Tensile strength particulate fillers

Carbon blacks are the most widely used fillers for elastomers, especially vulcanised natural rubber. They cause an improvement in stiffness, they increase the tensile strength, and they can also enhance the wear resistance. Other particulate fillers of an inorganic nature, such as metal oxides, carbonates, and silicates, generally do not prove to be nearly so effective as carbon black. This filler, which comes in various grades, is prepared by heat treatment of some sort of organic material, and comes in very small particle sizes, i.e. from 15 to 100 nm. These particles retain some chemical reactivity, and function in part by chemical reaction with the rubber molecules. They thus contribute to the crosslinking of the final material. 

Talc is a hydrated magnesium silicate that is composed of thin platelets primarily white in color. Talc is useful for lowering the cost of the formulation with minimal effect on physical properties. Because of its platy structure and aspect ratio, these extenders are considered reinforcement. Polymers filled with platy talc exhibit higher stiffness, tensile strength, and creep resistance, at ambient as well as elevated temperatures, than do polymers filled with particulate fillers. Talc is inert to most chemical reagents and acids. The actual chemical composition for commercial talc varies and is highly dependent on the location of its mining site. 

Polymers filled with platy talc exhibit higher stiffness, tensile strength, and creep resistance than do polymers filled with standard particulate fillers. These properties are maintained at both ambient and elevated temperatures. Surface treatments for talc particles include magnesium and zinc stearates, silanes, and titanates. 

Tensile strength and flexural modulus are generally increased and ultimate elongation is reduced in proportion to the amount of filler, when tested at room temperature. The reverse is generally true when the cured epoxy is tested at elevated temperatures. Impact strength is generally adversely affected by particulate fillers. 

Calcium carbonate filler is a particulate filler that is generally employed to impart thixotropic properties and as an extender. However, improvements in physical properties such as tensile strength, tear, and elongation have been noticed as a function of surface area. This effect is noted more so with the coated CaC03 products. 

Below Tg of polystyrene the glassy domains also fulfill another useful role by acting like a reinforcing particulate filler. It is also an apparent consequence of this role that SBS polymers behave like carbon-black-reinforced elastomers with respect to tensile strength. 

Fillers may be divided into particulate and fibrous types. Particulates include calcium carbonate, china clay, talc and barium sulphate. Fillers affect shrinkage on moulding and the dimensional stability of the finished plastic, increase tensile strength and hardness, enhance electrical insulation properties and reduce tackiness. They also impart opacity and colour (Figure 3.16). Carbon black is now the most widely used filler for polymers usually in the form of furnace carbon black, which has a particle diameter of 0.08 mm. Fibrous fillers reinforce polymers and greatly increase their tensile strengths. They include fibres of glass, textile and carbon. Plastics filled with fibrous fillers are known as composites. 

Warpage resistance 5 to lOo/o glass fibers 5 to lOPfo carbon fibers Particulate fillers Ductility, cost tensile strength Cost Cost Ductiiity, cost tensile strength... 

It has been seen that particulate fillers tend to increase the stiffness of a matrix resin, but may or may not increase the toughness or tensile strength. 

Reinforcement of elastomers by particulate fillers is pursued in order to improve, by an order of magnitude, static and dynamic moduli as well as ultimate properties such as tensile strength and elongation at break. The simultaneous improvement of modulus and elongation is known as the paradox of elastomers . 

Table 2.5 contains a general equation, Eq. (2.35), for the effect of particulate fillers on the tensile strength of a polymer, a common modification of this equation by Nicolais and Narkis, (Eq. (2.36)), and an additional equation proposed by Piggott and Leidner,... 

Eq. (2.37)) [9,17,19]. These equations predict that failure is either by matrix failure or by loss of adhesion without utilization of the inherent strength of the particulate. Experimental results for a variety of nondirectional filler particles show that in most cases, tensile strength decreases with increasing volume fraction relatively higher values, however, are obtained in the case of improved adhesion 9]. 

Keywords particulate filled composites, filler, aggregate, homogenization, mixing, internal mixer, single-screw extruder, twin-screw extruder, mechanical properties, tensile yield stress, tensile strength, stiffness, impact resistance, structure-property relationships, interface, interphase, reactive treatment, nonreactive treatment, surfactant, encapsulation, functionalized PP, coupling, specific surface area, application. 

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