Charles B, Vlck 
Lamination of Hardwood Composite Framing 

With an Emulsion Polymer-Isocyanate 

Adhesive and Radio-Frequency Curing 

Charles B. Vick 

Research Scientist 

Forestry Sciences Laboratory 

Athens, Georgia 

ABSTRACT 

An emulsion polymerlisocyanate adhesive was used 

to laminate strips of yellow-poplar and sweetgum 

parallel-laminated veneer to the edges of oriented 

flakeboard (of the same species) 5n composite 

framing. The adhesive was cured by radio-frequency 

generated heat, Critical strength and durability 

properties of adhesive bonds were measured over a 

range of assumed but typical material surface characteristics and factory assembly conditions. Dry shear 

strength and wood failure, wet shear strength, and 

resistance to delamination easily exceeded proposed 

minimum requirements, Wet wood failure on sweetgum 

was marginal in meeting the 70 percent requirement; 

however, certain combinations of assembly conditions 

corrected this problem. Bonds to yellow-poplar were 

decidedly better than those to sweetgum. Moisture 

content of materials at 3 or 6 percent was not critical to joint performance for most assembly conditions. 

Adhesive spread rate was important from the standpoint of both bond performance and cost, with the 

rate of 65 lb/M ftz near optimum. Generally, it was 

advantageous to spread the veneer surface rather than 

the core edge. The balance of moisture in the adhesive film, dependent on material moisture content, 

spread rate, spreading surface, and closed assembly 

time, was critical to joint performance, 

Keywords: Yellow-poplar, sweetgum, parallellaminated veneer, oriented flakeboard, shear 

strength, wood failure, resistance to delamination. 

Several adhesives have been 

researched for use in laminating veneer 

to composite lumber, Among them was an 

emu1 sion polymer/i socyanate (EPI) adhesive with a unique combination of high 

strength and durability, and an ability 

to cure at room temperature (>42 "F) 

within 1 hour (Vick 1984). This adhesive is ideally suited for a factory of 

limited production capacity without 

expensive heat-curing equipment. For a 

factory of greater production capacity, 

however, radio-frequency (RF) curing is 

the only practicable a1 ternative for 

high-speed production bonding. Conventional hot-press equipment cannot cure 

these bonds at high-production speeds 

hecause of the great distance between 

the innermost bondline and the heat 

source, and the relatively slow rate at 

which heat transfers through wood, 

Another EPI adhesive, similar in cornposition and cost, can be cured with RF 

heati ng without arcing, 

The purpose of this study was do 

investigate the working, strength, and 

durability properties of this second EPI 

adhesive when used to bond ye1 1 ow-pop1 ar 

and sweetgum veneer laminates to the 

highly porous edges of hardwood flakeboard core (of the same two species) by 

using RF heading. Bond properties were 

determined over a range of assumed but 

typical material surface characteristics 

and laminating assembly conditions, 
Perfomance Requirements Veneer Laminates 

Mi nimum performance requi rements 

and quality-control tests have been proposed for ensuring acceptable strength 

and durability of adhesive bonds between 

veneer and core in composite framing 

(Koenigshof 1985). They are based 

either on research in the composite 

framing program or on industry-accepted 

standards for bonded wood products: 

Minimum 

Properties requi rements 

Shear strengtha9 

Dry 500 lb/in7 

Wet 2563 1b/in2 

Wood fail urea 

Dry 

Met 

Resistance to 

del ami nat i onc 

80 percent 

70 percent 

(111) percent 

Material s 

Adhesive 

The adhesive was an aqueous 

emulsion of polymer with hydroxyl functional groups that cross-link with a 

polymeric isocyanate to form a urethane 

structure (Page1 and Luckrnan 1981 ; 

Terbilcox and Luckman 1985). It belongs 

to a generic group of adhesives called 

emu1 sion polymer/i socyanates, or EPI 's. 

