Sorption of liquids in advanced composite materials
Understanding how liquids penetrate advanced composites is important in many situations. The impact that water has on the structure of liquid crystalline polymers has been studied by the LINX teams at Aarhus University and the University of Copenhagen with Grundfos, and how resin penetrates fibre composites has been studied by the Technical University of Denmark and LM Wind Power.
Water can find its way into many materials and product encapsulation in plastic is a common first choice. However, as the molecules in plastics are held together through chemical bonds, over a long enough duration, exposure to water can result in degradation of the polymer molecules and properties of the materials. Once they begin to fail, the amount of water permeating can be considerable and possibly cause undesirable outcomes such as short-circuiting electronic components.
Wind turbine blades
The understanding of composited materials are a key point in producing wind turbine blades at LM Wind Power and for this reason LM Wind Power is and have been involved in a number of research projects with univeristies over the past many years. A lot of focus has been on the individual fibers and the the CINEMA project (2014-2018) LM Wind Power and DTU developed methods to study the individual fibers in unidirectional composites.
Read the interesting one pager from this project: Liquid crystalline polymers for protecting sensitive equipment.
Techniques and Methods
The LINX teams at Aarhus University (AU) and the University of Copenhagen (KU) used X-ray diffraction and small-angle X-ray scattering, respectively, to understand the impact that water had on components at both the surface (AU) and in the bulk (AU and KU). In an crystalline polymer, the polymer molecules are aligned to an extent but often randomly distributed otherwise. This helps to reduce and delay the water permeation. Despite the often low concentration of water within the polymer material and the slow diffusion of water through it, the performance of the material decreases with water exposure time.
By combining the surface-sensitive measurements at AU, where the crystallinity at the surface can be probed, and the bulk-sensitive measurements at KU at AU, where the nanometre-scale orientation structure and orientation (KU) and crystallinity (AU) can be probed, it has been possible to see the changes occurring as a function of exposure time. This has revealed that the changes happen more quickly at the interface than in the bulk, which suggests a possible mechanism for the changes imparted by water.
Wind turbine blades
Within this LINX focus project LM wind Power and DTU are looking into fiber bundles and how does resin penetrate the fiber composites. X-ray imaging has been used to study parts of composites where the resin flow has been stopped in order to study the different penetration processes in the fibre material.
Participants: Grundfos, LM Wind Power, VELUX, Aarhus University, Technical University of Denmark, University of Copenhagen.
Start date, end date: April 2016 – August 2018.
Title: Development of methods for Investigation of sorption of liquids and humidity in advanced composite materials (FP06.001, Sorption of liquids and humidity).