Calcium carbonate surface modification

In addition, there are many types of modifiers applied to calcium carbonate surface modification. We need to... 

Lucie, S., Kovacevic, V., Packham, D.E., Bogner, A., Gerzina, A., Stearate-modified calcium carbonate fillers and their effect on the properties of polyvinyl acetate, composites. Proc. 2nd Int. Symp. Polymer Surface Modification Relevance to Adhesion, Newark, NJ, 24-26 May, 1999. 

The production process is able to produce all three crystal modifications of calcium carbonate and a wide variety of particle sizes and shapes, including plates and acicular forms [107]. However, only the calcite form with a rhombic shape and a low aspect ratio seems to have found much commercial application in polymers. For filler applications the particles have an ultimate particle size of 50-100 nanometers, a specific surface area of 15-25 m g and a low aspect ratio. 

Calcium carbonate does not have functional groups (its surface is inert), therefore interaction can only be improved by chemical modification. Some hydroxyl groups can be found from admixtures such as Ca(OH)2 but these admixtures may limit the ways in which calcium carbonate can be used because these admixtures increase the amount of absorbed moisture. Functional groups are frequently hydrophilic thus they attract water molecules. In many applications, moisture can either cause product instability, reduce cure rate, or reduce reinforcement. Caution is needed in selecting surface treatment to generate functional groups. 

Surface modification of silica is much easier than that of calcium carbonate because silica has numerous surface groups. It is not the greater reactivity of the sil-... 

Special methods of incorporation usually surface modification of filler is performed prior to filler incorporation into the polymer high concentration of calcium carbonate (40 wt%) provides a fihn which has properties similar to paper but surpasses paper in resistance to moisture chlorinated PE containing carboxyl groups was used as compatibilizer with calcium carbonate " masterbatches of titanium dioxide contain 40-50 wt% pigment " rubber modification to incorporate zirconium silicate without a loss of mechanical strength ... 

A main line of development continuing today is multifunctional additives, such as fillers, which are treated to provide also a degree of reinforcement. For example, calcium carbonate improves surface gloss of PVC, talc is added to PP to improve stiffness and heat stability. An essential aspect is the compatibility with the resin matrix and there is intense development of surface-modification technology, to render fillers of all types more acceptable to the matrix. 

Much work has been carried out on other surface modifications of calcium carbonate [10] and a more detailed discussion can be found in Chapter 4. From the authors experience, many beneficial claims have been made (mostly in patents) for surface treatments and coupling reactions, but the evidence when examined is flawed. Certainly, the market place is sceptical of the supposed benefits because very few coupling agents/surface modifications are used commercially. 

Surface Modification and Characterization of Calcium Carbonate Whiskers... 

Like other inorganic whiskers, calcium carbonate whiskers have high polarity, and therefore surface modification is required for filling polymer materials. The common surface... 

Figure 5.9 shows that the activation index is almost zero for unmodified calcium carbonate whiskers, but increases significantly after surface modification. Thus it can be seen that sodium stearate is effective in modifying calcium carbonate whiskers. When the concentration of the modifier is less than 4.5%, the activation index of the whiskers gradually increases. 

As shown in Table 5.1, different modification times have different effects on whiskers. The activation index of calcium carbonate whiskers approach a maximum of 93.4% when the processing time is 50 minutes. With an increase of processing time, more modifier molecules are adsorbed on the surface of the whiskers, and the effect of the modification increases gradually. When the processing time is up to 50 minutes, the modification agent can make sufficient contact with the whiskers and fully coat their surface to the maximum activation index. When the modification time extends further, the already adsorbed modification agent on the material surface desorbs, and the modification effect deteriorates. 

There are many studies on calcium carbonate whisker surface modification. Some scholars, for example, Li et al., believe that the calcium carbonate whisker surface can form chemical bonds with the molecules of stearic acid. Infrared spectra are shown in Figure 5.12. 

Advantages of dry processing are that this method is convenient and simple and performance and microstructure analyses of the effect of the calcium carbonate whisker surface modification more intuitively and realistically reflect the interfacial action of whiskers and the matrix resin and dispersion of the whiskers in the matrix. Disadvantages are that because... 

Silane coupling agents could be used for modification of various different organic functional groups on the surface of inorganic materials. The current research in this area is still very active. The common silane coupling agents for the surface modification of calcium carbonate whiskers are mainly KH-550, KH-560, and KH-570. 

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