The degree of cross-linking, and to a 

lesser degree the rate of reaction, can 

be control led by the amount of reactive 

isocyanate added to the mixture. In 

this experiment, 20 parts (weight basis) 

of isocyanate were added to 100 parts of 

emulsion, The adhesive sets initially 

by loss of water either through evaporation or absorption into the wood structure, It also sets by chemical cross1 inking which takes place when the 

emulsion polymer and isocyanate come 

into close molecular proximity as water 

is lost and the isocyanate protective 

mechanism deactivates, 

Veneer laminates for sections of 2- 

by 8-inch composite framing were prepared from 1/4-i nch-thick rotary-cut 

ye1 1 ow-pop1 ar and sweetgum veneers, 

Four plies of veneer, a11 of the same 

species, were para1 lel -laminated so that 

open lathe checks in the veneer faced 

toward the core, Veneers of both species were dried to 3 percent moisture 

content (XMC) , then laminated with 

phenol -resorci no1 -formaldehyde (PRF) 

adhesive, The laminates were cut into 

strips 1-1/2 inches wide and 12 inches 

long, and were randomly divided into two 

groups of equal size. One group was 

conditioned to 6 XMC and the other group 

was reconditioned to 3 XMC, 

Fl akeboard Cores 

Flakeboard cores were prepared from 

3/4-inch-thick, 40 lb/ft3, homogeneous, 

electrostatical ly oriented fl akeboard 

with 6 percent phenol ic resin binder. 

The flakes were yellow-poplar and 

sweetgum mixed in equal proportions by 

weight. The drum-cut flakes were 

separated into 114- and 1/8-inch mesh 

screen sizes to make two types of flakeboard, To make the cores 1-1/2 inches 

thick, two 3/4-inch-thick fl akeboards 

were laminated together, Before laminating, the flakeboards were dried to 

3 XMC, They were laminated with a PRF 

adhesive, then cut into 5-1/4-inch-wide 

by 12-inch-1 ong sections. These core 

sections, representing 1/4- and 1/8-inch 

flake sizes, were randomly divided into 

two equal size groups and conditioned to 

either 3 or 6 XMC, 

Methods 

Experimental Design 

Thi s experiment was designed to 

determine how the critical strength and 

durability properties of EPI bonds would 

be affected by important material surface characteristics and assembly factors. These experimental factors, with 

respective levels, are listed below, 

The experimental design was in a randomized block with factorial arrangement 
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Specimen Preparation 

Camposi te framing assemhl ies were 

prepared by bonding one 4-ply veneer 

laminate of yellow-poplar and one of 

sweetgum, each 1-1/2 inches wide by 12 

inches long, to each edge of a 1-1/2- 

i nch-thick fl akeboard core, a1 so 12 

inches long, Adhesive was spread onto 

the appropriate bonding surface with a 

rof ler according to the prescribed 

spread rate for each treatment combination, The accuracy of the spread was 

control led by automatical ly weighing 

adhesive as it was spread on each surface, Adhesive-spread veneer laminates 

or cores were assembled and held 

together without pressure for the 

prescribed closed assembly time. 

The adhesive was cured by a MannRussel 1 , Model 200, 13 kVA electronic 

generator, A plate current of 0.75 

ampere with 2.88 kilowatts RF output was 

applied for 1 minute, with pressure 

maintained at 175 Ib/in2, This power 

density setting produced a bondline temperature of 165 + 5 OF by the end of the 

1-minute curing period, Optimum power 

density was not an experimental factor; 

however, expl oratory tests of settings 

indicated that a plate current of 1.0 

ampere at 4,31 kilowatts produced bonds 

of unacceptable qua1 i ty, The higher 

power density caused boiling of water in 

the adhesive and wood, Adhesive dilution, coupled with greatly increased 

adhesive mobility, caused the adhesive 

to overpenetrate the fl akehoard core, 

By lowering plate current to 0,75 

ampere, overpenetration was eliminated 

and bond quality improved. 

