Ask five suppliers for "rubber chemicals" and you will get five quotes that cannot be compared. The phrase covers an accelerator that sets cure time, a blowing agent that decides whether the part is solid or sponged, an antiozonant that governs whether a sidewall survives three summers, and a slip agent that controls surface behaviour. None of them substitutes for another, and price per kilogram tells you nothing across the four categories.

The accelerator sets the cycle time

2-Mercaptobenzothiazole, sold as accelerator M or MBT, is the reference thiazole: C7H5NS2, molecular weight 167.25, a pale yellow crystalline powder melting between 177 and 181 °C with a flash point around 243 °C and a water solubility below 0.1 g/100 mL at 19 °C. It is a general-purpose accelerator for NR, SBR, NBR and EPDM. The detail that matters behind that description is that MBT is an acidic accelerator, and an acidic accelerator is close to inert until it is activated.

MBT without an activator is wasted money

The activator is zinc oxide together with a fatty acid, and the ratio matters more than most formulators admit. Leave it out and the cure will be slow, underdone at the edges and inconsistent from batch to batch — after which someone orders a faster accelerator when the real problem was activation. MBT is normally run with a secondary accelerator; thiurams and dithiocarbamates push it into the fast range, and in latex it is paired with dithiocarbamates for room-temperature vulcanisation. Two further properties decide where it can be used at all. It disperses well and does not discolour, which is why it suits light-coloured goods, but it is intensely bitter, so it is off the list for anything in food contact. It is also the intermediate from which the DM, MZ, NS and NOBS accelerators are made, so a buyer who specifies MBT and receives a sulfenamide has not been short-changed — only handed a different material with a different cure profile.

Azodicarbonamide: the blowing agent with no drop-in replacement

Azodicarbonamide, CAS 123-77-3, C2H4N4O2, molecular weight 116.08, is the general-purpose chemical blowing agent, and the trade description is unusually candid: it is used across PVC, polyethylene, EVA, polypropylene, ABS and nylon-6, and no competitive product has yet appeared. The specification is short and worth reading line by line — gas yield at least 220 mL/g, decomposition temperature at or above 200 °C, average particle size 4 to 6 µm, purity 97% minimum, ash no more than 0.5%, pH 4 to 6, heating loss under 0.3%. Gas yield decides how much you need. Particle size decides the cell structure, and it is the parameter most often missing from an enquiry. It arrives as a yellow powder in 25 kg cartons and needs cool, dry, ventilated storage.

The semicarbazide question

Azodicarbonamide decomposes to a residue that includes semicarbazide, and that single fact shapes most of its regulation. As a flour treatment agent it is approved in the United States and Canada but was withdrawn from that use in the European Union in 2005, and its presence in food-contact articles and in articles for children is restricted in several markets. That is not an argument against the material, which remains the workhorse for EVA foam midsoles, PVC flooring backing and wallpaper. It is an argument for asking early: if the finished article is a food-contact gasket or a toy, settle before the tooling is cut whether azodicarbonamide is permitted, because the answer changes the whole formulation rather than one line of it.

The antiozonant that stains

Nickel dibutyldithiocarbamate, CAS 13927-77-0, C10H20N2NiS4, molecular weight 355.17, is a metal dithiocarbamate with a nickel content of 16 to 18% and a purity of at least 98%. It appears as a yellow-green to brown powder, decomposes above 200 °C and is insoluble in water. It is specified where heat ageing and ozone cracking matter at the same time: nitrile rubber, chloroprene, hydrogenated nitrile, and the oil-resistant seals, hose and rollers those materials go into. Two caveats belong with it. It is a staining antioxidant, so it will discolour white and light compounds and is the wrong choice for a light-coloured goods recipe. And as a nickel compound it carries a classification that shifts the labelling, exposure controls and shipping paperwork on the finished goods. Both are cheaper to discover at the quotation stage than at the border.

Erucamide has to migrate to work

Erucamide, CAS 112-84-5, C22H43NO, molecular weight 337.58, melting point 80 to 85 °C and purity 99% or better, is a C22 fatty acid amide that does nothing at all inside the polymer and everything at its surface. Added to polyethylene and polypropylene films as a slip and anti-block agent, it migrates to the surface after extrusion and lowers the coefficient of friction enough for the film to open on a high-speed converting line. That migration is the specification. Too much and the film is slippery before the print or the seal goes on, so the ink or the adhesive does not take; too little and the roll blocks on the reel. In rubber processing the same molecule is used differently — as an internal lubricant and mould release agent that cuts mixing energy and helps parts release cleanly. It also goes into masterbatches, where the migration rate has to be matched to the resin it will be let down into.

The rest of the compound

These four do not sit in isolation. The polymer sets the starting point: in nitrile rubber the acrylonitrile content, normally 15 to 45%, trades oil resistance against elasticity. Carbon black is the reinforcing filler, and its grade — iodine adsorption for surface area, oil absorption for structure — changes tensile strength and abrasion resistance more than any additive above will, while nano calcium carbonate is the usual diluent filler where cost is the constraint. Paraffin wax acts as a processing aid and a physical ozone barrier, which is why it often appears alongside a chemical antiozonant rather than instead of one, and petroleum resins supply tack in the unvulcanised compound. Vinyltrimethoxysilane couples silica in peroxide-cured systems, polyethylene glycol serves as a processing aid and activator in silica-filled compounds, and magnesium myristate and sodium stearate are the metallic and fatty acid soaps used for lubrication and release.

What to put on the enquiry

Five lines turn an ambiguous request into a comparable quotation: the function being bought — accelerator, blowing agent, antiozonant or slip agent — with the chemical name and CAS number; the polymer and its grade, including ACN content for nitrile; the processing temperature and cure system, since an acidic accelerator and a peroxide cure do not belong in the same sentence; the destination market and whether the article is food contact or child use; and the packaging you can handle. Ask for TDS, COA and SDS with the sample rather than with the first order. Packaging is straightforward across the four — 25 kg bags or cartons, 25 kg fibre drums for the antiozonant, 10 kg small packs on request — with a 24 month shelf life in cool, dry, ventilated storage.