TEMPERATURE TRANSITIONS IN NON-CRYSTALLINE DOMAINS OF CELLULOSE
When samples of various polymers are heated, there is a monotonic change of various physico-chemical, physical and chemical properties until achieving of certain transition temperatures at which an abrupt change in properties of the polymers is observed. Cellulose is known to be a linear stereoregular semi-crystalline polysaccharide composed of anhydroglucose units joined by 1,4-β-glycosidic bonds. This polysaccharide has a complex supramolecular structure consisting of ordered crystallites and less ordered noncrystalline domains. This review article contains the description and discussion of temperature transitions in non-crystalline domains of cellulose. It has been shown that due to structural heterogeneity the non-crystalline domains have three temperature transitions of relaxation type, where the α<sub>1 </sub>transition at 490-500 K and α<sub>2</sub> transition at 380-410 K are caused by the occurrence of segmentalmobility in dense mesomorphous and less packed amorphous clusters, respectively; whereas the β transition at 260-300 K is related to the mobility of small segments in loose packed amorphous clusters, which probably are located on the outer surface of cellulose fibrils. Under the action of water and other plasticizers all three isophase transitions are shifted to lower temperatures. Along with α and β transitions, also low-temperature γ transition at 180-200 K is observed due to mobility of hydroxy-methylene groups in noncrystalline domains of cellulose.