Methacrylate Resins - Industrial & Engineering Chemistry (ACS

Ind. Eng. Chem. , 1939, 31 (4), pp 382–387. DOI: 10.1021/ie50352a003. Publication Date: April 1939. ACS Legacy Archive. Cite this:Ind. Eng. Chem. 31...
0 downloads 0 Views 1MB Size
Download PDF
HIGHWAY BETWEEN DETROIT AND LANSING,M~cH.,O m LINED BY REFLECTORS MADE OF "LUCITE"METliSL METHACRYLATE PLASTIC The light from the headlamps strikes the reflectors and thus shows any curves that may lie ahead. During the first three months, night accidents were reduced 79 per cent over the corresponding period before the reflectors were installed.

METHACRYLATE RESINS D. E. STRAIN, R . GRICE KENNELLY, AND H. R. DITTMAR E. I. du Pont de Nemours & Company, lnc.. Wilmington. Del.

Tc

t

or rnoleciilar weight as long as a minimum average molecular weight value has been exceeded. Commercial polymers of medium iriolecular weight were employed in the tests subsequently described.

HE preparat.ion and properties of a number of methaT lic ester monomers and polymers were previously dey. scribed (3'). The present paper gives morecoinpletedata on the physical properties, solubilities, aird compatibilities with resins and plasticizers for five of the lower alkyl esters of polymethacrylic acid (methyl, ethyl, n-propyl, n-butyl, and isobutyl esters) which are now available for cotnniercial use. These nietliacrylic ester 1noIioincrs arc water-white, mobile, volatile liquids with pronounced hut agreca.hleodors. A number of physical properties are listed in Table I. The specific gravity decreases, a.nd refractive index, viscosity, and boiling point increase as the molecular weight of tlie esterified alcohol is increased. TABLEI. P a o m a n m

OY

P h y s i c a l Properties of Polymers Data 011 some physical properties are given in Table 11. These resins are characterized by relatively low specific pravities, varying from 1.19 for nietliyl methacrylate polymer to 1.02 for isolnityl inot.liacrylate. This is of distinct commer-

.

TYPICAL Moxonaaic ME~.IIACI~YLIC ESTERS

Methyl Ethyl "-PrOpYi

Imbutyl

100 117 141 155

0.950

0.913 0.902

0.889 0.889

*.Y"lYl 163 Ail are sulubla i n typioni orpsnio advents.

l

1.417 1.414

1.420 1.422 1 426

0.39

0.70 0.84

0.96 1.01

The liquid methacrylic cstcr inonoiiiers pulymerize to resinous products %,hensubjected to the influence of lieat, light, and catalysts. The polymerization may be effectcd in siicli a maimer that solid castings (5, 7 , 8, I # , 13, 17), solutions ( l a ) , and emulsions or granular products ( Z , l / i ) are obtained. The molecular weights of the polymers obtained in all of these processes vary vitli tlie conditions of po1ymerizatioi1-i. e., teniperature, catalyst and concentration of catalyst, and conccritrat.ion and nature of dilueirt when polymerization is carried out in solution. In geneml, the propcrtics of polymers are relatively independent of the polymerization process

I

382

I'olynierie methyl, ethyl, propyl, butyl, and iwbutyl esters of methacrylic acid are water-clear thermoplastic resins of estnblirhod commercial v d u o . Data are given on the physical properties, solubilities, and compatibilities with resins and plasticizers for this series of methacrylate resins. Polymeric methyl methacrylate is a hard rigid reair1 of high tensile strength which softens above 100" C. As the molcciilar weight of the esterified alcohol radical increases, the polymers become softer and more plastic. Film-forming and adhosive properties, as well as soliibility and eompatibility, also change markedly along the series from the methyl ester to the higher esters. blethyl mothacrylato polymer is soluble in il wicic rariery of solvents. The higher estezs become increusingly mort? miiicihlo with aliphatic-type solrents, the butyl and isobutyl ester polymers being sohchle in petroleuzn solvents. These resins arc compatible witb n large miniher of other msinour

