When applied to wheat straw, the CIMV organosolv process provides a lignin fraction that is composed of linear polymers. Physically, this fraction is obtained as brown powder, which according to Delmas (2008), displays a density of 0.9 g/cm3 (1.30 g/cm3 in the condensed state) and an average particle size of circa 2 microns. Mass spectrometry indicates that the lignin polymers are composed of a mixture of linear polycondensed coniferyl units and are thus polyhydroxylated
Among the potential applications for CIMV ‘biolignins’ figure:
Using CIMV Biolignins™ as a macromonomer, IWC has investigated synthesis of polyurethanes (PU) and proved that the lignin function is not limited by crosslinker role but it also provides higher thermostability of PU. IWC has applicated Biolignins™ as an active filler in the 100% bio-based (tall oil) polyol composition for rigid PU foam production and produced a novel foam, with high content of renewable materials in end-product, conforming to requirements of construction and refrigeration industries. Using CIMV Biolignins™, SYNPO has developed a solvent-free process for the production of a novel polyurethane (PU) cast resin, which is 100% bio-based and displays interesting properties, such as increased surface hardness (c.f. a benchmark PU cast resin formulation) and high electrical resistivity. These processes have been successfully validated at lab scale and are now ready for pilot scale trialling.
Also using CIMV Biolignins™, CHIMAR has investigated the production of biobased adhesives for wood-based panel production. Both chemically-modified and raw CIMV Biolignins™ have been tested as substitutes for fossil-derived phenol in phenol-formaldehyde (PF) adhesive formulations. Up to 70% of phenol could be substituted when using certain types of modified CIMV Biolignins™. Interestingly, resins having up to 50% phenol substitution were found to meet European standards EN314.1&2 and could be used to make plywood panels that are strong enough to be used for exterior applications without any covering (i.e. class 3 panels). Other resins, containing >50% modified lignins provided panels that reach class 1 standards (suitable for interior applications) and were characterized by free formaldehyde emissions that were lower than panels containing conventional PF resins, while meet CARB II regulations.
Lignin coming from the CIMV process
Work on heterogeneous catalysis has also made significant progress regarding the conversion of C6 cellulose pulp into useful chemicals. Using a multi-functional catalyst, KULeuven have successful demonstrated the impressive lab scale performance of a one pot process that allows cellulose to be converted into isosorbide in high yield and high selectivity.
BIOCORE researchers have succeeded to convert wheat straw-derived cellulose pulp (from the CIMV fractionation process) into a range of polyols, including pentitols and hexitols in high yields (>70 mol% carbon). Their technology relies on a bifunctional catalytic concept, which takes advantage of a joint action of acid and redox catalysts. To solubilize cellulose pulp, the technology uses catalytic amounts of soluble acids to selectively hydrolyse cellulose into sugar molecules. Moderate reaction temperatures up to 200°C are used to obtain relevant hydrolysis rates. To overcome degradation of the thermo-labile sugars, the reactor was pressurized with H2 and loaded with a hydrogenation catalyst – commercial Ru on carbon. Under the right balance of acid and redox functionalities, soluble sugar molecules are rapidly hydrogenated to a mixture of more thermo-stable polyols. The nature of the acid is very important to ensure the production of hexitols such as sorbitol in high yields. Sorbitol is an important platform molecule for the production of sorbitans and isosorbide – a potential polymer building block. The commercial heteropoly acid H4SiW12O40 shows a high hydrolysis activity, probably as a consequence of its high affinity for cellulose. Moreover, being in the same solution, interaction of the poly acid with the Ru catalyst drastically reduces undesired hydrogenolysis of hexitols into smaller molecules. To illustrate an actual achievement, the KULeuven group demonstrated a lab scale conversion of mechanically pretreated BIOCORE wheat straw cellulose to hexitols in yields as high as 80 mol% C (mol C in hexitols / mol C in cellulose x 100). Sorbitol (including its isomer mannitol) was obtained in yields as high as 60 mol% C. Catalyst recycling is currently under investigation.