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POLYMERIC MATERIALS 2 (COMPOSITES (Components (Reinforcement
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POLYMERIC MATERIALS 2
COMPOSITES
Definitions
- Engineered materials made with components with very diff. prop. and chemical prop. distinct on the macro level
- Homo material created by synthetic assembly to obtain specific char. and prop.
- Assembly of metal/alloy, plastic, ceramic/glass
Classification
- Particulate : part. in cont. matrix, low aspect ratio, randomly oriented
+ stiffness, wear, thermal/elec. res.
- Fibrous: high aspect ratio, well oriented, layers
+ mecha. prop/ in desired direction(s)
Components
Reinforcement
- Type: fibers (glass, C, aramide), glass (metal ox, talc), flakes (graphite, organic clays, mica)
- Task: most mecha. prop., cary load along fiber
- Continuous (unidirectional, cloth, roving) vs discont. (chopped, mat)
Matrix
- Type: polymer (PMC, TP, TS), metal (MMC), ceramics (CMC)
- Tasks: transfer stresses, det. operating T, processability, stab. fibres, protect reinforcements
- Requirements: good mecha. prop., good adhesion, ductility, environment res.
:warning: have to match with reinforcements: well bonded
- Prop. depends on the interfacial porp. + prop. of the fibres + prop. of the resin + ratio fibres/resin + geometry/orientation of fibres
Orientations and isotropy
- Orthotropic vs transversely isotropic (2 identical dire + 3rd)
- Lamine: unidirectional lay-up (same angle)
- Laminate: quasi-isotropic lay-up (angles diff. + mirror)
- Ply angle increases : reduce max strength
- Equations:
E1=Ef.Vf+Em(1-Vf)
1/E2=Vf/Ef+(1-Vf)/Em
Poisson12=Poissonf.Vf+Poissonm(1-Vf)
- Order of mag.:
E(fibres)= 220 MPa, E(matrix)=3.3 MPa
Poisson(fibres)=0,15, Poisson(matrix)=0,37
Applications
- Tailored prop.: strength, modulus, conductivity (heat/elec), density, acoustic insul., vabration damping, wear res.
- Limitations : Anisotropic, non-homogeneity/complexity, manufacturing techniques, T and moisture dependance, cost, recycling
- Aerospace, automotive, sport, transportation/infrastructure, industry/machinery
Composites vs Metals
- Almost purely elastic behavior + Effect of anisotropy
- C > M: stiffness, strength, fatigue res./strength
-M > C: weight, thermal exp., ductility/stress relief
Polymer matrix
Thermoset
- Adhesion: Epoxy > VE > Polyester
- Mecha. prop..: Epoxy > VE > Polyester
- Cure shrinkage: reorg. of mol. during curing (7%), better mecha. prop. if low CS
- : Degradation from H2O, micro-cracking
Polyester
- Most common
+: low cost, mecha. prop. +, weather res. shrinkage +
- Need post-curing
:warning: used of unsaturated polyester
- Process: base resin + crosslinking agent + initiator
Vinyl ester
- Similar struct. thn polyester
- Hardening controlled by the amount of accelerator
+: tough, good water/chemicals res., high MW
Epoxy
- Most common for high perf.
:warning: Ratio DGEBA/TGMDA
+: strength, adhesion, shrinkage, process, environment res.
T sensitivity:
- Amorphous TP: at Tg, V+, mecha. prop. -
- SC TP : at Tg, prop of amorph. phase - but crystalline parts determine most of them. at Tm: melt
- Thermoset : no strong changes
Thermoplastic
- Rarely used
+: toughness, damage tolerance, low processing cycle time, easier automatisation, lack of volatility, recyclability
- Crystallinity: increases mecha. prop. + can be improve with annealing
- Forms: hotmelt tape extrusion, solvent based techniques, powder coating, comingling fibers
Difficult melt impregnation dry reinforcements
Reinforcements/Fillers
Particulate 3D
- No preferred orientation, max 40-60 v%
+: cost, low shrinkage, good aesthetic
-: difficult to process, poor dispersion, viscosity +
Fibres 2D
- Ratio > 100, almost elastic behavior, strongly anisotropic
- Type: Filament < Strand, Yarns (twisted) < Roving, Tow (twisted) < Fabric, Milled (2-50 mm, used in injection-molding)
- Architecture:
UD: best prop. in the fibre dir.
