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Material World
Application

Adhesion and bonding

Joining without a fastener — and increasingly the only way to join two materials that cannot be welded to each other.

An adhesive joint spreads load over an area where a rivet or a weld concentrates it at a point, which is why bonded joints outperform mechanical ones in fatigue and why aircraft and vehicle structures use them so heavily.

It is also the answer to a problem modern design creates constantly: dissimilar materials. Carbon fibre cannot be welded to aluminium and drilling it cuts the fibres that carry the load. Adhesive bonding is often the only structural option, and the joint's weakness is almost always the surface preparation rather than the adhesive.

Uses

Structural bonding in aerospace, automotive and construction; laminating plywood and engineered timber; footwear; electronics assembly; and the enormous low-value trade in packaging and labelling adhesives.

The materials are mostly polymers: epoxies where strength matters, polyurethanes where flexibility and gap-filling matter, cyanoacrylates for speed, and phenolic and urea-formaldehyde resins holding together most of the world's sheet timber products.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

uses

  • Epoxy resin — material · the structural adhesive: it fills gaps, cures without shrinking, and bonds metals and composites that cannot be welded to each other
  • Polyurethane — material · where the joint must flex — construction, footwear, and the foam adhesive in a can
  • Phenolic resin — material · the largest use of the resin by tonnage: it is what holds plywood and every engineered timber panel together
  • Resin — material · as a tackifier, and as the birch-bark tar that hafted stone tools 200,000 years ago — the oldest manufactured adhesive there is

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Adhesion and bonding back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Adhesion and bonding → uses (the structural adhesive: it fills gaps, cures without shrinking, and bonds metals and composites that cannot be welded to each other) → Epoxy resin → is produced by (the resin is made first and the network second — cure is a polymerisation carried out by the user rather than the manufacturer) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
  • Adhesion and bonding → uses (where the joint must flex — construction, footwear, and the foam adhesive in a can) → Polyurethane → is produced by (a diisocyanate and a polyol reacting as they are mixed, so the polymer and the finished part are made in the same moment) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
  • Adhesion and bonding → uses (the largest use of the resin by tonnage: it is what holds plywood and every engineered timber panel together) → Phenolic resin → is produced by (phenol condensed with formaldehyde, releasing water) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
  • Adhesion and bonding → uses (as a tackifier, and as the birch-bark tar that hafted stone tools 200,000 years ago — the oldest manufactured adhesive there is) → Resin → is produced by (as tall oil rosin from the black liquor — a by-product of making paper, and now a larger source than tapping) → Kraft pulping → takes as input (with sodium sulfide, breaks the lignin into fragments soluble in the alkaline liquor) → Sodium hydroxide → is produced by (at the cathode, in fixed proportion to the chlorine whether demand agrees or not) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
  • Adhesion and bonding → uses (as a tackifier, and as the birch-bark tar that hafted stone tools 200,000 years ago — the oldest manufactured adhesive there is) → Resin → is sourced from (tapped from the living trunk — from the bark and sapwood rather than the wood itself, which is why a tree can be worked for decades and still be felled for timber afterwards) → Wood
  • Adhesion and bonding → uses (the structural adhesive: it fills gaps, cures without shrinking, and bonds metals and composites that cannot be welded to each other) → Epoxy resin → is produced by (the resin is made first and the network second — cure is a polymerisation carried out by the user rather than the manufacturer) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is produced by (electrolysis of potassium bifluoride, which is molten and conducts — there is no chemical oxidant strong enough to displace fluorine from a compound, so electricity is the only route and always has been) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite

These are the most distinct paths back. Adhesion and bonding can be traced through others besides.