CA1164141A

CA1164141A - Liquid novolak resin and products made therefrom

Info

Publication number: CA1164141A
Application number: CA000352555A
Authority: CA
Inventors: Carl A. Rude; David D. Watson
Original assignee: Quaker Oats Co
Current assignee: Quaker Oats Co; Penn Specialty Chemicals Inc
Priority date: 1979-06-20
Filing date: 1980-05-23
Publication date: 1984-03-20
Also published as: NO801834L; SE8004590L; GB2053250B; DE3022534A1; GB2053250A; JPS564646A

Abstract

ABSTRACT

This invention relates to a novel method for tha manufacture of 100% reactive liquid novolak resins which do not contain inert diluents. In accordance with this invention, in the original manufacture of novolak resin, the procedure is modified so that instead of cool-ing the novolak resin after stripping to remove water, the novolak resin is neutralized to the pH above six by the addition of a ?asic material thereto either prior to or after stripping, and a sufficient quantity of furfuryl alcohol, or furfural monomeric solvent is added to solu-bilize and liquify the resulting novolak resin solution at ambient room temperature. The resulting liquid novo-lak resin is storage stable.

Description

t ~64~

The present invention relates to a method making novolak resins. Ilovolaks are well known thermoplastic phenol-aldehyde type and phenol-ketone type resins ob-tained primarily by the use of the acid catalyst and excess phenol. Tl~ese resins are generally alcohol soluble, and typically require reaction with furfuryl alcohol, hexamethy-lenetetramine, para-formaldehyde, etc., for conversion to cured, crosslinked structures by heating, for example to 200-~00 F. The result of the acid-catalyzed reaction be-tween a phenol and an aldehyde or ketone when an excess ofphenol is present, is a completed reaction in which the in-dividual polymers have no ability to continue growin~ in molecular weight once the aldehyde or ketone in the batch has been consumed. Consequently, because of this stability it has been regarded as of no importance that the catalyst which is used in the manufacture of novolak reSi!lS be allow--ed to remain ul?neutrali~ed in the reaction mixture so that at the time that the water which is present in the reaction mixture is stripped off, the pH of the reaction mixture is between 2~5 and 1Ø ~rpically, upon stripping of the water from the reaction mixture and cooling of the resulting resin, a very high viscosity liquid or a solid novolak results. It has been well known to use these resins, for example, by grinding the resulting solid novolak resin and then mixing them with furfuryl alcohol for use as foundry bindcrs, and the like. Such mixtures are well known to be acid-curable 1 ~ 6Ql~l -- 2 ~
and provide the advantage of a "high-solids" resin mixture.
In addition, novolak resin, when cured, ls recog-nized to provide high perce~tage of carbon residue so that it ranks approximately at the same level as cured furfuryl alcohol resin with respect to efficiency in generation of high carbon residue.
One of the disad~antages of one of the widely used methods of manufacture of novolak resins heretofore avail-able has been the requirement of the intermediate step of converting the resin into a solid by cooling, e.g. in a fla-king step, and then grindijng the resulting solid and admix-ing the resulting powdered ~ovolak with a suitable solvent.
In order to make the "solid" novolaks grindable the resins had to be stripped drastically during original manufacture to remove substantially all traces of unreacted phenol. It has been regarded as good ~ommercial practice for stripping to continue until the melti~g point is elevated to at least 100C. to facilitate grlndi~g. Traces of phenol would ren-der the powdery ground material fusable on storage, and the resulting fused or lumpy solid resins were difEicult to work with. Such problems are only partially alleviated by an alternative method commonly using, methyl or ethyl alco-hol, for example, to dissolve the stripped, but unneutrali-zed novolak polymer in the reactive vessel. However, such a solution is not 100% rea~ctive, and cannot normally be used unless or until the inert solvent is volatilized in-to the atmosphere at the point of use.
Another object of the present invention is the elimination of the manufacturing steps in the manufacture of novolak resins in which the novolak resin is converted into an intermediate solid and in which an intermediate grinding step is required.
The present invention provides a method of manu-facturing a novolak resin comprising the steps of reacting, at an elevated reaction temperature, an excess of a phenol with aldehyde or ketone under acidic conditions, allowing the reaction to continue until substantially all the al-dehyde or ketone is reacted, stripping most of the water and unreacted phenol from the reaction mixture after the ., ~ 164~

