Non-Fickian Moisture Transport in Vegetable-Fiber-Reinforced Polymer Composites Using a Langmuir-Type Model

Abstract

The purpose of this article was to theoretically study the non-Fickian moisture absorption process in vegetable-fiber-reinforced polymer composites using a Langmuir-type model. Here, the focus was on evaluating the effect of the water layer thickness that surrounds the composite during the water migration process. The solutions of the governing equations were obtained using the finite volume method, considering constant thermophysical properties and non-deformable material. The results for the local and average moisture content and concentration, gradient values, and the transient rates of the free and bound (water) molecules in the process were presented and analyzed. It was observed that the water layer thickness strongly influenced the water absorption kinetics, the moisture content gradient values, and the equilibrium moisture content inside the material. It is envisaged that this new approach will contribute to better interpretation of experimental data and a better understanding of the physical phenomenon of water absorption, which directly affects the properties of composite materials.

Physicomechanical Properties of Rice Husk/Coco Peat Reinforced Acrylonitrile Butadiene Styrene Blend Composites

“…However, Guloglu et al [ 21 ] mentioned that most composites structures were in a range of abnormal water diffusion characteristics. This typical non-Fickian moisture absorption behavior of the thermoplastic-based composites was also reported by Melo et al [ 22 ] and Aziz et al [ 23 ] when the samples were continually exposed to a wet environment at a lower absorption rate and prolonged period.…”

Recent Progress of Rice Husk Reinforced Polymer Composites: A Review

“…The non-Fickian is justified at a 0.5 < n < 1.0 diffusion mechanism and does not obey the Fickian laws. At this condition, Melo et al [ 49 ] used a Langmuir-type model to closely interpret the physical phenomenon of water absorption relaxation of natural fibre composites. In some cases, when n is larger than 1, it is known as Super Case II kinetics [ 50 ]; however, when n < 0.5, this can be classified as ‘Less Fickian’ behaviour.…”

Non-Fickian Moisture Absorption in Vegetable Fiber Reinforced Polymer Composites: The Effect of the Mass Diffusivity

“…The absorption process was simulated considering an equilibrium moisture content Me = 0.14488 kg/kg, until approximately 2250 h (3 months of the process). The values for the parameters used in the simulation were defined based on the results previously reported in the literature [ 23 ]. Observe that two physical situations were considered: one where both the sides of the composites are submitted to a water layer of thickness 10 cm, and another where one side of the composite is submitted to a water layer of thickness 1 mm and another face to 10 cm water layer thickness.…”

“…The results show a good agreement with experimental data and allow a detailed interpretation of the physical phenomenon. Melo et al [ 23 ] presented a new approach for the Langmuir-type model in a one-dimensional and transient solution in order to evaluate the water layer thickness effect during the absorption process. The results of the free and entrapped water concentration, local and average moisture content, concentration gradients and variation rate of free and entrapped water molecules during the process were presented.…”

“…It is important to state that, in many works related to Langmuir’s model, the authors considered constant mass diffusivity [ 22 , 23 , 24 , 25 , 26 ]. However, this assumption is not completely consistent with the real process behavior, since the moisture migration rates are higher at the shorter process times and decrease for longer times; therefore, mass diffusivity varies with the water concentration inside the material [ 27 ].…”