Thermoplastics with very high lignin contents

Annually huge quantities of kraft lignins are generated as byproducts from the chemical conversion of wood chips into pulp for making paper. Traditionally these industrial byproducts have been employed as fuel, but the imperative to maximize output can create a surplus of kraft lignin which is difficult to use profitably. An important key to the effective utilization of kraft lignins may be discerned in their colligative behavior, which is dominated in a unique way by pronounced noncovalent interactions between the constituent molecular species; the resulting associated complexes appear to be assembled from the individual components in a specific order. The ensuing macromolecular domains in the solid state would be expected to contribute substantially to cohesiveness in lignin-based polymeric materials. Previously it had been very difficult to exceed an effective limit of 25-40% (w/w) for incorporating lignin derivatives into polymeric materials, but four or five years ago it proved possible to fabricate 85% kraft lignin containing thermoplastics that possess tensile strengths and Young's moduli which vary monotonically with the degree of intermolecular association. These could be the first authentic lignin-based plastics ever to have been made. More recently, alkylated 100% kraft lignin-based polymeric materials have been produced with tensile properties that are virtually identical to those of polystyrene. This may be the first time that substantial tensile strengths have been achieved with materials composed only of a simple lignin derivative. Efficacious plasticizers for alkylated kraft lignins could thus serve as a vital means for realizing large-scale lignin utilization.