Preparation of Polymers from Diisocyanates and Polyols H . L. HEISS, J. €1. SAUNDERS, II=IRJORIE R . ATORRIS. B. R. DAVIS, d N D EDGAR E. HARDY Research Department, Phosphute Division, .~Aronst~nto Chemical Co., Anniston, Ala.
HE reaction of an excess of a diisocyanak wit,h a polyhj-T drosy compound has been studied in conjunction with the preparation of Vulcollan, a highly abrasion-resistant rubber ( d ) , and adhesives (3). I n the case of the Vulcollan the polyhydroxy compound was a polyester with terminal hydroxyl groups; for the adhesive it was trimethylolpropane. A large number of adduct's have now been prepared from 2,4.-t,olylene diisocyanate and 4,4'-diphenylmethane diisocyanate and a variety of polyhydroxy compounds, using a 2 to 1 rat'io of isocyanate groups t o hydrospl groups. PR(NC0k
+ R'(0H)s
-+
OCN-R--NHCOO-R'-OCOSH-R-~CO
(1)
The adduct's thus obt,ained have been screened for the preparation of adhesives, films, and foamed resins. Certain phases of this preliminary study are being investigated in more detail, and will be reported later. h portion of this work has been described by the Monsanto Chemical Co. (4). PREPARATION OF I SOCYANATE-POLYOL ADDUCTS
Escept when noted in the discussion, a 2 to 1 equivalent ratio of isocyanate groups to hydroxyl groups was used. Thus with a dihydrosy compound a diisocyanate-glycol mole ratio of 2 to 1 was used, and wit'h a t'rihydroxy compound a 3 to 1 ratio was used. If the polyol contained a strongly basic catalyst, as is sometimes the case with ethylene oxide condensation products, the cat,alyst was first neutralized wit'h concentrated hydrochloric acid. This was necessary, because the presence of a strong base sometimes caused the reaction with the diisocyanate to he uncontrollably vigorous. The polyol was then dried and excess hydrogen chloride xae removed by degassing with dry nitrogen for 30 minutes a t 110' t o 150" C. The polyol was added slowly to the diisocyanate in a suit,able glass cont,ainer, with stirring. An induction period of 5 to 10 minutes somet,imes occurred, follovied by an exothermic reaction which caused the temperature to rise to 80" to 120" C. Small amounts of gas were evolved. Aft,er the reaction had subsided (usually about 30 minutes), the reaction mixture was heated a t goo to 100' C. for 30 minutes t>oensure complete reaction. Gpon cooling, the adducts thus prepared varied from clear, amber glasses to viscous liquids, being more fluid as t,he distance between hydroxyl groups increased. These adduct,s were stored in carefully dried bottles or metal tubes. Adducts were also prepared in dry benzene solution containing 25 to 50% of adduct,. The solvent could he added either before or after the reaction, with the same results. Whcn previously untried polyols were used, there was an advantage in adding t'he solvent before the reaction, as it reduced the possibility of a violent reaction. Toluene and xylene were also used, but' xylene was compatible with the adduct only at adduct concentrations of 50% or greater. I n a few cases the reaction with the polyol w a s very slow. I n order to hasten t,he reaction, a trace of N-methylmorpholine
was added to the mixtures. Considerable care must be employed when a catalyst is used, however, to avoid an uncontrollable reaction rate. Tertiary amines are recommended when catalysts must be used, as their effect is much milder than that of stronger bases. The use of a strong base is to be avoided. As an example, when 0.5% by weight of potassium hydroxide was used as a catalyst in the reaction between tolylene diisocyanate and ethylene glycol, a reaction of explosive violence occurred. llthough many types of polyols were reacted with diisocyanatee insolution form, most of the reactionswere performedin a standard manner and no att'empt was made to adapt reaction conditions to the characteristics of various materials. As examples of reactions that were not performed under ideal conditions theremay be mentioned those involving the higher polyols, such as the monoglycerides of fatty acids and the blown or polymerized castor oils. The monoglycerides and procesaed cast'or oils were mixtures arid so presented some difficulties. Kot only was it difficult to determine how much isocyanate they were capable of reacting with, but mixed adducts m r e obtained which tended to precipitate from the solution nn standing. Some work was done on developing a method for determining what was designated the "isocyanate equivalent" of an organic material. This isocyanate equivalent represented the weight of an active hydrogen compound required to neutralize one cquivalent' of isocyanate. This was determined by making t'he compound react with an excess of phenyl isocyanate, then destroying the excess isocyanate with a known amount of dibutylamine, and titrating t,he unreacted amine with hydrochloric acid. This was merely a niodification of the "amine equivalent" procedure used in determining