EoW July 2010

technical article

The unfunctionalised LPBDs served to better wet-out the mineral filler, so aiding in its dispersion. The LPBD-4 improved the elongation of the filled system by 450%. The LPBD-4 is likely to have had fewer interactions between the ATH surface hydroxyl functionality and the anhydride functionality, while maintaining a tail to compatibilise/entangle with the EVA. In addition to molecular weight and vinyl content, alternate functionalised LPBDs were evaluated. Figures 5 and 6 illustrate the results of these additives, in addition to the SR-732. Figures 5 and 6 demonstrate that reducing the anhydride loading on the LPBD (LPBD-5) will increase both the tensile strength and elongation. As mentioned previously, it is imperative to have an association between the additive and the filler surface, but also to ensure that there is sufficient chain entanglement between the additive and EVA. Reducing the MA content on the additive decreased the probability of multiple bonds being formed with the ATH surface, thus increasing the average chain length remaining to entangle in the EVA. LPBD-6 and LPBD-7 demonstrate that alternate functionalities can replace maleic anhydride in the form of epoxy and amine. Both functional groups performed analogously to equal loadings of anhydride in terms of tensile strength and elongation. Figures 5 and 6 also demonstrate the influence of the ionic monomer, SR-732, on the ATH/EVA system. Unlike the LPBD additives the SR-732 increased the tensile strength of the system and also statistically, if modestly, improved the elongation. It is believed that introduction of the ATH induced high shear environments within the melt during compounding that reacted with the acrylic functionality. Previous work indicates that these monomers have a tendency to cluster within a polymeric compound, which creates an ionic bridge, or crosslink, between adjacent chains. At ambient temperature the cluster will serve to increase the mechanical properties of the system. Unlike the LPBDs, the SR-732 altered the bulk properties of the EVA as opposed to the interface. 4 Conclusions Significant improvements in the elongation of highly filled ATH/EVA compounds were achieved by introduction of low molecular weight, functional polybutadienes. The functionality of the additive served to compatibilise at the organic/inorganic interface by reaction with the ATH surface, and chain entanglements with the EVA.

Molecular weight, or chain length, was an important attribute in improving the elongation properties. Alternate functionalities to maleic anhydride, such as epoxy and amine groups, proved to be equally valuable at improving the elongation. Increasing the tensile strength of the system was equally part of the objective. Introduction of a di-acrylic ionic monomer yielded improvement in tensile strength that the liquid polybutadienes could not obtain. Formation of an ionic network within the EVA is probably the mechanism by which the tensile strength was improved. Future experiments will further examine the influence of molecular weight on low functional LPBD. Increasing the length of the free chain should further increase the elongation phenomenon. Examining mixed additives systems to include both a LPBD and the SR-732 to increase both the tensile strength and elongation will also be considered. n 5 Acknowledgments The authors would like to thank DuPont USA and Almatis, for supplying material for this investigation; the team at Boy Machines, for moulding the tensile specimens on an XS microinjection moulder; and Brett Robb for careful preparation and characterisation of the EVA-ATH materials. 1 Plentz, RS, Miotto, M, Schneider, EE, Forte, MSM, Mauler, RS, and Nachtigal, SMB: Journal App. Polym. Sci., 101, 1799 (2006) 2 Jancar, J, and Kacera, J: Journal App. Polym. Sci., 30, 714 (1990) 3 Duval, J, Sellitti, C, Myers, C, Hiltner, A, and Baer, E: Journal App. Polym. Sci., 52, 591 (1994) 4 Sun, Y, Hu, G, Lambla, M: Polym. 37, 4119 (1996) 5 Mai, K, Li, Z, Qiu, Y, and Zeng, H: Journal App. Polym. Sci., 84, 110 (2002) 6 Wang, J, Tung, JF, Fuad, MYA, and Hornsby, PR: Journal App. Polym. Sci., 60, 1425 (1996) This paper was first presented at the 58 th International Wire & Cable and Connectivity Symposium, held in Charlotte, NC 8 th – 11 th November 2009, and is reproduced with the generous permission of the organisers. Jeremy R Austin Sartomer Company, Exton PA Email : jeremy.austin@sartomer.com Herbert S.-I Chao Sartomer Company, Exton PA Email : herbert.chao@sartomer.com 6 References

Conversely, the anhydride functionality containing analogues both provided higher tensile strength and, in the case of LPBD-3, better elongation. It seems evident that the anhydride functionality rendered the LPBD more compatible with the EVA phase, and that the lower Mw of LPBD-3 over LPBD-4 created smaller droplet dispersion. Introducing ATH into the system yielded the results presented in Figures 3 and 4 . Figure 3 demonstrates that the LPBDs all reduce the tensile strength at yield of the ATH filled EVA. The functionalised LPBD-3 and LPBD-4 outperformed their unfunctionalised counterparts, which in part suggests an improvement in interfacial adhesion between phases. In Figure 4 all but LPBD-3 improved the elongation at break. In the case of LPBD-3, the cause of a further reduction in elongation is possibly two-fold. First, the highly functional small chains (Mn 2,500) may have had multiple sites of interaction with the ATH surface and enveloped the mineral. Consequently, there would be no free chain segments to entangle with EVA to serve as a compatibiliser. Secondly, LPBD-3 was 70% vinyl, which could have crosslinked during compounding. An analysis of the elastic modulus indicated that LPBD-3 had induced a significant increase over the base material indicative of a crosslinked material. Figure 5 ▼ ▼ : Tensile strength results for alternate functionalities indicating that LPBD with 5% functionality (anhydride included) impact the tensile strength less

Tensile strength (MPa) Elongation (%) Tensile stre i ( )

Figure 6 ▼ ▼ : Elongation results using alternate functionalities demonstrating significant improve- ments in ductility over the neat EVA-ATH system

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EuroWire – July 2010