APRIL, 1939

INDUSTRIAL AND ENGINEERING CHEMISTRY

383

cia1 importance. I n hardness and thermal yield OF METHACRYLIC ESTERPOLYMERS TABLE 11. PROPERTIES point there is a gradual decrease with increasing Property Methyl Ethyl n-Propyl n-Butyl Isobutyl molecular weight of the esterified alcohol. For 1.11 1.06 1.05 1.02 1.19 example, methyl methacrylate polymer is among &e;;Atx;;d:!2is(& at 2 5 0 c., grams 220 141 100 1 210 65 38 30 70 the hardest commercially available thermoplasThermal yield point C. 125 5000 4000 1000 3400 9000 tic resins (12) and is unsoftened by contact with s ~ ~ ~ 9), kg, ~ $ ~ ~ 7.1 6.5 11.5 1.6 cm./sq. cm. 10.5 boiling water; n-butyl methacrylate polymer is Refractive index 1.490 1.485 1.484 1.483 1.477 soft and flexible a t room temperature. A Extensibility of 5-mil films, % a t break 4 7 5 230 2 marked difference exists between the two isomeric Toughnessa 9s 174 76 1000 23 Dielectric strength of O.OS-in. film, the isobutyl ester is butyl methacrylate resins; 740 .,. 650 625 ... volts/mil much harder, higher softening, and less flexible Power factor a t 250 c. and 60 cycles, % 6.5 . . . 3.8 6.2 ... than its straight-chain homolog. With the a Area under load-elongation curves, expressed in arbitrary units. straight-chain alcohol esters the tensile strength falls off as the molecular weight of the alcohol is increased; the decrease in tensile strength is, in general, accompanied by an increase in elongation a t break, OF METHACRYLIC ESTERPOLYMERS IN TABLE111. SOLUBILITY demonstrating extensibility. The thermoconductivity of ORGANIC SOLVENTS'" this class of resins is low; that for the methyl ester is 1.25 Isobutyl +Butyl Methyl Ethyl n-Propyl Solvent B. t. u./square foot/hour/" F./inch. S S S S S Acetone The methacrylic ester polymers form a series of waterS S S PS S Diisopropyl ketone S 8 S S S Cyclohexanone white resins of unsurpassed clarity and stability. They transmit high percentages of visible light and are superior to glass I I I I I Methanol PS PS PS I PS Ethanol (abs.) in the transmission of ultraviolet light. They are color stable S S S PS Isobutanol S 8 8 PS ps PS Cyclohexanol on exposure to light and have excellent aging properties (1, I I I I I 0

'!&;&,

IO). These resins are very stable to heat. Methyl methacrylate polymer, for example, is not decomposed or discolored a t temperatures up to 200" C.; at 350" C. or above, i t is depolymerized readily to monomer in good yields (16). The methacrylate resins are unaffected by water and are surprisingly resistant to aqueous solutions of inorganic reagents. At 50" C., 60 per cent sulfuric acid, 25 per cent hydrochloric acid, 60 per cent phosphoric acid, aqua ammonia, and 20 per cent sodium hydroxide are substantially without effect. These resins are inert to aqueous salt solutions, including potassium dichromate and sodium hypochlorite. The dielectric strength of the methacrylate resins is uniformly good. Although the power factors are definitely higher than that of polystyrene, in the case of the methyl ester at least, the value decreases to about 1.0 per cent as the temperature is increased to 100' C. Further, the power factor and dielectric constant of this resin decrease with frequency (4). The arc resistance of this resin is outstanding.

materials and plasticizers; in general, as with the solubilities, the higher methacrylate esters exhibit a wider range of compatibility than the methyl ester. The properties of the methacrylate polymers, especially the higher esters, render them suitable for general industrial uses as coating materials and as thermoplastic adhesives applied from solution. The films produced are fast drying, water-white, nonyellowing, tough, and durable, and possess good electrical properties. Adhesive, coating, or impregnating compositions suitable for application without solvent can be obtained by fusing the higher methacrylates with resinous or waxlike fluxing agents or by emulsifying a methacrylate composition in water. The wide compatibility of the methacrylate resins, along with their low specific gravities, unusual adhesive characteristics, heat and chemical stability, and general durability, has led to their use in a large numher of commercial applications.

