MSE Proposal Announcement - Abhiram Kannan
Title: Investigation of the Microstructural Response of Novel Polyethylenes on Mechanical Loading
Committee: Dr. David Bucknall (MSE) (advisor)
Dr. Donggang Yao (MSE)
Dr. Meisha Shofner (MSE)
Dr. Kyriaki Kalaitzidou (ME)
Dr. Aaron P. Eberle (ExxonMobil Research and Engineering)
Date: 23rd OCT 2013
Location: 3515 MRDC
Time: 10 : 00 AM
The mechanical behavior of films made from copolymers of ethylene and α-olefins is dependent on the morphology and the microstructure of the films. While the morphology is dependent on the processing conditions under which the films are fabricated, the microstructure is controlled by the choice of the molecular weight, branch content and distribution. By carefully controlling these three parameters, the crystalline and the amorphous content of these semi crystalline polymers can be modified. Such modifications to the microstructure coupled with morphological control via the choice of processing conditions, can then be used to manipulate the response of films to mechanical loading. However, the direct correlation between the molecular architecture and the macroscopic mechanical behavior is not well understood. As a result the engineering of specific mechanical properties in polymers by designing their microstructures is not an exact science. To address this issue requires characterizing the macro-scale mechanical response of these films directly to their morphology and their molecular architecture. This is the overall goal of this thesis proposal. As a means to achieve this, we exploit mechanical testing of polymer films with in situ synchrotron small- and wide-angle X-ray scattering (SAXS and WAXS, respectively).
In this study, highly anisotropic melt-blown films made from two branched polyethylenes that exhibit different film specific mechanical properties will be investigated. The macroscale mechanical response of the films will be understood by studying the deformation of the films in uniaxial and biaxial loading conditions. To perform the biaxial test, a unique strain rig compatible with servo-hydraulic load-frame instruments has been designed and built. The molecular and mesoscale structure of the polyethylenes will be determined by SAXS and WAXS, in situ with aforementioned deformation geometries by using high flux synchrotron X-ray sources. In situ studies investigating the influence of processing conditions on the morphology will be performed by simulating these conditions using combinations of strain rates and elevated temperatures. Preliminary data for uniaxial in situ experiments has shown that at low strains, large differences in morphological development are observed when films are deformed along their machine direction (MD) or perpendicular to it, i.e. the transverse direction (TD). Additional scattering studies from off-axis measurements, where the X-ray beam is not perpendicular to the polymer surface will also be undertaken to characterize the through-thickness structure of the films. The differences in scattering between the films made from the two different resins will ultimately be related to the differences in their architectures and their mechanical properties. Through all of these in situ scattering measurements, we will provide insight into the molecular origin of the mechanical behavior.