說明 
138 p 
附註 
Source: Dissertation Abstracts International, Volume: 6306, Section: B, page: 2919 

Chair: Rakesh K. Gupta 

Thesis (Ph.D.)West Virginia University, 2002 

This study examines the problem of shearinduced agglomeration of particles such as fillers and pigments in polymer solutions, where polymer molecules adsorb on the surface of particles and form a bridge between them causing agglomeration. The rate of agglomeration is usually obtained by multiplying the rate of collision of particles by the collision efficiency. In a laminar flow field, the collision frequency is readily given by Smoluchowski's expression. If agglomeration takes place by coagulation, the collision efficiency is well studied and the influences of hydrodynamic and colloidal forces are well understood. In case of polymer bridging, the collision efficiency is determined by probabilistic models based on fractional surface coverage of particles by the adsorbing polymer, neglecting the influence of hydrodynamic forces. A new model is required to determine the collision efficiency in case of shearinduced agglomeration of noncolloidal size particles by polymer bridging 

In this work, a new model is developed in terms of dimensionless groups and the fractional surface coverage. The dimensionless groups represent the relative magnitudes of the colloidal, hydrodynamic and steric forces. An expression for the optimum surface coverage needed to achieve the maximum collision efficiency is also obtained. In particular, a model is presented for the case where surface of the particles is completely covered by a polymer layer 

To validate this model, experimental collision efficiencies at various agglomeration conditions are determined by shearing a model suspension in a coneandplate device. The model suspension consisted of 4.9 mum diameter spherical hollow glass beads dispersed in an aqueous glycerin solution; polyethylene oxide was used as the flocculant. Using experimental collision efficiencies and nonlinear regression analysis, the parameters in the collision efficiency model were determined 

It was found that increasing the shear rate decreases the collision efficiency and it can be expressed as a power law. Increasing the molecular weight and concentration of flocculant also gives higher collision efficiency. Agglomerate growth and the equilibrium agglomerate size were also monitored under different flocculation conditions. It was found that the size to which agglomerates grow depends on the shear rate and this can be expressed as a power law as df,95% ∝ g&d2;0.258 . In addition, agglomerate breakage studies show that the agglomerate breakage occurs by floc rupture mechanism rather than by the surface erosion of primary particles 

School code: 0256 

DDC 
Host Item 
Dissertation Abstracts International 6306B

主題 
Chemistry, Polymer


Engineering, Chemical


0495


0542

Alt Author 
West Virginia University

