These are chemicals with particular effects, relating either to the manufacturing process or the function of the product. This group comprises:
a) Blowing agents
These decompose at elevated temperatures during gas evolution, as include carbon dioxide, nitrogen, bicarbonate, and ammonia. They are used in the manufacturing of cell and foam rubber/plastic. The recommended dosage is 2–8 phr depending on the desired effect and type of blowing agent.
b) Retarders
These delay the vulcanization reaction at processing temperature without significantly affecting it at vulcanization temperature. The recommended dosage is 0.3–1.5 phr depending on the type of retarder and desired retardation effect.
c) Coupling agents
These contain functional groups (eg silanes) that have the ability to create bonds between organic and inorganic substances. For example, they can link silicic acid to a polymer in order to increase modulus of elasticity and tensile strength. The recommended dosage is about 10% in relation to the light-colored filler.
d) Mold release agents
Applied to mold surfaces in order to facilitate the removal of the rubber product during demolding, and to reduce mold fouling effects.
e) Specialty plasticizers, primarily for use in blends which are based on polar polymer types. Delivered in dry liquid form, with an inorganic carrier. The delivery form is particularly advantageous for manual weighing out before adding to rubber batches in the mixing line.
f) Flame retardants. These are additives, the function of which is to reduce or eliminate the spread of fire. The different additives have different functions. Some evolve water vapor during heating, some form a protective shell, and others dilute the combustion air and have a catalytic effect on the combustion mechanism.
g) Coloring pigments. These can be organic or inorganic. Ferric oxide, titanium dioxide, and chromium oxide are common inorganic coloring pigments.
h) Moisture absorbents. These react with moisture to eliminate undesirable blistering. They are mostly used during unpressurized vulcanization, e.g. continuous vulcanization (CV), with excellent results.
I) Adhesives. These promote the formation of bonds between different polymer layers between e.g. inner- and outer-tube materials in hoses.
k) Advanced thermoplastic materials based on cyclic olefin polymers (COP).
