Leo Liu

Self-assembly of complex lignin molecules into nanosize structures in water

Blog Post created by Leo Liu on Jun 5, 2017

Lignin makes up approximately one third of the world’s biomass, second only to cellulose and it is generally known to be synthesized as structural material by the plants and some algae, and exists in soil, water and food.  About 50 million tons per year of lignin are generated by the pulp and paper industry alone, and more is to be produced as by-products from cellulosic derived fuels.  While most of the lignin is now burned for energy, there is a growing interest in utilizing lignin as a sustainable raw material.  Although lignin is now extracted from wheat straw or isolated from kraft black liquor through proprietary processes,  its large scale industrial utilization is often limited by its chemical heterogeneity and water-insolubility under mild conditions.


On the other hand, Nature has taught us that lignin undertakes supramolecular assembly to form plant biomass in mostly aqueous environment, but such nano-scale spontaneous self-assembly has not been observed with isolated native lignin.  Now, researchers in Solenis, a leading manufacturer of specialty chemicals, demonstrated that isolated lignin can undergo self-assembly into nanoparticle dispersions by simply heating its suspensions in water at neutral to weak alkaline pH.  They showed that the lignin nanoparticles so obtained to be associative with water soluble polymers and to have strong adsorption to common polymeric and inorganic solid surfaces, rendering the surface more hydrophilic.  Such nanoscale properties imply a more orderly structure through self-reorganization from the seemingly chaotic materials (US 20150166836).


The findings may have profound impact on how lignin functions in the biosphere in additions to what we have known as the otherwise
insoluble polymer can be “soluble” as more active nanoparticles in water at significant concentrations.  These findings could provide us clues to improve lignocellulose processing, especially in water-based ones, and lead us to build tunable lignin supramolecular structures, applicable in detergents, polymeric composite materials including carbon fibers as well as water-borne polyurenthane, encapsulation and controlled delivery.