Reinforcement Promoters

While division into coupling and noncoupling types is often based on chemical structures, this can be misleading. As will be shown later, some modifiers can act as either noncoupling or coupling types, depending on the formulation. The concept of reinforcement promoters, first introduced by Ancker et al. [1], and discussed in Section 6.2.3, is a potentially useful alternative way of classifying modifiers in some cases. 

R Godlewski. Efficient Reinforcement Promoters for Reinforced Polypropylene. Annul Technical Exhibition and Conference Society of Plastic Engineers (ANTEC), 1988, pp. 1481-1484. 

Reinforcement promoters are sometimes used in black loaded HR compounds, preferring those that promotes polymer-polymer linkages predominantly, e.g., 1,4-dinitrosobenzene (Polyac) or l,4-bis(4-nitro-sophenyl)piperazine (Promoter 127). A level of 0.2-0.4 phr is adequate and a mixing cycle in which the promoter is completely reacted is essential (needs 3 min at more than 160°C) to avoid undesirable effects on processing safety. 

Heat treating agents (discussed in connection with fillers as reinforcement promoters) are sometimes regarded as process aids. 

Silicone Heat-Cured Rubber. Sihcone elastomers are made by vulcanising high molecular weight (>5 x 10 mol wt) linear polydimethylsiloxane polymer, often called gum. Fillers are used in these formulations to increase strength through reinforcement. Extending fillers and various additives, eg, antioxidants, adhesion promoters, and pigments, can be used to obtain certain properties (59,357,364). 

Sohd rocket propellants represent a very special case of a particulate composite ia which inorganic propellant particles, about 75% by volume, are bound ia an organic matrix such as polyurethane. An essential requirement is that the composite be uniform to promote a steady burning reaction (1). Further examples of particulate composites are those with metal matrices and iaclude cermets, which consist of ceramic particles ia a metal matrix, and dispersion hardened alloys, ia which the particles may be metal oxides or intermetallic compounds with smaller diameters and lower volume fractions than those ia cermets (1). The general nature of particulate reinforcement is such that the resulting composite material is macroscopicaHy isotropic. 

Fillers. They are generally added to reinforce NBR adhesives. However, fillers can be added to promote tack, to increase the storage life, to improve heat resistance or to reduce cost. The most common fillers are carbon blacks. Precipitated silica can be used in applications where black colour is not acceptable, but excessive amounts tend to reduce adhesion. Titanium dioxide can be used to impart whiteness, improves tack and extend storage life. 

The performance of a product where adhesion plays a role is determined both by its adhesive and cohesive properties. In the case of silicones, the promotion of adhesion and cohesion follows different mechanisms [37]. In this context, adhesion promotion deals with the bonding of a silicone phase to the substrate and reinforcement of the interphase region formed at the silicone-substrate interphase. The thickness and clear definition of this interphase is not well known, and in fact depends on many parameters including the surface physico-chemistry of... 

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