EoW May 2008

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5.2 Viscosity considerations CM-d, when substituted directly for a chlorinated polyethylene resin in an existing compound, will typically result in a higher viscosity than the original compound. However, through the addition of increased levels of plasticiser and/or addition of EO-b at 10–15 phr, the viscosity of the compound can be reduced as seen in Table 2 . The highly filled compound with EO elastomer has processing characteristics comparable to the normally loaded CM-a compound. 5.3 Physical properties When filler levels are raised from ‘normal’ to ‘high’ in the compound based on CM-a, there is a corresponding loss of physical properties (see Table 3 ). In particular, tensile strength and retention of elongation after ageing show a significant decrease. However, when the ‘high’ filler level is used with CM-d (or a blend of CM-d and EO-b), the physical properties are comparable to those seen using ‘normal’ filler loading in CM-a. CM-d enables the compounder to modify a ‘normally loaded’ recipe by increasing the levels of fillers and oils, while still maintaining physical property performance. Typical high molecular weight CPE grades such as CM-a do not perform as well as CM-d in highly loaded compounds. CM-d was designed specifically to help the compounder achieve improved performance at similar or reduced cost (due to higher filler/ oil loadings). 5.4 The importance of elastomer chain architecture design

For example, CM-d is a developmental, amorphous grade of chlorinated polyethylene (CM) that has been designed to accept high loadings of fillers with comparable or better physical properties compared to standard CM products. CM-d has an excellent balance of heat and chemical resistance that makes it suitable for use in specific wire and cable applications. The data in Tables 1–3 illustrate the potential advantages of CM-d. 5.1 Higher filler loadings CM-d was designed to accept high filler loadings while maintaining physical pro- perties. To illustrate, CM-d was compared to CM-a in a Flexible Cord Jacket application as per Underwriters Laboratories (UL®) Standard 62. A typical formulation containing CM-a with ‘normal’ loading of fillers and plasticisers was compared to compounds containing a ‘high’ loading. The highly loaded compounds contained ~34% higher total phr than the ‘Normal’ compound (see Table 1 ). The compounds were extruded as a 0.76mm jacket onto 14 AWG solid aluminium wire (1.63mm diameter) using a 38.1mm single screw extruder with a length to diameter (L/D) ratio of 15. The wire was cured in the continuous vulcanisation (CV) tube for 2 min in 1.72 MPa steam. Slab samples (for low temperature brittleness testing) were cured 2 min at 200°C. Processing and curing data are shown in Table 2 . Samples were tested according to appropriate ASTM specifications: tensile Strength ASTM D412 • IRM 902 Immersion ASTM D471 • heat ageing ASTM D573 • low temperature brittleness ASTM D746 • physical properties are included in • Table 3

Figure 6 ▲ ▲ : Structure-property of olefinic elastomers

temperatures. The feed strips should be as cool as possible to minimise balling of the feed at the hopper. Minimisation of the use of process aids with the proper selection of aromatic oils can improve the contact of the strip at the screw surface and feeding. Some high viscosity or crystalline polymers may be needed to improve collapse resistance of the extrudate. With proper feeding either by strip or pellets, elastomer compounds then extrude rapidly and smoothly onto conductors with either rubber-type or plastic type screws or crosshead pressure dies as shown in Figure 9 . Crosshead temperatures are typically set high enough to soften the polymer to allow good flow but below the peroxide decomposition temperature so that scorch is not a problem. Most elastomer-insulated wire is then cured in a continuous vulcanisation (CV) tube. The reeled wire is either sold or used in subsequent cabling operations. The performance of wire and cable compounds is dependent upon the combinations of the performance attributes of the ingredients involved and the choice of polymer. The elastomeric matrix and its compatibility with the ingredients being incorporated into the elastomer strongly influence the success of a compound’s development. Therefore, the correct chain architecture design represents one of the most critical steps in the design of the compound for wire and cable applications. However, it is the properties of the elastomer matrix which determines the type and quantity of the various ingredients that can or should be used in the compound to control the end use performance of the product. Figure 7 ▲ ▲ : Limiting oxygen index versus chlorine content of CM 5. Chain architecture optimisation for wire and cable application

Figure 8 ▼ ▼ : Elastomer compound production

Figure 9 ▼ ▼ : Wire extrusion of elastomers

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EuroWire – May 2008