TREATMENT OF ALASKAN SPECIES BY DOUBLE-DIFFUSION AND MODIFIED DOUBLE-DIFFUSION METHODS

Transcription

1 TREATMENT OF ALASKAN SPECIES BY DOUBLE-DIFFUSION AND MODIFIED DOUBLE-DIFFUSION METHODS U.S.D.A., FOREST SERVICE RESEARCH PA PER FPL U.S. DEPARTMENT OF AGRlCULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY

2 ABSTRACT Poles of white spruce, Sitka spruce, mountain hemlock, and balsam poplar were subjected to several variations on a standard preservative process: Allowing the material to partially season (30-40% MC) before treatment; incising the material when green or partially seasoned; and elevating the temperature of the first solution (CuSO 4 ) and letting the wood cool before transfer to the second solution (Na 2 HAsO 4 ). As compared to conventional double diffusion, retention and penetration were increased by incising, but not enough to extend service life. All three conditions together provided best results; moisture content at time of treatment determined which schedule was most favorable.

3 TREATMENT OF ALASKAN SPECIES BY DOUBLE-DIFFUSION AND MODIFIED DOUBLE-DIFFUSION METHODS 1 By L. R. GJOVIK, Research Specialist H. G. ROTH, Chemist and H. L. DAVIDSON, Technician Forest Products Laboratory 2 Forest Service Department of Agriculture INTRODUCTION Alaskan officials have shown interest in the use of the more abundant important local species, such as white spruce, Sitka spruce, mountain hemlock, and balsam poplar, for treated poles, piling, and lumber in the industrial market and the proposed trans-alaskan pipeline. Previous treatment of these species by pressure-treating methods has been limited, and the data available would indicate that they would fall into the category of hard-to-treat species. The recent closing and dismantling of Alaska s only pressure-treating plant at Whittier indicates the operation of this type of business is not economically feasible in that area. Surveys show, however, that the market for preservative-treated material is steadily increasing in Alaska. Application of the double-diffusion and modified double-diffusion methods of preservative treatment of Alaska species could be quite adaptable to their treating problems because of the simplicity of the procedures and the small investment in equipment. The conventional double-diffusion process consists of soaking green woad first in one chemical solution and then in a second solution. the chemicals are each water-soluble, they diffuse into the free water in the wood, where they react with each other to form a relatively insoluble, leach resistant compound that is toxic to fungi and insects. The modified double-diffusion process involves basically the same mechanisms. Some refinements have been made to shorten the treating time and improve penetration of refractory species. These refinements are: (1) elevating the temperature of the first solution and allowing the wood to partially cool before transferring to the second solution, (2) allowing the material to partially season (30-40 pct. MC) before treating, and (3) incising the material either in the green or partially seasoned condition. The purpose of this study was threefold (1)to determine the feasibility of treating these Alaskan species by double diffusion and the modified double-diffusion processes that have been effective in other hard-to-treat species such as Engelmann spruce and Rocky Mountain Douglas- 1 Presented at the FPRS 26th annual meeting in Dallas, Tex., in June. 2 Maintained in cooperation with the University of Wisconsin, Madison, Wis.

