Abstract
This work consists in an experimental investigation of forced dynamic wetting of molten polymers on cellulosic substrates and an estimation of models describing this dynamic. A previous work of Pucci et al. (Pucci et al. 2018) showed that for totally wetting liquids (as paraffin oils), temperature-induced variations in dynamic wetting are included into the capillary number (Ca) and then a master curve of dynamic contact angle (θd) as a function of Ca can be obtained. The hydrodynamic theory (HDT) correctly describes the dynamic wetting for Ca > 2 · 10−3. For lower Ca, a change in the dynamic wetting behavior was observed. Here, partially wetting liquids (polyethylene glycols, a.k.a. PEGs) at different molecular weight (Mn) were used at temperatures above their melting point to investigate the dynamic wetting behavior on cellulosic substrates for a large range of Ca. It was found that the dynamic curves of θd vs. Ca depend on Mn. Moreover, the HDT correctly describes the experimental measurements for Ca > 2 · 10−3. Below this threshold the dynamic contact angle decreases towards the static one. A linear correlation between parameters obtained fitting the HDT and the molecular weight of polymer was found. The prediction of dynamic wetting for low Ca (Ca < 2 · 10−3) with the molecular kinetic theory (MKT) was also evaluated and discussed.
Highlights
Dynamic wetting occurs in many everyday situations, when water flows on a floor tile or pearl on a plant leaf for example
The flow of a molten polymer in a fibrous preform is governed by a competition of capillary and viscous effects that are included in the dimensionless capillary number Ca (Ruiz et al, 2006): ηv where v is the liquid velocity, η and γLV are the dynamic viscosity and the liquid surface tension, respectively
Forced dynamic wetting occurs when the liquid velocity v is set via an external force, in Dynamic Wetting of Molten Polymers contrast to the spontaneous wetting where only capillary effects drive the flow (Sauer and Kampert, 1998; Mohammad Karim et al, 2016)
Summary
Dynamic wetting occurs in many everyday situations, when water flows on a floor tile or pearl on a plant leaf for example. It concerns different industrial domains and among them, composite manufacturing (Bréard et al, 2003; Verrey et al, 2006; Park et al, 2011; Pucci et al, 2015, 2017b; Caglar et al, 2019). Depending on the equilibrium or static contact angle, liquids can be classified as totally wetting (e.g., paraffin and silicon oils), for which the θe is ≈ 0◦ and as partially wetting (e.g., polyethylene glycols), when the θe is different from 0◦
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