Note: Descriptions are shown in the official language in which they were submitted.
~i3~2
The present invention is concerned with certain
improvements in thermo-setting adhesive compositions containing
a heat-curable resin, preferably an aldehyde resin, such as a
urea-formaldehyde or phenol-~ormaldehyde condensation product.
There is an increasing need ~or new adhesives which
are strong and cheap for use in making bonded wood products.
Because of dwindling forest resources, solid wood has been
replaced in many instances by products, such as particle board,
hich are made from materials which used to be considered ~700d
wastes. In such products, adhesives account for up to 10% of
the weight and up to 50% of the cost of the product, and they
substantially determine the nature and quality of the resulting
product. Furthermore, new building technology encourages the
production of self-supporting, prefabricated laminated wood
panels and other bonded material which need to fulfill reliably
exacting standards.
Ideally, adhesives for such applications should
consist of readily available ingredients and shou'd be mixed
and formulated easily, preferably using customary procedures
or simpler modifications thereof. For this purpose, the
adhesives should have a long storage time, should be quick
s-etting on application and should be non-toxicl non-odorous,
and useable with standard equipment~ Additionally, the bonded
product obtained with the adhesive should have good strength,
elasticity, durability, acceptable color and no odor. Further-
more, the adhesive should be useful over a wide range of working
conditions because, even though good bonding strength may be
possible under certain conditions, the resin may not be
acceptable if such results cannot be readily achieved over a
Il ~ I
;34Z
wide variation of operations so as to accommodate accepted local
production methods or the use of different types of materials.
For example, a company for making bonded wood products might use
Southern Pine Veneer in one location and Douglas Fir in another,
and a good wood adhesive should be suitable for use with either
kind of wood. Finally, the adhesive and its application should
not be costly.
A variety of adhesive resins are now in use which
satisfy at least some of the forest product industry's
requirements. However, only few of the presently known
adhesives are suitable for large-scale use. Of these, the
isocyanates are excellent for making particle board. Howe~er,
they are expensive and their application requires stringent
quality control. Melamine--formaldehyde resins are also costly.
~;~ Phenol-formaldehyde resin has many o the desirable physical
pxoperties and is now the standard glue for making plywood and
; for exterior use, but its color and price make it undesirable
for assembling particle boards, which contain up to 10% of
their weight in glueO Furthermore, the phenols cure slowly,
and these adhesives are dark and thus not suitable for gluing
thin, decorative veneer.
For large-volume applications, especially wood
particle board, urea-formaldehyde resins are used almost
exclusively because they ha~e been the cheapest, most reliable
adhesive known. Unfortunately, their water resistance is
limited, and in order to obtain good bonding characteristics,
an excess of formaldehyde is necessary. This gi~es the board
. an objectionable odor which persists and can be noticed in the
processed p duct for many months. Other glues are either too
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~ 6~Z
expensive or are not used because they impart objectionable
properties to the product or cannot be applied with present
equipment and methods used in the forest product industry.
The principal object of the present invention is to
S provide an adhesive which is suitable for use in making bonded
wood products or the like which meets the requirements set forth
above and which obviates difficulties and disadvantages
encountered with prior art adhesives.
A more specific object of the invention is to modify
prior art wood adhesives so as to provide an adhesive which is
capable of use over a wider variety of conditions to give bor.ded
products ha~ing optimum properties. A further object o the
invention is to provide bonding compositions which make possible
; a significant reduction in cost while, at the same time,
permitting the use of conventional equipment and process
~ conditions.
; Other objects will also be hereinafter apparent from
the description of the invention which follows.
Broadly stated, the above and other objects are
realized by adding elemental sulfur to conventional wood
adhesive formulations, for example, adhesives based on heat-
curable urea-formaldehyde, phenol-formaldehyde or melamine-
foxmaldehyde csndensation products. The added sulfur may be
used to correspondingly reduce the amount of resin normally
used or the sulfur may be simply incorporated into a conventional
formulation containing the nor~al amount of resin. Thus, in one
illustrati~e example, 1-65~, preferably 3-50%, by weight, of the
urea-formaldehyde resin sol~ds in a conventional adhesive for
; making pressed wood particle board may be replaced by an equal
amount of sulfur added in elemental orm.