Plain: sym. + stable
Satin: low porosity, high smoothness
Twill: good wet out and drape
Chopped: low proce
- Sizing: mix of several complex chemistries (surface treatment, protect fibre)
- Prepregs: semi-finished prod., reinforcements are pre-impregnated with pol. resin. Developed for aerospace. High quality and cost.
Glass fibre
- Electrical glass : most used
+: mech. prop., cheap, loading bearing
-: poor fatigue res., alkalis
- Chemically res. glass:
+: res. strong acidic/alkalis conditions
- High strength glass: aviation
+: tensile strength, E
-: price
Carbon fibre
- 95-99% of C, manuf. in several phases at high T, X-rays go through
+: E, tensile strength, low density, fatigue res., elec./thermal cond., low thermal exp., stabe, res. to acid
-: price, low impact strength, anisotropy
- Standard mod: 220 GPa, cheapest
- High mod: 350-450 GPa, low strength, high cost
- Interm. mod: 270-320 GPa, similar to SM
- Ultra-high mod: > 450 GPa, pitchbased
Aramid fibre
- Organic/synthetic fibre, consist of microfibrils
- Linear, rigid chains (benzene) in fibre axis, soft surface, hard core
+: E>EG (<CF), low density, impact/abrasion, lower price than CF (>GF), chem., T, flame res., dimensional stability
-: low shear/compr. prop., hygroscopic, poor UV-res, adhesion to matrix, cost
Natural fibre
- Plant, animal, mineral
+: renewable, availability, porous, thermal/acoustic prop., health, low density, biodegradable
-: moisture abs., low thermal stab., burn easily, slow drying, moulding, quality variation, poor compatibility
HPPE-fibre
- High perf. PE, similar to aramid
- Application: ballistic, impact res. structure
+: low density, E, strength, wear res., low friction, chem. res., flex., impact, no water abs., UV stab.
-: thermal stab., flammability, comp. prop., creep, adhesion
Selection
- GF-E: low price prod., no high stiffness, low wieght
- GF-S: lighter but still low priced prod.
- CF: stiffness
CF-SM: lower price
CF-IM: high stiffness (aircraft)
CF-HM: stiffness ++ (airspace)
Manufcturing
- TS, short fibres: injection-molding, comp. mod., liquid mod., spray up
- TS, continuous fibres: lay-up, filament winding, liquid mold., pultrusion
- TP, short fibres: injection mold., compr. mold.
- TP, continuous fibres: lay-up, thermoforming, compr. mold.
- Defects in laminates: join, overlap, missing ply section, inclusion, disbond, blister, wrinkles, ply drop-offs
Testing
- Parameters : materials (fibres, sizing, matrix, fillers), manufacture (void, cure state, stresses), compo. (layer, laminates), environment (T, RH, chemicals)
- Mecha. testing: tesile test, compression tests, in-plane shear tests, bending test
Def. measured with strain gages/displ. transducers
Cracking/Failures: visual or acoustic emission
- Laminate failure modes: layer failures, delamination (1. fibre pull-out, 2. fibre bridging, 3. interphase fail., 4. fibre break, 5. matrix cracking), microbluckling, sublaminate blucking
- Tension, compression, flexure (3 points), shear (tube torsion, rai-shear, non-linear matrix behavior)
- Fracture toughness: 3 modes
- Adhesive wear: single lap shear, thick adherend, double lap shear
ELASTOMERS
Definitions
- Mat. capable of recovering from large defo. quickly
- Conditions: high MW (>10^5), weak innerchain forces, Tg<Troom, amorphous, crosslinking sites in chains
- Types: homopolymer (A)n (NR, BR, CR), copolymer (A-B)n (SBR, NBR, IIR), terpolymer (A-B-C)n (EPDM, XNBR)
- Prop: hardness, tensile/tear prop., friction, wear/chemical/env. res., bounce/thermal/dynamic prop.
- Absorbs, seals, protects, connects, are flex.
- Elastomer + Filler/Reinforcement + Plasticizer + Additives + Vulcanization
Elastomer types
Natural rubber NR
- From rubber trees
+: process, elasticity, tensile strength, elongation, tear/wear/cold res., little dissipation factor, electrical/water/acid res.
