Method of abating aldehyde odor in resins and products produced therefrom

Conventional aldehyde containing resins for making bonded products or insulation foam are deodorized by the addition thereto of a sulfur compound such as oxyacid salts of sulfur in a valence state ranging from +5 to -2 inclusive.

BACKGROUND OF THE INVENTION 
The present invention is concerned with the formulation and application of 
additives to cold or thermosetting resin compositions containing a curable 
resin such as urea-formaldehyde, melamine formaldehyde, phenol 
formaldehyde or any condensation product containing any mixture or 
combination, copolymer or blend thereof. The purpose is to retain and 
exploit all mechanical, chemical and economic advantages of these resins, 
especially those formulations containing a significant molar excess of 
formaldehyde, while reducing the release and odor of formaldehyde of such 
products during the manufacture thereof and in the finished state. 
There is an increasing demand for strong and economical adhesives and other 
resin for use in making bonded wood and other products such as insulating 
foams. In such products, cured resins substantially determine the nature 
and quality of the resulting product. New building technology and 
environmental concern increase demands that such materials reliably 
fulfill a variety of exacting standards. 
Ideally, ingredients for such resins should be readily available, and 
should be mixed and formulated easily, preferably using customary 
procedure or simple modifications thereof. For this purpose the resin 
should have a long storage life, should be quick setting on application 
and should be non-odorous and non-toxic and useable with standard 
equipment. Additionally, the bonded product obtained with the adhesive 
should have good strength, elasticity, durability and acceptable color. 
Furthermore, the resin should be useful over a wide range of working 
conditions, because, even though good bond strength may be possible under 
certain conditions, the resin may not be acceptable if such results cannot 
be readily achieved over a wide variation of operations so as to 
accommodate accepted methods used for specific products, or as necessary 
to meet local production standards and methods, or the use of different 
types of materials. Finally, the adhesive should fulfill environmental 
quality considerations, the highest standards of industrial hygiene, and 
its application should not be costly. 
The art of formulating and applying urea-formaldehyde, 
melamine-formaldehyde, phenolformaldehyde and similar resins is well 
established, [see B. Meyer, UF-Resins, Addison-Wesley, Waltham, Mass., 
1979, in press] and a wealth of modifications and combinations have been 
and are being formulated to fulfill specific needs arising from the 
materials to be bonded, or requirements of product performance. For 
example, a resin containing approximately 40% melamine, 50% urea and 10% 
phenol has well known properties which can be correlated to well known 
application and production standards of earlier or individual components 
resins [see, J. Mayer and C. Schmidt-Hellerau, German Off. No. 2,020,481, 
now: U.S. Pat. No. 3,734,918, "Phenol-urea-melamine resin adhesive for 
wood."]. 
However, for intrinsic chemical reasons, almost all good and economic 
resins contain a substantial molar excess of formaldehyde. Some of this is 
released during the curing of the resin, for example in the hot press 
during the manufacture of particle board, causing obnoxious fumes. Some is 
slowly released from the finished product, and imparts upon the product an 
odor which in many modern applications, e.g. the construction or furniture 
industry, is considered objectionable. In addition, the resins contain 
some methylol and other intermediates and reaction products which can 
readily and reversibly hydrolyse, yielding methylene glycol and, finally 
formaldehyde. Furthermore, some resins, especially those containing 
urea-formaldehyde, tend to slowly decompose during aging, hydrolysis, 
weathering and thereby likewise release objectionable formaldehyde. This 
formaldehyde release rate is in direct conflict with conditions for 
optimizing almost all other factors and properties. The release is 
especially noticeable in particle board and in insulation foams, both of 
which contain cured resin films with a very large surface and which 
enhance this release. These films are of uneven thickness, which makes 
uniform curing very difficult. In particle board, the wood can act like a 
sponge, holding water in contact with the resin, and the swelling and 
shrinking during changes in humidity exacerbates the problem. 
Several paths have been explored for many years for reducing formaldehyde 
release, but all entail significant mechanical, chemical or economic 
disadvantages. For example, a large number of urea-formaldehyde resins 
have been formulated incorporating sulfite wastes or lignosulfonates [see, 
for example, E. Roffael & W. Rand, Holzforschung, volume 27, page 178, 
1973; and U.S. Pat. No. 3,994,850]. However, in order to obtain products 
equivalent to traditional urea-formaldehyde resins, an excess of about 
1-5% of resin must be applied, a higher curing temperature is necessary 
and longer curing or press times are required, followed sometimes by 
autoclaving. Unfortunately, the products tend to be more brittle. Similar 
problems are encountered if traditional resins are post-cured with urea or 
phenol in order to reduce the free formaldehyde in the resin [see for 
example: C. T. O'Neill, U.S. Pat. No. 3,996,190], as all these methods 
modify the chemistry of the resin structure or skeleton, modify the 
properties during application, and modify the products. A summary of the 
problems are contained in H. J. Deppe and K. Ernst, "Taschenbuch der 
Spanplattentechnik", DRW-Verlag, Stuttgart, 1977. S. Imura and N. 