presence of aldehyde or ketone has substantially disappeared, neutralizing the resulting novolak resin to provide a pH above 5.5, and adding to the resulting neutralized, novolak resin in the reaction vessel, either before or immediately after strip-ping, while the resin is still liquid and at a temperature ofabout 100C, a furan-containing solvent which is at ambient room temperature, said solvent being selected from furfuryl alcohol, furfural, or mixtures thereof, said solvent being added in an amount sufficient to maintain the resulting novo-lak resin solution as a liquid having a viscosity of lO0 000cps or less at 20C. In accordance with the present invention, a stream-lined method of the manufacture of a 100% reactive liquid no-volak resin is provided, which method results in a novolak re-sin which is acid curable in addilion to being curable in theconventional manner, e.g. with hydroxymethylaminetetramine, and in preferred embodiments is either acid or base curable, and which provides high carbon residues, and from which no inert organic solvent must be used at point of application or use.
An advantage flowing from the present invention is the fact that in the original manufacture reactor, the pro-duct of the invention has reduced viscosity thus speeding up and otherwise facilitating the removal of the resin from the novolak reactor, or other containers.
In carrying out the present invention of a furan-containing solvent selected from the group consisting of fur-furyl alcohol and furfural and mixtures thereof is admixed with the freshly prepared novolak resin after it has been neu-tralized and either before or after it has been stripped,while it is still in the liq~id condition. In accordance with a preferred embodiment ~f the present invention the quantity of furan-containing solvent which is admixed with the neutralized, stripped novolak resin is sufficient to provide a fluid novolak resi~ at room temperature such as for example a solution having a viscosity lO0 000 cps or less at 20C., when the hot novolak solution is cooled to ambient room temperature within 30 minutes of the time at which the furfuryl alcohol is first added.

" ,, ~

- 3a -When the levels of furfuryl alcohol are admixed to provide the resulting novolak resin solution with approximate~
ly 10% furfuryl alcohol the resulting solution can be char-~ 16414~

