Polyacetal viscosity

TABLE 5.7 Viscosity and Melt Flow Index of Polyacetals... 

P.Y. 181 represents a reddish yellow pigment with excellent heat stabUity and lightfastness. It is especially suitable for polymers that are processed at higher temperatures. P.Y. 181 plays a role in the coloration of such plastics as polyacetals, polystyrene or polyester, as well as in spin dyed viscose rayon and viscose cellulose. 

This equation goes to a zero-shear viscosity as 0 and to a power law for k 3> i "" in the latter case, corresponds to the consistency index, K. The parameters appear to correlate with changes in molecular structure for polyolefins. The Cross equation, in which a = l - n, works well for many polymers, including polyesters and polyacetals. 

For polyacetal (POM), viscosity versus shear rate data were obtained from two sources [57,58]. One source was the renowned book on polyacetals by Barker and Price [57], whereas the other source was a research paper by Pritchard and Wissbrun [58]. Only 24 data points were analyzed and the master rheograms as shown in Fig. 4.19 were generated [56]. Even with limited data, two distinct master rheograms were revealed—one for linear polyacetal and the other for branched polyacetal. This is not an unexpected situation and is. similar to that observed earlier for polethylenes wherein HOPE (linear PE) and LDPE (branched PE) have two distinct master rheograms. 

The melt rheological analysis probed the two polyacetal resin samples for differences in their melt viscosities as a function of shear rate. The instrument used was a TA Instruments AR-1000 controlled stress rheometer with a parallel plate geometry (Figure 15-1-1). 

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