Abstract
Polybenzoxazine (PBz) is regarded as a promising material to be utilised in automotive, aerospace, and off-shore industries due to its near-zero shrinkage during curing, low-water absorption, and good thermal/mechanical properties. In common, with other thermosetting, network-forming polymers, PBz resins may develop high-crosslink densities. This may lead to high-ultimate glass transition temperatures (Tg) but also result in brittleness, meaning that toughening is required to exploit the wider potential as engineering materials. An established method of thermoset toughening is the incorporation of nanoparticles. Therefore, in this study, a series of toughened and processable benzoxazine/sepiolite systems are developed and investigated, to determine the formulation potential to be applied for reliable large-scale fibre-reinforced polymers (FRPs).The first challenge to address is the solid nature and relatively low reactivity of the conventional bifunctional benzoxazine monomer. Herein, the liquid cardanol-based benzoxazine (CA-a) and an effective catalyst (3,3’-thiodipropionic acid, TDA) were added to the solid bisphenol A-based benzoxazine (BA-a). The resultant formulation shows excellent fluidity, relatively low peak polymerisation temperature compared to BA-a, as well as comparable thermal and mechanical properties compared to poly(BA-a). The second focus point is the dispersion of sepiolite, which is essential for the final performance of composites. The sepiolite is modified by easily implemented and highly effective methods using quaternary ammonium surfactant and CA-a, respectively. The in-house prepared organophilic clays are comprehensively investigated and proved to be much more homogeneously dispersed compared to pristine sepiolite. The resultant nanocomposites show encouraging fracture toughness improvement, with the best one demonstrating a 40% increase of plane-strain fracture toughness (KⅠc) with a low amount of filler addition (< 1.5 wt%). Meanwhile, such nanocomposites show an increased char yield and glass transition temperature, with negligible sacrifice in water absorption, as well as an acceptable viscosity increase. In summary, these materials display excellent potential as a matrix for toughened, fibre-reinforced polymers.
| Date of Award | 1 Oct 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Sebastien Rochat (Supervisor), Ian Hamerton (Supervisor) & Jeroen S Van Duijneveldt (Supervisor) |