Medium density ®berboard (MDF) is one of the most rapidly growing composite board products available in the market. A key product attribute of MDF is the density pro®le through the panel thickness. A superior MDF panel for laminating, gluing and ®nishing should have an unbalanced density pro®le, in which the face density is considerably higher than the core density. The homogeneous core of MDF makes it especially suitable for embossing, moulding, and general machining. A uniform density throughout the panel thickness results in better fastening properties. A step-closure schedule to change the density pro®le of lab-made MDF panels is presented. MDF mats were pressed using eight different step-closure schedules. Our in-press density monitoring system was used during pressing to provide additional information about the formation of the density pro®le. The effects of step-closure on the density pro®le formation are discussed. The step-closure schedules signi®cantly changed the traditional shape of the vertical density pro®le of the laboratory, made MDF panels. The step-schedules resulted in multiple densi®cation peaks rather than the traditional two peaks associated with conventional pressing. The stepschedules resulted in increased core density, which was greater than the face density. Comparison is made to traditional MDF closing schedules and OSB step-closing schedules. Schrittweises Pressen von mitteldichten Faserplatten(MDF); Teil 1. Einfluû der vertikalen Dichteprofile Eine Schlu Èsseleigenschaft von MDF ist das Dichtepro®l quer zur Dicke der Platte. Eine hochwertige MDF-Platte fu Èr Beschichtung, Verleimung und andere Ober¯a Èchen-handlungen sollte kein gleichma Èûiges Dichtepro®l aufweisen, sondern die Dichte nahe der Ober¯a Èche sollte wesentlich ho Èher sein als die Kerndichte. Die homogene Kernschicht von MDF macht diese besonders geeignet fu Èr Bearbeitungen aller Art. Fu Èr die Herstellung von Laborplatten mit verschiedenen Dichtepro®len wurden acht verschiedene La Èufe mit schrittweiser Pressung untersucht. Die Plattendichte wurde mit einem speziellen System online wa Èhrend der Pressung gemessen, um zusa Ètzliche Informationen u Èber die Ausbildung der Dichtepro®le zu erhalten. Die Ein¯u Èsse der verschiedenen Preûmethoden auf die Dichtepro®le wird diskutiert. Es ergab sich eine wesentliche A È nderung der traditionell bekannten Form der Dichtepro®le. Der wesentliche Unterschied besteht im Auftreten von mehreren Dichtepeaks gegenu Èber nur zwei Peaks bei der konventionellen Pressung. Auûerdem ist die Kerndichte erho Èht; sie liegt zum Teil sogar ho Èher als die Ober¯a Èchendichte. Die neue Methode wird mit den bisher angewandten Preûverfahren verglichen.
The previous paper in this series discussed the stepclosure pressing schedule to change the density pro®le of lab-made MDF panels. The purpose of this research was to investigate the effect of the step-closure schedule on the end-product performance, especially on the layer thickness swell and its relationship with layer density. The results of this work showed that step-closure schedules resulted in improved internal bond strength of the tested specimens. The step closing schedule signi®cantly increased the core density and decreased the face density, resulting in lower bending properties. The results showed that greater core density did not result in higher internal bond strength. The more unsteady phase in a mat resulted in the poorer quality of the bond formation. The layer thickness swell after three water exposure times is significantly and positively related to layer density in all panels studied. The correlation coef®cient between the actual layer thickness swell and layer density increased with increasing water exposure time. The greater thickness swell in the surface layers of MDF suggests that efforts to improve dimensional stability of MDF should be focused on stabilizing the high-density surface layers. Schrittweises Pressen von mitteldichten Faserplatten (MDF) Teil 2. Einfluû auf das Verhalten der Platten und der einzelnen SchichtenIm vorhergehenden Artikel wurde das schrittweise Pressen vorgestellt, womit das Dichtepro®l von Labor-MDF-Platten vera Èndert werden kann. In dieser Arbeit wird der Ein¯uû auf die Eigenschaften der fertigen Platten untersucht, insbesondere auf die Dickenquellung der einzelnen Schichten und deren Beziehung zur Dichte der Schichten. Die Ergebnisse zeigen, daû durch dieses Verfahren eine verbesserte Querzugfestigkeit der gepru Èften Proben erreicht wurde. Die Dichte der Kernschicht stieg signi®kant, die der Deckschicht verringerte sich, was niedrigere Biegefestigkeiten zur Folge hatte. Die ho Èhere Kerndichte fu Èhrte nicht zu ho Èherer Querzugfestigkeit. Die unstabilere Phase in der Matte ist verantwortlich fu Èr eine schwa Èchere Ausbildung der Bindungen. Die Dickenquellung der einzelnen Schichten nach verschiedenen Wa Èsserungszeiten ist bei allen Platten signi®kat und positiv korreliert mit der Dichte der Schichten. Der Korrelationskoef®zient zwischen tatsa Èchlicher Dickenquellung und Dichte der Schichten stieg mit zunehmender Dauer der Wa Èsserung an. Wegen der erho Èhten Dickenquellung der Deckschichten bei MDF sollten ku Ènftige Bemu Èhungen zum Verbessern der Dimensionsstabilita Èt sich darauf konzentrieren, die hochverdichteten Deckschichten zu stabilisieren.
