CA1073140A

CA1073140A - Resol resins

Info

Publication number: CA1073140A
Application number: CA282,843A
Authority: CA
Inventors: John P. Gibbons; John P. Mudde
Original assignee: Unilever Bestfoods North America
Current assignee: Unilever Bestfoods North America
Priority date: 1976-07-22
Filing date: 1977-07-15
Publication date: 1980-03-04
Also published as: FI772247A; NO772600L; NL186770B; NO146205C; ATA528277A; NL186770C; DE2732993A1; CH627482A5; FI64607B; FR2359159A1; MY8000094A; FR2359159B1; AT361224B; BE856962A; NL7708041A; ZA774447B; GB1541996A; DE2732993C2; NO146205B; ES460908A1

Abstract

ABSTRACT OF THE DISCLOSURE

Carbohydrate-phenolic resol resins are produced in a process in which a phenolic compound is reacted with a carbo-hydrate in the presence of a basic catalyst to form a resin intermediate in a first stage, and then, in a second stage, the resin intermediate is reacted with a lower aliphatic aldehyde in the presence of a basic catalyst to form the resol resin. The resins produced in the practice of this invention are particularly well suited for laminating and adhesive applications.

Description

31~0 , S P E C I F I C a T I O N

This invention relates to carbohydrate-based ~ ;~
condensation resins and a process for producing same, and more particularly to a phenolic-carbohydrate resol resin. ~-~

Condensation resins based upon phenolic compounds such as phenol and aliphatic aldehydes have been in widespread use for many years. As is well known, the aldenyde, usually formaldehyde, is reacted with phenol in the presence of an acid or basic catalyst to form a condensation resin. There are generally two recognized types of phenol-formaldehydc resins currently in use for various applications. One orm o~ resin, referred to in the art as a novolak res;n, is prepared by reaction of excess phenol with formaldehyde to form a resin capable of thermosetting by the addition of a catalyst. The other form of phenol-formaldehyde resin is referred to in the art as a resol. Those resins are prepared by reaction of phenol with excess farmaldehyde to form a ~ ;
resin system having greater water solubility than the novolak resin.

Resol resins are widely used as the base for adhesives in, for example, paper laminating applications and in the manufacture of plywood.

I~e basic raw material for phenolic resins, whether they be novolak or resol resins, is petroleum.
Supplies of petroleum a.e becoming increasingly limited, and prices have accordingly increased significantly.
There is thus a need to re?lace at least a portion of the petroleum-b2sed components of the phenolic resinx with a less expensive, more abun~ant material. Carbohydrates, s~,~

.

~ 3~
.
rea~ily ava;lable from plant sources, are thus one typ~ of renewable resource ideally sui~ed for use in the manufacture of novolak and resol resins.

It has been proposed, as described in U. S.
Patent No. 1,753,030, to employ starch as a component or phenolic resins in which starch is reac~ed with pheno7 in the presence o~ an acid catalyst to form a solid, infusible resi.n which can be rendered water soluble by thereafter reacting the resin with fo~maldehyde. ~o proportions of reactants are set forth, and consequently it is not possible to determine whether or not the foregoing patent is directed to the production o a resol resin.

One o~ the dif~iculties which has been incurred in the production of resol resins by first forming a condensation resin by reaction of a carbohydrate such as starch with phenol followed by reaction with formalde~de resides in the apparent lack of reactivity of the phenol-carbohydrate condensation product. In U. S. Patent No. ;~
3,215,653, there is described an adhesive composition prepared by a complex reaction scheme wherein a phenol-formaldehyde resin said to be useEul in bonding applications is prepared by reaction of a phenol-formaldehyde resin, a formaldehyde-reactive filler and resorc;nol are reacted under alkaline conditions. The procedure described by the ~oregoing patent is a very cumbersome one, requiring complex reaction procedures.

It is accordingly an obJect of the present invention ~o provide a low cost ~esol resin system incor-porating an inexpensive carbohydrate at relatively high levels of substitution.

3~
~;

It is a more specific object of the invention to pro-vide a resol resin useful in bonding and laminating applications and a process for the production of same wherein a substantial portion of the resol resin is made up of a caxbohydrate mate-rial wherein the resol resin has improved adhesive and water resistant properties.
The concepts of the present invention reside in a phenolic-carbohydrate resol resin produced in a two-stage reaction. In the first stage, a phenolic compound is reacted in the presence of a basic catalyst with a carbohydrate to form a furan-type resin intermediate, in the second stage, that intermediate is reacted with a lower aliphatic aldehyde to produce a resol resin having good solubility, low viscosity and excellent water resistant properties. The resol resins of the present invention have been found to be particularly suitable for use in th~ manufacture of adhesives. !;
It is an essential feature of the present invention that the second stage reaction between the furan-type resin and the aldehyde be carried out under basic conditions, that is in the presence of a ba~ic cataly~t. Without the use of a basic catalyst, the aldehyde is apparently not sufficiently reactive with the furan-type intermediate resin for complete solubili-zation of the resin.
Thus in accordance with the invention there is pro-vided a proce~s for producing a carbohydrate-phenolic resol resin comprising (1) reacting in the presence of a basic catalyst a carbohydrate and a phenolic compound having the formula :
OH

