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Measurement and prediction of LDPE/CO 2 solution viscosity
Author(s) -
Areerat Surat,
Nagata Takefumi,
Ohshima Masahiro
Publication year - 2002
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.11113
Subject(s) - low density polyethylene , materials science , polymer , dissolution , viscosity , solubility , reduced viscosity , relative viscosity , supercritical fluid , thermodynamics , polyethylene , analytical chemistry (journal) , chemical engineering , composite material , chromatography , chemistry , organic chemistry , physics , engineering
When CO 2 is dissolved into a polymer, the viscosity of the polymer is drastically reduced. In this paper, the melt viscosities of low‐density polyethylene (LDPE)/supercritical CO 2 solutions were measured with a capillary rheometer equipped at a foaming extruder, where CO 2 was injected into a middle of its barrel and dissolved into the molten LDPE. The viscosity measurements were performed by varying the content of CO 2 in the range of 0 to 5.0 wt% and temperature in the range of 150°C to 175°C, while monitoring the dissolved CO 2 concentration on‐line by Near Infrared spectroscopy. Pressures in the capillary tube were maintained higher than an equilibrium saturation pressure so as to prevent foaming in the tube and to realize single‐phase polymer/CO 2 solutions. By measuring the pressure drop and flow rate of polymer running through the tube, the melt viscosities were calculated. The experimental results indicated that the viscosity of LDPE/CO 2 solution was reduced to 30% of the neat polymer by dissolving CO 2 up to 5.0 wt% at temperature 150°C. A mathematical model was proposed to predict viscosity reduction owing to CO 2 dissolution. The model was developed by combining the Cross‐Carreau model with Doolittle's equation in terms of the free volume concept. With the Sanchez‐Lacombe equation of state and the solubility data measured by a magnetic suspension balance, the free volume fractions of LDPE/CO 2 solutions were calculated to accommodate the effects of temperature, pressure and CO 2 content. The developed model can successfully predict the viscosity of LDPE/CO 2 solutions from PVT data of the neat polymer and CO 2 solubility data.