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Adhesives for Composites

Posted on 2/19/2019 11:14:29 AM By Deb Bhattacharjee
  

High performance adhesives have increasingly been used in transportation, construction, appliance, general industrial, marine, consumer electronics, sports equipment and biomedical/dental industries to assemble composite products primarily because they are lightweight with superior strength compared to incumbent heavier and weaker materials.Adhesively bonded composite joints has additional advantages in fewer parts and concentrated stress, fatigue resilience, load transfer, smooth contour and corrosion resistance while the disadvantages include difficulty in surface preparation, disassembling and inspection, thickness limitation, residual stress, etc.

The mechanical properties of adhesives should be designed by careful selection of resin chemistry (e.g. epoxy, polyurethane, acrylate, polyamide, etc.) to match those of the substrate materials, thereby adding to the strength of the finished product.  To achieve the optimum bond strength, it is important to:

  • Clean surfaces free from dust or debris
  • Abrade or energize the surfaces to be bonded
  • Use appropriate adhesive for the application
  • Provide uniform bondline thickness, and constant clamping pressure along bondline until complete cure

Conventional two-component epoxy adhesives are extensively used in the automotive industry to bond SMC, SRIM (structural reaction injected molding), and other substrates. However, many of these epoxy systems, particularly polyamide-based systems, have undesirably long open times and require post-baking in order to achieve full cure of the adhesive composition. This problem could be overcome by incorporation of a coupling agent with the epoxy resin and by using aliphatic amines as part of the curative.Acrylate monomers may be incorporated in the epoxy resins to further adjust open time and improve adhesion, in particular, to metal substrates.

An improved method and apparatus for fabricating adhesive fillers can reduce processing time and labor costs by extruding the fillers either directly onto a composite structural member in order to fill a void in a composite structure, or onto a tool that may be used to maintain the cross-sectional shape of the filler and place the shaped filler on a structural member. This method may substantially eliminate the need for prefabricating and storing fillers.

 

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