An abstract of the thesis of

Phenol Formaldehyde (PF) Resin 
The most common adhesive for structural wood-based composites is phenol 
formaldehyde (PF) resin. PF resin is a thermosetting resin with a mixture of phenol and 
formaldehyde in the presence of either an acid or base catalyst (see Figure 1.1). They are 
waterborne and polar (Frihart 2005). Unlike PF resins for OSB, PF resins for plywood 
are commonly blended with extenders, fillers and caustic soda. These additives will 
increased the resin viscosity (Ebewele, River et al 1986). PF resins are subdivided into 
novalaks and resole. Novolaks have a formaldehyde/phenol ratio of less than 1 and are 
generally made with an acid catalyst, while resole resins have a formaldehyde/phenol 
ratio of higher than 1 and are made with a base catalyst (Koch 1987). In most wood 
bonding applications resole resins are used because they have good wetting properties 
and the cure is delayed until activated by the heat, which allows extra product assembly 
time. These resoles have a formaldehyde/phenol ratio of 1.0-3.0 and a pH value of 7-13. 
After the PF resin is applied to wood, the low molecular weight components of the PF 
resin causes the cell walls to swell (Frazier and Ni 1998). This penetration into the cell 
walls is possible because PF resins have hydrogen bonding functionalities. The swelling 
allows some molecules to penetrate into the cell walls, but due to the small quantities of 
resin, only the immediate vicinity of the cell wall swells and not the whole cell wall 
(Wilson, Gregory et al 1979; Frihart 2005). Resole resins plasticize the wood, but they 
make the bonded panel more hygroscopic and can create excessive swelling of composite 
panels (River, Vick et al 1991). Despite this effect, resoles are still the most common PF 
resins. 
+
PF resin
acid/base-catalysed
Figure 1.1. Schematic representation reaction of PF resin. 
1.3.2 
Polyvinyl Acetate (PVA, Tite Bond Original) 
PVA is the most commonly used for wood furniture glue. As a wood glue, PVA is 
known as white glue or the yellow “carpenter’s glue”. PVA is produced from ethylene, 

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6 
ethanoic acid and a mercury (I) salt. The degree of polymerization of polyvinyl acetate 
typically gives 100 to 5000 g/mole molecular weight (MW) (see Figure 1.2). The ester 
groups of the polyvinyl acetate are sensitive to alkali and will slowly convert PVA into 
polyvinyl alcohol and acetic acid. Under alkaline conditions, boron compounds, such as 
boric acid or borax causes the polymer to cross-link forming tackifying precipitates or 
slime. As an emulsion in water, PVA emulsions are good adhesives for porous materials, 
particulary for wood, paper, and cloth, and as a consolidant for porous building stone, in 
particular sandstone (Young et al 1999). PVA has poor gap-filling abilities, water 
resistance and heat resistance. To improve the water resistance, heat resistance and 
mechanical properties once cured, various crosslinkable monomers such as N-
(hydroxymethyl)acrylamide can be added to modify PVA glues (Cho et al 1999, Lui et al 
2005). Once the PVA glue is applied to wood, it sets quickly (typically within 15 min) at 
ambient temperature and the peak strength for the adhesive bonds is quickly achieved. 
Figure 1.2. Chemical structure of PVA resin. 
1.4 Flow Chart of Tasks in this Research
Figure 1.3 shows a flow chart of the tasks in this research. In the interfacial 
experiment tasks, a double lap shear (DLS) test was used to measure the compliance 
response of adhesives. Wood strands with straight grain were used to prepare the DLS 
specimens. Prior to gluing the strand with PF or PVA resin, the stiffness of each 
individual strand was measured. Different amounts of adhesive coverage were then 
applied to DLS specimens. Finally, the interfacial stiffness parameters were extracted by 
using a shear lag model to interpret the measured compliance results from the DLS tests.
In the modeling tasks, the interfacial stiffness parameters were input into a 
numerical model to study their effect on mechanical properties. The modeling of wood 

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strands composites (OSB) involved mat formation by compaction. The mat formation 
process was started with a random structure based on strand length, width, and gap 
between strands along with their standard deviations. The individual strand mechanical 
properties were also measured and input into the numerical model. The numerical method 
used in this study was the material point method (MPM). An elastic-plastic with 
hardening law model was used to incorporate the effect of yielding during compaction. 
MPM calculations for bending and tension were compared to a simple laminate plate 
theory. The sensitivity of results to various physical and geometric parameters was 
studied. The results for vertical density profile of composite panels from MPM were 
compared to the experimental data by an X-ray profilometer. Most results were 2D 
simulations but some 3D simulations were needed for density profile studies. 
Yes
No
Sensitivity 
Analysis
Adjust 
Properties 
(Yielding, n & 
K)
Material 
Properties 
Input
Comparing to 
Laminate 
Plate Theory
Useful Predictions
DLS Specimens
MPM Calculations
Interfacial 
Interfacial 
Interfacial 
Interfacial 
Properties 
Properties 
Properties 
Properties 
Input
Input
Input
Input
Wood Strands 
Parallel to the Grain 
Specimens
Interfacial Experiment 
Modeling Of Wood Based Composites
Mat Formation Process and 
Compaction
Interfacial 
Properties
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035