Enhancing Circularity of Woven Flax Composites with Novel Vitrimer Resins

AI Quick Summary

Flax composites offer a lower carbon footprint versus traditional carbon fiber composites. To improve circularity, we will assess an innovative vitrimer resin where cure cycles and properties are comparable to conventional epoxies but also allow thermoforming and chemical recovery. EPFL and Bcomp will impregnate flax textiles with vitrimer resins and compare formability and mechanical properties with conventional epoxy resins and demonstrate flax and resin recovery and reuse by solution depolymerization. 1. THEMATIC FOCUSEnhancing circularity of flax composites with novel vitrimer resin systems To improve circularity and reduced embodied energy in composite materials, alternative fiber and resin systems can be considered. Existing flax composites using epoxy resins offer a lower carbon footprint alternative to traditional carbon or glass fiber reinforced composites. To enhance circularity, this collaboration between EPFL and Bcomp will examine how flax textile reinforcements can be impregnated with innovative dynamic covalent bond vitrimer resin alternatives to conventional epoxy resin systems. The resin system is designed to be depolymerized at end of life enabling recovery of both the flax fiber and resin. These can both be re-used and re-manufactured into new product forms, providing a key technical enabler to a composites circular economy with low GWP fibers.2. DEGREE OF INNOVATIONEpoxy vitrimer resins provide cure cycles and properties comparable to conventional aerospace epoxies but also allow a range of behaviors more akin to thermoplastics. Specifically, below the glass transition temperature the materials have thermoset properties, yet behave like a thermoplastic at elevated temperatures, such as 80°C above Tg. Hence we will examine in an EPFL Master's thesis in close collaboration with Bcomp the use of dynamic covalent bond polyimine-based vitrimer matrix systems to impregnate woven and non-woven flax textiles. The new chemistry platform is based on dynamically exchangeable imine-linked polymer networks. The reversible nature of this resin enables covalent welding, molding, reshaping, solution-based and solid state, closed-loop recycling of fully cured materials. Additionally materials can be stored and transported at room temperature, eliminating the inconvenience, cost, and energy of refrigeration. 3. EFFECT3.1 Cradle-to-gate data for typical compositesCradle-to-gate data for typical composite constituents is given below. Sequestration assumes that CO2 is transformed into biomass via photosynthesis. As the flax is then used in an engineering product with, for example in automotive molding with a 15 year life, and with the recovery potential that vitrimers offer, we argue that the flax biomass is not transformed back into CO2 in a relatively short time scale. Additionally, the flax used (unlike wood) can be replenished on a yearly basis, so we have accounted for sequestration. Composite constituents Global warming potential (GWP, kg CO2 eq./kg)flax -0.5Woven CF (dry) 49Woven GF (dry) 1.9epoxy resin 8.6PP 1.6 3.2 The potential of flax/vitrimer composites to reduce GWPRecycling processes for carbon epoxy can achieve a representative GWP reduction of 19 to 27 kg CO2 eq. Composites today generally follow a linear economic model with the best case being recovery of carbon fiber via pyrolysis, with recycling being the least effective part of a circular economic model. Assuming a 50:50 mass ratio for simplicity, 1kg of CF/epoxy has a GWP of 29 kg CO2 eq./kg. Generally this is not recovered at end of life. In comparison, this project will take the near or below zero GWP of flax fiber and combine this with a vitrimer resin that enables full recovery of the flax fiber and the vitrimer resin at end of life for re-use and re-manufacture of new components creating a circular approach for composites. This would reduce the GWP for a flax/vitrimer composite to between 0 and 8.6 kg CO2 eq./kg depending on the recovery yield of the resin. Up to 30% of the recovered resin can be used in new materials with no loss in mechanical performance. This GWP is an order of magnitude below that of conventional composites. A simplistic estimation shows a GWP reduction from 30 to 5kg CO2 eq./kg translating for an automotive part mass of 2kg made at 50'000 parts per year for 5 years into a CO2 saving of 12.5 kT versus CF/epoxy (assuming same part functionality as same mass). If this is used on 3 vehicles at 5 OEMs then the potential is nearly 200kT. 4. METHODOLOGICAL QUALITYEPFL is a leading international research organization with LPAC an established and reputable composite materials laboratory. Bcomp is an established start-up in flax based composites.5. GENDER and DIVERSITYEqual opportunitiesThe EPFL and Bcomp are equal opportunity employers and the respective gender and diversity HR policies will naturally apply to this project.6. SCOPE AND TASKS6.1 Impregnation trialsImpregnation trials will be performed at EPFL-LPAC (powder/film/liquid) to make pre-impregnated sheet. Process parameters (time/ temperature / pressure) will be optimized for the resin rheology and kinetics versus void content, mechanical properties and flax thermal stability. The pre-impregnated sheet will then be thermoformed and molded at Bcomp into generic flat plaque and 3D shapesfor comparison with conventional epoxy resin systems, examining both processing and mechanical properties (tension, off-axis tension, compression, DMA dry/conditioned). Another key advantage of vitrimer systems is that parts can be processed like thermoplastic composites by stamp-forming with 30s cycle times which is faster than snap-cure epoxy systems (e.g. HexPly® M77 2min cure at 150 deg C). Additionally, the increased Tg (up to 200 deg C) of the final part is a significant benefit versus PA materials (Tg when conditioned 25-90deg C, PA6 to PPA) giving reduced variation in composite properties in standard automotive temperature ranges of -40 to 120 deg C. 6.2 Recovery, re-purposing, and re-manufactureWe will also assess recovery of the resin, for re-purposing and re-manufacturing into new composite parts, via spontaneous depolymerization in a recycling solution. The depolymerized polymer may also be ground into a powder and reformed into new shapes with heat and pressure. We will assess how the recovered flax weave can be re-purposed, potentially by converting to a non-woven product for SMC prepreg with the recovered vitrimer resin. This both increases the input lifetime vis-a-vis recycling and reduces the energy required during re-purposing. 7. BUDGETWe request 25'000 CHF to cover the internal and external costs of running this project at the EPFL where a master(s) student will be funded. 8. CO-FUNDINGThe needed 20% financial contribution will be provided by Bcomp (10% to NTN Innovation Booster, 10% into the project). We will perform an internal assessment of the CO2 reduction potential between EPFL and Bcomp.9. Lead OrganisationEPFL, LPAC (Prof. Veronique Michaud)

