INDEX whiskers

The structural properties of the nanocomposites such as the size of the cellulose crystallites and the crystallinity index can be characterized using X-ray diffraction. X-ray diffraction is used to elucidate the eventual modifications in the crystalline structure of the matrix after the addition of the whiskers. 

Properties Vaiying proportions of MO, and SiOj wh. mass, crystals, or whiskers high str. insol. in water dens. 2.63 oil absorp. 35-45 GE brightness 82-92 ref. index 1.56 hardness (Mohs) 2 Toxicology Essentially harmless when given orally or applied to skin questionable carcinogen with experimental tumoriqenic data by implantation... 

In actual research, the activation index (H, mass ratio of the floating portion to total samples) is used to evaluate the surface modiflcation results of whiskers (refer to the national standard GB/T 19281-2006). The detection process is as follows. Add a certain amount of modified whiskers into 100 ml of deionized water and let it sit until clear after stirring for 1-2 minutes. Then remove the floating portion on the solution surface and collect the sunken powders at the bottom. The latter are Altered, dried, and weighed and the activation index is calculated using the following equation ... 

Figure 3.14 Activation indexes of CaS04 whiskers modified by different coupling agents.

Figure 3.15 Activation indexes of CaS04 whiskers affected by KFt-550 concentration.

As is shown in Figure 3.14, KH-550 has the best modification effect on calcium sulfate whiskers with an activation index (99.6%) higher than that of other coupling agents. The sample modified with KH-550 cannot be wetted by water. Figure 3.15 shows the modification results of calcium sulfate whiskers affected by KH-550 concentration. Modification results become much better with an increase of KH-550 concentration. But the rising trend of activation index is no longer obvious when the concentration of KH-550 is more than 8 wt%. 

Figure 4.9 Influence of different whiskers on the melt flow index of polypropylene.

The activation index of treated calcium carbonate whiskers is measured. The results before and after modification of calcium carbonate whiskers are shown in Figure 5.6. 

Figure 5.6 shows that with the increasing mass fraction of stearic acid, the activation index of whiskers increases at first and then decreases. The mass fraction of the highest activation index is 4.0% after that, with an increase of the mass fraction of stearic acid, the activation index decreases, which indicates that the activation index reaches the highest value when the whisker surface is completely coated by stearic acid. More stearic acid will cause excessive accumulation and then reduce the activation index. 

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. 

Figure 5.9 Effect of modifier concentration on the activation index of the whiskers.

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. 

As can be seen from Table 5.2, the modification temperature has little effect on the activation index of calcium carbonate whiskers, and all the activation indexes are greater than 90%. Taking into account the temperature of the esterification... 

Fig. 9(a) and (b) show transmission electron microscopic images and the corresponding electron diffraction pattern of the cross-section of an Sn whisker (Ref 12). The cross section is normal to the growth direction of the whisker. The diffraction pattern has been indexed to be a single crystal of 001 orientation. In the image shown in Fig. 9(a), there are several point images. Whether they are the images of screw dislocations or not is unclear. The cross section of these whiskers is not rounded, rather it is faceted and fluted. 

The DLS is one of the most popular techniques for light scattering, as it allows particles smaller than 1 nm to be analyzed. In the analysis of cellulose whiskers DSL is a complementary technique, since it provides a particles size frequency distribution and the polydispersity index of the sample [76]. 

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