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PRESENTATIONS ELASTOMERS (3D printing of elastomers (Methods (FDM
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PRESENTATIONS ELASTOMERS
Latex processing
Latex
- Juice » of the hevea tree
- Water emulsion of a synthetic rubber or plastic obtained by polymerization
- Humid Intertropical zone, South East Asia (95%)
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Different types of Latex
Natural rubber latex
- 60% of rubber particles, 2% of protein and neutral lipids
- Thin shaping is obtained with extrusion process
- Use of accelerators for fast gelling, precipitated silicas or precipitated chalks
- Washing, drying and vulcanization at low temperature
- Can be added before the vulcanization: Black carbon, Oils used as plasticizers, antioxidants, Protection agents against UV
- Products : gloves, condoms, balloons, diaphragms
Liquid latex
- One-third rubber, water, proteins, lipids
- Ammonia is added to keep it liquid and avoid coagulation (high or low ammonia latex)
- Creaming or centrifuging processes
- Products: Adhesives, paints
Synthetic rubber
- Styrene-butadiene copolymer is the most used
- Large range of properties: flame retardancy, gas impermeability or chemical inertess
- High price
- Better than natural rubber about high mechanical resistance and ageing
- Need protection: against UV and O3
Sector of latex uses
- Transport ( 90 % for tires)
- Medical and clothing
- Cinema ( special effect)
- Staff ( building materials)
- Bedding
- Paints (liquid form)
- Adhesives (liquid form)
Recycling of elastomers
Options
- Unvulcanized waste
- Mainly generated in the manufacturing processes
- May contain steel, textile fibre from reinforcement
- Can be vulcanized and grinded, used as fuel, etc
- Can be added to pristine
- Vulcanized waste
- Mainly post-consumer
- 17.2 Mtonnes/year
- 40 % NR, contains steel, textile fibre
- Recycling options: product reuse, material reuse, energy reuse
Retreading of the tires
- Inspection
- Buffing
- Smoothening of the rotation and tire sides
- Polishing, if rust is present
- Re-adhering of new (non-vulcanized) parts
- Sprinkling with rubber residue from the buffing (to prevent sticking)
- Curing
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Physical size reduction
- Ambient grinding, cryogenic grinding or wet grinding
- Crumb size from coarse (9-5 mm) to superfine (0.15-0.01 mm)
- When used as fillers for polymeric materials, additive/matrix adhesion is a problem
Devulcanization
- Challenge: selective bond cleavage
- Chemical, thermal, mechanical, thermomechanical, microbial and by irradiation (ultrasound and microwaves)
- Product: uncured rubber
Pyrolysis
- Heating the rubber waste in absence of oxygen (400 – 800 Deg.C)
- 3 products, all have industrial use
- gas and heavy oil as a fuel
- light oil as gasoline additive
- char as carbon black substitute
- By-products: steel, polymer residues
- Emissions: water, CO2, CO, SO2, NOx
Incineration
- Energy content of rubber is 32.6 MJ/kg
- Product: energy and cement additive
- Emissions: oxygen, CO2, water, hydrocarbons. Toxic gases, if temperature is not high enough
- Rubber crumbs: Used to supplement coal and wood
- Whole tire: Used by cement industry as energy source + clinker used in cement
Uses of recycled
rubbers
New tires
- Retreat worn tires to use in low speed rated cars
- Scrap powder tire can be used as a filler for virgin rubbers
- Devulcanized GRT can be used in blends with virgin rubbers
Rubber-Recycled Rubber Blends
- Incorporation of ground or devulcanized rubber into virgin rubber as filler
- Compatibility: typically the products have lower tensile properties due to insufficient bonding between the ground rubber and the virgin matrix
Flooring
- GRT is combined with premixed polyurethane to produce a soft, pliable, energy-absorbing rubber surface
Thermoplastic-Recycled Rubber Blend
- Thermoplastic elastomers
- Ground or devulcanized rubbers
- Blends that can be remelted and shaped in a wide variety of molded and extruded products
Dynamic vulcanization
Modified concrete
- Ground rubbers
- Increase of :
- Crack, freeze-thaw and impact resistance
- Shock wave absorption, thermal and acoustic performance
- Carbonation, chloride penetration and acid rain resistance
- Decrease of:
- Heat conductivity
- Compressive and flexural strength
Modified asphalt
- Crumbed rubber can be added two different ways: dry and wet process
- Increase of: Durability; Crack resistance; Skid resistance
- Decrease of: Noise; Cost
Crumb rubber in soil
- Addition of crumb tires
- Decrease of: Soil hardness; Soil shear strength; Water content
- Also possible to use rubber-soil mixtures to provide seismic isolation of buildings
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Electroactive elastomers
EAPs
- size and shape change when
they are stimulated by an electric fields
- ability to deform a lot, and to produce a big force (capable of deforming by 380 %)
- Electronic EAPs
- Dielectric Elastomer, Electrostrictive Graft Elastomer, Liquid Crystalline Elastomer, Electro-viscoelastic Elastomer
- Structure is composed of the electroactive
material sandwiched between two electrodes
- Ionic EAPs: no elastomers
+ : significant generated force, short response time, operates in ambient conditions, long service life
- : high operating electric field (from 20 to150 MV / m), sense of unique deformation for quadratic couplings
- Important Characteristic:
- The high voltage required for actuation
- Their speed
-Their important useful force.
Dielectric Elastomers
- Consists of polymer film between two compliants electrodes
- Huge deformation possible
- Capacitor with variable capacity
- Application: Biomedical applications, Biomimetic Robots, Sensors and power generator, Loudspeakers, pumps and valves, deformable surfaces
Electrostrictive Graft Elastomers
- Exhibits large electric induce strainà 4%
- Two components: Flexible backbone chains + Grafts (crystallisable side chains)
- Form physical cross-linking sites and polar crystal domains responsive to electric field
- Under E field à polar domains align
+ : No Hysteresis, Response speed in the region of ms
- : Required electric field
- Applications: sensor and an electrostrictive actuator
Liquid Crystal Elastomers
- Mesogene groups and Mesophase
- Weak reticulation of the Liquid crystal network
- Spontaneous elongations
- Activation of LCE is made by: E-field, T change, irradiation, G-field
+ : easy to miniaturize, lightweight, no need for lubrication, low stiffness, high tensile strength, requires small load
- : slower response time compare to classical liquid crystal
- Application: conductive polymeric matrice, Mechanical actuators, Sensors
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Self-healing elastomers
Principle
- Inspired by natures biological systems
- Products of highly refined, coordinated and complex metabolic activities
Bond cleavage
- Covalent bonds within the polymer chains break
- Homolytic bond cleavage: Each of the atoms of the cleaved bond get one electron, Radicals can repair the bond or cause other bonds to be cleaved
- Heterolytic bond cleavage: The two electrons of the cleaved covalent bond stay with one of the atoms of the bond, ions can repair the bond or cause other bonds to be cleaved
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