PART 6 POLYMERS

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 PART 6 POLYMERS

• 6.1 Terminology
• 6.2 Types
• 6.3 Uses
• 6.4 General properties
• 6.5 Forming processes
• 6.6 Modes of failure (durability)
• 6.7 Typical applications

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PLASTICS

• Polymer A material formed of large molecules
  which are built up (polymerised) from a large
  number of small molecules (monomers). The usual
  (but not only) example is the organic polymers.
• Organic materialsThese are materials originating
  from living organisms. Strictly all materials
  containing carbon are defined as organic.
• Plastics This term is used for a range of
  organic materials. Note that the term "plastic
  state" of concrete relates to the generally low
  modulus of elasticity and high creep of plastics.

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 PART 6 POLYMERS

• 6.1 Terminology
• 6.2 Types
• 6.3 Uses
• 6.4 General properties
• 6.5 Forming processes
• 6.6 Modes of failure (durability)
• 6.7 Typical applications

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Plastics are divided into two types

• Thermoplastics always soften when heated.
• Thermosetting plastics which set, i.e. polymerise
  when mixed with a "hardener" and will not soften
  when heated. Setting is accelerated by catalysts,
  heat, pressure and even ? radiation.

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Typical Thermoplastics and Thermosets
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 PART 6 POLYMERS

• 6.1 Terminology
• 6.2 Types
• 6.3 Uses
• 6.4 General properties
• 6.5 Forming processes
• 6.6 Modes of failure (durability)
• 6.7 Typical applications

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Plastics are used in different categories of
application

• As formed products (e.g. parts of electrical
  fittings). This is the only application for
  thermoplastics.
• As textiles, e.g. Geotextiles.
• As adhesives (e.g. epoxies)
• As surface coatings (e.g. polyurethane paint)
• As a matrix for reinforced products (e.g. Glass
  Reinforced Polyester - GRP or fibreglass)

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Plastic windows and fascias
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 PART 6 POLYMERS

• 6.1 Terminology
• 6.2 Types
• 6.3 Uses
• 6.4 General properties
• 6.5 Forming processes
• 6.6 Modes of failure (durability)
• 6.7 Typical applications

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Properties of Plastics (1)

• Strength high for short term
• Modulus low
• Creep high
• Behaviour in Fire

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Behaviour in fire poor because of

• Creep and loss of strength at high temperatures.
• High combustibility (fire retardant additives may
  help - these give off small quantities of gases
  such as chlorine which locally displace the
  oxygen)
• Toxic fumes from combustion.
• Hazards from burning liquid (e.g. droplets from
  burning light fittings)

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Properties of Plastics (2)

• Density Similar to wood
• Thermal Conductivity Similar to wood
• Electrical Conductivity Insulator
• Thermal Movement High
• Moisture Movement Low
• Permeability Surprisingly High
• Cost Material cost high but manufacture low

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 PART 6 POLYMERS

• 6.1 Terminology
• 6.2 Types
• 6.3 Uses
• 6.4 General properties
• 6.5 Forming processes
• 6.6 Modes of failure (durability)
• 6.7 Typical applications

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Forming Processes
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 PART 6 POLYMERS

• 6.1 Terminology
• 6.2 Types
• 6.3 Uses
• 6.4 General properties
• 6.5 Forming processes
• 6.6 Modes of failure (durability)
• 6.7 Typical applications

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Modes of failure (durability) (1)

• Biological Being organic many plastics are
  nutritious to some forms of animal/insect/fungus
  etc. Biocides may be added during manufacture.
• Oxidation Oxidation causes embrittlement and
  loss of strength. It is generally slow in the
  absence of heat or sunlight. Anti-oxidants may be
  used.
• Sunlight Most plastics are damaged by long term
  exposure to ultraviolet light. The process is
  known as degradation or photo-embrittlement. It
  may be reduced by adding a uv absorber, e.g.
  carbon black or silica fume.

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Modes of failure (durability) (2)

• Water In permeable plastics there may be loss of
  some components through leaching. Osmotic
  pressure from moisture ingress may also cause
  surface spalling.
• Leaching There has been a specific problem with
  pvc leaching plasticiser when in contact with
  insulating materials such as expanded
  polystyrene. Electrical wiring in loft spaces has
  been found to have premature embrittlement of the
  pvc insulation.

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 PART 6 POLYMERS

• 6.1 Terminology
• 6.2 Types
• 6.3 Uses
• 6.4 General properties
• 6.5 Forming processes
• 6.6 Modes of failure (durability)
• 6.7 Typical applications

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Typical Applications

• Polymers in Concrete
• Geotextiles
• Plastic Pipes
• Thermosetting Resins
• Transparent Plastics

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Polymers in concrete (1)

• Polymer Concrete is a mixture of resin (polyester
  or epoxy, see below) and aggregate (normally
  sand). It is used in thin sections for repairs.
• PIC Polymer Impregnated Concrete is rare and is
  made by vacuum impregnating a monomer into
  hardened concrete which is polymerised inside
  concrete with heat or ? radiation. Only used in
  factory produced precast units.

