Sometimes customers will ask us, “What is that white dust I sometimes see on my molded rubber product?” The short answer is that what you are seeing is commonly referred to as “rubber bloom.”

Rubber bloom occurs when curing agents, accelerators, or lubricating agents used in the curing process migrate to the surface of a compound. Bloom manifests itself as a milky-gray dry powder dusting which is visible on the surface of the rubber. It is particularly common in molded rubber products made from nitrile (NBR) and neoprene (CBR) rubber compounds

Rubber bloom is normal and does not affect the quality of a molded rubber product. When bloom is undesired for appearance reasons, it may be easily removed by washing the part in water or a light mineral oil solution. Other steps that can be taken to reduce the incidence of bloom include shielding parts from fluorescent light, or wiping the surface with a solution such as Armor All that will help to seal in the bloom.

Some compounds are formulated with a special agent designed to protect against exposure to UV light and/or ozone attack. These agents are designed on purpose to bloom to the surface and protect the compound. In these cases, washing the compound may not reduce the incidence of bloom.

In some applications involving molded rubber products, rubber bloom may actually have a desirable side effect. A few automotive customers have pointed out to us that fabricated rubber parts exhibiting bloom are actually easier to install in lineside operations due to the lubricating presence of bloom. When a compound is initially being mixed, a lubricating agent may be added to reduce friction within the compound as it cures. It is the portion of this lubricating agent that is unused in the curing process that migrates to the surface and causes the bloom, hence the side benefit of a “lubricated” part.

Canada Rubber Group Inc. (CRGI) supplies a wide variety of custom molded rubber products for both industrial and automotive applications. These products include seals, pedal pads, isolators and dampers, plenum plugs, grommets, and more. For further information about the custom molded rubber products we can supply, please contact our sales department at crg@canadarubbergroup.com.

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