acterized as a gummy viscous mass. On the other hand, gen-erally speaking, when levels of furfuryl alcohol are used that would provide between 25 and 30~ monomeric furfuryl alcohol in the resulting novolak resin solution, viscosi-ties less than 100,000, usually less than 50,000 cps at 20 C. are normally encountered. Generally speaking the amount of the furan-containing solvent which can be used in accordance with the present invention can be relatively high levels, e.g. up to 50~ and higher. It is preferred that sufficient solvent be added to result in a solution which has at least 15% solvent, based on the weight of the solution.
Furthermore, it is highly desirable in order to achieve maximum benefit of the present invention to apply positive cooling means to quickly drop the temperature of the novokal solution as soon as it is formed, so that am-bient room temperature conditions are quickly achieved.
The furfuryl alcohol or furfural is added while the novolak resin is still hot enough to be in a liquid, readily mixed condition, although the temperature can be decreased sub-stantially from the strippin~ temperature, e.g. by cooling, or by addition of incremented portion of the cold furfuryl alcohol or furfural, before the solution is completely form-ed by addition of the rest of the furan-containing solvent.
In the manufacture of novolak resins, a phenol, (this term is discussed more fully hereinafter), is allow-ed to react with an aldehyde, or ketone typically in the presence of water, at acid pH's, under reflux conditions.
For example, oxalic acid is used in quantities sufficient to provide a pH of about 2.5-4.0 in the aqueous system.
Typically the reactions are allowed to proceed at reflux conditions until the aldehyde or ketone is determined to be (by conventional titration) absent from the reaction mixture, and at least a slight excess of phenol is allowed to remain.
Up to this point the methods by which novolak resins are produced are entirely conventional, and the method of the present invention relates to an improvement in the subse-quent steps. Consequently any conventional method for re-acting phenol with an aldehyde in an acid medium with an ex-l 164~
-- 5 --cess of phenol are contemplated as within the purview of the practice improved by the present invention.
After the conventional manufacturing titrations have determined that the aldehyde or ketone level has been reduced substantially to zero, the reaction is regarded as "terminated". In typical conventional practice heretofore, the novolak-water mixture containing sufficient acid to pro-vide a pH in the range of 2.~-4.0, for example, is immedi-ately stripped usually under reduced pressure conditions with the result that the free unneutralized acid is typic~l-ly allowed to remain in the novolak resin upon the comple-tion of its manufacture.
However, ln acc~rdance with the practice of the present invention, the novolak is neutralized prior to fur-ther processing. This can be achieved, in accordance with the present invention, for example, by addition to the re-action mixture of any suitable basic material such as, for example, a solution of sodium hydroxide. Alkali metal hy-droxides, and carbonates, and other non-reactive alkaline materials can be employed. The amount of sodium hydroxide which is added, or other basic neutralizing material, is an amount sufficient to bring the p~l of the resulting resin to ~t least 5.5 and preferably substantially above 6Ø The preferred neutralizcd pH range is between 6.0 and 7. Neu-tralizing to a p~ above 7 i5 permissable unless the furfural cyclohexanone mixture is used as a solvent, in which case the pH should be below 7Ø The neutralization preferably takes place while there is a substantial amount of water still in the reaction mixture, although the novolak resin can be stripped to remove the water, either before or after the addition of the basic material to neutralize the reaction mixture.
The furan-containing solvent can be added either before or after the stripping is completed. However, it is preferred that it be added after stripping. Thus, in a pre-ferred embodiment, after the stripping step has been complet-ed and most of the water has been removed from the reaction mixture (for example up to 4~ or so water can remain, typic-ally) the furan-containing solvent is added. In a preferred t ~64141 embodiment the hot novolak resin is cooled substantially be-fore addition of the furan-containing solvent, e.g. to a temperature below 150 F. but at which the resin is still a liquid. Also, the furfuryl alcohol can be added incremental-ly so that the fluidity is maintained during cooling, with a large portion of the solvent being added near ambient temperature conditions. This is to maximize the effect of the solvent with respect to imparting fluidity. As used herein the term "cooling" is intended to denote a positive application of cooling means, such as, for example, con-tacting the liquid with a heat exchange surface maintained at temperatures substantially lower than the temperature of the liquid, resulting in a` rapid reduction in temperature of the liquid. "Cooling" does not necessarily indicate that temperatures below ambient room temperatures are achieved. Another positive application of cooling means in-cludes the addition of "cold" furan-containing solvent, e.
g. solvent at ambient room temperature. Addition of a sub-stantial quantity of cold solvent abruptly drops the tem-perature of the liquid, and because of increased flui~ity,increased cooling efficiency at the heat exchange surfaces are achieved, as well. As used herein, "cold" is intended to refer to a temperature which is at least 50 F. below the temperature of the liquid to which the "cold" material is added. For example, ambient oom temperature furan-con-taining solvent is "cold" as used herein for the purpose of addition of the solvent to the hot resin liquid resulting in abrupt drop of its temperature. The total amount of furan-containing solvent which is added is an amount sufficient to liquify the resulting novolak resin at room temperature, e.
g. 20 C. The preferred levels of furfuryl alcohol or furfur-al solvent which are included, however, are at least 15~
based on the weight of the resulting solution, and amounts sufficient to provide between 25 and 35~ of furan-containing solvent is preferred.
Generally speaking, as used herein, the term "novolak" and "novolak resin" denote a condensation product such as is obtained by causing a phenol to condense with less than an equimolar portion of an aldehyde or a ketone, in an l 16~