Ethylene glycol 8-Ethox yethanol (Cellosolve) Glycerol

S

I

S I

S S S

S S

S

S

9

S

S

I

I

S 8 S S S

S S

9

S

S S S S S

I

S S

S S

S S

S

Methylene chloride Chloroform Carbon tetrachloride Ethylene dichloride Chlorobenzene

S 5

Diethyl ether Diisopropyl ether Dioxane

I I

S

S

I S

S S S

S S

Benzene Toluene Xylene Hexane Cyclohexane Gasoline White oil (Nuiol) Turpentine

S S

S

S S

S

I I I I I

I I I I

S I PS PS I

S S

PS S

S

PS S S PS S

Acetic acid Formic acid (90%) Isobutyric aoid Formamide

a

S PS

S

9

S

S

S

Castor oil Linseed oil (alkalirefined)

I

S

S

PS

S S S S S

S S S

S

S S

S

S S

PS

S

S

I

S

S S

S S S S S S

S

PS S

I

S

I

I 6 I

I

I

PS

PS

PS

I

I

PS

S

S

S S

I

6 = soluble; I insoluble: PS soluble a t an elevated temperature. a

S

-

I

I

a t least partially insoluble cold but

Solubility The solubility of five methacrylate polymers in typical organic solvents is given in Table 111. One part of resin with nine parts of solvent were tumbled for 3 days and examined for solubility. If solution (dispersion) had not been effected, the mixture was warmed with stirring. In a number of instances polymer which remained undissolved on tumbling a t room temperature could be dissolved at 70-150" C. I n all cases where high temperature was required to effect solution, the resin precipitated on cooling to 25" C. In general, the polymers are soluble in aromatic hydrocarbons, esters, ketones, ethers, chlorinated hydrocarbons, and organic acids. As a rule, the solubility in alcohols, aliphatic hydrocarbons, terpenes, and drying and nondrying oils increases as the number of carbon atoms in the esterified alkyl group is increased. All of the resins are insoluble in methanol, ethylene glycol, glycerol, and formamide.

INDUSTRIAL AND ENGINEERING CHEMISTRY

384

VOL. 31, NO. 4

Certain petroleum solvents will dissolve n-butyl and isobutyl methacrylate polymers, to give comparatively high concentrations a t spraying and brushing viscosities. Concentration-viscosity data for these two polymers in Bayway solvent naphtha (boiling range, 100-130” C.) are as follows: Solids b y Weight20 30 1.38 20.1 0.65 8.8

7 %

10

n-Butyl Isobutyl

0.062 0.062

Plasticizers Compatibility data for five methacrylate polymers with twenty-four representative plasticizers and oils are given in Table V. Plasticizer was added to 15 per cent resin solutions in toluene in the amount required to give a 50-50 resin-plasticizer ratio; after being mixed, the solutions were flowed out on glass plates and air-dried. In the cases where incompatible films were obtained, additional films were flowed, using a 90- 10 resin-plasticizer ratio. TABLEV.

