Fusabond® Resins as Coupling Agents in Halogen-Free Wire & Cable Applications

DuPont™ Fusabond® maleic anhydride grafted resins can be used as coupling agents between polymers --mainly polyolefins such as polyethylene and polypropylene --and fillers, in order to increase the filler acceptability of polymers. Typical levels of Fusabond® are in the range of 2-5 weight % based on the entire compound. Fillers that show an affinity to Fusabond® maleic anhydride grafted resins include flame-retardant fillers, such as alumina trihydrate (ATH) and magnesium hydroxide (Mg[OH]2). Improvement in properties also can be seen when Fusabond® is used in combination with common fillers such as calcium carbonate.

Extensive trials have been undertaken using Fusabond® E as a coupling agent in halogen-free, flame retardant wire and cable formulations containing approximately 65% ATH in a LLDPE/EVA matrix.

Figure 1 compares typical property data for extruded sheet made from compounds containing varying levels of Fusabond®, versus a control compound containing a silane-based coupling agent. Result show that Fusabond® has a significant influence on elongation at break and, therefore, the flexibility of a compound. Compared with liquid silanes, Fusabond® resins are solid particles, which generally can be handled more easily and dosed more accurately.

Figure 2 shows how heat-aging of the described PE/ATH formulations affects tensile strength, elongation at break, and viscosity (melt flow index).

In a related application, compounds containing polypropylene with approximately 65% calcium carbonate were examined. Figure 3 is a photomicrograph comparing the microstructures of compounds made with and without Fusabond® coupling agent. With coupling agent added at 4% weight, based on the entire compound weight, properties mainly impacted are stiffness, tensile strength and impact strength as shown in Figure 4. Note that impact strength is significantly improved (by almost a factor of 3) at temperatures of -20°C (-4°F) and 4°C (39°F), in the compounds containing Fusabond®.




















FIGURE 3. Effect of PP-g MAH (Fusabond® M613-05 on Fracture Toughness of PP/CaCO3)

Left image: PP + 65 wt% CaCO3, No Coupler
Right image: PP + 65 wt% CaCO3, 4% Fusabond®















The above examples show that Fusabond® can be used as a coupling agent for flame retardant fillers in custom wire and cable formulations.