December, 1934
I N D US T R I A L A N D EN GI N EE R I N G C H E M I ST R Y
in finishing coats whererer i t is desired to increase the speed of drying and add slightly to the adhesive properties and gloss of an exterior house paint. It is also worthy of comment that the tinting of these special primers to a light pearl gray seems to extend their efficiency and life. Apparently ultraviolet light penetrates white paint made with certain pigments and affects the oil after long exposure, while dark colored pigments in a paint absorb ultraviolet light and prevent it from destroying the oil, thus making a more permanently elastic film. Small percentages of graphite, carbon black, lampblack, or aluminum powder may be used for this purpose. The color thus developed is not sufficiently dark to cause any difficulty in obscuring the surface rvith two subsequent coats of white paint.
EXPOSURE TEST I n connection with the above suggestion3 on special primers, it is of interest to note the results obtained, after exposure for 4 . 5 years in Washington, on four types of priming paints applied to second-grade cypress surfaces, which exhibited large areas of flat grain (Figure 1). The best results were indicated by a linseed oil-graphite paint containing a substantial percentage of siliceous pigment. While it is not recommended that graphite be employed in great percentage in primers for wood surfaces that are subsequently to be painted white, because of the difficulty of obscuring the black color with top coats of white, the results do indicate that it is possible to make a primer v i t h a linseed oil vehicle and secure excellent results.
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Some lumber mills in the South haye experimented with the mill priming of their lumber with aluminum-pigmented varnish. It is probable that even superior results might be secured through the use of linseed oil primers made with white opaque pigment mixtures with substantial amounts of graphite and small percentages of the inert type pigments (referred to above) that aid in producing films allowing the passage of interior moisture. Experimental work in this direction is apparently warranted. Special primers have also been used to prevent segregated spotting of paints. This condition is often observed upon new painting jobs when there is a wide difference between the qpring- and summerwood. Naturally, selective absorption occurs, and the difference in refractive index of the absorbed and unabsorbed spots is indicated by a light spotting of the Surface. Flat, dead spots lack the requisite binder to resist weathering, and they soon check and fade. Properly applied, dense primers usually overcome this condition. The composition of the primers used in the tests shown in Figure 1 was as follows. Aluminum primer contained one gallon of spar varnish, 2 pounds of aluminum powder, and one quart of thinner; trimetal primer consisted of red lead, zinc dust, and aluminum powder dispersed in linseed oil, turpentine, and drier; chrome orange primer consisted of pure lead chromate dispersed in linseed oil, turpentine, and drier; graphite primer consisted of graphite and silica dispersed in linseed oil, thinner, and drier, RECEI%ED tlugust 6, 1934 Presented before the Division of Paint and Varnish Chemistry a t the 88th Meeting of the 4merican Chemiral Society, Cleveland, Ohio, September 10 to 14, 1934
Preparation of Plastics from Ground Wood Pulp L. LOWENAND H. K. BEXSON, University of Washington, Seattle, Wash.
T
HE use of pentosan-containing material for the formation of resinous condensation products is well known.
Sweeney ( 2 ) describes such products made froin cornstalks and Jones (1) has patented a process for making similar products from peanut hulls. In view of the large uses of wood pulp as a constituent of wall board made by the addition of extraneous adhesives of various sorts, it seemed desirable to determine the feasibility of utilizing the pentosans in wood for the production of a resinous adhesive within the wood pulp which might serve as a binder for the rest of the wood as the filler or inert material. Commercial ground wood pulp made from hemlock and spruce was used as the raw material. The sheets or "laps" were disintegrated in a small laboratory pulp beater, and the resultant pulp was centrifugalized, fluffed, and dried. I t was stored in the air to an equilibrium moisture content. Either phenol or cresol was added in approximately equal weight, and hydrochloric acid in all cases constituted the condensing agent,. After thoroughly mixing these materials, the mixture was heated for 6 hours at 70" C. and air-dried for 5 or 6 days. It was then ground in a ball mill for half an hour. The ground powder was heated at, about 80". C. until plasticity developed, and it was placed in molds and subjected to a pressure of 5 t'ons per square inch (7.9 kg. per sq. mm.) for 5 minutes. The molded plastic mas then baked a t a gradually increasing temperature up to 150" C. until it became hard. The composition of a number of the plastics made is given in Table I together with their general characteristics. The addition of glycerol in all cases yielded a more plastic product prior to molding and seemed to increase the strength and homogeneity of the pressed and baked product. When the latter was sawed through by a hack saw or turned down in a lathe, it showed a hard shiny surface. Sample 15 was turned down to a thin sheet and tested for breakdown voltage.
Dielectric failure occurred a t 8000 volts across a section 0.07 inch (0.178 em.) thick. The electrical resistance was determined on two samples and compared with test sample of commercial hard rubber: -ARE.