the presence of isocyanate groups. Although the procedure appeared t o work well, it is being investigated further t,o establish its reliability more fully. The diisocyanates used were of the commercial distilled grades, having 97% minimum activity as measured by reaction with a secondary amine. Although the diisocyanate-polyol adducts contained free isocyanate and active hydrogen groups, t'he adducts were stable for reasonable periods of time. T o demorist'rate typical stability characteristics, mention is made of a series of adducts from 1 mole of polyethylene glycol of niolecular weight 400 (polyethylene glycol 400) and 2 moles of tolylene diisocyanate. The solvent-free adduct was a viscous, amber liquid which was stored for 12 months at room temperature without apparent change. On the other hand, 50% solutions of the adduct, in benzene (in this case containing in addition 2.5% of S-methylmorpholine catalyst) were initially mobile, amber liquids, but gelled to solid masses in from 2 to 3 months a t room temperature, or within 1 month at 50' C. Uncatalyzed benzene solutions were stable up to 12 months even at. 50" C. At 5" C. both catalyzed and uncatalyzed solutions were stable for at least 12 months. Although these storage results were typical, 8ome variation in stability was observed. The cause of this variation has not as yet, been determined, but it appeared to be related to variations in the lots of diisocyanates and polyols used, and is being investigated further. Similar variations were observed in the rate of
1498
July 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
cure of films and in adhesive strengths. The extreme values of storage life, rate of cure, and adhesive strengths are not reported. Unless noted otherwise, N-methylmorpholine was used as a catalyst in the curing, of the adducts for adhesive and film evaluations. I n 50% benzene solutions of the adducts a catalyst concentration of 2.5%, based on the solution weight, was used. EVALUATION AS ADHESIVES
The curing conditions used in the adhesive evaluations are described in the discussion of results, as are some illustrative data. The screening data on the use of the various adducts as adhesives are given here. The tensile values indicated were obtained on test assemblies consisting of two pieces of etched, cold-rolled steel bonded together with adhesives consisting of catalyzed 50% benzene solutions of the adducts. The adhesives were given 10-minute open cure at room temperature and 50 to 70% relative humidity, and 30-minute closed cure a t 150’ C. and 50 pounds per square inch gage pressure. Some of these values are lower than those obtained later using the high temperature bonding technique involving carriers. -411 tensile tests were made in a Scott tester at a rate of jaw separation of 0.2 inch per minute. The following polyols or mixtures of polyols were used in preparing adducts with tolylene diisocyanate. Tensile strengths in pounds per square inch of the adhesive assemblies are shown in parmtheses, and are the average of three values. Triethylene glycol (1 120), tetraethylene glycol (740), polyethylene glycol 400 (420), polyethylene glycol GOO (150), polyethylene glycol 1000 (200), propylene glycol (6601, dipropylene glycol (930), tripropylene glycol (1040), polypropylene glycol 750 (315), 0.5 mole of polyethylene glycol 400 plus 0.5 mole of butylene glycol (1,3-butanediol) (1250), 0.5 mole of polyethylene glycol 400 plus 0.5 mole of butylene glycol (2,3-butanediol) (1110), 0.5 mole of polyethylene glycol 400 plus 0.5 mole of 2-methyl-2,4-pentanediol (320), 0.5 mole of polyethylene glycol 400 plus 0.33 mole of triethanolamine (675), 0.5 mole of polyethylene glycol 400 plus 0.1 mole of sucrose (770), monoglyceride of lauric acid (470), monoglyceride of stearic acid (500), monoglyceride of oleic acid (280), monoglyceride of lard fatty acids (550), monoglyceride of hydrogenated lard fatty acid (630), monoglyceride of cottonseed fatty acids (510), monoglyceride of castor oil fatty acids (7901, castor oil (485), propylene glycol monoricinoleate (700), and dihydroxyoctachlorobiphenyl (770). The following were used with diphenylmethane diisocyanate with average tensile strengths as indicated. Tetraethylene glycol (280), polyethylene glycol 200 (go), polyethylene glycol 400 (340), polyethylene glycol 600 (340), polyethylene glycol 1000 (120), dipropylene glycol (490), txipropylene glycol (300), polypropylene glycol 400 (300), polypropylene glycol 750 (730), polvpropylene glycol 2000 (200), monoglyceride of lauric acid (1320), monoglyceride of stearic acid (lOOO), monoglyceride of oleic acid (1200), monoglyceride of lard fatty acids (1475), monoglyceride of hydrogenated lard fatty acids (885), monoglyceride of cottonseed fatty acids (1300), monoglyceride of castor oil fatty acids (470), castor oil (1230), and propylene glycol monoiicinoleate (1530). PREPARATION OF FILMS
