Page 374 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

5.54 CHAPTER 5

5.10.1.9 2,5-Dimethyl-2,5-di-t-Butyl Peroxy Hexyne-3. This, having a 10-hr half-life
temperature 135°C, was developed specifically for the higher temperature processing re-
quired in the cross-linking of HDPE.

5.10.2 Safety Precautions
• Peroxides are often sold and handled in dilute form to reduce the danger of explosive re-
action.
• Heat should be avoided in shipping, storing, and handling. Some must be kept refriger-
ated.
• Friction should be avoided, both in packaging (no tight-fitting or screwed lids) and in
handling and processing.
• Organic impurities should not be allowed to contaminate peroxides, as the attack on
them would be exothermic and kick off the entire batch.
• Peroxides and catalysts/promoters should never be mixed together in the pure state. The
batch of polymer should be divided in half. Then, the peroxide is added to one half and
the catalysts/promoters to the other half. In this diluted form, the two halves can then be
mixed to start the reaction.

5.10.3 U.S. Market Analysis
Table 5.33 provides an analysis of peroxides used in plastics in the United States.

TABLE 5.33 Peroxides Used in Plastics

Amount,
Type millions of pounds
MEK peroxide 11
Benzoyl peroxide 10
Peroxy esters 9
Dialkyl peroxides 5
Others 5

5.11 POLYMER BLENDS

Polymer properties may be improved by adding a second polymer. This is not a general
rule, but a number of polymer blends have offered so much improvement that 40 percent
of commercial plastics are now based on polymer blends.

5.11.1 Miscibility
If the two polymers are completely miscible down to the molecular and even segmental
level, they form a single homogeneous phase, and properties are generally proportional to

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