4 fir; 3 (2) to determine the best treating schedules and solution concentrations for the treatment of these species; and (3) to determine the retention of chemicals by assay of various zones of the treated pole sections by these methods, MATERIALS AND METHODS Materials The following species were included in the study: Mount ai n hemlock (Tsuga mertensiana (Bong.) (Carr.)) Balsam poplar (Populus balsamifera L.) Sitka spruce (Picea sitchensis (Bong.) (Carr.)) Western white spruce (Picea glauca var. albertiana (S. Brown Sarg.) Preservatives used in this study were copper sulfate and sodium arsenate. Arrangements for procurement of the four Alaskan timber species were made by Verner Clapp, Branch Chief, Forest Products Utilization, S&PF, Region 10, Juneau, Alaska. The mountain hemlock and Sitka spruce were cut in the Seward area from National Forest land; the balsam poplar and western white spruce were cut in the Chena Valley outside Fairbanks, Alaska. The round material was of pole size, 20 feet long and varying in diameter from 8 to 10 inches. Because some of the treatments were to be made on poles in green conditions, precautions were taken to prevent drying enroute to the Forest Products Laboratory in Madison, Wis. The poles were end-coated with a resorcinol adhesive, loaded into a railroad car, and covered with sawdust; the sawdust was soaked water, and the load was covered with polyethylene sheeting. Poles were shipped in late September 1970, to Cedar Services, Inc., Minneapolis, Minn., for debarking and incising. The 20-foot poles were incised to within 4 feet of each end, The depth of incision ranged from 3/8 to 1/2 inch. The poles were then reloaded using the same procedure as before, and shipped to the FPL in October A 1-inch cross-section 3 feet from the end of each pole was removed to determine moisture contents, specific gravities, and depth of sapwood as shown in table 1. The poles were then cut into 3-foot lengths, and each section numbered. No two sections of a pole would be given the same treatment. The 3-foot sections of each species were end coated with an epoxy rock tar to prevent end penetration during treatment. Pole sections to be treated while green were stored in the cold room at 36" and 80 percent relative humidity prior to treatment and the balance was divided into two groups; the first was kiln dried to 30 percent moisture content and the other to 12 percent moisture content prior to treatment. Treatments Three replicates of each of four species comprised each treatment charge, and treatment variables were different for each of the 12 treatments. Treatment and pretreatment variables included: (1) green and partially seasoned specimens, (2) incised and unincised specimens, (3) time immersed in preservative solutions, (4) concentration of the preservative solutions, and (5) temperature of the first solution. In each preservative treatment, specimens were completely immersed in the copper sulfate solution, rinsed with water, and transferred to the second solution, sodium arsenate. Table 2 illustrates the schedule of treatments and the conditions that prevailed for each specific treatment. The first five schedules were treatments made with both preservative solutions at room temperature, and the remaining seven schedules were treatments in copper sulfate at 190 F. for approximately 7 hours, followed by a hot-water rinse, then a transfer of the specimens to the sodium arsenate solution. Thermocouples were inserted to a depth of 2 inches in each of the four species and temperatures were recorded hourly during the immersion in the hot copper sulfate solution. Specimens attained a temperature in the range of 155 to 180 at the 2-inch depth at the end of the heating period in the copper sulfate solution. 3 Markstrom, D. C., Mueller, L. A., and Gjovik, L. R. Treating Resistant Rocky Mountain Species by Regular and Modified Double-Diffusion Methods. Forest Prod. J. 20(12): FPL 182 2

5 Table l.--characteristics of the poles as received WS -- White spruce SS -- Sitka spruce H -- Mountain hemlock P -- Balsam poplar 1 -Basedon oven-dry weight andvolume. 3

6 Table 2.--Pretreatment conditions and atxu for -schedules Specimens were covered with polyethylene sheeting after each treatment schedule and remained covered for a period of 2 weeks to permit additional diffusion of chemicals and to prevent them from drying too rapidly. Specimens were then uncovered and allowed to dry lor 6 weeks before cutting of samples to determine preservative retentions. Treatments made by the conventional doublediffusion method were done on green pole sections, and the modified double-diffusion treatments were made using green material and material kiln dried to 12 percent and 30 percent moisture contents. Difficulty was encountered in the drying of the balsam poplar so, consequently, it was treated at a slightly higher moisture content than the other three species. Assay of Specimens Two cross-sectional disks, approximately 1/8 inch thick, were cut for assay from the center of each of the three replicates of each species. Three disks, one from each of the replicates, were ground together to an entire cross section composite sample; the other three disks from each species were cut into zones. The zones were determined as the outer 1/4 inch, 1/4 to l/2 inch, 1/2 to 3/4 inch, and 3/4 to 1 inch, and in each case the complete zones of each of the three disks were removed, combined, and prepared for analysis for copper and arsenic. Two additional zones, the 1- to l-1/4-inch and the 1-1/4- to 1-1/2-inch, were assayed from the pole section treated in schedule No. 8. The samples were prepared by grinding the specimens in a Wiley mill to 2 mm. or less, drying the dust samples at 105 C. overnight, and cooling them in a desiccator. Copper was determined gravimetrically by the thiocyanate method; arsenic was determined by the AWPA Standards Method A American Wood Preservers Association Standards, AWPA, 1625 Eye Street, NW., Washington, D.C FPL 182 4

