Analysis of properties of synthetic mineral microparticles for retention and drainage system.

摘要

Over the past 20 years there has been a revolution involving the use of nano- or macro-sized particles as a component of drainage and retention systems during the manufacture of paper. More recently a group of patented technologies called Synthetic Mineral Microparticles (SMM) has been invented and developed. This system has potential to further promote the drainage of water and retention of fine particles during papermaking. Prior research, as well as our own preliminary research showed that the SMM system has advantages in both of drainage and retention, compared with montmorillonite (bentonite), which is one of the most popular materials presently used in this kind of application. In spite of the demonstrated advantages of this SMM system, the properties and activity of SMM particles in the aqueous state have not been elucidated yet.; To help understand the molecular mechanisms involved in SMM technology, streaming current and potentiometric titration were employed to characterize the charge behavior of SMM, depending on the synthetic conditions, which included variation of the Al/Si ratio, partial neutralization of Al species, salt addition and shear rate. Surface area of SMM and the distribution of SMM particle size were investigated with scanning electron microscopy in order to elucidate the relationship between the morphology and coagulation behavior of SMM, versus the pre-stated synthetic conditions, as well as to estimate the optimal conditions to produce SMM as a retention and drainage aid for use during papermaking.; Through the streaming current titration experiments it was found that pH variation, caused by the change of Al/Si ratio and partial neutralization of aluminum's acidity, profoundly affects the charge properties of SMM. These effects can be attributed to the variation of Al-ion speciation and the influence ionizable groups on the Si-containing particle surfaces. The relationship between Al/Si ratio and isoelectric pH, measured by potentiometric titration, was estimated through statistical estimation, using a factor, the OH/Al ratio. This procedure permits estimation of the Al/Si ratio values at which the SMM particles can be expected to have net negative charges, as required for a microparticle system for promotion of retention and dewatering during papermaking.; It was found that the structural characteristics of SMM particles could be explained in terms of the effects of ionic charges on colloidal stability of primary particles during formation of the SMM.; Finally, a combination of moderate pH condition (from 5 to 8), relatively low Al/Si ratio (from 0.63 to 0.88), and partial neutralization of Al species in the range of OH/Al ratio between 0 to 1 were concluded to produce an optimal SMM product in terms of a fine-particle retention and effectiveness as a drainage aid component.