Matrix polymers, crystallization behavior

Changes in the crystallization behavior of the thermoplastic phase of the IPN have been observed in DSC (differential scanning calorimetry) experiments (i3). In Figure 7, a series of DSC scans on silicone-nylon 6,6 composites of various silicone contents are presented. The characteristic melt peak of the nylon matrix is observed in all of the thermograms, but a second, slightly lower temperature melt peak becomes more pronounced as the concentration or the cross-link density of silicone polymer in the IPN is... 

Some binary systems do not show any depression at all, indicating that T and T do not depend on blend composition. This is found when the second dispersed phase does not influence the normal crystallization behavior of the matrix polymer no nucleating activity, no influence on sphemUte growth rate, etc. 

It can be stated that the crystallization behavior of a semicrystalline polymer phase, dispersed into an amorphous matrix, is characterized by ... 

Because the phases are physically separated in the melt, the theory concerning the crystallization behavior as discussed in Parts 3.4.3 (matrix crystallization) and 3.4.4 (dispersed droplet crystallization) can be combined to understand the crystallization and melting behavior of most crystalline/ crystalline polymer blends. In general, both crystal-lizable phases crystallize separately around then-characteristic bulk T-value (as long as the minor phase is not dispersed into very fine droplets). The T-values can be somewhat shifted due to... 

For most commonly studied polymer blends, crystallization of the matrix occurs in the presence of a molten dispersed phase. The crystallization behavior of the continuous phase can be compared to that found for crystalline/amorphous blend systems in which the dispersed amorphous phase was in the molten state. 

However, when compared with pure copolymer, the highly stretched nanocomposite exhibited a higher amount of unoriented crystals, a lower degree of crystal orientation, and a higher amount of 7-crystals. This behavior indicated that polymer crystals in the filled nanocomposite experienced a reduced load, suggesting an effective load transfer from the matrix to MCNF. At elevated temperatures, the presence of MCNF resulted in a thermally stable physically cross-linked network, which facilitated strain-induced crystallization and led to a remarkable improvement in the mechanical properties. For example, the toughness of the 10 wt% nanocomposite was found to increase by a factor of 150 times at 55°C. Although nanofillers... 

The immiscible semicrystalline polymer blends may be classified in terms of crystalline/crystalline systems in which both components are crystallizable and crystalline/amorphous systems in which only one component can crystallize, being either the matrix or the dispersed phase (Utracki 1989). Numerous authors have been investigating the crystallization behavior of immiscible blends. In Tables 3.14 and 3.15, an overview is given of a number of important immiscible crystallizable blend systems. 

The crystallization behavior of a dispersed melt phase, for example, discrete melt droplets, in an amorphous matrix can be dramatically affected compared to that of the bulk polymer. It has been reported by several authors that crystaUizable dispersed droplets can exhibit the phenomenon of fractionated crystallization originating from the primary nucleation of isolated melt particles by species with different nucleating activities (heterogeneities, local chain ordering)... 

Composites of isotactic PP with Hemp fibers with various compatibilizers (PP-g-GMA, SEES, SEBS-g-GMA) were studied. All modified composites showed improved fiber dispersion in the polyolefin matrix and higher interfacial adhesion when compared with the unmodified system (PP/Hemp) as a consequence of chemical bonding between fiber and polymer. The spherulitic morphology and crystallization behavior of PP were changed in the composites due to the nucleating effect of Hemp fibers. All composites displayed higher tensile modulus (about 2.9 GPa) and lower elongation at break compared with plain PP [41]. 

Due to their rigid nature, clay platelets can function as nucleating agents that are able to modify the ciystallization behavior of the polymer matrix such as PVDF-HFP. Organically modified clay promotes an a- to 3-transformation of the polymer crystals. The degree of transformation depends on the nature of the clay surface modifier and the strength of the interactions between the clay and the polymer. ... 

Numerous studies have indicated that CNTs can nucleate PSCs, and it was suggested that both isothermal and nonisothermal crystallization behavior can be used as a bellwether of CNT/polymer soft epitaxial matching for templated crystallinity. With the addition of CNT fillers into polymer matrices, some new properties (electrical conductivity, flame resistance) can be imparted, while others (mechanical strength, thermal conductivity) can be enhanced. Again, these properties are dependent on the interplay between CNT and polymer matrix, as well as the organization of the two. 

Polymer-Specific Effects It is expected that the incorporation of nanoparticles in a semicrystalline polymer matrix would substantially affect the crystallization behavior of the polymer. Depending on polymer-filler interactions, three types of behavior can develop. 

The crystallization behavior of a dispersed melt phase in an amorphous or semi-crystalline matrix phase has generated a lot of interest in recent years. In polymer blends in which the crystallizable phase is dispersed into tine droplets in the matrix, crystallization upon cooling from the melt can occur in several temperature intervals that are initiated at different undercoolings, often ending up with a crystallization at the homogeneous crystallization temperature T(.,hom- This phenomenon is often called fractionated crystallization [73, 74]. The phenomenon of delayed crystallization was directly related to the... 

When the nanocomposite matrix is semi-ciystalline, incorporation of [nano)particles such as CNTs frequently aims at modifying the crystallization behavior of the polymer in order to improve its properties like, for example, its mechanical performance, and/or to shorten processing cycle times. This way, high levels of mechanical reinforcement can be achieved at low CNT loadings due to the formation of a highly crystalline layer in the immediate vicinity of the CNT walls, ensuring effective interfacial stress transfer. In addition, dispersion of electrically conductive particles into a semi-crystalline [as well as amorphous) polymer matrix also leads to the production of conductive materials. 

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