Masters Theses

Date of Award

12-1998

Degree Type

Thesis

Degree Name

Master of Science

Major

Forestry

Major Professor

Paul Winistorfer

Committee Members

Richard Bennett, Arnold Saxton

Abstract

A study was completed to examine the relationship of processing variables and the vertical density profile with the performance of modulus of elasticity (MOE), modulus of rupture (MOR), water absorption (WA), thickness swell (TS) and internal bond (IB) of oriented strandboard (OSB). Twenty-seven, 40 lb/ft3, 1/2 inch thick southern pine, laboratory strandboards were manufactured with furnish at three moisture contents (3, 6 and 9%) and employing three press closure rates (20, 40 and 60 seconds) in a completely randomized split-plot design with three replications. Applications of phenolformaldehyde resin (3%) and emulsion wax (0.5%) were held constant. All tests were conducted in accordance with the American Society for Testing and Materials D-1037-92 (1992).

The data were analyzed in three ways: (1) to determine the effect of furnish moisture content and press closure rate on MOE, MOR, WA, TS and IB; (2) to find the effect of furnish moisture content and press closure rate on the vertical density profile; (3) to search for the relationship of the vertical density profile with MOE, MOR, WA, TS and IB.

Furnish moisture content and press closure rate were found to have varying effects on panel properties. In general, a lower furnish moisture content resulted in higher MOE and MOR, more WA and TS, and higher IB. With our custom made resin system, the intermediate (6%) furnish moisture content treatment level allowed the best compromise between bending strength, dimensional stability and bond performance. A faster press closure rate generally resulted in higher MOE and MOR, less WA and TS, and lower IB. The intermediate (40 seconds) press closure rate provided an adequate trade-off between bending strength, dimensional stability and bond performance.

For subsequent analysis, the vertical density profile was divided into 5 zones, the minimum and maximum density and their respective locations within each zone were recorded. Zones 1 and 5 were considered face layers, 2 and 4 were considered intermediate layers, and 3 was considered the core. The vertical density profile zone data was used to determine the relationship of the vertical density profile with MC and PCR.

Furnish moisture content influenced the vertical density profile minimum and maximum density in all zones, and the location of the density in the intermediate zones. As furnish moisture content increased the density increased and the peaks of the vertical density profile located closer to the panel surface. Press closure rate influenced the maximum density in the face zones and the location of the minimum and maximum density in the face and intermediate zones. At faster press closure rates the density in the face zones increased and the peaks of the vertical density profile narrowed while simultaneously locating closer to the panel surface. The location of the minimum and maximum density in the core zone was unaffected by furnish moisture content or press closure rate.

The interaction of furnish moisture content and press closure rate was significant for density in the intermediate and core zones and for the location of the density in the face and intermediate zones. Generally, the lowest densities resulted when lower furnish moisture contents were combined with slower press closure rates. Higher furnish moisture contents combined with faster press closure rates allowed the density locations to position closer to the panel surface.

A correlation matrix and a stepwise regression method were utilized to examine the relationship of the vertical density profile data with MOE, MOR, WA, TS and IB. MOE and MOR were most related to location of the density rather than the actual density values themselves. WA and TS were generally most effected by the location of the maximum density in the face zones. For WA and TS, there was an exposure time effect of different vertical density profile zone variables giving significant contributions to the absorption and swell of a specimen as water exposure time lengthened from two to twenty-four hours. IB was most effected by the location of the maximum density in one intermediate zone.

In general, the density location variables emerged as highly influential over panel properties. The knowledge gained in this study on the ability to control the location variables by manipulating process parameters could be used to predict panel properties.

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