JEC COMPOSITES MAGAZINE - Issue #47 - March/April 2009 - 114

KNOW-HOW Resin …/… Blocbuilder RC-50: a novel reactivity controller renders SG-1 more effective in the cure control of UPR systems, i.e., based on the lower dissociation temperature, typical UPR curing temperatures (and line speeds) can be utilized. Fig. 2: DEPN (SG-1) structure. Material considerations Because of its high efficiency, SG-1 has to be diluted in an appropriate solvent to guarantee precise dosage with the common metering equipment used in the composite industry. Arkema commerciali-zes BlocBuilder RC-50, which is a ready-to-use dilution of SG-1 in a reactive solvent. In the rest of this document, the name of BlocBuilder RC-50 will be used in place of the SG-1 appellation. cured by DSC in order to see the effect of the BlocBuilder RC-50 concentration on overall cure. The first system tested was a typical pultrusion initiator system consisting of 0.3 phr Luperox 223V75, 0.4 phr Luperox 575, and 0.3 phr Luperox MC. A plot of onset and peak temperatures for the DSC curves is shown in Figure 4. These results show that the onset-to-peak time is reduced dramatically. This allows longer wet-out time in the pultrusion die without affecting the overall cure rate. In addition, the usable resin life has been extended by over 500%. Similar blends were used to test a moulding compound initiator system consisting of 0.5 phr Luperox 575 and 0.5 phr Luperox 231. The results of this test are shown in Figure 5. The results confirm Fig. 4: The effect of BlocBuilder RC-50 on UPR that the BlocBuilder curing using a pultrusion initiator system. RC-50 serves to delay the onset of polymerization without drastically affecting the peak time for the polymeriza-tion exotherm. Customers therefore have the advantage of longer mould fill times without a change in cycle times. In addition, the overall exotherm heat was found to be unaffected due to the “controlled” nature of the curing polymerization. Experimental Bath stability Because of how the nitroxide interacts with a propagating polymer chain, one of the most obvious benefits from these materials is that it can sufficiently slow down gelation of a particular resin system to make efficient use of all of the formulated resin material without sacrificing any significant amount of curing ability. This is the unique property of nitroxides: they react ONLY with carbon radicals, not oxygen or nitrogen radicals. Due to this fact, the presence of nitroxides does not interfere with the polymerization initiators. Once the polymer chains are propagating, the critical temperature of 60°C, must be reached before the propagation step can continue. Thus, nitroxide effectively builds up in a switch, giving the user control over the moment and speed at which polymerization will occur. To better define the magnitude of difference in pultrusion bath stability, a series of elevated resin temperature studies were carried out to ensure the improved performance of Fig. 3: Comparison of pultrusion resin bath lives BlocBuilder RC-50 as a with and without BlocBuilder RC-50 at bath stabilizer. Three 42°C. samples were run to complete cure using: 1) the standard Arkema pultrusion initiation system consisting of Luperox 223V75, Luperox 575, and Luperox MC, 2) the standard Arkema pultrusion initiation system with 1 phr BlocBuilder RC-50, and 3) an “industry standard” initiator system (solid peroxy-dicarbonate and TBPB). The results of the potlife test are shown in Figure 3. Conclusions The most significant advantage of the BlocBuilder RC-50 technology is its ability to efficiently delay curing in pre-initiated UPR systems at room temperature. BlocBuilder RC-50 stops Fig. 5: The effect of BlocBuilder RC-50 on moulding compound formulations. any propagation reaction by forming, with the propagating polymer chain, stable compounds: the alkoxyamines. However, chain propagation will restart and continue once the equilibrium temperature of the alkoxyamine is reached (approximately 60oC). This mechanism differs from the use of inhibitors because it involves equilibrium reactions rather than merely trapping radicals. Contact: alfredo.defrancisci@arkema.com More information: www.arkema.com References [1] Georges, M. K.; Veregin, R. P. N.; Kazmaier, P.M.; Hamer, G. K. Macromolecules 1993, 26, 2987. [2] Grimaldi, S.; Lemoigne, F.; Finet, J.P.; Tordo, P.; Nicol, P.; Pléchot, M.; Gnanou, Y. U.S. Pat. 6,255,448, priority Feb. 7th, 1995 assigned to Atofina) Curing profiles Resin samples were prepared using a general-purpose isophthalic unsaturated polyester resin containing rising quantities of BlocBuilder RC-50 blended directly into the resin. Afterwards, two different peroxide initiator systems were blended in and 114 jec composites magazine / No47 March-April 2009

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JEC COMPOSITES MAGAZINE - Issue #47 - March/April 2009

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