Minemura, Hokkaido Fosert Prod. Res. Institute, Rinsan Shikenjo Geppo Vol. 
305, pages 1-5, 1977, have reported reduction of formaldehyde odor from 
finished plywood by washing it with aqueous solutions of several oxyacids 
of sulfur. Their procedure differs from this invention in that the 
finished product is treated. This includes wood as well as cured UF-resin. 
Their procedure is less effective, requires far more effort and might 
cause corrosion and other problems which are not found in our invention. 
Thus, there is a need in the art to provide an additive suitable for simple 
blending with a wide range of formaldehyde containing resin formulations, 
such as those currently used or tested for use in making insulating foams 
or thermo-pressed bonded products. Such an additive should not 
significantly or adversely affect the properties and behavior of the 
stored or ready-to-use resin, so that it can be used in every way in an 
equal manner to that of the resin without addition of the additive. 
Furthermore, the curing of the bulk, or at least a large fraction of the 
resin should not be significantly altered, and the chemical structure and 
skeleton of the ready-to-use resin should not be basically changed, so 
that a bonded product of equal or better qualities to those of the 
unmodified resin is obtained, but excess formaldehyde and release of free 
formaldehyde is greatly reduced, and thus the objectionable odor 
significantly abated. 
Accordingly, an object of the invention is to modify a variety of prior art 
formaldehyde resins with a sulfur containing additive so as to retain and 
provide optimum properties as characteristic for the resins, while 
exhibiting reduced odor during curing in a hot press and/or in the cured 
resin. 
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 a sulfur 
containing compound to ready-to-use, conventional, formaldehyde containing 
resins, such as for example, urea-formaldehyde, phenol-formaldehyde, 
melamine formaldehyde, or any cocondensation products such as 
melamine-urea-formaldehyde, or melamine-urea-phenol-formaldehyde. The 
sulfur is preferably present in any valance state other than +6, or any 
intermediate state or combination of such states, e.g., +5 to -2. Sulfur 
in the oxidation state of six, e.g. sulfate, is not found effective. The 
sulfur compounds can be introduced alone, in combination, or in 
combination with other resin components or odor reducing agents such as 
ammonia, ammonium chloride, quanidine, etc. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
Among the suitable compounds are all oxyacids of sulfur containing the 
proper oxidation states, for example: thiosulfates, polythionates, 
sulfites, pyrosulfites (disulfites), dithionites, elemental sulfur and 
sulfides. An overview of these compounds is found, for example, in B. 
Meyer, "Sulfur, Energy & Environment," Elsevier, Amsterdam, 1977, or in 
earlier reviews quoted therein. Of the above compounds, dithionites, 
elemental sulfur and mixtures thereof are particularly suitable 
deodorizers. Indeed, dithionites, sulfur and mixtures thereof not only 
produce a significant deodorizing effect, in and of themselves, but seem 
to interact synergistically with the other sulfur compounds of the present 
invention to produce an enhanced deodorizing effect. 
Any and each of the mentioned anions may be used in form of inorganic 
salts, such as the sodium, potassium, ammonium or other salts, their 
aqueous or alcoholic solutions or from organic compounds or inorganic 
compounds capable of releasing sulfur or its oxyacids in the proper 
oxidation state. Likewise, sulfides may be organics, such as mercaptans, 
metastable disulfides, etc, or may derive from inorganic sulfide or 
hydrosulfide salts or compounds, such as those of alkali metals, alkaline 
earths, transition metals or ammonium. The additive may contain any one or 
a mixture of the above in aqueous or alcoholic solution, suspension, 
slurry, as a solid or suspended in phenolic, amineous or heterocyclic 
solvents. The additive may be used to supplement normal resin quantities, 
or in some cases where the additive contributes directly or indirectly to 
bonding, some resin might be substituted. It is also desirable to use 
resins with high formaldehyde content, such as commonly used in the years 
prior to environmental concern, or reinforce the normal resin with excess 
formaldehyde to take advantage of strength of other properties added by 
this excess formaldehyde. 
To produce a deodorizing effect, the sulfur containing composition should 
be added to the resin in an amount sufficient to bind excess formaldehyde. 
In numerical terms, the additive composition of the invention will 
normally contain from about 0.3 to 30% by weight, preferably 1 to 10% of 
sulfur value based on weight of total resin solids. The sulfur containing 
additive best matches formaldehyde excess in the hardened resin in a molar 
ratio of 0.1 to 5.0. The best ratio depends on the material to be bonded, 
the press time and press temperature, pH and buffer capacity as well as 
other unreacted resin components. The blended modified resin can be 
extended or filled and hardened by conventional techniques before or after 
additive is fully added. 
