Grades 6–8 · Materials & Matter
How does vulcanization help rubber keep its shape?
Unmodified natural rubber contains long, flexible polymer chains. Those chains can slide past one another, especially when the material is warm. A rubber object may therefore deform permanently rather than springing back in a useful way.
In the diagramChemical bridges limit free chain slidingLinked networkNetwork stretchedblue polymer chains + orange sulfur bridges
Vulcanization adds chemical links between some neighboring chains. In a classic sulfur process, sulfur-containing bridges connect parts of the polymer molecules. The connected chains form a network instead of acting only as separate strands.
When this network stretches, chain shapes change and the links limit how far strands can slide apart. After the force is removed, the network can recover much of its original shape. This helps produce useful elastic rubber.
The number and type of links influence stiffness, heat resistance and deformation. Too many links can make a much more rigid material. Manufacturers therefore control the network and add other ingredients to obtain the different properties needed for seals, tires or other products.
About this explanation
Starting knowledge: Recognize long polymer chains and distinguish temporary stretching from permanent sliding of material.
Sources
- International Union of Pure and Applied Chemistry — Gold Book: Vulcanization