Mineral fillers applications

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. 

Although generally ignored in plastics literature the bituminous plastics are still of interest for specific applications. The moulding compositions consist of fibrous and mineral fillers held together by a bituminous binder together with a number of minor ingredients. 

A plastics material of particular application in electrical components. It consists of a thermosetting polyester resin, mineral fillers, fibrous reinforcement and a hquid crosslinking medium such as diallyl phthalate. Down-Stroking Press... 

The principal mineral fillers used in thermoplastics and the reasons for using them are identified, together with those features that have to be controlled in order to achieve the optimum results and to avoid associated deleterious effects. General methods of filler production are outlined in the light of these requirements and their application to the fillers in most use is described. Attention is given to the use of surface modification methods where these are part of the production process. 

It is estimated that over one million tons of mineral fillers were used in thermoplastic applications in western Europe in 1986 [2], and the figure is doubtless much greater today. Mineral fillers are used to some extent in virtually all the commercially important thermoplastic polymers but, in volume terms, the principal markets are in PVC and polyolefins, where calcium carbonate dominates the filler types with over 80% of the volume consumption [2]. 

The importance of the use of mineral fillers to the growth of applications for thermoplastic polymers has already been described. The addition of such materials affects most of the significant properties of the matrix, some beneficially, others detrimentally. Only some of these altered properties are important to the use of thermoplastics, and an appreciation of what these are is critical to identifying those filler characteristics that are important and in understanding how certain filler types and production methods have come to dominate the market. 

Many of the chemical and physical properties of mineral fillers are important in their application in thermoplastics. These include purity, specific gravity, hardness, electrical, thermal and optical properties, surface area, particle shape and size. The determination and importance of many of these has been covered in several reviews [65,66]. Only a brief coverage is given here for the less ambiguous properties such as specific gravity, hardness and standard thermal and optical properties, with most attention being concentrated on properties such as size and shape which have been found to give particular problems in measurement and interpretation. 

The hardness of mineral fillers is of considerable importance in thermoplastics applications. In general soft fillers are preferred, as the harder ones tend to cause... 

Another application of PTFE dispersions is the preparation of a variety of compositions with other materials, such as mineral fillers, other polymers in powdered form by co-coagulation. The dispersion of the other component is blended with the PTFE dispersion and the blend is then coagulated. The resulting composition can be processed by extrusion with lubricants (see processing of fine powders) or by compression molding.16... 

Marosi, G., Keszei, S., Marton, A., Szep, A., Le Bras, M., Delobel, R., and Hornsby, P. Flame retardant mechanisms facilitating safety in transportation. In Fire Retardancy of Polymers New Applications of Mineral Fillers, M. Le Bras, C.A. Wilkie, S. Bourbigot, S. Duquesne, and C. Jama (Eds.), pp. 347-360. Cambridge, U.K. The Royal Society of Chemistry. 

FIGURE 8.10 Rate of heat release curves of TPU, TPU/DP-POSS, and TPU/FQ-POSS as coating of woven PET fabrics at heat flux 35kW/m2. (From Bourbigot, S. et al., Fire Retardancy of Polymers New Applications of Mineral Fillers, Bras, M., Bourbigot, S., Duquesne, S., Jama, C., and Wilkie, C.A., Eds., The Royal Society of Chemistry, Cambridge, MA, 2005, 189. With permission.)... 

Secondary ingredients in epoxy adhesives include reactive diluents to adjust viscosity mineral fillers to lower cost, adjust viscosity, or modify the coefficient of thermal expansion and fibrous fillers to improve thixotropy and cohesive strength. Epoxy resins are often modified with other resins to enhance certain properties that are necessary for the application. Often these modifications take the form of additions of elastomeric resins to improve toughness or peel strength. 

One material that has been used to replace asbestos in certain applications is wollas-tonite or calcium metasilicate. This is also a fibrous mineral filler but with a lower aspect ratio than asbestos. Surface-treated versions are available to improve adhesion to the epoxy matrix. It can be applied at relatively high loading levels to provide for high strength and improvements in moisture resistance.25... 

Many mineral fillers are also commercially available with an organofunctional silane surface treatment. Suppliers of treated mineral fillers are shown in Table 10.2. These fillers are used in a variety of applications having critical property requirements that must be protected from moisture. Surface treatment of the mineral fillers also provides the formulator with a tool to reduce the viscosity of highly filled systems. 

Monoalkoxy titanate Chelate titanate Quat titanate Neoalkoxy titanate Cycloheteroatom titanate Stearic acid functionality aids in dispersion of mineral fillers in polyolefins Greater stability in wet environments Water-soluble, aids adhesion of water-soluble coatings and adhesives Eliminates pretreatment associated with fillers, can be used as a concentrated solid additive Ultrahigh thermal properties for specialty applications... 

Mineral fillers find application for melamine-formaldehyde resins, thus enabling compositions to be obtained with heat resistance in excess of 200 °C. 

In this application, it is necessary for the adhesive to pronde a quick, strong bond to both the carpet components and the mineral filler, Carboxylated latex is desirable because of the enhanced adhesion provided, particidarly to the filler, by enactment of the electrical charge distribution mechanism. 

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