Structural change of amorphous cellulose by water‐ and heat‐treatment

Strips of amorphous cellulose film were conditioned under wet atmospheres of 80 and 100% relative humidity or heated at 393 K in vacuo for different time intervals. The structural change of these samples was investigated using differential scanning calorimetry (DSC), IR spectrometry, x‐ray diffractometry (x‐ray), and the density‐gradient column method. In the initial stage of conditioning of cellulose samples at a wet atmosphere, it was found that the thermally determined relative volume fraction (α) of the amorphous part of cellulose stays constant while the diffusion coefficient ( D od ), calculated from the rate of H → D exchange of OH groups observed in IR, decreases rapidly. This fact seems to show that the rearrangement of cellulose molecules does not occur as a whole but only partly in the vicinity of the OH groups which affect the process of H → D exchange. If large amounts of water are supplied, however, cellulose molecules rearrange freely and provide a crystalline structure, as observed clearly by x‐ray. On the other hand, during the heat‐treatment of amorphous cellulose, the decrease of α and D od can be clearly observed by DSC and IR from the initial stage of treatment. Judging from the change of α and D od , it was inferred that the hydrogen bond formation occurs step by step simultaneously with the rearrangement of cellulose molecules by heat‐treatment.