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Polymers in concrete (2)

• PMC Polymer Modified Concrete (Polymer Portland
  Cement Concrete). Catalysed polymer is added into
  ordinary concrete at the mixer and polymerises
  insitu. Used for concrete repairs with
  thicknesses of 50-100mm, overlays for bridge
  decks etc.
• Silanes and silicones. Used as coatings for
  hardened concrete.
• Polymer reinforcement (e.g. polypropylene fibres)
• Epoxy coated rebar

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Typical Applications

• Polymers in Concrete
• Geotextiles
• Plastic Pipes
• Thermosetting Resins
• Transparent Plastics

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Geotextiles

• These have 3 main functions
•  As filters (e.g. to keep fine materials out of
  gravel drains)
• As reinforcing nets (e.g. under roads)
• As ties (e.g. in reinforced earth)
• Non-woven materials are used as filters and for
  light structural applications. Woven materials
  are more expensive and are used for main
  structural applications.
• The performance of the materials is adversely
  affected by the low elastic modulus and low
  durability if exposed to sunlight.

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Drain Filter Layer
Topsoil
Geotextile filter
Granular
Subsoil
Permeable pipe for storm drainage
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Geotextiles

• These have 3 main functions
•  As filters (e.g. to keep fine materials out of
  gravel drains)
• As reinforcing nets (e.g. under roads)
• As ties (e.g. in reinforced earth)
• Non-woven materials are used as filters and for
  light structural applications. Woven materials
  are more expensive and are used for main
  structural applications.
• The performance of the materials is adversely
  affected by the low elastic modulus and low
  durability if exposed to sunlight.

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Reinforced Earth
Geotextile Ties
Precast slabs
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Geotextiles

• These have 3 main functions
•  As filters (e.g. to keep fine materials out of
  gravel drains)
• As reinforcing nets (e.g. under roads)
• As ties (e.g. in reinforced earth)
• Non-woven materials are used as filters and for
  light structural applications. Woven materials
  are more expensive and are used for main
  structural applications.
• The performance of the materials is adversely
  affected by the low elastic modulus and low
  durability if exposed to sunlight.

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Typical Applications

• Polymers in Concrete
• Geotextiles
• Plastic Pipes
• Thermosetting Resins
• Transparent Plastics

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Plastic pipes.

• These are rapidly replacing conventional
  materials. They are almost universal for above
  ground waste and are increasingly used for below
  ground and supply applications. They are often
  resistant to chemicals and good at accommodating
  movement during service.
• High density polythene is often used for this.
• Note that the water services have very strict
  controls on the types of polymer which may be
  used for potable water supply because the
  polymerisation is not normally complete and
  residual monomers can be leached out and these
  may be toxic.

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Typical Applications

• Polymers in Concrete
• Geotextiles
• Plastic Pipes
• Thermosetting Resins
• Transparent Plastics

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Thermosetting resins.

• These are mixed on sites, e.g. for setting in
  holding down bolts into existing slabs.
• Epoxies. Two components must be mixed in exact
  proportions ("hooks and eyes"). Will cure down to
  5oC.
• Polyesters. Sets with a catalyst. More catalyst
  gives faster setting. Can be recognised by the
  characteristic "fibreglass" smell.

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Application of Polyester Resin
Base Plate
Threaded bar
Resin in drilled hole
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For all Thermosetting resins.

• The components are toxic - always wear gloves.
  The organic catalysts used with polyesters are
  particularly carcinogenic. The dust arising from
  cutting/abrading the hardened resin is
  carcinogenic. The odourless vapour which evolves
  during curing of epoxy is toxic.
• For low permeability the resins must be cured
  correctly in VERY DRY conditions. A white "bloom"
  on the surface indicates moisture during curing.
• The setting reactions are exothermic (especially
  polyesters). If use is delayed after mixing the
  set may be delayed by placing the material in a
  shallow metal container.

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Typical Applications

• Polymers in Concrete
• Geotextiles
• Plastic Pipes
• Thermosetting Resins
• Transparent Plastics

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Transparent plastics

• These are used in windows etc. in place of
  glass
• Acrylics (e.g. Perspex) are cheap but have poor
  impact resistance.
• Polycarbonates are more expensive but have good
  impact resistance (may be used for bullet proof
  laminates).
• Both have high thermal expansion.

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Polythene (polyethylene)

• Polythene is used for many applications and is
  available in HD (high density) form which is less
  permeable.
• Black polythene lasts longer because it is
  resistant to UV light.
• 1000 gauge polythene is 0.01", i.e. 0.254mm thick.