Filled composite materials, study

Applications. ESR spectroscopy was used to monitor the orientation and distribution of filler particles in polymer composites, " and molecular movement in filled, crosslinked material was studied. ... 

Parallel-plate rheometers are often more useful for studying rheology of filled polymers or composite materials, particularly when the size of the fillers is comparable fo fhe disfance between the truncated cone and the surface of the plate. Again, the torque M and the normal force N tending to separate the two plates are measured. In steady-shear flow, the shear rate and the shear stress at the edge of the disks located atr = R are given by... 

Dynamic rheometry was not (and, apparently, cannot be) employed for studying melt fracture of neat plastics and composite materials. This has been done so far only using capillary rheometry. However, dynamic oscillatory measurements can produce the most reliable rheological data on filled polymers [2,4]. It should be noted that measurements at dynamic oscillatory conditions bellow frequency of 0.1 rad/s likely produce erroneous results due to the increased time for reaching steady state at low frequencies [4]. 

The calculated dimensions D, based on the aforementioned method, are adduced in Table 6.2. The values for the studied nanocomposites are varied within the range of 1.10-1.36, i.e., they characterize more or less branched linear formations ( chains ) of nanofiller particles (aggregates of particles) in elastomeric nanocomposite structure. Let us remind that for particulate-filled composites polyhydroxyether/graphite, the value changes within the range of 2.30-2.80 [4, 10], i.e., for these materials filler particles network is a bulk object, but not a linear one [36]. 

Experimental [23] as well as theoretical [24-26] studies of percolation phenomena have been reported. In random and macroscopically homogeneous materials it has been demonstrated [27-29] that at concentrations of metal particles below the percolation threshold (p < Pc) a short-range percolation coherence length, exists. Electrical conductivity is probable for length scales less than Thus even if the metal-filled composite exhibits no bulk electrical conductivity, conduction can occur within domains that are smaller than As the concentration of metal particles approaches oo and the composite becomes isotropically conductive. 

The second, obvious application is studying polvmer-filler interactions in filled and reinforced composites. Some data are presented for wollastonite and quartz filled Bisphenol-A based and cycloaliphatic epoxies [6]. These data show, that Tg shifts observed by different relaxation methods (dielectric spectroscopy, DSC, thermomechanical measurements) are not necessarily the same (Table 1.), they depend on the effective frequency, changes in activation energy have also to be taken into account. Correlations between Tg shift and polymer adsorption can be understood using Lipatov s theory [7]. Positive Tg shift usually indicates strong adhesion, while negative Tg shift can be explained by the fact that the adsorbed polymer layer forms a looser structure than that of the bulk material. If both the neat resins and their composites are studied dielectrically, the origin of the low-... 

On the other hand, when the effects of aging on calcium sulfate-filled PLA composites were studied for 1 year under a normal environment, molecular, thermal, and viscoelastic properties showed that the performance of the PLA-calcium sulfate composites was maintained after aging [25]. The storage modulus of the samples actually increased after aging. The structural reorganization of the PLA material in terms of increase of local order in the amorphous phase of PLA was thought to be responsible for such behavior. 

In the indirect method, surface-modified whiskers are filled into polymers to prepare composite materials and the surface modification effects of whiskers can be evaluated by studying characteristics of composites, such as mechanical, thermal, and electrical properties. This method is the most often used. 

Li et al.33 studied the performance of PEEK composite cofilled by calcium carbonate whiskers and polytetrafluoroethyl-ene (PTFE) and found that under dry friction conditions, filling calcium carbonate whiskers significantly reduces the friction coefficient and wear rate of composite materials. Both properties decrease with an increasing amount of whiskers. The composite material still has very good comprehensive friction when the whisker content is 30%. 

The development and the application of polymeric composite materials filled with nanosized rigid particles (essentially inorganic) has attracted both scientific and industrial interest. The development of new polymer electrolytes is needed for many kinds of electrochemical applications such as separators in high-energy density lithium batteries. Poly(oxyethylene) (POE)-based polymer electrolytes are the most commonly studied, due to their cationic solvation ability [188]. 

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