The odor of formaldehyde in a hardened or cured resin is attributable, to a 
large extent although not exclusively, to the presence of free 
formaldehyde remaining therein, or to methylol and other compounds 
containing formaldehyde in loosely bonded form. Theoretically, in a 
urea-formaldehyde system, urea, which has four amine hydrogen atoms, is 
capable of reacting with formaldehyde in a 1:4 ratio in order to form a 
hardened resin. As a practical matter, however, resin formation is a 
complex multiple step process and a small portion of the formaldehyde is 
never incorporated into the polymeric resin structure, even when less than 
a theoretical excess of formaldehyde is employed in the original 
urea-formaldehyde reaction mixture. Furthermore, formaldehyde may be 
released from fully or from incompletely cured resin by hydrolysis, 
thermolysis or ageing. The mechanism of formaldehyde release from finished 
products has been and is being widely studied, but is not yet well 
understood. [R. Myers, U.S. Forest Products Laboratory, Madison, Wisc., 
Technical Reports, 1977-1979.] In the case of insulation foams or bonded 
wood products, especially in particle board in which wood has a large 
surface area, the release is influenced by secondary processes such as 
adsorption, absorp-tion desorption and vaporization. 
Due to its complex origin, this uncombined, loosely bonded or excess or 
free formaldehyde in the hardened resin is not measurable precisely by 
present technology. Different analytical techniques yield different 
values, and current standard methods for the determination of formaldehyde 
release from finished products are not yet reliable. For example, the 
European perforator test, the Japanese desiccator test, and various tests 
currently used in the U.S. do not reliably correlate. One problem in 
measurement results from decomposition of the resin during the measuring 
process. However, according to best estimates, free formaldehyde, in well 
formulated and well cured resins amounts to approximately 0.1% or more of 
the original formaldehyde used. 
The additive can be easily applied by addition to dry or aqueous resin 
before shipping, by addition during the final glue formulation at the 
plant, when filler and extenders are added, and water content is adjusted, 
and independent or jointly with the hardener if such is separately 
applied. If desired, a pH buffer may be added. The modified resin can be 
applied to wood or other practicles, chips, strands or fibers or similar 
particles made from different materials such as perlite, or the like, or 
any other material which can be bonded with the generic resin. The 
application of the modified resin and its curing can be achieved using the 
same conditions and equipment as normally used with the corresponding 
additive-free resin. This is a particularly important advantage of the 
present compositions, since their use does not require modifications of 
existing processes and equipment either in the resin factory or the 
application plant. Thus, their use can rely on all existing art and 
techniques. 
The composition can be used in a variety of ways, for example, as 
components in cold cured insulating foam, hot-setting formulations for 
making wood particle board, the manufacture of plywood, the assembly of 
laminated boards, the impregnation of wood, paper and textiles, for 
surface coatings or as an adhesive layer connecting materials such as 
wood, rubber, metals, aminoplasts and phenoplasts. Furthermore, the 
present compositions are suitable for fillers for adhesive or molding 
products, as gap-filling cement, and in conjunction with all uses for 
which urea-formaldehyde, phenol-formaldehyde, melamine-formaldehyde and 
their blends and copolymers and their modified or extended or filled 
variations can be used. 
While the composition of the invention may be prepared by adding one of the 
above mentioned materials in the exact molar ratio necessary to bind 
excess formaldehyde under individual application conditions determined by 
the nature of the bonded product, various modifications are also 
contemplated. For example, the desired sulfur content may be obtained by 
using a mixture of the sulfur compounds mentioned above, say dithionite, 
thiosulfate and polythionate of sodium, or sodium and ammonium salts of 
thiosulfates, etc, reagents which lead to mixtures, such as for example 
sulfur dioxide and hydrogen sulfide, as recovered from "After Claus" 
recovery plants, or from certain sulfur abatement processes used in 
connection with power plants. Such mixtures, including the so called 
Wackenroder liquid, may be applied as solutions, slurries, etc. 
Additionally, sulfur, or in situ sulfur may be incorporated during the 
last stage of resin preparation. In all cases care must be taken to 
balance pH and buffer capacity of resins. Thus, the ammonia content must 
be balanced with other ions. Furthermore, the influence of all chemicals, 
especially ammonia on wood must be considered, as well known to all those 
skilled in the art. In the case of sulfides, care must be taken due to 
their great reactivity, toxicity, and because molar excess if sulfides 
might lead to release of gases during pressing, a process which leads to 
the "blowing" of bonded products during thermosetting. 
In order to achieve maximum effects, the additive should be finely ground, 
dissolved or suspended and thoroughly mixed with the resin. This can be 
achieved, for example, by blending and stirring the additive into the 
resin, just before spraying the resin as insulating foam, or as an 
adhesive onto the material to be bonded. The resulting liquid or liquid 
slurry can be used in a conventional way alone, or modified as indicated 
above for different applications, such as all or part of different layers 
of composites, multi-layers or laminated or so-called sandwich boards or 
products. 
While not wishing to be limited to the reasons therefor, it appears that 
the success of the invention is due to the selective interaction between 
the above sulfur compounds and methylene glycol formed from formaldehyde 
in the presence of the semi-aqueous resin. In the case of thermosetting 
resins, success appears to be attributable to the temperature dependence 
of the interaction, while in the case of cold setting resins, the pH 
dependence of the interaction is apparently important. 
The basic reactions of aqueous formaldehyde have been explored [J. R. 