-: poor weather/ozone res., restricted high T res.; swelling in oil/fuel res.
Isoprene rubber IR
- Synthetic counterpart to NR
+: toughness, abrasion/cold res., price, process, adherence; uncured track, tensile strength, high resilience, hot tear strength
-: life time at high T/ox., poor oil res., need protection against O2/O3/light
Butadiene rubber BR
- Mix with other elastomers (NR, SBR)
+: cold/hot tolerance, high resilience, wear res.
-: process, poor mecha. prop.
Styrenebutadiene rubber SBR
- Second most used, similar to NR
+: wear res., ageing res.
-: poor mecha. prop., adhesion, low elongation at break
Special Rubber
Ethylene propylene rubber EPM, EPDM
+: O3/weather res., high op. T, res. at low T, elec. prop.
-: poor res. to oils/hydrocarbons, poor attack
Butyl rubber IIR, CIIR, BIIR
- Prop. dep. on length of chain and saturation level
few C=C : good O2/O3 res.
lot of C=C: faster vulcanization, greater crosslink density
+: low gas permeability, stable at high T, ox/polar solvent/O3/weather res., wide elasticity range, low water abs.
-: poor wear res., not res. to hydrocarbon/oil, low elasticity
Nitrile rubber NBR
+: oil/heat/aliphatic/aromatic hydrocarbon/abrasion/water res., high swelling with solvents/oils
-: low weather/O3 res.
Silicons rubber Q
- Inorganic main chain, orga. side groups
- Silica reinforced or more benzene to impr. strength
- Side groups: fluoro-, phenyl-, nitrile (oil/heat res.)
+: heat/cold res., UV/O2/O3 res., elec. insulation, elasticity ++, non-toxic, tasteless, odorless
-: price, weak oil res., mecha. prop., high shrinkage after molding, high die swell in extrusion
TP elastomers
Copolymer, mix. of pol., possibility to process using extrusion/injection, hard (strength, heat res.) and soft (low T prop.) phases (triblock structure ABA)
TPE-S
- Most used
+: electricity res., low price
-: poor heat res., solvent res.
Elastomeric alloys
-TPO, TP vulcanized, melt processable rubbers
TPU
First group of TPE, 3 components : di-isocyanate (hard), polyether/polyester (flex.), chain extender (diol, glykol)
TPE-E ; ester-ether
crystallizable polyester, flexible polyether
TPE-A amide
- Hard segment: aromatic polyamide
- Soft segments: aliphatic polyesters.ether
Filler & reinforcements
- Mod. mecha. prop., processability, price
- Reinforcing: impr. prop. (strength), D=10-50 nm, strong bonds between filler and polymer (C, silica)
- Non-reinforcing: weak/no bond filler/pol., lower prop., low cost, D= 100-5000 nm (barium sulphate, magn. silicate, carbonate)
- Semi-reinforcing: D=100-1000 nm (clay, prec. calcium carbonate, silicate)
Plasticizers
- Reduce hardness, better processability
- Mineral oils: praffinic, naphtenic, aromatic
- Natural oils
- Synthetic plast.: phtalate, stearate
Additives
- Degradation: :warning: aged rubber becomes harder or softer
Ageing res. agents: antiox., antiozonants, wax prot.
Fire retardent
- Vulcanization agents: chains become crosskinked by reaction with VA
Sulfur: accelerator, acc., activator
Peroxide, metal oxide
4R
Reuse
- Use again for same function:
- Design practical collection system
- Challenging to adapt (hygiene)
- Washing/Transp. have env. impact
- Create a new function
- Manufacturing: repair + reconditionning
- Cat Reman Process: return as same as new cond.
Recover
- As energy:
T>100°C, used for steam, electric power, no harmful substance
- Compost:
biodegradable plastic, demand suitable env., increasing use of biopol.
- handling of residual left-overs materials from process of recycle mat.
- Cardboard:
20 = corrugated cardboard
21 = mixed papers, magazines
22 = Paper
- Wood fibre: recyclable 4-6 times
- Waste legislations:
EU: directives, regulation (65% of municipal, 75% of industrial waste by 2030)
Finland: 2011, 2016, importers responsability (tires, elec., packages)
Recycle
-
Definitions
- Upcycling: trans. prod. into new mat/prod. of better quality/env. value
- Downcycling: trans. prod. into prod. of lesser quality/funct.
