We report here the auxetic (negative Poisson's ratio) response of cellulose based fiber networks. Auxetic materials grow fatter when stretched and are extremely rare in nature. It has been reported that fibrous paper increases in thickness when stretched in planar direction. Recently, researchers have also induced auxetic behavior in polyurethane foams, expanded PTFE and ultra-high-molecular-weight polyethylene through special processing techniques. By measuring the thickness increase with stretch in different types of paper, we determined their Poisson's ratio to be negative (0 to -3.0). We propose that the mechanism of this auxetic response stems from the non-woven network structure of cellulose fibers having rich hydroxyl surface. During compressive stages of papermaking, hydrogen bonding between fibers locks them into a crumpled microstructure which expands when stretched. Auxetic behavior arising from supramolecular surface chemistry of polymeric networks is a novel concept that can potentially be applied to new functional and structural material designs.

Auxetic behavior in cellulose based fiber networks

245th National Meeting (2013)

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