After bonding, test assemblies were 

cut into specimens as shown in figure 1, 

Before testing for dry shear strength, 

specimens laminated at 3 %MC were conditioned to a moisture content of 

approximately 6 percent. Specimens 

already near 6 XMC were reconditioned to 

the same moisture content, 

Specimen Testing 

Tests for strength and wood failure 

in dry and water-soaked conditions were 

conducted according to the gl uel i ne 

shear test in ASTM D 1037-78 (ASTM 

1982), except that dimensions of the 

specimen were changed as shown in figure 

1 and the rate of loading was increased 

from 0.024 to 0.10 inch per minute, 

Bl ock-shear specimens were saturated with water by submerging them in 

tapwater in a pressure vessel. A vacuum 

of 25 inches of mercury was drawn and 

held for 30 minutes, Afterward, a 

pressure of 75 + 2 lb/in2 was applied 

for 2 hours, Specimens were tested 

immediately after the soaking procedure. 

Del ami nati on specimens were subjected to AITC Test T110, Cyclic 

Del ami nation Test (AITC 1983), Thi s 

procedure was extremely severe and 

essentially consisted of two cycles of 

vacuum-pressure soaking, as described 

above, with each cycle followed by 10 to 

15 hours of drying in dry air at 160 OF, 

Delamination was measured in the test 

bondline across the 1-1/2-inch width at 

both ends of the composite section. 

Open joints were measured to the nearest 

0.05 inch, Delaminations that measured 

less than 0,10 inch, and were more than 

0.20 inch apart, were ignored. The 

total length of open joints on both end 

surfaces, divided by the total length of 

end joints (about 3 inches), constituted 

the measure of del amination, 

Results and Discussion 

Flake Size 

Whether flakes were retained on 

1/4- or 1/8-inch mesh screens was not a 

significant factor for any of the five 

properties tested (table 11, This was 

indicated in the first series of ANOVA 

where screen size was included as an 

experimental factor, Since screen si ze 

was not significant, it was excluded 

from a1 1 subsequent ANOVA where only 

species, moisture content, spread rate, 

spreading surface, and closed assembly 

time were experimental factors, 

Spec i es 

The EPI adhesive bonded significantly better to ye1 1 ow-pop1 ar veneer 
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dry and wet shear strength, wet wood 

failure, and resistance to delamination. 

Wfth the exception of the 67 percent 

average wet wood failure of bonds to 

sweetgun, a1 1 other property averages 

exceeded the minimum requirements in the 

proposed qual ity-control standards 

(Koenigshof 1985). 

No interactions of any importance 

occurred between species and any of the 

other experimental factors. 

It is quite probable that wet wood 

failure of bonds to sweetgum veneer 

1 aminates could be improved by several 

percentage points and exceed the 70 percent mi nimum requi rement (Koeni gshof 

1985). To investigate this possibility, 

subanalyses were conducted on bonds to 

sweetgum only. The analysis indicated 

that wet wood tail ure improved signi fi - 

cantly when adhesive was spread on the 

veneer rather than the core edge. 

Resistance to delamination also improved 

significantly. Further subanalysi s of 

sweetgum veneer-spread surfaces did not 

reveal any other experimental factors 

that significantly affected wet wood 

fail ure--at least in a statistical 

sense. However, from 68 percent, wet 

wood failure increased to an average of 

75 percent when moisture content was 

lowered from 6 percent to 3 percent. 

A1 so, average del ami nat ion decreased 

from 6.3 percent to 2.3 percent by 

1 owering moisture content to 3 percent. 

Moisture content was a significant factor in decreasing percentage of delamination. It was not a significant factor 

in increasing percentage of wood failure 

because of the confounding effects of 

closed assembly time and spread rate. 

Nevertheless, by 1 oweri ng moisture content of materials to 3 percent and 

spreading adhesive on the veneer surface 

only, wet wood failure of bonds to 

sweetgum should be increased enough to 

exceed the 70 percent minimum requirement. Resistance to delamination should 

be increased as well. 