- Closed loop recycling: prod. system in which the waste of one process is used in making another prod.
- Open loop cycle: con. of mat. from one or more prod. into a new prod. (change in inherent prop., lower quality)
For plastics
- Symbols: (1) PET, PTFE, (2) HDPE, (3) PVC, (4) LDPE, (5) PP, (6) PS, (7) Other (ABS, PC)
- Characterictics:
Lots of plastics, additives, disposal packages
Low density
Composite mat. + reinforcement cause troubles
Household waste difficult to handle
- Challenges: inadequacy of markets, mixed waste, contamination, diff. prop. even for same plastic, prop./perf. diminished
- Applications: still limited,films, hoses, sheets
Sorting
- Other mat. easy to separate
- Challenge for diff. plastics
- Manual separation vs Automated
Mechanical sorting
Dry gravity sep.
- For paper/film granules, based on airflow
+: More reliable, cheap
Froth Flotation
- Grinded plastic mixed in water with additives
- Based on the additives: 1 po. hydrophobic, 1 hydrophilic
- Air bubbles attached to hydrophobic pol. > surface
Wet gravity sep.
- For granular plastic, flow or sink
+: Big amount at the same time
-: Drying stage, sewage
Chemical sorting
Selective dissolution
- Pol. diss. in organic solvent
- Filtred out, isolated, resolidified
Based on color
- Machine vision
- For plastic bottles
Near IR reflectance
- Spectroscopy
+: Speed, cheap, contactless
-: not for black plastic
Without sorting
- Filling mat.: increase insulation prop., noise barrier, road soils/surface, sport fields
- Storing for later uses
Mechanical recycling
- Recovery of mat. from waste while maintaining the mol. structure of pol. into original or some other purpose
- Easy for industrial waste
- Stages : Collection > Transportation > Separation > Grinding > Washing > Drying > Remelting/Stabilization > Product
- Effect:
Decrease MW (break chains, free rad.)
Increase branching, crosslinking
Reprocessing reduces prop.
Appearance lower
Chemical recycling
- Break chain to monomers, consume lots of energy, no need to separate/wash, need large amount of waste
- Thermolysis: Pyrolysis, Gasification or Hydrogenation
- Chemolysis: pol. to monomer with depolimerization, Hydrolysis, Alcolysis, Glycolysis
Reduce
- Prevention: primary traget
- Primary waste streams, care in prod., more durable/lighter/thinner plastics, recycling friendly designing
TESTING OF POLYMERS
Polymers vs Metals
- Design more complicated: non-linear mat., many players, lack of public data, many materials/properties
- Higher thermal expansion (10x steels)
- Less stiff (3-5x)
- More flammable
- Deteriorate more with ageing
- Electrical/thermal insulator
- Much softer
- Can not be shaped by cold forming processes
- Need greater tolerances
- Wrapping issues, ageing issues
- Lower mecha. prop.
- Absord moisture
- Benefits: lower cost, no paint necessary, better corr. res., light weight
Testing
Process related prop.
- Bulk prop.: density
- Fluid prop.: rheological prop., rotational rheometers, capillary rheometers, melt-flow index, viscosimetry
Physical prop.
- Thermal prop.:
DSC: melting=endo., crystal.=exo.
Tg
TMA, DMTA
-
-
Standards
- ASTM, ISO, DIN
- SFS online
- MSDS: Material Safety Data Sheet (info on potential hazards)
- SDS: Safety Data Sheet
- PSDS: Product Safety Data Sheet
Mechanical prop.