Project Idea Metadata

• Project Idea Name: Enhancing Circularity of Woven Flax Composites with Novel Vitrimer Resins
• Date: 3/28/2022 8:05:06 AM
• Administrators:
  • Martyn wakeman

Project Idea Description

1. THEMATIC FOCUS

Enhancing circularity of flax composites with novel vitrimer resin systems

To improve circularity and reduced embodied energy in composite materials, alternative fiber and resin systems can be considered. Existing flax composites using epoxy resins offer a lower carbon footprint alternative to traditional carbon or glass fiber reinforced composites. To enhance circularity, this collaboration between EPFL and Bcomp will examine how flax textile reinforcements can be impregnated with innovative dynamic covalent bond vitrimer resin alternatives to conventional epoxy resin systems. The resin system is designed to be depolymerized at end of life enabling recovery of both the flax fiber and resin. These can both be re-used and re-manufactured into new product forms, providing a key technical enabler to a composites circular economy with low GWP fibers.

2. DEGREE OF INNOVATION

Epoxy vitrimer resins provide cure cycles and properties comparable to conventional aerospace epoxies but also allow a range of behaviors more akin to thermoplastics. Specifically, below the glass transition temperature the materials have thermoset properties, yet behave like a thermoplastic at elevated temperatures, such as 80°C above Tg.

Hence we will examine in an EPFL Master's thesis in close collaboration with Bcomp the use of dynamic covalent bond polyimine-based vitrimer matrix systems to impregnate woven and non-woven flax textiles. The new chemistry platform is based on dynamically exchangeable imine-linked polymer networks. The reversible nature of this resin enables covalent welding, molding, reshaping, solution-based and solid state, closed-loop recycling of fully cured materials. Additionally materials can be stored and transported at room temperature, eliminating the inconvenience, cost, and energy of refrigeration.

3. EFFECT

3.1 Cradle-to-gate data for typical composites

Cradle-to-gate data for typical composite constituents is given below. Sequestration assumes that CO2 is transformed into biomass via photosynthesis. As the flax is then used in an engineering product with, for example in automotive molding with a 15 year life, and with the recovery potential that vitrimers offer, we argue that the flax biomass is not transformed back into CO2 in a relatively short time scale. Additionally, the flax used (unlike wood) can be replenished on a yearly basis, so we have accounted for sequestration.