acidic environment. Structurally the molecules of a novo-lak consist essentially of alkyl-substituted or unsubsti-tuted phenylol nuclei connected together by methylene or substituted methylene links. Although phenol and formal-dehyde are preferred condensation reactants, other sub-stances may be used. For example, phenol may be substi-tuted with cresol, xylenols, mixtures of cresols and xylen-ols, and epoxy resins such as the condensation products of bis-phenol with epichlorohydrin; and formaldehyde can be substituted with other water-soluble and phenol-reactive aldehydes such as acetaldehyde and propienealdehyde. In fact, the manufacture of any phenolic resin of the novolak type can he improved in accordance with the present inven-tion. Such resins, for example, are produced by condensing phenol such as phenol itself, m-cresol, p-cresol, o-cresol, 3,5-xylenol, 3,4-xylenol, 2,5-xylenol, p-ethylphenol, p-ter-t-butylphenol, p-tert-amylphenol, p-tert-oxtylphenol, p-phenylphenol, 2,3,5-trimethylphenol, resorcinol, and the like.
In the following examples, unless otherwise indi-cated, all percents are expressed in percent by weight, parts are parts by weight, and temperatures are expressed in F.
Example 1 A mixture of phenol and aqueous formaldehyde is prepared at a ratio of 1.15 phenol to 1.00 moles of for-maldehyde. A sufficient quantity of oxalic acid is admixed therewith to provide a pH of about 3.0 and the reaction mix-ture is allowed to react under atmospheric reflux tempera-ture conditions until all of the formaldehyde disappears.
~0 Thereafter, a sufficient quantity of aqueous sodium hydro-xide is added to the reaction mixture to elevate the pH of the reaction mixture to approximately 6.3. Thereafter the refluxing condensor is removed and most of the water and un-reacted phenol is allowed to be removed from the reaction mixture in the conventional reduced pressure distillation stripping step. ~hen the water removal, stripping step is substantially completed, sufficient furfuryl alcohol is ad-ded to the stripped novolak resin which is at an elevated temperature of about 100 C. to provide a resulting solution ~ 1641~4~

having about 20 percent of furfuryl alcoholO Immediately after admixing the solution is cooled to room temperature within 30 minutes. The resulting neutralized solution is storage stable.
Example 2 The procedure of Example 1 is repeated, except that, instead of furfuryl alcohol, the same quanitity of furfural is added to the hot, neutrallzed, stripped, nov-olak liquid resin. Likewise a liquid solution result which has similar fluidity at ambient temperature conditions.
This resulting novolak resin solution is storage stable.
Example 3 The procedure of Example 1 is repeated except that instead of furfuryl alcohol, the same amount of a sol-ution of 66% furfural and 33% cyclohexanone is added to the hot novolak resin. Likewise a similarly fluid solution of novolak resin is obtained. The resulting resin solution is found to be readily curable under either acidic or basic conditions, but is storage stable, as produced in accordance with this invention.
Example 4 Relatively fine particulate carbon is admixed with a pre-catalyzed novolak resin mixture comprising catalyst and resin, the catalyst being a 50:50 mix oE maleic anhy-dride and furfural, the resin being produced in accordance with Example 1. The catalyst and resin were used in respec-tive amounts sufficient to provide about 4% maleic anhydride based on the weight of the resin and about 24% weight of resin based on the weight of the particulate carbond. The resulting admixture is shaped into the form of an electrode, and heated to about 200 F. Upon heating the binder- cures in-to a solid, and a strong carbon form in the shape of an elec-trode is produced.
E_ ple 5 Particle board ingredients comprising wood chips, saw dust, wood dust, and the like, are admixed with a pre-catalyzed novolak resin mixture comprising catalyst and resin, the catalyst being a 50:50 mix of maleic anhydride l 16~14~
g and furfural, the resin being produced in accordance with Example 1 the catalyst and resin were used in respective amounts suffi`cient to provide approximately 5% maleic an-hydride based on the weight of the resin and 6% by weight of the resin solution based on the weight of the wood par-ticulate ingredients. The resulting mass is pressed into the shape of a board and heated to 300 F. to trigger the curing of the resin. A hiyh-strength particle board re-sults from the curing step.
Example 6 Calcined magnesite is admixed with a pre mixture of triethanolamine, and th~ liquid novolak resin solution produced in Example 1 (in which furfural-cychlohexanone mixture was used instead of furfuryl alcohol). The trie-thanolamine catalyst is used in an amount sufficient to provide between 5--10% based on the weight of the resin, and the amount of resin solution which is used is sufficient to provide 6% by weight based on the weight of the basic magnesite. qhe resulting mixture is formed into a de-sired brick form, heated, and the resin cures into a solid.The resulting magnesite brick can be used under very high temperature conditions. At high temperatures the binder is carbonized and the carbon formed improves the perfor-mance and prolongs the life of the brick.
Example 7 Furfuryl alcohol, novolak resin, and the novolak resin solution produced in accordance with Example 1 and 3 are respectively tested to determine carbon residue using the Conradson Carbon Residue Test identified as follows:
In this test a weighed quantity of the material, or solu-tion to be tested, is admixed with a known quantity of catalyst, and placed in a crucible containing glass boiling beads. The assembly is then weighed and post cured by heating 2 hours at 180 F., 2 hours at 200 F., and 16 hours at 300 F. The resulting post cured assembly is then placed in a Conradson apparatus which comprises a second crucible 1 ~B~

partially filled with a coke flour. The entire unit is heated to temperatures set forth in the ASTM Procedure, about 900 C. The cured material or solution then thermal-ly disinter~rates. The weight loss is finally determined and the residue (carbon) is calculated. The results of the test are summarized in Table I.

