Information


IDENTIFYING PLASTIC MATERIALS
Floats or sinks
Polyolefins (Polyethylene and Polypropylene)
float in water/all other plastics sink
(If the density is below 1 materials float)
Burn tests
Colour of flame
Colour of smoke
Soot generation or not
Odour
Speed of Burn
Chemical analysis
Infrared Spectrometry/Gas Chromatography
Impact Tests

WEATHERING & THE EFFECT OF UV

Most materials are adversely affected by continued outdoor exposure
Materials reflect, absorb and transmit UV light in varying amounts
White/Opal/light colours reflect more UV/IR than black and colours which reflect and/or transmit little or     no light but absorb light and heat
Some materials transmit nearly all UV light and absorb very little (eg acrylic)
Other materials absorb nearly all UV light and transmit very little (eg polycarbonate)
Factors influencing UV degradation include amount of exposure, orientation, ink coverage, atmospheric     pollution, etc

THERMOPLASTICS & WEATHERING

ABS – Has high impact strength and can be used outdoors but needs to be especially stabilised for prolonged exposure.
PS – not recommended for outdoor use.
Acrylics – Extruded MI and cast acrylic don’t absorb UV and therefore weather exceptionally well.
Impact Modified acrylic – the UV light ultimately attacks the modifier and over time, the impact strength will reduce
PETg - UV stable grades are available but our standard material is not for outdoor use
Polycarbonate – Absorbs UV light and material loses surface gloss. Can be co-extruded with a UV layer which improves its performance
HDPE and PP - Correct grade or special additives necessary for outdoor usage

MATERIAL DENSITIES

Plastic materials have different densities/SG
(SG = specific gravity)

The density/SG for various grades of the same polymer will vary

Density/SG is required to calculate the sheet weight

How to calculate the sheet weight -
length x width x thickness x SG
Example - ABS 2500 x 1250 x 3mm
2,5 x 1,25 x 3 x 1,1 = 10,31kg

COSTING DENSITIES

ABS
   1.1
PS
   1.06
Acrylic
 MI 1.19
HM17 1.17
UHI 1.15
MI Prismatic 0.904
Polycarbonate
 Smooth 1.2
Prismatic 0.912
PETg
 Smooth 1.27
  Prismatic 0.965
Polypropylene
 Smooth 0.9
  Prismatic 0.840
Polyethylene
 High Density 0.963
  Low Density 0.920

THE EXTRUSION PROCESS

Sheet extrusion is a process to make flat plastic sheets from a variety of resins
Raw material (in pellet form) is fed into a hopper, and by means of a rotating screw within the barrel, melts and feeds the raw material to the die.
Die lips set for required thickness
Calendering rollers determine final thickness and finish
Edges are always trimmed
The process is volume driven and generates scrap when setting up, changing the material, thickness, width, length, colour, finish.
Sheets off the extruder are never exactly square – produced within specified tolerances in terms of width, length and squareness

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