Automated DPX process - Gerstel

M
onomers are generally
low molecular weight
compounds with special
functional groups that enable polymerization.
Depending on the structure
and properties of monomers, and
on the conditions chosen, polymerization
can lead to the formation
of linear, branched, or crosslinked
polymers, which have different
chemical and physical properties.
In order to determine the
structure of a polymer, pyrolysis
GC is often used as the technique
of choice; it is a powerful tool in the
characterization of complex polymers
whether they are in solid or liquid form
or in emulsion.
Curie-Point pyrolyzers are widely used
for polymer analysis. Some are based on resistive
heating, some on microwave technology.
Technical aspects aside, the use of
special pyrolyzers can be labor intensive,
sometimes requiring additional cumbersome
sample preparation steps as well as
significant added investment volume. A
different, simpler, and more cost-effective
way has been described by scientists from
GERSTEL Solutions Worldwide Innovation
Polymer analysis
Efficient Automated Pyrolysis GC
Scientists from Dow, a leading producer and supplier of chemicals and
polymer products, have collaborated with GERSTEL scientists in developing
a novel method for determining the structure and composition
of polymers. The approach: Following a high-temperature liquid sample
introduction, pyrolysis is performed in the high-temperature version
Cooled Injection System 6 (CIS 6) GC inlet. Pyrolysis break-down products
are subsequently determined using GC/FID or GC/MS.
DOW and GERSTEL who cooperated on
developing an attractive alternative to standard
methods.
“Instead of a dedicated pyrolyzer, we
used the CIS 6, the high-temperature version
of the GERSTEL Cooled Injection
System (CIS)”, says Patric
Eckerle, Dow Germany. The
GERSTEL CIS is the most widely
used PTV-type inlet in the world.
Liquid polymers and polymer
mixtures were pyrolyzed directly
in the GC inlet in an oxygen-free
carrier gas atmosphere. Pyrolysis
break-down products were then
transferred to the GC column,
separated and determined using a Flame
Ionization Detector (FID).
To prove the validity of the method, the
scientists analyzed different polymer mixtures:
1. An emulsion based on a 1:100 styrenebutadiene
polymer mixture diluted
with water was examined in order to
determine recovery rates. In this context,
Eckerle examined the influence of
the GERSTEL CryoTrap System (CTS)
on the quality of the separation.
Improved peak shape: The GERSTEL CryoTrap System (CTS) significantly improved both
separation capacity and accuracy in the determination of volatile pyrolysis fragments by
focusing these and sharpening the peaks.
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2. A styrene-butadiene polymer mixture
containing varying amounts of emulgated
copolymer (butylacrylate-styrene)
was analyzed in order to verify
the quantitation.
3. Polyethylene (PE), dissolved in hot xylene,
was analyzed using two-dimensional
GC (2D GC and GCxGC).
For the polymer analysis, the experts
used a GC system with a GERSTEL Multi-
Purpose Sampler (MPS), which was used
for automated sample preparation and sample
introduction. The MPS was equipped
with a headspace syringe adapter, a heated
10 µL syringe and a heated agitator. The GC
6890 from Agilent Technologies was fitted
with a GERSTEL CIS 6 programmed temperature
vaporizer as well as an FID.
And this is how Eckerle and his colleagues
approached the task: Following
sample preparation, 0.5 to 2 µL of the dissolved
polymer was introduced into the
cool CIS liner. Solvents were then purged
from the inlet through the split vent, leaving
the polymer material condensed on the
CIS liner walls. The temperature of the CIS
was kept at 90 °C for 3.5 minutes during the
First class results: Repeatability of 10 CIS pyrolysis runs of an S/B
copolymer. The CIS was not cleaned or replaced over the course
of these runs.
GERSTEL Solutions Worldwide – March 2009