Friction polymer-filler

Next 129Xe experiments on an EPDM terpolymer, which is present as the elastomer component in a composite material with carbon black will be discussed. The question investigated for these materials is whether the existence of any polymer-filler interaction can be detected by 129Xe NMR. This interaction influences the mobility of the elastomer chains in a relatively large shell around the filler particles. This fraction is called the bound rubber fraction. It is generally believed that the bound rubber fraction influences the mechanical and frictional properties of the filled elastomer [17, 18]. 

The concept that friction between filler particles and breakdown of filler network is heat generating is applied to an understanding of the fusion behaviour of PVC. It is shown that the treatment of a PVC melt as a filler-containing polymer provides information on the anomalous effects observed in the rheological properties of PVC and that differences in the fusion behaviour of PVC compounds containing different impact modifiers and lubricants can be explained with the aid of this approach. 17 refs. 

PTFE is a unique polymer in the formulation of composites, since it may be either the material of the matrix or a friction-reducing filler. It is a very soft polymer, which in the absence of reinforcement will wear rapidly, and it will cold flow under load. As a matrix material it must therefore be effectively reinforced. As a friction-reducing filler it may be used in the form of particles or fibres. Table 12.6 shows the effect of different fillers on the properties of PTFE. Spengler et aP reported an... 

Polymer Filler Amount, wt% Dynamic coefficient of friction... 

Tribo-chemical Wear. Besides the above three wear mechanisms, we should discuss tribo-chemical wear. Tribo-chemical wear(7) takes many forms. Some of these wears result from the interactions of the polymer with its environment, e.g., oxygen, ozone, heat (e.g., friction heat), surface contaminants, etc.- The application of mechanical energy at the interface can also cause mechanochemical degradation(35) to generate free radicals which can further lead to cross-linking or other interactions. In the composites, polymer-filler interactions can also take place through mechanochemical mechanisms. 

Their mechanism can be presented as follows. During thermal treatment, FO contact the polymer melt and the oxides partially reduce to metals [72]. This leads to the generation of microchains M1-P-M2 in the lubricant bulk and formation of an MPE as a result of electrochemical interactions of unlike metal components. As a consequence, adhesive interactions between the filler and binder intensify. In our view, the high level of antiscoring properties and low friction coefEcient can be attributed to the catalyzing effect of the reduced metals on the formation of the friction polymers from the products of mechanical destruction of organic components of the lubricant. 

During repeated flexing of a viscoelastic material, such as rubber, heat is produced internally. This results from the fact that the rubber is not perfectly elastic but is a viscoelastic material. The viscous element of the rubber leads to internal frictional heating on repeated cycling. This is influenced strongly by the nature of the polymer and its crosslink structure. It is also affected by the filler system in use and the polymer-filler interface. 

There was proposed another view on the mechanism of reinforcement of plastics. The main factor in reinforcement is ascribed to the forces of friction at the polymer-filler interface, which determine the possibility of their joint functioning. These forces occur as a result of shrinkage of the poljnner on curing. In this case, the elasticity and stressed state of the ciued binder in the layers contacting the siuface of the fibers are the decisive factors, not the adhesion. ... 

Matrix polymer Nano-filler Surface treatment Lowest wear rate " (10 mm /Nm) Filler loading corresponding to the lowest wear rate Lowest frictional coefficient Filler loading corresponding to the lowest frictional coefficient Ref. 

It is well known, that under industrial conditions a method of introducing filler into the polymer mixture is used. In this case, the filler is introduced in the form of paste containing up to 60 per cent water in order to reduce viscosity, As heating is affected by viscous friction, the temperature conditions are not stable on mixing and, therefore, conductivity of the conducting polymer composite becomes unreproducible. Up to now this factor has not been taken into consideration. 

Tribological filler Polymer Coefficient of friction Wear (arbitrary unit)... 

For hundreds of years sticky surfaces have been dusted with powder (e.g., talc) to keep them separated. Talc is broadly used in cable and profile extrusion to obtain a smooth surface. Similarly, in injection molding, the application of aluminum trihydroxide gives a better surface finish. Talc, CaCOs, and diatomite provide anti-blocking properties. Graphite and other fillers decrease the coefficient of friction of materials. PTFE, graphite and M0S2 allow the production of self-lubricating parts. Here, PTFE, a polymer in powder form, acts as a filler in other polymers. Matte surfaced paint is obtained by the addition of silica fillers. 

Polytetrafluoroethylene, molybdenum disulfide, graphite, and aramid fibers reduce the frictional coefficient. These may be used as single friction additive, in combination with other fillers, and in combination with silicone oil. Table 5.17 illustrates effect of PTFE on the frictional properties of different polymers. 

Shang et al. (1995) show that the work of adhesion between a silica filler surface and a polymer matrix is directly related to the dynamic viscosity and moduli. Additionally, at lower frequencies there is a greater influence of the work of adhesion. The influence is shown to be described well by an effective increase in interphase thickness due to the increase in the work of adhesion, such that polymer chains are effectively immobilized around the filler, and the friction between the immobilized layer and the polymer then governs the dynamic rheology. It was noted that the immobilized layer could be reduced in extent at higher frequencies. 

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