Because of the ready adhesion of the adducts to most solid surfaces, films were cast on mercury. Sufficient mercury to cover the bottom was poured into a flatbottomed pan of suitable size. A pan made of metal that will amalgamate with mercury was preferred, because this eliminated the formation of a meniscus a t the edges and thus presented a fimoother surface. Provision was made for loosely covering the pan. The pool of mercury was skimmed so as to present a clean surface, and acetone was poured over it, about 0 2 5 ml. per square inch of surface. The pan wars then covered and allowed
1499
to stand for a few minutes, so that most of the air was displaced by acetone vapor. A catalyzed 50% solution of the adduct in benzene was added to the layer of acetone, about 0.5 inl. per square inch of surface. The pan was again covered and allowed to stand undisturbed a t room temperature. Upon evaporation of the solvent, the adduct slowly cured into a film about 0.015 inch thick. About 8 to 16 hours were required for this process. The cured films were easily removed from the pan, were relatively uniform, and were free from bubbles. The melting points of the films were measured on a FisherJohns melting point apparatus, using a heating rate of about 15’ per minute. The films actually went through a gradual softening process, and the melting point was taken as the point a t which the material began to flow appreciably. As the samples were heated be ond this melting point, the tolylene diisocyanate adducts tenakd to bubble to a greater extent than did the corresponding diphenylmethane diisocyanate adducts. The tensile properties were determined by clamping sti ips of film 1 inch wide and 3 inches long in a Scott testing machine and stretching the samples a t either 20 or 2 inches per mnute, depending on ultimate elongation. By properly adjusting the tester it was possible to obtain a continuous stress-strain curve of per cent elongation plotted against load in pounds per square inch of film cross section. Some of the samples which stretched during this rocess tended to slip in the Scott grips, owing to decrease in &m thickness. This amount of slip varied from 0% in the samples of low extensibility to about 15% for the samples which were elongated to around 800%. As the precision of these tests was not very great, this amount of slippage was disregarded in the routine evaluation of these films. The following characteristics were com ared: yield point, the load in pounds per square inch at whic1 the sample began to stretch; tensile strength, the load in pounds per square inch at the instant of rupture; and per cent elongation a t the point of rupture.
V. 1-1, and
Typical data on the films are given in Tables IV,
7.”. PREPARATION OF FOA.MS
ii wooden mold 5 X 5 cm. in horizontal cross section and 8 em. high was used in the foaming experiments. A paper cup just
fitting the inside of the moldqwas inserted in the mold, and 10 grams of the adduct to be tested was weighed in. A predeterinined weight of solution containing catalyst, water, and Triton X-100 emulsifier was added and mixed in well with a flat-tipped spatula. When the mixture was homogeneous, a 5 X 5-em. cardboard square was placed over the surface of the foaming mixture. A counterbalanced wood top was then placed on the cardboard square. A force of only 0.8 gram per sq. cm. was required to raise the top of the mold, and the extent of movement of the top could be observed on a scale. In this way the final volume of foam and the rate of foam expansion could be measured with moderate accuracy. CURING OF ADDUCTS
The diisocyanate-polyol adducts were cured to polymeric materials of higher niolecular weight by allowing them to react with water. The curing reaction is believed to proceed by steps which may be represented by the following equations.
+
H20 + O C N R N H C ~ ~ R ’ O C O N H R N H ~co, (2)
R’(OCOKHRNCO)*
+
The relatively slow hydrolysis of an isocyanate group ~ o u l d be followed immediately by a fast reaction of the liberated amine with more isocyanate, as shown, using more simplified formulas: -RNHZ
+ -RNCO
-+
-RNHCONHR-
(3)
Such reactions will lead to linear polymer chains. Crosslinking may occur a t a relatively slow rate by reaction of free isocyanate groups with the active hydrogen in urea and urethan links. -RNHCONHR-
+ -RNCO
+
-RNCONHR-
(4)
AO”R--RNHCQOR’-
+ -RNCO
-+
-RNCOOR’boNHR-
(5)
1500
Vol. 46, No. P
INDUSTRIAL A N D ENGINEERING CHEMISTRY
These reactions are of the same type as those proposed for the preparation and curing of T'ulcollan rubber ( 8 ) . Carbon dioxide is liberated during the curing reaction, Equation ( 2 ) . This was put to advantage by using the adducts as foamed-in-place resins which expanded to fill irregularly shaped voids. Khen thin layers or coatings of the adducts were cured, the carbon dioxide was able to diffuse from the material and no foaming occurred. This was utilized when the adducts were used a s adhesives or films.