TABLE I
Material Tested C rbon Residue Straight Furfuryl Alcohol (acid cured 48 10 Novolak Resin (hexamethyltetramine-acid cured . 48 The product of Example 1 (acid cured) 48 The Product of Example 3 (base cured) 33 The Product of Example 3 (acid cured) 45 Example 8 The tests oE Example 1 were repeated, except that in Example 8, sufficient furfuryl alcohol was used to pro-ide about 2a% by weight in the resulting novolak resin.
The resulting solution was found to be acid curable, and 20 had a stable viscosity of about 40,000 cps at room tem-perature.
Example 9 This example provides a comparison of the effect of pH, solvent concentration and effect of hot-holding time on the viscosity of the novolak resin produced in accordance with the invention.
TEST A
In a laboratory glassware kettle, the novolak resin was prepared in accordance with the general method 30 described in Example 1. TTowever, the novolak was neutrali-zed to a pH of 5.7 with a sodium hydroxide solu-tion while refluxing, the resin was then stripped and furfuryl alcohol in an amount sufficient to provide 30% furfuryl alcohol in t 1641~

the resulting solution was addecl. The urfuryl alcohol was added while cold, i.e. at ambient room temperature. The stirring was allowed to continue, and the temperature of the resulting solution was allowed to gradually achieve ambient room temperature condition without further cooling other than ambient air cooling. The viscosity of the resulting product was found to be 39,000 cps at 20 C.
TEST B
In this test, the novolak resin was again pre~
pared by the identical procedure used in Test A above, and in a pilot plant reactor equipped with a water cooling jacket. After the phenol ormaldehyde reaction was com-plete, the novolak was neutralized to a pH of 6.9, with a sodium hydroxide solution while refluxing, the resin was then stripped, and furfuryl alcohol in an amount sufficient to provide 30~ furfuryl alcoho] in the resulting solution was added. The furfuryl alcohol was added cold, and im-mediately upon completion of the addition of the furfuryl alcohol, cooling was applied rapidly by means of cold water in the water jacket. The resulting solution was found to have a viscosity of 3,500 cps at 20 C.
TEST C
In this test, the procedure of producing the novolak resin of Tests A and B above was repeated in sep-arate production runs, except that after stripping, the hot liquid neutralized resin was sampled and six separate sam-ples of each respective resin batch were aliquoted into glass laboratory beakers which were placed on a laboratory hot plate and maintained at 200 F. Into each of the re spective beakers of each series of samples, different quantities of furfuryl alcohol were added, to provide in the respective beakers resulting solutions having 20, 25, 30, 35, 40 and 45% furfuryl alcohol respectively for each series. The alcohol in this test, however, was added at the same high temperature as the resin namely 200 F. After thorough sti`rring, the resins were allowed to gradually be l 16~14~

cooled with ambient air cooling to ambient room temperature condi`tlons.
- The results of the two serles of tests of Test C
are reported on Table II.
TABLE II
_.

Viscosity (cps/room temp.) % Furfuryl Alcohol pH 6.9 pH 5.7 5,000,0007.000,000 1,600,000 `246,0001,500,000 79,000 512,000 36,000 83,000 40 (100 C/8 hr.) 71,000 141,000 It is noted that in Test A and B, cold furfuryl al-cohol was- added, and this resulted in a substantial decrease in temperature immediately. In Test A, in which the resin was allowed to be maintained at elevated temperature prior to addition of the furan-containing solvent, and were main-tained at elevated temperature for a long time as a result of inefficient ambient air cooling, however, the result-ing viscosities were relatively high, e.g. almost ~0,000 compared to the relatively low viscosity i.e. 3,500 cps at 20 C. which was achieved in Test B in which the mixture was cooled quickly to ambient temperature conditions.
~lso, it is apparent from Table II that neutralization to the pH of 5.7 produced viscosities which are generally speaking, almost twice that achieved by corresponding di-lutions of novolak resin which had been neutralized to the pH of 6.9. Nonetheless, in Test C in which hot furfuryl al-cohol is added to the novolak resin, and in which the re-sulting solutions are not cooled quickly, the viscosities for corresponding levels of furfuryl alcohol are vastly higher than the viscosities which are achieved with sudden cooling of the solution by addition of cold (ambient tempera-t 16~4~

