Thermoplastic behavior of lignin with various synthetic plasticizers

The thermoplasticization of thiolignin (TL) and dioxane lignin (DL) with various synthetic plasticizers has been investigated. The thermal softening temperatures Ts of the lignin–plasticizer systems were measured applying the flow tester technique which is useful for investigating the thermal properties of polymers. It was found that the Ts of the lignins were lowered considerably as the solubility parameters (after Hildebrand) of the plasticizers approach close to that of lignin, namely, around 11. The lowering in the Ts of the lignins with the plasticizers was described by a linear equation with respect to the plasticizer concentration which ranged up to 20 wt‐%. The sorption of the limited amounts (< 5%) of water to the lignins also considerably decreased the Ts, however, the extent of lowering in the Ts by water sorption is less than that by the plasticizer addition at their contents over about 15%. The relationship of Ts to water content (up to about 30%) was curved, not linear. It was clearly shown that a combined use of the plasticizer and water brought about the most effective plasticizing for the lignins compared with the use of either of those alone.