A. Willem deGroot

Characterization of high-molecular-mass polyethylenes by gel permeation chromatography—low-angle laser-light scattering

Abstract Gel permeation chromatography—low-angle laser-light scattering (GPC-LALLS) has been applied to the analysis of high-molecular-mass polyolefins. It was found that changing the particle size of the column packing from 10 to approximately 50 μm resulted in an increase in the molecular mass of NBS 1476 of from 100 000 to 195 000. It was also found that changing the flow-rate from 1.0 to 0.1 ml/min resulted in an increase in the molecular mass of the same sample of from 195 000 to 280 000 for the large particle size gel columns. Increases were also seen with commercial low-density samples when changing these same conditions, but the increases were not as large in magnitude. A change in the frit size on the columns did not seem to have an effect on the measured molecular masses of the NBS 1476 samples. Another finding in this study was that slurry high-density polyethylene samples which previously had been very difficult to characterize using GPC-LALLS gave much higher molecular masses which were much more reproducible when characterized using the large particle size columns with low flow-rates.

Comparison of Crystallization and Melting Characteristics of Quiescent and Melt-Spun Poly(ethylene-co-octene) Copolymers

Abstract An experimental study of crystallization and melting of polyethylene and its octene copolymers under quiescent conditions and their melt-spun fibers is presented. This includes copolymers produced by both Dows Insite® Technology homogeneous catalyst and by a Ziegler heterogeneous catalyst. It is found that with increasing comonomer content, both isothermal and non-isothermal crystallization rate decrease. The melting peaks become broader and the melting temperatures decrease for polymers with more comonomer. Multiple melting peaks are observed for copolymers. Except the unchanged peak with the highest melting temperature, the other peaks move to higher temperature after being annealed under higher temperature. Attempts were made to correlate crystallization kinetics and melting behavior under quiescent conditions with melting temperatures and crystallinities determined for their melt-spun fibers. The results show that besides cooling effects, the melt temperatures and the crystallinities of the melt spun fibers are also affected by the degree of molecular orientation, which is mainly decided by the spin-line stress. These two competitive factors determine the final melt temperatures and crystallinities of the melt-spun fibers.

Quality Control of Columns for High-Temperature Gel-Permeation Chromatography

Publisher Summary The purpose of this chapter is to relate Dows experiences in designing columns for high temperature gel-permeation chromatography (GPC) and monitoring the quality of GPC columns for high temperature GPC of polyethylenes in such a way that others can benefit from the experience. Some of the criteria for column selection include linearity of calibration, narrow particle size distribution of gel, peak asymmetry, resolution, and molecular weight accuracy. High temperature GPC data is represented in three ways:(1) data is standardized of GPC column, (2) implement a quality control procedure to make sure that data stay at a high quality, and (3) a procedure in place to approve future batches of gel to assure that the chromatograms will be very comparable from batch to batch.