Using the Instron Tester, a procedure has been developed for measuring wood/bark adhesion on small samples. Using very small, specially prepared samples, wood/bark adhesion measurements were made on twenty-four hardwoods and eighteen conifers. High dormant season wood/bark adhesion in hardwoods was found to be associated with the presence of fibers in the inner bark. The procedure appears to be useful in identifying difficult-to-debark species and evaluating methods of reducing adhesion

Einspahr, D. W.

Fiscus, M. (Harder)

Van Eperen, R. H.

English

Wood and Fiber Science (E-Journal)

METHOD FOR OBTAINING WOODIBARK ADHESION MEASUREMENTS ON SMALL SAMPLES M. (Harder-) Fiscus Research Fellow R. H. Van Eperen Research Fellow and D. W. Einspahr Senior Research Associate The Institute of Paper Chemistry, Appleton, WI 54912 (Received 10 March 1982) ABSTRACT Using the lnstron Tester, a procedure has been developed for measuring woodlbark adhesion on \mall samples. Using very small, specially prepared samples, woodlbark adhesion measurements were made on twenty-four hardwoods and eighteen conifers. High dormant season woodlbark adhes~on in hardwoods was found to be associated with the presence of fibers in the inner bark. The procedure appears to be useful in identifying difficult-to-debark species and evaluating methods of reduclng adhesion. Kc,yn,ords: Woodlbark adhe\ion, debarking, shear parallel to grain. Adhesion between wood and bark has been the subject of research for many years. A number of apparently satisfactory but relatively crude techniques were developed for measuring adhesion (Wilcox et al. 1954; Berlyn 1965; Zakharov 1963). A major part of the woodlbark adhesion research was initiated during the 1950s when there was considerable interest in the chemical debarking of standing trees (McIntosh 1951; Wilcox et al. 1956; Schutt 1960). Most of these early tests were designed for use on bolts or standing trees and were judged to be unsatis- factory for examining adhesion changes in smaller samples or chips. A test developed at The Institute of Paper Chemistry for accurately measuring seasonal changes in woodlbark adhesion is described. This test was designed for small woodlbark samples and measures shear parallel to the grain. The test is also useful in assessing the effects of treatments to reduce woodhark adhesion. METHODS A N D  MATERIALS Field sampling techniques involved either removing a disk at breast height (495 feet) from an appropriate, typical tree or else removing a wedge-shaped sample with a chain saw. The disk or wedge was placed in a plastic bag and kept cold (approximately 40 F) until tested. A storage study indicated that samples could be kept this way for up to 72 hours with no appreciable change in adhesion. From these disks, a small ( 3 1 ~ ~ -  x 3 / ~ ~ -  x 11/4-inch) tab was prepared, with incorpo- Wired ii,ir/ bih,,, \~ . r i , , / c , , ,  1513). 1%'.  pp. 219-222 ( Ithi? h y  ~ h c  Soc~cty  clf Wood Sc~vnce and  rechntrlogb 220 WOOD A N D  FIBER SCIENCE. JULY 1983, V.  15(3) FIG. I. Small test samples suitable for use in the Instron Tester were prepared by cutting thc sample to approximate size on the band saw. The samples were then: (A) shaved to  the exact di-. mensions, (B) cuts made through the bark and wood to the cambium, (C)  removed from the jig usetl in holding the sample during cutting. (D) tested for adhesion (shear parallel to grain) in the Instr-c)rl Tester. rated both wood and hark. The specimens were first cut on a band saw to a n  approximate size of I14 x '14 x Ill4 inches long. Next, wood and bark surf;ices were trimmed with a razor blade to make them as nearly parallel to the interface as possible. The two surfaces were then clamped in a jig, as shown in Fig. 1A: the specimen was aligned so that the grain direction was parallel with the long dimension of the jig; and the two exposed surfaces were trimmed flush with the 31~s-inch dimension of the jig. The specimen was then turned in the jig and aligned F;!CM.) ( ' I  (11.-W001)IBARK ADHESION MEASUREMENTS / \ 'A- - Bark - - Cambium Wood y/ \cuts  made in bark and wood FIG. 2. Diagram of the uoodibark adhesion test sample. The dimensions of the test tab are ;/I(; >: Illti x 1'11 inches, and the area between the two cuts tested for adhesion is 0.0234 square inches (0.15 1 square cm). so that the woodlbark interface corresponded with the bottom of the :'/,,,-inch cutout of the jig and the wood and bark surfaces again trimmed flush. The re- sulting tab had the woodlbark interface centered with respect to the thickness of the specimen. To facilitate making the final two cuts in the specimen, the apparatus shown in Fig. IB was used, together with the shaper attachment on a machine Lithe. The specimen was held in a U-shaped jig and supported on the bottom durin,g cutting. The cutting tool was an X-acto No. 23 two-sided blade with a ground- down cutting edge held in the chuck