- Tensile test: standard shape 1A
- OoM:
PEHD: E=1040 MPa, Sm=28 MPa
PELD: E=280 MPa
ABS: E=2400 MPa, Sm=38 MPa
Silicone: E=10 400 MPa, Sm=24 MPa
- Tear test
- Compression
- Torsion
- Bend test
- Impact testing: Charpy, Izod (edgewise, flatwise)
- Fatigue S-N curve
- Hardness: Vickers, Shore A/B, Barcol, Test T, load rise time
TESTING OF FIBRES
General
Consumption of technical fibres
- Types: Nonwovens > Fabrics > Textiles > Composites
- App: Transport > Industry > Home > Medical > Construction > Agriculture > Clothing
Standardization
- Framework of agreements to facilitate the life of authorities/eco/consumers. ensure quality prod. + comparable conclusions
- Setting guidelines
Organisation
- ISO: Intern Orga. for Standardization
- CEN: Europe
- SFS: Finland
- DIN: Germany
- ASTM, AATCC: USA
Testing of single fibre
Factors
- Affected by atmo. moisture
- Standard: RH 65%, T=20°C
- Conditioned at least 24h before
Finess
- Most important parameter of fibres
- = Linear mass density
- Unit: tex=1 g/1000m, dtex=1 g/10 000m
A[cm2]=W[mtex]/(density[g/cm-3].10^8)
Gravimetric
- For filament: mass fibre/length
- For spun fibres in spinning mill: mass fibre bundle/length
Vibroscopic method
- Single fibre with known length (20 mm) vibrates at its fundamental
- M=T(1/2Lf)^2
Tensile prop.
- Breaking strength=tensile strength if the max force recorded in extending a test piece to breaking point, prop. to A
- Stress= Force applied/cross-section area
- Tenacity: specific stress corr. with the max force on a force/extension curve
Measurement of tenacity
- :warning: need to eliminate the effect of the difference in A by div. the obs. strength by weight/unit length
- Tenacity=max tensile force/fineness
- Method: fibres clamped btw jaws, the lower the jaws is moving with a constant elong. rate
- Rem: tensile prop. of fabrics determine the max elong. force
Equations
- 0,1 [N/tex] = 1 [cN/dtex]
- 1 N/mm2 = MPa
- tenacity [N/mm2] = tenacity [N/tex].1000.denisty [g/cm3]
TESTING OF PACKAGING
Important prop.
- Tightness, barrier pro
- Sealability, hot track
- Friction
- Adhesion
- Toughness, res. to abrasion, mecha. prop.
- Printability
- No pinholes
- Food compliance, no odor/taste
- Appearance, clarity
- Even thickness/coating profile
- Biodegradability, compostability
:warning: Dep. on conditions, must be noted
Testing
- Mecha. prop.: tensile strength, stiffness, elasticity
- Barrier prop.: OTR, WVTR, CO2TR, grease, aroma, liquid
- Optical prop.: brightness, gloss, opacity
- Food compliance: contact, barrier prop., compo., purity
- Other: thickness, grammage,coat weight, glueability, chem. res., electrical prop.
Barrier prop.
- Against: O2, water, CO2, grease, aroma, light
- Small molecules (O2, H2O) penetrate: absorption on the surface > dissolution in the matrix > diffusion > desorption from the other side
- Factors: T, RH, thickness, Tg, Mn, moisture, crosslinking, crystalinity
- *Measurement:
- WVTR: gravimetric cup (easy to start with)
- Transmission rate test system: Mocon aquatran model 1G, high sensitivity coulometric water vapor :warning: if not too impermeable
- Carbon dioxide transmission rate: CO2TR
Grease barrier test
- :warning: in converting operations
- Optimum situation: no sliding, no sticking, piles do not fall
- Plastic/plastic, plastic/metal, plastic/paper
-
Pinholes
- Reduce barrier prop.
- Formation: before coating, film/subs. meeting, nip, release from chill roll
- Caused by: air bubbles, impurities, uneven/rough substrate, imp. on the chill roll
- Analysis: Optical microscope, visual analysis with coloured liquid
Adhesion
- Evaluated by fibre tear while sep. pol. coating/fiber substrate
- Good adhesion in cohesion failures
- Grades:
- 0: Layer do not adhere
- 3: Fibre tear < 50% of the surface area
- 5: Total fibre tear
- Peel test: more precise test, force required to peel the layer appart (vary with the peel angle)
Surface energy
- Attractive intermolecular force which act in the surface layer of the mat.
> 90°: lyophobic
< 90°: lyophilic
- Water:
> 0°: low energy surface
= 0°: high energy surface
- Angle(surface)=Angle(polar)+Angle(dispersive)
Sealability
- Hot bar sealing and hot track + hot tacking
- TUT: Hot air sealing and Ultrasonic sealing
Biodegradability
- Lots of standards and institures