Infrared spectroscopic studies on polyethylene, 4. The examination of drawn specimens of varying stress crack resistance

Abstract

Infrared spectra, with both unpolarised and polarised radiation, have been obtained for a series of Phillips type high density polyethylenes of varying stress crack resistance. They were examined after cold drawing, by neck propagation, under standard conditions, and the presence of uniaxial orientation was confirmed by X-ray pole figure measurements. Intensity measurements with unpolarised radiation on the bands at 1080, 1352, and 1894cm-' showed that with samples of bad stress crack resistance both the folds and the tie chains increase in concentration at the expense of the regularly folded chains in crystalline regions, whereas only the tie chains increase with samples having good stress crack resistance. Dichroic measurements on nine bands, the majority of them characteristic for methylene groups in gauche and trans conformations in amorphous regions, show that there is no marked degree of orientation of the chain folds or tie chains with samples of good stress crack resistance. However, there is significant orientation, particularly of the tie chains, for samples with poor stress crack resistance. ZUSAMMENFASSUNG :Fur eine Reihe wenig vermeigter Polyathylene (vom Phillips-Typ) verschiedener Spannungsrififestigkeit wurden sowohl mit unpolarisierter als auch mit polarisierter Strahlung IR Spektren aufgenommen. Die Polymere wurden unter Standardbedingungen kalt verstreckt; danach wurden rnit Hilfe der Rontgenstreuung (Messung der Reflex-Indices, ,,pole figures") uniaxiale Orientierungen festgestellt. Intensitatsmessungen mit unpolarisierten Strahlen an den Banden bei 1080, 1352 und 1 894 cm-' zeigten, daB bei den Proben rnit geringer Spannungsrififestigkeit sowohl die Faltungen als auch die diese verbindenden Ketten (,,tie chains") auf Kosten der regelmafiig gefalteten Ketten in kristallinen Gebieten zunehmen, wohingegen bei Proben rnit hoher SpannungsriBfestigkeit nur die Konzentration der ,,tie chains" zunimmt. Messungen des Dichroismus an 9 Banden (wobei die meisten Banden charakteristisch sind fur Methylengruppen in trans und gauche Konformationen in amorphen Bezirken) zeigen, daB fur Polymere rnit hoher SpannungsriBfestigkeit kein erheblicher Orientierungsgrad der Kettenfaltungen und ,,tie *) Part 3: M.

X-Ray Diffraction Orientation Studies on Blown Polyethylene Films

“…The first, probably the more normal, is the result of the type of stress crystallisation process described by Keller and Machin (6) and has the a-and c-axes inclined at an angle to the plane of the film. The second type of orientation is analogous to that found in cold drawn polyethylene under conditions where necking occurs (7,8), in having the c-axis distribution substantially along the machine direction. We have called this high stress orientation and have found that its occurrence is dependent both on the blowing conditions and the particular polyethylene used.…”

An infra-red spectroscopic and X-ray diffraction study of cold-drawn high density polyethylene samples

“…These differences are also evident from absorbance measurements on the three bands at 1894, 1303 and 1080cm -1 . The method of calculating the absorbance ratios A1894/A1303 and A1894/A1080, which proved useful in a recent study on specimens drawn from linear polyethylenes having different stress crack resistances [10], has been applied and the results are given in Table II. The 1894 cm -1 band is associated wholly with methylene groups in crystalline regions whereas the one at 1303 cm -1 relates to such groups in gauche conformations in amorphous regions and the one at 1080 cm -1 to methylene groups in both gauche and trans conformations in the amorphous phase.…”

“…The precise values of the two dichroic ratios, for a given draw ratio, differ among the three samples. However, as it has already been shown [10] that these values are influenced by the stress crack resistance of the polymer, and this parameter varies considerably among the three polymers examined, it is the change of dichroic ratio with draw ratio that is of significance in the present context. The overall conclusion to be drawn from the three types of infra-red measurements is that they are in line with and provide additional confirmation for the Peterlin model of plastic deformation.…”

“…Previous studies [10] on a series of heavily colddrawn polyethylene samples of varying stress crack resistance, using unpolarized and polarized infrared spectra, showed the value of studying the absorbance ratios of pairs of bands characteristic for methylene groups in the lamellae and in gauche and trans conformations in the amorphous phase. The gauche methylene groups are present in random chains and the trans methylene groups in tie molecules.…”

Correlations between processing parameters, morphology, and properties of blown films of LLDPE/LDPE blends, part 2: Crystalline and amorphous biaxial orientation by WAXD pole figures

“…2 In view of the known variation of orientation with film thickness 9 and of the experimental evidence that it is very difficult to produce a blown film with constant thickness along the extension, 3 the samples for the IR measurements were cut along the transverse section of the blown films, where the variation of the film thickness was very low. The pure LLDPE film had an average thickness of 60 mm and the blends specimens had approximately a thickness of 30 mm.…”