CA1185736A - Alloys of epoxy and homopolymers of furfuryl alcohol - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A mixed resin system is disclosed which, when cured by a crosslinking agent which is a poly-functional amine or amide, yields a tough, flexible product having excellent chemical resistance and high temperature resistance as well as the ability to adhere well to virtually any substrate including metals and Portland cement or concretes based thereon. The resin system is a mixture of furfuryl alcohol homopolymer and epoxy resin in various weight ratios dependent upon the physical properties desired.

Description

BACKG~OUND OE~ SE I~VENT LON
This invention relates to resin sys~ms particularly adapted for use as corrosion-resistant coatings on a wicle variety of materials or substrates.
Homopolymers of furfuryl alcohol are known to be excellent for use as corrosion-resis~ant coatings having, when cured, a wide range of chemical resist~nce such as renders them suitable for service in non-oxidizin~ acids alkalies, salts, g~ses, oils, gre~ses, detergents and most solvents at temperatures up to 375DF.
The principal drawbacks of ~uch coatings are that they are brittle, do not adhere to steel, aluminum, copper or any other metal, and cannot be used on alkaline ma-terials, such ~s concrete, due to the requirement for acidic curiny agents in connection with these resins. As a result, coatings and cements ~ased on homo~olymer of fur-furyl alcohol are restricted in use ~rincipally to wood and ceramic mat~rials.
Another drawback of acid cured homopolymers of furfuryl alcohol is the high de~ree of shrinkage and hicJh porosi~y incidental to the loss of water as by-product of -the condensation reaction during cure. However, despite the above limitations, furfuryl alcohol homopolymers when cured have considerable commercial importance as corrosion-resistant coatings and cement.
Epoxy resins, on the other hand, are noted for their low shrinkage during cure, since epoxy resins r~act with very little rearrangement and ordinarily with no volatile by-products being evolved. Also, unlike the above mentioned homopolymers of furfuryl alcohol, 5~3~
epoxy resins may be cured with a wide range of agen-ts including acid curing agen-ts such as carboxylic acid anhydrides, dibasic organic acids, phenols and Lewis acids, and basic curing agents such as Lewis bases, inorganic bases, primary and secondary amines and amides. Epoxy resins, due also to their low shrinkage during cure, are capable of strongly adhering to vir-tually any substrate.
Epoxy polymers, when cured, also exhibit reasonable chemical resistance. secause of the carbon~-to-carbon or ether linkages within the epoxy resin molecule, these resins are ex-tremely stable to the reaction of alkalies and have reasonableresistance to most acids and many solvents. Generally speaking, the chemical resistance is depenclent upon the curing agent and the degree of cure.
However, eured epoxy resins are inferior to cured homo-~olymers of furfuryl aleohol in regard to ehemical resistanee a~d to high temperature resistanee. In regard to the la-tter, cured èpoxy resins tend to beeome brittle at high temperatures.
The present invention is based upon the diseovery that a mixture of homopolymer of furfuryl aleohol and epoxy resin ean be crosslinked by -the use of polyamide or polyamine euring agents arld that the reaetivity of the euring agent is signifieantly en-hanced by the presenee of the homopolymer of furfuryl aleohol even when the euring agent is not effeetive to cure this resin alone. This is dramatieally illustrated by the fact that a polyfunctional amine or amide cur-ing agent for the epoxy .resin, when used in amount insufficient to cure a specific amount of epoxy resin alone, nevertheless will ef-fect cross-linking of the same amount of resin when it consists of a mixture of homopolymer of furfuryl alcohol and epoxy resin. Si-milarly, the same curing agents when used in greater amounts suf-ficient to effect progressively greater curing of -the epoxy re-sin alone, allow the characteristics of ~lexibility and hardness to be controlled to yield a wide range of highly chemlcal- and high temperature-resistant alloys to be obtained.
Accordingly, the present invention provides an article comprising a structure having thereon a temperature- and corrosion resistant cured coating which adheres to various subs~rates includ-ing metals and concrete, which coating consists essentially of an intimate mixture of homopolymer of furfuryl alcohol and epoxy re-s:irl cured with an agent selected from the group consisting of poly-function~l amines and amides, said homopolymer being present in w~ight ratio with respect to the epoxy resin in the range 10/90 to 90/10, to provide the cross-linking necessary to make the cured Z~ coating self-supporting~
Generally speaking, as little as 10% homopolymer of fur-furyl alcohol and as much as 90~ of this homopolymer in the homo-polymer/epoxy resin mixture yield useful products, although it is somewhat easier in most cases to obtain the desired balance of hard~
ness and fl.exibility when the weight ratio is in the range of about 30/70 to 70/30.
Again, it is the case in general that for a given weight ratio of furfuryl alcohol homopolymer/epoxy, as the relative amount of curing agent is increased, the cured resin alloys progress first from soft, extremely fle.xible products, then to relatively hard, tough still flexible products, then to very hard, relatively in-flexible products, and finally back to softer and more 5~36 flexible produc-ts. In the latter stage, the curing agent is in excess and acts as a plastici7ing diluent.
The resin system of this invention is a furfuryl alcohol homopolymer/epoxy system crosslinked with a polyfunctional amine or amide. The physical characteristics of hardness and flexi-bility of the cured material are controlled by the weig}lt ratio of the two resins and -the degree of cure effecte~ (obtained by the amount of curing agen-t used and/or -the conditions of cure) withou-t significant effect on the chemical and temperature resistance properties. Surprisingly, despite the inherent brittleness of cured furfuryl alcohol homopolymer alone and the high temperature embrittlement of cured epoxy polymers alone, the combined system of this invention can exhibit a high degree of toughness, flexibility and adhesiveness at room temperature and retain the majority of these properties even at temperature of ~00F and greater.
In order to unders-tand -this invention from a point of view of mechan:Lsm reaction, the simplified molecular structures of ~1-1e reactive species are presented as follows:
Eurfuryl alcohol polymer

