What makes cotton different from most material made up of cellulose is that the crystallinity in the fibre increases the strength the wetter it becomes. In other material primarily made up of cellulose, like paper, the strength decreases when it becomes wet.
This can be explained in terms of intermolecular hydrogen bonding between cellulose chains and their degree of crystallinity. Hydrogen bonds occur between the hydroxyl groups of adjacent molecules and are more prevalent between the parallel, closely packed molecules in the crystalline areas of the fibre. When the cotton is wet, the water present forms additional hydrogen bonds within the crystalline areas, increasing the strength of the cotton.
The extra hydrogen bonding occurs not only along the cellulose chains, increasing their longitudinal strength, but between them as well, creating an overall stronger structure.
So Jackie Chan was right, cotton is stronger when wet. But merely having a wet shirt isn’t the only reason that Jackie Chan manages to break out of jail. The secret is also in his method.
Chan ties his shirt around the steel bars, places a wooden stick as a handle/lever and turns the handle to bend the bars-amazing! All this is with good old muscle power, so why does this work? We can’t bend steel with our bare hands (well most of us can’t!) The wooden handle acts as a lever multiplying Chan’s muscle power.
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