Document 7OBJvzxq3JQOVwp5OzGV0rq3o

. Figure 3. Tray water analysis on 39 lb. magazine grade. Figure 4. Effect of asbestos and talc on abietic acid removal from water solutions. it has frequently proved to be signifi cantly more effective than talc. This would indicate that some other prop erty is also important. Tentatively, this has been attributed, in part, to the high surface area and, in part, to the cationic surface charge of asbes tos. Laboratory tests have been made in an attempt to compare the rela tive effectiveness of asbestos and talc in removing pitch. Since abietic acid is the most common of the resin acids, it was used to simulate pitch In the laboratory study. The abietic acid solution was adjusted to a pH of 4.0 it 0.2, the level where many papermaking circuits operate. Be cause abietic acid is quite insoluble in add solutions, a visible precipitate could be seen. Additions of four grams per liter of higb-purity asbestos and talc were then made to different solutions. The suspensions were allowed to stand until , a superstate free of asbestos or talc floes could be withdrawn. The .floc-free solutions were then analyzed with spectrophotometer at a wave length of 250 mu to determine the abietic add concentration.. As shown in Figure 4, asbestos re moved abietic add effectively at all concentrations. Talc was effective at low levels but became less effective and gave more erratic results as the abietic add concentration increased. Thus, to the extent that the abietic add simulates pitch, the effectiveness of asbestos for pitch control is largely due to its ability to flocculate and re move suspended solids and to a lesser degree by adsorption of dissolved matter. As yet, no one has developed a satisfactory method of analyzing for pitch and, therefore, in thtvmill- the only criterion, has been performance. In most of the mills now employing asbestos it has been used because their problem has been suffidently severe that no other product has worked satisfactorily. In many in stances, the asbestos is performing a dual role. In addition to controlling pitch,- it has contributed to improved filler retention, sheet formation and printability. Because of its success in pitch con trol,' its use has been extended to areas such as control of organic mat ter in waste pulps. Only recently, it was tried in a board mill that had been experiencing problems of as phalt agglomerates in the final prod uct. It was reasoned that the same properties that make asbestos effec tive in pitch control should be appli cable to the problems encountered in asphalt dispersion and control. It. was first tried at 1.25 per cent asbestos level in a 21-Ib./1000 ft.1 chip board consisting of printed news and corrugated boxes. Little or no improvement was observed during the first 8-10 hours; however, after it had been on the machine for 18 hours, marked improvements were noted' both in the number and size of the asphalt agglomerates. This type of response would indicate that the asbestos can do little once the agglomerates have formed, and its function is one of adsorption or co flocculation of dispersed asphalt be fore it has an opportunity to coagu late. As is customary with retention and pitch Control applications, the asbestos was added with the pulp at the hydropulpers. As of the time of this writing, the asbestos is still being used in this grade and doing a satis factory job. In a subsequent trial on a light weight kraft grade, 1.25 per cent asbestos was employed for pitch con trol. This particular grade was also plagued with a polyethylene prob lem. Agglomerates would form in the sheet; which resulted in breaks on the rewind. It was observed- in this grade that the asbestos not only im proved the asphalt condition but re duced the problem attributed to the polyethylene. Modified asbestos products The very fact that chrysotile as bestos has a positive surface charge as well as a somewhat reactive sur face makes it a prime candidate for modification. With high-purity asbes tos as a base product, it is relatively simple to affect the physical proper ties by either physical or chemical means. For some uses, it has been advantageous to use a combination of treatments. The most successful modified as bestos product is currendy marketed under the name asbestos T.~ During the cource of refining the asbestos, a highly-dispersed stream of titanium dioxide is blended with the purified asbestos and manufactured in such a way that the TiO* becomes an inti mate part of the product. Once this has been accomplished, the material resembles a fibrous titania. The result is a single product that combines the properties of both constituents. The retention capabilities of the "T" are comparable to the natural product, and its opacifying power is greatly enhanced by the titania. In the mill trials completed, it has been used to replace titanium dioxide on a pound-for-pound basis in quantities up to five per cent of the total furnish. This is possible due to the high optical efficiency achieved and to the improved retention of the fur nish components. In one. mill trial asbestos "T" was ' substituted on a pound-for-pound basis for'titanium dioxide in a 50-lb. PULP & PAPER -- Jonuory 10. 1966