Walker, "Formaldehyde", ACS Monograph Series, Rheinhold Publishers, 3rd 
edition, New York, 1965]. In such systems formaldehyde exists in the form 
of an equilibrium mixture containing methylene glycol and polyoxymethylene 
glycol. If methanol is present as a stabilizer, hemiacetals are also 
formed. Likewise, the sulfur compounds of this invention are well known 
[B. Meyer, Sulfur, Energy and Environment, Elseviev, Amsterdam, 1977], but 
the mechanism of their reactions is still poorly understood. 
Thiosulfate reacts with formaldehyde at low pH forming unidentified 
products. [A. Kurtenacker, Z. Anorg. Anal. Chem. Volume 238, page 348, 
1938]. In the resin system it is initiated by the action of the hardener 
or catalyst. At a very low pH, thiosulfate can also undergo auto redox 
reactions yielding sulfur compounds in their nascent state, containing 
labile intermediates. 
Sulfites form adducts with formaldehyde which contain C-S bonds. These 
complexes are stronger than those of thiosulfate, and are used in 
analytical chemistry to mask sulfite so that thiosulfate can be titrated 
in mixture with sulfite [A. Kurtenacker, Z. Anal. Chem. volume 64, page 
56, 1924]. In fact, the sulfite interaction is so strong that excess 
sulfite is capable of degrading and solubilizing cured formaldehyde resin 
[B. Meyer, "U-F Resins", Addision-Wesley, Waltham, Mass., 1979, in press]. 
Elemental sulfur and polythionates do not combine with formaldehyde under 
resin storage conditions. In contrast, all sulfides except insoluble 
sulfides react quite readily with formaldehyde and yield over a period of 
days or several hours various thiane products, the nature and yield of 
which depends on pH, concentration and many other conditions. Volatile 
sulfides are usually more reactive and must be treated with caution 
because of their toxicity. 
Dithionite reacts in a complex manner yielding at least two types of 
products, one being CH.sub.2 (OH)SO.sub.3, as in the case of sulfite, and 
a lens stable compound, probably CH.sub.2 (OH).sub.2-x SO.sub.x, where x 
is 1 or 2. Hydroxymethane sulfinate is well known in the polymerforming 
industry [B. Meyer, "Sulfur, Energy and Environment," Elsevier, Amsterdam, 
1977]. Furthermore, dithionite also has a tendency to decompose alone in 
aqueous solution yielding complex compounds [L. Peter, Ph.D. Thesis, Univ. 
of Washington, Seattle, 1979, "Raman Spectra of Oxyacids of Sulfur."]. 
The sulfur compounds of this invention are characterized by the fact that 
they react with free formaldehyde, especially during curing conditions 
under the influence of heat or acid but that they do not complete their 
reaction with the pre-cured resin materials under storage conditions. 
Thus, all additive compositions can be prepared, applied, sprayed 
according to practice currently in use for urea-formaldehyde or other 
formaldehyde resins, and such practice is well known by those skilled in 
the art. 
The nature of the sulfur compounds in the products is not yet known. 
However, Raman spectra of cured foam surface samples and fracture surfaces 
of bonded wood products show vibrational bands at 777 cm.sup.-1 which 
correspond to the C--S bond, and sometimes at 1020-1150 cm.sup.-1 which 
corresponds to the symmetric stretch motion of S-O. From this it can be 
concluded that depending on pH, concentration and temperature, several 
types of CH.sub.2 --S bonds can be formed. Among them are CH.sub.2 
(OH)SO.sub.3 and compounds of the thiane and polythiane type. The thianes 
are known to be capable of copolymerization with formaldehyde [U.S. Pat. 
No. 3,300,445, H. Sidi]. The active sulfur form depends on the reagent and 
reaction conditions. A desirable sulfur form for the purpose of our 
invention is sulfur in an oxidation state between -2 and +5, and native 
sulfur resulting from decomposition of the parent compound by ionic and 
radical degradation [B. Meyer, L. Peter and K. Spitzer, Inorg. Chem., 
Volume 16, page 27, 1977] or by autodissociation or redox reaction, which 
in the case of thiosulfate, for example, can lead to a mixture of either 
elemental sulfur (S.sup.0) and sulfite (S.sup.+4), or sulfide (S.sup.-2), 
dithionate (S.sup.+5) and sulfate (S.sup.+6) [O. Schmidt, Chem. Ber. 
Volume 39, page 2413, 1906, and L. Vanino, Chem. Ber., Volume 47, page 
2562, 1914]. 
Urea does not react with sulfur additives under storage conditions, nor 
does melamine or phenol in the presence of the precured resin mixture. 
However, it is known that several of the above sulfur compounds can be 
incorporated into the basic composition during preparation of 
urea-formaldehyde molding resins [I. Kreidl, U.S. Pat. No. 2,113,485; 
Pfenning-Schumacher, Brit. Patent No. 313,455, and ICI, Brit. Patent No. 
