Filler modification affects

Filler modification affects the viscoelasticity since the variation in storage modulus with strain changes with rate of dispersion. This is illustrated in Fig. 6. The unmodified fillers in mbber cause agglomeration and thus result in high Payne effect due to strong inter-aggregate interaction of filler. With modification, the Payne effect of the filled compounds changes as the filler-filler networks is... 

Modification of filler s surface by active media leads to the same strong variation in viscosity. We can point out as an example the results of work [8], in which the values of the viscosity of dispersions of CaC03 in polystyrene melt were compared. For q> = 0.3 and the diameter of particles equal to 0.07 nm a treatment of the filler s surface by stearic acid caused a decrease in viscosity in the region of low shear rates as compared to the viscosity of nontreated particles more than by ten times. This very strong result, however, should not possibly be understood only from the point of view of viscometric measurements. The point is that, as stated above, a treatment of the filler particles affects its ability to netformation. Therefore for one and the same conditions of measuring viscosity, the dispersions being compared are not in equivalent positions with respect to yield stress. Thus, their viscosities become different. 

The formation of polymer-filler nanocomposite affects the thermal behavior of the matrix because the well-dispersed nanofillers lead to modification of the degradation pathways [165-168]. This concept was first introduced by researchers from Toyota [169] who discovered the possibility to build nanocomposites from nylon-6... 

The -potential of colloidal silica surface treated by acrylate copolymers is affected by pH. The -potential of untreated colloidal silica at a pH of 4 is -7 mV and it decreases to -32 mV at a pH of 7. Modification of the surface of colloidal silica changes its surface properties and behavior. In another study on filler modification, hydroxyapatite was modified for medical applications with several differ-... 

Figure 3.38 shows that reaction between Al(0H)3 and dicarboxylic acid anhydride affects the sedimentation volume of filler.The limiting value of sedimentation was obtained by modifying the filler surface with a monolayer of a suitable modifier. A similar modification affects the performance of this filler in polymer-filler composites. Thus, different properties were affected by the surface coverage of filler and by the filler-matrix interactions. 

The surface modification technique of inorganic fillers directly affects the filling modification. The common surface modification methods can be classified into three types inorganic filler pretreatment, blending, and masterbatch methods. 

The permeability of small penetrant molecules through an organic matrix is determined by the solubility and diffusivity of the small molecule in the matrix as well as by the mean-square displacement (total path length traveled) divided by the sample thickness. In principle, the addition of a filler in the polymer matrix is expected to affect the solubility and diffusivity of a penetrant molecule, especially in the vicinity of the filler (i.e in the filler-polymer interfacial region and at least one polymer Rg away from the filler surface). Also, it is expected that fillers will affect the path tortuosity (mean-square displacement of penetrant versus film thickness) directly, when penetrants are forced to travel around impermeable fillers, and indirectly, when fillers induce polymer chain aUgnment or alignment and modification of polymer crystallites. ... 

Certain types of fillers, even though unreactive, will affect the pot life and exotherm of the adhesive system. Generally, modifications of cure or reactivity are not the prime functions of... 

Nanotube nanocomposites with a large number of polymer matrices have been reported in the recent years. The composites were synthesized in order to enhance mechanical, thermal and electrical properties of the conventional polymers so as to expand their spectrum of applications. Different synthesis route have also been developed in order to achieve nanocomposites. The generated morphology in the composites and the resulting composite properties were reported to be affected by the nature of the polymer, nature of the nanotube modification, synthesis process, amount of the inorganic filler etc. The following paragraphs review the nanocomposites structures and properties reported in a few of these reports and also stress upon the future potential of nanotube nanocomposites. 

Table 6.5 lists the properties affected by various filler modifiers. Table 6.5 is not given as a comprehensive list of applications of these fillers. Fillers and specific properties of filled materials are dealt in detail in other parts of the book. The table summarizes the types of changes which can be expected from modifications. 

All of these mechanisms which affect crosslink density were confirmed by experimental studies. The classic case of a reactive particle filler is silica filled polysiloxane (Figure 6.25). Silica particles have numerous OH groups which react with the crosslinking component of polysiloxane. Modification of silica by silanes reduces reinforcement. 

One function of a coupling agent is to interact with filler. It is thus proven a priori that coupling agents affect filler properties, and modified fillers affect the system. Numerous works use this modification. In this discussion, we summarize the effects obtained. Table 13.1 contains this summary. 

Duvdevani(40) have been directed at modification of ionomer properties by employing polar additives to specifically interact or plasticize the ionic interactions. This plasticization process is necessary to achieve the processability of thermoplastic elastomers based on S-EPDM. Crystalline polar plasticizers such as zinc stearate can markedly affect ionic associations in S-EPDM. For example, low levels of metal stearate can enhance the melt flow of S-EPDM at elevated temperatures and yet improve the tensile properties of this ionomer at ambient temperatures. Above its crystalline melting point, ca. 120°C, zinc stearate is effective at solvating the ionic groups, thus lowering the melt viscosity of the ionomer. At ambient temperatures the crystalline additive acts as a reinforcing filler. 

Many physicochemical properties of fumed silica depend significantly not only on the primary and secondary particle size distributions but also on the concentration of adsorbed water (C ) in the form of intact molecules and =SiOH groups (Cqh) [1-3,6,7]. For instance, marked amounts of adsorbed water can negatively affect the characteristics of fumed silica as a filler of liophilic media or polymers. There are several methods to change C and Cqh such as chemical modification... 

The incorporation of fillers can induce modifications in the thermal properties of the polymers. Factors that affect the thermal conductivity of composites are the dispersion and orientation of the filler particles, the filler aspect ratio, and the relative ratio of thermal conductivity of the filler and the matrix. The thermal conductivity was found to be increased when the Ti02 volume fraction increases. The measured values of thermal conductivity have been compared to different theoretical models. 

Many factors such as adhesion between components, fiber topography, and kinetic parameters of crystallization of semicrystalline matrix have been reported to influence transciystallinity. The transcrystallinity phenomenon in the natural fibers/polypropylene system is affected by the different type of chemical treatment of lignocellulosic materials. Moreover, the ability of natural filler to induce nucleation in polypropylene matrix is also dependent on the kind of chemical modification of surface fibers. Predominant nucleation ability was found for unmodified fibers. However, chemical modification of fiber surface slightly depressed the nucleation of polypropylene matrixes. 

Surface modification can be introduced prior to the crystallization and it may affect the nucleation process. These modifications are now being discussed. One such common modification is coating of the surface of filler with organic coating, such as, for example. 

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