COMPATIBILITY OF METHACRYLIC ESTERPOLYMERS WITH PLASTICIZERS‘

Plasticizer Methyl Ethyl n-Propyl n-Butyl Isobutyl Methyl abietate sc C C C C Octadecanediol diacetate SI sc C C C Dicyclohexyl adipate sc sc sc sc C Aroclor 1242 (chlorinated diphenyl) C C C C C Benzyl benzoate C C C C C Butyl benzoyl benzoate C C C C C Camphor sc sc sc sc sec-Alcohol carbamates with 6-12 carbon branched chains C C C C C Diethylene glycol diisobutyrate C C C C C I Castor oil sc sc C C Tung oil I SI SI SI SI I Linseed oil I I I I I White oil (Nujol) I I I sc Trioresyl phosphate C C C C C Alcohol phthalates with 6-9 carbon branched chains C C C C C Dibutoxy ethyl phthalate C C C C C Dibutyl phthalate C C C C C Hydrogenated castor oil phthalate SI sc sc Glyceryl tripropionate C C C sc c sc c Santicizer B-16 (butyl rhthalyl butyl glycoC ate) C C C C Santicizer 8 @-tolylethylsulfonamlde) C C C C C Butyl stearate I sc sc C C I Stearyl alcohol I I I I Dibutyl tartrate C C C C C 5 C = comnatible a t 50-50 resin-plasticizer concentration: SC = compatible a t 90-10 resin-plasticizer concentration but incompatible a t 50-50; SI = s!ightly incompatible a t 90-10 resin-plasticizer concentration but incompatible a t 50-50; I = incompatible a t 90-10 resin-plasticizer concentration.

sc

SPARKLING “DIAMONDS”OF CAST “LUCITE” METHYL METHACRYLAT~ PLASTIC The larger of the two “gems,” corresponding t o a diamond of about 57,000carats, was cut from one of the largest “Lucite” castings ever made.

The solubility of a methacrylic ester polymer is influenced by its molecular weight. Certain relatively poor solvents will dissolve a given polymer of low molecular weight but are incapable of dissolving high-molecular-weight polymers prepared from the same monomer. For example, ethyl methacrylate polymer of very low molecular weight is readily soluble in ethanol; polymers of higher molecular weight become increasingly less soluble and eventually completely insoluble in this solvent. Commercial ethyl methacrylate polymer is insoluble in ethanol a t room temperature. TABLE IV.

CONCENTRATION-VISCOSITY DATA FOR METHACRYLIC ESTERPOLYMERS Viscosity (Poises a t 25O C.) in Toluene a t Weight % of:

Methacrylate Methyl Ethyl n-Propyl n-Butyl Isobutyl

10 0.65 0.32 0.22 0.22 0.22

20 148.0 0.85 0.70 0.65 0.50

30

40

7:4 3.4 2.7 1.25

10b:O

22.7 12.1 8.5

50

..

..

80:4 69.0

Resins derived from polymerization of these methacrylic esters under relatively comparable conditions exhibit marked differences in viscosity as the concentration of polymer in a given solvent is increased. This is illustrated in Table IV and graphically in Figure 1 with data on viscosities in toluene. The percentage polymer dissolved at a given viscosity increases as the number of carbon atoms in the esterified alcohol is increased. These viscosities are representative of commercial polymers, Polymers of either higher or lower viscosity can be prepared from any of the esters.

The methacrylate resins are compatible with a large number of plasticizers of varied chemical nature. Compatibility with highly aliphatic type plasticizers increases with the number of carbons in the alcohol esterified with methacrylic acid. Phthalic, tartaric, phosphoric, and benzoic esters, sulfonamides, carbamates, phthalyl glycolates, and esters of polyhydric alcohols are generally compatible with the series of resins; butyl stearate, methyl abietate, castor oil, and octadecanediol diacetate are more compatible with the higher esters than with the methyl ester. The compatible plasticizers vary considerably in their ability to render methacrylate polymers flexible. The results of a film flexibility study indicate that dibutyl phthalate, dicyclohexyl phthalate, dibutoxy ethyl phthalate, dibutoxy ethoxy ethyl phthalate, triethylene glycol dihexoate, and 6-12 carbon branched-chain secondary alcohol carbamates are among the plasticizers which produce higher degrees of flexibility.

INDUSTRIAL AND ENGINEERING CHEMISTRY

APRIL, 1939

COMPATIBILITY OF METHACRYLIC ESTERPOLYMERS WITH OTHERRESINOUS MATERIALS

TABLE VI.

Methacrylic Ester Polymera -Ethyl---n-Propyl--ButylSO% 50% 20% SO% 50% 20% SO% 50%

7

,

Resinous Material Manila copal Dammar Shellac Rosin Amberol 109 Phenac 605-N Beckacite (Super 2000) Paraplex RG-2 Petrex 5 Rezyl Rezyl Rezyl Rezyl Resin

19

110 408

821-1

KM

Chemical Composition

.....