Composite constituents Global warming potential (GWP, kg CO2 eq./kg)

flax -0.5

Woven CF (dry) 49

Woven GF (dry) 1.9

epoxy resin 8.6

PP 1.6

3.2 The potential of flax/vitrimer composites to reduce GWP

Recycling processes for carbon epoxy can achieve a representative GWP reduction of 19 to 27 kg CO2 eq. Composites today generally follow a linear economic model with the best case being recovery of carbon fiber via pyrolysis, with recycling being the least effective part of a circular economic model. Assuming a 50:50 mass ratio for simplicity, 1kg of CF/epoxy has a GWP of 29 kg CO2 eq./kg. Generally this is not recovered at end of life. In comparison, this project will take the near or below zero GWP of flax fiber and combine this with a vitrimer resin that enables full recovery of the flax fiber and the vitrimer resin at end of life for re-use and re-manufacture of new components creating a circular approach for composites. This would reduce the GWP for a flax/vitrimer composite to between 0 and 8.6 kg CO2 eq./kg depending on the recovery yield of the resin. Up to 30% of the recovered resin can be used in new materials with no loss in mechanical performance. This GWP is an order of magnitude below that of conventional composites. A simplistic estimation shows a GWP reduction from 30 to 5kg CO2 eq./kg translating for an automotive part mass of 2kg made at 50'000 parts per year for 5 years into a CO2 saving of 12.5 kT versus CF/epoxy (assuming same part functionality as same mass). If this is used on 3 vehicles at 5 OEMs then the potential is nearly 200kT.

4. METHODOLOGICAL QUALITY

EPFL is a leading international research organization with LPAC an established and reputable composite materials laboratory. Bcomp is an established start-up in flax based composites.

5. GENDER and DIVERSITY

Equal opportunities

The EPFL and Bcomp are equal opportunity employers and the respective gender and diversity HR policies will naturally apply to this project.

6. SCOPE AND TASKS

6.1 Impregnation trials

Impregnation trials will be performed at EPFL-LPAC (powder/film/liquid) to make pre-impregnated sheet. Process parameters (time

/ temperature / pressure) will be optimized for the resin rheology and kinetics versus void content, mechanical properties and flax thermal stability. The pre-impregnated sheet will then be thermoformed and molded at Bcomp into generic flat plaque and 3D shapes

for comparison with conventional epoxy resin systems, examining both processing and mechanical properties (tension, off-axis tension, compression, DMA dry/conditioned). Another key advantage of vitrimer systems is that parts can be processed like thermoplastic composites by stamp-forming with 30s cycle times which is faster than snap-cure epoxy systems (e.g. HexPly® M77 2min cure at 150 deg C). Additionally, the increased Tg (up to 200 deg C) of the final part is a significant benefit versus PA materials (Tg when conditioned 25-90

deg C, PA6 to PPA) giving reduced variation in composite properties in standard automotive temperature ranges of -40 to 120 deg C.

6.2 Recovery, re-purposing, and re-manufacture

We will also assess recovery of the resin, for re-purposing and re-manufacturing into new composite parts, via spontaneous depolymerization in a recycling solution. The depolymerized polymer may also be ground into a powder and reformed into new shapes with heat and pressure. We will assess how the recovered flax weave can be re-purposed, potentially by converting to a non-woven product for SMC prepreg with the recovered vitrimer resin. This both increases the input lifetime vis-a-vis recycling and reduces the energy required during re-purposing.

7. BUDGET

We request 25'000 CHF to cover the internal and external costs of running this project at the EPFL where a master(s) student will be funded.

8. CO-FUNDING

The needed 20% financial contribution will be provided by Bcomp (10% to NTN Innovation Booster, 10% into the project). We will perform an internal assessment of the CO2 reduction potential between EPFL and Bcomp.

9. Lead Organisation

EPFL, LPAC (Prof. Veronique Michaud)

Flax composites offer a lower carbon footprint versus traditional carbon fiber composites. To improve circularity, we will assess an innovative vitrimer resin where cure cycles and properties are comparable to conventional epoxies but also allow thermoforming and chemical recovery. EPFL and Bcomp will impregnate flax textiles with vitrimer resins and compare formability and mechanical properties with conventional epoxy resins and demonstrate flax and resin recovery and reuse by solution depolymerization.