Loblolly Pine

In tests with Pinus taeda L., most properties of wet. formed hardboard were improved by using fiber refined from wood having short, slender tracheids with thin walls. A theoretical analysIs suggested that the fibers fail in bending while under stress induced by the pressing operation. Such bending failures improve conditions for hydrogen bonding, thus improving board properties. Trachelds havmg narrow dIameters and thin walls flex easily and collapse readily. Short tracheids are more desirable than long tracheids because of a greater number of fiber crossIngS per unit weight in the pulp mat. Charles W. McMillin measured on samples used in the earlier study and were currdat~d with th~ board properties determined in that ,. study (3). Wood was selected and stratificd into 12 categories." Two growth rates (less than six rings per inch and more than si¥ rings per inch), two specifIc gravities (less than 0.49 and more than 0.49). and three radIal positIons in . the trce (0 to 10, 11 to 20, and 21 to 30 rings from the pith) were considered in a factorial design. The wood in each category was chipped and the chips ran. I domly divided into four within-sample replications A subsample was drawn from each replication for deter.' mination of fiber characteristics. Four morphological properties were measured for' both earlywood and latewood single cell-wall thickn('ss, radial lumen diameter, radial tracheid width, and tracheid I~Dgth-and correlated with seven board properties. . Tracheid length was determined from 40 chips. randomly selected from each subsarnple. Chips were dis~ected into earlywood and latewood slivers and macer. ated in a ~0/'0 solution of 30 percent hydrogen. peroxide and glacial acetic acid for 48 hours at ~O'(" Samples of the macerated material were mounted 10 ' water on 10 glass slides. With a calibrated projectinn ) APREVIOUS PAPER (3) examined the interrelationships between gross wood characteristics and the physical properties of f1berboa.rds made from loblolly pine. Wood specific gravity, proportion of latewood, and growth rate were shown to affect the strength of boards 1n tension and bending, as well as their dimensional stability. For the refining condItions and formation pro.. cedures employed, and after allowance for the effect of board specific gravity, most properties were improved by using ftber refined from dense wood having low late. wood content. Because earlywood near the pith is relatively dense, and because the Ia.tewood content of loblolly pine characterIStically is at a. mintmum near the pith, corewood appeared to be a desirable raw ma.terial from a strength standpoint. Gross wood characteristics, being reasonably easy to measure, are useful 1n 1dentifying wood types. It is difficult however, to interpret them in terms of their causal relationships with board properties. For example, wood specific gravity is, in part, detennined by the mor. phological characteristics of earlywood and latewood trachcids and the proportions of each tissue type (4). Therefore, a study was made of the interrelationships between fiber morphology and the physi(al properties of boards.