...... ......

c

C

Modifiedphenol-formaldehyderesin Ester-gum-modified phenol-formaldehyde resin Phenol-formaldehyde resin

I I

I I

Sebacic-acid-modified alkyd resin Terpsne-maleio anhydride alkyd resin Nondrying-oil-modified alkyd resin Drying-oil-modified alkyd resin Same Same Modified alkyd resin

I I C S I I I C SI S I S I I I I I

...... ...... ...... ......

Kopol (500) Ester gum

Esterified Congo copal Esterified rosin

Plioform No. 20 Tornesite

Isomerized rubber Chlorinated rubber

Asphalt (soft albino) Cumar V-1/2 Aroclor 4465 Santolite M H P Vistanex No. 6 Meta styrene a

C

=

---Methyl--. SO%& 50%

S I C SI I S I 1

.....

Cellulose nitrate (1/z-sec.) Cellulose acetate Ethylcellulose Benz ylcellulose

Polyvinyl acetate Vinylite H

385

c

c

I I I I SI I

I I I I I I

c C

S

c C

I

C

I 1

I

C

C

c

I

SI

c

c

c

I

I 1 I I 1 1 1

I 1 I I 1 1 I

I I I I I I S I

I 1 I I 1 1 1

I 1 I I 1 1 I

c

c

c

c

c

c

c

I I I I

c I

c

c

c

S

I

c

I

c

......

I

I I

1 1

SI

I

compatible; I = incompatible; SI

=

I

I I

c c c I I

1 1

films appear homogeneous but hazy.

Since the pure methacrylate polymers differ so much from each other in flexibility, it is obvious that the amount of plasticizer required to produce a given degree of flexibility will vary from resin to resin. Using a good Plasticizer as mentioned in the previous paragraph, it has been observed that 100 parts of butyl methacrylate containing 5 Parts

c c c 1 1

b

I

I20

J METHYL

ETHYL

I

I I

c

I I S

c

SI S

c

c

I

c

c I 1 I I 1 1

I 1 I I 1 1

I I I I

c

c

c

c

1 I 1 1

c

1 SI 1

c

I 1 1 I

1 I 1 1

1

I

1

I

1 I

I I

I I I I I S C

I

SI I I I I

SI

I

c

I

c

I 1 I I

1

c

1 1 1 1

1 1 1 1

c

c

c

c

c

c . c

1

1

1

1

1

1 1 1 S I 1 1 I I I

c C

c

c

I

I

I

c c c c

c c c c

c c c

c c c

c c c

1 1 1

1 1 1

I I I

1 1 1

1 1 1

c

SI

c c c c

SI

c c

c c c c

1 1

C I I

I 1 1

I 1 1

I I I

c

c

I

c I

c c c c

c c c

1 SI 1

1

I 1 I I 1 1 I 1

I I I

1 1 1 1

c

20%

I

c

S

I

C

C

All percentages refer t o methacrylate resin.

Compatibility of Methacrylate Resins with One Another Toluene solutions (20 per cent) of each of the five commercial methacrylate polymers were mixed thoroughly with equal amounts of 20 per cent toluene solutions of the other four polymers and, after standing, were examined visually for homogeneity. The observations are as follows: Methacrylatea

I40

1 1 1 1

c

c

I

1 I

c I

c

c c

I I I I

1 1 1 1 1 1 1 1 S I S I 1 1

c

C f

SI I

I I I SI I I S I

c

C

c

I

I I I I I 1 1 1 1 1 I 1

I

I I S

c

c

c

......

I

C

c

c c

c

S

c C C

1

1 SI 1

C

c

C

1 I

S

C

I

I

I

Vinyl chloride-vinyl acetate interpolymer Cumarone-indene resin Chlorinated diphenyl Toluene sulfonamide-f ormaldehyde resin Aliphatic hydrocarbon polymer

I I S

I S 1 1 I I SI S I 1 1

1 SI 1

c

c

......