463,433, etc.] and into phenol-formaldehyde resins [I. Kreidl, French 
Patent No. 806,286]. For this purpose, urea, formaldehyde and sulfur 
compounds are mixed in molar ratios of 4:8:0.4 and are reacted at high pH 
at 40.degree. to 80.degree. C. for several hours, yielding a moldable 
resin. Our invention differs in that our sulfur is not part of the 
original resin, and does not react to become part of the basic 
urea-formaldehyde or phenol-formaldehyde resin skeleton which makes the 
ready-to-use resin, but reacts essentially selectively with terminal and 
excess free formaldehyde during the curing of the already prepolymerized 
resin. As used herein, the term "prepolymerized resin" is intended to 
refer to synthetic resins composed of an aldehyde and at least one monomer 
polymerizable therewith which have been partially reacted to form said 
resin, but are not in the hardened or finally cured state. Such resins are 
also commonly referred to as "ready-to-use resins". 
According to the present invention the sulfur additive reacts under storage 
conditions only in a preliminary way with formaldehyde, and achieves its 
formaldehyde-binding action partly or primarily during the curing of the 
resin. Thus, it binds both free formaldehyde present in the resin and 
formaldehyde released from the resin during the process of application or 
curing after the finished resin mixture is applied and spread onto the 
surface of the wood, perlite or other material to be bonded, and while the 
bonded material is being shaped and pressed or during the spraying and 
curing of the foam. Under acid or high temperature curing conditions all 
of the sulfur compounds of this invention are capable of reacting with 
formaldehyde forming a mixture of products such as hydroxysulfonates, 
thianes, polythianes and polymethylene polysulfides, the detailed 
composition of which depends on individual factors one of which is pH. 
In the art of curing thermosetting formaldehyde resins, a variety of agents 
are employed to accelerate final curing of the resin. Most of these act by 
lowering the pH of the resin mixtures. Cold setting resins are often cured 
by agents containing phosphoric acid. Among hardening agents for 
thermosetting compounds are compounds which upon heating release acid to 
lower the pH of the resin so that its polymerization is enhanced. A 
typical hardener is ammonium chloride which is believed to decompose under 
hot press conditions to ammonia and hydrogen-chloride of which the first 
reacts with formaldehyde or escapes or penetrates the wood, and the second 
dissolves in the resin, thereby affecting the pH. Sulfur dioxide has long 
been proposed [A. Curs & H. Wolf, I. G. Farbenindustrie, G.P. 636,658] as 
a hardening agent because of its acidic reaction in contact with aqueous 
media. Likewise, ammonium sulfite has been proposed as hardener [B. Meyer, 
U-F Resins.] Several of the sulfur compounds of this invention, especially 
the ammonia salts, intrinsically contain the same ability. Thus, ammonium 
disulfite or polythionate can readily release sulfur dioxide which not 
only reacts with formaldehyde, but also acts as a biprotic acid with 
pK.sub.1 =1.92 and pK.sub.2 =7.2. Thus, hardening action of the sulfur 
compounds can be used to substitute or complement traditional hardeners 
which are normally added at the time of resin application or are built 
into the resin formulation. 
The mechanical and chemical properties of the products prepared with resins 
of this invention are essentially the same as those of the unmodified 
resin. However, in some instances, minor changes are observed which do not 
detrimentally affect these properties. Raman spectra indicate the presence 
of supplemental CH.sub.2 --S bonds [B. Meyer, U. F. Resins, "Reactions of 
Formaldehyde"], and, sometimes, of excess sulfur which, if present, acts 
as indicated in a previous U.S. application Ser. No. 749,381 of Dec. 10, 
1976. 
In many cases, the sulfur-formaldehyde products constitute a viable polymer 
product component and contribute significantly to the product strength. 
Thus, in order to achieve various enhanced structural properties, it is 
desirable to reinforce the original resin with formaldehyde before sulfur 
compounds are added, to add sulfur compounds partly complexed with 
formaldehyde or to employ a resin especially rich in formaldehyde. The 
trend of properties of such bonded products is demonstrated for 
illustrative purposes by the following test results obtained on three 
different types of boards. One board was made from Douglas fir chips 
coated with 6% weight, based on solid content, of a urea-formaldehyde 
resin containing a 0.3 M excess of formaldehyde; a second board was made 
exactly in the same manner, using the same ingredients, except that 0.6% 
weight, based on solid content, of formaldehyde was added to the resin 
before application; and a third board was made exactly as the second, 
except that 0.6% weight of thiosulfate was added to the resin before 
application. The internal bond strength of the three boards was 140, 140 
and 170 psi, respectively, and their modulus of rupture was 3940, 4300 and 
5700 psi, respectively. Furthermore, reinforced resins have the potential 
of being made better weather resistant. 
The compositions of this invention are generally prepared in an aqueous 
medium, or in a slurry, using an aqueous medium, alcoholic medium or a 
portion of the resin as a carrier. If dry resins are used, the additive 
may be added in dry form and premixed or shipped as part of the precursor 
of the ready-to-use resin. 
