Rheology of Plastisol Formulations for Coating Applications Yamina Abdesselam, 1,2 Jean-Franc¸ois Agassant, 1 Romain Castellani, 1 Rudy Valette, 1 Yves Demay, 1,3 Diego Gourdin, 2 Richard Peres 2 1 CEMEF - Center for Material Forming, CNRS UMR 7635, MINES ParisTech, PSL - Research University, Sophia Antipolis 06904, France 2 Z.A Salzbaach, Tarkett GDL, Wiltz L-9559, Luxembourg 3 Laboratoire J.A. Dieudonn  e, UMR CNRS 6621, Universit  e de Nice Sophia Antipolis, Nice 06108, France A plastisol is a suspension of PVC particles and mineral fillers in a liquid phase composed of plasticizer and adju- vants. Plastisol formulations are commonly used in coat- ing processes for flooring application. In the knife-over- roll process, they are subjected to a wide range of shear rates (0–10 5 s 21 ). They are adjusted in order to fulfil the target end-use properties but their processability depends on their rheology. Plastisol based on three PVC resins with or without mineral filler have been investigated using a Couette device and a capillary rheometer. Results show a high impact of PVC particle content, particle sizes and distribution on rheology: a polydisperse formulation dis- plays a shear-thinning behavior in the whole shear rates range and exhibits yield stress; a monodisperse formula- tion shows a shear thinning behavior at low shear rate, followed by a Newtonian plateau, then a more or less pro- nounced dilatancy peak depending on plasticizer rate and finally another shear-thinning behavior; a bidisperse resin stands in between. Filler content also impacts the rheolo- gy: shear thickening effects at intermediate shear rates decrease or even disappear; however, the viscosity increase is important for low shear rates and depends on the filler particle size and particle size distribution. POLYM. ENG. SCI., 00:000–000, 2016. V C 2016 Society of Plastics Engineers INTRODUCTION A plastisol is a suspension of PVC particles in a liquid con- tinuous phase composed of plasticizer, adjuvants such as stabil- izers, pigments, blowing agents, and sometimes, mineral fillers. Plastisol formulations are mostly used for flooring applications, which are made using different spreading processes. In the so called “knife-over-roll process” plastisol is coated at ambient temperature on a substrate between a supporting cylinder rotat- ing at high velocity (up to 20 m/min) and a knife. A very nar- row gap is adjusted between the knife and the cylinder (between 100 and 200 mm) to achieve the targeted plastisol deposited thickness (Fig. 1a). Figure 1b shows a typical knife geometry. The flooring gelation is then achieved at high temperature (140– 2008C) in an oven downstream the knife-over-roll coater [1]. When coated, the plastisol formulation is subjected to a wide shear rates range (up to 10 5 s 21 ) and a too high viscosity at low shear rate makes its introduction between the knife and the rotating cylinder difficult. At high shear rates, jamming effects may develop flow instabilities at knife exit. In addition, a too large separating force exerted on the knife will induce its elastic deformation, leading to a more important deposited thickness along the center line of the coating machine than at the periph- ery. Finally, in the industry, the trend with new formulations development is now to reduce the plasticizer content, to opti- mize the PVC particle size distribution and to replace an increasing proportion of PVC resin by mineral fillers, thus inducing drastic modifications of the plastisol rheology and some processing problems. The complex composition of plastisol formulations, the inter- action between PVC resins and plasticizer, the PVC and filler particles size and particles size distribution, make plastisols a unique kind of suspensions. Even though typical dense suspen- sions rheological behavior is expected, only a few papers have been devoted to plastisol rheology at room temperature. We will discuss their behavior compared to the abundant literature on suspensions rheology. First, many authors have addressed how spherical monodis- perse particles behave and influence the flowing properties of a suspension, from dilute to more concentrated systems [2–6]. A rise in viscosity is expected, as particles are added, which then diverges when a maximal volume fraction is reached, that is, packed state prevent particles to flow freely. Additionally, at low shear rates, a shear-thinning behavior is observed as the sheared suspension microstructure changes with the flow: “ordered” layers of particles are formed when Brownian effects are no more dominant, lowering the viscosity when increasing the shear rate. Accordingly, Marcilla et al. [7] showed on plastisol formula- tions the existence of a Newtonian plateau at very low shear rates, followed by a shear thinning behavior and a second New- tonian plateau at intermediate shear rates (around 100 s 21 ). They pointed out that the polydispersity of PVC resin particles has an influence on the shear thinning behavior. Indeed, it is well known that adding particles of different sizes to a suspen- sion greatly affects its rheology [8]. First, maximum volume fraction is modified, and the drastic increase in viscosity with the solid volume fraction observed for the monodisperse case is postponed to higher particle concentrations [2, 8]. Using broad particle size distributions has the same effect on rheology [9]. Size distribution impacts also the behavior of particles suspen- sions at high shear rates. When volume fractions are high and distributions are narrow, dilatancy, and shear-thickening effects are observed [10–18]. Particle clusters that block the flow are formed, leading to instabilities. Viscosity dramatically increases, as well as normal forces, especially in confined geometries. Nakajima et al. [19] measured such dilatancy peak on plasti- sols at intermediate shear rates. They also mentioned the Additional Supporting Information may be found in the online version of this article. Correspondence to: J.-F. Agassant; e-mail:jean-francois.agassant@ mines-paristech.fr DOI 10.1002/pen.24475 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2016 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2016