The same solvents, same IR detector and similar calculation parameters to
those presented in Sect. 4.1.2 for TREF are applicable for CRYSTAF analysis.
The calibration of temperature to comonomer content can be performed by using
narrow composition standards (metallocene-type resins) of the same comonomer
type, with similar results to TREF as discussed in Sect. 4.1.2. Octene and hexene
copolymers follow the same calibration curve [92].
Reviews of the CRYSTAF technique and applications have been presented
[80, 83, 84]. Mathematical modeling of CRYSTAF crystallization kinetics has
also been investigated [100].
Comparison of TREF and CRYSTAF
Both techniques share the same principles of fractionation on the basis of
crystallizability. TREF is carried out in a packed column and demands two full
temperature cycles, crystallization and elution (dissolution), to obtain the analysis
of the composition distribution. In CRYSTAF, the analysis is performed in a
single step, the crystallization cycle, which results in faster analysis time and simple
hardware requirements.
TREF has the advantage that a continuous elution signal is obtained and
molar mass detectors can be easily added to obtain composition molar mass
interdependence; an autosampler can also be added for multiple sample analysis.
CRYSTAF takes advantage of discontinuous sampling to analyze a set of samples
simultaneously.
Both techniques provide similar results; the comparison of TREF and
CRYSTAF has already been discussed [84] and the most significant difference
is the temperature shift due to the undercooling, as analytical conditions are far
from equilibrium; CRYSTAF data are obtained during the crystallization whereas
TREF data are obtained in the melting-dissolution cycle. Both techniques, however,
can be calibrated and the results expressed in branches/1000C will be similar for PE
copolymers.
The large difference in undercooling between polypropylene and polyethylene
makes the analysis of complex resins containing both PE and PP an interesting
case, whereby both TREF and CRYSTAF must be used to obtain unequivocal
results, as discussed in a recent publication [101]. TREF, which analyzes samples in
the dissolution (melting), provides best resolution for the analysis of blends containing isotactic polypropylene and polyethylene; on the other hand, CRYSTAF,
which obtains the data during the crystallization, is the preferred technique when
analyzing combinations of polyethylene with ethylene-propylene copolymers resins,
as seen in Fig. 25.
232
B. Monrabal
those presented in Sect. 4.1.2 for TREF are applicable for CRYSTAF analysis.
The calibration of temperature to comonomer content can be performed by using
narrow composition standards (metallocene-type resins) of the same comonomer
type, with similar results to TREF as discussed in Sect. 4.1.2. Octene and hexene
copolymers follow the same calibration curve [92].
Reviews of the CRYSTAF technique and applications have been presented
[80, 83, 84]. Mathematical modeling of CRYSTAF crystallization kinetics has
also been investigated [100].
Comparison of TREF and CRYSTAF
Both techniques share the same principles of fractionation on the basis of
crystallizability. TREF is carried out in a packed column and demands two full
temperature cycles, crystallization and elution (dissolution), to obtain the analysis
of the composition distribution. In CRYSTAF, the analysis is performed in a
single step, the crystallization cycle, which results in faster analysis time and simple
hardware requirements.
TREF has the advantage that a continuous elution signal is obtained and
molar mass detectors can be easily added to obtain composition molar mass
interdependence; an autosampler can also be added for multiple sample analysis.
CRYSTAF takes advantage of discontinuous sampling to analyze a set of samples
simultaneously.
Both techniques provide similar results; the comparison of TREF and
CRYSTAF has already been discussed [84] and the most significant difference
is the temperature shift due to the undercooling, as analytical conditions are far
from equilibrium; CRYSTAF data are obtained during the crystallization whereas
TREF data are obtained in the melting-dissolution cycle. Both techniques, however,
can be calibrated and the results expressed in branches/1000C will be similar for PE
copolymers.
The large difference in undercooling between polypropylene and polyethylene
makes the analysis of complex resins containing both PE and PP an interesting
case, whereby both TREF and CRYSTAF must be used to obtain unequivocal
results, as discussed in a recent publication [101]. TREF, which analyzes samples in
the dissolution (melting), provides best resolution for the analysis of blends containing isotactic polypropylene and polyethylene; on the other hand, CRYSTAF,
which obtains the data during the crystallization, is the preferred technique when
analyzing combinations of polyethylene with ethylene-propylene copolymers resins,
as seen in Fig. 25.
232
B. Monrabal