This article discusses adhesive bond failure modes on polypropylene. There are three main failure modes: adhesion failure at the interface between the adhesive and substrate, cohesion failure within the adhesive layer, and mixed mode failure exhibiting characteristics of both. To determine the cause, it is important to identify which failure mode is occurring. Adhesion failures usually originate in manufacturing, while cohesion failures can be from joint design issues or material properties. Once the failure mode is identified, the solution becomes clearer whether to examine manufacturing processes or product design.

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LATEST ISSUE Q&A: Adhesive Bond Failure Modes
By Scott R. Sabreen
Question: We’re having bonding problems on polypropylene, even when using
corona pretreatment. The problem comes and goes, how can we find a
solution?
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Answer: I would first recommend determining the adhesive bond failure mechanism
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mode. Essentially, there are three distinctive types:
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Adhesion failure interfacially between the adhesive and one of the adherends.
Association Cohesion failure by fracture of the adhesive layer leaving traces of adhesion on
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Mixed-mode failure exhibits characteristics of both adhesion & cohesion failure.
CALENDAR Adhesion failures occur at the interface between the adhesive and the adherend
March 27 (substrate). Visually, there will be residual adhesive remaining at any location on only
ABC’s of IML: A Basic Course, March 27, Skokie, IL., one surface. Adhesion failures that occur in-the-field almost always originate in the
(480) 473-0301, info@rbstechnologies.com manufacturing process; materials, adhesives, surface preparation, contamination,
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procedures/workmanship, environment, quality control testing and combinations
NPE2012, The International Plastics Showcase, thereof. The remaining cause is interfacial degradation, as a function of field service
Orlando, FL, www.npe.org life. This latter problem can be prevented during the product design/qualification
phase.
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Cohesion failures result in fracture of the adhesive and are characterized by the visual
presence of the adhesive material on the matching faces of both adherends
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(substrates). Bonds which fail by cohesion exhibit high-strength performance
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(achieving optimal dry adhesive bond properties). The adhesive surface may appear
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“rough” and may be lighter in color than the adhesive material, as applied. Failure is
usually by shear, but peel stresses or a combination of shear and peel can produce
cohesion failure. Cohesion failures that occur in-the-field are typically caused by poor
joint design, e.g., insufficient overlap length, or excessive peel forces. Excessive
porosity (humidity exposure), and the presence of voids below a critical size can also
result in cohesion failure.
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Mixed-mode failures exhibit characteristics of both adhesion failure and cohesion
failure because the interface is partially degraded. Essentially, this failure mode is a
transitional phase in which the strength of the adhesive bond is lower than the
cohesion failure strength.
The use of surface pretreatments, either gas-phase glow discharge (such as corona
discharge, flame and pressurized cold-gas plasma) or chemical primers, does not
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bond failure mode, the mechanism will guide you toward identifying and solving the
critical problem(s). If cohesion failure, examine the product design joint and materials.
If adhesion failure, scrutinize your manufacturing process!
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