of the lathe. The specimen was positioned just behind the blade with the latter displaced ' I , ,  inch with respect to the center of the U-shaped jig. The specimen was raised until the tip of the blade coincide'd with the woodlbark interface. and the setting of the depth index was noted. The specimen was then lowered to a position where the blade just cut the surface and a cutting pass was made by moving the shaper forward. The specimen was raised 0.010 inch and a second cutting pass was made by moving the shaper backward. Similarly, additional cutting passes were made until the depth of cut was 0.005 inch below the woodlbark interface. The specimen was then inverted and a cut made in the same manner from the opposite side, again with the blade positioned 'I,,; inch off center of the U-shaped jig. Hence, the distance between the two cuts was '18 inch, the bottom of the two cuts overlapped 0.010 inch, and the surface area of the woodlbark interface tested was 0.0234 square inch or 0. I51 square cm. Figures 1C and 2 illustrate the size and shape of the test specimens. For testing, the specimens were mounted in an Instron Tester, as  shown in Fig. ID. The clamping jaws were 0.02-inch wide and were separated by a distance of 0.75 inch. The specimens were strained at a rate of 0.2 inch per minute. At least four specimens were tested for each sample. Tests can be made in any normal room temperature and humidity environment. The specimens should be kept in small, closed containers before testing to prevent moisture loss. Preferably, they should also be stored under refrigerated conditions if more than a few hours elapse before testing. 7 7 7  --- WOO11 AN11 FIBER SCIENCE. J U L Y  1983. V .  lX31 KESUl  TS A N D  DISCUSSION WoodJbark adhesion was measured for twenty-four hardwoods and eighteen conifers. Growing season woodlbark adhesion was very similar for all species tested, ranging from 245 to 588 kPa. The failure zone was consistently located in the cambium zone or in the newly formed, nonlignified xylem cells just outside the cambium zone. Dormant season woodlbark adhesion varied greatly from species to species, ~isually being higher for hardwoods than conifers. Hardwood dormant season adhesion varied from 3,000 kPa for shagbark hickory to 706-765 kPa for white oak. Conifer dormant season adhesion varied from 1,775 kPa for black spruce to 43 1 kPa for western larch. High dormant season woodlbark adhe- sion in hardwoods was associated with the presence of fiber in the inner bark. Sclel-eids in the inner bark resulted in decreased dormant season woodlbark adhe- sion. An important limitation of this method is that, during the dormant season, when fi~ilur-e occurs in the bark, the magnitude of the test value is dependent upon the strength of the inner bark of the species involved. All that can be said about the values obtained during this period is that adhesion in the cambium zone and in the bark and wood elements immediately adjacent to the cambium zone is in excess of the values obtained. The principal limitation of the test is that it does not provide a suitable value that can be used to compare woodlbark adhe5ion differences between species during that part of the year when adhesion is high but instead measures the strength (resistance to shear) of the inner bark. How.- ever, it does identify those species with extremely high woodlbark adhesion which would be difficult to debark. Within-species comparisons, between-species com- parisons during the growing season, and the evaluation of methods of reducing adhesion can be adequately measured by the testing procedure. REFERENCES H E R [  Y K .  K. W .  1965. The effect of variation in the strength of the bond between bark and v~oocl on mechanical barking. Woodlands Research Index, Pulp and Paper Research Inst. of Canacl,i No.  174. 32 pp. MCINTOSH. D. C'. 19.51. Effects of chemical treatment of pulpwood trees. Forestry Branch, Fore\t Products Laboratories Div.. Dep. of Forest Products and Development, Ottawa, Canada Hull. No.  100. 29 pp. SCHUI  I ,  C'. 1960. Chemical debarking of trees; a review of literature. Papen Puu 11:579-598. W I L  cox. H .  E . .  F. J .  CLAB \TOR, A N D  G .  G I K O L A M I .  1954. Seasonal variations in bark-peeling characteristics of some Adirondack pulpwood species. J .  Forestry 52(5):338-342. --- , D. MORELAND, A N D  R .  SMITH. 1956. Chemical debarking of some pulp- wood \pecies. State Univ. of New York College of Forestry at Syracuse, Tech. Pub. No. 77. 43 PP. ~ K H A K O V ,  V .  V. 1963. l 'he strength of the adherence of bark to wood at low temperature\. Del-evoobritbat. PI-om. 12(9): 10. 

Method For Obtaining Wood/Bark Adhesion Measurements on Small Samples

https://wfs.swst.org/index.php/wfs/article/download/2051/2051

Method For Obtaining Wood/Bark Adhesion Measurements on Small Samples

Abstract

Similar works

Full text

Available Versions

Wood and Fiber Science (E-Journal)