Manufacture of lignin microparticles by anti-solvent precipitation: Effect of preparation temperature and presence of sodium dodecyl sulfate

- Lignin microparticles can be produced via a solvent precipitation process.
- Particle size and structure are influenced by precipitation temperature.
- Surfactant inclusion reduces particle size and enhances microparticulate stability.

An anti-solvent precipitation technique was explored for the ability to produce lignin microparticles. An aqueous-organic solution of lignin was dispersed into a much larger volume of water, whereby leaching of organic solvent from the dispersed phase into the water resulted in progressive precipitation of the lignin solute, ultimately producing a suspension of hardened microparticles. Temperature and addition of surfactant were investigated as a means of controlling particle properties. Increasing initial water temperature between 4 and 80 °C produced increasingly large agglomerates of uniform sub-micron primary particles, increasingly fused into monolithic masses. Although the glass transition temperatures of dried lignins were in the range of 75-87 °C, depression of glass transition temperature in the presence of water during particle formation may be associated with the increasing agglomeration of particles with increasing temperature. Incorporating sodium dodecyl sulfate (SDS) in the water at temperatures of 20-60 °C inhibited agglomeration producing smooth, spherical, monodisperse particles in the range of 0.1-0.2 μm. However, SDS concentrations greater than 1% caused the formation of some larger particles. Once safety, consumer acceptance and aspects of functionality have been established, spherical particles in the 0.1-0.2 μm size range may have application as food industry fat mimetics, fillers or even as solid particle emulsifiers.Industrial relevanceIncreased biorefining of lignocellulosic feedstocks to produce bioethanol may lead to an abundance of lignin that could be well-utilised as a sustainable, non-caloric food ingredient. Microparticulation provides a route for the transformation of lignin into a useful food ingredient, on the basis that particles with suitable properties for use in food systems can be produced: notably, a particle diameter preferably between 0.1 and 25 μm, spherical shape and stability against aggregation.