9: Recycling and Reuse Flashcards
What is the motivation for recycling of composites?
-Expensive fibres (Carbon fibre=£10,000/T-£50,000/T, Glass fibre = <£1,000/T)
-Growth of CF use in industry (6,000-8,000 end-of-life aircraft by 2030= 120,000T-160,000T)
What is the energy comparison of Carbon Fibre production between recycling and new?
Mechanically recycled: >0.01
Thermally/chemically recycled: 3-10
Virgin (new): 55-165
What is the energy comparison of Fibre Glass production between recycling and new?
Mechanically recycled: >0.01
Thermally/chemically recycled: 3-10
Virgin (new): 4-10
What is the scope for composite recycling?
Prioritise reuse (lower energy)
End-of-life parts:
-Primarily cured thermoset epoxy/carbon fibre waste
-End of life parts are most likely contaminated
Manufacturing scrap:
-Dry fabric/bobbin ends
-Uncured trim scam (dry fabric and prepreg)
-Cured trim scrap
What is the recycling hierarchy (upside down pyramid) from top to bottom?
(least preferable, most likely)
-Landfill
-Incineration
-Recycling
-Re-use
-Waste reduction
(most preferable, least likely)
What are the challenges of recycling composites?
-Thermosets cannot be remoulded (must be thermally/chemically broken down)
-High contamination (poor traceability)
-Difficult to separate composites from other recyclables within assembly
-No infrastructure supporting composite recycling
-End-of-life Carbon fibre is low quality (low bulk density)
-Supply of recycled Carbon Fibre is greater than the demand (high variability)
-Unknown costs (new technology)
-Batch process rather than continuous
What are the aims for the End of Life Vehicle (ELV) Directive?
-Prevent use of some heavy metals (Cd, Pb, Hg, Cr(VI))
-Collect vehicles at suitable treatment facilities
-De-pollute fluids and specific components
-Provide coding and/or information on parts and components
-Ensure information for consumers and treatment organisations
-Achieve reuse, recycling and recovery targets
What are the 3 R’s of recycling?
-Reuse (used again for the same purpose)
-Recycle (reprocessed into other products)
-Recovery (Extract by-products of other processes, including energy)
What are the minimisation methods for waste reduction?
-Personnel practices (training and incentives)
-Better procedural measures (documentation)
-Inventory control (for prepregs with finite shelf-life)
-Maximise production runs (machine set-up waste reduction)
-Automation (remove operator error, optimised ply nesting (higher material usage))
-Inspection and quality control at each stage
-Alternative manufacturing routes (avoid intermediates)
What are the separation techniques for recycling of fragmented waste?
-Pneumatic
-Magnetic
-Gravity
-Eddy-current
-Chemical
Give an overview of disassembly of components during recycling
-Required to perform structural repairs or prepare for end of life
-Products designed for disassembly (component modularity, choice of fasteners/adhesives)
-Material choice for reversal joints activated by: Heat, moisture, stress or electrical current (risks unexpected disassembly_
-Apply tags for valuable materials (automatic sorting techniques)
-Difficult to automate (higher cost compared to assembly)
-Standardisation required
What are the current technical barriers to increased composite recycling?
-Difficult to maintain product consistency across a range of operating conditions and material types
-High levels of hand labour (preparation of fibre recovery)
What are the 3 types of recycling routes (in increasing fibre value and process complexity)?
-Mechanical methods (shredding, grinding)
-Thermal methods (pyrolysis, fluidised bed)
-Thermo-chemical processes (solvolysis)
What factors distinguish recycling processes to be used?
-Fibre mechanical properties
-Fibre length and length degradation
-Fibre surface chemistry
-Degree of contamination (char)
-Hardware issues (automation, yield, energy cost)
Explain the incineration energy recovery process
-Used for low value materials (E-glass) to be cost effective
-Combustion for energy recovery from polymers
-Combustion in cement kilns for fibres to reinforce cement materials
Explain the Shredding (Mechanical Recycling) process
-Size reduction required (low process volume rates (kg/hr), high size reduction ratio (m to mm)
-Low input energy and good results with 2 step process: Twin screw shredder, hammer milling (fragments or powder)
Explain the Pyrolysis (Thermal Recycling) process
-Feedstock composite heated without air (400-800 degrees)
-Some char contamination on fibres (mechanical property decrease)
-Hydrocarbon (gases and liquids) to be used as fuels or chemical feedstock
-Low temperature Catalytic pyrolysis (200 degrees) available for carbon fibre
Explain the Fluidised Bed (Thermal Recycling) process
-Composite waste shredded and fed into fluidised bed
-Heat fluidised bed (sand~1mm) removing polymer
-Fibres are carried away in hot gas stream
-Fibres separated from gas stream in a cyclone
-Passes to high temperature combustion chamber to clean (and energy recovery)
-Temperature = 450-550 degrees
-Fluidising air velocity = 1.3m/s
-Removes contaminants (metals remain in fluidised bed, Organic materials are oxidised)
Explain the Solvolysis (Thermal Recycling) process
-Chemicals speed up the thermal process (lower operating temperatures ~370 degrees)
-Yields highest quality fibres
-Solvent (water, ethanol, methanol, propanol, acetone) heated to break resin, releasing fibres
-More suitable for carbon fibres (glass degrades)
-Bad for the environment (increased cost for handling)
Give an overview of the properties from Pyrolysis (process, fibres, modulus, UTS, material recovery, scalability)
Process: Continuous
Fibres: Char
Modulus: ~95%
UTS: ~80%
Material Recovery: <55%
Scalability: Medium
Give an overview of the properties from Fluidised Bed Processing (process, fibres, modulus, UTS, material recovery, scalability)
Process: Continuous
Fibres: Clean
Modulus: >90%
UTS: ~66%
Material Recovery: <55%
Scalability: High
Give an overview of the properties from Solvolysis (process, fibres, modulus, UTS, material recovery, scalability)
Process: Batch
Fibres: Clean
Modulus: ~99%
UTS: ~99%
Material Recovery: >80%
Scalability: Low
What are the advantages of the pyrolysis process?
