Page 349 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

PLASTICS ADDITIVES 5.29

FIGURE 5.8 Commercial coupling agents.

5.3.2.3 Methacrylato Chromic Chloride. This was one of the earliest coupling agents
for glass fibers in thermosetting polyesters. Presumably, the Cr-Cl groups react with the
Si-OH groups on the glass surface to create Si-O-Cr bonds, while the methacrylate groups
copolymerize with the styrene and unsaturated polyester during cure, producing true pri-
mary covalent bonding from glass to coupling agent to polymer matrix.
5.3.2.4 Organosilanes. These have been the leading class of coupling agents for many
years. The general type structure (RO) SiR´X contains three R = methoxy, ethoxy, or ace-
3
toxy groups that react with the Si-OH surface of glass fibers or mineral fillers to produce
Si-O-SiR´X bonds to the coupling agent. In thermosetting polymers, the X group is cho-
sen to copolymerize with them during cure, producing true covalent bonding from filler or
fiber, through coupling agent, to the polymer matrix. In thermoplastics, the R´X group is
chosen for similar polarity and/or hydrogen-bonding to give optimum secondary attraction
to the polymer matrix.
5.3.2.5 Organotitanates. Organotitanates appear analogous to organosilanes at lower
cost. Experimental results vary, but their main service appears to be as dispersing agents.
More recently, zircoaluminates and other organometallics have been added to this broad
family.

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