Neoprene CR properties
Chemical composition
Section titled “Chemical composition”Neoprene (CR, polychloroprene) is synthesized by free-radical emulsion polymerization of the monomer chloroprene (2‑chloro‑1,3‑butadiene). The main chain consists of repeating units –[CH₂–CCl=CH–CH₂]– with a chlorine content of approximately 40 % by weight, which confers flame and weather resistance.
| Component | Proportion (% by weight) |
|---|---|
| Chloroprene | > 95 |
| Comonomers (e.g., sulfur, acids) | < 5 |
Industrial crosslinking is carried out with zinc oxide and thioureas (accelerators) at temperatures between 150 °C and 200 °C, forming crosslinks that fix the elastic structure.
Mechanical properties
Section titled “Mechanical properties”The Shore A hardness of neoprene used for wetsuits is between 30 and 50. Commercial general-purpose vulcanized formulations exhibit a hardness range of 30 to 90 Shore A depending on the reinforcing filler.
| Property | Typical value (SI) | Typical value (Imperial) | Condition |
|---|---|---|---|
| Hardness | 30 – 90 Shore A | — | Vulcanized |
| Tensile strength | 10 – 25 MPa | 1450 – 3630 psi | Vulcanized |
| Elongation at break | 300 – 700 % | — | Vulcanized |
| Modulus at 300 % | 2 – 10 MPa | 290 – 1450 psi | Vulcanized |
| Tear strength | 20 – 60 N/mm | 114 – 342 pli | Vulcanized |
The upper values correspond to grades reinforced with carbon black; the lower values to unfilled compounds. Expanded neoprene (closed-cell foam) exhibits tensile strength between 0.5 MPa and 2 MPa (73‑290 psi).
Physical properties
Section titled “Physical properties”The density of solid neoprene is 1.23 g/cm³ (77 lb/ft³). Closed-cell foam, used in wetsuits, has a density between 0.1 g/cm³ and 0.3 g/cm³ (6‑19 lb/ft³).
| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Density (solid) | 1.23 g/cm³ | 77 lb/ft³ |
| Density (foam) | 0.1 – 0.3 g/cm³ | 6 – 19 lb/ft³ |
| Water absorption (24 h, 23 °C) | < 1 % | — |
| Air permeability | Low | — |
| Natural color | Light amber to whitish | — |
Thermal properties
Section titled “Thermal properties”The continuous service temperature of neoprene ranges from –40 °C to 115 °C (–40 °F to 239 °F). The glass transition (Tg) occurs around –43 °C (–45 °F).
| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Brittleness temperature | –40 °C | –40 °F |
| Maximum continuous use temperature | 115 °C | 239 °F |
| Glass transition temperature (Tg) | ≈ –43 °C | ≈ –45 °F |
| Thermal conductivity | 0.19 W/(m·K) | 1.32 BTU·in/(h·ft²·°F) |
| Flame behavior | Self-extinguishing (oxygen index ≈ 30 %) | — |
At temperatures above 120 °C (250 °F), neoprene loses elasticity due to progressive chlorine degradation, and below –40 °C it partially crystallizes, increasing its rigidity.
Chemical and environmental resistance
Section titled “Chemical and environmental resistance”Neoprene resists ozone, weathering, moderate mineral oils, brake fluids, seawater, and dilute acids. It is not suitable for prolonged contact with aromatic hydrocarbons, esters, ketones, or concentrated nitric and chromic acids.
| Agent | Behavior | Observations |
|---|---|---|
| Ozone / weathering | Excellent | Minimal cracking after prolonged exposure |
| Oxygen (hot air, ≤100 °C) | Good | Retains > 50 % elongation |
| Mineral oils (ASTM 1) | Good | Swelling < 15 % |
| Aromatic oils (ASTM 3) | Moderate to poor | Swelling > 50 % |
| Dilute acids (HCl, H₂SO₄) | Good | Low property loss |
| Seawater | Excellent | Ideal for prolonged immersion |
Chemical resistance is influenced by the degree of crosslinking and the presence of fillers. Neoprene foams exhibit reduced permeability but lower solvent resistance due to their porous structure.
