The thermal expansion of cellulose, hemicellulose, and lignin

Abstract

The thermal expansion of wood constituents has been measured dilatometrically both in the dry and the water‐swollen state. Dry measure meats were made with mercury as the confining liquid on samples pressed into dense pellets at elevated temperatures and pressures. Between −30 and 30°C, the thermal expansion coefficients for various celluloses and hemicelluloses ranged from 5.1 to 6.0 × 10−4 ml./g./°C. For lignin, the coefficient increased to about 10 × 10−5 ml./g./°C. A second order transition was noted in all samples at 19–33°C. A further transition at 8G‐110°C. was detected for the dioxane lignin, periodate lignin, and Avory cellulose. All transitions in the dry state produced an increase in the expansion above the transition temperature. In the water‐swollen state, samples were in the form of powders or broken pellets, with distilled water as the confining liquid. The thermal expansion coefficients of the water‐swollen samples were several times as great as the expansion coefficients measured in the dry state. The second order transition near 20°C. persisted, but in water the transition was negative with expansion decreasing above the transition temperature. Analogous results were obtained for glucose and cellobiose, both in the dry state and in solution. The transition in the dry state is attributed to increased thermal motion caused by the rupture of weak hydrogen bonds. The large and interesting discrepancy found in the expansion of the water‐swollen materials is interpreted as arising from the perturbation of the water structure by the hydrophilic surfaces of woody macromolecules, and a quantitative assessment of this effect is attempted.

Mechanical and thermal characterization of native brazilian coir fiber

“…Nevertheless, Ramiah and Goring, 19 carrying out a detailed study of the thermal expansion of cellulose and lignin compounds in the dry and the water-swollen states, established, in our opinion, a clear basis for the discussion of the thermal transitions associated with these materials near room temperature. In their work, drying procedures, in some cases at temperatures Ͼ 150°C and for Ͼ 9 h, were applied.…”

“…For water-swollen wood compounds, the secondary transition appearing near 20°C showed an expansion decreasing above the transition temperature. Ramiah and Goring 19 proposed that the breaking of weak hydrogen bonds produces the second-order transition observed in the plot of specific volume versus temperature for various dry cellulose and lignin compounds between 19 and 33°C.…”

“…The glass transition temperature (T g ) of cellulose itself, both in extracted cellulose and in natural fibers, is the object of significant controversy in the literature. 18,19 Values between Ϫ30 and 160°C have been cited. 18 Other second-order transitions are reported 19 for cellulose and lignin compounds around room temperature.…”

“…18,19 Values between Ϫ30 and 160°C have been cited. 18 Other second-order transitions are reported 19 for cellulose and lignin compounds around room temperature. Lignin, a commercial product from the Kraft pulping process, shows a T g of approximately 135°C as measured by DSC.…”

Effect of the fine structure and electrolytic contaminations on the specific conductance of some cellulosic materials

“…[28][29][30] Hence, the greater increase of u and the lower AE, values above T, of samples exhibiting such transition compared with the corresponding changes below this transition could be attributed to the increased flexibility of cellulose chain molecules which enhances the mobility of the concerned ions.…”