Investigation of unusual orientation in polyethylene by infrared spectroscopy

Abstract

A quantitative analysis of the 725 cm.−1 doublet in the infrared spectrum of polyethylene is given and used to check the “row” model of polyethylene, as it naturally crystallizes from drawn melt. This analysis depends on a new interpretation of the 725 cm.−1 doublet, according to which the 730 cm.−1 component has its transition moment along the a crystallographic axis, and the 720 cm.−1 component along the b axis. The amorphous polymer gives only a band at 720 cm.−1. The analysis in certain cases enables the amount and orientation of the amorphous component of the polymer to be determined. From similar considerations, variations in the relative intensity of the two peaks in the course of drawing unoriented polyethylene are explained.

Computer simulation of the film blowing process incorporating crystallization and viscoelasticity

“…This is consistent with the observation of most researchers, such as Keller (1955Keller ( , 1967, Desper (1969) and Zhang (2001). The film samples are divided into two sets, as shown in Table 12.…”

“…Keller and Machin (1967) reported that in polyethylene films, random or weak orientation of the amorphous chains was encountered when low or intermediate stresses were applied. Most researchers showed that the crystalline a-axis is more oriented in the machine direction, [Keller and Sandeman (1955), Keller (1967), Desper (1969) …”

“…He concluded that the unit cell is orthorhombic and that the chain axis lies along the crystallographic c-axis. Keller (1955) and Keller and Sandeman (1955) investigated the orientation in polyethylene for hot-drawn polyethylene tubes and suggested two models, based on observations from X-ray diffraction patterns and infrared spectroscopy. The first model (row structure model) is a structure where the crystallographic b-axis is oriented perpendicular to the draw direction (or in our case machine direction), and the a-and c-axes were twisting around the b-axis.…”

“…We considered that orientation of the crystalline phase is determined by the orientation of the crystalline c-axis with regard to the direction of interest [Keller and Sandeman (1955), Aggarwal et al (1959)]. …”

“…Fourier Transform Infrared (FTIR) analysis is the most common method for measuring chain orientation [Cole and Ajji (2001)]. Orientation is strongly affected by the degree of crystallinity and the magnitude of tensile stress [Keller (1955[Keller ( , 1967]. White and Spruiell (1981) defined the orientation factors for both the chain axis arid the three crystallographic axes (Figure 55).…”