2~ ~ 2 ~ ~ ~Ct~2- C~2 ~ C~2-C~12- 1~ Cli~_ ~ H20~1 Epoxy polymer (bisphenol A-type) CH
C ~ - C~i_C~12_E0 ~ 3 ~ ~ U - C~1 polyamine The polyfunctional amine crosslinks with the epoxy as well as the homopolymer by means of i-ts active hydrogens, as follows:

Il 2 ~ 2N--r~ - Nl~+~
o o o --C~2-- I ~
o - .
R OH

~N C~i2~ CI~CH2 y~ _ _ Example 1 Furfuryl alcohol homopolymer obtained from Hooker Chemi-cal Corporation, Durez Division was blended with vari.ous portions of Epon 828 (a trademark), an epoxy resin produced by Shell Chemi-cals and Versamid 125 (a trademark), a polyamide resin manufac-tured by General Mi:Lls.
Ater thoroughly mixing 100 grams of resin and 3 grams Ver.~amld (a trademark) w:ith spatula, patties (15 grams each) were ~,re~parc-~d by pl.aci.ng the material in an aluminum dish 2 3/8" in di~ clter and 5/8" deep and left for 10 days at room temperature.
The degree oE cure is related to the weight ratio o epoxy and ~ur~uryl alcohol homopolymer as listed in Table I.
Table I
~esln by weight Degree of Cure homopolymer Epoxy 100 0 sot, uncured gel gel soft, some cure soft, some cure softer, sligh-t cure 3n 30 70 softer, slight cure softer, slight cure 0 100 tacky, uncured ~5~3~
Table I clearly indicates that in amounts insufficient to effect, after 10 d~ys, room temperature cure of epoxy alone, the polyfunctional amide is effective nevertheless to achieve varying degrees of cure provided the weight ratio of homopolymer to epoxy of the alloy is about in the range of 30/70 to 70/30.
If the degree of cure is increased by introducing a high temperature cure regime, useful produc-ts exhibiting excellent corrosion resistance and high temperature resistance and, in most cases, a high degree of flexibility can be obtained, as illus-trated in Example II.
Example II
The formulation of Example I was repeated and sampleswere prepared b~ application of the different resin combinations at 55 mils film thickness on steel panels, 1~" x 6", cleaned by aluminum oxide blasting. I'he samples were cured for 44 hours at eoorn temperature followed by 4 hours at 140F. After 1 hour cool-incJ, they were deformed around a 1" bar or mandrel. In the folL~wincJ 'rable, the product was considered to pass the flexi-biLLty test if the resin alloy remained bonded on -the substrate ~U ~nd was considered to fail if cracks appeared with or without particll or comple-te disbonding of the resin alloy from the sub-strate:
Table II
Resin by Weight flexibility test .
homopolymer Epoxy passed passed passed ~ passed passed passed passed

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failed failed 0 100 failed As illus-trated by the brittleness of -the 100% epoxy sample in Table II, the high temperature cure regime significarltly increased the degree of cure compared with Example I. The 20/80 and 10/90 samples also cured to brittleness whereas all the products in the range 10/90 and 30/70 were`flexible.
Example III
In this example, the furfuryl alcohol homopolymer and epoxy resins of Example I were used by the curing agen-t Versamid 125 (a trademark) was increased to 35 grams per 100 grams of resin and 3 grams of Calidria (a trademark) asbestos, RG-244 sold by Union Carbide was also added as filler. After thorough mixing by spatula, two 30 gram patties were cast in an aluminum dish and were allowed respectively to cure at room temperature for 48 hours ~s~mple ~) and at room tempera-ture for 44 hours followed by 4 hou~s at 140F (sample B), af-ter which their hardness (durometer hardrless, type D) was -tested as follows:
Table III
Resin b~ weight Hardness, Shore D
homopolymer Epoxy Sample A Sample B