20%

1

-IsobutylSO% 50% 20%

Ethyl

n-Propyl

n-Butyl

Isobutyl

N-PROW

Films were then flowed from these solutions (after thorough mixing), air-dried, and examined for compatibility: Methacrylate Ethyl Methyl I Ethyl n-Propyl +Butyl a SI = slightly incompatible.

CCBCEhTRATIOh ( W T O b T X I

FIGURE 1. CONCENTRATION-VISCOSITY CURVESFOR METHACRYLIC ESTERPOLYMERS IN TOLUENE

of plasticizer is approximately equivalent in flexibility a t 0-25" C. to: 100 parts of n-propyl methacrylate with 22 parts plasticizer, or to 100 parts of ethyl methacrylate with 25 parts plasticizer, or to 100 parts of isobutyl methacrylate with 33 parts plasticizer, or to 100 parts of methyl methacrylate with 50 parts plasticizer. Films of these compositions are flexible but relatively nontacky a t room temperature.

n-Propyl

n-Buty

Isobutyl

I I

I I

I I SI

SIa

C

Of the ten possible solutions, only four were homogeneousnamely, the ethyl-propyl, propyl-butyl, propyl-isobutyl and butyl-isobutyl solutions. Of the dried films, the only case of complete compatibility occurred with the butyl-isobutyl mixture. It is surprising that members of a homologous series of compounds so closely related should not be more compatible with one another, especially when they are dissolved in a common solvent. Indications are that these resins show a wider range of compatibility with one another when mixed in unequal proportions. In spite of the fact that methacrylate polymers cannot be mixed in all proportions to give compatible blends, one can readily obtain homogeneous compositions by copolymerization of a mixture of monomers. I n this manner, copolymers can be prepared with physical properties dependent on the ratio of the monomers.

