chemistry and physics of casting materials - aado · cotton : crinoline and leno cloth. synthetic...
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Chemistry and Physics of Casting Materials
Dr Stephen Hsu
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Gypsum
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Plaster of Paris ( 1800 – 1850 )
CaSO4.1/2 H20
CaSO4.2H2O
+
Heat
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Plaster BandagesCotton : crinoline and leno cloth
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Synthetic Resin – 1970’s
Polyurethane Cellulose acetateAluminosilicate glassThermoplastic linear polymer
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Activation of Resin
Material Activator
Polyurethane Water
Cellulose acetate Acetone solvent
Aluminosilicate glass Water
Thermoplastic polymer Hot Water
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Polyurethane Resin
The prepolymer urethane resinStablilizerAnti-foaming agentSurfactant
C6H5.NCO
N C O
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Resin Bandages
Fabric Material
Glass Fibre Fibre Glass
Nonglass Fibrea. Cottonb. Polyesterc. Polypropylene
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Physical Properties Strength of POP and Synthetic Cast
• Factors Affecting strength of POP
• The Effect of Gauze on the Strength of POP
Vapour Permeability Stickiness Adhesiveness Conformability Friction Weight
Breaking of Below-Knee cast
Wear
Consistency of Materials Setting Properties Deformation to Failure Water Immersion
Activation Recommendations
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Strength of POP and Synthetic Cast
The strength of these materials is anisotropic
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Factors Affecting Strength of POP
Water ContentSetting TimeTemperature of Soaking Water
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Factors Affecting Strength of POP
Water ContentSetting TimeTemperature of Soaking Water
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The Effect of Gauze on the Strength of POP
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Breaking of Below-Knee Cast
To reduce the chance of breakingAdequate setting timeThicker POP at ankle and thinner at
calf or solePosition of walking heelDesign of walking heel
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Consistency of Materials
POP is found to have a greater variability in strength than synthetic materials
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Deformation to Failure
The deformation to failure of synthetic materials is usually gradual while that of plaster of Paris is usually sudden
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Water Immersion
POP casts deformed permanently after water immersion
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Vapour PermeabilityMoisture Vapour
Permeability(mg/hr/m2)
POP 62.9
Glass fibre / resin 2 68.32
Glass fibre / resin 1 79.63
Polyester / resin 86.1
Cotton / resin 112.30
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Stickiness
A. DeltacastB. DeltaliteC. Deltalite SD. Dynacast
XRE. Scotchcast
PlusF. ScotchflexG. Zimflex
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AdhesivenessA. DeltacastB. DeltaliteC. Deltalite SD. Dynacast
XRE. Scotchcast
PlusF. ScotchflexG. ZimflexH. Gypsona
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Conformability
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Friction
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Weight
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Wear
A. DeltacastB. DeltaliteC. Deltalite SD. Dynacast
XRE. Scotchcast
PlusF. ScotchflexG. ZimflexH. Gypsona
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Setting Time
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Setting Properties
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Activation RecommendationsDelta-Cast Immerse in cold water
Deltalite Immerse in water atbetween 21°C and 27°C
Dynacast XR Dip of 2-5s in warm water
Plaster-of-Paris Dip for 10s in water of 20-25°C
Scotchast Plus Dip in water at 21-24°C
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Advantages of Non-fibre glasscasting materials over Fibre-glass
LighterMore X-ray lucentLess sharp edgesNo carcinogenic dust
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Price differential per cast
Non-fibre glass Fibre-glass POP
3.5 2.5 1
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HAPPY LEARNING