TABLE 11. EFFECT OF CARRIER O N BOYDSTRENGTH Adhesive Film Thickneas. Inch 0,003Z
Carrier Aluminum foil (0,001 inch) Copper foil (0.002 inch) Lead foil (0.0035 inch) Tissue paper (0.0015 inch)
Average Tensile Strength Lb./Sq.ofInch Bond, 1640
0.0031
626
0.0030
936
0.0021
722
USE A S ADHESIVES
The preliminary screening of the adducts as adhesives showed several which were better than the tolylene diisocyanate-polyethylene glycol 400 adduct, notably the diphenylmethane diisocpanat'e monoglycerides. However, the tolylene diisocyanatepolyethylene glycol 400 adduct was easily prepared, was sufficiently fluid and stable for ready evaluation, and after some experimenting gave much improved bonds. Consequently this adduct was used for much of the subsequent testing. 1. LON TEMPERATURE BONDING.The diisocyanate-polyol adducts were used succeesfully for bonding a t room temperature, thus showing them t o be promising as adhesives for heatsensitive materials. A catalyzed .50% benzene solution of the adduct was applied in a thin layer to each of the surfaces to be bonded. The adduct was given an "open cure" of about' 10 minutes, varying with the room temperature and relative humidity. During this time the solvent evaporated and reaction with moisture from the atmosphere began, T h e n the adhesive layer has cured to a very tacky state, the coated pieces were brought together with enough pressure to insure good contact. Closed cure was then allowed t o proceed to completion a t room or slightly elevated temperatures. Although the rate of cure increased with increasing temperature, the advantage of this method was t,hat high temperatures were not required. The low temperature curing of the adducts was difficult to COP.trol and was not easily reproducible. The principal source of difficulty was in determining the desired extent of the open cure. The required open cure appeared to vary with changes in room t,emperature and relative humidity, and with different lots of a given adduct'. The effects of the variations in the open cure were reduced considerably by performing the closed cure at 100" C., however. Table I illustrates typical adhesive tensile strengths for several combinations. All assemblies were given an open cure of 10 minutes at room temperature and 50 to 70% relat'ive humidity and a closed cure of 30 minutes a t 100" C.
TABLE 111. METAL-TO-METAL BOXDINQ Materials Bonded Steel (cold rolled) Aluminum (24 ST) Magnesium (Dow metal FS-I)
Average Tensile Strength of Bond, Lb.,/Sq Inch 1600 Greater than 2000 800
solution of t,he adduct on a metal surface. Uncatalyzed solut'ions deposited films t,hat could be completely cured in dry steam within 10 minutes a t 60" to 100" C., or within 24 hours at room temperature. Catalyzed solutions provided films that totally cured in dry steam within 1 minute a t 60" to 100" C., or within 2 hours at room temperature. The curing reaction appeared to be autocatalytic, and layers of adduct applied to a previously cured layer required less curing time than did the first coat. The bonding operation consist,ed of bringing the coated surfaces together, again under sufficient pressure to establish good contact, and heating until the adhesive layer melted. This occurred between 150" and 300" C., depending on adduct' composit,ion. After cooling, the bond had developed full strength. The bonding operation need not be performed immediately aft'er the open curing. Good assemblies were prepared wherein the bonding operation was performed 1 month after the adhesive layer had been cured. As 511example, steel blocks Kere coated with a
STREKGTHS OF ISOCYANATE ADHESIVES TABLE I. TEXSILE
Materials Bonded Steel to glass Steel t o cellulose acetate Aluminum t o polymethyl methacrylate Aluminurn t o cellulose acetate
Adduct Used T o l y l e n e diisocyanate-p 01y ethylene glycol 400 Diphenylmethane diisocyanatemonoglyceride of lard f a t t y acids Diphenylmethane diisocyanatepolypropylene glycol 750 Tolylene diisocyanate-tripropylene glycol
-
I
Average Tensile Strength of Bond, Lb./Sq. Inch 900
I
/
600 330
430
2. HIGH TEMPERATURE BONDING.Where the materials t o be bonded were not heat-sensitive, a wider selection of adducts was operable. In this method, adhesive was applied to one or preferably both of the surfaces to be joined and completely cured before assembly of the pieces. This curing was done in a variety of ways. As an example, thin coatings of the adduct of 1 mole of polyethylene glycol 400 and 2 moles of tolylene diisocyanate were deposited by spraying, dipping, brushing, or spreading a
30
60
93
I20
REACTION TIME, M I Y Figure 1. @
Effect of Catalyst on Rate of Foaming
No catalyst (point not shown, 170 ml. at greater than 4 hours) Dimethylaniline A Triethylamine Quinoline A Tripropylamine ridine 3 N-Methylrnorpholine A'-Ethylmorpholine %amylamine
8 8
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1954
curing 10 minutes a t 175' C. and 50 pounds per square inch, three typical metals were bonded, as shown in Table 111.
