Crystallization of dilute polyethylene solutions: influence of molecular weight

Macromolecular Symposia

2007

Summary: A series of ethylene homopolymers and ethylene/1-hexene copolymers with different molecular weight distributions (MWD) and chemical composition distributions (CCD) was analyzed by crystallization analysis fractionation (Crystaf) at several cooling rates to investigate the effect of MWD, CCD, and cooling rate on their Crystaf profiles. Using these results, we developed a mathematical model for Crystaf that considers crystallization kinetic effects ignored in all previous Crystaf models and can fit our experimental profiles very well.

Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Crystaf Modelmentioning

confidence: 99%

See 1 more Smart Citation

A Mathematical Model for the Kinetics of Crystallization in Crystaf

Macromolecular Symposia

2007

“…This equation can be used not only for crystallization from polymer melts, but also for crystallization from polymer solutions. [13][14][15] The fractionation in Crystaf is not isothermal. However, for a narrow Crystaf fraction of chains having similar microstructures, the crystallization temperature range is very small.…”

Section: Semiempirical Crystallization Kinetics Equationmentioning

confidence: 99%

Mathematical modeling of crystallization analysis fractionation of ethylene/1‐hexene copolymers

J Polym Sci B Polym Phys

et al. 2007

Crystallization analysis fractionation (Crystaf) is a polymer characterization technique for estimating the chemical composition distributions of semicrystalline copolymers. Although Crystaf has been widely used during the recent years, it is still a relatively new polymer characterization technique. More quantitative understanding of its fractionation mechanism is essential for further developments. In this work, three ethylene/ 1-hexene copolymers with different 1-hexene fractions, but similar number-average molecular weights, were analyzed by Crystaf at several cooling rates. A mathematical model was proposed to describe the effect of comonomer fraction and cooling rate on Crystaf fractionation from a fundamental point of view. The model describes the experimental Crystaf profiles of ethylene/1-hexene copolymers with different 1-hexene fractions measured at distinct cooling rates very well.

“…For isothermal polymer crystallization, the relationship between crystallinity, X ( t ), and time, t , can be described using the Avrami equation, where n and k are the Avrami parameters. This equation can be used to describe crystallization from polymer melts and from polymer solutions 10–12. The parameter n is generally assumed to be constant, while the parameter k is a function of the crystallization temperature.…”

Section: Crystaf Modelmentioning

confidence: 99%

Mathematical modeling of crystallization analysis fractionation (Crystaf) of polyethylene

J Polym Sci B Polym Phys

et al. 2006

Crystallization analysis fractionation (Crystaf) is a polymer characterization technique for estimating the chemical composition distributions (CCDs) of semi-crystalline copolymers. Although Crystaf has been widely used during the recent years, it is still a relatively new polymer characterization technique. More quantitative understanding of its fractionation mechanism is essential for further developments.In this work, a series of ethylene homopolymers and ethylene/1-hexene copolymers with different molecular weight distributions (MWD) and chemical composition distributions (CCD) was analyzed by crystallization analysis fractionation (Crystaf) at several cooling rates to investigate the effect of MWD, CCD, and cooling rate on their Crystaf profiles. Using these results, we developed a mathematical model for Crystaf that considers crystallization kinetic effects ignored in all previous Crystaf models and can fit our experimental profiles very well.