The adhesive compositions of the invention will usually
contain from about 0.05-99%, preferably 1-65%, and most preferabl~
3-50~, by weight, of added sulfur, based on total solids content.
The sulfur-containing adhesive compositions of the present
invention possess bonding strengths equal to or greater than the
adhesive containing the same total amount of solids but no sulfur.
Surprisingly, the substitution of 10% upwards (e.g., 10-60%) of
adhesives with sulfur provides resùlting adhesives exhibiting
comparable or increased strengths. The remaining solids will
comprise one or more of the conventional urea-formaldehyde,
phenol-formaldehyde, melamine-ormaldehyde or like heat-curable
adhesive resins, possibly with minor amounts of optional
additives, such as fill~rs, extenders, etc.
The compositions of the invention are easily prepared
by adding the desired amount of elemental sulfur to conventional
aqueous wood adhesive formulations or to one or more of the
indicated adhesive resins in liquid medium, advantageously water,
with appropriate mixing. The addition of a further amount of
water may be desirable in some cases to give the final
composition the viscosity preferred for use. The resulting
sulfur-containing suspension can be applied to wood particles
or other material to be bonded and then cured using the same
conditions and equipment as normally employed with the
corresponding sulfur-free adhesives. This is a particularly
important advantage of the present compositions since their use
does not require modification of existing processes and equipment
for making bonded wood products.
The compositions of the invention can be used in a
wide variety of ways, for example, as hot setting formulations
for making wood particle boards, the manufacture of plywood, the
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assembly of laminated boards, the impregnation of wood, paper
and textiles, for surface coatings or as adherence layers for
adhesives for connecting metals or metal alloys to wood, rubber,
aminoplasts or phenoplasts. Furthermore, the present
compositions are suitable as fillers for adhesives or molding
products, as gap-filling cements for plywood and as fillers fcr
knotholes or the like. Additionally, these compositions can
serve as extenders for adhesives, as modifiers, as molding
materials and, in general, wherever a fast-setting, high-
molecular ~leight adhesive resin is needed.
While the compositions of the invention may be preparedby adding only elemental sulfur to otherwise conventional wood
adhesive resins of ormulations containing the same, vaxious
modifications are also contemplated. For example, the desired
sulfur content may be obtained using a mixture of elemental
; sulfur and one or more polysulfldes, i.e., metal or organic poly-
sulfides. The polysulfides may be preformed or they may be formed
in situ. Additionally, as a further modification, sulfur in
elemental or combined form, e.g., as H2S or polysulfide, may be
added at any of a variety o~ production stages for the resins.
Thus, for example, elemental sul~ur mlght be dissolved in sodium
hydroxide or in an aqueous formaldehyde solution, or melted with
pnenol or urea, before the normal glue preparation procedure
begins, or the sulfur might be added in part at any int~rmediate
preparation steps, for example, in "stage A" as defined by L. H.
Baekeland for phenolic resins in hls article, "The Synthesis,
Constitution and Uses of Bakelite," published in The Journal
of Ind. and Eng. Chemistry, Volume 1, No. 3, March 1909, pages
¦149-155, or e sulfur may be added to the finished conventional
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adhesive when it is ready to be applied. For khis purpose,
commercial grade sulfur can be mixed with a commercial resin and
the mixture milled or ground by a variety of techniques, or the
sulfur can be first ground and then added to the adhesive. The
viscosity of the resin solution can be adjusted by adding various
additives, often plain water. Furthermore, the composition of
the invention can be used in mixed batches which can be processed
jointly with conventional resins. For example, a high-sulfur,
high-impact strength coating can be applied in direct contact
with a formulation optimized for wood particle bonding, or a high-
phenol mixture can be used to bond sheet metal parts directly and
in one setting operation to wood particle board. Furthermore,
high-strength compositions can be blended to reinforce parts of
boards which will be used to attach ~he board to hingesl frames
lS or studs, or a specially low-priced composition can be used to
prepare the core or intermediate layers of insulating boards
which do not need to have high elasticity or strength. The
preparation of the adherent surface is usually similar or
identical to that used for conventional adhesives.
