without compromising on strength, thus saving material and reducing costs. The
toughness of LLDPE opens new horizons of application areas. The major share in
global applications of LLDPE is film applications that include food and non-food
packaging, shrink/stretch film and non-packaging applications. Metallocene or
single-site catalysts revolutionized LLDPE research. New resins were synthesized
that allow faster and more stable operations along with improved downgauging of
films. Processing of LLDPE grades is also facilitated by improved and more
effective methods. Today, major application areas of LLDPE are agricultural
greenhouse films, multi-layer cast stretch films, lamination packaging films and
medium to heavy duty bags.
2.1.1.1 Aim
An important step in the development of new or improved materials is the correlation of molecular structure and material properties. For molecular structure elucidation of complex polyolefins, TREF has been shown to be an invaluable tool. For
LLDPE, TREF fractionation produces copolymer fractions that differ in comonomer content. These fractions are then analysed by spectroscopic methods (chemical
composition, microstructure), SEC (molar mass) and calorimetric methods (melting
and crystallization behaviour) for the development of structure–property
correlations. A very useful approach is the online combination of TREF and
FTIR spectroscopy, which will be discussed in the present application.
2.1.1.2 Materials
• Polymers. Ethylene-1-octene copolymers: sample 1 is a commercial random
copolymer, sample 2 is a laboratory product. PE homopolymer (SRM1484a
from the National Institute of Standards and Technology, Gaithersburg, USA;
M w 119.6 kg/mol). Eicosane
2.1.1.3 Equipment
• TREF system. CRYSTAF-TREF 200+ (Polymer Char, Valencia, Spain).
• Detector. FTIR flow cell (Polymer Laboratories, Church Stretton, UK), 1 mm
optical path length, 70 μL volume, CaF 2 windows. The cell was placed in a
TENSOR 27 FTIR spectrometer (Bruker, Rheinstetten, Germany).
• Solvent. TCB stabilized with 2,6-di-tert-butyl-4-methylphenol (BHT).
• TREF column temperature. Temperature gradient between 140
C and 25
C.
• TREF sample concentration. 40–150 mg in 20 mL TCB per reactor vessel.
2.1.1.4 Preparatory Investigations
One of the challenges that TREF presents is to extract quantitative compositional
information on the copolymers from the TREF elution profile. The raw data are
presented as a plot of TREF elution temperature vs. eluate concentration. The
correlation between the TREF elution temperature and the copolymer composition
(wt% comonomer) can be obtained in different ways. Typically, a set of well
defined copolymers with narrow CCDs and known compositions (from NMR) is
measured by TREF and the peak maximum elution temperature for each sample is
determined. This peak maximum elution temperature is then plotted against the wt
22
2 Crystallization-Based Fractionation Techniques
toughness of LLDPE opens new horizons of application areas. The major share in
global applications of LLDPE is film applications that include food and non-food
packaging, shrink/stretch film and non-packaging applications. Metallocene or
single-site catalysts revolutionized LLDPE research. New resins were synthesized
that allow faster and more stable operations along with improved downgauging of
films. Processing of LLDPE grades is also facilitated by improved and more
effective methods. Today, major application areas of LLDPE are agricultural
greenhouse films, multi-layer cast stretch films, lamination packaging films and
medium to heavy duty bags.
2.1.1.1 Aim
An important step in the development of new or improved materials is the correlation of molecular structure and material properties. For molecular structure elucidation of complex polyolefins, TREF has been shown to be an invaluable tool. For
LLDPE, TREF fractionation produces copolymer fractions that differ in comonomer content. These fractions are then analysed by spectroscopic methods (chemical
composition, microstructure), SEC (molar mass) and calorimetric methods (melting
and crystallization behaviour) for the development of structure–property
correlations. A very useful approach is the online combination of TREF and
FTIR spectroscopy, which will be discussed in the present application.
2.1.1.2 Materials
• Polymers. Ethylene-1-octene copolymers: sample 1 is a commercial random
copolymer, sample 2 is a laboratory product. PE homopolymer (SRM1484a
from the National Institute of Standards and Technology, Gaithersburg, USA;
M w 119.6 kg/mol). Eicosane
2.1.1.3 Equipment
• TREF system. CRYSTAF-TREF 200+ (Polymer Char, Valencia, Spain).
• Detector. FTIR flow cell (Polymer Laboratories, Church Stretton, UK), 1 mm
optical path length, 70 μL volume, CaF 2 windows. The cell was placed in a
TENSOR 27 FTIR spectrometer (Bruker, Rheinstetten, Germany).
• Solvent. TCB stabilized with 2,6-di-tert-butyl-4-methylphenol (BHT).
• TREF column temperature. Temperature gradient between 140
C and 25
C.
• TREF sample concentration. 40–150 mg in 20 mL TCB per reactor vessel.
2.1.1.4 Preparatory Investigations
One of the challenges that TREF presents is to extract quantitative compositional
information on the copolymers from the TREF elution profile. The raw data are
presented as a plot of TREF elution temperature vs. eluate concentration. The
correlation between the TREF elution temperature and the copolymer composition
(wt% comonomer) can be obtained in different ways. Typically, a set of well
defined copolymers with narrow CCDs and known compositions (from NMR) is
measured by TREF and the peak maximum elution temperature for each sample is
determined. This peak maximum elution temperature is then plotted against the wt
22
2 Crystallization-Based Fractionation Techniques