~o 50 25-30 40-45 In this Example, the effect of increased cure both by increased amount of curing agent and high temperature curing is evident~ Cer-tain trends related to weight ratio of the alloy con-stituents and degree of cure are evident from Table III, and these hold true in general for the resin systems of this invention.
Thus with re~erence to samples A, it is in general always possible -to obtain a cured, relatively soft and highly flexible product toward the higher end of the weight ratio range of 90/10 to 10/90;
relatively harder but still highly flexible products are obtained at somewhat lower ratios; the hardness increases with decreased flexibility, usually peaking at some particular value (see 20/80, samples A), followed by decreasing hardness (10/90, samples A),.
This last may be followed by another increase in hardness (see the range ~0/60-10/90, samples B). However, as is illustrated in 'L'able II, it is always the case that if bri.ttleness if reached a~: some value of alloy constituents weight ratioJ products of sli:L.L lower weight ratio will also be brittle, given the same d~cJree oE cure. Thus, both the weight ratio and the degree of ~u~e can be controlled to -tailor the properties of hardness and ~lexibility over a wide range to suit par-ticular requirements.
Example IV
Generally speaking, it is easier to tailor the charac-teristics of the end product within the weight ratio range of about 30/70 to about 70/30. To illustrate, six samples were pre-pared from either a 70/30 furfuryl alcohol.homopolymer Epon 828 (a trademark) mix-ture (samples C, D and E) or a 30/70 mixture (samples F, G and H), with varying amounts of curing agent Versa-mid 125 (a trademark). Samples C and F were prepared using 13 parts Versamid 125 ~a trademark) per 100 parts resin mixture;
samples D and G were prepared using 35 parts Versamid (a trade-mark) per 100 par-ts resin; and samples E and H were prepared using 100 par-ts Versamid 125 (a trademark) per 100 parts resin.

_ g ~

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Hardness (Shore ~ where applicable) was tested for each sample after 3, 7 and 14 days cure at room -temperature, as follows:
Table IV
Sample Resins Ratio Hardness 3 days 7 days 14 days F 30/70soft, foamy 22 39 Comparison between Samples C-E and Samples F-H shows that the amoun-t of curing agent affects the hardness (or the flexibility) less when a greater amount of furfuryl alcohol homo-po:Lymer is present in the alloy. Samples E and H illustrate that the amount of curing agent reaches an "excess" amount more rapidly i.n the p.resence oE greater amounts of homopolymer in the alloy and acts, when present in "excess", as a plasticizing diluent.
This ef~ect is probably due to the much greater number of reactive ~0 5i~.es present in the epoxy resin and indicates that -the cross~
linking mechanism is complex.
E _ ~
In this Example, the curing agent used was diethylene-triamine (DETA). In I'able Va 13 parts DETA were used per 100 parts resin mixture (resins as in Example I), as follows:
Table Va Resins Ratio Hardness! Shore D where applicable 3 days 7 days 14 days 100/0v.soft,sticky v~soft soft 80/20soft,sticky gelled gelled 60/40 foamy ------ ------~5;73~

30/70 very foamy 20/80 foamy 0/100 58 6~ 64 The amount of DETA was reduced to 8 parts DETA per 100 parts resin, and aluminum panels coated as in Example II, with the following results:

Table Vb Resins Ratio Hardness,Shore D where applicable . _ 3 days 7 days 14 days 100/0 v.soft,sticky v.soft same 80/20 gelled same same ~/100 6~ 62 63 The coated panels of Table ~b, after 14 days cure at room temperature were subjec-ted to the mandrel -test of Example II
wi~l the following results.