It will be appreciated that an inherent advantage of
the invention is the fact that elemental sulfur is available in
large quantities. Additionally, it is non-toxic and non-odorous
and has properties which are intrinsically compatible with the
hydroxy groups and double bonds of wood. For the purpose of
this invention, elemental sulfur is d~fined as any allotrope of
this element, soluble or not, that contains up to 10% of any
natural or artificially added impurity. Claus sulfur, ~rasch
sulfur and sulfur recovered from SO2 abatement are usually 98~
pure or even better and are suitable for use in the compositions
of the present invention in any of the commercial forms. The
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physical state of the sulfur will influence its reactivity and
bonding rate. Preferably, the sulfur is ground, if necessary,
so that it is compatible with commercial glue spray and spreader
systems, but such need not be ground to the ex~ent necessary to
S achieve a homogenous mixture.
While not wishing to be limited to the reasons therefor,
it appears that the success of the invention is due to some kind
of synergistic effect resulting from the combined use of sulfur
and resin. The reasons for this are not completely un2erstood,
but apparently the sulfur reacts with the adhesive resin, the
wood and possibly the natural wood resin, and these components
and/or their reaction products otherwise coact to give results
which are not attainable using either sulfur or the resin
components alone. Thus, while it has been known that elemental
sulfur and polysulfides, when properly applied, can yield a
strong, quick-setting and water-resistant bond to wood (see, for
example, U.S. Patents Nos 3,855,054 and 3,252,815), these
materials have not previously been suitable for largç-scale use
because they have to be applied at a temperature too high to be
compatible with wood, .he product must be formed at high pressurel,
and during the manufacturing, unpleasant and corrosive vapors are
released. Furthermore, the products, due to the manufacturing
methods, are of undesirably high density and brittle.
It has been discovered that in the bonding reaction
with wood above 140C, sulfur extracts some of the natural wood
resins with which it is miscible and slowly reacts, and partly
exchanges position in the cellular structure, giving an excellent
. surface bond. However, during this process, because of
¦~ temperature d change in solubil ty, the wood loses its moi~ture
'~ '
~,
~ 3~
and its surface water film, and thus some of its hydrogen bonding.
Thls leads slowly to irreversible, destructive changes at and
below the glue line. All known economical modifiers and
plasticizers which could prevent the brittleness also react
destructively with wood and, furthermore, exude a lasting,
undesirable odor. However, by using the sulfur and wood resin
adhesives together according to the present invention, it has
been found possible to tal-e advantage of the desirable wood
bonding characteristics of sulfur while avoiding the indicated
disadvantayes such as brittleness and odor previously encountered.
That sulfur reacts with aldehyde resins and their
precursors is a well known fact. Thus, it is known, for example,
that sulfur reacts with phenols alone or with phenols in the
presence of caustic to yield phenoplasts (see, for example, U.S.
Patents Nos. 3,717,682 and 2,035,098) which ha~e useful and
attractive properties and can be reinforced with 5-150 wei~ht
percent sulfur to yield curable resins (see U.S. Patent No.
3,438,931). The compounds referred to herein as phenols are
- those potentially reactive aromatic hydroxy compounds, such as
phenol, resorcinol, ~ylenol, cresylic acid or other mono- or
dihydric phenols known in the art. Unfortunately, however, such
phenols release H2S during the initial step of their reaction
with sulfur, when polythioliphenols are formed (see again U.S.
Patent No. 3,717,682). Furthermore, the resulting rPsins are
not water-soluble, and the setting of these resins requires too -
much time or too high a temperature (see Cherubim, Kaut. Gummi
19, 676, 1966) and otherwise defies con~entional wood or forest
product industry technlques to find use in making bonded wood
products~
~:: , . _g_
~- ~ 3~
Urea-sulfur mixtures have also recently been careully
studied for use as fertilizer compositions (see U.S. Patent No.
3,313,613; Ger~ Offen. 2,451, 723; U.S. Def. Publ. T 912,014;
and U.S. Patent No. 3,295,950~.
Sulfur is miscible with urea to a lLmited extent and
does not react quickly at the temperature at which wood adhesives
must be used. With formaldehyde solutions, sulfur reacts over the
entire aqueous temperature range, and in the pE~ range (see U.S.
