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How Plastics are Made… Understanding the Physical Properties of Plastics. Prepared by the IAPD Education Committee (Module 1) Presented courtesy of Modern Plastics, Inc. Why use plastics. Plastic are easily formed materials. - PowerPoint PPT Presentation
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The International Association of Plastics DistributorsThe International Association of Plastics Distributors
The IAPD Plastics Primer, Module 1The IAPD Plastics Primer, Module 1
Prepared by the IAPD Education Committee (Module 1)
Presented courtesy of Modern Plastics, Inc.
How Plastics are Made…
Understanding the Physical Properties of Plastics
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Why use plastics• Plastic are easily formed materials.
• The advantage to the manufacturer is that plastic products can be mass-produced and require less skilled staff.
• Plastics require little or no finishing, painting, polishing etc. Plastic is referred to as a self-finishing material. Particular finishes can be achieved at relatively low cost.
• Plastics can be easily printed, decorated or painted.
• Plastics are corrosion resistant, and generally waterproof although certain types of plastics such as UPVC can become brittle and it is possible for the sun’s rays to cause the colour of the plastic to fade. It becomes bleached.
• Plastics are lighter than metals, giving deeper sections for a given weight, and hence stronger sections.
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Origins of Plastics - synthetic plastics.
• The main source of synthetic plastics is crude oil.
• These gases are broken down into monomers. Monomers are chemical substances consisting of a single molecule.
• A process called Polymerisation occurs when thousands of monomers are linked together. The compounds formed as called polymers.
• Combining the element carbon with one or more other elements such as oxygen, hydrogen, chlorine, fluorine and nitrogen makes most polymers.
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Thermoplastics• There are a wide range of
thermoplastics, some that are rigid and some that are extremely flexible.
• The molecules of thermoplastics are in lines or long chains with very few entanglements. When heat is applied the molecules move apart, which increases the distance between them, causing them to become untangled. This allows them to become soft when heated so that they can be bent into all sorts of shapes.
• When they are left to cool the chains of molecules cool, take their former position and the plastic becomes stiff and hard again. The process of heating, shaping, reheating and reforming can be repeated many times.
Long chain molecules
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
General properties: low melting point, softer, flexible.
Typical uses: bottles, food wrappers, toys, …
Examples:
Polyethylene: packaging, electrical insulation, milk and water bottles, packaging film
Polypropylene: carpet fibers, automotive bumpers, microwave containers, prosthetics
Polyvinyl chloride (PVC): electrical cables cover, credit cards, car instrument panels
Polystyrene: disposable spoons, forks, Styrofoam™
Acrylics (PMMA: polymethyl methacrylate): paints, fake fur, plexiglass
Polyamide (nylon): textiles and fabrics, gears, bushing and washers, bearings
PET (polyethylene terephthalate): bottles for acidic foods like juices, food trays
PTFE (polytetrafluoroethylene): non-stick coating, Gore-Tex™ (raincoats), dental floss
Plastic types: Thermoplastics
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
General properties: more durable, harder, tough, light.
Typical uses: automobile parts, construction materials.
Plastic types: Thermosets
Examples:
Unsaturated Polyesters: lacquers, varnishes, boat hulls, furniture
Epoxies and Resins: glues, coating of electrical circuits,composites: fiberglass in helicopter blades, boats, …
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Plastic types: Elastomers
General properties: these are thermosets, and have rubber-like properties.
Typical uses: medical masks, gloves, rubber-substitutes
Examples:
Polyurethanes: mattress, cushion, insulation, toys
Silicones: surgical gloves, oxygen masks in medical applicationsjoint seals
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Clear Acrylic (Perspex)
• It was first used to make aircraft canopies. It is ten times more impact resistant than glass.
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Polystyrene
• Polystyrene is used to make plates, cutlery and model kits.
• It is stiff hard and comes in a wide range of colours.
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Nylon • Nylon is hard, tough, self-
lubricating, has a high melting point and has very good resistance to wear and tear.
• It has been used to make fibres, clothing, bearings and propellers.
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
PVC • The rigid type is used to
make pipes, guttering and roofing. It is very lightweight and is resistant to acids, alkalis & the weather.
• The plasticised type is used for suitcases, hosepipes, electrical wiring and floor coverings.
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Polythene
• High-density polythene has been used to manufacture milk crates, bottles, buckets, bowl and gear wheels.
• It is stiff, hard, can be sterilised and is dense.
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
The Performance of a Plastic Part is Affected By:
• Type of load • Size and application of load • Frequency of application of load • Speed of load • Temperature the part will see, and for how long• Use and environment of load
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Mechanical Properties
• Tensile strength• Elongation• Compressive strength• Creep• Shear strength• Flexural strength
• Torsional strength• Modulus• Impact strength• Specific gravity• Water absorbtion• Coefficient of Friction (COF)
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Tensile Strength
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Elongation
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Compressive Strength• Measured in Kg/m2• Higher Kg/m2 = harder to compress
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Creep• Associated with compressive strength• Creep at room temperature is called “cold
flow”
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
The IAPD Plastics Primer, Module 1The IAPD Plastics Primer, Module 1
Shear Strength
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Flexural Strength
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
The IAPD Plastics Primer, Module 1The IAPD Plastics Primer, Module 1
Torsional Strength
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Modulus
• Also referred to as “stiffness”
• Used in conjunction with strengths (flexural modulus, tensile modulus, etc.)
