WHY FABRICS WRINKLE?


Why do some fabrics wrinkle and others don't? Close examination of this question reveals a relationship between moisture absorption and wrinkling. Wool and cotton fabrics wrinkle, both fibers absorb water. Polyester and nylon fabrics are more restive to wrinkling; they absorb much less than the other two.

To understand wrinkling of cellulose fibers, consider the stress and strain forces within a smooth rod as it bent - see figure 43. The stretching stresses at the outer reaches of the bend provide lateral forces to adjacent polymer chains which can cause them to move. The inner polymer chains are under compression stresses – also
providing lateral forces. A large diameter rod, because the radius of curvature is bigger, will exhibit greater strains than a thinner rod.

Under stress, the hydrogen bonds between adjacent cellulose chains can break allowing the chains to slip past each other. New H-bonds can form as the hydroxide groups re-associate with different partners. Having done so, there are no forces to pull the neighboring chains back to their former position. The stressed shape of the fiber is just as stable now as was the original shape.
Bending Forces in a Thin Rod

 

Bending forces in a Thick Rod





Water will facilitate the disruption of these bonds by forming H-bonds between the water molecule and the cellulose hydroxides. Now the hydrated polymer chains can slide past each other more easily so the strain level to deform the fiber is even lower than before. Water acts as a lubricant allowing the chains to slide past one another easily. Illustrative of this point is ironing wrinkles out of a cotton garment. It is impossible to iron out wrinkles from a dry garment. However, when the garment is dampened first or if a steam-iron is used, the wrinkles will iron out and the fabric becomes flat and smooth.

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