Linear low-density polyethylenes (LLDPE) are copolymers that are widely used for thin film packaging applications. In such applications, it is necessary to match the required puncture and tear properties with correct formulation of the LLDPE. However, despite significant studies there still remains a disconnect between the molecular architecture, i.e. branch content, molecular weight between branches, etc, and the macroscopic mechanical properties of the polymers. To address this issue, in-situ X-ray scattering methods have been widely employed to study polymer uniaxial deformation behavior. The nature of the uniaxial deformation behavior of polyolefins can be explained using continuum models, a surprisingly simple yet effective example of which is the spring and dashpot model of Haward and Thackray. Such models try and interpret the observed behavior in terms of viscous and elastic components associated with the crystalline and amorphous phases within the semi-crystalline polyolefins. However, these continuum models only provide a very indirect correlation between the observed mechanical behavior and the molecular architecture. In this talk we discuss the recent work we have been undertaking on metallocene LLDPEs possessing controlled architectures, where we have exploited in-situ X-ray scattering to develop a more complete molecular interpretation of the deformation processes. In these studies we incorporate results from both small- and wide- angle X-ray scattering to extract morphological information about the crystalline and amorphous regions of the film during deformation. We show that the dimensional and orientational behavior of the LLDPEs determined from the scattering is directly related to the variation in ethylene run lengths of the polymers. Furthermore, detailed analysis allows us to show that the mechanical properties of the LLDPE films, ie their tear and dart resistance values, can be predicted from the dimensional and orientational parameters. As such we are able to demonstrate direct correlations between LLDPE molecular architecture and mechanical properties.<br/>

Relationships between polyethylene architecture and mechanical properties

251st National Meeting (2016)

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