Hydrophobic cellulose: a material that expands upon drying

A chemically modified hydrophobic cellulose material was wetted by force in vacuo and allowed to dry under ambient conditions. Most known materials shrink upon drying and swell upon wetting, a phenomenon known as dry-shrinkage; and thus are characterized by a dry-shrinkage coefficient either equal or greater than zero. Different from conventional materials, sheets of hydrophobic cellulose fibres expand upon drying, which implies that they exhibit dry-expansion. This property is calculated as a negative dry-shrinkage coefficient. We are unaware of any other material with this property. Such sheets can expand to over 500 % in thickness upon drying in the first cycle of use. This property degrades with each cycle because more hydrophilic areas come in contact with water as a result of mechanical damage to the material, thus making the sheets less hydrophobic. With increasing solid content, a decrease in tensile strength is observed, which is opposite to the conventional trend in wet web strength. A mechanism for the dry-expansion of this material is being proposed.