Patent No. 2,174,000) of 1 to 10 for~s a variety of rubbery resins
from which m~lded articles with many outstanding properties can be
shaped ~see U.S. Patents Nos. 3,303,166; 3,342,620; 2,195,248;
2,174,000; 2,429,859; 2,454,635; 2,255,228; 2,012,347; 2,206,641;
2,255,228; 2,039,206; 1,890,191; 1,991,765; and 1,964,725; and
"The Chemistry of Synthetic Resins," Reinhold, 1935, p. 1183).
These compositions suffer from similar drawbacks as the sulfur
phenoplasts and cannot be used with conventional equipment and
techniques for making bonded wood products.
Notwithstanding the problems indicated by the prior art,
when using sulfur alone for wood bonding purposes or for reaction
with aldehyde resins or their precursors, the combined use of
elemental sulfur and aldehyde resins, e.g., urea- or phenol-
formaldehyde resin, as proposed herein offers numerous advantages.
These apparently result from a combination of possible reactions
between, for example, sulfur and wood, sulfur and formaldehyde
and sulfur and phenol or urea to yield strong elastic and
chemically stable bonds. This is apparently partly due to the
fact that whatever reaction products are formed allow the wood
to retain much of its natural moisture, and to "work'l, i.e.,
expand and contract in response to changes in humidity in the
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environment. Retaining such natural propertieC of wood is vital
for establishing a strong, stable, lasting product. Likewise,
the present adhesive facilitates the bond between wood products
and metal or metal alloys. Additionally, as noted, the
compositions of the invention avoid certain disadvantages which
are inherent in prior wood adhesive compositions based on the use
of aldehyde resins. Thus, for example, the present adhesives are
substantially more economical than urea-formaldehyde or phenol-
formaldehyde adhesives; they are more moisture resistant than
conventional urea-formaldehyde, and they give equal or better
mechanical properties as measured by many of the common ASTM 1037
and 1038 tests. Furthermore, the compositions of the invention
can be made in such a manner as to optimize strength, to minimize
costs or to optimize elasticity while still meeting other standard
requirements for particle board or plywood adhesives. As noted,
`~ the present compositions can be applied with equipment and methods
identical to those conventionally used in the art. A further
advantage of the present compositions is their color. Thus, for
~; example, sulfur urea-formaldehyde products are light yellow and
the sulfur phenol-formaldehyde resins are light, not dark brown
~; as is the case with phenol alone. Furthermore, the invention
yields odoxless materials which lack the objectionable odor of
formaldehyde that is common to products prepared by conventional
formaldehyde adhesives. Additionally, the bonded products of the
~; 25 invention lack the odor of organic or inorganic sulfides which is
common to sulfur-phenoplasts, formaldehyde-sulfur compositions
and to modified sulfur. Furthermore, in some of the present
compositions, the sulfur appears to decrease the inflammability
of the produ s, probably by ~ ;~chanism similar to that observed
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i3~ ..fi~
when sulfur is added to polyurethane resins and o~ns (see U.S.
Patent No. 3,542,701), and it may also prevent the discoloring
observed for polyurethane (see U.S. Patent No. 3,222,301).
It will be appreciated that the basic chemical
composition of the invention always includes added elemental
sulfur, although modifications thereof may also be included. In
any event, the added elemental sulfur may ultimately be present in
the adhesive composition or bonded products obtained therewith, at
least in part, in the form of a variety o reaction products.
I0 The compositions o~ the invention are generally
prepared in aqueous medium, and if caustic is present when tne
elemental sulfur is added, the sulfur slowly reacts to form poly-
sulfides of an average rank of 4.5 and sulfite. In the resin
reactions of this invention, unreacted elemental sulfur, poly-
sulfides and sulfite all contribute to the formation of products.
If desirable, adhesive compositLons can be formulated with poly-
sulfide and sulfite as separate ingredients, but this is usually
not economical.
As noted, the total sulfur content of the present
compositions varies from 0.05-99% on the basis of total solids.
~7hen a urea-formaldehyde resin is used, the fol~maldehyde-to-
; urea ratio preferably will range from 1:50 to 50:1, i.e., the
formaldehyde content may exceed that normally used in urea-
formaldehyde resins, but should not be more than one mole in
excess of the sum of the urea and sulfur. In the case of the
phenol-formaldeh~de resins, the phenol-to-formaldehyde ratio will
also preferably vary from 50:1 to 1:50, but formaldehyde should
not be more than two moles in excess of phenol and sulfur. The
best formulations contain mixtures ~n which there is a slight
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surplus (e.g., about 15~) o sulfur in excess of that needed to
theoretically react with all other reactable components.