DIISOCYANATE-POLYOL FILM PROPERTIES TABLE IV. TOLYLENE Film M.P, C. 220
Poly01 Used Tetraethylene glycol
Yield Point, Lb./Sq. Inch
Tensile Stren t h , Lb./gq. Inch 4100n 4100"
Elongation,
%
Oa
1501
Appearance Opaque, brittle Transparent, brittle Transparent Transparent,
FREE FILMS
The properties of cured films were of interest in the evaluation of the films themselves, and also of Polyethylene glycol 400 230 IfiOO 3000 400 the adhesives prepared from the diisocyanate210 0 300 1000 Polyethylene glycol 1000 soft polyol adducts. Illustrative data on several films "--_ Polyethylene glycol 400 (0.51 are shown in Tables IV and V. mole). nlvceroll5 E.O. (0.33I 360 900 3600 500 Transparent mo1e)'b- By varying the polyol or combination of polyols Polyethylene glycol 400'(0.5{ used, films were prepared which varied from trans. TransparenL, mole) triethanolamine brittle (0.33 h o l e ) 270 parent to opaque, and from elastic to brittle in Polyethylene glycol 400 (0.5 , Transparent, .. mole), pentaerythritol (0.251 300 . properties. Most of the films melted between 180" brittle and 220' C., but the melting point could be raised Po*i;lle'ti;ylene glycol 400 (0.51 mole), propylene glycol 230 35005 7000a 350-400' Transparent, by replacing a portion of a linear diol with a triol. (05) brittle (1.2 - propanediol) I mole) These properties of films 1 to 3 weeks old are illus0 Transparent, 210 >6000 >6000 Piopylene glycol monoricino-' trated in Tables IV and V, using a stretching rate leate flexible .. 2200 3600 325 Hydrogenated castor oil of 20 inches per minute except as noted. The 0 Measured a t 2 inches per minute. stress-strain properties did not change! significantly b Reqction product of glycerol with 15 moles of ethylene oxide after aging 1 year. Several general trends in film *~ DroDerties were apparent. Those prepared from diphenylmethane diisocyanate were tougher and higher melting than the cor50% benzene solution of the tolylene diisocyanate-polyethylene responding films from tolylene diisocyanate. When the polyol glycol 400 adduct containing 2.5% catalyst. The film was perwas varied throughout a homologous series, such as the polymitted to cure completely a t room temperature. The blocks ethylene glycols, the films increased in softness, flexibility, were then assembled and cured 1 minute a t 225' C. and 150 and extensibility as the distance between the hydroxyl groups pounds per square inch. The tensile strength of the resulting increased. The melting points of the films varied inversely bond was 1500 pounds per square inch. as the distance between the hydroxyl groups. As is to be 3. THERMOPLASTIC BONDINGWITH DRY ADHESIVE. A expected, substituting a triol for a portion of the glycol used modification of Method 2 was developed which made it unnecesgave more rigid films which melted a t higher temperatures. sary to apply adhesive to the surfaces to be bonded. This The use of polyols having the hydroxyl groups close together was accomplished by coating a "carrier" with adhesive and comand having long side chains, as in the monoglycerides, gave pletely curing the adhesive layer. Such materials as metal films which were of low elasticity. Finally, films from a mixfoil or paper were coated by dipping, spraying, or spreading. ture of polyethylene glycol 400 and a glycol with its hydroxyls Where maximum bond strength was desired, the use of metal foils, especially aluminum, as carriers was preferred.
Polyethylene glycol 200
250
1
3GOO
3600
0
"
.
I
TABLE V. DIPHENYLMETHANE DIISOCYAXATE FILMPROPERTIES Poly01 Used Tetraethylene lycol Polyethylene gfycol 200 Polyethylene glycol 400 Polyethylene glycol 600 Polvethvlene KIYCOI 1000 Polyprdpylene glycol 400 PolvDroDvlene elvcol 2000 Moi>gl$Eeride -2 stearic acid Propylene glycol monoricinoleate
Film
M.P., O C.
