Characterization of flax fibres for application in the resin infusion process
Bibliographic record
Abstract
Increasing concerns over depleting natural resources has led to the development of so-called biocomposites based on fibres from renewable resources such as flax. Although these fibres are seeing use in some applications, there is a lack of understanding concerning their processing requirements in relation to their unique physical and chemical properties. Furthermore, there is limited information regarding the links between their processing behaviour and mechanical performance. With the aim of addressing these missing links, this thesis presents a methodology for characterizing flax fibres for application in the resin infusion process and considers two important case studies with the overall goal of improving the state-of-the-art for this class of materials.Flax fibres were first characterized at the fibre level by advancing contact analysis, thermal gravimetric analysis, scanning electron microscopy and helium pycnometry. The advancing contact analysis revealed a reduction in the polar component of surface free energy after the application of silane and diluted epoxy treatments. A methodology was then developed for the characterization of the compaction and permeability of flax-based fabrics for the modelling of the resin infusion process. These parameters were quantified and used as input in a 1D process model that included capillary pressure. The model predictions for flow front evolution were shown to be in good agreement with experimental data. Alkaline treatments were shown to increase the required compaction pressure for a given porosity due to an increase in fibrillation. This had direct implications in the context of resin infusion processing due to the coupled nature of flow and compaction in this process. Consequently, a mechanical characterization revealed a decrease in flexural properties for alkaline-treated flax/epoxy composites manufactured by resin infusion due to a decrease in fibre volume fraction. A decrease in flexural properties was also noted with increasing void content.In an effort to improve the state-of-the-art for this class of materials, a case study was carried out on the incorporation of nano-modifiers in the resin infusion process. Nanocellulose was incorporated by two novel techniques; a 'grafting' method and a wet-layup method that incorporated an aqueous NC solution in the resin infusion pre-filling stage. Both methods were shown to lead to an increase in damage to the composites after subjection to a drop-weight impact event which suggested that the nano-modifier did not increase the interlaminar properties. However, an increase in interlaminar shear strength was observed by a short beam test due to an increase in fibre volume fraction as a result of softening and lubrication effects arising from the use of the aqueous NC solution.A second case study addressed the primary source of voids in a class of flax/epoxy prepregs which are generally used as a benchmark for composites manufactured by the resin infusion process. A series of compaction tests and thermal gravimetric analysis suggested that moisture and resin starvation were the primary source of voids in commercially available prepregs. Panels manufactured in an autoclave at varying pressures suggested that the latter of these issues was the dominant problem for the studied materials. The presence of voids was finally shown to lead to increased moisture sorption for flax/epoxy composites.This study stresses the coupled nature of the resin infusion process and the full implications of the use of chemical treated flax fibres. Additionally, it demonstrates the negative consequences of process-induced voids on the performance of flax/epoxy composites. It also provides useful data on the fibre surface chemistry, permeability, compaction and mechanical performance of flax-based composites. This assists in furthering the development of this class of materials with the goal of increasing their potential for use in load-bearing structures.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".