Strength of incompatible amorphous polymer interfaces

Journal Article · Mon Sep 27 04:00:00 EDT 1993 · Macromolecules; (United States)

DOI:https://doi.org/10.1021/ma00072a010· OSTI ID:5840743

Willett, J L; Wool, R P ^[1]

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1. Univ. of Illinois, Urbana, IL (United States)

The mechanical strength of incompatible polymer interfaces welded above T[sub g] was investigated as a function of time, temperature, and composition. Three pairs of polymers were used: polystyrene-poly(methyl methacrylate), poly(styrene-co-acrylonitrile)-poly(methyl methacrylate), and poly(styrene-coacrylonitrile)-polycarbonate. For each pair, the weld strength G[sub 1c], measured by wedge cleavage, attained a constant value which increased with welding temperature. While the plateau strengths are typically only about 5-10% of bulk G[sub 1c] values, they 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 Flory-Huggins interaction parameter, [chi], was a minimum. These results are in agreement with a model based on Helfand's molecular theories of the structure of incompatible interfaces, coupled with a microscopic deformation mechanism, which predicts that G[sub 1c] [approximately] 1/[chi]. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis of the fracture surfaces revealed dissimilar fracture surfaces for a given pair, with evidence of stick-slip crack growth. XPS revealed residues of one polymer on the other's surface, indicating cohesive fracture occurred to some extent. In each case, the cohesive fracture occurred in the polymer with the lower entanglement density and lower craze stress.

• DOE Contract Number: AC02-76ER01198
• OSTI ID: 5840743
• Journal Information: Macromolecules; (United States), Journal Name: Macromolecules; (United States) Vol. 26:20; ISSN MAMOBX; ISSN 0024-9297
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
CRACK PROPAGATION
FABRICATION
INTERFACES
JOINING
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
ORGANIC COMPOUNDS
ORGANIC POLYMERS
POLYMERS
TENSILE PROPERTIES
WELDING