Rubber Materials
Natural Rubber (NR) Technical Guide: Properties, Specifications and Industrial Applications
Comprehensive technical guide to Natural Rubber (NR): molecular structure, physical properties (tensile 14-30 MPa, elongation 150-850%), temperature range (-50 to +85°C), strain-induced crystallization, compounding, and applications in tires, anti-vibration mounts, marine fenders, and conveyor belts.
Article Info
- Category
- Rubber Materials
- Tags
- NRNatural RubberPolyisopreneStrain CrystallizationDynamic FatigueRubber Compounding
- Keywords
- natural rubber / NR rubber / polyisoprene / rubber properties / tensile strength / Nanjing Yuhang Rubber
Expertise Signal
- Technical review
- YuHang Rubber Technical Team
- Review Role
- Industrial Rubber Product Technical Review
- Known For
- Rubber FenderRubber TrackRubber SheetRubber HoseRubber ExtrusionCustom Rubber Parts
Industrial rubber product manufacturer covering rubber fenders, rubber tracks, rubber sheets, rubber hoses, extrusions, belts and custom molded rubber parts.
Natural Rubber (NR) Technical Guide: From Rubber Tree to Industrial Products
Published: 2025-08-12 | Reading time: 10 minutes
Executive Summary
Natural Rubber (NR), chemically cis-1,4-polyisoprene, is the only major non-synthetic elastomer in commercial use, accounting for approximately 40% of global rubber consumption. Harvested as latex from the Hevea brasiliensis tree, NR possesses a unique combination of properties unavailable in any single synthetic rubber.
The defining characteristic of NR is strain-induced crystallization (SIC) — under dynamic stress and large deformation, polymer chains align and form micro-crystalline domains that act as self-reinforcing structures. This phenomenon makes NR irreplaceable in applications such as rubber tracks, bridge bearings, and marine fenders where dynamic loading conditions prevail.
Molecular Structure & Property Relationships
NR's high cis-1,4 content (>99%) governs its critical properties:
- • Strain crystallization — molecular chain alignment under stress creates reinforcing micro-crystallites
- • Low glass transition temperature (Tg = −70°C) — excellent low-temperature flexibility
- • High elasticity & low hysteresis — rebound resilience 30–65%, relatively low heat build-up
- • Non-polar backbone — resistant to water, alcohols, and polar solvents; swells in non-polar oils
Key Physical Properties
| Property | Typical Range | Test Standard |
|---|---|---|
| Hardness (Shore A) | 25–95 (commonly 40–70) | ASTM D2240 / ISO 7619-1 |
| Tensile Strength | 14–30 MPa (reinforced ≥27.6 MPa) | ASTM D412 / ISO 37 |
| Elongation at Break | 150–850% (commonly 500–600%) | ASTM D412 / ISO 37 |
| Tear Resistance | ≥25 N/mm (high-grade up to 80 N/mm) | ISO 34-1 |
| Abrasion Loss | ≤80 mm³ (ISO 4649) | ISO 4649 |
| Compression Set | 20–40% (70°C × 22h) | ASTM D395 / ISO 815-1 |
| Density | ~0.93 g/cm³ (pure) / 1.0–1.2 g/cm³ (filled) | ISO 1183 |
Properties by Hardness Grade
| Hardness (Shore A) | Tensile (MPa) | Elongation (%) | Typical Application |
|---|---|---|---|
| 50 | 10–14 | ~600 | Soft seals, cushion pads |
| 60 | 17–20 | 500–515 | General industrial rubber parts |
| 70 | 20–25 | 300–400 | Marine fenders, vibration mounts |
| 80 | 25–30 | 200–300 | High-load wear components |
Temperature Limits
| Parameter | Value |
|---|---|
| Minimum service temperature (static) | −50°C to −55°C |
| Minimum temperature for sealing | −40°C |
| Maximum continuous service | 70–85°C |
| Maximum intermittent/peak | 100°C |
| Glass transition temperature (Tg) | −70°C |
Critical limitation: Above 85–100°C, NR degrades rapidly — heat aging causes hardening, elongation loss, and tensile reduction.
Chemical Compatibility
| Media Class | Rating | Notes |
|---|---|---|
| Water, alcohols, polar solvents | ★★★★★ Excellent | Non-polar backbone inert to polar media |
| Dilute acids & bases | ★★★★ Good–Excellent | — |
| Concentrated acids & bases | ★★★ Fair–Good | — |
| Ketones, aldehydes | ★★★ Fair | — |
| Ozone, UV, weathering | ★ Poor | Requires antiozonant protection |
| Mineral oils, fuels, greases | ★ Poor | Severe swelling and dissolution |
| Aromatic & chlorinated hydrocarbons | ★ Poor | — |
Typical Compounding (phr)
- • Cure system: Sulfur (2–3) + accelerator CBS/TBBS (0.5–1) + ZnO (3–5) + stearic acid (1–2)
- • Reinforcement: Carbon black N330/N550/N774 (30–80) or silica
- • Antidegradant system: 6PPD (antiozonant/fatigue) + TMQ (antioxidant) + microcrystalline wax (surface bloom protection)
- • Processing aid: Aromatic/naphthenic oil (5–15)
NR vs. Synthetic Rubbers
| Property | NR | SBR | CR |
|---|---|---|---|
| Tensile Strength | ★★★★★ | ★★★ | ★★★ |
| Tear Resistance | ★★★★★ | ★★★ | ★★★ |
| Dynamic Fatigue Life | ★★★★★ | ★★★ | ★★★ |
| Resilience | ★★★★ | ★★★ | ★★★ |
| Ozone Resistance | ★ | ★ | ★★★★ |
| Oil Resistance | ★ | ★ | ★★★ |
Key Industrial Applications
| Application | Critical NR Property | Typical Products |
|---|---|---|
| Dynamic load-bearing | High elasticity, low hysteresis, SIC | Rubber tracks, bridge bearings, anti-vibration mounts |
| Impact protection | High energy absorption, tear resistance | Marine fenders, dock buffers |
| Abrasion service | High abrasion & tear resistance | Conveyor belt covers, chute liners |
| Tire industry | Low heat build-up, cut resistance | Truck tire treads, OTR tires |
FAQ
Q: Why does NR outperform most synthetic rubbers in dynamic applications?
NR's strain-induced crystallization (SIC) is the key differentiator. Under high dynamic stress, the oriented polymer chains form micro-crystalline domains that act as an "in-situ reinforcement" mechanism. Most synthetic rubbers (except CR) lack this capability and fail earlier under equivalent dynamic loading conditions.
Q: Can synthetic polyisoprene (IR) replace NR?
IR has the same chemical structure as NR but slightly lower cis-1,4 content (~98% vs. NR >99%) and narrower molecular weight distribution. This results in weaker SIC behavior and lower tensile/tear strength. IR can substitute NR in non-critical applications (footwear, general molded goods), but NR remains essential for high-stress dynamic applications such as tires, bridge bearings, and marine fenders.
Inquiry & Technical Support
Nanjing Yuhang Rubber Co., Ltd. has over 30 years of experience in NR compounding and processing, with products covering rubber tracks, marine fenders, anti-vibration mounts, conveyor belts, and industrial rubber sheets. For technical consultation and samples:
FAQ
Can this article be used as the final selection basis?
It is intended for preliminary technical review. Final material or product selection should be confirmed with the actual medium, temperature, load, dimensions, drawings and sample testing when needed.
What information should be provided for an inquiry?
Please provide the application equipment, working medium, temperature range, dimensions, quantity, drawing or sample information so the technical discussion can be organized faster.