Not only is sweetgum more difficult 

than yellow-poplar to bond to porous 

flakeboard core edges with EPI adhesive, 

it is also difficult with phenolformaldehyde (PF) adhesives. Furthermore, sweetgum veneers are difficult to 

bond with PF adhesives when making 

plywood, Part of the solution to 

problems with both aqueous adhesives is 

to control moisture content of the 

sweetgum at an unusuatly low 2 to 3 XMC 

and within narrow limits. Excessive 

moisture leads to increased adhesive 

mohility and overpenetration of the core 

edges at elevated temperatures. Sweetgum has higher density than yellowpoplar and is more difficult to 

penetrate with adhesive, Extractives 

are also present at the surfaces of 

sweetgum, which may inhibit wetting and 

penetration of adhesive. The net effect 

of excessive moisture in the sweetgum 

veneer laminates and flakeboard core is 

overpenet rat ion of fl akeboard core and 

inadequate penetration of the veneer. 

Having learned that ye1 1 ow-pop1 ar 

can be bonded more effectively over a 

wider range of assembly conditions than 

sweetgum with the EPI adhesive, a laminator can use this knowledge to advantage in his operation--particul arly if 

veneer species are to be mixed in the 

same 1 ami nate. During veneer lay-up, 

yellow-poplar veneer can be located at 

the bottom of the laminate so that it is 

always bonded to the edge of the flakeboard core, This one step would do much 

to ensure higher qual i ty bonds, and certainly lessen problems that would be 

associated with bonding sweetgum to the 

core edge, 

Moisture Content 

Moisture content of materials was a 

significant factor in tests of dry shear 

strength, dry wood failure, and wet 

shear strength (table 1). Significantly 

stronger dry bonds developed on wood at 

6 %MC than at 3 XMC, Likewise, wet 

shear strength on 6 XMC wood was significantly stronger than on 3 %MC wood. 

The results of dry wood failure tests 

were inconsistent with the above findings in that the higher (95 percent) 

wood failure occurred at 3 XMC rather 

than at 6 XMC. 

Even though small differences between property val ues were si gni f i cantly 
different at the 3 and 6 XMC levels, 

from the standpoint of adequacy of product performance, these small di fferences seem inconsequential in determining whether the wood should be dried to 

the 3 or 6 %MC 1 evel , From an operational standpoint, the relatively wide 

range of moisture content from 3 to 6 

percent would be a distinct advantage in 

that narrow moisture content limits need 

not be strictly maintained. However, it 

is important to consider what was 

discussed earlier--that wet wood failure 

and resistance to delamination of bonds 

to sweetgum can be improved by drying 

materials to 3 XMC. From a property 

value standpoint, it did not matter 

whether yellow-poplar was dried to 3 or 

6 XMC, More energy is requi red to dry 

to 3 than to 6 %MC, however, 

There were signi ficant interactions 

between moisture content and spread 

rate, In these interactions, the 

influence of moisture on mobility of the 

EPI adhesive caQ best be seen, Note in 

table 2 that dry shear strength was 

lowest and delamination highest at the 

lowest of the three spread rates, and 

lowest of two moisture contents. 

