Polymer blends factor analysis

Physical properties span across aU size scales and serve to define the state of a polymer, polymer blend, or engineered design without alteration to its chemical identity. The list of physical properties for sports helmet materials is extensive and extremely important, as the impact performance and structural integrity are controlled by these factors. Unlike chemical properties, the characterization techniques for the analysis of physical properties vary substantially. 

Factor analytical methods can clearly be coupled to chemical intuition to enhance the understanding of processes such as controlled pyrolysis. The real power of the use of factor-analytical methods in the analysis of complex chemical phenomena, such as the pyrolysis of ruhher hlends, lies in the ability to gain molecular chemical insights that might otherwise he obscured. The belief that temperature control and knowledge of the process temperature is of major importance in avoiding thermal decomposition in a polymer blending process is confirmed by these workers. Further use of these mathematical methods could help discover why nominally identical materials from different batches are, in fact, very different in their performance in actual use. 

In the field of polymer science, the crystallization behavior of polymer blends represents a key issue for the analysis of structure-properties relationships of macro-molecular systems. The presence of the second polymer component, either in the melt or in the solid state, can infiuence the whole crystallization process of the polymer phases, thus the morphology, phase behavior, and physical/mechanical properties. The crystallization processes are controlled by several factors, which are related to equilibrium thermodynamics, kinetic aspects, thermal conditions, melt rheology, as well as chain structure and polymer/polymer interactions. In the present chapter, an overview of the thermodynamic conditions, accompanied by a description of main morphological features of blends containing one or both crystallizable components, is reported. 

Factor analysis can be used as a quantitative method to establish the existence of a measurable interaction spectrum [23]. To determine whether the interaction spectrum is a contributing factor to the spectrum of the blend, a series of polymer blends with different volume fractions of each homopolymer is prepared, and the spectrum of each blend is obtained. The number of components present in these blend spectra is then determined by factor analysis. In the case of compatible blends, three components are expected, but for incompatible blends, only two should be observed. 

The range of cocontinuity for a polymer blend can be measured by a variety of techniques, including solvent extraction, rheology, and SEM with image analysis. We have shown that SEM coupled with a novel image analysis technique (shape factor determination) provides a powerful method for qualitatively and quantitatively determining this range. 

To overcome the problems related to SEC of complex polymers, multidetector systems have been developed over the years. One approach is the combination of SEC with multiple concentration detectors. If the response factors of the detectors for the components of the polymer are sufficiently different, the chemical composition of each slice of the elution curve can be determined from the detector signals. Typically, a combination of UV and RI detection is used another possibility is the use of a diode array detector. In the case of non-UV-absorbing polymers, a combination of RI and density detection yields information on chemical composition. Similar information can be obtained by coupling SEC with spectroscopic detectors like FTIR, NMR, or mass spectrometry (MS). This approach is addressed in Section 2.03.5. Such detector combinations, however, are normally not able to differentiate between copolymers and polymer blends. In this case, it might be more suitable to carry out a separation according to chemical composition in a first step followed by a molar mass analysis (see for more details. Section 2.03.6). 

Elastomeric systems are quite commonly monitored by thermal techniques. Mohler [5] has discussed how DSC is used to characterize the quality of blends of elastomers. Changes in polymer Tg can point to miscible phases that might otherwise require a microscopic techmque to establish. The cold crystallization of a polymer in a blend can also be examined using the relaxation enthalpy of the sample. Vacuum TG can look at plasticizer content separate from polymer degradation. Dynamic mechanical analysis (DMA) is always a powerful technique with elastomers. Dimensional stability, storage modulus, loss modulus and loss factor are all important for this class of materials and are... 

The first class of blends to be analyzed is that of a homogeneous, disordered liquid phase in equilibrium with a pure crystalline phase, or phases. If both species crystallize they do so independently of one another, i.e. co-crystallization does not occur. With these stipulations the analysis is relatively straightforward. The chemical potentials of the components in the melt are obtained from one of the standard thermodynamic expressions for polymer mixtures. Either the Flory-Huggins mixing expression (7) or one of the equation of state formulations that are available can be used.(8-16) The melting temperature-composition relations are obtained by invoking the equilibrium requirement between the melt and the pure crystalline phases. When nonequilibrium systems are analyzed, additional corrections will have to be made for the contributions of structural and morphological factors. 

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