Depending on the physical and chemical form of the
ingredients and their ratio, and depending on pH, temperature,
reaction time and reaction sequence, the adhesive resin contains
different reaction products, different degrees of polymerization
and different degrees of cross linkage, which gives the adhesive
different tack and other physical and che1ical propertiQs, whlch,
in turn, determine the reaction c1uring the setting of the
adhesive, and thus the process conditions and final properties
of the product. For example, formulations in which formaldehyde
is slowly p~emixed with part of the sulfur tend to yield tough
; products (see E. Baumann, Ber. ~3, 60, 1890) which contain poly-
methylene polysulfides which exhibit excellent high-temperature
stability and are usually solvent resistant; high-sulfur resins
possess high tensile strength, but tend to be more brittle: If
the reaction of formaldehyde and sulfur or its derivatives is
~- conducted at low pH, trithiane is formed as an intermediate
(see Walker, "Formaldehyde", ACS Monograph Series, Rheinhold
Pu~l., London l960).
The role of the various lngredients in the present
- invention is not in all compositions the same and, furthermore,
different intermediates may engage in different synergistic
interactions. For example, in low-sulfur compositions, the
sulfur partly provides S-S linkage and stabilization of terminal
groups, forms some thio-aldehyde products and serves as filler.
All these functions can be used to improve the bonding of the
urea-formaldehyde or phenol-formaldehyde resin. In high-sulfur
compositions, sulfur and its copolymerlzation products which are
~ ;3~
partly miscible in natural wood resins substantially contribute
to the adhesive bonding function, and the urea-formalaehyde or
phenol-formaldehyde serves partly as a wetting agent, as well
as polymer component. In intermediate compositions, the urea-
formaldehyde and phenol-formaldehyde components help prolong the
water-soluble stage of the reaction, while the sulfur helps to
shorten the setting time and substantially reduces the solubility
of the fully set adhesi~e.
The invention is illustrated, but not limited, by the
following examples~ As used herein, all percentages and ratios
are by weight unless otherwise noted.
EXAMPLE 1
95 grams commercial grade prilled sulfur from a sour
gas Claus plant was mixed with 160 grams commercial urea-
formaldehyde particle board resin containing 95 grams, i.e., 60
resin solid, and water was added to adjust total solid to 60
~` weight percent of mixture. The mixture was blended for 2 minutes
in a mechanical blender until the sulfur broke into particles and
the mixture could pass through the nozzles of a commerclal paint
spray gun. At the time of applicationr the viscosity was about
160 cp (at 25C) and the gel time about 3 minutes at 100C. 100
grams of this glue was applied to 950 grams o~ Douglas Fir chips
-with a dimension o 0~015 x app. 1/8-3/8 x app. 1 inch and a
moisture content of about 6%~ This composition was used to press
; 25 sixteen 10 x 10 x 5/8 inch particle test boards ha~ing a density
of 0.70-0.75 gr/cm , i.e~, the density of the commercially most
common particle board. The glue application, mat formation and
pressing folIowed common practice known to those skilled in the
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art. The boards were pressed at 300F or about 5 minutes and
then stored for 1 week at room temperature in air at 70F and 50
humidity. The finished boards con~ained urea-formaldehyde and
sulfur in a weight ratio of 1:1, and an average 6 weight percent
o~ resin solid. After 24 hours soaking in room-temperature water,
the sixteen sulfur-containin~ boards exhibited only about 13-20%
thickness swell, while sixteen similax sulfur-free boards made
without including sulfur in the urea-formaldehyde glue swelled
about ~2-50%, i.e., about 3 times more.
The boards made with the sulfur-containing glue
exhibited an average tensile strength of 110 lb~sq inch as
compared to an average value of 105 lb/sq inch for boards made
from the same chips and the same urea-formaldehyde glue without
sulfurl and the same total resin solid content. Both batches of
boards had the same color, hardness and odor.
