Page 380 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

5.60 CHAPTER 5

temperature catalysts like BF :amine adducts and dicyandiamide are often precom-
3
pounded, giving systems that are fairly stable at room temperature. For flame retardance,
halogenated anhydrides are often used in place of normal anhydrides.
5.12.1.3 Unsaturated Polyesters. Copolymerization and cure of the fumarate esters
with styrene monomer is initiated by peroxides, choosing the peroxide appropriate to the
processing temperature chosen. For room-temperature cure, MEK peroxide is generally
used; it can be accelerated by cobalt naphthenate and further catalyzed by tertiary amines.
For higher-temperature cure reactions such as BMC and SMC, higher-temperature perox-
ides are chosen (Sec. 5.10).
5.12.1.4 Polyurethanes. The two major types of catalysts, for the polyol-polyisocyanate
reaction to form polyurethanes, are tertiary amines and/or organotin compounds such as
dibutyl tin dilaurate. For delayed reactions, the amines and/or the isocyanates can be tem-
porarily blocked by adducts, which are removed and liberated during the cure reaction.
5.12.1.5 Furfuryl Alcohol Resins. Polymerization and cure, and copolymerization/cure
with urea-formaldehyde and phenol-formaldehyde, are generally catalyzed by acids such
as p-toluene sulfonic acid and zinc chloride.

5.12.2 Surface Properties
A variety of additives are used primarily to modify surface properties, either during pro-
cessing or during use of the finished product. They are collected here for this general pur-
pose.
• Hyperdispersants are low-molecular-weight block copolymers designed to separate
filler and pigment particles from each other, disperse them more readily in liquid sys-
tems, and stabilize these dispersions for more efficient use of the solid particles. One
block is designed to be attracted to the surface of the solid particle, the other block to be
attracted into the plasticizer, polyolefin, or other matrix being used for the masterbatch,
and also into the final matrix polymer in the finished product. The exact nature of these
block copolymers is still a secret of their developers and producers.
• Corrosion inhibitors are commonly included in coatings on steel. These include phos-
phates of iron, manganese, and zinc; chromates of zinc and strontium; soaps of calcium,
lead, sodium, and zinc; lead oxide, carbonate, and sulfate; ferric complexes; and zinc
dust. Some newer types include organic phosphates and sulfonates. Due to worries
about toxicity and the environment, this entire field is in a state of change.
• Prebonding etch is needed to activate the perfluoro surface of PTFE before it can be
bonded with adhesives. This is typically a solution of sodium in naphthalene, which is
extremely alkaline. It pulls some fluorine atoms off the surface, or even carbonizes it,
leaving a surface which is more ready to accept adhesives such as epoxy resins.
• Antiblocking agents are often fine filler particles that roughen film surfaces enough to
prevent them from coming into good contact with each other, and thus reduce adhesion
between them. These are typically 0.1 percent of chalk or 1 percent of amide wax.
• Antislip agents are sometimes needed to overcome excessive lubrication. For example,
lubricants are added to films to keep them from sticking together during handling. If the
films are converted into bags, filled with heavy solids, and stacked on a pallet, they may
be so slippery that they slide off the stack and fall all over the floor. In such cases, an an-
tislip agent may be added to the formulation to create enough friction/adhesion to pre-

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