-High fibre property retention
-Recovery chemical feedstock from the resin
What are the disadvantages of the pyrolysis process?
-Clean waste feed required
-Deposition of char on fibre surfaces
-Environmentally hazardous gases released
What are the advantages of the Solvolysis process?
-Very high retention of mechanical properties and fibre length
-High potential for material recovery from resin
What are the disadvantages of the Solvolysis process?
-Fibres have reduced adhesion (inter-shear strength)
-Low contamination tolerance
-Hard to scale
-Environmentally hazardous solvents
What are the advantages of the Fluidised Bed process?
-Continuous process
-High tolerance to contamination and varied polymer types
-No presence of residual char on fibres
-Energy recovery
What are the disadvantages of the Fluidised Bed process?
-Strength degradation (20%)
-Fibre length degradation
-Unstructured fibre architecture
-Impossible to recover resin
What are the properties of the physical form of recycled Carbon Fibre?
-Low density
-3D random
-Single filaments
-Discontinuous
-Fibre length distribution
What are the volume fractions available for recycled carbon fibre composites by Fluidised Bed Recovery?
-Fillers, BMC (random CF): <10%
-SMC, low Vf Prepreg compression moulding (random mat): 10-40%
-Thermoplastic injection moulding (random CF): 20-40%
-Prepreg, compression moulding (aligned CF): 30-60%
What are the properties of Milling and Pelletising recycled products?
-Fibre length: 100-200 micrometres
-Binder content: 0.3-6%
-Pellet diameter: 1-5mm
-Injection moulding (limited applications due to scale)
-Increase: electrical conductivity, dimensional stability and stiffness
-Electromagnetic interference shielding
-Antistatic paint and coating
How are Intermediate Mats developed?
-Wet lay process
-Random preforms give limited Vf (~35% max before fibre breakage, reducing length)
-Fibre dispersion (distributed) and viscosity modification
-Binder and fibre rolled under vacuum, heat applied giving a nonwoven mat
-2-400g/m^2
What are applications of 2D random mats?
-Surfacing veil
-Electro-magnetic shielding
-Heating elements
-Static dissipation
-Fuel cell electrode
What are recycling Fibre alignment techniques?
Dry alignment:
-Carding and spinning (requires long fibres ~20mm)
-Magnetic fields (limited to low areal mass)
-Electric fields (limited to low areal mass)
Wet alignment:
-Hydrodynamic (converging flow process)
Explain the High Performance Discontinuous Fibres (HiPerDif) process
-Momentum change of fibre suspension in low viscosity fluid aligns fibres
-Plates spaced at 1/3 of fibre length
-Partially aligned fibres fall on moving belt, further aligning
-Water is removed by a vacuum pump
Explain some Intermediate Compound Development methods and their corresponding fibre volume fractions
-Direct mixing of recovered filaments in viscous resin - BMC (Vf <15%)
-Conversion of dry fabrics to chips - SMC (Vf <30%)
-Chipping of partially cured prepreg for ASMC (Vf<55%)
What are the advantages of Intermediate Compound Development methods?
-Potentially a high volume solution
-Low added cost in intermediates development
What are the disadvantages of Intermediate Compound Development methods?
-Wide range of mechanical properties obtained
-Problems with matrix viscosity and in-tool flow
-Very competitive virgin fibre market
What are the composites recycling cycle steps?
-Raw materials
-Production
-In-use
-End-of-life
-Recycling
(Repeat)
What do the energy requirements of the Fluidised Bed Process depend on?
-Feed rate per unit fluidised bed area
-In-leakage of ambient air
-Thermal energy requirement reduces for higher feed rates
-Energy required is 85-95% lower than virgin (new) fibre production
