Titania melt index

Unreacted ester groups are then burned away during the calcining. Owing to its simplicity this method permits commercial silicas to be treated with any amount of titania up to 5-6% Ti, at which point saturation is usually reached.6 The method increases melt index and tends to broaden the molecular weight distribution, which can be useful in some applications such as blow molding. 

Fig. 14. The melt index of the polymer, which reflects the catalyst termination rate, is also promoted by titania, at least at the lower activation temperatures.

This explains the melt index behavior of coprecipitated silica-titania catalysts which is shown in Fig. 16. With each catalyst, the MI rises with increasing calcining temperature until sintering begins, then it drops. The... 

Fig. 16. The relative melt index potential (RMIP) of a series of cogelled Cr/silica titania catalysts rises and then falls with calcining temperature, indicating first dehydroxylation then sintering. However, the more titania in the catalyst, the more easily it sinters and therefore the lower the temperature at which peak RMIP develops.

Fig. 19. The termination rate, plotted here as relative melt index potential (RMIP), reflects the extent of surface dehydroxylation in two series of Cr/silica-titania catalysts, calcined in (Y) air or ( ) CO and then air to reoxidize the chromium, both at the temperatures shown. The third series ( ) shows the additional benefit of low-temperature attachment. It was calcined in CO at the temperatures shown, then air at a lower temperature (760°C).

FIGURE 40 Melt index of polymers made at 105-109 °C with Cr/silica-titania catalyst (870 °C) in the presence of various amounts of butene isomers. 

FIGURE 49 The influence of the mesoporosity of the catalyst on its activity and on the polymer melt index and MW. Cr/silica-titania hydrogel (450 m2g ) was dried by first replacing the pore water with a solvent of varying surface tension to produce catalysts having a variety of pore volumes that were then activated at 800 °C and tested at 105 °C. 

FIGURE 50 Pore volume distribution of Cr/silica-titania catalysts dried by various methods and then activated at 800 °C. The mesoporosity of the catalyst influences its activity and the polymer melt index (tested at 105 °C with 1.5 mol C2H4 L ). 

FIGURE 77 Impact resistance of films as a function of the polymer melt index. The addition of poisons to the reactor affects LCB levels in the polymer. In contrast to 02, CO diminishes elasticity, which in turn results in less orientation in the blown film, and therefore improved impact and tear resistance. (Cr/silica-titania catalyst, activated at 650 °C, polymer density of 0.938 g mL, film thickness 25 pm). 

FIGURE 82 Response to shear stress, shown here as the polymer HLMI/MI ratio, as a function of catalyst activation temperature for polymers made in the slurry process with Cr/silica-titania catalyst. Reaction temperature was varied (102-110 °C) to produce three series of polymers of constant melt index. (Compare with Figure 83.)... 

FIGURE 107 Fluidity (inverse of melt viscosity) of polymers made with cogelled Cr/silica-titania catalysts of varying titania contents. In this plot, the fluidity (similar to melt index) is increased (lower MW) by titania, but titania also promotes sintering at high temperatures. (Ti02 listed in mol%.)... 

FIGURE 123 Melt index potentials of Cr/silica-titania catalysts that were activated in various gases by the R R process. Catalysts were reduced 3 h in the gas shown at the temperature shown, then reoxidized 2 h in air at the same temperature. Reduction in CS2 produced polymers of the highest melt index. 

FIGURE 124 Properties of polymers made with R R-activated catalysts. Cr/silica-titania was calcined 3 h at 871 °C in N2, CO, or CS2, then in air 2 h at the indicated temperature. The MW and the fluidity (similar to melt index) of the resultant polymers are plotted. Fluidity is the inverse of the melt viscosity, measured at 0.1 s 1. 

FIGURE 125 Melt index potentials of two series of R R-activated catalysts. Amorphous Cr(lIl)/silica—titania was heated to 870 °C in N2. Crystalline Cr(lll)/silica—titania was heated to 650 °C in air, then to 870 °C in N2 to form a-Cr203. Both catalysts were then treated in CO at 870 °C for 3 h, followed by 2 h in dry air at the temperature shown. The crystalline catalyst was more difficult to reoxidize, and therefore it produced polymers of lower melt index. 

FIGURE 126 The presence of titania on an R R-activated catalyst greatly lowers the polymer MW and raises its melt index (Ml). Titania also destabilizes the Cr(VI) and thus lowers the conversion. (Titanated Cr/silica was calcined in CO 3 h at 871 °C, then in air 2 h at 600 °C.)... 

FIGURE 243 Polymers were made with Cr/silica-titania at constant melt index with various amounts of H2 in the reactor. The subsequent rise in Ml during polymer extrusion is diminished by even small amounts of H2 in the reactor. (Melt index of 0.2-0.4 g (10 min)-, density of 0.960 g mL. )... 

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