Thermal analysis for the assessment of antioxidant content in polyethylene

Karlsson, Kristina; Assargren, C.; Gedde, Ulf W.

doi:10.1016/0142-9418(90)90033-a

Cited by 24 publications

(9 citation statements)

References 9 publications

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“…purified pipe material obtained at temperatures between 155 and 165°C. The OIT data of the samples taken from the center of the pipe wall of the unexposed pipe followed the Arrhenius equation with an activation energy of 21 1 kJ/mol, which is very similar to reported values of the activation energies for resins stabilized with hindered phenols (10,11). The OIT data thus indicate a small residual concentration of antioxidant in the center of the pipe wall.…”

Section: Resultssupporting

confidence: 80%

Degradation of unstabilized medium‐density polyethylene pipes in hot‐water applications

Viebke

Elble

Ifwarson

et al. 1994

Polymer Engineering & Sci

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Pipes of an unstabilized medium‐density polyethylene have been pressure tested with internal stagnant water and moderately circulating air as the external medium at temperatures ranging from 70 to 105°C and changes in molecular structure and crystallinity have been studied. The stage III (fracture induced by thermal oxidation) life of the unstabilized polyethylene pipes was less than 12% of the life of the corresponding stabilized polyethylene pipes. Infrared spectroscopy and size exclusion chromatography showed an earlier and more extensive increase in the quantities of oxidation end‐products and a more pronounced decrease in molar mass of the outer‐wall‐material than of the inner‐wall‐material of the pipe. Mass crystallinity, measured by differential scanning calorimetry, increased on an average by a quantity corresponding to 45 methylene groups per chain scission event. The life of the unstabilized pipe was divided into an induction period during which no detectable thermal oxidation occurred and a subsequent polymer degradation period. The induction period exhibited an Arrhenius‐temperature‐dependence with an activation energy of 75 kJ mol−1.

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Section: Resultssupporting

confidence: 80%

Degradation of unstabilized medium‐density polyethylene pipes in hot‐water applications

Viebke

Elble

Ifwarson

et al. 1994

Polymer Engineering & Sci

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“…For a given polyolefin/stabilizer compound, the OIT values and, although significantly less sensitive, the T ox values are frequently used as a measure for changes in the active stabilizer concentration (i.e., including all residual functional groups in stabilizers) due to the exposure of compounds to different thermal and environmental histories 63–66…”

Section: Resultsmentioning

confidence: 99%

Effect of stabilization on creep crack growth in high‐density polyethylene

Pinter

Lang

2003

J of Applied Polymer Sci

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Polyolefins, particularly polyethylene, are known to fail via crack initiation and crack propagation when exposed to multiaxial long-term static stresses at elevated temperatures. Using concepts of linear elastic fracture mechanics, this article describes and discusses the effects of stabilization on the kinetics of creep crack growth (CCG) in high-density polyethylene (PE-HD) and the failure micromechanisms involved. As for the influence of stabilization, six PE-HD formulations (two polymer types, each with three stabilizer systems) were investigated. CCG initiation times and CCG rates were determined at 60 and 80°C in distilled water as functions of the crack tip stress field characterized by the stress intensity factor. Although no influence of the stabilizer type was found in either polymer type for CCG initiation times and CCG rates at high crack speeds, significant effects of the added stabilizer type and concentration were detected for low CCG rates. The observed phenomena were explained in terms of local aging processes in the immediate vicinity of the crack tip, which were controlled by the presence and content of various stabilizers.

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“…Rej. 12). Figures 14 through 16 show induction time profiles for pipes exposed at 80°C 95°C and 105°C.…”

Section: Resultsmentioning

confidence: 99%

“…Thermal analysis by dynamic DTA showed that the oxidation temperature is much lower in the degraded area than in the surrounding material (1). The oxidation temperatures recorded for samples taken from the oxidation spots was always less than 180"C, which indicates that essentially all antioxidant had been consumed in these samples (1,12).…”

Section: Introductionmentioning

confidence: 96%

Molecular structure, morphology, and antioxidant consumption in medium density polyethylene pipes in hot‐water applications

Karlsson

Smith

Gedde

1992

Polymer Engineering & Sci

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Changes in polymer structure and antioxidant concentration have been systematically studied as functions of temperature, hoop stress, exposure time, and location in pipe wall on pressure tested pipes of medium density polyethylene. The pressure tests have been performed with water as the internal medium and air as the external medium at temperatures in the range 80 to 105°C. Infrared spectroscopy shows that oxidation is initiated at the inner wall surface just prior to the onset of the so-called stage 111 fracture. X-ray diffraction and size exclusion chromatography show that oxidation involves only the amorphous phase and results in a significant molar mass reduction. The near-inner-wall material exhibits a 10% reduction in mass average molar mass before the onset of stage I11 fracture and thereafter a more dramatic decrease. Oxidation induction time measurements by differential scanning calorimetry show that the antioxidant concentration is almost twice as high in the center of the wall as in the near-inner-wall and outer-wall material of the unexposed pipe, that the loss of antioxidant is anomalously rapid at the beginning of the high temperature exposure, and that the antioxidant concentration profile gradually becomes more skewed towards the outer wall on prolonged exposure. The data presented in this paper are used in a parallel paper for modeling purposes.

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Thermal analysis for the assessment of antioxidant content in polyethylene

Cited by 24 publications

References 9 publications

Degradation of unstabilized medium‐density polyethylene pipes in hot‐water applications

Degradation of unstabilized medium‐density polyethylene pipes in hot‐water applications

Effect of stabilization on creep crack growth in high‐density polyethylene

Molecular structure, morphology, and antioxidant consumption in medium density polyethylene pipes in hot‐water applications

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