Tensile Strength Comparison of Common Plastics

Tensile strength, measured in MPa, is a critical mechanical property that determines a plastic's ability to resist breaking under tension. It is a primary factor in material selection for load-bearing applications. This document provides a concise comparison of tensile strength data for common plastics based on ISO 527 standards, analyzes key influencing factors, and offers practical selection guidance for manufacturing.

1. Tensile Strength Comparison

1.1 Commodity Plastics

LDPE (Low-Density Polyethylene): Tensile strength ranges from 7-15 MPa. It features excellent toughness but low rigidity due to its branched molecular structure, making it ideal for films, bags, and flexible tubing.

HDPE (High-Density Polyethylene): Tensile strength ranges from 20-30 MPa. With a more linear molecular structure, it offers better rigidity and chemical resistance than LDPE, suitable for crates, pipes, and blow-molded containers.

PP (Polypropylene): Tensile strength ranges from 25-40 MPa. It is known for its heat resistance and chemical stability. Glass fiber reinforced (GFR) PP can reach 50-70 MPa, suitable for automotive interiors and structural parts.

PVC (Polyvinyl Chloride): Rigid PVC (unplasticized) has a tensile strength of 40-55 MPa, used for pipes and profiles. Flexible PVC contains plasticizers, reducing strength to 10-20 MPa, suitable for wire insulation and seals.

PS (Polystyrene) & HIPS: General PS has a tensile strength of 40-60 MPa but is brittle. HIPS (High Impact Polystyrene) sacrifices some strength (25-40 MPa) for improved toughness, used in appliance housings.

1.2 Engineering Plastics

ABS (Acrylonitrile Butadiene Styrene): Tensile strength ranges from 40-55 MPa. It offers a balanced combination of rigidity, toughness, and processability, widely used in electronics and automotive bumpers.

PC (Polycarbonate): Tensile strength ranges from 60-75 MPa. It exhibits exceptional impact resistance and dimensional stability, suitable for optical lenses, safety glazing, and medical devices.

PA (Polyamide / Nylon): PA6 has a tensile strength of 60-70 MPa, while PA66 ranges from 70-85 MPa. Both have good fatigue resistance. GFR grades can exceed 100-150 MPa, ideal for gears and engine components.

POM (Polyoxymethylene): Tensile strength ranges from 60-80 MPa. It has excellent creep resistance and low friction, making it suitable for precision gears, bearings, and sliding parts.

PMMA (Acrylic): Tensile strength ranges from 50-70 MPa. It offers high optical clarity (92%) but is relatively brittle compared to PC.

2. Key Influencing Factors

2.1 Material Modification

Adding glass or carbon fibers creates a reinforcing "skeleton," significantly increasing tensile strength (e.g., +8-12 MPa per 10% glass in PP). Conversely, adding plasticizers or elastomers improves toughness but reduces strength.

2.2 Molding Process

In injection molding, proper melt temperature and high injection pressure promote molecular orientation, enhancing strength. Insufficient pressure or low temperature can cause voids or sinks, reducing strength by 10-20%.

2.3 Environmental Conditions

Elevated temperatures reduce tensile strength (e.g., PA6 may lose 25-30% strength at 80°C). Moisture acts as a plasticizer for hygroscopic materials like PA and PBT, slightly reducing their strength.

3. Selection Recommendations

Non-load-bearing parts: LDPE, Flexible PVC, EPS (focus on flexibility/weight).

Medium load parts: HDPE, PP, HIPS (balance cost and strength).

High load/ precision parts: PA6/66, POM, PC (consider temperature and friction requirements).

Critical structural parts: Glass-filled PA66 or PC (maximum strength and rigidity).