Thesis title: New and innovative pathways for recycling and recovery, and potential reuse of fibers (Glass and Carbon) obtained from Wind Turbine blade waste in fabrication of recyclable composite sheets for lightweight and electronic automotive application
Sustainable development and circular economy have compelled global leaders to legislate laws and policies on several critical hot topics in order to prevent further environmental issues such as global warming: (1) enhancement of green and renewable electricity utilization (wind turbine implants, as an example); (2) waste transformation into high-added value materials; and (3) material and energy recovery and circularity. Accordingly, scholars and researchers have predicted that installed wind power capacity will increase dramatically by 2050. However, our ecosystem will have to face and deal with an enormous amount of decommissioned turbine blades. These blades are mainly composed of fiber-reinforced thermoset composites (FRPs), which make their recycling challenging. The possible recycling methods can be divided into landfilling, incineration, mechanical, thermal, and chemical recycling. Considering the EU Directive 2008/98/EC, no ban on using conventional disposal routes (landfilling and incineration) is mentioned; instead, it prioritizes reuse and recycling over these disposal methods. Mechanical recycling is the only feasible method currently available to manage EoL turbine blades—mechanical processing results in a degradation of the mechanical characteristics of the recovered materials. Therefore, according to the author’s knowledge, pyrolysis and co-processing in a cement kiln seem to be two possible choices. On the other hand, co-processing provides a sustainable and circular solution to recycling EoL composite materials with GFs. The outputs of mechanical recycling can be re-utilized in cement co-processing, where the resin content of the composite’s waste is combusted as a secondary fuel energy resource, and the fibrous content of the waste provides minerals to the feedstock. This type of recycling technology not only helps us reduce the extraction of natural raw mineral materials and replace fossil energy resources but also reduces the carbon footprint of cement production by 16%. An in-depth investigation into these two recycling scenarios was conducted.
To verify the applicability of co-processing, a comparative life-cycle quantitative assessment is conducted among landfilling, incineration, and co-processing as three disposal routes in various European countries to determine which scenario has the least environmental impact from multiple perspectives.
Another way to recover both matrix and obtain also secondary materials from short, recycled Carbon (CFs) and Glass fibers (GFs), is the coarse ground EoL blades went through a pyrolysis process, of which the conditions were as followed: The materials were thermally treated in two steps, once with temperature around 500°C in N2 atmosphere and second with temperature higher than 500°C in Air atmosphere to remove the char remaining on the fibers by O2. After this first step it is advisable to fabricate secondary materials for further utilization, such as possible new rovings and/or non-woven fabrics, to obtain new secondary raw materials useful for composites market. The term nonwoven fabric has gained significant attention in recent decades due to its versatile applications and impressive features, such as energy absorption, drawability, electromagnetic shielding, and high productivity, which can be of high interest to the automotive sector. In this regard, lightweight composite production reinforced with the nonwovens was one of the applications foreseen for the recyclates. Composites are heterogeneous materials that combine two or more distinct materials (such as a matrix and reinforcement) characterized by a distinct phase interface separation. According to sustainability and circular economy objectives, a green shift in composite manufacturing is necessary. This green transition involves the use of thermoplastic resins instead of thermoset counterparts, as they are recyclable and can be recovered, thereby avoiding the further production of raw materials. Therefore, sustainable acrylic thermoplastic composites were fabricated via vacuum-assisted resin infusion molding. Elium C040 was chosen as the thermoplastic resin, which simultaneously enables in-situ polymerization and offers comparable mechanical behavior to thermoset resins, such as epoxy.
Another tangible example of a cross-linked material that is challenging to recycle is automotive car tires. According to statistics published in 2019 by the European Tyre and Rubber Manufacturers’ Association (ETRA), the majority of used tires in Europe have been abandoned, incinerated, or illegally landfilled. Various recycling routes exist for rubber material. However, material mechanical recycling is favored among all since it involves the reutilization of ground tire rubbers (GTRs) in producing brand-new goods. Currently, research and investigation are focused on modifying or functionalizing GTRs to manufacture high-value-added products for engineered uses, ranging from blending with other thermoplastics and rubbers to asphalt modifiers and infills in artificial turf for sports playgrounds. As another possible application of fibrous recyclates, in this research, green rubber devulcanization via a twin-screw extruder with the utilization of recycled GFs was done to have the benefit of rGFs as a devulcanization agent and filler. Processing parameters such as screw speed and GFs content were varied to investigate the properties of the reclaimed rubber. Lastly, elastomeric sheets were produced through compression molding to study the material characteristics.