Total sulfur content of the present invention varies between 0.3 to 30% on 
the basis of resin solids. When urea-formaldehyde resins are used, the 
formaldehyde to urea molar ratio, as originally prepared or as fortified 
with additional formaldehyde, may be between 1.3 and 5, i.e., it may 
exceed the presently acceptable formaldehyde content substantially, 
without loss of effectiveness as deodorant. For example, the formaldehyde 
content may be as high or even higher than commonly used during the period 
of 1920-1940 when the art of formulating urea-formaldehyde resins are 
optimized for mechanical criteria rather than the modern environmental 
criteria. This is a specific advantage, because high formaldehyde resins 
constitute the basis for many materials which have fire resistant 
properties, superior to modern and more expensive substitutes, and are 
based on a sophisticated art which is in progress of being abandoned 
primarily because of environmental odor concerns which the results of our 
invention nullify. Furthermore, urea-formaldehyde resins can be easily 
disposed of after use as they constitute a nitrogen-rich fertilizer. The 
sulfur compounds employed according to the present invention all can 
degrade to nontoxic products which significantly contribute to the plant 
nutrient value. 
In terms of excess formaldehyde in a hardened resin, the formaldehyde to 
sulfur molar ratio may be between 1 to 10 and 10 to 1, but it is best kept 
in a range yielding molar matching of reagents. However, the molar ratio 
necessary for matching depends on several factors, some of which depend on 
the resin, some on the manufacturing conditions and some on the products 
to be treated. They have to be established in each case by careful 
consideration. For example, in some cases one sulfur will be able to bind 
two formaldehyde molecules, while under other conditions, only one 
formaldehyde entity might be bound. Likewise, some sulfur-sulfur bonded 
compounds, such as dithionate, dithionite, thiosulfate or polythionate 
might yield one reactive sulfur for each reagent molecule, and some two, 
depending on pH and redox-conditions, which can cause disproportionation 
into sulfide and sulfate, of which the latter is ineffective. Finally, 
some sulfur might form disulfide or polysulfide bridges which, depending 
on purpose of the composition can be a distinct advantage, as it usually 
imparts flexibility to the product. It is furthermore possible to add 
excess elemental sulfur, as such or in nascent form to the formulation, as 
indicated in U.S. application Ser. No. 749,381 of Dec. 10, 1976. 
The role of the various ingredients is not in all compositions the same, 
and furthermore different intermediates may engage in different 
synergistic interactions.

The invention is illustrated, but not limited by the following examples. As 
used herein, all percentages and ratios are by weight and are based on dry 
weights unless otherwise noted. 
EXAMPLE 1 
48 g of a commercial urea-formaldehyde particleboard resin containing 64% 
resin solid and a urea-formaldehyde ratio of 1:1.3 was mixed with 1.5 g 
sodium thiosulfate dissolved in 4 ml of a 2 M ammoniumchloride solution. 
The resulting adhesive was sprayed onto 500 g of Douglas fir chips 
containing 6% moisture, and the resulting mixture was pressed into a board 
with the dimensions 5/16.times.12.times.12 inches. A press temperature of 
310.degree. F. was used, and the press time was 4 minutes including 
2.times.20 seconds for press closure and release, respectively. Comparison 
with a control board made from the same materials by the same method, 
except that sodium thiosulfate was omitted, showed that all properties 
were undistinguishable, except that the board prepared according to the 
present invention exuded no formaldehyde odor, while the control board 
released substantial amounts of formaldehyde during press operation, and 
distinctly smelled from formaldehyde after cooling to room temperature. 
EXAMPLE 2 
45 g of a commercial urea-formaldehyde particleboard resin containing 62% 
resin solids and formaldehyde excess of 0.3 was mixed with an additive 
solution prepared by combining 15 ml of 38% formaldehyde solution with 5 g 
ammonium thiosulfate. The resulting resin was applied to 700 g Douglas fir 
chips, as described in Example 1 and 550 g were used to prepare a board. A 
comparison of the properties of this board with a control board containing 
only commercial resin and 4 ml hardener, and a second board containing 
only resin, hardener and 15 ml of a 38.5% formaldehyde solution showed 
that all properties of all three boards are within experimental limits the 
same, except that the board containing thiosulfate additive had an 
internal bond strength of 170 psi, as compared to a value of 140 for the 
others, and a module of elasticity of 5700 psi as compared to a value of 
4200 psi for the others, all other conditions being the same. 
EXAMPLE 3 
48 g of a commercial urea-formaldehyde particleboard resin containing 64% 
resin solid and a urea-formaldehyde ratio of 1:1.3 was mixed with 3 g 
sodium dithionite dissolved in 4 ml of a 2 M ammoniumchloride solution. 
The resulting adhesive was sprayed onto 500 g of Douglas fir chips 
containing 6% moisture, and the resulting mixture was pressed into a board 
with the dimensions 5/16.times.12.times.12 inches. A press temperature of 
310.degree. F. was used, and the press time was 4 minutes including 
2.times.20 second for press closure and release respectively. Comparison 
with a control board made from the same material by the same method, 
except that sodium dithionite was omitted, showed that all properties were 
undistinguishable, except that the board prepared according to our 
invention exuded the odor characteristic for wood, while the control board 
released substantial amounts of formaldehyde during press operation, and 
distinctly smelled from formaldehyde after cooling to room temperature. 