386

INDUSTRIAL AND ENGINEERING CHEMISTRY

VOL. 31, NO. 4

Compatibility with Other Resinous Materials

proportion of the fluxing agent. These blends are heat stable, and no appreciable change takes place on heatData on the compatibility ing for prolonged periods a t of methacrylate resins with 150-200 C. representative resinous prodThe higher methacrylate ucts in 80-20, 50-50, and 20polymers can be dissolved 80 methacrylate-modifying readily in molten waxes, such resin ratios are given in Table as paraffin, beeswax, and carVI. When solutions were nauba wax to produce soluprepared for flowing films, 25 tions which, on cooling, form per cent toluene solutions of toughened, rigid, or flexible the methacrylate polymers masses. The higher softening were mixed with 20 per cent methacrylate polymers tend solutions of the modifying to form harder, more rigid wax resin (toluene was used whenblends; the softer, more pliever possible) to give the able methacrylates in general weight ratios indicated above ; produce pliable, elastic blends. after thorough mixing, films Solution temperatures of the were flowed, air-dried, and wax blends (temperature a t observed for compatibility. which a clear methacrylateWhen toluene could not be wax solution is obtained) vary used as a solvent for both with the methacrylic ester resins, the solvent mixture used and with the nature and was balanced in such a manner TONGUE DEPRESSOR MADEOF A CURVED RODOF "LUCITE" concentration of the wax. I n that it would remain a comMETHYLMETHACRYLATE PLASTIC, WITH CONCENTRATED paraffin, for example, the solumon solvent for both resins LIGHTCOMING OUTAT THE END tion temperature decreases as until evaporation was comB y combining t h e light and depressor into a single instrument, t h e operator's hands are not so encumbered as is usually t h e oase, Bnd the molecular weight of the plete. the examination is simplified. This instrument gives a light which alcohol esterified with methaThe methacrylate resins is white and brilliant, and shows up the tissues in their true colpr; the light is shadowless because it is concentrated a t the exaot point crylic acid is increased; and are, in general, compatible desired. with a given polyester, the with cellulose nitrate, rosin, s o l u t i o n t e m p e r a t u r e inchlorinated rubber, vinyl creases as the percentage of paraffin is increased. Solution chloride-vinyl acetate interpolymers, phenol-aldehyde, coutemperatures also vary directly with the melting point of the marone-indene, and chlorinated diphenyl resins. The higher paraffin and the molecular weight of the methacrylate polymer. methacrylates are more compatible with ester gum and asphalt; Blending agents of various types can be added to these comthe lower esters are more compatible with sulfonamide-aldepositions to reduce solution temperatures and modify the hyde resins, polyvinyl acetate, and Manila copal. One modiphysical properties of the blends a t lower temperature. fied phenol-aldehyde resin was compatible with ethyl and Methacrylate-paraffin blends with solution temperatures as propyl methacrylate polymers but incompatible with the low as 100" C. can be obtained readily. others. The methacrylate polymers are generally not comSuch toughened melts are extremely fluid in the molten pletely compatible with dammar, shellac, alkyd and hydrostate and are suitable for coating purposes by roller coating, carbon resins, and the acetate, ethyl ether, and benzyl ether immersion, and spreading methods. Paper coated from of cellulose. these melts is far superior to paraffin-coated paper in water The methacrylate resins possess excellent film-forming and and oil resistance, especially after it is folded, and gives much adhesive properties in their own right, and because of their stronger bonds on heat sealing. wide compatibility with solvents, plasticizers, and resinous Emulsions of these wax-methacrylate compositions can be materials, they enter readily into more complex formulations. prepared readily. This enables coating to be carried out b y Methacrylate Resin Hot-Melt Blends spraying, brushing, or dipping at normal temperatures. Films flowed from emulsions are characterized by the same toughThe methacrylate polymers do not fuse to a liquid state ness and flexibility as films deposited from the melt. when heated above their thermal yield points but maintain a The properties of the methacrylic ester polymers, esperubbery consistency over a wide temperature range. For cially the higher esters, render them suitable for general inthis reason the pure polymethacrylates cannot be used readily as hot melts for coating and adhesive purposes. The rubbery dustrial uses as coating materials and as thermoplastic adhesives applied from solvents. The films produced are fast consistency can be reduced and the fluidity greatly increased drying, water-white, nonyellowing, tough, and durable, and a t temperatures between 150" and 200" C. by blending with adhere well to most surfaces. This series of resins affords a resinous fluxing agents of lower molecular weight, such as wide gradation in physical properties and, owing to the ready rosin, ester gum, dammar, and the coumarone-indene resins. compatibility of the methacrylate resins with plasticizers and By variation of the methacrylate polymer and the nature and other resinous materials, an exceedingly wide range of therconcentration of the added fluxing agent, a series of resin moplastic products is made available. When it is desirable blends can be obtained which differ widely in fluidity in the to avoid the use of solvents in coating, adhesive, or impregmolten state but closely resemble the methacrylate polymers nating compositions, the methacrylate resins can be applied in all properties. The melt viscosity of the methacrylate as hot melts which lend themselves to high-speed operations polymers with a given percentage of fluxing agent decreases and as emulsions which take their final form through the evapoas the molecular weight of the alcohol esterified with metharation of water. Because of their outstanding properties crylic acid is increased. When the blends are used as adheand versatility, the methacrylate resins are finding outlets in sives, their bond strengths a t elevated temperatures vary with a number of industrial applications. the nature of the methacrylate polymer and the nature and

I

APRIL, 1939

INDUSTRIAL AND ENGINEERING CHEMISTRY

Literature Cited (1) Axilrod and Kline, J. Research Natl. Bur. Standards, 19, 367 (1937). (2) Crawford and McGrath, U. S. Patent 2,108,044 (Feb. 15, 1938). (3) Du Pont de Nemours, E. I., 8z Co., IND.ENQ.CHEM.,28, 1160 (1936). (4) Elec. Rev., 118, 784 (1936). ( 5 ) Fields, U. S7 Patents 2,057,6734 (Oct. 20, 1936). (6) Gardner, "Physical and Chemical Examination Of Paints, Varnishes, Lacquers and Colors," 8th ed., P. 300, Washington, D. C., Inst. of Paint and Varnish Research, 1937.

