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The Universal Source for Selecting, Testing and Verifying Adhesives

Posted on 5/31/2018 12:06:41 PM By Dr. Cynthia Gosselin (guest blogger, ChemQuest)
  

Recently one of my long-time colleagues with an electrical engineering background retired. My colleague, being the inventive sort, had developed a multipurpose product with potential use in transportation OEM applications. In this case, “transportation” has a truly diverse meaning: vehicle types ranging from passenger cars to light-, medium-, and heavy-duty trucks to big-rig cabs.

In theory, his invention had a potential fit in other applications, but he targeted automotive as his first foray to solve a vexing industry problem. He had to define many material characteristics and ultimately prove that the product would be functional, durable and corrosion-resistant in the aggressive transportation environment, which was no easy feat. This seemingly daunting task did not faze him, however, as he had ample time to devote to it. His work was proceeding smoothly – that is – until he was faced with proving that the adhesives he planned to use would be compatible with multiple materials and substrates. Given that his expertise didn’t extend to materials engineering, he quickly conceded he needed technical advice, ideally from established adhesives suppliers.

Of course, that was only the beginning: Which suppliers would speak to him, he mused – and which questions when properly answered would facilitate material compatibility?  Further, how could he verify supplier data found on a typical technical data sheet (TDS) in a manner that would be universally accepted as adhering (no pun intended) to good scientific and documentation principles without necessarily running every adhesives test known to the automotive world? After all, he had unlimited time, but not unlimited money.  He sought a practical methodology that would yield the necessary data.  Equally important, the data had to be easily verifiable, and his proven methodology had to be universally accepted for verifying the required adhesive bonding properties. 

While my colleague’s situation is an intriguing example of an entrepreneur looking for rigorous methods for proving with conclusive data that a material meets certain requirements, it is by no means new or unusual.  Even well-established manufacturers are seeking cost-effective (yet scientifically rigorous) testing protocols in 2018!

There is one “go-to” source for properly testing and verifying adhesive characteristics:

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ASTM Committee D14, which is devoted to all things adhesive.
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ASTM D4800 Standard Guide for Classifying and Specifying Adhesives provides a method for identifying the right adhesives for use with various materials and substrates. It even provides a means for specifying these materials through the ASTM standards that it references. Reviewing this guide brings perspective not only to the product under development, but also any necessary testing. 

For aerospace applications, ASTM D6465 Standard Guide for Selecting Aerospace and General-Purpose Adhesives and Sealants is recommended. In either case, these guides can be leveraged as a springboard to a productive discussion with an adhesives supplier. 

Likewise, ASTM provides myriad testing protocols for adhesive bonding. Subcommittee D14.80 on Metal Bonding Adhesives has produced forty-one standard methods for testing adhesive bond strength.  For virtually any type of adhesive joint you’re researching, there is a corresponding well vetted test method. These methods include, of course, the typical lap-shear (D1002 and D4896) and peel tests (D903).  Some applications require more complex information related to aging, durability, flexural strength of laminated assemblies and impact strength.  Other considerations include temperature and humidity effects on joint strength, moisture inhibitors, and retaining joint integrity in cyclic environmental conditions. Conveniently, all these tests and more are represented in Subcommittee D14.80.

With aluminum playing a larger role in vehicle production, surface preparation of that naturally aging substrate is critical to achieving bonding success. To that end, ASTM D3933 Standard Guide for Preparation of Aluminum Surfaces for Structural Adhesives Bonding, released in 1998 and updated in 2017, is critical for structural adhesives bonding since aluminum surfaces degrade over time.

ASTM D3762 Standard Test Method for Adhesive-Bonded Surface Durability of Aluminum (Wedge Test), while one of the few qualitative tests in ASTM, is “very discriminating in determining variations in adherend surface preparation parameters and adhesive environmental durability”.  This test has assisted in controlling surface preparation operations for a wide variety of aluminum alloys that are ultimately adhesive bonded.  It is recommended for screening durability of surface preparation-primer-adhesive systems through the analysis of crack growth and mode and locus of joint failure.  This test method is also useful for providing information on the durability of other metals and plastics, provided thickness and rigidity are considered. If quantitative fracture strength is required, D3433 Standard Test Method for Fracture Strength in Cleavage of Adhesives in Bonded Metal Joints is the correlating specification.

The ASTM Committee on Adhesives also provides guidance and detailed specifications for adhesive bonding of wood (Subcommittee D14.30), plastics (Subcommittee D14.40) and construction adhesives (Subcommittee D14.70).  The Working Properties Subcommittee (D14.10) contains nineteen specifications for testing the practical aspects of working with adhesives.  Examples include: D1084 Standard Test Methods for Viscosity of Adhesives, D1337 Standard Practice for Storage Life of Adhesives by Viscosity and Bond Strength, and D5113 Standard Test Method for Determining Adhesive Attack on Rigid Cellular Foam.

There is even a standard related to adhesive odor: D4339 Standard Test Method for Determination of the Odor of Adhesives. This standard is useful in determining suitability of an adhesive in applications where the odor level associated with end use is critical, such as vehicle interiors. These standards reflect many routine and practical applications. Rather than depending upon historical precedent within individual companies, ASTM standards can codify the results, rendering them universally accepted.

The ASTM motto is “helping our world work better.”  Standards in Committee D14 are universally accepted and thus allow everyone – from those who are immersed in adhesive bonding science – to those who only occasionally dip their toe into it – speak the same language by understanding universally accepted test results.

As for my colleague, he studied the standards with the tenacity of an electrical engineer. Consequently, his adhesive compatibility program was a success.

ChemQuest1-May2018
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         from: adhesivetest.com

ChemQuest2-May2018
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               from: AZO Materials

ChemQuest3-May2018
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Coating and Converting Technologies and Principle of the Lap Shear Test
Industrieverband Kiebstoffe e.V.