Appearance
>300 >300 270
220 200 >300 230 290
Brittle
300
Translucent; flexible, elastic
The bonding operation was performed by placing a piece of the coated carrier, cut to suitable size and shape, between the pieces to be bonded, heating under pressure until the adhesive fused, and cooling. Bonds prepared in this way were equal to those prepared by Method 2 if the carrier had been properly selected. For example, cold-rolled steel test pieces were bonded by means of various carriers. The adhesive used was a catalyzed 50% benzene solution of the adduct of 1 mole of polyethylene glycol 400 and 2 moles of tolylene diisocyanate. This was applied to the carrier and was fully cured in 2 minutes using a steam-air mixture heated t o 100' C. Bonding was accomplished by heating the coated foil between pieces of steel for 1 minute at 225" C. under 150 pounds per square inch. The adhesive film thickness in Table I1 was measured by subtracting the thickness of the original carrier from that of the coated carrier, and dividing by 2. Using the coated aluminum foil described in Table 11, and
30
60
90
IiO
ROOM TEMF! REACTION TIME, MIN. Figure 2. Effect of Catalyst (N-Methylmorpholine) Concentration on Foaming Rate e€ No catalyst 0 0 0.18% 0.36%
8
0.54%
1.30%
A 2.50% 5.00%
INDUSTRIAL AND ENGINEERING CHEMISTRY
1502
TABLE VI. SOLVENT RESISTANCE PROPERTIES O F CURED FILMS Isocyanate Used Tolylenediisocyanate Tolylenediisocyanate Diphenylmethene diisocyanate DiDhenvlmethane dii’socyinate Diplienylmethane diisocyanate
I’olyol 10% Used \Vater S a 0 1 3 Polyethylene glycol G X ;io0 E E Tripropylcne glycol Piopslene ali-col E E monoricinoleate PolvuroDvleneelrcol G E 400 - -Polyethylene glycol E E 200
Solvent Resistancea HexHC1 3leO€I ane G r E
10’7,
Beneene G
Acetone P
F 1‘
F
F
P
E E
G
E P
E
F
P
E
E
E
E
P
E
E
a E . Excellent resistance, little or no change. G. Good rcsistancc, slight smelling of surface. F. Fair, considerable swelling and loss of strength P. Poor, rigorous attack on film. X . Sample disintegrated.
TABLE
1’11. DIELECTRIC PROPERTIES
.
Adduct Composition XIoles 2
Polyethylene g1j col 400 Tolylene diisocyanate
1
Dipropylene glycol Tolylene diisocyanate
1
e
Propylene glycol nionoricinoleate
FILMS
Dielectric Properties of Cured Adduct Dielectric Dielecstrengtlll tric 25-mil D . C. F ~ con~ P o w e r ~ films, ~ resistivity. ~ lic. stant factor volts/mil ohm-om. Gp cycles f 0 l P 910 81 X 10’ I 4.4 0 089 0 OB1 10 4 0 100 3.9 0 044 0.08” 1100 7 . 5 X 10”a 60 cycles 3.95 1 3.48 0.033 10 3.44 0.017 100 3.40 0.014 60 cycles 3.15 0 014 1650 250 X 101lC 1 3 08 0 012 10 3 05 0 012 100 3.05 0 012
6
Tolylene diisocyanate
1 2
2
b
-
OF CURED ISOCYAXATE-POLYOL
Value obtained by extrapolation .4t 70’ C . .4t 50’ C .
