Primers for Wood York Ave., Washington, 1). C. rrtrriisli to produee an cxtrenrely uuisture-re may not be good practice. It might cause many eases of peeling wliiclr otherwise would not occur. It is apparent that the priming system for siiclr dwellings slwold be of such a nature as to allow tile passage of moisture frorii the interior of the dwelling through the siding and tliroogll tlie filru. Snr:li it film sliould liave a vitlve-like action and resist the passage rrf aiiy substantial arnount of water from without. If objectioii is miscd t,list si~draction, while ideal, is impossible, the fact reiriaiiis that the results are tlie same. Exteri d iuoisturc usually is applied in large doses (rain) for short periods. Interiial trioistiire is applied in arnall doses (vapor) fur lrmg periods. The t.inie clement is vastly Inore important tlixn the intensity elcinenb. The type of prirner pniiit wliiali t i l e writer lins iiiuiid suitable oii refractory ,sImies uf wood i s one w l i i c l t embodies oil as the iirjuirl ratlicr tliarr spar \.ariiisli, since a rlriod filui of linseed oil is tiiore poroirs to nroiatitre than a i l r i d filiir of varni4i. hlmiviver, blie writer has found that an admixture of pigments might prefcrably be erirployefd in mcb primers aid suggests t.liat it is good practice to use in the p i y r n o n t 1, i t r t i o II about 10 per cciit of diatomaceous ear t li (skeletonized diatoms) or similar porous inerts which liave t h e p e c u l i a r property of forming witit linseed oil, ill the presence of other pigments, a film whiclr is quite porous to the nroisture that comes through siding. For i n s t a n c e , prirning p a i n t s m a d e of a heavily pigmented, white IcaiIMn~ecdoil cumpositirq and eont.ttiuiiig i n tire pigment portion about 10 per c e n t of diatonraceous earth, as well Ss percentages of zinc and titanium pigments, havegiven excellent results. Tile final film formed lry such linseed oil paints p r o d u c e s a surface uinm wliiali siibscqiieiitly applied coats of linseed oil paint will properly ailbere, whereas proper adherence is not nlways abserrwl w l m finisiring coak of oil paint are applied to pinvclered metallic pigrrrent-varnish primers. The above remarks regarding varnish a.ppIy to this product when used as the total portion of the paint liquid. Varnish nia.1, of COIITSR, be used in moderation not only in special primers but fjliit
It is also important that the builder realize tire advantage n f using edge-grain s i d i n g , as sucli surfaces lrold paint iriucli better than Aatgrain boards. The Iiiglier the grade of lumber and the fewer t h e knots, t h e greater will be tiie success [if the pailltirig job. 1)mellings of tlie future \vi11 to a great ext.ent bo provided with air-conditioiririg and liumidifying nysteins. It is easy to v i s u a l i z e tlre large aimmiits of inoizlure which could be forced t h r o u g h the siding ni a lioiise duri n g tire w i n t e r m o n t l i s , because of the coiitinuous relat i v e l y high v a p o r pressure e x i s t i n g within t h e house. Peeling of the p i n t will t h e n be observed, sirice peeling is due almost entirely to tiis passage of water from tlie back through tlm siding, where it finally strikes tho paint coating and causes blisters arid other defects. It is evident, tliereforc, that the primer paint to he used on the siding of air-conditioned dwellings sliould Ire of a relatively porous charartcr rather than notiporour. For instance, tlie applicat~ionof metal powders iliapcrscd in spar
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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.
1273
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.
