This work presents a theoretical study of the anomalous behavior of moisture transient diffusion in vegetable fiber-reinforced composites materials using Langmuir-type model. For obtain the analytical solution was used the Laplace transform technique. Results of the absorption kinetics and concentration distribution of water (free and trapped water molecules) within the material along the process are presented and analyzed. Predicted results compared to experimental data of average moisture content have shown that the model was effective for description of the phenomenon, allowing a better understanding about the effects of moisture migration mechanisms.

Water uptake studies of composite materials reinforced with vegetable fibers shows that they are highly sensitive to environmental influences such as water and temperature. The presence of moisture leads to impregnation and imperfect interfacial fiber-matrix adhesion, which generate internal stresses porosity and premature system failure. Accordingly, the aim of this work is to study theoretically water absorption in unsaturated polyester composites reinforced with caroá fiber (Neoglaziovia Variegata) at 25, 50 and 70°C by using a transient 3D mathematical model via ANSYS CFX® Software. The samples has composition 30% caroá fiber/70% unsaturated polyester resin and dimensions 6 x 20 x 20 mm3. Results of the average moisture content and moisture content distribution during the water uptake are presented and analyzed. Comparison between numerical and experimental data of the average moisture content showed good agreement. It can be concluded that the water absorption rate is faster in the vertex region of the composites, and mainly at higher temperature.

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This work presents a non-steady state and three-dimensional mathematical modeling to predict moisture transport (based on the Langmuir-Type Model) inside the vegetable fiber-reinforced composite materials. The numerical solutions of the governing equations have been obtain using the finite-volume method. The model was apply for vegetable fiber-reinforced polymer composites. Emphasis to the geometrical dimension effect of the composite in the water absorption process was given. Results of the average moisture content, free and entrapped water molecules concentration kinetics and free and entrapped water molecules concentration distributions inside the material along the process are shown and analyzed. In the distributions of the analyzed properties, it was observed that the geometric dimensions of the composite has influence in the water absorption process.

This chapter provides information in the area of vegetable fiber-reinforced polymer composites. It includes discussion about definition and classification of the composites and their constituents, composite manufacturing process and current application in different industrial sectors. Factors affecting the fiber/matrix interfacial adhesion and physic-chemical and mechanical properties of vegetable fiber-reinforced polymer composites are also revealed. The aim is to show for both academy and industry the viability on the use of vegetable fibers as reinforcement in polymer materials, because it offers many advantages and high potential in terms of unlimited availability, lightweight, reasonable cost, acceptable mechanical properties, and socio-economic and environmental benefits.