RHEOLOGICAL BEHAVIOR OF HIGH-RESIN-LEVEL PLASTISOLS

The rheological behavior of PVC plastisols that vary in volume fraction of resin from 0.567 to 0.670 was studied. Different particle-size “cuts” from Tenneco Chemicals, Inc.’s 1730 dispersion-grade-poly (vinyl chloride) resin and di-2-ethylhexyl phthalate (DOP), n-butyl benzyl phthalate (BBP), and di-2-ethylhexyl adipate (DOA) plasticizers were used to prepare the plastisols. In the range of concentration studied, both shear-thickening and shear-thinning behaviors were observed. In all cases discontinuous-viscosity behavior was observed at a critical shear rate. The shear rate at which this viscosity discontinuity occurred depended strongly on the particle-size characteristics of the resin and the compatibility of the plasticizer with the resin. This study has led to the following contributions: 1. An experimental blending technique was developed that permits the determination of the maximum volume fraction of resin which will produce a fluid plastisol. This maximum volume fraction of resin, <£mix, is related to the particle-size characteristics of the resin and the compatibility of the plasticizer with the resin. 2. The resin content of the plastisols studied was expressed in terms of a reduced volume fraction, ΦR, that was calculated with the following compositional mixing formula: n m ΦR= Σni=1Σmj=1xiyj Φ—ΦMIX ij, where xi = volume fraction of the ith liquid phase, yj = volume fraction of the jth solid phase,Φ= total volume fraction of resin(s), n = number of plasticizers, m = number of resins, and ΦMIXij = ΦMIX of the ith plasticizer with the yth restndhin. Since.this expression involved only the determination of ΦMIX for each resin/plasticizer combination, irtin can be easily determined for variations in both the content of resin and the relative amounts of plasticizers and/or resins present in multiple-component plastisols. 3. A correlation was developed that relates ΦR to the shear rate, γd, at which the viscosity discontinuity occurs. © 1979, The Society of Rheology. All rights reserved.