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Feats of Engineering Part 1: A Sea-Change in Adhesive Chemistry

( 01/22/2020 ) Written by: John Hill

Did you know:

  • Wind turbine blades can be almost as long as airplane wings; the longest blades spin at up to 180 mph at their tips—and load-bearing structural adhesives are often part of blade assembly.
  • The Jeddah Tower, currently under construction in Saudi Arabia, is designed to have an elevator rise of 660 meters and travel at speeds higher than 10 meters per second. This elevator and other visionary designs push the boundaries of current technologies, but cutting-edge engineering and materials, including structural adhesives, are making previously impossible heights and speeds a reality.
  • There are an estimated 15 million heavy trucks registered in the United States and trucks account for 63 percent of vehicle fuel purchases. Reducing vehicle weight by using lighter materials to construct the bodies is an important strategy for achieving lower fuel use—and adhesives are a critical part of aluminum and composite panel assembly.

These rigorous applications require an adhesive that dramatically improves upon “old-school” chemistries. Next-generation acrylic adhesives—two-component systems comprising an adhesive and an accelerator—are delivering. These acrylics have evolved to offer higher elongation, superior lap-shear strength, impact and fatigue resistance, improved peel strength and excellent failure mode across difficult-to-bond metal substrates. They also offer excellent high and low temperature performance and more robust bonding to a wider variety of substrates. In many instances, their bond strengths can approach or exceed the strength of substrates.

Compared to traditional fastening methods such as rivets, welds and tapes, structural adhesives eliminate the costs associated with metal preparation and finishing operations. They are formulated to offer a wide range of open times and cure speeds to improve manufacturing processes and final products.

Read on to see where we are in terms of adhesive development—and how engineers and manufacturers are relying on next-generation acrylic adhesives for cutting edge designs.

A Short History of Acrylic Adhesive Development

Significant commercial use of acrylic adhesives began in the 1960s. Early acrylic formulas were polymethyl methacrylate dissolved in methyl methacrylate, with an accelerator used at a high mix ratio. These first-generation systems, which tended to be brittle, were used mostly for bonding plastics. 

By the 1980s, second-generation products were formulated that incorporated butadiene rubber tougheners and metal adhesion promoters. They featured 1:1 and 4:1 mix ratios with formulated accelerators. Second generation systems were adopted for various commercial applications and have delivered effective bonding with better low-temperature performance and improved bonding to bare metals.

Next-generation acrylic systems feature advanced terpolymer and core-shell rubber tougheners, blends of polymerizable monomers (with methyl methacrylate being the most commonly used) and a 10:1 mix ratio. These systems are able to deliver bond strengths that approach or exceed the strength of the substrate, enabling them to withstand many types of loading. They can also tolerate the high temperatures associated with e-coat, paint and powder curing. The new adhesive systems are made without toxic components, meeting the European Union chemical regulations known as REACH.

One important reason next-generation acrylic adhesives offer such improved performance is that their elongation is much higher than that of second-generation acrylics, with elongations up to 100 percent or more. This is achieved without loss of tensile strength, which remains at or more than 18 MPa. 

A benefit that is important to fabricators is the ability to bond different substrates, including those that were difficult to bond with second generation products. Tests show consistent, uniform failure mode of next-generation adhesives.

Changes to adhesive chemistry allow for dramatic developments in engineered products. Stay tuned for Part 2 of our blog series and see how auto manufacturers are not only enhancing assembly processes, but helping vehicles achieve better fuel performance as well.


John Hill

John Hill has been with LORD for 24 years and is a principal engineer in the structural adhesives group. He has bachelor degrees in chemistry and microbiology from the University of Minnesota and a PhD in organometallic chemistry from Purdue University.

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