EXAMPLE 2
. ~
Several boards were made accordiny to the same procedure
as Example 1 but flowers of sulfur were used, the total resin
solid content was 8% (average) and the ratio of the urea-
formaldehyde to sulur was 9:1. These boards and several boards
made with ~ weight percent of solid resin urea-formaldehyde with-
out sulfur both had average tensile strengths of 150 lb/sq inch
~- and a similar modulus of rupture.
As in Example 1, the sulfur-containing boards could
be immediately recogniæed a~ter soaking for 24 hours in room-
temperature water because of their distinctly lesser swelling.
The sulfur-containing boards also were distinctly more fire
resistant than sul~ur-free samples, as measured by ASTM-1692-59
~ ll.lf;34Z
tests. This corresponds to the effect sulfur is known to have on
the fire resistance of polyurethanes (V. Raamsdonk, U.S~ Patent
No. 3,542,701 and British Pa~ent No. 1,107,237), and might be
connected with the increased fire resistance elemental sulfur is
known to gain from admixture of ~arious organic materials tLudwig
U.S. Patent No. 3,440,06~; Kobbe U.S~ Patent No. 1,853,818).
EX~MPLE 3
A sulfur urea-formaldeh~de resin was prepared from 250
~; grams 47% formaldehyde sclution and 130 grams urea by miY~ing for
60 minutes at 75C at pH 8.5, and subsequent condensation at 80C
at pH 5.0 until the viscosity reached 85 cp, according to
procedures known to those skilled in the art. 190 grams of this
resin were blended with 90 grams commercial prilled sulfur and 80
grams water were added. The viscosity of the resulting glue was
` ~ 15 180 cp and the gel time was 9 minutes at 100C. The sulfur-free
resin had a viscosity of 200 cp and a gel time of 7 minutes.
The glue containing urea-formaldehyde and sulfur in a
weight ratio of 1:1 was applied to 3 kg wood chips. A mat was
prepared and an 18 x 18 x 5/16 inch par~icle board was pressed
with techniques known to those skilled in the art. The internal
bond strength was 130 lb/sq inch, the modulus of rupture was 5430
lb/sq inch, the modulus of elasticity was 600,000 lb/sq inch and
the swelling after 96 hours of soaking in room-temperature water
corresponded to a weight gain o~ 69~ All tests were conducted
according to ASTM 1037-72a.
.,~ "
EXAMPLE 4-11
The urea-formaldehyde resin of Example 3 was mixed with
sulfur to give a ratio of urea formaldehyde resin solid to sulfur
of 99:1; 9:1; 4:1; 3:2; 1:1; 2:3; 4:1; and 1:9. In all ca~es,
the total resin solid, sulfur and urea formaldehyde combined
added up to 120 grams and was applied to 1600 grams wood chips
containing about 5~ moisture to yield a total resin solid content
of 8~, by weight. The viscosity of the resins varied between 160
and 200 cp at the time of application. The gel times of the
resins were between 7 and 11 minutes at lOO~C.
Boards were made as in Example 3. All of those boards
had cornparable internal bon~ stren~ths of 120 ~ 20 lb/sq inch.
~; 10 Boards made using a urea-formaldehyde:sulfur ratio equal to 1
were distinctly strongest, and the strength seemed to decrease
with shift in sulfur content towards both higher and lower values.
After soaking the boards for 24 hours in room-temperature water,
it was noted that swelling decreased almost linearly with sulfur
content. However, after 90 hours of soaking, all samples had
swollen similarly. All boards had the yellow color characteristic
for urea-formaldehyde bonded board. Compositions containing 5 or
more percent of sulfur were free of the offensive formaldehyde
odor common to finished urea-formaldehyde boards. Boards
containing more than 50% of sulfur in the resin gave off a faint
smell of elemental sulfur during the last minute of hot pressing.
When the board was released, and still hot, the vapox imm diately
ceased and no odor was noticeable. When samples of the boards
were stored at 150C for 20 days, they initially exuded a faint
but noticeable smell, reminiscent of organic sulfones, which
subsided after about 5 days~ At the end of the test, sulfur-
",r",` containing boards were not recognizable from sulfur-free boards.
;~ ~634Z
EXAMPLE 12
A resin containing urea-formaldehyde in the ratio 1:1.6
was fortified with 40% furfuryl alcohol according to practice
known to those skilled in the art (U.5. Patent No. 2,518,388).
