Dynamic Wetting of Molten Polymers on Cellulosic Substrates: Model Prediction for Total and Partial Wetting

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. (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 (θ d) 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 θ d 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 toward 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.

Temperature-dependence of the static contact angle: A transition state theory approach

“…This model is based on the transition state theory and could be seen as a static treatment of the molecular kinetic theory used for dynamic contact angles. 34,36,37 This model encompasses regular wetting but also wetting on real surfaces, i.e. Cassie-Baxter or Wenzel states, and the transition to complete wetting.…”

“…9,[29][30][31][32] Interestingly, the dynamic contact angle d can be well described using Eyring's reaction rate theory at small capillary numbers. 22,24,[33][34][35][36][37] In this theory, the rate of a liquid molecule jumping in or out of an active site located at the solid surface near the triple line determines the triple line speed. In this theory, the temperature is an explicit variable.…”

Capillary Effects in Fiber Reinforced Polymer Composite Processing: A Review

“…from sessile drop or droplet-on-fiber measurements (Wu and Dzenis, 2006;Behroozi and Behroozi, 2019). In the case of structural fibers, a tensiometric method coupled to Wilhelmy's equation is usually applied to measure the dynamic contact angle and capillary forces (Pucci et al, 2016;Pucci et al, 2017a;Wang et al, 2017a;Hansen et al, 2017;Pucci et al, 2020). This method measures the force needed to pull or push a fiber or a tow partially submerged in a liquid as a function of the length of the immersed region.…”

Capillary pressure contribution in fabrics as a function of fibre volume fraction for Liquid Composite Moulding processes

“…During the impregnation of resin in the fibre network, there is a competition between viscous and capillary effects that are related to the dimensionless capillary number Ca [13][14][15][16][17]. Different type of defects at different localisation can occur during manufacturing depending on the Ca.…”