Clearly, adhesive mobil ity was inhibited 

by low moisture availability from the 3 

%MC wood and low spread rate. Adhesive 

transfer to the unspread opposite surface improved significantly by the 

increase in moisture content from 3 to 6 

percent. At the 65 lb/M ft2 spread rate 

where bond strengths increased, the 

effect of increasing moisture content to 

6 percent was not as pronounced over all 

three properties. However, when spread 

rate increased to 80 lbfM ft2, indications of excessive adhesive mobility in 

the form of overpenet rat i on and squeezeout appeared at the 3 percent 1 evel , 

With the higher spread rate, the lower 

moisture content led to improved property values, 

There were a1 so significant interactions between moisture content and 

closed assembly time (table 3). Larger 

amounts of moisture in the wood, as at 

the 6 XMC level , compensated for 

moisture losses from the adhesive at the 

1 ongest 15-mi nute assembly time, thereby 

significantly increasing wet strength 

and wood fail ure and resistance to delamination, Property values were lower at 

the 3 %MC level because insufficient 

moisture was available to cause effective adhesive transfer. On the other 

hand, at the shorter assembly times of 

10 and 5 minutes, higher moisture content proved detrimental to devel opment 

of the best bonds, and 3 %MC produced 

Table 2.--Interactions of adhesive spread rate and moisture content for 

dry shear strength, dry wood failure, and delamination of EPI bonds 

Spread Moisture Dry Dry 

rate content shear strength wood fai 1 ure Delamination 

(lb/M ft2) (%I (1 b/in2) (XI (x> 

In comparisons of treatment means within a given property, means followed 

by the same letter are not significantly different at P 2 0.05. 
Table 3,--Interactions of closed assembly time and moisture content for 

wet shear strength, wet wood failure, and delamination of EPI bonds 

Assembly Moisture Wet Wet 

time content shear strength wood fai 1 ure Delamination 

(mi n) (%) (1 b/inz) (XI (%) 

In comparisons of treatment means within a given property, means followed 

by the same letter are not significantly different at P 0.05. 

more favorable results, Here, excessive 

adhesive mobil i ty, occasioned by 

excessive moisture from within the wood 

and the lack of drying of the adhesive 

film during the short assembly time, led 

to adhesive overpenetration, Neither 

adhesive dry-out nor overpenetration was 

serious within the parameters of this 

experiment; however, the effects were 

becoming evident, As indicated in table 

3, it appears the optimum combination of 

moisture content and assembly time was 

10 minutes closed assembly at 3 %MC and 

15 minutes at 6 %MC. Again, the key to 

successful bonding with this aqueous 

adhesive is careful control of adhesive 

mobility through control of moisture in 

the adhesive films. Such control is 

particularly critical with RF curing 

where boiling occurs within seconds and 

the adhesive becomes highly mobi 1 e, probably leading to overpenetration of the 

highly porous flakeboard core edges by 

the adhesive, 

Spread Rate 

Spread rate was a most influential 

factor in determining property values 

(table 1). Only in wet wood failure was 

spread rate not a significant factor. 

The lowest spread rate (50 lb/M ft2) 

generally produced the lowest property 

values, However, it did not necessarily 

follow that the highest spread rate (80 

1 b/M ft2) produced the highest values. 

Statistical comparisons in table 1 indicate the 65 lb/M ft2 spread rate did not 

produce significantly inferior results 

to the 80 lb/M ft2 spread rate, except 

perhaps in dry wood failure where the 

difference was only 2 percent, 

The discussion of the interaction 

between moisture content and spread rate 

offers an explanation of why the 65 1b/M 

ft2 spread rate is near optimum when 

compared with the other rates, In a 

broad sense, the overall property values 

at the 80 lb/M ft2 spread rate were 

lowered by somewhat poorer bonding 

results at the 6 XMC level, At the 50 

1 b/M ft2 rate, property values were 

lowered by poorer performance at the 3 

%MC level , On ha1 ance, property values 

at the 65 lb/M ftz spread rate were 

least affected by either of the two 

moisture content levels (tables 1, 3). 

Signi ficant interact ions between 

spread rate and spreading surface 

occurred in tests of wet shear strength 

and delamination, Comparisons from subanalysis show these effects (table 4). 

At the 50 lb/M ft2 spread rate, the 

advantage in spreading the veneer sur- 
Table 4.--Interactions of adhesive spread rate and spreading surface 

for wet shear strength and delamination of EPI bonds 

Spread Wet 

rate Spreading shear strength Del aminat ion 

(Ib/M ft2) surface (1 b/inZ) (9j) 

Core 

Veneer 

Core 

Veneer 

Core 

Veneer 

In comparisons of treatment means within a given property, means 

followed by the same letter are not significantly different at 

P 0.05. 

