Additives for enhanced processing, cure rate

White elastomer compounds typically include two major ingredients that act synergistically; precipitated and fumed silicas, along with polyethylene glycol. Harwick Standard offers PPG’s precipitated silicas, including the Hi-Sil™ and Silene® product lines. Precipitated fillers can typically include both reinforcing types such as Hi-Sil 233, 243-LD, 210, & 134G, and semi-reinforcing types, Hi-Sil 532-EP & Silene 732-D.

The synergistic additive from Environmental Fluids consists of their polyethylene glycol (PEG) product line, which acts as a multi-purpose process aid. PPG’s silicas provide a highly active silanol surface, and therefore are very reactive fillers. The zinc cation from zinc oxide has an affinity to react with this active surface, thereby scavenging a portion of the zinc oxide from the polymer system and possibly interfering with the cure system. The polyethylene glycol, which surface treats the silica, reduces the amount of available silanols to react with zinc oxide. This can result in protecting the surface from the zinc cation. Likewise, silica also contains free moisture which can lead to silica-silica interaction instead of silica-polymer reaction. That reaction can hinder silica-polymer bonding and can reduce physical property development. The PEG can replace a portion of the water and aid in silica bonding. The addition of PEG also allows for the formation of a more neutral pH compound allowing for an enhanced cure rate rather than a possible retardation of the cure rate that occurs with acidic and slightly acidic fillers. PEG’s can also act as plasticizers by reducing the compound viscosity.

In general, precipitated silica and polyethylene glycol can be combined to help in several different ways to enhance ease of processing, allow for enhanced cure rate, and provide better physical properties by helping polymer-silica bonding for non-black compounds. (Harwick Standard)

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