Table Vc ~esins ratio mandrel test results ~ _ . _ _ . _ 80/20 soft, no cracks 60/40 no cracks or disbonding 20/80 cracked and completely disbonded 0/100 many cracks, no disbonding Following Example IV, four patty samples were prepared in which samples I and J consisted of a 70/30 mixture of homo-polymer/epoxy cured at room temperature respectively with 13 and 35 parts DETA per 100 parts resin m~xture, and samples K and L

consisted of a 30~70 mixture of homopolymer/epoxy cured at room temperature respectively with 13 and 35 parts DETA per 100 parts resin. Hardness was tested with the following results:

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Table Vd Sample Resins ratio Hardness, Shore D where applicable 3 days 7 days 14 days J 70/30 v.soft same gelled K 30~70 v.foamy same same Example VI

In this Example, the homopolymer of furfuryl alcohol and epoxy resins of Example II were crosslinked with an aromatic amine in amount of 50 parts per 100 parts resin mixture. The arGmatic amine was Ancamine LT, (a trademark~ available from Pacific Anchor Chemical Corporation, Richmond, California.
The indicated weight ratios of the resins were applied to aluminum substrates, as in Example II, and tested for hardness and adhesion to the substra-te af-ter mandrel based test, as follows:
Table VI
l~e~ins ratio Hardness adhesion, mandrel test 3 days 7 days 1~ days 1~0~0 v.softsoft soft -------------------80/20 gell same same no cracks or disbonding 60/~0 13 18 18 no cracks or disbonding 20/80 65 76 79 cracked, complete disbonding 0/100 69 78 78 cracks, no disbonding The above Examples demonstrate that the physical characteristics of Elexibility and hardness in a corrosion-resis-tant coating can be controlled by varying the weight amount o~
furfuryl alcohol homopolymer used in the resin mix and/or by varying the amount or type of curing agent employed. Generally speaking, the coating must first of all be self-supporting where-by to preserve its integrity. If considerations of flexibility 73~

and hardness are not of particular concern, a wide range of choice both in weight ratio of resin components and in amount of curing agent and/or cure regime is available. If, on the other hand, either one of both flexibility and hardness is a factor which must be considered, the weight ratio of resin components and the amount of curing agent and/or cure regime must be selected -to pro-vide the desired flexibility and/or hardness characteristics.

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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An article comprising a structure having thereon a temperature- and corrosion-resistant cured coating which adheres to various substrates including metals and concrete, which coat-ing consists essentially of an intimate mixture of homopolymer of furfuryl alcohol and epoxy resin cured with an agent selected from the group consisting of polyfunctional amines and amides, said homopolymer being present in weight ratio with respect to the epoxy resin in the range 10/90 to 90/10, to provide the cross-linking necessary to make the cured coating self-supporting.

2. An article comprising a structure having thereon a temperature- and corrosion-resistant cured coating which adheres to various substrates including metals and concrete, which coating consists essentially of an intimate mixture of homopolymer of fur-furyl alcohol and epoxy resin cured with an agent selected from the group consisting of polyfunctional amines and amides, said homopolymer being present in weight ratio with respect to the epoxy resin in the range 30/70 to 70/30 to provide the cross-linking ne-cessary to make the cured coating self-supporting.

3. A two-component coating system which comprises, as a first component, a mixture of homopolymer of furfuryl alcohol and epoxy resin in weight ratio of from 10/90 to 90/10, and, as a second component, a curing agent for said first component, said curing agent being selected from the group consisting of polyamines and polyamides.

4. A coating system as defined in claim 3 wherein said first component contains said homopolymer and said epoxy in weight ratio range of 30/70 to 70/30.

5. The method of producing a coating on a substrate which may be a metal or an alkaline material , which comprises the steps of: (a) providing a resin mixture con-sisting essentially of homopolymer of furfuryl alcohol and epoxy resin in weight ratio of homopolymer to epoxy of from 10/90 to 90/10; (b) mixing the resin mixture of step (a) with a curing agent selected from the group consisting of polyamines and poly-amides; and (c) applying the mixture of step (B) to the substrate and effecting cure of such mixture.

6. The method of producing a coating on a substrate which may be a metal or an alkaline material, which comprises the steps of: (a) providing a resin mixture consisting essentially of homopolymer of furfuryl alcohol and epoxy resin in weight ratio of homopolymer to epoxy of from 30/70 to 70/30; (b) mixing the resin mixture of step (a) with a curing agent selected from the group consisting of polyamines and polyamides; and (c) applying the mixture of step (b) to the substrate and effecting cure of such mixture.

7. A cured, flexible resin alloy which comprises a cross-linked product of from 10/93-90/10 weight ratio of homo-polymer of furfuryl alcohol and epoxy resin crosslinked with a polyfunctional amide or amine.

8. An article comprising a structure having thereon a corrosion-resistant coating possessing the characteristics of toughness and flexibility up to temperature in the order of 400°F
and greater, which coating consists essentially of an intimate mixture of epoxy resin and homopolymer of furfuryl alcohol cross-linked with an agent selected from the group consisting of polyfunctional amines and amides, in which the homopolymer and epoxy resin are present in weight ratio of about 30/70 to 70/30.