Temperature effect on dynamic wetting of cellulosic substrates by molten polymers for composite processing

Abstract

Impregnation of plant fibre reinforcements by a molten polymer involves many phenomena still poorly understood, related to the solid morphology and its surface chemistry, but also to the temperature effect on liquid properties and solid/liquid interactions. The present work focuses on the temperature effect on forced dynamic wetting, using the Wilhelmy method and two model materials: a cellulosic film and two totally wetting paraffin oils. The results show that the dynamic contact angle vs. the capillary number (Ca) plot appears as a master curve. This curve is split in two domains. The domain associated with Ca>10 −3 is well described by the hydrodynamic approach. The domain with Ca<10 −3 corresponds to wetting processes operating on a smaller scale, which are more sensitive to the physico-chemical heterogeneities of the substrate. This study addresses the mechanisms governing the capillary pressure, void formation and interface generation during composite manufacturing.

Role of interface formation versus fibres properties in the mechanical behaviour of bio-based composites manufactured by Liquid Composite Molding processes

“…The interfacial bonding is thus significantly weakened after treatment. This result was indeed predictable since the surface free energy was lowered by a weakening of its polar component as it was proved in previous studies [7,38] by tensiometric methods [39,40].…”

“…However, it is not the only parameter that should be taken into account for interfacial interactions since the fibres roughness could have an effect on mechanical interlocking. The effect of the thermal treatment on the fibres surface roughness will be investigated in further studies using some specific techniques such as the Atomic Force Microscopy (AFM)[40].…”

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

“…For total wetting, the equilibrium contact angle can be set to 0 and then Ŵ is the only free parameter in the HDT. It was proven in a previous work (Pucci et al, 2018) with totally wetting liquids that this theory describes well dynamic wetting for Ca > 2 • 10 −3 at different temperatures. In fact the effect of temperature is included in the Ca and physical parameters of Ŵ were found.…”

“…In this work, a procedure easily applicable to different types of substrates and fibers and at different conditions of temperature and liquid viscosity was carried out at a large range of Ca, using the weight tensiometric method. This method, based on the Wilhelmy principle, becomes more interesting for studying forced wetting under different conditions for total and partial wetting, imposing the liquid velocity and in both advancing and receding modes (Pucci et al, 2018). Polyethylene glycols, a.k.a.…”

“…Polyethylene glycols, a.k.a. PEGs, at different molecular weight (Mn) were characterized in terms of surface tension and viscosity as a function of temperature and used for tensiometric tests of forced wetting on cellulosic substrates having a very low roughness (<< 100 nm) and with an homogeneous chemical composition of surface (Pucci et al, 2018), in order to validate this protocol. Results are then relevant for a better understanding of dynamic wetting behavior of molten polymers and to estimate the prediction of this behavior by existing models in literature.…”