Network filler reinforcement

Monte Carlo computer simulations were also carried out on filled networks [50,61-63] in an attempt to obtain a better molecular interpretation of how such dispersed fillers reinforce elastomeric materials. The approach taken enabled estimation of the effect of the excluded volume of the filler particles on the network chains and on the elastic properties of the networks. In the first step, distribution functions for the end-to-end vectors of the chains were obtained by applying Monte Carlo methods to rotational isomeric state representations of the chains [64], Conformations of chains that overlapped with any filler particle during the simulation were rejected. The resulting perturbed distributions were then used in the three-chain elasticity model [16] to obtain the desired stress-strain isotherms in elongation. 

Load Sharing of Filler Particles. Comparison of ultimate strength of a propellant and its unfilled binder matrix almost always shows that the propellant has up to several times the tensile strength of the matrix. This filler reinforcement is presently thought to stem from additional crosslinks formed between filler particles and the network chains of the binder matrix (5, 8, 9, 34). Effective network chains are defined as the chain segments between crosslinks. From the classical theory of elasticity, the strength and/or modulus of an elastomer is proportional to the number of effective network chains per unit volume, N, or... 

A filled rubber may be regarded at once as a two-phase composite material and as a polymeric network containing giant multifunctional cross-links. Neither concept alone leads to very useful generalizations. The physical properties of a filled vulcanizate do not appear capable of close description in terms of the component filler and rubber properties. On the other hand no degree of cross-linking per se produces effects identical to filler reinforcement. 

B. If fillers act as additional fixed cross-links of the rubber network, why reinforcing effects are not alike to gum network with additional cross-links ... 

Finite elements analysis has shown that filler properties such as surface area, shape and structure have strong infiuence on the filler reinforcement and filler rubber properties. Another approach to understand the filler network and the filler-rubber interactions more closely is to study the electrical and mechanical behaviour of the filled elastomer under strain for various different conditions. Jha et have investigated the effect of surface area and structure of filler... 

A number of specialized elastomeric quantities have also been investigated. PDMS networks have been particularly useful in investigating the Mullins Effect, in which filler-reinforced elastomers exhibit a reduction... 

In a filled rubber, agglomeration of the particles produces a filler network, in addition to the network of covalently-bonded polymer chains. In fact, Reichert et al. [30] modeled the deformation of single network of filled rubber as a double network, adopting an approach similar to that used to analyze unfilled double networks [35-37]. This implies that double-network mbber reinforced with filler can be viewed as a composite of three distinct networks. 

It should be noted that the ability of the filler to form the structural network is largely responsible for its reinforcing action [28, 33], These aspects of the problem have been discussed at length in a number of monographs (e.g. [7, 53, 54]) and we do not think it proper to dwell on them here. On the other hand the structurization in melt increases the viscosity of the material and hampers its processability. 

Mark and his co-workers reported the reinforcement of poly(dimethylsiloxane) networks by silica gel particles [1-6]. For example, bis(silanol)-terminated poly-(dimethylsiloxane) was reacted with tetraethoxysilane in the presence of acid-catalyst to produce the reinforced siloxane networks. The reaction proceeded homogeneously. The content of the silica filler can be controlled by the feed ratio of polysiloxane and tetraethoxysilane. 

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