Flame-Retardant Cable Formulation
Hydrated fillers such as ATH achieve their flame retardance by decomposing endothermically, with the release of water close to the temperature at which the polymers themselves decompose. They do not have the smoke and corrosive gas problems associated with other types of flame retardants. For a highperforming HFFR compound to be produced at very high ATH loadings of 60 to 65 wt. %, the ATH particle size and shape have to be carefully controlled. Experience suggests that large and thick particles of ATH with a low surface area are required for effective flame retardation. When Multifunctional Silane SystemsTM are used in HFFR materials, a small amount of peroxide is required to obtain good coupling.
Lower VOC
Oligomeric vinylsilanes will release a significantly reduced quantity of alcohol (and hence lower VOC emissions) upon reaction with moisture. Correct use of Dynasylan® oligomeric vinylsilanes may also reduce compound viscosity and produce a smooth, defect-free surface. When vinylsilanes are used in HFFR materials, a small amount of peroxide is required to obtain good coupling.
Mechanical Properties
For oligomeric silanes, the absence of peroxide results in poor tensile strength. In the presence of peroxide, however, the overall picture changes dramatically. As the ATH couples to the EVA, tensile strength increases and water pick-up is reduced, both through increasing the cross-link density and also by rendering the compound hydrophobic. Elongation at break is not significantly affected by the presence of peroxide. Oligomeric vinylsilanes perform better than monomeric vinylsilanes, even at a lower concentration of 1.6 phr. At these low silane levels, the vinylsilane/ peroxide ratio has to be monitored carefully. At a silane concentration of 1.6 phr, the peroxide concentration should not exceed 0.04 phr because of the risk of scorch.
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