Comparison of formaldehyde release using the test of Mohl [see, H. R. Mohl, 
Holz als Roh- und Werkstoff 36, 69 (1978), "Saug- und Spaltmethode zur 
Bestimmung der Formaldehydabgabe von Hozwerkstoffen und Leimen sowie zur 
allgemeinen Luftanalyse, l. Mitteilung: Methodenbeschreibung."] showed 
reduction by 48% after 24 hours in the sulfur modified board. 
EXAMPLE 4 
45 g of a commercial urea-formaldehyde particleboard resin containing 62% 
resin solids and a formaldehyde excess of 0.3 was mixed with an additive 
solution prepared by combining 15 ml of a 38% formaldehyde solution with 
1.2 g ammonium dithionite. The resulting resin was applied to 700 g 
Douglas fir chips, as described in Example 1 and 550 g were used to 
prepare a board. A comparison of the properties of this board with a 
control board containing only commercial resin and 4 ml hardener, and a 
second board containing only resin, hardener and 15 ml of a 38.5% 
formaldehyde solution showed that all properties of all three boards were 
within experimental limits the same, except that the board containing 
dithionite additive had an internal bond strength of 170 psi, as compared 
to a value of 140 for the others, and a module of elasticity of 5700 psi 
as compared to a value of 4200 psi for the others, all other conditions 
being the same. After 24 hours the formaldehyde release was measured in 
the board containing the dithionite additive and found to be 40% lower 
than in a similar board not containing the additive. 
EXAMPLE 5 
15 g of a commercial melamine-urea-formaldehyde resin containing 47% resin 
solids and 0.2 excess of formaldehyde was blended with 0.5 ml of 2 M 
ammoniumchloride in which 1.3 g potassium pentathionate were dissolved. 
The resin was applied to 1500 g Sugar Pine chips containing 5% moisture, 
and the mixture was pressed into a 0.8.times.15.times.15 cm board of 0.7 
density of pressing the material for 6 minutes at 330.degree. F. After 24 
hours the formaldehyde release was measured and found to be 33% lower than 
in the reference board. 
EXAMPLE 6 
50 g of a urea-plywood resin containing 55% resin solids and a 1 M excess 
of formaldehyde was mixed with 1 g ammonium polysulfide (of an average 
sulfur content of 4.5 S per molecule, as determined by NMR) dissolved in 5 
ml of a 2 M solution of ammonium chloride, and the resulting resin was 
sprayed on 1 kg expanded perlite and pressed into a 1/2 inch thick board 
by heating the mixture to 330.degree. F. for 5 minutes and maintaining a 
pressure of 1500 psi. The resulting board exuded no formaldehyde odor 
whatsoever, but otherwise resembled in every respect a similar board made 
from the same ingredients by the same method. After 24 hours the 
formaldehyde release was measured and found to be 19% lower than in the 
reference board. 
EXAMPLE 7 
45 g of a urea-melamine particle board resin containing 60% resin solids 
and 0.3 M formaldehyde was mixed with 2 ml of a saturated ammonium sulfide 
solution and subsequently with 2 ml water in which 1 g ammoniumpyrosulfate 
was suspended. The resulting resin was applied to 700 g sugar pine chips 
and tested as in the preceding samples, and no formaldehyde odor was 
noted, while a control board released the distinct formaldehyde odor. 
After 24 hours the formaldehyde release was measured and found to be 20% 
lower than in the reference board. 
EXAMPLE 8 
3 g potassium disulfite (pyrosulfite) and 3 g borax were stirred with 5 ml 
water, and the slurry was blended in a medium speed blender with 50 g of a 
60% solid content urea-formaldehyde resin, and the resin was used to make 
sugar pine board as above. The product did not smell from formaldehyde, 
while a control board strongly smelled from formaldehyde. After 24 hours 
the formaldehyde release was measured and found to be 30% lower than in 
the reference board. 
EXAMPLE 9 
5 g sodium thiosulfate and 5 g urea-formaldehyde resin were blended and 
added to 40 g resin prepared by condensing urea, melamine and phenol in 
the ratio of 4:4:1 with 10 molar parts of formaldehyde was mixed with 1 kg 
sawdust and the mixture pressed into a 5/8 thick board. The resulting 
product, pressed 5 minutes at 350.degree. F. did not exude any 
formaldehyde odor and swelled only a fraction of that observed for 
commercial resin. After 24 hours the formaldehyde release was measured and 
found to be 15% lower than in the reference board. 
EXAMPLE 10 
2 g ground commercial grade sulfur and 2 g ammonium polysulfide solution 
and 2 g sodium tetrathionate were mixed with 45 g resin as in Example 2 
and tested as in Example 2. The board did not exude any formaldehyde odor 
whatsoever. 
EXAMPLE 11 
45 g phenol-formaldehyde resin containing 60% resin solids and a molar 
excess of 0.3 of formaldehyde was mixed with 5 ml of a slurry containing 4 
g of a mixture of iron, calcium and magnesium oxide which had been used to 
wash the sulfur oxyacids from an aqueous air pollution abatement pilot 
reactor in which coal combustion fumes containing 1% sulfur dioxide had 
been treated. The blended mixture was used as a resin to make a 3-layer 
plywood sheet. 
