additives feature | Nucleation and reinforcement
FIGURE 11. 1% SECANT MODULUS OF PP CONTAINING HPR-803I VS. TALCUM WITH LOADING
FIGURE 12. HDT OF PP CONTAINING HPN-803I VS. TALCUM WITH LOADING
in MD and TD, while HPN-20E gives low and balanced shrinkage in this plane (Figure 9). Blends of these nucleating agents can “tune” shrinkage to specific requirements by the converters or from blends of resin grades, while benefitting from the increased crystallization temperature afforded by nucleation. Such solutions are not possible with either sodium benzoate or phosphate ester salts, which induce shrinkage preferentially in the TD direction of all fabricated PP parts.
PP reinforcement In contrast to nucleation, reinforcing agents, while orienting strongly in polymer melt flows, do not typically nucleate the PP crystals, therefore do not induce crystalline orientation. Figure 10 shows a typical SEM of a freeze-fractured surface from Milliken’s latest product, Hyperform HPR-803i reinforcing agent, in a PP matrix (Figure 10). A direct result of the strong particle orientation in PP
flow is the enhanced flexural modulus of the PP matrix. Figure 11 shows a comparison with talcum. The stronger effect on flexural modulus at equivalent
loadings allows a lighter weight PP construction. As expected, the HDT performance also follows (Fig. 12).
References 1. Kurja, J.; Mehl, N. A., in “Plastics Additive Handbook”, Chapter 18, Ed. H. Zweifel, 2001. 2. Binsbergen, F. L. Polymer 1970, 11, 253. 3. Van Krevelen, D. W. “Properties of Polymers”, 3rd
Ed. 1990.
4. Hieber, C. A. Polymer 1995, 36, 1455. 5. Eder, G.; Janeschnitz-Kriegel, H. Mat. Sci. & Tech. 1997, 18, 269. 6. Lotz, B.; Wittmann, J. C. J. Poly. Sci., Phys. Ed. 1981, 19, 1837. 7. Lotz, B.; Wittmann, J. C. Makromol. Chem. 1984, 185, 2043. 8. Hoffmann, J. D. J. Chem. Phys. 1958, 28, 1192. 9. Avrami, M. J. J. Chem. Phys. 1939, 7, 1103; 1940, 8, 212; 1941, 9, 177. 10. Wunderlich, B. “Macromolecular Physics”, Academic Press, New York, 1976.
38 COMPOUNDING WORLD | April 2012
FIGURE 10. HYPERFORM HPR-803I PARTICLES ORIENTED IN A PP PART (FLOW DIRECTION ACROSS)
Summary Recent advances in nucleation and reinforcement of PP by Milliken have generated an enhanced understanding of the mechanism of nucleation, and most significantly, the importance of orientation in PP structure/property relationships. Nucleating agents that impart orientation balance in the MD/TD plane of fabricated PP parts, such as Hyperform HPN-68L, HPN-20E and HPN-600ei, give the resin producer or fabricator the flexibility to generate non-warping complex parts by having the ability to “tune” orientation using these nucleating agents. Finally, the introduction of Hyperform HPR-803i as Milliken’s first true reinforcing additive for polyolefins opens up new value space in large part injection moulding, particularly in automotive applications which require the ultimate in stiffness, while maintaining a decreased part weight.
About the Author Darin L. Dotson is a senior scientist at Milliken & Company’s Chemical Division, located in Spartanburg, South Carolina, USA. ❙
www.millikenchemical.com
www.compoundingworld.com
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