The Dependence of the Gelation Temperature of Cellulose Ether Plasticizers on the Applied Shear in the Powder Metallurgical Paste Extrusion

摘要

Hydroxypropyl methylcellulose and other cellulose ethers are main plastification aids for the cold pasteextrusion of powder metals, whether it is solvent or water based. Due to the gelation of the celluloseether in the aqueous paste above a certain temperature defects in the extrudates occur and theextrusion pressure increases significantly. The maximum extrusion temperature depends on thecellulose ether gelation temperature which is influenced by different well-known parameters likecellulose ether substitution, concentration, solvents and the presence of other ingredients. Here a newparameter is described: the gelation temperature increases with the applied shear which is importantto know for a high-shear application like the extrusion process. Several examples demonstrate theeffect.