close together, as propylene glycol, could be cold drawn. The stress-st,rain relationships showed no elongation as the load i ~ a s increased t o the yield point. The load then remained constant while the film TTas drawn. Finally load and elongation both increased until rupture occurred. The cured films were not soluble in any solvent tested, hut were swelled and weakened by some, such as dioxane, diniet,hylformamide, and acetone. The films generally Tvere resistant to water, 10% hydrochloric acid, hexane, and benzene. There was a tendency toward sensitivity to alkali and methanol, but certain of the films were resistant to these solvents, also. The use of nonlinear polyols tended to improve solvent resistance, and resistance to specific solvents was achieved by the choice of the poly01 used. The use of polyethylene glycols gave hydrocarbon-resistant films, while monoglycerides or castor oil gave alcohol- and water-resistant films. Typical solvent resistance properties, as measured by immersion of strips for 18 to 20 days a t room temperature, are summarized in Table VI. The dielectric properties of three films are shown in Table VII. The moderate dielectric strength, resistivity, and power factors of the ether glycol films (Table 1’11)may have resulted from the slight hydrophilic properties of the ether glycol components. These properties mere all improved considerably in the morc hydrophobic tolylene t~iisocyanate-propylene glycol monoricinoleate film. FOAMS
The preparation of foamed resins from the diisocyanate-polyol adducts was investigated only briefly. Several. cat8alystsu~erc evaluated first, in an attempt to find a useful foaming recipe. The result,s using 10.0 grams of adduct from tolylene diisocyanate qnd polyethylene glycol 400, 0.28 gram of Triton X-100 emulsifier, and 0.1 gram of catalyst are shown in Figure 1. N-hlethylmorpholine wap chosen as the st,andard catalyst for further work became of its good activity and suitable boiling
Vol. 46, No. 7
point. The apparent inhibitory effert of diinethglaniline w a s u n e x p e c t e d . Baker and Holdsworth ( 1 ) found that this tertiary amine was not a catalyst for the reaction between monoisocyanates and simple alcohols, but, no inhibitory effect was noted. I n anot’her series of experiments it vias desired to det’erminet’heeffect of varying the amount’ of m-ater added to the adduct. In one series the amount of water was merely decreased, while in another the missing a a t e r was replaced 11)- a11 equivalent amount of ethylene glycol. These results are eummarized in Table
VIII.
The note in Table VI11 refers to the shrinkage experienced by some of the ~ foams ~ ~ first ,24-hour aging. during the Shrinkage was greatest in the foams of greatest’ volume. The reason for thie was not immediately ascertained. but a limited number of experiments dcmonstrated that it was not due alone to cooling of the foam following the react,ion. The foams of medium density produced by replacing half the theoretical amount of water with an equivalent, amount of glycol were the best from the standpoint of uniformity. Thcsc irere then used t o determine the effect of catalyst concentration on rate of foaming, as illustrated in Figure 2 . The ioaming mixture used was 10.0 grams of the adduct of tolylerie diisocyanate and polyethylene glycol 400, 0.14 gram of aater, 0.42 gram of ethylene glycol, and .\--methylmorpholine as notad.
TABLEVIII. EFFECT OF Noies of HzO pel Mole of Adduct 1.16 0.88 0.88 0.58 0.58
+ ~ ~ V O U ? \OF T T ~ ~ A T EUSED R ou
J-OLCME
Moles of Ethylene Glycol per 3Iole of S d d ~ c t 0 0.23
0
0.51
0 0.7F 0 0 1.01 Foam volumes after shrinkage 0.29 0.29
-Foam 2 hr.
215 150 180 95 116 55
60 25
FOAM
Volume, hll 48 hi * 170
130 I50 90 110 55 60 25
The foams produced from the tol) lene diisocyanate-polyethglene glycol 400 adduct were soft and Fere subject to shrinking. Foams from tolylene diisocyanate and polyethylene glycol 200, on the other hand, were brittle and easily crushed. The substitution of diphenylmethane diisocyanate for tolylene diisocyanate in these foams increased the toughness of the foam, but the products still did not compare favorably with commercial tolj lene diisocyanate-alkyd resin foams. Consequently, adducts of a more complex nature Ivere prepared using triols of a high molecular n eight and hydrophobic nature. One such material was castor oil, which is essentially glyceryl triricinoleate and so contains three widely separated hydroxyl groups attached to aliphatic chains. Adducts composed of 3 moles of tolylene diisocyanate and I mole of Baker’s rlA castor oil produced foams which were tougher and more water resistant than those prepared from
July 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
polyethylene glycols, but still soft. Replacement of up to half the castor oil with equivalent amounts of lower molecular weight triols such as glycerol resulted in firmer foams, but the mixed adducts tended to be nonhomogeneous. The preparation of adducts from castor oil and diphenylmethane diisocyanate resulted in much improved foams. I t was observed, however, that these adducts were unstable and tended to harden during storage. As this had previously been associated with incomplete reaction of the hydroxyl groups, the molar ratio of diphenylmethane diisocyanate to castor oil was increased. At a ratio of 4.5 a product was formed which produced a foam somewhat comparable to rigid types in use on a commercial scale. The adduct of 2 moles of diphenylmethane diisocyanate and 1 mole of polypropylene glycol of average molecular weight 750 produced a very tough, rubbery product which was similar to sponge rubber.
