Covalent Adaptable Networks in Fiber Composites
A Path to Recyclability and Performance
Time: Fri 2025-05-16 09.00
Location: Kollegiesalen, Brinellvägen 8, Stockholm
Video link: https://kth-se.zoom.us/j/62942074699
Language: English
Subject area: Fibre and Polymer Science
Doctoral student: Karla Itzel Garfias González , Polymerteknologi
Opponent: Professor Renaud Nicolaÿ, ESPCI Paris – PSL, Frankrike
Supervisor: Professor Minna Hakkarainen, Polymerteknologi; Professor Karin Odelius, Polymerteknologi
QC 2025-04-22
Abstract
Fiber reinforced polymer composites are entering a new stage, where durability, performance and recyclability, are no longer a choice but a requirement. This work contributes to these efforts by merging the field of covalent adaptable networks (CANs) with reinforcing fibers of different functionality. Two dynamic thermosets were developed; an epoxy thermoset with transesterification exchange reactions (TVx) and a phase-separated crosslinked elastomer with disulfide exchange reactions (BlendSS). Fibers bearing complementary functionalities to the reversible chemistry, were developed and incorporated in the respective matrix. Chemical recycling and mechanical recycling; through compression moulding and melt-extrusion; were used to study the role of fiber surface on composite performance, before and after recycling. Epoxy functionalized aramid fibers (PDA-Si) were introduced to TVx in the form of fiber meshes and short-cut fibers. This yielded PDA-Si composites having ≈22% higher ultimate strength and meshes of 46% higher lap shear strength compared to unmodified aramid fibers (UA). The contribution of PDA-Si for property retainment was suggested after chemical recycling by the 23% higher lap shear strength and in mechanical recycling by the 75% higher tensile stress at break of PDA-Si, compared with UA. Similarly, tetrasulfide functionalized glass fibers (SGF) were developed to promote bonding through the disulfide bonds in BlendSS. This resulted in SGF composites (CompSS-SGF) with 25% higher strength, and 36% higher creep resistance compared to composites with as received and clean glass fibers. After three recycling cycles by melt-extrusion, CompSS-SGF demonstrated ≈10% and ≈26% higher tensile strength and storage modulus compared to its counterparts. This was likely related to the increased availability of sulfur in CompSS-SGF for disulfide exchanges, which also affected the performance at higher temperatures. This works implements commercially available polymers, fibers and chemicals to construct fiber reinforced CANs, demonstrating the promise of the fiber functionality to leverage performance. Moreover, a simple solution to process and recycle CANs with industrially relevant methods such as melt-extrusion, and a route to use fibers to suppress creep was proposed.