results from the thermal or photo-initiated dissociation of chemical bonds, alkyl
radicals react with molecular oxygen to form peroxy radicals [90]. The oxygencontaining functionalities like ketones, alcohols, carboxylic acids, esters and
γ-lactones are due to the propagation reactions [91–96]. Fractionation is an important approach to obtain information about degradation and the distribution of
degradation products. CRYSTAF and TREF separate semi-crystalline polyolefins
based on crystallizability. These methods in combination with spectroscopic
methods shall now be used for the analysis of degraded polyolefins.
2.1.3.1 Aim
In Sect. 2.1.2, the compositional heterogeneity of a commercial IPC was measured
by hyphenation of TREF fractionation with SEC-FTIR analysis. The chemical
composition as function of MMD of all fractions was determined. The morphological nature of the components was further confirmed by determination of ethylene
and propylene crystallinity distributions across the MMDs.
In the present application, the thermo-oxidative degradation of IPC shall be
addressed. IPC is degraded at different times and temperatures like in previous
reports on PP and PP-1-pentene copolymers [97, 98]. The bulk sample analysis by
SEC, FTIR, SEC-FTIR, CRYSTAF and DSC is used to monitor the process of
degradation. A degraded sample is fractionated by P-TREF and the fractions are
analysed for molar mass and chemical composition in order to obtain information
on degradation of individual components of IPC. A comparison of two different
IPC samples with regard to chemical composition will be presented. The degree of
degradation as a function molar mass, chemical composition and crystallinity will
be determined for the fractions of degraded materials. Finally, samples shall be
evaluated and compared with respect to thermo-oxidative stability.
2.1.3.2 Materials
• Polymers. The bulk properties of two non-stabilized commercial IPCs from
SASOL Polymers (Secunda, South Africa) are presented in Table 2.3 (samples
were labelled 3V and 4V, O h indicates original samples before degradation). To
prevent degradation during film extrusion and sample preparation, 0.05 % of
phosphite processing stabilizer, Irgafos 168, was added for compounding of the
materials. Dry-blending of the IPC powder and Irgafos 168 was followed by
melt-blending at 200
C on a Brabender PL 2000-6 single-screw extruder
equipped with a 19 mm diameter screw, length-to-diameter ratio of 25 and
screw speeds of 40–100 rpm. The extrudates were cooled and pelletized. Thin
films (1 g of material, ca. 160 μm) were prepared by compression moulding at
190
C. A typical compression cycle consisted of melting of the pellets for
1.5 min and compression at 10–12 bar for another 1.5 min, with subsequent
quench cooling in an ice/water mixture.
• Accelerated oven ageing. The thermo-oxidative degradation of thin films at
90
C and 110
C was accomplished in a heat-circulating oven with digital
temperature control (SMC manufacturing, Cape Town, South Africa). The
visual (for physical changes) and FTIR (for chemical changes) monitoring of
the degradation followed the degradation process and samples were removed at
36
2 Crystallization-Based Fractionation Techniques
radicals react with molecular oxygen to form peroxy radicals [90]. The oxygencontaining functionalities like ketones, alcohols, carboxylic acids, esters and
γ-lactones are due to the propagation reactions [91–96]. Fractionation is an important approach to obtain information about degradation and the distribution of
degradation products. CRYSTAF and TREF separate semi-crystalline polyolefins
based on crystallizability. These methods in combination with spectroscopic
methods shall now be used for the analysis of degraded polyolefins.
2.1.3.1 Aim
In Sect. 2.1.2, the compositional heterogeneity of a commercial IPC was measured
by hyphenation of TREF fractionation with SEC-FTIR analysis. The chemical
composition as function of MMD of all fractions was determined. The morphological nature of the components was further confirmed by determination of ethylene
and propylene crystallinity distributions across the MMDs.
In the present application, the thermo-oxidative degradation of IPC shall be
addressed. IPC is degraded at different times and temperatures like in previous
reports on PP and PP-1-pentene copolymers [97, 98]. The bulk sample analysis by
SEC, FTIR, SEC-FTIR, CRYSTAF and DSC is used to monitor the process of
degradation. A degraded sample is fractionated by P-TREF and the fractions are
analysed for molar mass and chemical composition in order to obtain information
on degradation of individual components of IPC. A comparison of two different
IPC samples with regard to chemical composition will be presented. The degree of
degradation as a function molar mass, chemical composition and crystallinity will
be determined for the fractions of degraded materials. Finally, samples shall be
evaluated and compared with respect to thermo-oxidative stability.
2.1.3.2 Materials
• Polymers. The bulk properties of two non-stabilized commercial IPCs from
SASOL Polymers (Secunda, South Africa) are presented in Table 2.3 (samples
were labelled 3V and 4V, O h indicates original samples before degradation). To
prevent degradation during film extrusion and sample preparation, 0.05 % of
phosphite processing stabilizer, Irgafos 168, was added for compounding of the
materials. Dry-blending of the IPC powder and Irgafos 168 was followed by
melt-blending at 200
C on a Brabender PL 2000-6 single-screw extruder
equipped with a 19 mm diameter screw, length-to-diameter ratio of 25 and
screw speeds of 40–100 rpm. The extrudates were cooled and pelletized. Thin
films (1 g of material, ca. 160 μm) were prepared by compression moulding at
190
C. A typical compression cycle consisted of melting of the pellets for
1.5 min and compression at 10–12 bar for another 1.5 min, with subsequent
quench cooling in an ice/water mixture.
• Accelerated oven ageing. The thermo-oxidative degradation of thin films at
90
C and 110
C was accomplished in a heat-circulating oven with digital
temperature control (SMC manufacturing, Cape Town, South Africa). The
visual (for physical changes) and FTIR (for chemical changes) monitoring of
the degradation followed the degradation process and samples were removed at
36
2 Crystallization-Based Fractionation Techniques