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

Abstract

ABSTRACT:The biaxial molecular orientation of blown films made of blends of linear low density polyethylene (LLDPE) with low density polyethylene (LDPE) was characterized by two different methods: complete pole figures obtained by wide angle X-rays diffraction (WAXD) and polarized infrared spectroscopy (IR) using the Krishnaswamy approach. The molecular orientation of the blends amorphous phase was also evaluated by polarized IR. The crystallinity of the blown films was determined by WAXD. A good correlation between the X-ray pole figures and the polarized IR results was obtained. At all blends compositions, it was shown that the a-axis of the polyethylene orthorhombic cell was preferentially oriented along the machine direction, the orientation degree along this direction increasing with the increase of the LDPE amount in the blends. The b-axis changed its preferential orientation from film thickness in the 100/0 LLDPE/LDPE film to along the transverse direction with increasing LDPE in the blends. The c-axis changed its orientation from orthogonal to normal direction in the 100/0 LLDPE/LDPE film to along the film thickness with increasing LDPE in the blends. Polarized IR characterization showed a negligible orientation of the amorphous phase. The amount of crystallinity was dependent on blend composition decreasing with the increase of LDPE content in the blends.

Orientation and Epitaxy in the Injection-Molded Bars of Linear Low-Density Polyethylene/Isotactic Polypropylene Blends: An Infrared Dichroism Measurement

“…The 841 and 998 cm −1 vibrations were observed to be associated with the PP crystalline phase, , while the 1153 cm −1 vibration was assigned to amorphous peak. However, 1153 cm −1 was not used to calculate the orientation function because of overlapping with the crystalline vibration at 1165 cm −1 . As we know, the 973 and 1256 cm −1 vibrations were observed to be associated with both crystalline and amorphous phases, , so the orientation function for amorphous phase can be obtained through an indirect way.…”

“…Besides other techniques such as X-ray diffraction, birefringence, polarized fluorescence, Raman depolarization and sonic techniques, the measurement of infrared dichroism is one of the most frequently tools for the analysis of anisotropy in polymers, especially for polyolefins. − Because of the characteristic peaks in infrared spectrum of polyethylene, the orientation of crystalline a -axis and b -axis could be detected, and many works have been done in terms of the Keller−Machin model. − The measurement of the orientation and corresponding structure of polyolefin blends is also a research focus. ,, …”

Determination of the Composition of LDPE/LLDPE Blends via 13C NMR

“…Therefore, blends of different types of PE, which differ in terms of density (HDPE, LLDPE and LDPE), catalyst (Ziegler–Natta, Phillips, and metallocene), and branch content (1–40 branches per 1000 carbon atoms), have drawn much attention of researchers, both from industry and academia over the last few decades. The properties of these blends have been investigated using different types of techniques like differential scanning calorimetry (DSC), [ 1 ] rheology, [ 2 ] wide angle X‐ray diffraction, [ 3,4 ] small angle neutron scattering, [ 4,5 ] small angle X‐ray scattering, [ 4 ] small angle light scattering, [ 4 ] Fourier‐transformed infra‐red (FTIR) spectroscopy [ 6 ] and microscopy, [ 4 ] either individually [ 1–5 ] or in combination. [ 4,6 ] Most of these research works were focused on understanding the miscibility and phase segregation of PE components in the melt state, phase segregation in solid state, effect of cooling rate on crystallization, and co‐crystallization.…”

Fundamentals of structure–property relationships in blown films of linear low density polyethylene/low density polyethylene blends

“…less than 20%, to a LLDPE to understand the impact of the LDPE addition on LLDPE film physical properties such as tensile properties, Elmendorf tear strength, dart impact strength, etc. 15–18 However, the effect of higher level of LDPE in the blends (LDPE-rich blends) has not been studied as much, and hence is not as well understood. Falla 19 studied blown films of LLDPE/LDPE blends over the entire composition range from 0 to 100%.…”