Self-Seal Adhesives

Self-Seal Adhesives

  • Submitted By: dionysoss
  • Date Submitted: 12/01/2013 1:45 PM
  • Category: Science
  • Words: 1828
  • Page: 8
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50
Self-Seal Adhesives
50.1 Introduction ......................................................................50-1
Adhesion and Cohesion • Seal Performance

Larry S. Timm
Findley Adhesives, Inc.

50.2 Application Techniques.....................................................50-3
Handling • Procedures

50.1 Introduction
Cohesives, often referred to as “self-seal adhesives,” are coatings which in a dry state exhibit the unique ability to selectively stick to themselves when brought together under pressure.

50.1.1 Adhesion and Cohesion
Natural rubber is the ingredient common to all self-seal adhesives. It is this raw material, generally utilized in the latex form, which confers or facilitates the ability to cohere. Natural latex consists of long chain, high molecular weight molecules, the ends of which are thought to contain an extra double bond protected with a weak hydrogen-bonded protein molecule. It is believed that when such molecules are positioned in intimate contact and mechanical or thermal energy is introduced, the following reaction takes place. First, the weakly hydrogen-bonded protein molecule breaks from the long chain and second, stored elastic energy from within the molecule is released, causing molecular vibration. The subsequent entanglement of the chains and joining at the now-available bonding sites produces a molecular inseparable condition referred to as a cohesive seal (Figure 50.1, Figure 50.2, and Figure 50.3). In application, the greater the number of bonding sites utilized to impart adhesion, the smaller the number remaining to facilitate subsequent adhesion. Laboratory evaluation on the functionality of self-seal formulations confirms the significance of achieving an appropriate adhesive/cohesive balance relative to a specific substrate. Through product selection or formula modification, it is possible to enhance or accentuate the adhesive or the cohesive properties, but not, however, without inversely diminishing the other...

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