Injection Molding Materials & Their Properties (South African Guide)

Choosing the correct plastic material determines part strength, surface finish, cycle time, and long-term durability. This guide explains the most common polymers used in South African molding factories, along with melt temperatures, drying requirements, mechanical properties, and recommended applications.

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Polypropylene (PP)

Properties

• Semi-crystalline
• Excellent flowability
• Low density (lightweight)
• Chemical and fatigue resistant
• Good for living hinges

Typical Values

Parameter	Value
Melt Temperature	200–250°C
Mold Temperature	20–50°C
Shrinkage	1.0–2.5%
Tensile Strength	30–40 MPa
Drying	Not required

Best Uses

• Caps
• Containers
• Automotive trims
• Food packaging
• Hinged lids

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Acrylonitrile Butadiene Styrene (ABS)

Properties

• Strong and rigid
• Good surface finish
• Easily painted and glued
• Moderate chemical resistance

Typical Values

Parameter	Value
Melt Temperature	210–250°C
Mold Temperature	40–80°C
Shrinkage	0.4–0.9%
Tensile Strength	40–50 MPa
Drying	2–4 hours @ 80°C

Best Uses

• Electronics housings
• Toys (e.g., LEGO)
• Automotive interior parts

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Nylon (PA6 / PA66)

Properties

• Very strong
• Abrasion resistant
• High temperature resistance
• Hygroscopic—absorbs moisture

Typical Values

Parameter	Value
Melt Temperature	240–290°C
Mold Temperature	60–90°C
Shrinkage	1.0–2.0%
Tensile Strength	70–90 MPa
Drying	Required (2–4 hours @ 90°C)

Best Uses

• Gears
• Bearings
• Industrial mechanical parts

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High-Density Polyethylene (HDPE)

Properties

• Excellent chemical resistance
• High impact strength
• Low density
• Flexible

Typical Values

Parameter	Value
Melt Temperature	180–230°C
Mold Temperature	20–60°C
Shrinkage	1.5–4.0%
Tensile Strength	20–35 MPa
Drying	Not required

Best Uses

• Bottles
• Caps
• Chemical containers
• Automotive fuel tanks

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Polycarbonate (PC)

Properties

• Extremely tough
• Transparent
• High heat resistance
• Dimensionally stable

Typical Values

Parameter	Value
Melt Temperature	260–320°C
Mold Temperature	80–120°C
Shrinkage	0.5–0.7%
Tensile Strength	55–75 MPa
Drying	3–4 hours @ 120°C

Best Uses

• Safety shields
• Automotive lights
• Lenses

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Acetal (POM / Delrin)

Properties

• Low friction
• Excellent wear resistance
• Strong and stiff
• Dimensionally accurate

Typical Values

Parameter	Value
Melt Temperature	190–230°C
Mold Temperature	60–100°C
Shrinkage	1.8–2.2%
Tensile Strength	60–70 MPa
Drying	Optional (80°C for 1–2 hours)

Best Uses

• Gears
• Bushes
• Precision components

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Thermoplastic Elastomers (TPE / TPU)

Properties

• Rubber-like
• Flexible
• Good abrasion resistance
• Excellent impact absorption

Typical Values

Parameter	Value
Melt Temperature	170–220°C
Mold Temperature	20–40°C
Shrinkage	1.2–2.0%
Tensile Strength	5–50 MPa
Drying	2 hours @ 80°C

Best Uses

• Grips
• Seals
• Soft-touch components

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Material Comparison Table

Material	Tensile Strength (MPa)	Shrinkage %	Melt Temp °C	Drying Required
PP	30–40	1.0–2.5	200–250	No
ABS	40–50	0.4–0.9	210–250	Yes
PA6/66	70–90	1.0–2.0	240–290	Yes
HDPE	20–35	1.5–4.0	180–230	No
PC	55–75	0.5–0.7	260–320	Yes
POM	60–70	1.8–2.2	190–230	Optional
TPE	5–50	1.2–2.0	170–220	Yes

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FAQ: Injection Molding Materials

Which material has the least shrinkage?

Polycarbonate (PC) and ABS have extremely low shrinkage.

Which material is the strongest?

Nylon (PA66) and Polycarbonate (PC) offer the highest strength.

Which is most commonly used in South Africa?

PP, ABS, HDPE, and Nylon are the most widely available locally.