Nanofibrillar single polymer composites SPCs

New polymer nanocomposites which seem to be particularly promising for structmal apphcations as a result of their exceptional mechanical properties, are nanofibrillar single-polymer composites (SPCs). These novel materials are reinforced with polymer nanofibrils with diameters in the range of 50-150 nanometers [31]. 

Polymer-polymer composites or self-reinforced polymeric materials (SRPM) are materials where both the reinforcement and matrix components have been made from all polymeric materials. This can include two polymers coming from the same family of polymers or simply the same polymer. Micro- and nanofibrillar single polymer composites (SPCs) are a subcategory of self-reinforced polymeric materials which are made by combining the properties of molecularly aligned and oriented forms with randomly disoriented forms of the same polymer material. It can be debated whether or not such a material can still be called a composite as it is not made of two or more dissimilar materials. However, one thing is for sure, the two forms of the material can exhibit very different mechanical properties. 

Another important feature of the SPC prepared according to this combined approach as compared with common composites, is the amount of the matrix and the material s resulting density. Since the material is created during compression molding only as a result of partial surface premelting, the quantity of isotropic matrix amounts to only 10 to 20 wt% compared to the typical 50 to 70 wt% required in common composite materials. The SEM observations presented in Figure 19.8 demonstrate that a PET nanofibrillar single-polymer composite (PET-NSPC) has indeed been produced. 

Quite different application opportunities are offered after the isolation of neat nanofibrils. At the first place is their usage for preparation of nanofibrillar single polymer composites (i.e., the case when the matrix and the reinforcement are of the same chemical composition). Regardless of some controversy from terminological point of view [62-64], this rather novel type of polymer composites represents possibly the best solution of the problem regarding the adhesion quality between matrix and reinforcement. In addition, recyclability after disposal is other main merit of SPCs [65]. 

The most recent development in the area of SPCs is the creation of micro- or nanofibrillar single polymer composites, where the starting material represents neat microfibrils or nanofibrils [21, 66-71] instead of commonly used highly oriented textile fibers and strips or their products [72-77]. This was possible due to the fact that the MFC and NFC concept allows not only to convert the dispersed polymer into highly oriented fibrils but also to isolate them as a neat material using selective solvent for removing of the second blend component [40]. 

Fig. 12.5 SEM micrographs of the various stages of pieparation of nanofibrillar SPCs a ciyo actured surface made parallel to the draw direction of nanofibrillar polymer-polymer composite based on LLDPE/PVDF highly drawn blend subjected to compression molding, b neat PVDF nanofibrils after extraction with selective solvent of IXDPE from the IXDPEfPVDF polymer-polymer composite (a), c cryofractured cross section of nanofibrillar single polymer composite prepared via compression molding of the parallel aligned neat PVDF nanofibrils (b), d surface of the nanofibrillar SPC shown in (c) demonstrating the adherence of PVDF nanofibrils due to surface premelting only...

The micro- and nanofibrils isolated in a neat form after selective dissolution of the second blend component, even after preparation of fabrics or knitted articles from the blend yarn, can be used as a starting material for preparation of nanostructured single polymer composites. A PET nanofibrillar SPC prepared via hot compaction using one constituent shows a modulus competitive with that of the glass fiber/PE (40/60 by wt) composites. 

Fundamental contributions to the field of single polymer composites were made by Ward et al. (e.g., [4—12]). They not only succeeded to prepare SPCs of large number of homopolymers, to develop new techniques for their manufacturing but they also patented [8] and commercialized products with SPC structure. Interesting contribution to SPCs was made also by J. Karger-Kocsis demonstrating that such composites can be prepared using the polymorphic phenomenon in polymers (e.g., [13]). And, finally, to the SPCs was recently added the family of nanofibrillar... 

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