ture~ furan-containing solvent thereto.
We know of no chemical or physical explanation of this phenomenon at this time.
Thus, it will be appreciated from the above dis-closure that the method of manufacturing liquid novolak resin in accordance with this invention has been sub-stantially streamlined with no significant adverse impact with respect to the production of high carbon -residue acid curable binders. Also this invention gives an alkaline 10 curable binder, e.g. with furfural cyclohexanone solvent, which ranks very high among alkaline curable resins, with respect to relatively high carbon residues.
The convention of the novolak resin to an inter-mediate solid, with the inherent requirement of grinding and other processing of the solid material, has been elimin-ated, in accordance with the present invention. An easily handled, readily applied liquid novolak resin solution is produced.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of manufacturing a novolak resin compri-sing the steps, reacting, at an elevated reaction temperature, an excess of a phenol with aldehyde or ketone under acidic con-ditions, allowing the reaction to continue until substantially all the aldehyde or ketone is reacted, stripping most of the water and unreacted phenol from the reaction mixture after the presence of aldehyde or ketone has substantially disappeared, the improvement comprising neutralizing the resulting novolak resin to provide a pH above 5.5, and adding to the resulting neu-tralized, novolak resin in the reaction vessel, either before or immediately after stripping, while the resin is still liquid and at a temperature of about 100°C, a furan-containing solvent which is at ambient room temperature, said solvent being selec-ted from furfuryl alcohol, furfural, or mixtures thereof, said solvent being added in an amount sufficient to maintain the re-sulting novolak resin solution as a liquid having a viscosity of 100 000 cps or less at 20°C.

2. The method according to Claim 1 in which the phenol is phenol itself, and in which the aldehyde is formaldehyde.

3. The method according to Claim 1, in which the reac-tion mixture is neutralized with a strong base and in which the solvent is furfuryl alcohol.

4. The method according to Claim 1, in which novolak resin is neutralized to a pH between 6.0 and 7.0, and in which the solvent is a solution of cyclohexanone and furfural.

5. The method according to Claim 1, wherein the sol-vent is added while the resin is still at a sufficiently high temperature to remain in liquid condition.

6. The method according to Claim 1, wherein the sol-vent is cold when added to the novolak resin.

7. The method according to Claim 6, in which the mix-ture of novolak resin and furan-containing solvent is cooled rapidly to ambient room temperature conditions immediately after the addition of said furan-containing solvent thereto.

8. The method of manufacturing the novolak resin comprising the steps reacting at an elevated reaction temperature an excess of phenol with aldehyde or ketone under acidic conditions, allowing the reaction to continue until substantially all of the aldehyde or ketone is re-acted, stripping water from the reaction mixture after presence of aldehyde or ketone has substantially disappear-ed, the improvement comprising: neutralizing the resulting novolak resin to provide a pH above about 5.5; adding to the resulting stripped novolak resin a furan-containing solvent selected from the group comprising furfuryl alcohol, furfural, and mixtures thereof, said addition being made in-crementally in which some of the furan-containing solvent is added to the neutralized stripped novolak resin while at an elevated temperature which is sufficiently high to main-tain the resin in liquid condition; a first incremental portion of the added solvent being large enough, however, to maintain the resulting solution as a liquid at reduced temperatures, said resulting stripped novolak resin and/or solutions resulting therefrom being cooled rapidly; a final incremental portion of the solvent being added to the re-sulting initially prepared solution at substantially am-bient room temperature condition in an amount sufficient to provide the desired viscosity at ambient room tempera-ture.

9. A liquid novolak resin solution comprising admixture of neutralized novolak resin and a monomeric solvent consisting essentially of a mixture of furfural and cyclohexanone.