Abstract: Starch is added to the thinstock in a papermaking process in the form of a coagulated slurry containing undissolved starch particles, cationic polymeric flocculant and anionic microparticulate network agglomeration aid, such as bentonite. The flocculant and agglomeration aid interact to give network flocculation in which the starch particles are trapped. Improved retention of the starch in the resulting paper is achieved.

Abstract: Paper strengthened by starch, typically in amounts of 3 to 15% dry weight, is made by flocculating a cellulosic suspension using a polymeric retention aid which can be dissolved cationic starch but is preferably a synthetic polymer having IV above 4 dl/g, optionally shearing the resultant flocculated suspension and reflocculating it by adding bentonite or other microparticulate anionic material, draining the flocculated or reflocculated suspension and drying the resultant wet sheet, wherein insoluble particles of starch are added to the suspension as a slurry of substantially freely dispersed particles in part or all of the aqueous solution of the polymeric retention aid or in part or all of the aqueous suspension of microparticulate anionic material.