Hemicellulose is generally regarded as amorphous in form and therefore more hygroscopic than cellulose whose crystalline interior is seen as impenetrable by water. In a set of experiments and simulations, we examined how the interplay of cellulose and hemicellulose affects the water uptake and ended up with several unexpected results. First, a 2D setup was utilized with ultrathin films of cellulose nanocrystals embedded in a continuous, amorphous xylan matrix. Second, a delignified holocellulose fiber from hardwood was investigated. In both cases, the cellulose/hemicellulose ratios were systematically varied and the water uptake of the system under incremental relative humidity values was monitored. It turned out that at relatively high hemicellulose contents, the water vapor uptake in both systems decreased as the crystalline cellulose content increased. This can be deemed as an expected result. At low hemicellulose contents, however, the water vapor uptake in both systems increased as the cellulose content increased. The case was further investigated with molecular dynamics simulations. The results yield insight to the complex relationship between crystalline and amorphous polysaccharides in plants.

Role of hemicellulose in water vapor uptake of cellulose-based matrices

ACS Spring 2022

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