Calcium filled thermoplastics

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. 

The rheology of filled polymers has been reviewed extensively [44,45], In general, viscosity curves of highly filled polymers show a yielding behavior at low shear rates followed by a power-law behavior at high shear rates [44], For most of the filled thermoplastics with small particles such as glass beads, calcium carbonate, talc, and carbon black, etc., the viscosity increases with the filler concentration. For some filled systems, however, the viscosity increases with the filler content up to the critical concentration, then decreases [46] or becomes little dependent on the filler concentration [47], This is particularly true for glass fiber-filled polymers. 

Thermoplastics represent more than 80% of all plastics manufactured. Of these, the four major commodity plastics PE, PP, PS and PVC represent nearly 75% of all synthetic polymers produced annually, or about 75 million tons worldwide. Filled thermoplastics represent a huge and growing market for all types of manufactured products. It is estimated that each year 20 million tons of fillers are used in plastic materials. Currently, the most important fillers are calcium carbonate, talc, silica, mica, clay, aluminium trihydrate, glass fibres, starch and cellulosic powders. 

Particulate-filled thermoplastic polyolefins are used in vehicle applications. Talc, calcium carbonate, and kaolin are typical fillers. Fillers do not change the transition characteristics of the plastic. Fillers increase the temperature-dependent elastic moduli of the plastics, increasing the forces required to form the plastics in the plateau-temperature regions. Matched-mold thermoforming is necessary if the product cannot be formed using a conventional pressme box over a single-surface mold. 

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]. 

At the request of an international petroleum company, a major manufacturer and supplier of down-hole equipment performed tests of the various elastomers commonly used in the construction of packers and other oil field tools. Seven of the nine most commonly used thermoplastic materials were found to be completely inert to TKPP solutions. The test included continual immersion in saturated TKPP for 21 days at 280°F. Only two elastomers, Vi-ton and Fluorel, showed any adverse reaction. O-rings made from these two elastomers showed minor cracking at the termination of the test. A listing of the elastomers that tested inert to TKPP solutions include nitrile, saturated nitrile (HNBR), Aflas, Kalrez, PEEK, Glass-filled Teflon, and Ryton. Several of these elastomers are attacked or degraded by conventional clear completion fluids containing calcium and zinc halides. The inertness of commonly employed elastomers to TKPP is an important advantage for TKPP fluids in normal operations. 

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. 

Chem. Descrip. Calcium carbonate CAS 471-34-1 EINECS/ELINCS 207439-9 Uses Filler for plastics, PVC, polyolefins, polyesters, BMC/SMC, paint, caulks, sealants, adhesives, paper, foam urethane, modified acrylics, filled thermosets/thermoplastics, and rubber Features Improves impact str., dimensional stability Regulatory NSF approved for potable water materials Properties Wh. powd. 2 avg. particle diam. 99.9% finer than 8 0.15% sol. in water sp.gr. 2.70-2.71 dens. 22.57 Ib/gal bulk dens. 38 Ib/tP (loose) oil absorp. 23 01 cc/100 g brightness (Hunter) 95 ref. index 1.6 pH 9.5 (sat.) hardness (Mohs) 3.0 Toxicobgy Nontoxic Camel-TEX [IMERYS]... 

Fig. 5.71 Semicrystalline thermoplastics, such as a polyacetal, shown in polarized light (A) do not appear spherulitic after the addition of calcium carbonate (B). llie surface of such a filled, molded part can exWbit a matte finish due to poor wetting of the particles with the pol)nner. SEM observation of the molded surface (C) shows pock marks which are particles in cavities not filled with pol)nner. EDS mapping (D) shows the particles contain calcium.

There seem to be only limited published studies of calcium carbonate s influence on the mechanical properties of thermoplastics and elastomers. Clearly, the Young s modulus and tensile strength are increased. H. Kim et al. [98] showed the addition of calcium carbonate into polypropylene, poly(propylene-random ethylene) copolymer, and poly( propylene-ethylene-butene) terpolymer increases Young s modulus and decreases elongation to break. Kwon et al. [99] observed the same trend for high-density polyethylene, low-density polypropylene, and linear low-density polyethylene compounds that tensile stress of calcium carbonate-filled compounds were higher than unfilled systems. 

Large amoimts of calcium carbouate, almniua trihydrate, aud barite are used to fill foam imderlay for carpets. The base polymers are rubber, syuthetic thermoplastic and polyurethane in latex form. The fillers serve two fimctions - to add weight so that the carpet lies flat on the floor and does not shift with traffic, and to reduce flammability. 

Mica provides similar benefits in a wide range of thermoplastic and thermoset composites including polyolefins, polyamides and styrenics. It is also reported that surface coated mica further increases tensile strength, flexural strength and modulus, and heat deflection temperature. The automobile industry is the main user of mica-filled composites, either with polypropylene or nylon as polymer matrix. Up to 40% mica loadings are used, sometimes in association with calcium carbonate, to produce various injection... 

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