~ 3 -~ 3~
,. 'wherein R is selected from the yroup consisting of Cl to C3 alkyl, Cl to C3 alkoxy, halogen, hydroxy and hydrogen, to form a resin intermediate, and (2) reacting the resin intermediate with a lower aliphatic aldehyde in the presence of a basic catalyst to form a resol resin.
The intermediate resin formed by the condensation reaction between the carbohydrate and the phenolic compound is preferably in liquid form: and preferably water is produced in the condensation reaction in an amount between about 0.75 mole to less than about 5 moles, per mole of carbohydrate, expressed as monosaccharide.
In the practice of this invention, a preferred carbo-hydrate is starch. Suitable starches include all varieties of starch, such as corn starch, tapioca starch, wheat starch, grain sorghum, potato starch, rice starch, sago, etc. That includes all types of grades of starch, such as waxy starches, high amylose starches, non-waxy - ~

~ 1 ... .. .. .. . .. . ...

( ~73~0 starches, etc. Also included in the practice of this in~enticn are chemically modified starches, dextrins, thin boiling sta~ches and pregelatinized starches. Starches as used herein also include crude starches such as mill st~rch, corn flour9 wheat flour, br~wer's grits, broken rice, etc.

In general, use can be made of starches having the following structure:
.
r~
C~2H I CH20H I ~H OH
H ~ O ~ I ~ ~ ~ I H ~ O~H

~OH ~i o ~ OH H~o - ~ OH
HO ~ ~ ~ ~
] [ ~H I ] I ~H ~ ~1 OH

wherein n> designating the number of repeating units, can range up to 106.

In addition to starches~ use can also be made of mono-, di- and trisaccharides such as dextrose, maltose, ~ -maltotriose, lactose, glycogen, glucosides, corn syrups and the like.

As the phenolic compound used in the practice of this invention, preferred are the phenolic compounds having the formula:

OH
~ ' wherein R is a group selected from Cl to C3 alkyl, Cl to C3 alkoxy, halogen, hydroxy and hydrogen. The preferred ~73~4~

phenolic compound is phenol, but other phenolic compounds include cresol, chlorophenol, bromophenol, resorcinol and the like~
The relative proportions of phenol and carbohydrate employed in the first stage reaction to produce a furan-type resin can be varied within relatively wide limits. In general, the amount of phenol employed ranges from 0.5 to 10 moles of the phenolic compound for each mole of carbohydrate employed, and preferably 0.75 to 5 moles of phenolic compound per mole of carbohydrate (expressed as monosaccharide). One of the advantages of the present invention stems from the fact that the resin system of the present invention can incorporate relatively high levels of carbohydrate without deleteriously affecting the properties of the resulting resol resin.
The first stage reaction is generally carried out at a relatively high temperature, preferably temperatures in excess af 100C~ Best results are usually obtained when the reaction temperature ranges from 109-200C. The reaction is best effected by reacting the phenolic compound with the carbohydrate in an a~ueous reaction medium, the preferred technique being refluxing the reactants in the presence of the catalysts to produce the first stage furan-type resin. Preferably the reaction is continued for long enough to generate at least 0.75, but less than 5 moles of water of condensation per mole of carbohydrate reactant (expressed as monosaccharide) to form a liquid intermediate resin.
In the second stage o~ the reaction, formaldehyde is added in an amount sufficient to solubilize the furan-type resin formed in the first stage and thexeby form a resol resin.
The amount of formaldehyde employed should be an amount sufficient to solubilize the resin system. It has `been ~ourld that best result3 can be obtained when the amount oE aldehyde ~' , ~LO ~ 4~

(formaldehyde, acetaldehyde or propionaldehyde) ranges from 1.05 to 2.0 moles of aldehyde per mole of phenol, preferably 1.05 to 1.75 moles of aldehyde per mole of phenol.
The use of a basic catalyst in the second stage reaction in which the aldehyde is reacted with the furan-type resin intermediate is, as noted above, an important concept of the invention. Any of a number of basic catalysts can be used in the practice of this invention, all of which are well known ;
to those skilled in the art. Included are the alkali metal hydroxides te.g. sodium hydroxide, potassium hydroxide, etc.), ;
alkaline earth metal oxides and hydroxides (e~g. calcium oxide, barium oxide, magnesium oxide, etc.) as well as ammonia and like bases. In general, the basic catalyst should be used in an amount sufficient to adjust the pH of the second ~tage reaction medium to at least 8Ø
Because the resol resins produced in the second stage of the reaction tend to form gels under vigorous con-ditions, it is generally preferred to employ relatively mild reaction conditions in the second stage. Best results are usually obtained when the temperature of the second stage reaction medium is below 100C.
In accordance with the invention by conducting both the first and second stage of the reaction in the presence of a basic catalyst of the type described above, there is obtained the advantage of avoiding neutralization of an acid catalyst at the completion of the first stage of the reaction.

~1 ~73 .
This invention is further illustrated by thê
following examples, which, ho~.~ever, are not to be ta~en as limiting in any respect. All parts and percentages, unless expressly stated to be othen~ise~ are by weight.
~ .