EXAMPLE 12 
UF-insulation foam was produced from commercial UF-dry resin, conditioner 
and hardener according to practice known to those familiar with the trade, 
using two solutions, (a) a dilute resin solution containing 33% resin 
solid and the commercial conditioner, and (b) a resin hardener solution 
matched to water hardener. Five gallons of each solution were prepared and 
foam was sprayed by pumping the two solutions in a ratio of 1:1 into a 
commercial foam gun. After 2 gal of each liquid were converted to foam and 
cast into 4 in..times.1 yd..times.1 yd. slabs of foam, commercial wettable 
grade elemental sulfur was stirred into the residual 3 gal resin in the 
ratio indicated in Table I, and foam was produced without any modification 
of procedure or equipment. The resulting foams were indistinguishable in 
every respect, except for a faint, yellowish tint in the case of the 
highest sulfur concentration. The gel time was identical, and the foam was 
homogenous and could be sliced normally after one minute. Foam densities 
were 55-60 g/liter of wet foam, and 12-14 g/l of foam air dried for 3 
weeks. The relative rate of formaldehyde release after 3 weeks is 
summarized in Table I. Formaldehyde release from ground foam gave similar 
results. 
TABLE I 
______________________________________ 
RELATIVE FORMALDEHYDE RELEASE 
FROM UF-FOAM WITH AND WITHOUT 
3 SULFUR CONTAINING ADDITIVES** 
(wt %)* 
Additive 0 2 4 
______________________________________ 
Elemental sulfur 100 48 30 
Sodium dithionite 
100 36 18 
Sodium sulfite + sodium 
100 69 73 
bisulfite (1:1) 
______________________________________ 
*On basis of resin solid content 
**Air dried three week old sample 
EXAMPLE 13 
Foam was prepared as in Example 12, except that sodium dithionite was 
substituted for elemental sulfur. The results are shown in Table I. All 
samples were white and undistinguishable. 
EXAMPLE 14 
Foam was prepared as in Example 12, except that a 1:1 (molar basis) of 
sodium sulfite and sodium bisulfite was used. The results are shown in 
Table I. Samples were white and not distinguishable. 
The present invention describes simple additives containing sulfur in an 
oxidation state other than +6 which can be blended as a liquid, a solution 
or a slurry or a solid into conventional urea-formaldehyde, melamine 
formaldehyde, or phenol-formaldehyde resins, yielding conventional 
products, except for greatly reduced or fully suppressed formaldehyde 
odor. The sulfur to formaldehyde ratio depends on excess formaldehyde, 
which would not be expected to be incorporated into the resin structure 
upon curing, present in ready-to-use resin, but advantageously is in the 
range of 10:1 to 1:10. 
The term "ready-to-use resin", as used herein and the claims which follow, 
is intended to connote the various resins which are prepolymerized to a 
resinous state but which are capable of being hardened or cured upon 
further treatment. 
The average valence states of illustrative effective oxysulfur compounds 
useful according to the invention are as follows: 
______________________________________ 
Valence Formula Name 
______________________________________ 
+5 S.sub.2 O.sub.6.sup.-2 
Dithionate 
+4 SO.sub.3.sup.-2, S.sub.2 O.sub.5.sup.-2 
Sulfite, Pyrosulfate 
(=Disulfite) 
+3.3 S.sub.3 O.sub.6.sup.-2 
Trithionate 
+2.5 S.sub.4 O.sub.6.sup.-2 
Tetrathionate 
+2 S.sub.2 O.sub.3.sup.-2 
Thiosulfate 
+2 S.sub.2 O.sub.4.sup.-2 
Dithionite 
(=Hydrosulfite) 
+10/x S.sub.x O.sub.6.sup.-2 
Polythionate 
+0 S.sub.8 Elemental Sulfur 
-1 S.sub.2.sup.-2 
Disulfide 
-2/x S.sub.x.sup.-2 
Polysulfide 
-2 HS.sup.-, S.sup.-2, RSH 
Sulfide, (organic: 
mercaptans 
______________________________________ 
For references giving the structures and reactions of these compounds, see: 
B. Meyer, "Elemental Sulfur", Chemical Reviews, Volume 76, page 367, 1967, 
and B. Meyer, "Sulfur, Energy & Environment", Elsevier, Amsterdam, 1977, 
and B. Meyer, "U-F Resins", Addison-Wesley, Waltham, Mass., 1979, in 
press. 
The present invention may comprise, consist of, or consist essentially of 
the hereinabove recited constituents and steps. 
It will also be appreciated that various modifications may be made in the 
invention as described above. Thus, while the invention has been described 
with particular reference to three types of formaldehyde resins, other 
aldehyde resins based on, say resorcinol, acetaldehyde, or furfural, etc., 
may be usually employed. Hence, the scope of the invention is set forth in 
the following claims wherein: