Thermoplastics calcium carbonate

Finishing of the filler surfaces may also greatly affect the system viscosity. For mica-filled PP [31] and various thermoplastics filled with calcium carbonate [202, 261] it was shown that the relative viscosity of filled systems was lower than that of systems which contained equivalent quantitied of unfinished filler. Note that in contrast to viscosity in shear, the viscosity in stretching is higher for systems with treated filler [202]. 

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]. 

While organo-silane treatments are extensively used in both thermoset and elastomer applications, their use in thermoplastics has so far been somewhat restricted. This is because they do not react with the surface of calcium carbonate, one of the principal fillers used in this type of polymer and because of the lack of a suitable reactive functionality for most of the thermoplastic polymers. Today they are principally used in conjunction with glass fibres, calcined clays, aluminium and magnesium hydroxides, micas and wollastonite. The main thermo-... 

Ground natural calcium carbonate is, on a volume basis, the main filler material used in thermoplastics. The principal appHcations by far are in PVC, but significant quantities are also used in other polymers, notably polypropylene and polyamides. A wide range of particle sizes is used according to the nature of the application. 

Much of the natural calcium carbonate used in thermoplastics is fatty acid treated. Manufacturers give little detail about their coating processes but it is likely that both wet and dry coating procedures are utilised. 

In the thermoplastics area, precipitated calcium carbonate is principally used in PVC applications, a market with which it has been associated since the early days of the polymer. Despite some erosion by coated natural products, the combination of small particle size and fatty acid coating continues to give a unique blend of properties in both unplasticised and plasticised PVC formulations. The advantages include easier processing, better surface finish, good low temperature properties and resistance to crease whitening and to scratching. 

Various investigations have considered the effects of titanate treatments on melt rheology of filled thermoplastics [17,41]. Figure 10, for example, shows that with polypropylene filled with 50% by weight of calcium carbonate, the inclusion of isopropyl triisostearoyl titanate dispersion aid decreases melt viscosity but increases first normal stress difference. This suggests that the shear flow of the polymer is promoted by the presence of titanate treatment, and is consistent with the view that these additives provide ineffective coupling between filler particles and polymer matrix [42]. 

To conclude this brief digression into history, we may point out one more important aspect the high efficiency of the combined shear in molding of filled thermoplastics. One of the first works in this field was 31) which described experiments carried out with polypropylene filled with a disperse aggregate calcium carbonate (chalk) and a short-fiber material-asbestos. 

Asbestos-reinforced organic binders (thermoplastics, duroplasts and elastomers) are widely utilized e.g. hardenable molding materials on the basis of asbestos-reinforced phenol or melamine resins for the manufacture of insulating components for combustion engines, components for electrical installations, cogwheels etc. Possible fiber substitutes are glass fibers, carbon fibers and other synthetic fibers (e.g. aramide fibers) and non-fiber fillers such as calcium carbonate, clay or talcum. 

U.S. Pat. No. 5,153,241 [66] discloses composites made of thermoplastic polymers such as low-density polyethylene, polypropylene or polystyrene (90-60%) and wood pulp or sawdust (10-40% by weight) grafted with a titanium coupling agent (isopropyltri[n-ethylaminoethylamino] titanate) in acetone, along with some inorganic fillers, such as calcium carbonate and Portland cement. 

U.S. Pat. No. 6,207,729 [69] describes a similar thermoplastic composition comprising shredded and sheared cellulosic materials (33-59% by weight) such as old newspapers, magazines, kenaf, kraftboard, and so on, HDPE (33-50%), calcium carbonate (11-17%), and a coupling agent (Eusabond lOOD, 2%). 

Minerals, such as calcium carbonate, talc, silica, are quite common fillers in plastic industry. They, often at abont 6-15 cent/lb, replace a much more expensive plastic, increase stiffness of the filled product, and render the plastic more flame resistant. The world filler market for plastics is dominated by carbon black and calcium carbonate. Of abont 15 billion pounds of filler in America and Europe, about half the filler volume goes into elastomers, a third into thermoplastics, and the reminder into thermosets. About 15% of all manufactured plastics contain fillers. 

Polyvinylacetate (PVAc) and vinyl acetate-acryUc copolymers (VAc-A), thermoplastic polyurethanes, polyethylene, polystyrene and polycap-rolactone are some of the candidates for low-profile shrinkage additives to SMC and BMC. PVAc and VAc copolymers are the most widely used thermoplastic additives. Typically a low-profile SMC recipe contains about 15% unsaturated polyester resin, 8% thermoplastic additive, 50% calcium carbonate and 27% glass fiber. 

It is well accepted that the good properties of the isotactic polypropylene as an engineering polymer matrix in thermoplastic composite materials and engineering blends are seriously affected by the inability of this polymer to develop an adequate level of interfacial interaction with polar components such as mineral fillers (calcium carbonate) and reinforcements (talc, mica, wollastonite), synthetic reinforcements (glass fibers, carbon fibers, and nanotubes), or engineering polymers such as polyamide, aliphatic polyesters, and so on. 

Mineral fillers such as mica, kaolin, calcium carbonate, and talc are frequently incorporated in thermoplastics to reduce the costs and improve the properties of the polymers such as rigidity, durability, and hardness [30]. Talc is common filler in plastics as it serves as the most cost effective filler. Previous researchers have... 

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