Vamac terpolymers

Vamac terpolymers require the standard release package Armeen 18D (Octadecylamine) 0.5 phr... 

Standard antioxidant systems Vamac terpolymers Vamac dipolymers... 

The expected relationships between carbon black particle size and stracture, and the properties of vulcanizates, can be extended to Vamac. Tables 6.10 and 6.11 show the effect of carbon black particle size on the physical properties of Vamac terpolymers and copolymers, respectively. 

TABLE 6.10 Carbon Black Fillers in Carbon Blacks MT (N990) Vamac Terpolymers Compounds 60 ... 

The potential for the formation of ionic crosslinks with Vamac terpolymers precludes the use of fillers that may contain soluble divalent metal ions. Metal stearates, metal stearate-coated fillers, clays, and precipitated silicas are not recommended for use in Vamac terpolymers. Precipitated fillers can contain impurities, which can lead to ionic bonding. Another potential source of soluble divalent metal ions is the pigment used to color mineral-filled compounds. Ionic bonds can significantly increase the viscosity of the uncured stock and increase the compression set of vulcanizates. The effect of metal ions and ionic bonds on stock and vulcanizate properties can vary considerably from batch to batch and is dependent on the impurity concentration in the lot of filler as well as the mixing/processing procedures. 

Vamac terpolymers are usually cured with a combination of primary diamines and guanidine accelerators... 

This section describes suggested starting compound formulations based on both Vamac terpolymers and copolymers. Most have proven satisfactory in prototype or... 

Commercial Forms. Eour different base polymers of VAMAC ethylene—acryhc elastomer are commercially available (Table 1). Until 1990, existing grades of ethylene—acryhc elastomers were based on a single-gum polymer. VAMAC G, defined as a terpolymer of 55% methyl acrylate, ethylene, and a cure-site monomer (5). In 1991, a higher methyl acrylate terpolymer, VAMAC LS, was introduced. The composition of this polymer was specifically chosen because it significantly increases the oil resistance of the polymer while minimizing losses in low temperature fiexibihty (6). 

A terpolymer rubber was introduced by Du Pont in 1975 (Vamac). This is based on ethylene, methyl acrylate and a third, undisclosed, monomer containing carboxylic acid groups to act as the cure site (see Section 11.9). 

More recently, in 1975, Du Pont introduced a terpolymer (Vamac) based on ethylene, methyl acrylate and a third monomer of undisclosed composition which contained a carboxylic acid group to provide a cure site for use with peroxides or amines. Both types of rubber exhibit good heat, oxygen and ozone resistance. 

Terpolymers in which the acrylate monomer is the major component are useful as ethylene-acrylate elastomers (trade name Vamac) [Hagman and Crary, 1985]. A small amount of an alkenoic acid is present to introduce sites (C=C) for subsequent crosslinking via reaction with primary diamines (Sec. 9-2d). These elastomers have excellent oil resistance and stability over a wide temperature range (—50 to 200°C). They are superior to nitrile and chloroprene rubbers. Although not superior to silicone and fluorocarbon elastomers, they are less costly uses include automotive (hydraulic system seals, hoses) and wire and cable insulation. 

Fluoroelastomers, silicone rubbers, butyl rubbers, ethylene-propylene terpolymer (Nordel), ethylene-acrylic copolymer (Vamac), and polyacrylate (Hycar 4054) were evaluated for the PS (preformed seal or gasket) compounds. 

In another set of experiments, ethylene methacrylate acid terpolymer (Vamac ) was mixed with PPand MPP. The rubber was then crosslinked with the crosslinldng agent also acting as a bridging compound to form a compatibilizer between the acid-terpolymer and MPP. Several experiments were carried out by varying the rubber to plastic ratio and the level of M PP. The results are shown in Figure 3.26 [6], where true... 

Terpolymers must be post-cured to attain optimum properties. If a post-cure is either not practical or not desired, and excellent compression set is a requirement, the copolymer Vamac D grades are the preferred choice. 

As with most elastomers, various fillers have different effects on the properties of the compoimd. Because of the potential for the formation of ionic crosslinks with the terpolymer, some fillers are not suitable for use with terpolymers. Table 6.9 is a brief overview of filler performance when incorporated into Vamac. 

As expected, as the particle size of the carbon black decreases, the hardness, modulus and tensile strength of Vamac vulcanizates increases, while the elongation at break decreases. There is essentially no difference in the behavior of the terpolymer... 

TABLE 6.12 Mineral Fillers in Vamac Mineral Fillers Cypnibond Terpolymers Compounds 60 — ... 

AEM polymers, both terpolymers and copolymers, must be cured under pressure to avoid sponging. Pressures of 413.7 kPa and higher, preferably higher, are recommended for curing Vamac compounds without sponging. High viscosity compounds with fast cure systems can be molded at the lower end of the pressure range. If compression set is not a consideration, the viscosity of a terpolymer-based compound can be increased sufficiently with ionic crosslinks to be cured at atmospheric pressure [3]. 

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