Lignocellulose has emerged as one of the most important material systems of recent times. It is a promising green platform that can be used in structural and functional applications. Wood has millennia of engineering history behind it—lignocellulose based materials are a natural evolution of wood engineered after extracting the raw material from wood/woody biomass itself.
Researchers have been able to tune the properties at the cellular level and learnt how to fibrillate wood into its constituents or apply steam and pressure to mold it like plastics. The paper and pulp industry has played a prominent role in helping us understand lignocellulose chemically and develop chemical tools to manipulate it.
Lignin, largely a byproduct of paper and pulp , has been receiving a lot of attention by chemists not only because it constitutes 30% of mass of the plant materials but also because of its unique chemical properties —ring like structures and hydroxyl groups that can be functionalized.
Advancement in lignin processing has enabled researchers to spin fibers that can be carbonised, make vanillin, build UV protection molecules and apply it in cosmetics.
Prof Orlando Rojas’ talk last week highlighted some of these developments. The key point in his talk was that when woody lignocellulose material was transformed, say via carbonisation, it retained its wood like cellular structure that conferred on it distinct properties quite different from those had it been fibrillated and reassembled. For example wood delignification ,while preserving cellulose fibers, produced foam-like structures. Carbonisation while avoiding high temp graphitisation produced a cellular insulation material. Other routes produced ultra black blackbodies for EM shielding. Dispersed lignin particles themselves could be turned into functional colloids and assembled into adsorbent, photonic crystals or turned into emulsions. Because they are biocompatible and non toxic they can be applied in the food sector. The applications are endless.
While the scientific community has done terrific work in demonstrating application of lignin the truth is they are still underutilised. The sulfonated lignin produced by pulp and paper have undergone chemical modification and it takes complex processing steps to reclaim the original structure. It can be done as is proven by synthetic vanillin manufacturers but it's tough. The NaClO process is similarly difficult. Organosolv processes using formic acid +H202 are far easier for downstream lignin applications. But even then economics doesn't work so well. Lignins face competition from synthetic materials —plastics and consumption demand from applications like bio fuels that are simpler to produce and more profitable than chemicals or materials.
The big advantage of lignocellulose is cheap raw material. Every tonne of food grain produces a tonne of fiber waste. If used strategically this tonne of waste could turn into several hundred kilograms of valuable carbon/carbon composite especially with new faster carbonisation routes like molten salt processing that enables rapid pyrolysis and cheap furnace designed because the molten salt acts as liquid heat transfer media through which O2 solubility is low. In the best case this has the potential to upgrade farmlands from just food producers to food + material producers. This is vastly superior to the chemical production of nano cellulose and the challenges associated with dispersion and building a matrix for composites. In addition to moisture sensitivity that renders it ineffective in certain conditions.
Despite some of our best technical achievements wood remains a masterpiece of materials engineering combining structural and functional applications in a single highly adaptable material. The thick tree trunk and the slender straws of food grains doing exactly the same thing with tiny structural modifications.The nanoscale cellular structures giving rise to micro capillaries transporting food,water and oxygen,cemented together to bear loads. Not with a thousand different polymers and a million complex raw materials required to make them. But with simple carbohydrates and phenols. Nature remains endlessly inspirational and infinitely fascinating. I thank treesearch @KTH Sweden for organising these high quality talks and pushing the boundaries of biomaterials.
Comments
Post a Comment