Table 5.--Interactions of adhesive spread rate and 

closed assembly time on delamination of EPI bonds 

Spread Assembly 

rate time Del ami nat ion 

(Ib/M ft2) (min) (%) 

In comparisons of treatment means within a given 

property, means followed by the same letter are not 

significantly different at P 2 0.05. 
face rather than the core was clearly 

evident, The core surface was quite 

porous relative to the veneer surface, 

and, at a low spread rate, insufficient 

adhesive was avai 1 able for transfer 

after penetration of the core surface, 

These surface effects were not stat istical ly significant at the other two 

spread rates, 

Another significant interaction 

between spread rate and assembly time 

occurred in the test of resistance to 

delamination (table 5). Again the 

effects of moisture on bondline 

integrity were statistical ly evident. 

At a spread rate of 50 lb/M ft2, 

assembly times of 5 and 10 minutes were 

short enough to avoid overdryi ng of the 

adhesive film, But at 15 minutes, 

drying had progressed to the point where 

delamination increased significantly, 

At the 65 lb/M ft2 spread rate, length 

of closed assembly had no significant 

effect and, as previously indicated, was 

near optimum. At the 80 lb/M ft2 spread 

rate, the shorter assembly times tended 

to lower bond integrity because of 

excessive adhesive mobility and overpenetration, However, during the 15- 

minute assembly time, sufficient time 

was avail able for excessive moisture to 

dissipate from the heavier adhesive 

spread, and improved bond integrity was 

the result, 

Spreading Surface 

By spreading adhesive on the veneer 

surface rather than the core edge, 

resistance to delamination and wet wood 

failure were significantly improved. 

However, in tests of the other three 

properties, signi ficant differences were 

not detected (table 1). A subanalysis 

of the interaction between spreading 

surface and spread rate (table 4) provides some insight into why resistance 

to delamination was improved by 

spreading the adhesive on the veneer. 

As discussed, the core edge was porous 

relative to the veneer, and, when spread 

at the 50 Ib/M ft2 rate, not enough 

free-fl owing adhesive was avai 1 able, 

after penetration and drying, for 

transfer to the opposite surface, 

A1 though there were no significant di fferences in delamination due to spreading surface at either the 65 or 80 1bfM 

ft2 spread rate, slightly improved bond 

integrity did result by spreading veneer 

rather than core, 

Closed Assembly Time 

In the ANOVA for main effects, 

closed assembly time was marginal ly 

significant only in the test of dry 

shear strength, Even though the test 

for differences between averages shows 

that the 5-minute assembly time produced 

significantly higher strength than the 

10-minute assembly time, these di fferences are considered of 1 i ttle practical 

significance (table 1). Significant 

differences between averages in dry wood 

fai 1 ure have been ignored because signi ficant differences were not detected, 

Assembly time does show up as a 

significant interaction with moisture 

content in tests of wet shear strength, 

wet wood failure, and resistance to 

delamination (table 3). At longer 

assembly times, the higher moisture content leads to better performance, 

whereas at shorter assembly times, the 

lower moisture content produces more 

favorable bond performance, The proper 

balance of moisture in the adhesive film 

during cure avoids the extremes of dryout and overpenetration, and is the key 

to successful RF bonding with the EPI 

adhesive, 

The other significant interaction 

that occurred with assembly time involved spread rate in the test of resistance to delamination (table 5). 

General ly , the 1 ongest assembly time at 

the lowest spread rate tended to cause 

increasing delamination, and short 

assembly time at the highest spread rate 

also led to increasing delamination. The 

longest assembly time at the highest 

spread rate tended to decrease 

del ami nation, 

Concl usions 

The EPI adhesive developed very 

strong and durable bonds in most of the 

72 treatment combinations tested, Dry 
shear strength and wood failure, wet 

shear strength, and resistance to delamination easily exceeded proposed minimum 

property-vat ue requi renents, Met wood 

failure of sweetgun was marginal in 

meeting the 70 percent wood failure 

requi rement, However, by spreading 

adhesive on the veneer laminate rather 

than the core, and drying the wood to 3 

rather than 6 XMC, wet wood failure of 

bonds to sweetgum can be improved enough 

to meet requirements, 

Species was a strong factor influencing property values. Bonds to 

ye1 low-pop1 ar were decidedly better than 

those to sweetgum. If veneer lay-up 

procedures could be designed so that 

ye1 1 ow-pop1 ar veneer was a1 ways bonded 

to fl akeboard core edges, qua1 i tycontrol problems associated with bonding 

sweetgum could be avoided. 