90 grams of this resin and 30 grams wettable sulfur were mixed
and applied to l kg commercial wood woodchips as used for the
intermediate layer of a 5-layer particle board. The face and
center layers were formed from the above, fortified urea-
formaldehyde glue and commercial wood chips used for face and
center, but without any sulfur. This board had comparable
properties to a board made with the same procedure, but without
sulfur in any of the layers.
'~
~ ExAMæLE 13
:`
~; A l x 1 foot board was made according to Example 11,
-~ ~5 but 1% of a commercial wax of the type used in particle boara
manufacturing was added to the glue composition. Again, the
sulfur-containing and the conventional board exhibited similar
properties, but in the soak test, the swelling of all boards was
re~uced.
~O EXAMPLE 14
Pairs of pine blocks l x 2 x 2 inch were preheated to
160C and the glues of Examples 3, 5, 71 9 and 11 were spread on
the faces which were then assembled and clamped to yield glue
lines of about 0.1, 1 and 3 mm thickness. The tensile strength
of all samples exceeded 300 lb~sq inch, and 3 samples prepared
fxom pine blocks quickly preheated to 200C and jointed by an
,, .~
adhesive made from 95% liquid sulfur to which 5~ urea-formaldehyde
was added immediately before a glue line of 1 mm was assembled,
had tensile strengths in excess of 325 lb/sq inch (= 24 kg/cm2).
In all three samples, failure occurred across solid wood without
damage to the glue line.
EXAMPL~ 15
A 3-layer plywood was constructed from three sheets
of 1 foot x 1 foot x 1/10 inch hard wood veneers according to
procedures and practice known to those skilled in the art, and
pressed for 11 minutes at 150C. The glue was prepared from the
resin o~ Example 1, using a commercial extender. 30 grams of
the glue were spread on the 1 foot x 1 foot samples using a
commercial glue spreader. The sulfur-containing glue and a
conventionally-formulated glue using the same resin exhibited
similar sheer propeeties according to ASTM test 1038.
EXAMPLE 16
Commercial urea-formaldehyde adhesive was used to
prepare grade Type III plywood, but instead of using 150% wheat
flour as an eY.tender, 150% of a mixture of sulfur and wheat 10ur
was used.
., ~ . The adhesives containing extenders containing ratios
of 1:10, 1:3, 1:1, 3:1 and 10:1 sulfur to wheat flour were tested.
- A ratio of 1:3 to 3:1 was found to be particularly suitable,
probably because the wheat flour can absorb water while
maintaining a high viscosity. The mixtures are thus suitable
for the separate control of wate~ and vlscosity.
~ 34Z
EXAMPLE 17
_
The composition of Example 1 was mixed with wood flour
and ground walnut meal and used in place of boat, router,
circular or dogbone plugs to make patches to ill knotholes and
to repair defects. The resulting hot-cured patches had good
adhesion, a pale color, could be easily sanded and painted and
the product was not brittle.
~"
EX~IPLE 18
~- A urea-formaldehyde resin was prepared according to
Example 4, but part of the sulfur was added to the NaOH when it
was first applied, the remainder being added to the finished
resin. The properties of the resin were similar to those in
Example 4.
EXAMPLE 19
The resin composition was that of Example 4, but part
- of the sulfur was melted with the urea and stirred, and the
solidified mixture was ground and used as if it were urea, and
- the rest of the sulfur was added when the resin was finished.
~ Products prepared with this resin had similar properties to those
;~ 20 of Example 4.
.~
~ EXAMPLE 20
,
The composition was the same as that in Example 4, but
part of the sul~ur was added to the formaldehyde and part after
the resin was prepared. The properties of products made with
this resin were similar to those of Example 4.
' '
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:~ ~ 6~3~Z
EXAMPLE 21
The composition was the same as that in Example 4.
However, instead of elemental sulfur, a mixture of elemental
sulfur with sodium sulfide with a sulfur rank of 4 was used.
The procedure was that used in Example 20. The properties
of products made with this resin were similar to those of
Examples 4 and 20.
E~PI,E ~2
The composition was the same as that in Example 4.
