Showing papers in "Wood Science and Technology in 1969"

The distribution of lignin in sprucewood as determined by ultraviolet microscopy

Abstract: The distribution of lignin in black spruce has been determined quantitatively by the study of 05 μm transverse sections in a UV microscope The average lignin concentration in the compound middle lamella was about twice that in the secondary wall The lignin concentration of the middle lamella at the cell corners of adjacent tracheids was nearly four times that in the secondary wall but the volume of the secondary wall was much greater than the volume of the middle lamella Thus, for earlywood, 72% of the total lignin was in the secondary wall leaving only 28% in the compound middle lamella and cell corner middle lamella regions The corresponding values for latewood were 82% and 18% respectively Use of oblique longitudinal sections of 01 μm thick permitted the resolution of the compound middle lamella The lignin concentration in the true middle lamella was found to be equal to that in the cell corner middle lamella and the primary wall lignin content to be about twice that in the secondary wall

The longitudinal Young's modulus of Pinus radiata

Abstract: The variation of the longitudinal Young's modulus with mean cellulose microfibril angle of the wood substance of the earlywood of a softwood has been determined from small clear samples. The longitudinal Young's modulus falls steeply as the angle between the longitudinal axis and the mean microfibril direction in the cell walls increases. The variation has been explained in both form and magnitude by applying the elastic theory of a fibre composite material with distributed fibre directions to a model of the experimental material. It confirms the two phase concepts of the plant cell wall, as far as the elastic properties are concerned, of rigid crystalline microfibrils embedded in an isotropic matrix of amorphous and paracrystalline materials.

The application of ultraviolet microscopy to the distribution of lignin in wood description and validity of the technique

Abstract: A method has been developed for the determination of lignin distribution in the wood cell wall by ultraviolet microscopy. The method incorporates some important advances on previus applications of UV microscopy to the study of lignin distribution. Ultrathin cross-sections of wood are obtained by the sample preparation and sectioning techniques of electron microscopy. The specimens are examined in monochromatic ultraviolet light using quartz reflection optics. The microscope image is photographically recorded and the negative is subsequently subjected to densitometric analysis. Each stage of the analytical procedure has been critically assessed to determine its validity and limitations. The method is ideally suited to the study of the removal of lignin from the wood cell wall during cooking and possesses other important applications in wood technology.

A contribution to the ultrastructure of tension wood fibers

Abstract: Pronounced tension wood from four North-American hardwood species has been examined by light and electron microscopy. Delignified fibers were also studied. The gelatinous layer was in all cases loosely attached to S2 but varied considerably in thickness within each species and was in one case terminated towards the lumen by a layer resembling S3. A terminal lamella was not observed. After considering both earlier evidence and the present results, it was concluded that the gelatinous layer has neither a honeycomb nor a homogeneous texture, as has been suggested, but that it consists of concentric lamellae of cellulose microfibrils. In the absence of hemicelluloses and lignin, the microfibrils are probably bound together less firmly than they are in other cell wall layers. The gelatinous layer is more readily separated from the remainder of the cell wall by mechanical forces than by chemical reagents.

Micromorphology of the bacterial attack of wood

Abstract: This paper describes fully the various patterns of bacterial attack to be observed in wood. It is based on many observations made with bacterially infected wood, both in pure laboratory cultures and in naturally attacked wood from diverse environments. Patterns of attack are described for tracheids, fibres, vessles and rays and three types of pit border decay are figured, together with attack of the pit margo and torus. A brief section also deals with the macroscopic appearances of wood subject to bacterial attack.

Seasonal development of secondary xylem in Pinus Strobus L.

Abstract: Secondary xylem, or wood, is the tissue that conducts water and minerals in the tree; thus it performs physiologically one of the most important functions for the tree. In addition secondary xylem is the tissue that primarily determines the suitability of a tree for various economic uses.

Distribution of lignin in normal and tension wood

Abstract: The distribution of lignin in normal and tension wood of four hardwood species has been studied by examination in the electron microscope of the lignin skeletons remaining after removal of the polysaccharides with hydrofluoric acid. In normal wood fibers, the S1 had a higher lignin concentration than the S2 layer, which was not as highly lignified as in conifer tracheids. Vessels had a high concentration of lignin in both normal and tension wood, while the extent of lignification of the parenchyma was variable.

Analysis and design of furniture frames

Abstract: The engineering design of furniture frames was investigated. The stiffness method of matrix structural analysis was applied to furniture frame design, and modifications of it which are needed to treat frames with semi-rigid, elastically non-linear joints of finite size were developed. A method of designing two-pin moment-resisting dowel joints was also developed. An experimental furniture frame was designed using the theories formulated. Results of tests performed on this frame agreed satisfactorily with those predicted theoretically.

Transitional variation and relationships among properties within loblolly pine growth rings

Abstract: Loblolly pine microtome sections 100μm thick were tested wet in tension. This thickness was approximately double the outside diameter of tracheids. Results indicate a curvilinear relationship between tensile strength and specific gravity of microspecimens combining both earlywood and latewood zones. Contrary to expectations the rate of change in slope of curve, expressed as tangent angles, decreased as specific gravity increased. Both tensile strength and stiffness values of these microspecimens are low in relation to their specific gravity. This reduction in strength and stiffness is probably related to the low ratio of microspecimen thickness to tracheid diameter, but needs further investigation. If the proper ratio between microspecimen thickness and tracheid diameter is determined, the transitional variation in tensile strength and stiffness within growth ring may be accurately established. The transitional variation in specific gravity can be successfully established from microtome sections, however the method is time consuming and not completely free of errors.

On the formation and fine structure of septate wood fibres of Ribes sanguineum

Abstract: The septate wood-fibres of Ribes sanguineum result from a genuine mitosis of the still functioning nucleus in lignified cells. The development of the septa occurs first in the vicinity of protoxylem and spreads centrifugally outwards and from the basis of the shoot towards the vegetative apex. Because there is no wall-layer fusion of the septum with the fibre-wall, the terms ‘chambers’ or ‘compartments’ are proposed for the partitions resulting from cytokinesis. The septum is built up by a middle lamella with primary-wall structures and plasmodesmata; it possesses a cellulose-pectin character and does not evince secondary wall appositions or lignification.

Stress relaxation of wood at several levels of strain

Abstract: Stress relaxation tests were performed with six tropical American species. Stress relaxation was not found to be a linear function of strain at any level of strain. At qual low levels of strain, stress relaxation in compression was much greater than in tension. A mechanical model consisting of an isolated spring in parallel with a spring and dashpot in series was used as an aid in the derivation of equations describing stress relaxation. An attempt to apply Newtonian viscous theory to the model was unsuccessful in accounting for rate of relaxation. However, when the hyperbolic sine law of viscous flow was applied, mathematically derived curves fitted the data very well. Stress relaxation appears to be related to “departure strain” which may be obtained readily from static stress strain diagrams.

Shrinkage properties of second-growth southern yellow pine

Abstract: Several factors which may affect the shrinkage of wood had been studied using loblolly pine (Pinus taeda L.). It was observed that volumetric, tangential and radial shrinkages decreased as the height increased. Longitudinal shrinkage increased with height. Only tangential shrinkage was significantly affected by the distance from the pith factor. All shrinkages were found to vary significantly according to cardinal directions. For the trees studied, lower volumetric, tangential and radial shrinkages were observed for specimens from the south side of the pith. Longitudinal shrinkage was noticeably higher in this direction.