1503
ACKNOWLEDGMENT
The physical testing of a number of the films and adhesives by the Physical Testing Laboratory and the Dielectric Laboratory, Monsanto Chemical Co., at Dayton, Ohio, and Springfield, Mass., respectively, is gratefully acknowledged. LITERATURE CITED
Baker, J. W., and Holdsworth, J. B., J . Chem. Soc., 1947, 713. (2) Bayer, O., Muller, E., Petersen, S., Piepenbrink, H -F., and Windemuth, E., Angew. Chem., 62, 57 (1050); Rubber Chem. and TechnoZ., 23, 812 (1950). (3) DeBell, J. M., Goggin, W. C., and Gloor, W. E., “German Plastics Practice,” p. 303, Cambridge, Mass., Murray Printing (1)
Go., 1946. (4)
Monsanto Chemical Co.. “Polyurethans and Their Use as Adhesives,” Tech. BzrZZ. P-151 (Aug. 1, 1953).
RECEIVED for review October 26, 1953. ACCEPTED April 5 , 1954 Presented in part before the Division of Polymer Chemistry a t the 124th Meeting of the AMExrcAs CHEMICAL SOCIETY, Chicago, Ill.
Sludge Return for Control of Scale Formation FOLLOWING LIME NEUTRALIZATION WILLIAM A. PARSONS AXD HOVHANESS HEUKELEKIAB New Jersey Agricultural Experiment Station, New Brunswick, N . J .
L
I3IE or limestone neutralization of waste acid is one of the most common processes for treatment of industrial waste. Sulfuric acid is a constituent of most acid wastes, because on an equivalent basis i t comprises some 90% of all acid manufactured. One of the problems arising from neutralization of sulfuric acid wastes with lime or limestone is that under certain conditions the neutralized mixture becomes greatly supersaturated with calcium sulfate. This supersaturation is relieved through “afterprecipitation” of crystalline calcium sulfate-forming deposits, which vary in form from loose material to hard scale. Hard scales may be formed in pipes and treatment units following neutralization. The distinction as to where ordinary sludge precipitation stops and afterprecipitation starts is arbitrary. Throughout this study sludge was defined as material deposited within 1 hour following neutralization. Afterprecipitation ww defined as material deposited during sedimentation from l to 24 hours following neutralization. An earlier paper ( 4 ) reviewed most of the available published material dealing with afterprecipitation and scale formation from sulfuric acid neutralization and presented data concerning the effects of several factors on afterprecipitation, including degree of neutralization and dilution subsequent to sedimentation. METHODS AND MATERIALS
Limes, both high-calcium and dolomitic, employed throughout the study were of commercialgrade supplied by member companies of the National Lime Association. All acid solutions neutralized were composed of 9 parts of sulfuric acid and 1 part of hydrochloric acid on an equivalent basis, except where noted differently in the text. Lime was added as a 10% slurry. Neutralization experiments were made on a %liter scale, involving a 5-minute mixing period, 1-hour sedimentation of the neutralized mixture, and 23-hour aging of settled effluent in Imhoff cones for observation of afterprecipitation. Effluent aging
was done a t room temperature. The p H value of the effluent from sedimentation was determined to indicate degree of neutralization. Three methods were employed for estimation of afterprecipitation: The dry weight of the deposited material was determined gravimetrically, the calcium ion concentration of the neutralized effluent was determined by flame photometric analyses a t 1 and 24 hours of aging, and the hardness of the neutralized effluent was determined a t 1 and 24 hours of aging by titration with disodium Versenate ( 1 ) . Hardness is nearly proportional to the calcium ion concentration when high-calcium lime is employed for neutralization and to the equivalent calcium-magnesium ion concentration when dolomitic lime is employed for neutralization. Where the effect of. a given condition on afterprecipitation was examined in a series of experiments, the experimenta were made as rapidly as possible during the same day, so that aging conditions would be nearly comparable for all samples. EFFECT OF VARYING CONDITIONS
ACIDCONCENTRATION A N D DEGREE OF KEUTRALIZATION. Published results of experiments made by Lewis and Yost (3) dealing with effluent quality from lime-neutralized sulfuric acid solutions indicated afterprecipitation to be decidedly more pronounced from 0.25% sulfuric acid solutions than from 3 % solutions. These results stimulated a more comprehensive investigation of the effect of acid concentration on afterprecipitation. Figures 1 and 2 give abridged results of experiments made to determine the relation between acid concentration and afterprecipitation from lime neutralization of solutions composed of 9 parts of sulfuric acid and 1part of hydrochloric acid to effluent pH values of approximately 4 and 11. The essential information conveyed by these graphs was that extensive afterprecipitation from high-calcium quicklime neutralization to pH 4 and 11 was confined to an acid concentration range between 3000 and 12,500 p.p.m.. and wap maximum at an acid concentration of 6000