However, instead of elemental sulfur, ~2S was forced into the
farmaldehyde solution which was carefully kept neutral with NaOH
to minimize polymer ~ormation. In this reaction, polymethylene
polysulfides are known to be formed. The reaction products were
processed as if they were formaldehyde solutions in the
preparation for the resin of Example 4.
E ~ ~PLE 23
.:,,.,,,'~
The composition of Example 1 was mixed with wood flour
and carbon blacX and molded into a shallow dish which was cured
for 30 minutes at 130C. The product ~erves as an ashtray.
EXAMPLE 24
._.
A commercial phenol-fo~maldehyde plywood resin was
treated with elemental sulfur in a ratio of PF-to-S of 10:1 and
used as basis for a glue for a 1 square ~oot section of a 3-layer
Douglas Fir plywood which was prepared according to practice and
technique known to those skilled in the art. This plywood
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:~ '
perf-ormed almost identically with plywood glued with the
unmodified pheno' adhesives, according to AST~ tests 1038-70.
EXAMPLES 25-30
The commercial phenol resin of Example 24 was mi-~ed
with ~lowers of sulfur in the ratio 4:1; 3:2; 2:1; 2:3; 1:4;
and 1:9; and a 1 square foot section of a 3-layer plywood were
prepared as in E~ample 24. All boards had comparable, equal or
better properties than board made from the pu~e phenol resin, as
judged by ASTM 1038-70
EXAMPLE 31
A phenol-formaldehyde resin was prepared by mixing 21
parts 100~ phenol, 14 parts 50% formalin, 31 parts water and 1.3
parts 50% sodium hydroxide, according to conventional methods.
After re1uxing, 24 parts 50% formalin and 6 parts 50% NaOH were
added, and finally 2 parts 100~ phenol were added. The mixture
was processed according to the art known to those skilled in the
field until the viscosity was 400 cp at 25C. This phenol resin
was used to compose a particle board glue in which sulfur was
substituted for phenol in vaxious ratios. In all tests performedlr
the properties of boards prepared with sulfur were equal or better
to those obtained from the conventional phenol resin alone.
EXAMPLE 32
A resin was prepared by the method used in Example 31,
but the first 21 parts of phenol were heated with 10 parts of
sulfur at 150C for 5 hours before the resin was prepared. This
~ l ¦ adheslve pe ormed similasly to that of Example 31.
,~ -22-
3~s;~ ,
EXAMPLE 33
A commercial melamine-formaldehyde resin was fortified
with sulfur and used to bond thin, decorative veneer to particle
board. The veneer could not be delaminated with a knife,
exhibited no formaldehyde odor and the color of the finished glue
line remained pale.
EX~MPLE 34
A re~orcinol a~hesive ~as fonmulated, such as used to
form an adherence layer for bondlng metal to vulcanizable rubber
or polysulfide thermoplasts tU.S. Patent No. 2,711,383). The
resorcinol was fortified with sulfur in a ratio of 1:1, 5:1 and
1:5. This mixture was used to form an adherence layer for bonding
aluminum sheet to particle board, Example 1. The laminate
exhibited excellent mechanical strength.
EXAMæLE 35
:
~ The sulfur-containing adhesive resins of Examples 1-15
; were u~ed to impregnate the surface of particle board and cured
as in Example 1. It ~ias found that the surface could be painted
without the application of a primer.
: The present invention provides a simple modification of
the urea-formaldehyde glue or phenol-formaldehyde glue used in
making pressed boar~s by either replacing some of the urea-
formaldehyde or phenol-formaldehyde resin with elemental sulfur
or by simply adding the sulfur to the otherwise conventional
formulation. Advantageously, the ratio of urea resin to sulfur
in the glue will be in the range of 10:1 to 1:10. The sulfur-
~'
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~ I
~: ~ 3~
modified adhesives of the present invent~on are thus in all
respects compatible with existing conver 3al procedures for
formulating pressed wood products and the like.
It will be appreciated that various modifications may
be made i.n the invention as described above. Thus, while the
invention has been described with particular reference to the use
of elemental sulfur with urea- and phenol-formaldehyde resins,
other aldehyde resins based on, for example, acetaldehyde,
resorcinol, melamine, etc. may be usefully employed. Hence, the
scope of the invention is set forth in the followiny claims
wherein:
