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The use of dynamic mechanical analysis was explored as a possible method of screening for wood quality in breeding programmes. Viscoelastic properties along the grain of wood from 18-month-old Pinus radiata saplings were measured using a humidity-controlled dynamic mechanical analyser. Storage modulus and tan δ were determined independently for opposite wood (OW) and compression wood (CW) in 25 trees in the temperature range from 10 to 45 °C at 5 °C intervals at three frequencies (0.1, 1 and 10 Hz) at constant moisture content of 9 %. Storage modulus and tan δ were frequency and temperature dependent. The two wood types did not differ significantly in their storage modulus. But OW exhibited significantly higher tan δ values than CW. The relationship of viscoelastic properties with physical (acoustic velocity, basic density and longitudinal shrinkage) and chemical wood properties was explored. There was a strong correlation ( R = 0.76) between storage modulus and dynamic MOE (measured by acoustics). In addition, tan δ was positively correlated with longitudinal shrinkage. Monosaccharide compositions of the cell wall polysaccharides and lignin contents were determined and showed significant differences in the relative proportion of major cell wall components in OW and CW. Correlations between tan δ and xylose, originating from heteroxylans, and lignin content were found for CW, suggesting that the damping behaviour of cell walls is controlled by the matrix between cellulose fibril aggregates. [ABSTRACT FROM AUTHOR]

Mechano-sorptive strain was generated in strips of rectangular section stressed in torsion with the humidity cycled between 38% and 84%. After a number of humidity cycles the specimen was unloaded, the applied stress was reversed and further humidity cycles were imposed. All the initial strain was recovered and reversed strain was developed. Tests were carried out at two maximum shear stress levels, 1.12 MPa and 5.05 MPa. After seven humidity cycles at the higher stress a large mechano-sorptive strain of about 0.06 was developed, which was nearly nine times the initial elastic strain. During the development of this strain no significant change of the shear modulus occurred, from which it is concluded that the large MS strain produces no permanent change of the features of the cell wall structure that determine the shear modulus. There are close parallels between the mechanism generating the MS strains and that responsible for the large plastic strains reported by Keckes et al. in wet compression wood loaded in tension. In both cases it is suggested that the shear strains arise from the breaking and reforming of hydrogen bonds between parallel polymer chains. [ABSTRACT FROM AUTHOR]

A method was reported in a previous paper (Entwistle and Terrill, J. Mater. Sci. 35 (2000) 1675) for the measurement of the micro-fibril angle in the S2 layers of softwood. The small-angle X-ray scattering pattern was recorded with the beam directed at 45° to the radial direction in the cell structure. A cruciform scattering pattern was produced and the micro-fibril angle was deduced from the angle between the arms of the cross. The analysis assumed that all the cell walls lay in either the radial or the tangential direction. Real cell structures do not conform to this ideal. The objective of the work now presented was to calculate the error in the deduced value of the micro-fibril angle arising from the assumption that the specimen cell walls all lie in either the radial or in the tangential direction. To this end, the length and orientation of over 1000 cell walls was measured on two specimens using an image analyser. From these data the azimuth angle at the peak of the scattered intensity was calculated as a function of the micro-fibril angle and the standard deviation of the spread of intensity. The true micro-fibril angle was determined by comparing these data with the measured azimuth angle at the peak intensity. A value for the micro-fibril angle was also calculated from the measured value of the azimuth angle at the peak intensity using the relation for a square-section cell structureThe values differed from the true values by between 1° and 2° for micro-fibril angles between 25° and 30°. For many purposes this degree of error is tolerable and in those circumstances the above relation can be used to extract a micro-fibril angle value. [ABSTRACT FROM AUTHOR]

A previous paper (K. M. Entwistle and N. J. Terrill, J. Mater. Sci 35 (2000) 1675) reported measurements of the micro-fibril angle of the cellulose fibres in the S2 layers in softwood. The method involved irradiating a specimen with X-rays directed at 45° to the radial and to the transverse direction. The determination of the micro-fibril angle from the distribution of intensity round the (002) diffraction circle assumed an idealised structure in which all the cell walls were oriented precisely in either the radial or the transverse direction. The real cell structure diverges significantly from this ideal. The error involved in assuming the ideal structure has been assessed by making a quantitative image analysis of the length and orientations of the cell walls in a section of the specimen comparable in cross-section to that irradiated by the X-rays. The position of the S2 intensity peaks round the (002) diffraction circle has been calculated and compared with those predicted from the idealised structure. It is demonstrated that the error involved in extracting a value for the micro-fibril angle from the measured intensities using the assumed ideal cell structure of the previous paper (cited above) is not more than one degree in the range of micro-fibril angles 20°–30°. So the approximate analysis is adequate for many purposes. [ABSTRACT FROM AUTHOR]

The following paper summarises a number of international research projects being undertaken to understand the mechanical properties of natural cellulose fibres and composite materials. In particular the use of novel techniques, such as Raman spectroscopy, synchrotron x-ray and half-fringe photoelastic methods of measuring the physical and micromechanical properties of cellulose fibres is reported. Current single fibre testing procedures are also reviewed with emphasis on the end-use in papermaking. The techniques involved in chemically modifying fibres to improve interfacial adhesion in composites are also reviewed, and the use of novel fibre sources such as bacterial and animal cellulose. It is found that there is overlap in current international research into this area, and that there are complementary approaches and therefore further combining of these may make further progress possible. In particular a need to measure locally the adhesion properties and deformation processes of fibres in composites, with different chemical treatments, ought to be a focus of future research. [ABSTRACT FROM AUTHOR]

The paper explores the measurement, using X-rays, of the micro-fibril angle of the cellulose fibres in the S2 layers of the cell walls of soft-wood, particularly pinus radiata. It is demonstrated that unambiguous values of the micro-fibril angle can be obtained from small angle X-ray scattering patterns if the X-ray beam is directed at 45 degrees to both sets of cell walls, with the cell axes vertical. The theory of the method is presented and justified. Examples of the measurement of the micro-fibril angle in pinus radiata specimens are given. It is demonstrated that the scattering patterns obtained with the X-ray beam directed normal to one set of cell walls are not capable of yielding micro-fibril angle values. The wide-angle diffraction pattern from the (002) planes with the X-ray beam equally inclined to both sets of cell walls has been analysed. The analysis has been justified experimentally and it is shown that the S2 fibres give rise to eight intensity maxima round the (002) circle and that the azimuthal angles can be related to the micro-fibril angle. It has not been possible to resolve the eight peaks. Wide-angle diffraction patterns revealed four peaks, each comprising two merged adjacent peaks. The azimuth angle at the centre of each of the four peaks is the average of those for the two constituent peaks. It is demonstrated that values of the micro-fibril angle can be obtained from this average azimuth angle. [ABSTRACT FROM AUTHOR]

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Copyright of Tropical Animal Health & Production is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)