Stearic acid treatment

In stearic acid treatment, solution of stearic acid is used to induce interfacial adhesion of the sisal fiber. It was found that due to the presence of hydroxyl groups on the sisal fiber, stearic acid enhanced the viscosity of the hybrid composite [35]. 

Water molecules are eliminated during silane bonding reactions, and oxane linkages (M-O-Si) are formed. Since calcium carbonate is not responsive to chemically reactive silanes, stearic acid treatment has become an important technique, widely used in calcium carbonate filled PVC, including rigid PVC products, flexible PVC and plastisols. 

Papirer and co-workers have also used IGC to study stearic acid coated calcium carbonates [17]. In their work, a high surface area precipitated filler was used, and coating was from toluene solution. They also prepared fractional coating levels based on solution adsorption isotherms. Stearic acid treatment was again found to decrease both the dispersive and polar contributions of surface energy to values typical of a hydrocarbon. Both acidic and basic probes were used in this work and interestingly, the uncoated filler was found to contain sites capable of interaction with both. 

Fulmer and co-workers [22] have shown clear evidence of faster incorporation and lower melt viscosity in calcium carbonate filled polypropylene homo-polymer. However, despite the widespread use of fatty acids for improving processability, melt viscosity reductions are not always obtained. Bohlin and co-workers have published an interesting paper on the effect of stearic acid treatment of a dolomite filler in polypropylene [23]. They found... 

The surface energy of fibers is closely related to the hydrophilicity of the fiber [38]. Some investigations are concerned with methods to decrease hydrophilicity. The modification, of wood cellulose fibers with stearic acid [43] hydrophobizes those fibers and improves their dispersion in polypropylene. As can be observed in jute-reinforced unsaturated polyester resin composites, treatment with polyvinylacetate increases the mechanical properties [24] and moisture repellency. 

Modification of filler s surface by active media leads to the same strong variation in viscosity. We can point out as an example the results of work [8], in which the values of the viscosity of dispersions of CaC03 in polystyrene melt were compared. For q> = 0.3 and the diameter of particles equal to 0.07 nm a treatment of the filler s surface by stearic acid caused a decrease in viscosity in the region of low shear rates as compared to the viscosity of nontreated particles more than by ten times. This very strong result, however, should not possibly be understood only from the point of view of viscometric measurements. The point is that, as stated above, a treatment of the filler particles affects its ability to netformation. Therefore for one and the same conditions of measuring viscosity, the dispersions being compared are not in equivalent positions with respect to yield stress. Thus, their viscosities become different. 

Damle et al. observed that the reduction of the Pd(II) ions in the stearic acid-Ag nanocomposite film leads to the formation of a mixture of individual Ag and Pd nanoparticles as well as particles in the Ag-core/Pd-shell structure. Thermal treatment of the stearic acid-(Ag/Pd) nanocomposite film at 100 °C, however, resulted in the formation of an AgPd alloy [142]. 

Esterification over Amberlyst BD20 was evaluated by processing a model mixture in a fixed-bed reactor. The model reaction mixture was prepared by dissolving 10 wt.% of pure stearic acid (> 97%, Fluka, Germany) in a low-acid vegetable oil (0.04 %) bought in the supermarket. Methanol (> 99.5%) was used without any preliminary treatment. 

The ratio of palmitic acid to stearic acid (P/S) can be used to differentiate between drying oils, since these two saturated monocarboxylic acids are less subject to chemical reactions during treatment and ageing. Also, they have a similar chemical reactivity, so their ratio can be hypothesized to be relatively unaltered during ageing. The P/S ratio approach was pioneered by Mills [10], and has been subsequently adopted in a number of studies [7 9]. Typical values of the P/S ratio are 1 2 for linseed oil, 2 3 for walnut oil, 3 8 for poppy seed oil and 2.5 3.5 for egg. 

Dry coating is extensively used with fatty acid treatment of natural calcium carbonates. The challenge is to convert as much as possible of the coating to a bound surface layer, with as little unbound salt and remaining free acid as possible. There is little scientific literature on this procedure but some useful studies have been made[51,64]. A number of different methods are employed. In most cases, unless a small amount of solvent is used, it is necessary for the procedure to be carried out at a temperature where the fatty acid blend is molten. With stearate mixtures this is about 80 °C. Some fatty acids such as iso-stearic acid have the advantage of being liquid at room temperature, but are not widely used as they are more expensive. 

The amount of bonded surfactant can be determined by simple techniques. A dissolution technique proved to be very convenient for the optimization of non-reactive surface treatment and also for the characterization of the efficiency of the treating technology [74,84]. First the surface of the filler is covered with increasing amounts of surfactant, then the non-bonded part is dissolved with a solvent. The technique is demonstrated in Fig. 11, which presents a dissolution curve of stearic acid on a CaC03 filler. Surface treatment is preferably carried out with the proportionally bonded surfactant (cioo)j this composition the total amount of surfactant used for the treatment is bonded to the filler surface. The filler can adsorb more surfactant (Cjnax)>but during compounding a part of it can be removed from the surface by dissolution or simply by shear and might deteriorate properties. 

The specific surface area of the filler is an important factor which must be taken into consideration during surface treatment. The proportionally bonded surfactant depends linearly on it [74]. ESCA studies carried out on the surface of a CaC03 filler covered with stearic acid have shown that ionic bonds form between the surfactant molecules and the filler surface and that the stearic acid molecules are oriented vertically to the surface [74]. These experiments have demonstrated the importance of both the type of the interaction and the alignment of sur-... 

Fig. 12. Effect of non-reactive surface treatment of a CaC03 filler with stearic acid on its interaction with PP, r=1.8 am (O) non-treated, (A) 75%, ( ) 100% surface coverage... 

---