Patent GB-729220-A (GB)
Title: Improvements relating to methods of preparing lignin resins from alkaline lignin solutions
Inventor: MULLER HANS FRIEDRICH
IPC: C08H5/02
Filed: 1952-06-27
Abstract: Lignin resins obtained from alkaline lignin solutions by adding mono- or polyhydric phenols or mixtures of phenolic substances and precipitating with an acid are rendered thermosetting by the addition of hardening agents such as formaldehyde, hexamethylene tetramine and furfural.  Phenols mentioned are phenol, cresols, xylenols, alkyl phenols, methoxy phenols, phenol aldehydes, creosotes and tar fractions or phenols obtained by lixiviating tars.  Alkaline lignin solutions may be obtained as by-products in the paper industry.  When treatment with an aldehyde is effected in aqueous alkaline solution it is preferred to use oxalic acid in any subsequent acid treatment of the resin.  The products are used as wood or cellulose binders and may be admixed with substances such as colophony, copal, shellac, coumarone resins, phenol-formaldehyde resins, aniline and urea resins, calcium oxide, sodium oxide and magnesium hydroxide. Solvents or plasticizers such as alcohols, esters, ethers, ketones, glycols, glycerol and pentaerythritol may also be present.  Examples are given illustrating the preparation of synthetic resin preparations containing lignin resins admixed with resol and novolac phenol- and cresolformaldehyde resins hardened with hexamethylene tetramine if necessary and their use as binders in the manufacture of plywood, laminated and pressed wood.ALSO:Lignin resins are obtained from alkaline lignin solutions by adding phenols containing one or more hydroxyl groups or mixtures of phenolic substances and subsequently precipitating with an acid.  Phenols mentioned are phenol, cresols, xylenols, alkyl phenols, methoxy phenols, phenol aldehydes, creosotes and tar fractions or phenols obtained by lixiviating tars.  Alkaline lignin solutions may be used to extract phenols from tars or other distillation products containing phenols advisably after concentration if the phenolic content is low and with removal of substances such as paraffins or emulsifiers.  The alkaline lignin solutions may be obtained from paper manufacture.  Strong mineral acids, carbonic or sulphurous acid may be used for precipitation. When the alkali salts are to be regenerated or used subsequently it is preferable to precipitate with weak acids and subsequently treat the resins with strong acids.  During precipitation the reagents should be intimately mixed.  When the quantity of phenol used is small precipitation is preferably effected so that the lignin is in a fused state.  Precipitation with sulphurous acid is preferably initiated at a higher temperature, e.g. 70-80 DEG  C., subsequently completed at gradually decreasing temperatures, optionally in a series of vessels, and in the final stages the acid should be introduced under pressure.  The lignin solutions may be atomised into sulphurous acid.  The products may be mixed with substances such as colophony, copal, shellac, coumarone resins and phenol-formaldehyde, aniline and urea resins and dissolved in organic solvents, many being specified.  In examples, alkaline lignin solutions are treated with cresols or used to extract phenols from coal tar fractions with subsequent precipitation of lignin with sulphurous acid.  The lignin product is used in the preparation of synthetic resin binders for the wood industry (see Group IV (a)).