Strength Development at Incompatible Polymer Interfaces

Mechanical strength of incompatible polymer interfaces welded above T$\sb{\rm g}$ has been investigated as a function of time, temperature, and composition. Three pairs of polymers were used: polystyrene-polymethylmethacrylate, polystyrene-co-acrylonitrile-polymethylmethacrylate, and polystyrene-co-acrylonitrile-polycarbonate. For each pair, the weld strength, as measured by G$\sb{\rm IC}$, attained a constant value which increased with welding temperature. While only five to ten percent of bulk G$\sb{\rm IC}$ values, these plateau values are orders of magnitude greater than the work of adhesion calculated using intermolecular forces. For the copolymer-homopolymer pairs, the maximum plateau strength was reached when the interaction parameter was a minimum. These results are in agreement with a model of the interface based on current molecular theories of incompatible interfaces coupled with a chain pull out microstructural deformation mechanism, which predicts that G$\sb{\rm IC}$ increases inversely with the interaction parameter, X. Microscopic investigation of the fracture surfaces revealed dissimilar fracture surfaces for a given pair, with evidence of stick-slip crack growth. X-ray photoelectron spectroscopy revealed residues of one polymer on the other's surface, indicating cohesive fracture occurred to some extent; in each case, the residue was always from the polymer with the lower entanglement density.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Metallurgical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Willett, Julious Lee

Contributors dc:contributor

• Wool, Richard P.

• Engineering, Materials Science

Identifier

(UMI)AAI8823290

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/71853