Crystaf Applications

The same solvents, same IR detector and similar calculation parameters to those presented in Sect. 4.1.2 for TREF are applicable for CRYSTAF analysis. The calibration of temperature to comonomer content can be performed by using narrow composition standards (metallocene-type resins) of the same comonomer type, with similar results to TRFF as discussed in Sect. 4.1.2. Octene and hexene copolymers follow the same calibration curve [92]. 

Reviews of the CRYSTAF technique and applications have been presented [80, 83, 84]. Mathematical modeling of CRYSTAF crystallization kinetics has also been investigated [100]. 

One of the main applications of Crystaf analysis is the estimation of the CCD of semicrystalline copolymers, specifically LLDPE. The CCD of copolymers can be obtained from the Crystaf profile with the help of a cahbration curve relating the CC and the crystallization temperature. For routine analysis, a calibration curve can also give a quick estimation of the CC from the Crystaf peak temperature. Evidently, because of the crystallization kinetics and cocrystalhzation effects described before, in general only an approximation of the actual CCD is possible with Crystaf and Tref. 

The application of Crystaf analysis for detecting blend composition is, of course, limited by cocrystalhzation, particularly if accurate quantitative information is required. As previously discussed, cocrystalUzation is found to be significant when two chain populations crystallize at relatively close temperature ranges (small A Tq), even for very slow CRs. Therefore, the use of Crystaf for determining blend compositions will be more adequate when the blend components have distinctly separated Crystaf peak temperatures (large ATc). Preferably, the difference between Crystaf peak temperatures should be more than 10 °C, particularly in the case where the blend components have similar molecular structures. 

Factors contributing to the CCD include catalyst type, polymerization conditions, and reactor nonhomogeneity. Ziegler-Natta multiple-site catalysts produce polymers with broad distributions of chemical composition in copolymers and of tacticity in polypropylene, and such distributions are important in plastics applications. For example, low-crystaUinity fractions are extractable and render a material unsuitable for food packaging, while high-crystallinity fractions result in haze and low impact strength in plastic films. A thorough review of TREF and the closely related technique, CRYSTAF, by Soares and Hamielec was recently published [92]. 

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