Filler polymers specific resistance

Strength and most important commercial fillers for a particular polymer have a lower reduction in these properties at a given volume fraction than other fillers. The applications of composites that depend primarily on mechanical property specifications are too numerous to list some examples are airplane and automotive components. Other important mechanical properties that often justify the use of a filled system vs. one without a filler are abrasion resistance, for instance, automobile tires and resistance to creep, e.g., weightbearing structural components. 

The effect of fillers on the resistance to change or deterioration in the presence of liquids is quite marked. Fillers influence the degree of swelling by replacement of polymers that swells by filler that does not, resulting in reduced swelling through reduction of the volume fraction of polymer in the compound. Some fillers are obviously not suited to specific applications, e.g., carbonate fillers decompose in the presence of acids. 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

Fillers may be broadly defined as solid particulates or fibrous materials, substantially inert chemically, incorporated in polymer compositions to modify the properties and/or to reduce cost. Cost reduction is not the primary reason to incorporate fillers in adhesives but they are used to impart specific properties such as flow, improved adhesion, mechanical, thermal, electrical and optical properties, chemical and weather resistance, and rheological behaviour. 

The specific surface area of fillers is closely related to their particle size distribution however, it also has a direct impact on composite properties. Adsorption of both small molecular weight additives, and also that of the polymer is proportional to the size of the matrix/filler interface [14]. Adsorption of additives may change stability, while matrix/filler interaction significantly influences mechanical properties, first of all yield stress, tensile strength and impact resistance [5,6]. 

Exfoliating layered particles such as the clays, mica, or graphite is being used to provide very effective reinforcement of polymers at loading levels much smaller than in the case of solid particles such as carbon black and silica.77 81 Other properties can also be substantially improved, including increased resistance to solvents, and reduced permeability and flammability. A number of such studies specifically address the effects of introducing layered fillers into polysiloxanes 42,82 88... 

To obtain the lowest electrical volume resistivities (in the 10 to 10 ohm-cm range) and the lowest contact resistances, polymer resins must be highly Ailed with 70-80% by weight (25-30% by volume) of metal particles and must be thoroughly cured. Silver and silver alloys are the most widely used fillers but, in specific applications, other metal fillers including gold, copper, nickel, and even carbon are used. Carbon-filled polymers are often used to dissipate static electricity or to protect from electromagnetic interference (EMI). 

In the growing plastics industry, there is often need to identify polymer formulations. Whether the analysis is done to reproduce the material, identify another supplier, or provide insight into the cause of failure, the filler is an important aspect. Fillers are used for several reasons to extend the amount of polymer for overall eost reduction, to add structural stability or impart specific physical characteristics to the polymer sueh as chemical, temperature, or flame resistance, or to add eolor to a polymer. Several commonly occurring fillers include silicates, aluminum trihydrate, ealcium carbonate, fiberglass, and tale. These fillers have eharacteristic FTIR bands whieh can be easily identified within a speetrum of the polymer. The amount of filler present in the formulation can be of great importanee to the performanee of the polymer. 

---