Although moisture content of 

materials proved significant in its 

effect on several property values, the 

difference appeared inconsequential from 

the standpoint of product performance-- 

particularly for ye1 low-poplar. A relatively wide range in moisture content 

(from 3 to 6 percent) would be a 

distinct advantage in that narrow limits 

in moisture control need not be strictly 

maintained. Certain property val ues on 

sweetgum were improved by the 3 %MC 

1 eve1 , however, 

The balance of moisture in the 

adhesive film was critical to joint performance and hi ghly interrel ated with 

material moisture content, spread rate, 

spreading surface, and cl osed assembly 

time, The ability of the adhesive to 

transfer, flow, and penetrate the opposite surface was dependent on moi sture 

in the adhesive film. 

Spread rate was highly significant 

in determining joint performance in most 

tests, and, of course, spread rate will 

be even more important because of its 

direct effect on costs of production, 

Of the three rates tested, the 65 fb/M 

ft2 spread rate was near optimum. 

However, a spread rate approaching 50 

1 b/M ft2 could produce acceptable property va1 ues if the material moisture 

content was near 6 percent, the veneer 

surface was spread with adhesive, and 

closed assembly time was near 10 

minutes, 

By spreading adhesive on the veneer 

surface rather than core edge, resistance to delamination and wet wood 

fai 1 ure were improved si gni fi cantly-- 

primarily at the lowest 50 lb/M ft2 

spread rate. By spreading adhesive at 

the near optimum rate of 65 1b/M ftz, 

the di f ferences between spreading veneer 

or core became inconsequential. 

Closed assembly time was marginal ly 

significant as a single main effect in 

dry shear strength and wood failure. 

However, assembly time had important 

interactions with moisture content of 

materi a1 s and spread rate. General ly 

these interactions pertained to the 

optimum balance of moisture in the adhesive film that could ensure effective 

transfer, flow, and penetration of adhesive on the opposite surface, 
Li bratun? Cited 

Amrlcan institute of Timber Constructton. Lamlnator" qualfty control system, AITC 201-83. 

In: Inspection Manual AlTC 200-83. Englewood, 

CO; 1983:50-51. 

American Society for Testing and Materials. Standard methods of evaluatfng the propertfes of 

wood-base and partfcIe panel materials. ASTN D 

1037-78. ASTN Stand., Part 22. Philadelphia, 

PA; 1982:310-311. 

Koenfgshof, Gerald A. Performance and qualitycontrol standards for compos f te f loor, wa l I, 

and truss framing. Gen. Tech. Rep. SE-33. 

Ashevf Ile, NC: U.S. Department of Agriculture, 

Forest Service, Southeastern Forest Experiment 

Station; 1985. 20 pp. 

Page t, Horst; Luckman, Edward Re Emulsion polymer 

Isocyanate: a durabfe, water-based wood adhesive. Reprinted from Adheslves Age 24(t0). 

unlcat ions Channe Is, I nc.; 

1981. 6 pp* 

Terbilcox, Thomas Fa; Luckman, Edward R. How 

emulsion polymrllsocyanate adhesives solve 

bond l ng prob !ems. RPN Tech n l ca l Notebook, 

Emphasis on Adhesives/Sealants. Reprlnted from 

Rubber d Plastlc News. March 11, 1985. 4 pp. 

Vick, Charles 6. An emulsion polymer/isocyanate 

adhesive for lam1 nating composite lumber. 

Forest Products Journal 34(91:27-34; 1984. 
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