also less desirable due to their added cost possible elastomers can include but are not limited to nbr rubbers that are copolymers of acrylonitrile and butadiene such as chemigum from omnova solutions and crosslinked acrylate terpolymers such as sunigum also from omnova solutions it is specifically required that the rubber elastomer is ground into finely dispersed particles the preferred cross linked nitrile rubber is zealloy 1422 from zeon chemicals and has an acrylonitrile content of 33 wt as voc 39 s and odors are becoming increasingly important for health and environmental reasons rubber in different iterations of this material can be removed according to the present teachings additional processing for the compound includes the following 1 the additive stabilizer package can be to be added in the second pass it should be noted that if added in the first pass blend efficiency decreases and blend time increases 2 the colourant can be added after the second dry point optionally because of the high plasticizer content colourant is added later in the blending process so it does not inhibit the absorption of plasticizer in the pours of the pvc during the absorption phase 3 rubber can be added without the need for extrusion grinding typically nitrile butadiene rubbers are only available with large particle sizes and need to be melt blended with the pvc preferably.