Different pulping processes and lignin extraction method to obtain the main physical and chemical properties include the following:
1, the color of lignin
Original lignin is a white or nearly colorless material. We see the color of lignin, in isolation, caused by the preparation process. With the separation of the different preparation methods, showing different shades.
Acid lignin, ketoamine lignin, lignin over iodate darker, light brown to dark brown in between, the Brayns separated and his name is pale cream spruce lignin.
2, the molecular weight distribution of lignin
Usually polymers, relative molecular mass is generally hundreds of thousands, millions, or even tens of millions, although it has also lignin polymers, but the separation relative molecular mass of tangled wood is much lower, generally a few dry to tens of thousands, only the original lignin to reach the hundreds of thousands. The level of relative molecular mass and separation methods.
An important feature of the polymer molecules having a polydispersity, that is the molecular weight range of a certain size. The average molecular weight of the polymer having a statistical significance test methods using different measured results are different. Often measured number average molecular weight average molecular weight, weight average molecular weight and number average molecular weight ratio of said dispersion.
Wood is a natural polymer tangled, also showed a molecular weight polydispersity. Groundwood softwood lignin has a weight average molecular weight of 2,000, hardwood groundwood lower lignin; with sulfuric acid precipitated from the black liquor quality wood trees between the molecular weight of 330-63000, 65% -80% lignin molecular weight between 500-50000. Straw lignin molecular weight polydispersity showing, the dispersion coefficient is generally greater than 2.
3, the solubility of lignin
The dissolution process is essentially polymer molecules into the polymer in the solvent, to overcome the force of macromolecules, to molecules and solvent molecules mixed with each other in the process. Compared with the low molecular weight substances, polymer dissolution process generally has two phases – swelling and dissolution, the entire dissolution process is relatively complex and slow.
Lignin is a aggregates present in the structure of many polar groups, more particularly hydroxyl groups, lignin with strong intramolecular and intermolecular hydrogen bond energy, and therefore the original lignin insoluble in any solvent . Separation of lignin, because of reduced synthesis and degradation occurs, many physical properties change, the change in solubility resistance.
Alkali lignin in acidic and neutral media, insoluble in water, but the composition Los having strong hydrogen bonding solvent such as an aqueous solution in NaoH (the pH value of 10.5 or more), dioxane, acetone, methyl cellosolve-based solvent, pyridine and the like; soluble in various lignin sulfonate aqueous solution PH value. Fu not in organic solvents.
4, the glass transition temperature of lignin
In addition to lignin and copper amine acid lignin, the original separation of lignin and lignin most polymer material is a thermoplastic, non-defined melting point, having a glass transition temperature. The glass transition temperature of the plant species, separation method, the relative molecular mass member, while its wet and dry state is also very different.
5, the chemical reactivity of lignin
Lignin molecule containing o-anisidine (a OCH3), ether bond (-O-), amino (a COOH), carbon-carbon double bonds, benzyl alcohol, hydroxy (PH-CH20H), a phenolic hydroxyl group (PH one OH), carbonyl (C = O) and benzene, etc. Reactivity of lignin plays an important role in functional groups are phenol polyethylene group, a benzyl alcohol hydroxyl group, amino group and carbon, the structure can be further alkylation show, hydroxymethyl, esterification, acylation reaction. For example, by methylation initial nucleophilic reaction, causing the ether chain cleavage; through the magnetic reaction, resulting in demethylation effect, but be converted into water-soluble products; UV absorption properties via the carbonyl group photochemical discoloration; through the activation of a phenolic hydroxyl group ortho-and para-electrophilic reactions can occur.
6, colloidal lignin chemistry
In alkaline pulping black liquor lignin colloid state, in the PH value of not less than 10, with a strong hydrophilicity. In alkaline solution, the formation of amorphous lignin molecules interacting groups by being combined with aggregates, which hydrophobic groups are internal, the hydrophilic group forms the outer surface of the aggregates. As the acid added, the PH bit lower, H + and lignin limb negatively charged groups on the electrophilic reaction occurs, the intermolecular condensation of lignin, coalesce to form precipitation.
7, lignin Biodegradability
Lignin was originally a class of biodegradable polymers difficult polyarylate, unit mass lower BOD value of lignin, such as black liquor from the soda straw lignin BOD of 0.10-0.11g / g lignin, but in some special bacteria under the effect of lignin derivatives can be a significant degradation and bio-absorption, and thus removed from the straw; addition, lignin and hemicellulose degrading enzymes also have some options of lignin degradation effect.