• Higher modulus = stiffer material
• Measured in N/m2 (Kg/m2)
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Impact Strength
Izod Impact
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
The IAPD Plastics Primer, Module 1The IAPD Plastics Primer, Module 1
Specific Gravity
• Related to the density of material• Can be used to determine the weight of material• Specific gravity of less than 1.0 will float in water
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Water Absorption
• Measured by the percentage of swell
• Think of a sponge as having high percentage absorption
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Chemical Resistance
• Typically expressed in terms of alkali or acid resistance
• Inertness; or the ability not to dissolve or react to chemicals
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Coefficient of Friction (COF)
• Resistance to sliding (slickness)
• Low COF = more slippery (think of “wet ice” as having lowest COF)
• Static COF refers to initial movement from rest
• Dynamic COF refers to being already in motion
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Thermal Properties
• Coefficient of thermal expansion
• Heat deflection temperature
• Continuous service temperature
• Melting point
• Thermal conductivity
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Coefficient of Thermal Expansion (CTE)
• Change in size as temperature changes
• Lower value = less change with temperature
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Continuous Service Temperature (CST)
• Highest temperature a material can withstand and
still retain at least 50% of its properties
• Measured in degrees Fahrenheit, in air
• In high temperatures, both CST and HDT must be
considered
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Melting Point
Temperature at which a crystalline thermoplastic
changes from solid to liquid
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Thermal Conductivity
• How much heat a material will conduct
• Most plastics are good “insulators” (do not conduct
heat well)
• Higher value = more heat conducted
• Thermal conductivity of plastics is 300 to 2,500 times
less than most metals
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Mouldability
• The ability of a plastic to flow into a complex mould
• Determined by its liquid viscocity, &
• Rate of cooling
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Electrical Properties
• Volume resistivity
• Surface resistivity
• Dielectric constant
• Dielectric strength
• Dissipation factor
• Arc resistance
• Flammability
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
• Most favorable ratings are given to materials that extinguish themselves rapidly, and do not drip flaming particles
• Scale from highest burn rate => most flame retardant is HB, V-2, V-1, V-0, 5V
Flammability
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
• Ranging from PP & PE @ ~ £0.90/kg
• & Nylon @ £3 - £4/kg
• to PTFE @ £10/kg …
Cost…
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Processing• Injection molding• Extrusion
– Ram extrusion– Screw extrusion– Coextrusion
• Casting• Compression molding• Rotational molding• Transfer molding• Calendering
• Hand (or spray) lay up• Laminating• Filament winding• Polymer orientation
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
The IAPD Plastics Primer, Module 1The IAPD Plastics Primer, Module 1
Injection Moulding
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
The IAPD Plastics Primer, Module 1The IAPD Plastics Primer, Module 1
Blow mouldingheated glass
3-piece mold
(a) The hollow piece of heated glass (parison)is first created by a blow mold(see text-book Fig 17.25)
(b) The mold is put together
(c) Plunger and hot air push theglass up
(d) Hot air blows the glass out towardsthe mold surface
(e) Mold comes apart, bottle is removed
heated glass
3-piece mold
(a) The hollow piece of heated glass (parison)is first created by a blow mold(see text-book Fig 17.25)
(b) The mold is put together
(c) Plunger and hot air push theglass up
(d) Hot air blows the glass out towardsthe mold surface
(e) Mold comes apart, bottle is removed
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Extrusion• Ram• Screw• Coextrusion
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Casting
Base Material Reactive Additive
Oven
Mold
Casting
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Compression Moulding
• Sheet and block moulding• Parts moulding
Mold Lid
Mold Resin
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Rotational Moulding• Low cost• Low pressure• Used in many markets• Easily adapted for short production runs
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Transfer Moulding
Widely used in the semiconductor industry…
Ideal for thermosets but slow…
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Calendering
for films & sheets…
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Hand (or Spray) Lay Up
• Used to make large parts• Used to produce fiberglass boats and camper
shells
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Laminating
Heat and pressure applied to the top and bottom of the material
Resin Binder
Reinforcing Substrate
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Filament Winding
• Used to make containers and tubes• Items used for transportation of liquids or
gasses
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Polymer Orientation
Used to manufacture polymer fibers, strapping, webbing, film, sheet and profiles
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Plastics Fabrication • CNC machining centers• CNC lathes• Cutting and drilling• Profiling• Routing and milling• Thermoforming• Forging • Milling• Welding• Bending• Bonding
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Thermoforming• Single station
thermoforming• Rotary station
thermoformers• Pressure forming• Twin sheet
thermoforming
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Welding• Extrusion welding• Hot gas welding• Butt welding• Spin welding• Solvent welding
The International Association of Plastics DistributorsThe International Association of Plastics Distributors
Bonding
The union of materials by adhesives; to unite materials by means of an adhesive