Laminar sorption and swelling theory for wood and cellulose

Abstract: The known requirements for the sorption and swelling of wood are reviewed. These are shown to be compatible, in the case of softwoods, with the following simplified model. The fibers are continuous with either rectangular or circular cross sections and lumen of the same shape with a constant size. The fiber walls consist of concentric lamina made up of small repeating units 100 A by 100 A, consisting of a microcrystalline core surrounded by an amorphous sheath. All sorption and swelling occurs at the surfaces of or within the amorphous sheath. The major portion of the sorption and swelling is inter-laminar with just sufficient intra-laminar sorption and swelling to avoid laminar distortion. Calculations give the generally accepted internal sorption surface for water of about 200 square meters per gram. The portion of the total sorption that is intra-laminar varies from 5 ... 20 percent in going from wood with a specific gravity of 0.3 ... 1.0. Thickness of sorption in water molecules per sorption site vary from 6.1 ... 4.9 for inter-laminar sorption and 0.35 ... 1.35 for intra-laminar sorption in going from wood with a specific gravity of 0.3 to one of 1.0. Similar values are obtained from experimental swelling data where lumen cross sections change. Similar calculations for super swelling of wood and pulps show that laminar separations may become sufficiently great to be microscopically visible. The calculations show that bound water fiber saturation points for wood normally fall in the range of 25 ... 40 percent. Super swollen wood, chemically isolated fibers and beaten fibers may as a result of reduced restraints have fiber saturation points greater than 150 percent. The latter are attributed to dispersion or diffusion forces rather than the conventional bound water forces of hydrogen bonding for intact wood.

Contribution to the study of internal stresses in the wood of eucalyptus

Abstract: Research was carried out to reduce internal stresses in E. camaldulensis. Altogether, 74 trees of the Circeo National Park were examined; 25 eucalypts were girdled, the cut affecting the entire sapwood, while the remaining trees were taken as controls. They were utilized at different periods after girdling, viz. after 5, 8 and 17 months. The investigations were carried out on butt-logs (up to a height of 3 m) of which diametral boards, 3 m long, were taken, having a thickness proportional to the mean breast height diameter of each tree. The measurements were taken of a total length of 100 in. by a tensodeformometer with an approximation of 0.0001″, determining, together with the length, also the deflection of all the outer strips gradually removed from the board in order to evaluate the strip unit contraction. As concerns board lengthening, the arithmetical difference was determined between the lengths taken before and after the cut. While for unit contractions—expressed by 8 d/l 2 —the values are given in in./sq.in., for unit lengthenings the variations are given in inches. The results obtained must be considered as positive: in fact, deformations were reduced, on the average, to 50 percent. These positive results are accompanied by others, of practical nature, all supporting the effectiveness of the method followed. Mention should be made, in fact, that in sawing logs from control trees diverse cracks occurred very often along the pith, separating diametrical boards almost completely, while no fissure was observed on boards from girdled trees.

Tracheid length variation in a single tree ofPinus kesiya Royle ex Gord.

Abstract: Two radial samples were sawn from nine levels in a single tree ofPinus kesiya Royle ex Gord. (syn.P. khasya, P. insularis). Twentyfive tracheids were measured on two microscope slides for the earlywood of rings 2... 21 in each radial sample. The statistically significant difference between radii had litile practical importance and the systematic difference between rings was consistent over all levels. The effect of differences between levels was important and multiple regressions were calculated, incorporating linear and quadratic effects of ring number and height in stem. The best model accounted for 82% of the total variation. Exponential regressions were calculated for each level independently (75... 89%) and for the entire tree (77%). Both types of model are acceptable for description of variation up to ring 21 but beyond this ring number the exponential model will be most useful for description and prediction. For future work the minimum sampling strategy per tree will be three levels, two radii per level, and three or four rings per radius if quadratic models are required; five or six rings will be necessary to fix exponential models.

An assessment of research in wood rheology

Abstract: The reasons for the interest in the rheology of wood and the favoured lines of research are stated. The response of wood can often be predicted adequately on the basis of previous studies but notable gaps remain in our knowledge. Future research should avoid going over well trodden ground and should concentrate on filling some of the gaps listed. The factor of greatest importance is the interaction of load with change in moisture content. International cooperation in rheological research on wood would be of great benefit.