7 RESULTS OF TREATMENT AND DISCUSSION tions are illustrated in figures The doublediffusion treatment, using green or partially seasoned material as in treating schedules 1 to 5 with solutions at room temperature, showed penetrations Measurements of preservative penetration were taken from freshly cut cross sections of each of approximately 1/2 inch, while sched- ules 6-12 using hot copper sulfate and sodium species and treating schedule, using the Chrome arsenate at room temperature showed penetration Azurol-S indicator for copper. These penetra- to a depth of about 1 inch or more. The dark, stained areas indicate the depth of penetration of copper sulfate obtained by treatment according to each schedule. Species are, from top to bottom in each figure: White spruce, Sitka spruce, mountain hemlock, balsam poplar. Figure 1.--Schedule 1. M

8 Figure 2.--Schedule 2. M

9 Figure 3.--Schedule 3. M

10 Figure 4.--Schedule 4. M FPL 182 8

11 Figure 5.--Schedule 5. M

12 Figure 6.--Schedule 6. M FPL

13 Figure 7.--Schedule 7. M

14 Figure 8.--Schedule 8. M FPL

15 Figure 9.--Schedule 9. M

16 Figure 10.--Schedule 10. M FPL

17 Figure 11.--Schedule 11. M

18 Table 2 gives the details of each treating schedule with regard to variables included in each specific treatment. The oxide retention in pounds per cubic foot of total salts of the composite samples, anti the different assay zones of the four species are shown in table 3. The chemical analyses as shown in table 3 tend to confirm the visual results depicted in figures Based on these results, schedule No. 3 provided the best treatment of those which did not involve a heated first solution. However, it is felt that this would not be an effective treatment for normal ground contact exposure. Of the variables tested in schedules 1-5, it appears that incising is the most important. Analysis of samples treated according to schedules 6-12 indicate comparatively good distribution and adequate retentions of preservatives are obtained. white spruce, schedules 8, 11, and 12 provided acceptable treatment. The Sitka spruce received adequate treatment in schedules 8 and 12. The mountain hemlock treated effectively in schedules 6, 7, 8. and 11. Of the four species tested, the balsam poplar was found to be more readily treated than the spruces or the hemlock. The best preservative treatment based on depth of penetration and on total retention in all four species resulted from schedule 8. Figure 12.--Schedule 12. M FPL

19 Table 3.--Preservative retentions of double-diffusion treated Alaskan species by assay of 1/4-inch zones and total cross sections 1 1 All retention values are composites of 3 samples, and are based on the oxide of total salts (CuO + As2 O 5 ).

20 CONCLUSIONS (1) The results of treatment of the four Alaskan timber species studied reveal that retention and penetration of the conventional double diffusion is improved by incising, but not sufficiently to provide extended service life in use. (2) The pretreatment conditions of partial seasoning and incising in conjunction with the elevated temperature of the first solution provide remarkable penetration and retention capabilities. (3) From the data in this paper, it may be concluded that, if the material to be treated is green, the best schedule is probably No. 12. If the material to be treated is dry or partially dry, it appears that the best schedules are Nos. 6, 7, or 8 with a slight preference for No. 8. FPL

21 ACKNOWLEDGMENTS The authors gratefully acknowledge the Clayton Logging Company, College, Alaska, the Kenai Lumber Company, Anchorage, Alaska, and the Alaska Department of Natural Resources for their assistance in procuring the pole species used in this study. We also wish to thank Cedar Service, Minneapolis, for debarking and incising the poles. 19

22 ABOUT THE FOREST SERVICE.... As our Nation grows, people expect and need more from their forests--more wood; more water, fish and wildlife; more recreation and natural beauty; more special forest products and forage. The Forest Service of the U.S. Department of Agriculture helps to fulfill these expectations and needs through three major activities: * Conducting forest and range research at over locations ranging from Puerto Rico to Alaska to Hawaii. * Participating with all State forestry agencies in cooperative programs to protect, improve, and wisely use our Country s million acres of State, local, and private forest lands. * Managing and protecting the 187-million acre National Forest System. The Forest Service does this by encouraging use of the new knowledge that research scientists develop; by setting an example in managing, under sustained yield, the National Forests and Grasslands for multiple use purposes; and by cooperating with all States and with private citizens in their efforts to achieve better management, protection, and use of forest resources. Traditionally, Forest Service people have been active members of the communities and towns in which they live and work. They strive to secure for all, continuous benefits from the Country s forest resources. For more than 60 years, the Forest Service has been serving the Nation as a leading natural resource conservation agency. FPL