Synthetic Lattices: CR, NBR, and SBR
Chemistry literacy. Switching polymer changes oil, solvent, and ozone behavior, and it changes the cure package. Synthetics have no NR latex proteins. Type IV chemistry from accelerators can still apply. See Allergy and Skin Contact.
Executive summary
Industrial wearable films also use polychloroprene (CR), nitrile (NBR), and SBR latices when the target is oil, ozone, solvent, or modulus that NR does not meet. You pick the polymer before you pick accelerators. CR film needs at least 5 phr zinc oxide and 2 phr antioxidant, fully dispersed. Carboxylated NBR is chosen for wet-gel strength in dipped goods, and the mixed compound ages in the pot.
Use this when a project needs oil or outdoor ozone resistance, or when NR allergy literacy is pushing you toward a synthetic. Synthetics are not a blanket “hypoallergenic NR.” Oils and solvents against the finished film: Compatibility Matrix. Joins: Adhesives and Seam Integrity.
Why these polymers show up
CR (polychloroprene, often sold as neoprene latex). Sunlight, ozone, heat-aging, solvent, abrasion, flame, and barrier resistance. The first large CR latex use was oil, grease, and solvent industrial gloves. Light colors are often impractical: CR is photosensitive. Dark carbon black or red iron oxide films age best outdoors.
CR cure package. Films need ≥5 phr ZnO and 2 phr antioxidant, fully dispersed. For long sun or heat exposure, raise ZnO toward 15 phr. That is a CR rule, not an NR bottle habit.
Carboxylated NBR (nitrile). Household-glove formulations pick carboxylated latex for wet-gel strength. As the mixed compound sits, it prevulcanizes. Wet-gel strength drops. Dry film can mud-crack. Replenish with fresh compound; do not store a mixed NBR pot like a stable NR concentrate. 2 phr dibutyl phthalate (DBP) helps the ingredients knit with little modulus change. Limit dry temperature: NBR has low water-vapor permeability, so water leaves slowly.
SBR. Low polarity, like NR. Used when the target is modulus or a blend, not NR’s oil or ozone profile.
What is wet-gel strength?
Wet-gel strength is how well a freshly deposited, still-wet rubber skin holds together before it dries. Dipped goods need enough wet strength to survive the next dip and the leach without tearing. Carboxylated NBR is used because that wet skin is stronger. As the pot ages, prevulcanization steals that advantage.
What is mud-cracking?
Mud-cracking is a dry-film defect that looks like dried pond mud: a network of cracks in a skin that shrank while it was still weak. On aged carboxylated NBR it is a process defect from a pot that has prevulcanized, not random bad luck.
What does phr mean?
phr is parts per hundred rubber. 5 phr ZnO means 5 parts zinc oxide per 100 parts dry polymer.
Polarity when you join
Adhesive-to-substrate polarity in the handbook:
- High: NBR, carboxylated NBR (XNBR)
- Medium: CR
- Low: NR, SBR
Match the glue family to the rubber. A cement that wets NR well can starve on NBR. Concrete example: a nitrile-dipped glove film wants a high-polarity adhesive; an NR cast film wants a low-polarity one. Walk that in Adhesives and Seam Integrity.
Decision cues
CR when the piece will see sun, ozone, or oil and grease, and you can run a ZnO-plus-antioxidant package (5 and 2 phr as the floor; ZnO toward 15 phr for long heat and sun).
Carboxylated NBR when you are dipping and need wet-gel strength. Mix what you will use. Watch for mud-crack on dry as a sign the pot is old.
SBR when polarity and modulus line up with an SBR TDS, not as a silent swap for NR.
Allergy. No NR proteins. Accelerators and other cure chemicals can still drive Type IV reactions.
Deep dives (optional)
Deep dive: CR dipped-film factory example
Handbook Neoprene 571 dipped film (example only, not a home costume card): DARVAN SMO 3, DARVAN WAQ 1, ZnO 5, antioxidant 2, optional McNAMEE clay 10, plus accelerators; coagulant-dipped, leached, dried, cured. Uncured tensile about 14 MPa, elongation about 840–950%. After 60 min at 141°C, an ETHYL TUADS plus BUTYL NAMATE system reaches about 25 MPa.
CR is photosensitive. Dark carbon black or red iron oxide ages better outdoors than a light pastel.
Deep dive: NBR pot age
Carboxylated NBR household-glove compounds lose wet-gel strength as they sit (prevulcanization). Mud-crack on dry is the matching defect. Replenish with fresh compound. 2 phr DBP helps integration. Keep dry temperatures modest because water vapor moves slowly through NBR.