Glass transition temperature lignin

It is anticipated that the possibility of producing elastomeric lignin-containing PU s strongly depends on whether crosslink density can be held on a low level or not. It is also necessary to include soft segments, so that the glass transition temperature (Ta) of the PU falls below room temperature. 

Figure 1. Effect of lignin content on the glass transition temperature (Ta) of networks crosslinked with HDI. Formulation type A ( ) type B ( ) and type C (0).

Table I. Hydroxyl content and glass transition temperature of lignins derivatized with acetic anhydride (Ac), diethyl sulfate (Et), and propylene oxide (Pr)...

Fig. 4.8.12. Diagram showing the effect of degree of acetylation and water content on the glass transition temperature, Tx, of dioxane lignin. (Hatakeyama and Hatakeyama 1983)...

Chemical Modifications. Unmodified lignin is well known for its poor solubility characteristics and its high glass transition temperature. Methods for improving the solubility (and/or reactivity) of lignin prior to crosslinking in specific network forming systems are summarized in Table I. Such systems may be based on aqueous solutions at pH below or above neutral or on solutions in polar or nonpolar solvents. Typical modifications that enhance the solubility of... 

There are several reports in the literature describing the effect of chemical structure on the observed thermal properties of lignin. " In the thermal processing of lignin for structural applications, the relationship between chemical structure and thermal properties is of extreme importance. Differential scanning calorimetric (DSC) analysis of HKL and SKL is shown in Fig. 3. The glass transition temperature (Tg) of the HKL appears at 93 "C, much lower than that of the SKL, ID C. 

H Hatakeyama, K Iwashita, G Meshizuka, J Nakano. Effect of molecular weight on glass transition temperature of lignin. Mokuzai Gakkaishi 21 618-623, 1975. 

The thermal properties of the regenerated wood ester product reveal a single glass transition temperature (Tg) (Fig. 4) which varies with both degree of substitution (DS) (i.e., reaction-time) (Fig. 5) and (to a lesser extent) lignin... 

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