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Correlation between processability and properties of a high density polyethylene by a rheological approach
Author(s) -
Mariani Paolo,
Carianni Graziana,
Menconi Francesco,
La Mantia Francesco P.
Publication year - 2002
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/1521-3935(200207)203:10/11<1602::aid-macp1602>3.0.co;2-c
Subject(s) - high density polyethylene , rheology , rheometer , materials science , composite material , polyethylene , polymer , branching (polymer chemistry) , rheometry , elastic modulus , polymer degradation , low density polyethylene , sweep frequency response analysis , dynamic mechanical analysis , physics , quantum mechanics
The thermal‐oxidative and thermal‐mechanical stability of high density polyethylene (chromium based catalyst technology) was examined at many different temperatures using a rheological approach. The changes in molecular structure, which take place during processing, have been studied using a Clextral co‐rotating twin‐screw extruder in comparison with dynamic measurements performed with a rotational rheometer under definite conditions of temperature, strain and frequency and in presence of air. In order to evaluate the degradation response, an investigation of elastic modulus G ′ as a function of frequency ω on the residual sample after ageing has been carried out. The molecular weight increase, probably due to the formation of small amounts of long chain branching, is clearly observed through the growth of the elastic properties, mainly at low frequencies (i.e. high relaxation times). The stabilised polymer shows a less pronounced tendency towards degradation, even if a critical temperature (240 °C) has been found at which antioxidant has not any effect in avoiding degradation.Effect of the ageing time on elastic modulus G ′ vs. frequency ω from a frequency sweep test in a rotational rheometer at 220 °C for HDPE+ 1 600 ppm antioxidant.