Rubber filler-matrix interaction

ESR has been used to investigate the role of the filler-matrix Interaction in filled rubbers at cryogenic temperatures (10). The breakdown In adhesion between filler and matrix results In vacuoles or voids in the material. Figures 3 and 4 show a contrast In behavior for Sp glass spheres In rubber with and without a silicone coupling agent treatment. In the first case strength Is low and very few free radicals are produced... 

Micron-sized fillers, such as glass fibers, carbonfibers, carbon black, talc, and micronsized silica particles have been considered as conventional fillers. Polymer composites filled with conventional fillers have been widely investigated by both academic and industrial researchers. A wide spectrum of archival reports is available on how these fillers impact the properties. As expected, various fundamental issues of interest to nanocomposites research, such as the state of filler dispersion, filler-matrix interactions, and processing methods, have already been widely analyzed and documented in the context of conventional composites, especially those of carbon black and silica-filled rubber compounds [16], It is worth mentioning that carbon black (CB) could not be considered as a nanofiller. There appears to be a general tendency in contemporary literature to designate CB as a nanofiller - apparently derived from... 

In view of the long history of research efforts on filled rubbers, it is not surprising that the initial works on filled polymer blends appeared in publications authored by rubber compounders and carbon black vendors [17, 18]. For instance, Walters and Keyte [17] observed that the compound ingredients, such as CB and zinc oxide, were not homogenously dispersed in rubber blends. Hess et al. [18] also reported a series of fundamental observations. First, they observed that filler particles tend to remain in the lower viscosity phase, in the absence of significant filler-matrix interactions. However, in the presence of strong polar-polar interactions between the filler particles and one of the phases, the particles were found to be selectively dispersed in the more polar phase and the viscosity became less important. More recently. Portal et al. [19] also presented similar observations about selective localization of CB particles in the natural rubber (NR) phase in NR/ polybutadiene blends. 

Abstract The present chapter is written as an introduction towards this book on nonlinear viscoelasticity of rubber composites and nanocomposites. Rather than introducing the concept of the book to the readers this chapter reveals the basics behind rubber viscoelasticity and explains both linearity and nonlinearity from this behavior. Various filler reinforced rubbers are introduced emphasising the flow behavior of such nanocomposites. Major mathematical models proposed by Kraus, Huber and Vilgis and Maier and Goritz for the Payne Effect are briefly addressed based on the filler matrix interactions existing in the composite systems. 

It is well known that the lower the AGM value, the better is the rubber-filler interaction. As for the Ch/MEK solvent combination x is zero, hence the A CN, cp2X term of (27) is zero for such a solvent combination. In all other solvent combinations, where x 0. the A l N r tp2X term of (27) is positive. Thus, AGM of the system for the Ch/MEK solvent combination is the least, and dispersion (if clay is in the rubber matrix) is also best in this solvent combination, giving rise to the highest polymer-filler interaction. 

Figure 8.62 shows the compression set of rubber with different fillers at 1 1 proportion to rubber.Fillers, such as precipitated calcium carbonate, whiting, calcinated clay, each of which have limited interaction with the matrix give a substantially lower compression set. As the interaction between filler and the matrix... 

In the case of filled vulcanizates, the reinforcement efficiency depends on a complex interaction of several filler-related parameters including particle size, particle shape, particle dispersion, surface area, surface activity, structure of the filler, and interactions between the fillers and the rubber matrix. 

In addition, the layer structure of the clay in the nanocomposite can strongly restrict the motion of rubber molecules and hinders the propagation of the crack during tearing. These results indicate that 50 phr of silica can be replaced by 4 phr of OC with a reduction of the filler content by 12.5 times without adversely affecting the final properties of the material. The enhancement of the mechanical properties is due to the better dispersion of OC in the NR matrix and strong rubber-filler interaction. 

In order to determine the influence of rubber matrix polarity on filler dispersion and rubber-filler interaction, two kinds of rubber NBR and SBR, were chosen. SEM pictures of the rubber vulcanizates, filled with reference and 48 min plasma treated wollastonite, are presented in Fig. 12.4. Morphology of SBR/wollastonite samples does not reveal any changes, explaining strengthening of the material (see Section 12.3.3). 

Pictures of NBR-W-REF samples (Fig. 4a, b) present broken needles of wollastonite in the area of fracture, whereas in the case of NBR-W-48 sample (Fig. 4c, d) needles of wollastonite are non-broken but pulled out fi om rubber matrix. This change to morphology, reflected by lower rubber-filler interactions, responsible for worse mechanical properties of rubber vulcanizates (see Section 12.3.3), is undoubtedly the result of an increase of SFE polar component of filler after plasma treatment. The SEM pictures of the vulcanizates, no matter, containing virgin or modifies wollastonite particles, do not reveal any filler agglomeration. 

The level of measured improvements in toughness attributed to liquid rubber additives is somewhat dependent on the type of test performed as well as the specific SMC recipe. The toughening mechanisms in effect for rubber modified SMC materials have not been well documented. The presence of a low profile additive (LPA), mineral filler, and glass fibers affects the dispersion of the rubbery additive and its effectiveness in toughening the polyester matrix. Interactions between the rubbery additive and each of the typical SMC components have not been well researched. 

Abstract This chapter describes the influence of three-dimensional nanofillers used in elastomers on the nonlinear viscoelastic properties. In particular, this part focuses and investigates the most important three-dimensional nanoparticles, which are used to produce rubber nanocomposites. The rheological and the dynamic mechanical properties of elastomeric polymers, reinforced with spherical nanoparticles, like POSS, titanium dioxide and nanosdica, were described. These (3D) nanofillers in are used polymeric matrices, to create new, improved rubber nanocomposites, and these affect many of the system s parameters (mechanical, chemical, physical) in comparison with conventional composites. The distribution of the nanosized fillers and interaction between nanofUler-nanofiUer and nanofiller-matrix, in nanocomposite systems, is crucial for understanding their behavior under dynamic-mechanical conditions. 

In the rubber industry the distribution of particle size is considered to be important as it affects the mechanical properties and performance. Aggregate size also varies with particle size. Aggregates can have any shape or morphology. The fundamental property of the filler used in a filled elastomer is the particle size. This affects the reinforcement of elastomer most strongly. One of the sources of reinforcement between the carbon black surface and the rubber matrix is the van der Waals force attraction. Also, rubber chains are grafted onto the carbon black surface by covalent bonds. The interaction is caused by a reaction between the functional group at the carbon black particle surface and free radicals on polymer chains. Hence, filler-rubber interface is made up of complex physical-chemical interaction. The adhesion at the rubber-filler interface also affects the reinforcement of rubber. When the polymer composites are filled with spherical filler (aspect ratio of the particle is equal to unity), the modulus of the composite depends on the modulus, density, size, shape, volume ratio, and number of the incorporated particles. 

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