The Performance of Fillers

The intimacy of the filler/matrix bond is the main key to the performance of fillers and. with the latest technology, it is possible to achieve very good dispersion and an almost molecular bond. Tiny filler particles - sub-microscopic and also nanosized - have been shown to produce better mechanical properties at considerably lower loadings, and also give better flow, high barrier properties, inherent flame retardancy, and different surface textures in the same moulded part. 

The performance of fillers can be improved by the use of combinations of organic fire retardants and mineral fillers. Substantially better results can be ob-... 

Fillers have been used in the formulation of rubber compounds since the early days of the rubber industry. Whilst their primary function is to reduce cost, it has been found that fillers have a reinforcing effect in the rubber mechanical properties sueh as tensile strength, modulus, tear resistance and abrasion resistanee and thus very few mbber compounds are prepared without substantial quantities of filler. The performance of filler in the rubber matrix is governed by its characteristics, such as the particle size and concentration, particle shape, surface activity, degree of interactions with rubber matrix and structure of the particle agglomerates. 

The properties of fillers which induence a given end use are many. The overall value of a filler is a complex function of intrinsic material characteristics, eg, tme density, melting point, crystal habit, and chemical composition and of process-dependent factors, eg, particle-si2e distribution, surface chemistry, purity, and bulk density. Fillers impart performance or economic value to the compositions of which they are part. These values, often called functional properties, vary according to the nature of the appHcation. A quantification of the functional properties per unit cost in many cases provides a vaUd criterion for filler comparison and selection. The following are summaries of key filler properties and values. 

Moisture. The presence of water in a filler is not usually beneficial. Most fillers added to adhesives have a moisture content lower than 1 wt%. Only precipitated silicas and sepiolite contain about 5-10 wt% moisture. For some applications, fillers must be completely dried to exhibit adequate performance. Moisture absorbed on the surface of fillers impacts the rate and extent of curing of rubber base adhesives. 

Another advantage of the addition of inorganic filler is the significant increase in density of the silicone, which helps the dispensing process. The use of fillers also reduces the total cost of the product, as the expensive high performance silicone does not require 100% volume occupancy to fulfil its function. 

By far the preponderance of the 3400 kt of current worldwide phenolic resin production is in the form of phenol-formaldehyde (PF) reaction products. Phenol and formaldehyde are currently two of the most available monomers on earth. About 6000 kt of phenol and 10,000 kt of formaldehyde (100% basis) were produced in 1998 [55,56]. The organic raw materials for synthesis of phenol and formaldehyde are cumene (derived from benzene and propylene) and methanol, respectively. These materials are, in turn, obtained from petroleum and natural gas at relatively low cost ([57], pp. 10-26 [58], pp. 1-30). Cost is one of the most important advantages of phenolics in most applications. It is critical to the acceptance of phenolics for wood panel manufacture. With the exception of urea-formaldehyde resins, PF resins are the lowest cost thermosetting resins available. In addition to its synthesis from low cost monomers, phenolic resin costs are often further reduced by extension with fillers such as clays, chalk, rags, wood flours, nutshell flours, grain flours, starches, lignins, tannins, and various other low eost materials. Often these fillers and extenders improve the performance of the phenolic for a particular use while reducing cost. 

A method for the estimation of composite material performance from the characteristics of fillers and the matrices and from the configuration of filler is generally called the law of mixture. In the most basic form of the law of mixture, the characteristics of a composite material are represented as a function of characteristics of constituent components and their volume fractions, as shown in Fig. 3. For a composite material (characteris-ticsiA f) that consists of component A (characteristics Xa, volume fraction ) and component B (characteristics Xf, volume fraction b), the basic formulae of the law of mixture are as follows ... 

Note Glass filler can considerably extend the performance of the above polymers. PEI = polyetherimide PES = polyether sulfone PPS = polyphenylene sulfide PSF = polysulfone PC = polycarbonate. 

Biopolymers have diverse roles to play in the advancement of green nanotechnology. Nanosized derivatives of polysaccharides like starch and cellulose can be synthesized in bulk and can be used for the development of bionanocomposites. They can be promising substitutes of environment pollutant carbon black for reinforcement of rubbers even at higher loadings (upto SOphr) via commercially viable process. The combined effect of size reduction and organic modification improves filler-matrix adhesion and in turn the performance of polysaccharides. The study opens up a new and green alternative for reinforcement of rubbers. 

Jha A., Dutta B., and Bhowmick A.K., Effect of fillers and plasticizers on the performance of novel heat and oil-resistant thermoplastic elastomers from nylon-6 and acrylate rubber blends, J. Appl. Polym. Sci., 74, 1490, 1999. 

The tire industry is by far the largest consumer for carbon black, so it should not be surprising that a major focus for research and development at carbon black producers has been understanding and improving the performance of carbon black and other fillers in tires. This chapter will describe... 

The performance of stabilisers in respect of their physical persistency can also be improved by physical adsorption on surfaces of reinforcing fillers, e.g. of CB or amorphous microground silica [589]. Mineral fillers are well known to adsorb polymer additives, especially stabilisers necessary for processing and... 

The performance of aluminium hydroxide/magnesium hydroxide-filled systems can be enhanced by incorporation of zinc hydroxystannate in halogen-free rubbers giving reduced smoke and toxic gas emission, coupled with higher flame retardancy. This action will be complimentary to the water release and endothermic effects of aluminium hydroxide/magnesium hydroxide filler systems. 

A process additive is an ingredient which is added in a small dosage to a rubber compound solely to influence the performance of the compound in factory processes, or to enhance physical properties by aiding filler dispersion. 

Table 3.5 shows some examples of the property effect ratios for mineral filler-reinforced polypropylene. The effect ratio is the performance of the reinforced polymer divided by the performance of the neat polymer. Properties of low-level glass fibre reinforced polypropylene are given for comparison. 

In addition to the amount of filler content, the shape, size and size distribution, surface wettability, interface bonding, and compatibility with the matrix resin of the filler can all influence electrical conductivity, mechanical properties, and other performance characteristics of the composite plates. As mentioned previously, to achieve higher electrical conductivity, the conductive graphite or carbon fillers must form an interconnected or percolated network in the dielectrical matrix like that in GrafTech plates. The interface bonding and compatibility between... 

Morphology is one of the key factors determining the performance of mineral fillers in all polymers including thermoplastics. While an apparently simple concept, it is very complex in practice, and probably accounts for a great deal of the problems and misconceptions that are experienced in this field. A detailed discussion of the subject has recently been given by Rothon and Hancock [75]. Because of its importance in determining the production methods that are used and the choice of filler types its characterisation is covered in some detail here. 

The thermal properties of fillers differ significantly from those of thermoplastics. This has a beneficial effect on productivity and processing. Decreased heat capacity and increased heat conductivity reduce cooling time [16]. Changing thermal properties of the composites result in a modification of the skin-core morphology of crystalline polymers and thus in the properties of injection molded parts as well. Large differences in the thermal properties of the components, on the other hand, lead to the development of thermal stresses, which also influence the performance of the composite under external load. 

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