| Cellulose derivatives are versatile polymers with broad industrial applicability. Their performance is critically dependent on their interaction with water. In this work we seek an in-depth understanding of how variations in humidity affect surface properties of Hydroxypropyl Cellulose (HPC). Using the Surface Force Balance technique and Atomic Force Microscopy we studied the properties of adsorbed HPC layers as a function of ambient humidity. We found that HPC layers shrink following adsorption of moisture. Based on our observations; the hysteresis noted in the HPC layers compression-decompression cycles and the recovery of the layer's properties upon drying, we propose a two-step mechanism of water sorption by fibers of HPC. In step one, adsorption of moisture is dominated by capillary condensation in the voids and capillaries of the fiber-like HPC layer. In step two, water penetrates inside the fibers and forms a surface gel, whereas the inner cores of the fibers retain their rigidity. |
