NMR study of water-filled pores in one of the most widely used polymeric material: The paper

An NMR study of good quality paper is reported. Good quality paper is a polymeric bicomponent material made with cellulose and water plus impurities. Water is located into pores. The removal of even a small amount of the water from paper causes an irreversible destruction of the material. According to the IT method, the intensity of the water resonance as a function of the temperature has been used for obtaining the pore size distribution. A strongly asymmetric distribution with a well-defined maximum at 1.4 nm has been found. The average size of water pools has been confirmed applying NMR techniques suitable for studying spin diffusion processes, i.e., dipolar filtered methods and 2D WISE. Both techniques show that the water pools are surrounded by amorphous cellulose. Crystalline domains surround amorphous domains which in turn include the water pools. Dipolar filtered methods allow a rough evaluation of the distance between crystalline domains, this is, about 3 nm. This distance agrees with a previous result obtained by transmission electron microscopy (TEM) methods. Our results give an insight into the paper morphology. It must be pointed out that a clear description of the paper morphology is important for the restoration and preservation of ancient paper.