Infrared spectra of some woods of taxonomic interest

Abstract: Infrared spectra (4000...250 cm-1) of thin sections (12μm) of woods from some pored gymnosperms of the order Gnetales and of a non-pored angiosperm of the family Winteraceae have been obtained and found to resemble closely the spectra of typical angiosperms rather than gymnosperms. These results indicate that the gross chemical composition of a wood is not related to its anatomical structure and show that chemically the Gnetales resemble angiosperms.

Aspects of fiber morphology affecting properties of handsheets made from loblolly pine refiner groundwood

Abstract: InPinus taeda L., burst, breaking length, and sheet density were improved by using fiber refined from wood having long, narrow-diameter tracheids with thick walls. Only narrowdiameter tracheids with thick walls were required to improve tear factor. A theoretical stress analysis revealed that thick-walled cells of small outside diameter fail by diagonal tension or parallel shear, depending on the fibril angle, while under torsional stress during refining. Such failures result in ribbon-like fragments which research elsewhere has demonstrated to provide the coherence necessary for strength development in mechanical pulps. In contrast, thinwalled cells of small outside diameter fail by diagonal compression and yield few ribbons. Long fibers are more desirable than short fibers because of greater induced stresses and improved chances of axial alignment between the disks.

The torsion of an orthotropic rod in the theory of creep

Abstract: The analysis of the torsion problem for a rod of orthotropic material is presented. The analysis is based on Norton's law generalised for a multi-axial state of stress for an orthotropic medium. The components of displacement have been assumed to be similar to those given by the theory of elasticity. The resultant stress τ at the periphery of the rod has been assumed to be a function of θ. An expression giving the twist as a function of the time has also been derived.

Wood Chemical Composition as Related to Properties of Handsheets Made from Loblolly Pine Refiner Groundwood

Abstract: Burst and tear strengths of handsheets made from 48 pulps disk-refined from chips of varying chemical composition decreased with increasing extractive content after the independent effects of fiber morphology were specified. This result was attributed to lessened bond strength caused by reduced surface tension forces and blocking of reactive sites on the fiber surfaces.

Quality of refiner groundwood pulp as related to handsheet properties and gross wood characteristics

Abstract: Pupl quality, in terms of a fiber shape factor S and a fiber length factor L, was determined for 96 pulps disk-refined from chips of varying characteristics. S was evaluated in terms of the Canadian Standard Freeness of the 48/100 fiber length fraction and is a parameter inversely proportional to specific surface. L is the percentage, by weight, of pulp retained on a 48-mesh screen and reflects the distribution by weight of fiber length in the whole pulp. S and L accounted for as much as 83 percent of the variation in handsheet properties. Properties were improved by using pulps displaying low values of S and relatively high values of L. Both S and L were related to specific refining energy and wood quality. S increased with increasing unextracted chip specific gravity and rings per inch of growth rate but decreased with increasing latewood content and refining energy. L decreased with increasing refining energy, rings per inch of growth rate, and unextracted chip specific gravity but increased with increasing latewood.

The effect of light deficiency on the formation of secondary xylem

Abstract: Light is one of the most important environmental factors influencing the cambium activity and consequently the formation of the secondary xylem. Its deficiency more or less inhibits the lignification of cell walls and also the formation of conductive tissues represented by the vessel system. From these results, if compared with those of bent stems, the conclusion may be drawn that some growth substances, namely the indoleacetic acid are the most important metabolites taking part in the formation of the quality of secondary xylem determined by the action of light. The importance of the total leaf area is assumed, acting as a perceptor of external light impulses and balancing to a certain extent the metabolic supply of the cambium by its own inertia.

Rupture of pit membranes during embedding procedures

Abstract: Embedding of small wood blocks for study of changes in pit structure during treatments of wood, such as various drying methods, may cause considerable damage to the pit membranes. The sapwood of three species was studied: Sitka spruce, Douglas-fir, and Pacific silver fir. Drying was done by air-drying, freeze-drying, and solvent-seasoning. The principal embedding medium used was butyl-methyl methacrylate. Other media used were celloidin, paraffin, and commercial epoxy and polyester resins.