About Different Types of Acrylic Adhesives

Rebecca Wilmot
Adhesive Selection, Adhesive Selection and Use
November 4, 2016

Acrylic Adhesives

In the glue biz, we use the term acrylic adhesive loosely, and in doing so, we can create some confusion.  There are many types of adhesives based on acrylic chemistry in the form of one and two-component adhesives as well as no-mix resin and activator, even solvent or water-based adhesives, not to mention a variety of acrylic-based pressure-sensitive adhesives (tapes).  There are also many adhesives that have an acrylic nature that aren’t categorized as acrylic adhesives.

Acrylic Adhesives with Other Names

  1. Anaerobic adhesives are based on acrylic chemistry but we classify them as anaerobics, not acrylics. Anaerobic adhesives are used for threadlocking, thread sealing, retaining, and gasketing metal components.  To cure these materials they need to be in contact with metal and not in contact with oxygen (when the adhesive is confined between two metal surfaces.)
  2. UV curable adhesives may be of acrylic nature, but like anaerobics we generally categorized by the cure mechanism (UV), not the adhesive composition.
  3. Cyanoacrylate adhesives are acrylic but we classify them as cyanoacrylate or instant adhesives. These are also called super glues or crazy glues.
  4. Methylmethacrylate adhesives are a type of acrylic adhesive that may be grouped into an acrylic category or separated out as MMA’s.

Rest assured; Permabond and other adhesive manufacturers do not avoid calling these adhesives acrylic adhesives to be deceptive – it’s simply that due to the variety of acrylic adhesives available, the cure mechanism is often a better descriptor to understand if that particular type of adhesive is suitable for an application.

Anaerobic Adhesive Uses

Consider that for anaerobic acrylic adhesives, both substrates should be metal, and the adhesive/sealant must be confined between two surfaces or cured with an activator.  Often anaerobic adhesives are used as weld sealants, which seems contra-indicated as weld sealants are brushed on a warm surface and not confined between two surfaces.  When using anaerobic adhesives for weld sealants, the parts are warmed, and low-viscosity adhesive/sealant is applied and allowed to wick into the small pores in the welds. This does, in fact, deprive the adhesive of enough air to cure.  After cure, wipe away the excess or spray it with an activator to cure it off.

Another application in which the anaerobic acrylic adhesives leave a residue of adhesives that isn’t between two surfaces is munition sealing.  The adhesive that is between the bullet and the shell is cured anaerobically; however, due to the high-speed manufacturing required, spraying with an activator or wiping away residue is not possible. Permabond developed specialty acrylic adhesives with NATO approval. These cure anaerobically as well as with UV light – so is this adhesive an acrylic, an anaerobic, or a UV curable adhesive?  Yup, you got it – it is all three!

Structural Acrylic Adhesives

acrylic adhesive 2

For industrial bonding applications, structural acrylic adhesives, many manufacturers sub-categorized by application.  We define Structural Adhesives as adhesives that can support a structural load when fully cured

They also provide:

  • impact and vibration resistance
  • high upper-temperature limits
  • durable bonds in harsh environments

There are several types of structural acrylic adhesive. In this article, we’ll discuss…



Methyl Methacrylate Adhesives

Methyl methacrylate adhesives (MMAs) have the most memorable smell.  Not only is the smell offensive, it reminds many of the dentist – which doesn’t help most to find it pleasant.  If an adhesive specialist recommends an MMA as the best type of product for your application, ventilating the area is recommended.  MMAs are very good for bonding plastic. Permabond has both two-component and surface activated MMA adhesives.

Advantages of Methyl Methacrylates
  • Excellent adhesion to many substrates, including; thermosets, thermoplastics composites, and metal
  • Fast cure at room temperature
  • High shear and peel strength
  • Good impact strength
  • Good chemical resistance
Limitations Methyl Methacrylates
  • Flammable
  • Strong odor
  • Accurate mixing is imperative
  • Limited pot life once mixed

Surface-activated Adhesives

Surface-activated or surface-initiated acrylic adhesives. Create strong bonds between metals, ferrites, glass, and some plastic.  Generally, the activator is applied to one surface and a bead of adhesive to the other surface, and upon joining, enough mixing occurs to form a very strong bond.  Some of these products can be used wherein the adhesive is applied to the same substrate as the activator – but care must be given to assemble the products before cure begins.

Bead–on–bead Acrylic Adhesives

Bead–on–bead structural acrylic adhesives.  For this type of adhesive, you place a bead of one part on one surface and a bead of the other part on top of it.  If you need more time to assemble the parts you can apply the second bead to the other surface.  Specialty products are available in which the two beads free-fall together onto a part, providing assembly is done consistently within the time frame allowed.

Two-component Acrylic

You can measure and mix two component adhesives by hand; however, the most consistent way to get sufficient mixing without incorporating air is through static mix nozzles.  We don’t advise mixing bead-on-bead adhesives through static mix nozzles as the cure is too fast.

Surface-activated, Bead on Bead, and Two-Component Acrylics have similar advantages listed below.

  • Rapid room temperature cure – no ovens required
  • 100% solids – Environmentally friendly
  • Nonstringing – Clean, efficient process
  • Thixotropic viscosity –Easy to dispense
  • Lower odor – Worker comfort
  • Most are Non-flammable – Reduced shipping and handling costs
  • High shear strength – Strong
  • Toughened – Impact, vibration, and peel resistance
  • Durable in high moisture environments
  • High-temperature resistance up to 390°F

The limitations of each type vary

Limitations of Surface Activated
  • Performance degrades with excess gap
  • Adhesive squeezed out of the bond line will not cure
  • Most grades are not flammable (MMA surface activated is flammable.)
  • Two-part application
Limitation of Bead on Bead
  • Short open time
Limitation of external mix system –
  • An accurate dispensing system is required.

Most structural acrylic adhesives do not have a strong odor. However, specialty low-odor grades are available.

How to decide which type is best?

Here are the questions an adhesive specialist may ask:

  1. What are the substrates and required strength?

Most acrylic adhesives will bond well to metals.  MMAs have good adhesion to most plastics.  New specialty grades even bond polyolefins.

  1. What is the gap?

Surface-activated and bead-on-bead types likely have less gap-filling ability than the two-component mixed products.  Keep in mind that the maximum gap fill listed for the two-component mixed adhesives merely indicates the best shear strengths; you may fill larger gaps with less strength. However, for the surface-activated products, maximum gap fill is key. If you require more depth of cure, you may need to activate both surfaces.

  1. What is the preferred assembly process?

There may be several options, so knowing what is preferred is ideal.

Why use a structural acrylic adhesive instead of an epoxy?

Often I’ve seen adhesive specialists ask engineers for two lists of adhesive requirements, one being the ‘must haves’ the second being the ‘nice to haves’.  The selection between structural acrylics and structural epoxies fall into two categories.

  1. Adhesion – although both epoxies and acrylics bond most metals, some acrylics have excellent adhesion to plastics.
  2. Fixture speed – The cure speed of heat cure epoxies is dependent on the temperature, but they take 15 minutes or more to cure – (some exceptions for induction curing apply.) Two-part epoxies are available in a variety of cure speeds, but the quickest take 4-6 minutes to fixture.  Conversely, many acrylics provide a good amount of handling strength in 30 seconds.

Aren’t all acrylic adhesives flammable?

MMAs or methyl methacrylates are classified as flammable; solvent-based grades may also be.  However, there is a large variety of solvent-free, non-flammable structural acrylics available.

For more information on Permabond acrylic adhesives, contact our technical team.

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