wood yield was 330 pounds per acre at the 0.75 ft spacing, 106 pounds 2 2 at the 1 ft spacing, 31 pounds at the 2 ft spacing, 8 pounds at the 4 2 2 2 ft spacing, 2 pounds at the 8 ft spacing, and 1 pound at the 12.7 ft spacing. Mean annual increment for total dry wood weight yield per acre reached a maximum at 10 years age for the three narrowest spacings and 15 for the three largest spacings. Ek et al. (1983) demonstrated similar trends for coppice yields from several clones at three spacings. Some Characteristics of Populus Since Populus has been the principal species under investigation in the SRIC program, a considerable amount of literature now exists for certain growth and quality characteristics. Some growth and yield data have been reported for both the original planted stand and subsequent coppice growth. The majority of the available quality data refers to the frequently measured parameters of specific gravity and fiber length. Unfortunately, the literature is quite sparse in reference to quality measurements made on coppice grown material. Populus is a diffuse porous hardwood exhibiting above average growth rate and is of average quality. These characteristics, plus the fact that Populus coppices easily, has moderate disease resistance, has a wide genetic base suitable for selection, and is easily hybridized, all were considered in its selection for extensive testing in the SRIC program (Dickman, 1975). 13 Height and diameter Average height and diameter growth of numerous clones at various high planting densities is noteworthy. Dawson et al. (1976) reported height growth for Populus "Tristis #1" at the end of the second growing season of 5.8 feet at a 9 x 9 inch spacing; 5.86 feet at a 12 x 12 inch spacing; and 6.17 feet at a 24 x 24 inch spacing. After the third growing season, these heights were 10.10 feet, 11.10 feet, and 12.55 feet, respectively. Basal diameter of these same trees increased from 0.60 inch to 0.84 inch for the 9x9 inch spacing; 0.69 inch to 0.93 inch for the 12 x 12 inch spacing; and 0.91 to 1.32 inch for the 24 x 24 inch spacing, from the end of the second to the end of the third growing seasons. Bowersox and Ward (1976) measured height and diameter (at 15 cm) for poplar clones NE-49 and NE-388 for four years at growing 2 spacings approximating 0.09, 0.19, 0.28, 0.37, and 0.46 m. Differences in height and diameter growth among clones and spacings were not evident until after the second growing season. After four growing seasons, average height growth was 3.93 m for the smallest spacing, and 4.42, 5.03, and 5.00 m for increasing spacing levels, respectively. Diameter measurements at age four followed similar trends as height growth with 2 spacing. Diameter was 2.26 cm at the 0.09 m spacing and increased with 2 increasing spacing to 3.81 cm at the 0.46 m spacing. Height and diameter growth at various ages after coppicing have been reported. Ek et al. (1983) made measurements on seven poplar clones at the end of each year for three years following coppicing. Included were clones NC-53...
Eight copolymer resins in two groups of resin formulation, one heavily methylolated with a 2.75 molar ratio of formaldehyde to phenol and another with a low formaldehyde to phenol molar ratio of 2.1, were manufactured incoiporating a 40% weight replacement of phenol with peanut hull extracts in the laboratory. A commercial phenolic resin as a control and a lab resin without extracts were included. These resins were evaluated for their ability to bond flakeboards of sweetgum (Liquidambar styraciflua), white oak (Quercus alba), and southern pine (Pinus taeda) flakes.Homogeneous flakeboards of 1.27cm (1/2 inch) thickness were made with a target density of 0.705 g/cm 3 (44 pounds per cubic foot). A resin solid of 5.5% was used for all boards. The hot press was applied at platen temperature of 177 °C (350 °F) for five minutes at the maximum pressure. Flakeboards properties evaluated include dry bending strength (MOE) and stiffness (MOR), internal bond (IB), thickness swell (TS), water absorption (WA), and linear expansion (LE). Strength retention after an oven dry-vacuum pressure soak cycle (OD-VPS) was also reported.Experimental resin formulations performed as well as or better than the commercial resin formulation for all properties evaluated. There were significant differences among the three species for most resin formulations and physical properties. White oak flakeboards exhibited unacceptable strength retention after the OD-VPS cycle, regardless of resin formulation. The method of resin synthesis was significant for internal bond strength for all species, and only in the case of MOR strength for southern pine. There were 30 experimental treatment combinations, with a statistical analysis of variance incorporating a single degree of freedom using preplanned comparisons for specific resin formulation of interest.
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