials tested in this work were Apiezon grease L, TCP, SE-30, OV-1,OV-17, DC-200, DC-550, PEG-20M and FFAP. Among them, a 6-m-longcolumn containing 15% Apiezon grease L showed the best separation
performance.

Pyrolysis temperature
Seven kinds of pyro foils (358°C, 445°C, 590°C, 670°C, 740°C, 920°C
and 1040°C) were tested to observe the effect of temperature on thepyrolysis characteristics of standard tire tread rubbers. The functional
relationships between the production yields of isoprene, styrene and dipentene and pyrolysis temperature are summarized in Fig. 1. At 358°C, nopyrolyzates were produced. Yields of both isoprene and styrene were highest
at 740°C, while the maximum dipentene production was observed at445°C. Thus, only the 740°C pyrofoil was used for routine sample analysis.

Quantification of tire tread rubbers
For quantitative determination of tire tread rubbers, the pyrograms ofsamples were compared with those of standard tire tread rubbers. Typicalpyrograms of the SBR group and NR group tire treads, and atmospheric
dusts trapped in the fourth stage of the Andersen sampler, are shown in Fig.
2. The styrene peak was used for the determination of SBR group tire rubber
and the isoprene peak for the determination of NR group tire rubber.
Theoretically, dipentene can also be used for NR group determination but,in this work, the amounts of NR group rubber in the dust samples were too
small to produce sufficient dipentene. The reproducibility of the pyrolyzate
formation was investigated by varying the particle size from 14 to 100 meshIt appeared that the reproducibility was strongly related to the particle size.
The best reproducibility was obtained when 50-100 mesh particles wereused (Table 3). In the pyrograms SBR group (styrene peak) and NR group(isoprene peak) were 74 ± 5.2 area unit / ì g and 380 ± 20.8 area unit / ì g,respectively.
Particle size distribution of rubber components
Atmospheric dust samples were collected using the Andersen sampler
which was operated continuously for 10 days in March 1987. The samples
were analyzed for NR and SBR rubbers and weighed at each stage. As
summarized in Table 4, it can be seen that the mass size distribution ofrubber components is not bimodal, but unimodal. This implies that almost
all of the rubber particulates were produced from automobile tire tread bymechanical abrasion.
It is generally known that atmospheric dusts trapped below the sixth stageof an Andersen sampler can penetrate into alveoli [13]. It appeared that
32.4% of the total atmospheric dust could penetrate into alveoli, of which
the rubber components formed 0.2%. The concentrations of NR group andSBR group tire tread were 0.23 ì g /m3 and 1.98 ì g /m3, respectively.
ACKNOWLEDGEM ENTS
This work was supported by a grant from the Korea Science and Engineering Foundation in 1986. Standard tire tread rubbers were provided byHan Kook Tire Manufacturing Company, for which the authors are grateful.

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