387

(7) Gordon, U. S. Patent 2,101,061 (Dec. 7, 1937). (8) Hill, Ibid., 2,045,651 (June 30, 1936). (9) Instruments, 9, 218 (1936). (IO) Kline, Modern Plastics, 15, 47 (April) and 46 (May), 1938. (11) Kline and Axilrod, IND. ENQ.CHEM.,28, 1170 (1936). (12) Kuettel, U. S. Patent 2,063,315 (Dee. 8, 1936). (13) Loder, Ibid., 2,045,660 (June 30, 1936). (14) Macht, Ibid., 2,071,932 (Feb. 23, 1937). (15) St,rain, IND. ENQ.CHEM.,30, 345 (1938). (16) Strain, U.S. Patent 2,030,901 (Feb. 8, 1938). (17) Tatersall. Ibid., 2,071,907 (Feb. 23, 1937).

WATER CONDITIONING IN STEAM GENERATION

.

During the past twenty years boiler pressures have increased from 350 to 2500 pounds per square inch, rates of evaporation per boiler from 150,000 to 1,000,000 pounds per hour, and total steam temperatures from 660" to 950" F. This remarkable development has occurred parallel to, and at least in part as a result of, corresponding progress in the conditioning of boiler water, so that steam could be safely and economically produced continuously at high rates, even from water supplies of inferior quality. From the viewpoint of the chemical engineer, the proper conditioning of water for contemporary boilers is a never-ending series of problems in clarification, filtration, fluid flow, heat transfer, and properties of materials, in the solution of which he must apply all that is known concerning the physical chemistry of aqueous solutions, the phenomena of the colloidal state, and the factors influencing corrosion. The major developments in boiler design, the external softening of feed water, and the internal conditioning of boiler water during the past twenty years are described.

N 1918new boilers just placed in operation a t a pressure of 375 pounds per square inch represented an outstanding advance of about 75 pounds beyond regular practice and were recognized as approaehing the limit for the type of design then standard (1). Engineers were, however, visioning boilers which would produce steam a t 800 pounds pressure, superheated to 800 F. (7). In 1938 a million pounds of steam per hour were produced from a single boiler a t a pressure of 1375 pounds and a temperature of 900"F., and a boiler designed to operate a t 2500 O

EVERETT P. PARTRIDGE Hall Laboratories, Inc., Pittsburgh, Penna

A. C. PURDY Bull & Roberts, New York, N. Y.

pounds per square inch and to produce steam superheated to 950" F. is under consideration. For this rapid change during the last two decades much credit must go to the men who have learned how to burn fuel efficiently a t high rates; to design heat-absorbing surfaces so that the resultant radiant energy would be utilized in the production of steam instead of the destruction of the boiler furnace; to fabricate and assemble the massive and intricate components of these designs; and to control, by sensitive automatic instruments, practically every operation in the making of steam. The combustion engineers, the mechanical engineers, the metallurgical engineers, and the engineers devoted to instrumentation must, however, share some of the credit with the chemical engineer, whose contribution has been the conditioning of water so that it can be evaporated continuously a t a high rate without damage to the boiler. Water conditioning is more than water softening, in the same sense that operating an integrated plant differs from supplying the raw materials for the process. In water conditioning the emphasis is necessarily not merely on the hardness of the water fed to the boiler, but on what is actually taking place a t some particular locality in the boiler or its auxiliaries or in the turbine or process equipment to which it supplies steam. The viewpoint is that of the physical chemist determining the essential factors of a problem and of the chemical engineer applying this knowledge in devising a practical solution. Control of the conditions in the boiler by systematic analysis of samples of the boiler water, which is accustomed routine today, had scarcely been imagined in 1918. In retrospect, it seems as if the developments in steam generation in the following years led inevitably to the necessity for boilerwater conditioning. In turn, the improvement in operation resulting from proper conditioning must have been a factor in stimulating the subsequent great advances in boiler design.