Structural Bonding: Epoxy or MMA (Methyl Methacrylate)?

Recommending the Right Bonding Technology for Structural Bonding Specs

Ask yourself the following questions to find the right solution:

  •   One-part epoxy?
  •   Two-part epoxy?
  •   Standard MMA?
  •   MMA Core-Shell®(some MMA adhesives are filled with elastomer beads that have hard shells and soft centers to give them greater flexibility and unique fatigue-resistance properties).This patented technology (Core-Shell® technology) is available only in the ITW Plexus range.?
  1.      Should a room-temperature-cure adhesive be used? Or should the parts be heated (to 150°C/302°F, for example)? One-part epoxies can be immediately ruled out if it is not possible for the user to heat the parts.
  2.      What is the maximum temperature the bond will be exposed to?Only one-part epoxies are suitable for high temperatures (up to 180°C [356°F]. Methyl methacrylates withstand temperatures up to 120°C (248°F) while two-part epoxies withstand temperatures up to 80°C (176°F) (120°C [248°F] in the case of Permabond ET540and Permabond ET5401).
  3.      What is the required mechanical strength? 1K (one-part) epoxies have a shear strength of up to 40 MPaversus 20-25 MPa for 2K (two-part) epoxies and standard MMAs. Note that Core-Shell® MMAs have a lower shear strength of around 12 MPa.
  4.      Is flexibility a requirement? Although not as flexible as an adhesive sealant, Core-Shell® MMAs and some two-part epoxies are relatively flexible and withstand vibrations better than one-part epoxies and standard MMAs, ensuring better fatigue resistance.
  5.      What is the gap to fill? Two-part epoxies do not yield good results with gaps measuring less than 1 mm.
  6.     What is the substrate to be bonded? All the technologies are possible with standard metals. The Plexus range of special adhesives (MA-3940 and MA-3940LH) works best for composites and plastics. Note that glass is not an easy substrate for structural bonding. Some epoxies may work.
  7.      Will the bond be in contact with chemicals? If the answer is yes, one-part epoxy is the best solution. MMAs (methyl methacrylates) are more susceptible to attack.
  8.      Is clarity a requirement? If the answer is yes, ET500ET515 and MA685 are the only suitable products.

Summary table

One-part epoxy Two-part epoxy MMA
Standard
MMA
Core Shell
RTV curing No Yes Yes Yes
Maximum temperature 180°C (356°F) 80°C (176°F)
(120°C/248°F for ET540 and ET541)
120°C (248°F) 120°C (248°F)
Mechanical strength 40 MPa 20 MPa 25 MPa 15 MPa
Flexibility No Depending on grade No Yes
Fatigue resistance + + +++
Chemical resistance Excellent Good Average Average
Clarity No ET500/ET515 MA685 No
Min. gap 0.25 mm 1 mm 0.5 mm 0.5 mm
Max. gap 5 mm 5 mm 4 mm 10 mm
Metal bonding +++ +++ + +++(MA830 / MA832)
Glass bonding
Plastic bonding + ++ +++(MA3940 / MA3940LH)
Composite bonding + + +++ +++

For more information:

Epoxy Selector Guide
MAA Adhesive Selector Guide

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