Definition
A chemical process in which adjacent long-chain polymer molecules are joined to one another by additional chemical bonds, forming a stronger, more rigid, and more heat-resistant three-dimensional network. Cross linking is used in the curing of rubber, plastics, sealants, and composite resins to give the finished material its final mechanical and thermal properties.
Plain English
It is the process of tying long molecule chains together with extra bonds, so the material becomes tougher, stiffer, and better able to handle heat. Before cross linking, the chains slide past each other easily; after cross linking, they hold together as one connected structure.
Context Anchor
Seen in aircraft maintenance discussions about composite repairs, sealants, adhesives, rubber parts, and protective coatings.
Derivation
From 'cross' (across, from one side to another) and 'link' (a connection). The chemical bonds run across from one polymer chain to a neighbouring chain, linking them together — hence cross linking.
Why Pilots Care
Many parts on an aircraft — O-rings, seals, hoses, tires, sealants, and composite skins — depend on properly cross-linked materials to hold their shape, resist fuel and heat, and stay flexible without breaking down. If cross linking is incomplete or has degraded with age, the part can soften, crack, or leak.
Analogy
Think of two loose ropes with short ties added between them. The more ties you add, the harder it is for the ropes to slide around separately. Cross linking does something similar inside a curing material.
Intuition Check
Cross linking does not mean connecting two aircraft systems together. Here it means internal chemical bonds forming inside a material as it cures.
Example Sentence 1
The composite repair manual specified a cure temperature high enough to ensure full cross linking of the resin.
Example Sentence 2
Insufficient heat prevented complete cross linking, leaving the paint soft and prone to damage.