Permanent nanocomposite

Generally, isotropic permanent magnets with a remanence ration JJJS > 0.5 are referred as remanence enhanced materials. However, the theoretical limit for the remanence of noninteracting grains depends on the crystal symmetry, the crystallographic orientation of the easy directions, and the volume fraction and the saturation polarization of the phases. The remanence ratio a two-phase nanocomposite magnet is... 

Journal of Materials Science 38, No. 10,15th May 2003, p.2143-7 PREPARATION OF NANOCOMPOSITE FIBERS FOR PERMANENT ANTIBACTERIAL EFFECT... 

PP/silver nanocomposite fibres were prepared with the aim of achieving permanent antibacterial activity in a common synthetic textile. The fibres were melt-spun by coextmsion of PP and PP/silver masteibatches using general conjugate spinning. Masteibatches were made up of a mixture of PP chips and nano-sized silver powder. The antibacterial efficacy of spun fibres was high when the masteibatch was used as the sheath rather than the core. The antibacterial activity of nano-silver in fibres was evaluated after a certain contact time and calculated by percent reduction of two types of bacteria. Staphylococcus aureus and Klebsiela pneumoniae. DSC and wide-angle X-ray diffraction were used for analysis of stractuie, thermal properties and crystallisation behaviour of the spun fibres. SEM was carried out in order to observe particle distribution on the nanocomposite fibres. 17 refs. (2nd International Conference on Polymer Fibres, Manchester, UK, July 2002)... 

The nanocomposite PET-PEN/MMT clay was smd-ied under steady shear, instantaneous stress relaxation, and relaxation after cessation of steady flow [83]. Relaxation times of the slow mode in instantaneous stress relaxation were longer for the systems that have presumably permanent crosslinking networks (PET-PEN) or dynamic networks (PET-PEN-MMT). These results are consistent with those found in relaxation after cessation of flow (Fig. 31.4). Nanoclay addition somehow restricts the slow relaxation (due to polymer-particle interactions). The nanocomposite exhibits lower steady-state viscosity as compared to the polymer-matrix system. This is thought to be caused by polymer-polymer slipping, as revealed by the SEM observations (Fig. 31.5a and b). 

Yuan, M.,Brokken-Zijp,J., and de With, G. 2010. Permanent antistatic phthalocyanine/epoxy nanocomposites— Influence of crosslinking agent, solvent and processing temperature. Eur. Polym. J. 46 869-880. 

Polymer nanocomposite properties are related to a variety of parameters, among which the most important are the features of the constituent phases, the dispersion and the interfacial interaction between the nanomaterials and the matrix [33,39], Nanomaterials tend to agglomerate due to Van der Waals forces in order to achieve a stable dispersion in polymers that lack a permanent dipole moment or suitable mechanism to favorably interact with carbon nanomaterials, physical or chemical modification of either the nanofiller or the polymer matrix is necessary [39],... 

Fig. 12 SME of a nanocomposite consisting of magnetic nanoparticies and a poiyethemrethane matrix induced in an alternating magnetic field H = 30kAm / = 258kHz) generated in an inductor. Upon stimulation the nanocomposites transforms within 24 s from the rod iike temporary shape into the spiral like permanent shape, (Reproduced with permission of Nature Publishing Group, http //dx.doi.org/10.1038/nature03496)...

Cyclic, thermomechanical tensile tests were performed for the nanocomposites with POSS/polyol ratio = 2.63 (see Fig. 15b). The sample was firstly heated to 80°C (T > Tg) and deformed (1) by ramping to a load of 0.3N. The sample was cooled under this load (2) to 10°C, to fix the temporary, elongated shape. After unloading (3) the sample was heated (4) to 80°C to recover the permanent shape. The first cycle showed about 5% creep occurring between the elongation and fixing step over... 

Fig. 21 Series of photographs showing the macroscopic SME of a nanocomposite from TFX and 10 wt% magnetic particles. The permanent shape was a plane stripe and the temporary shape was a corkscrew-Uke spiral. The pictures show the transition from temporary to permanent shape in a magnetic field of / = 258kHz and H = 30kAm generated in an inductor. Reprinted by permission from ref. [85]. Copyright 2006, National Academy of Sciences, U.S.A.

The SME of this nanocomposite fiber was investigated by heating the fiber to 70°C, and stretching it to 100% strain at a speed of 10mm min . The fiber was cooled to ambient temperature (22°C) while keeping the applied stress. After unloading, the fiber was heated to 70°C under stress-free condition to recover its original permanent shape. This cycle was repeated four times for each fiber. The Rf N) and Ri N) at the Ath cycle as well as the total recovery ratio / rtot(/V) after Ath cycle were calculated and are listed in Table 2. 

Most commonly used layered silicate is montmorillonite clay, which is composed of micron-sized particles. The particles are constructed of platelets with thickness of lnm and width of 100-200 nm. Platelets have permanent negative charge and they are held together by charge balancing cations such as Na" or Ca [2-i] ions. The significant disruption of individual silicate layers in polymer matrix with nanoscopic dimensions (exfoHated structure) leads to improvements of the nanocomposite properties. However, in many cases, the isolated silicate layers are not completely dispersed throughout the polymer matrix, instead, the clay particles in polymer matrix maintain the hierarchical architecture, and an interlayer expansion occurs (intercalated structure). 

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