Applications by industry
Section titled “Applications by industry”Neoprene is used in sectors requiring moderate oil resistance, weather resistance, and low-temperature flexibility.
| Industry | Applications |
|---|---|
| Sports and diving | Wetsuits, booties, gloves |
| Automotive | Timing belts, hoses, bushings, sealing gaskets |
| Construction | Sealing profiles, elastomeric membranes, expansion joints |
| Electronics | Laptop sleeves, cable insulation, flexible connectors |
| Medicine and orthopedics | Surgical gloves, knee braces, orthopedic splints, soft prosthetics |
| General industrial | O‑rings, diaphragms, anti-corrosion coatings, roller coverings |
Comparison with other elastomers
Section titled “Comparison with other elastomers”| Elastomer | Oil resistance | Ozone resistance | Temperature range | Relative cost |
|---|---|---|---|---|
| Neoprene (CR) | Good | Excellent | –40 to 115 °C | Medium |
| Natural rubber (NR) | Poor | Poor | –55 to 85 °C | Low |
| SBR (styrene‑butadiene) | Poor | Fair | –50 to 82 °C | Low |
| Nitrile (NBR) | Excellent | Poor | –55 to 82 °C | Low‑medium |
| EPDM | Poor | Excellent | –50 to 150 °C | Medium |
Neoprene represents a balance between oil and weather resistance, being preferable to natural rubber or SBR when ozone stability and some hydrocarbon resistance are required, and less expensive than fluorocarbons.
Advantages and disadvantages
Section titled “Advantages and disadvantages”Advantages
- Excellent ozone and weather resistance.
- Flame resistance (self-extinguishing).
- Good low-temperature flexibility.
- Moderate resistance to mineral oils and seawater.
- Wide hardness range and foaming capability.
Disadvantages
- Swelling in contact with aromatic oils and polar solvents.
- Higher cost than natural rubber and SBR.
- Crystallization below –40 °C without suitable plasticizers.
- Accelerated thermal aging above 115 °C.
Processing and transformation
Section titled “Processing and transformation”Neoprene is supplied in the form of solid sheets, tapes, latex, or granules. Forming methods include compression molding, extrusion, calendering, and injection molding. Neoprene foam is obtained using chemical foaming agents during vulcanization in an autoclave or press. Conventional crosslinking uses zinc oxide (ZnO) combined with thioureas as accelerators; peroxide systems are also used to improve aging resistance. Vulcanization temperatures are in the range of 150 °C to 200 °C and cycles last between 5 and 60 minutes depending on thickness and formulation. The vulcanized part can undergo post-cure to stabilize dimensions and remove volatile by-products.
Summary table of properties
Section titled “Summary table of properties”| Property | Value | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Density (solid) | 1.23 | g/cm³ | 77 lb/ft³ |
| Hardness | 30 – 90 | Shore A | — |
| Tensile strength | 10 – 25 | MPa | 1450 – 3630 psi |
| Elongation | 300 – 700 | % | — |
| Modulus at 300 % | 2 – 10 | MPa | 290 – 1450 psi |
| Service temperature | –40 to +115 | °C | –40 to +239 °F |
| Glass transition (Tg) | ≈ –43 | °C | ≈ –45 °F |
| Thermal conductivity | 0.19 | W/(m·K) | 1.32 BTU·in/(h·ft²·°F) |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum continuous use temperature of neoprene?
Section titled “What is the maximum continuous use temperature of neoprene?”The maximum continuous use temperature is 115 °C (239 °F). Above this value, chlorine degradation reduces the service life of the elastomer.
What Shore A hardness does a typical neoprene for gaskets have?
Section titled “What Shore A hardness does a typical neoprene for gaskets have?”Neoprene gaskets typically have a hardness between 50 and 70 Shore A. For applications requiring greater flexibility, grades from 30 to 50 Shore A are used.
Is neoprene resistant to motor oil?
Section titled “Is neoprene resistant to motor oil?”Neoprene resists paraffinic mineral oils with swelling below 15 %, but oils containing aromatic additives can cause swelling above 50 %.
How does low temperature affect neoprene?
Section titled “How does low temperature affect neoprene?”Below –40 °C (–40 °F) neoprene significantly loses flexibility due to partial crystallization of the polymer matrix. With suitable plasticizers it can remain flexible down to –50 °C.
What is the minimum thickness of a neoprene foam sheet?
Section titled “What is the minimum thickness of a neoprene foam sheet?”Neoprene foam sheets are commercially available from 1 mm (0.039 in) thickness. For wetsuits, thicknesses between 3 mm and 7 mm are used.
How much water does solid neoprene absorb?
Section titled “How much water does solid neoprene absorb?”Water absorption at 24 h and 23 °C is less than 1 % by volume. This low absorption makes it suitable for seals in contact with seawater.
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?ArticleID=317
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/elastomers-rubbers-d_1788.html
- steelnumber.com: https://www.steelnumber.com/index.php