- EXAMPI.E 1 Use o BaO as Cata~yst 310 g phenol (containing ~8 g water) 3 moles 180 g dextrose 9 g barium oxide were placed in a 500 ml resin kettle equipped with a stirrer, tnermometer and take-of condenser. The materiaLs were heated wi.th stirring to 178C for 3,5 hours, and 83 cc of water was collected ~about 3 moles of water/mole of dextrose). The resulting resin was very low in viscosity æt the reaction temperature. It ~as cooled to 70C and 284 g of 37% formaldehyde (3.5 mole) were added gradually.
Since no exotherm was noted, the temperature was raised to reflux (103C) and 10 cc of concenkrated ammonia w~s added.
Refluxing was continued for 4 hours, until the viscosity reached 24 centistokes. The resin was adjusted to 50%
solids with methanol and neutralized to pH 6.0 with ~2SO4.
The resin solution was then tested in laminates. The resulting paper lamlnate withstocd a boiling water test for 24 hours without blistering.

Although the resulting laminate did not pass the iinal test (48 hours), the example illustrates the great stability of the resin and it shows an effective way to control the exothermic reaction of formaldehyde with the first stage reaction product.

1~731~

The following example demonstrates the necessity of using a basic catalyst in the second stage of the reaction in which the furan-type resin is solubilized with aldehyde.
In the following example, the teachings of McIntosh were followed to the extent indicated, without obtaining satis-factory results, employing an acidic catalyst in the first stage.
EXAMP~E 2 ::~
315-g phenol (containing 33 g water) 10180 g dextrose 5 cc 5 ~ H2S4 were placed in a 1000 ml xesin kettle and heated with stirring for 130 minutes at 160C. During this period, 83 cc of water was distilled off, together with 15 cc of phenol. Allowing for the 33 grams of water preqent in the phenol, the ~83 ~ 33 = : :
50) water corresponds closely to the removal of 3 moles of water per dextrose unit to form HMF.

g _ ... ;

-: . -. .

~ c The resin so obta;ned ~as cooled to 70~C and18~ ~ forrnald~hyde (37%) was added. The t2mperatuLe ~-as kep~ at 70C by means of a water bath for 4 hours.

The resin was then used to impregnate Kraft paper as describe~ in the foregoing disclosurP. It did not cure completely wllen pressed at 275F, and the laminate ~ell apart when immersed in boiling water. This example illustrates that: basic conditions are necessary to obtain a suitable cure of the formaldehyde extended phenol~carbohydrate resin.

As an additional check on the procedure of U. S.
Patent No. 1,753,030, the procedure described by McIntosh was followed. 100 g each of phenol, starch and water ~as re~luxed for 5-1/2 hours in the presence of H2S0~. The resulting liquid was separated in two layers. The lower layer (clear) weighed 169 gram while the darX upper liquid weighed 113 grams. (18 gram might have escaped ~1uring the prolonged reflux period).

The 169 gram layer appears to be a solution of dextrose in water, while the upper layer i5 mostly phenol.
After washing once with water, only 100 g dark liquid wzs left. Since no directions were given on how to proceed in the next step, and since the dark layer is obviously mostly phenol, the experiment was not continued.

It will be apparent from the foregoing description and examples that the present invention provides a simple technique for the production of less expensive resol resins as compared to the prior art. The resins produced in accor~
dance with the practice of this invention are particularly ~` ( 3~4~
sui.table in applications where the adclition of a curing agent to the resin (such as the hexameth~-lenetetramine usually used with novolak resins) is dif-fi.cult~ as in ~he manufacture of laminates, particle boarcl adhesives and the like as described.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptions of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within know~ or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, as fall within the scope of the invention.

Claims

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

1. A process for producing a carbohydrate-phenolic resol resin comprising (1) reacting in the presence of a basic catalyst a carbohydrate and a phenolic compound having the formula - wherein R is selected from the group consisting of C1 to C3 alkyl, C1 to C3 alkoxy, halogen, hydroxy and hydrogen, to form a resin intermediate, and (2) reacting the resin intermediate with a lower aliphatic aldehyde in the presence of a basic catalyst to form a resol resin.

2. A process as defined in claim 1, wherein the carbo-hydrate is starch.

3. A process as defined in claim 1, wherein step (1) is carried out at a temperature above 100°C.

4. A process as defined in claim 1, 2 or 3, wherein the mole ratio of phenolic compound to the carbohydrate is within the range of 0.5 to 10.

5. A process as defined in claim 1, 2 or 3, wherein the mole ratio of aldehyde to phenolic compound is within the range of 1.05 to 2Ø

6. A process as defined in claim 1, 2 or 3, wherein step (2) is carried out at a temperature below 100°C.

7. A process according to claim 1, 2 or 3, wherein step (1) is continued for long enough to generate at least about 0.75 mole, but less than about 5 moles of water of condensation per mole of said carbohydrate, expressed as a monosaccharide, to form a liquid intermediate resin.

8. A resol resin produced by the process of claim 1, 2 or 3.