Unfilled systems

Figure 7 also shows the plots of (tan8)//(tan8)g versus volume fraction of the filler (0) at Tg and T. Here / stands for the silica filled system and g denotes the gum or unfilled system. The results could be fitted into the following relations [27] ... 

Note that, apart from the filler particle shape and size, the molecular mass of the base polymer may also have a marked effect on the viscosity of molten composites [182,183]. The higher the MM of the matrix the less apparent are the variations of relative viscosity with varying filler content. In Fig. 2, borrowed from [183], one can see that the effect of the matrix MM on the viscosity of filled systems decreases with the increasing filler activity. In the quoted reference it has also been shown that the lg r 0 — lg (MM)W relationships for filled and unfilled systems may intersect. The more branches the polymer has, the stronger is the filler effect on its viscosity. The data for filled high- (HDPE) and low-density polyethylene (LDPE) [164,182] may serve as an example the decrease of the molecular mass of LDPE causes a more rapid increase of the relative viscosity of filled systems than in case of HDPE. When the values (MM)W and (MM)W (MM) 1 are close, the increased degree of branching results in increase of the relative viscosity of filled system [184]. 

Fibrous fillers have often been reported to increase considerably 1 in comparison with unfilled systems [171,176, 189, 197, 198]. In this case, however, the inlet loss is due not to the highly elastic properties of the melt but to other reasons, such as pushing of the binder through the package (plug) of filler in the inlet zone. Pushing of the filler package forth into the channel, etc. 

According to AFM micrographs, the surface roughness of porous spheres of DMN-DVB copolymer increases in the presence of methyl-containing silica. At the same time, the availability of methylsilyl and silicon hydride groups on the silica surface promotes surface smoothing upon filling, similar to an unfilled system. 

Another possibility mentioned above is the addition of nanoscale particles to a liquid matrix system where the nanoscale particles are grown outside of the system. Experiments have been carried out with boehmite in a matrix derived from Si(OR)4/Al(OR)3 and glycidyloxypropyl triethoxy silane (GTPS) [22]. Even the addition of 5 % by volume of y-alumina or boehmite leads to systems which show a remarkably increased scratch-resistance compared to the unfilled material. The optical transparency is not influenced if the particle size of the boehmite is below 20 or 30 nm. In Fig. 21 the scratch resistance by the Vickers diamond test of the unfilled system is compared to the filled system and, as one can see, the scratch resistance is increased remarkably. 

In this study, both the normal mode relaxation of the siloxane network and the MWS processes arising from the interaction of the dispersed nanoclay platelets within the polymer network have been observed. Although it is routine practice to observe the primary alpha relaxation of a polymeric system at temperatures below Tg, in this work it is the MWS processes associated with the clay particles within the polymer matrix that are of interest. Therefore, all BDS analyses were conducted at 40°C over a frequency range of 10 to 6.5x10 Hz. At these temperatures, interfacial polarization effects dominate the dielectric response of the filled systems and although it is possible to resolve a normal mode relaxation of the polymer in the unfilled system (see Figure 2), MWS processes arising from the presence of the nanoclay mask this comparatively weak process. 

For the investigation and prediction of the mixing efficiency at the processing of solid filled systems, as well as for the interpretation of test results, the same approach is useful as described earlier for the processing of unfilled systems. 

The filler presence affects constants which can be used in comparison with the unfilled system. 

Rheological properties of filled systems are complex and formulation specific, largely dependent on fillers and other materials, especially materials which form a matrix.Flow through tubes demonstrates the unusual properties of filled system. Plug flow is typical of filled systems much different from the characteristics of unfilled system. This phenomenon is frequently observed with highly filled systems which behave in a manner similar to both solids and liquids. 

The process of crystallization is slower in filled than unfilled system (the right halves of photographs)... 

PHYSICAL PROPERTIES OF SOME POTENTIAL ENCAPSULANTS (Unfilled System)... 

Small nitrile-rubber inclusions in epoxy resin electrical en-capsulants have been examined in both amine (29-31) and acid (32) epoxy cures, in filled and unfilled systems. The value of rubber inclusion in a boron trlfluorlde/amine complex epoxy cure has also been demonstrated (33), where elevated-temperature, high-humldlty testing showed electrical properties retention to be better than a comparable system cured with dodecenylsucclnic anhydride. Rubber benefits low-temperature properties specifically and thermocycling in general. It affects high temperature insulation properties negatively therefore, the amount of rubber incorporated must be judiciously chosen. 

It is only fair to say that the trade literature [17] is emphatie that it is critical to use the correct amount of titanate eoupling agent. The use of excessive amounts is probably the most significant factor in application failure tests. It is strongly recommended that selected titanates should be examined in a range of concentrations from 0.1 to 2.0% by mass in a filled system and even lower for unfilled systems. Excess titanate will result in unreacted alkoxy groups on the surfaee and in a loss of adhesion of the polymer. This could lead to the mistaken eonclusion that a particular titanate was unsuitable or even harmful. 

Self-leveling floors are produeed from low-viscosity epoxy systems. Low-exotherm, unfilled systems are preferred. The entire floor should be cast in one operation, and thickness should preferably be at least 5 mm over the entire area. Because of their excellent chemical resistance to a wide range of chemicals, epoxies are often selected for flooring in chemical plants. Systems vary from trowelable to pourable or brushable and are usually filled. Choice of hardener and filler will depend on the specific chemicals encountered. Although tables of chemical resistance from suppliers will aid in selection of a suitable system, this system should always be tested using the chemicals that the floor is expected to withstand. 

The high damping capacity of filled viscoelastic polymers makes them useful as vibration-damping materials (Thurn, 1960) damping is not only increased, but high damping exists over a wider range of temperature than in an unfilled system (see Section 13.5). 

Combination of equation (12.33) with an approximation for the ratio of permeability in the filled (PJ to the unfilled system (Pp) (Barrer et ai, 1963 Michaels and Bixler, 1961),... 

ESR signals increases with increasing initial strain. The intensity of ESR signals of filled and unfilled SBR vulcanizates are dilferent from each other due to the dilference in the degree of chain scission caused by the considerably higher mixing torque for silica filled system than that for unfilled system. 

Lower cost than polymers Can replace more costly resins Maintain or improve desired properties over unfilled systems... 

Polymer-filler interactions have been studied by deuterium NMR spectroscopy. In unstrained networks, two regions of local chain mobility were identified, that within the absorption layer and that outside. In a uniaxially strained sample, the chains were immobilized near the filler surface. Chain order is increased in filled systems relative to unfilled systems (390). Molecular orientation... 

This equation deals with the temperature-depeaidence and crystallite-size- dependence of crystallinity. Frequently, the crystallization half-time, Xm, is reported in the research data. The time to reach one half of the total crystallization is Xyi. The time to achieve maximum crystallization isX (o°). Figure 10.2 shows the relationship between X a and temperature, T, for silica-filled PDMS. The value for x (o°) is higher for the filled system than for the unfilled system. The value increases as the temperature increases. Only a small difference was noted for two different filler loadings. The temperature shift shows that less supercooling is required with the filled than with the unfilled system. Fillers produce a nucleation effect which initiates the crystallization process. ... 

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