Composites nanofibrillar

Lin STC, Bhattacharyya D, Fakirov S, Matthews BG, and Cornis J. (2011) Comparison of nanoporous scaffolds manufactured by electrospinning and nanofibrillar composite concept 18th International Conference on Composites Material, JeJu, South Korea, August 22-26, 2011,... 

Mechanical Properties of PLA/PGA Nano-/Microfibrillar Polymer-Polymer Nanofibrillar Composites... 

Table 11.1. Tensile strength, a, and tensile modulus, E, (and their specific values, cjp and Ejp) of knitted and compression molded neat PP, PP/PET nanofibrillar composite and PP/glass fiber (GF) composite...

In this case study, the results of attempts to prepare nanofibrillar composite materials starting from nanofibrils are presented. This approach is based on (i) the concept of polymer/polymer NFCs produced by in situ formation using polymer blends, which have recently been manufactured by Fakirov et al. [33], (ii) on the opportunity to isolate aligned neat nanofibrils through selective dissolving of the second blend component, and (iii) subsequent consolidation via hot-compaction. 

The observed narioporosity demonstrates that in this type of composite, as well as in previously reported polymer-polymer nanofibrillar composites [111], the reinforcing elements are fused together in truss-like structures of single nanofibrils and not adhered in bundles or aggregates as is the case with other nano-sized materials used as reinforcement. 

However, PET-based nanofibrillar composites can be considered a member of this group of SPCs. These nanofibrillar PET composites were prepared by the two-constituent approach. Again, the extremely low crystallization rate of PET, as compared with other polymers, particularly with polyolefins, was utilized in this case. This fact allows one to prepare completely amorphous, transparent films via quenching the polymer melt. Duhovic et al. [51] explored this opportunity recently and prepared nanofibrillar SPC from PET. For this purpose, the authors used their experience gained from the development of polymer-polymer micro- (MFC) [52] and nanofibrillar composites (NFC). The starting material... 

In the present chapter, in addition to the description of these polymer-polymer composites, it is demonstrated that the reinforcing nanofibrils can be isolated as a separate material and used for completely different purposes. This nanofibrillar composites (NFC) concept [76] allows orre to trarrsform any polymer into a fibrillar nanomaterial suitable for further processing and apply it for technical or biomedical purposes. 

Directional, thermal and mechanical characterization of polymer-polymer nanofibrillar composites... 

Using the experience gained during the development of MFC, anothei- type of polymer-polymer composite, the nanofibrillar composites could be developed. For this purpose, two immiscible polymei-s, PP and PET in the present case, were intimately melt blended in a twin screw extruder and further spun as textile fibers with a diameter of 30 pm. After thermal treatment of knitted samples above the of PP but below the of PET, one obtains a composite structure where the isotropic PP is reinforced with PET nanofibrils with diameters of 50-150 nm and an aspect ratio of up to 7000. The NFC shows an improvement of Young s modulus of 50% and tensile strength of 22% as compared to the neat PP. 

Inspired by the intrinsic deformation nature of polymer melt, various proposals have been put forward to constmct particular structure in polymer blend, aiming at the achievement of excellent performance. One of the typical examples is the methodology of in situ micro/nanofibrillation, in which, under the process of melt extrusion-hot stretching-quenching, the spherical dispersion domains in situ deform into micro/nanofibrils, realizing the scalable achievement of in situ micro/nanofibrillar composites, accompanied with greatly improved mechanical... 

Fig. 8.2 Scanning electron micrograph (SEM) images of LDPE/iPP a common blend, higher magnification image is inserted b in situ nanofibrillar composite (the flow direction is indicated...

Fig. 8.4 Morphological observation of in situ fibrils in the nanofibrillar composites. SEM images of cryofracture surfaces of al PLA/PBS (90/10), bl PLA/PBS (80/20), and cl PLA/PBS (60/40) composite samples. a2, b2, and c2 present the fibrillar morphology of PBS after etching the PLA matrix of al, bl, and cl, which produce the quantitative analyses in terms of the distribution of PBS nanofibrils as shown in a3, b3, and c3, respectively. The average diameter (D) is marked in the right up comer of a3, b3, and c3...

F. 8.7 Selected 2D-SAXS patterns of LDPE/iPP in situ nanofibrillar composite during heating from room temperature to 150 °C and cooling from 150 °C to room temperature. The right model illustrates the crystalline structure of iPP nanofibrils (The flow direction is vertical)... 

Fig. 8.9 SEM micrographs showing crystalline filaments of PLA at PBS nanofibrils for a PLA/PBS (90/10), b PLA/PBS (80/20), and c PLA/PBS (60/40) composite samples. Cryofracture surfaces of in situ nanofibrillar composites after etching the amorphous PLA component are employed for SEM observation. The existence of 40 wt% PBS makes it difficult to clearly expose the lamellar stmcture in c during the same etching processing. The big arrows indicate the stretching direction, while the small brown and yellow arrows refer to the nanofibrils serving as hybrid shish and oriented PLA lamellae, respectively...

Excellent and Comprehensive Mechanical Properties of In Situ Nanofibrillar Composites... 

Fig. 8.11 Tensile strength, Young modulus, and elongation at break of a pure LDPE b LDPE/iPP common blend c LDPE/iPP in situ nanofibrillar composite with epitaxy structure d LDPE/iPP in situ nanofibrillar composite with NHSK structure e pure iPP...

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