Acrylic Rubber (ACM)
Common chemical composition:
Polymers of acrylic acid esters with additional comonomers
Acrylic rubber consists of elastomers which produce vulcanizates with mediocre mechanical properties and poor elastic properties that exhibit good oil and heat resistance at up to 170/190°C. They are polymers of acrylic acid esters with additional comonomers featuring points or groups susceptible to cross-linking. The esters normally used are ethyl acrylate, butyl acrylate, methoxy ethyl acrylate and ethoxy ethyl acrylate.
The elastomers contained in acrylic rubber are not very versatile, as they are connected to well-defined formulations. Traditional acrylic rubber is based on ethyl and/or butyl polyacrylates and contains chloroethyl vinyl ether as a comonomer. Those based on butyl acrylate exhibit better cold resistance but worse oil resistance, compared to those based on ethyl acrylate. A combination of ethyl acrylate, butyl acrylate and alkoxy acrylate produces different levels of the two aforementioned properties. Containing chlorinated comonomer as a vulcanizing site, they vulcanize with the addition of diamine or thiourea derivatives or polyamino compounds.
Acrylic rubber that cross-links through hydrolysis also exists. It is also based on ethyl and/or butyl polyacrylates, but contains vinyl chloroacetate or glycidic compound as comonomer.
With both of these comonomers, vulcanization systems based on metal soaps (sodium or potassium) are used, in combination with sulfur or sulfur donors. The soaps give the chloroacetate or glycidic groups belonging to the different polymer chains a hydrolytic effect, thus creating cross-linking conditions.
With rubber containing vinyl chloroacetate, vulcanization systems based on amines and/or metal oxides can also be used. With those containing glycidic groups, ammonium compounds can also be used.
Ethylene/methyl acrylate carboxylate acrylic rubber also exists and is encompassed by the term VAMAC DuPont, differing from ethyl and butyl acrylate polymers by exhibiting lower heat resistance but better cold resistance. It also shows better values for elongation at rupture.
Fields of Application:
Acrylic rubber consists of elastomers which have been designed to produce heat-resistant items (up to 190°C). It is a difficult material to process as it normally exhibits strong nerve. It is generally integrated by FEF black or more reinforcing blacks (HAF) or mineral fillers.
It is mainly used for the production of O-rings and shaft seals. It is particularly suitable for the latter purpose due to its oil and heat resistance and surface characteristics. In addition, it is also used for precision-moulded items.
VAMAC is also used for special types of radiator hoses for diesel engines, the external parts of which are required to be oil resistant.