P r e s e n t e d before the Division of P a i n t , Plastics, and P r i n t -
UNSATURATED POLY SINS POLYESTER RESIN-GLASS FIBER LAMINATES
APPLICATIONS AND USES
Arthur L. Smith . . . . . . . . . . . . . . . . .
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PHYSICAL PROPERTIES O F POLYESTER RESINS
Earl E. Parker and E. W. Moffett. . . . . . . . . . 1615
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T. E. Bockstahler, G. E. Forsyth, J. J. Gouza, F. R. Shirak, and E. M. Beavers. . . . . . . . . .
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Johan Bjorksten, L. L. Yaeger, and J. E. Henning . EFFECT OF FILLER PARTICLE SIZE O N RESINS
R. K. Witt and E. P. Cizek.
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INHIBITION O F UNSATURATED POLYESTERS
W. E. Cass and R. E. Burnett . . . . . . . . . . . 1619 ACIDIC AND ALCOHOLIC COMPONENTS OF POLYESTERS
THERMAL PROPERTIES OF POLYESTER RESINS
R. W. Stafford and J. F. Shay . . . . . . . . . . . 1625 MALEIC-FUMARIC ISOMERIZATION I N UNSATURATED POLYESTERS
FLAME-RESISTANT POLYESTERS FROM HEXACHLOROCY CLOPENTADIENE
P. Robitschek and C. Thomas Bean.
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S. S. Feuer, T. E. Bockstahler, C. A. Brown, and I. Rosenthal . . . . . . . . . . . . . . . . . . . 1643
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 46, No. 8
-Unsaturated
Polyesters-
Applications and Uses ARTHUR L. SMITH Rohm & Haas Co,, Washington Square, Philadelphia 5, Pa.
Although unsaturated polyesters vary in type and composition, they are generally solutions of unsaturated polyesters made from difunctional glycols and acids in a vinyl monomer. When catalyzed with a free radical catalyst, such as benzoyl peroxide, they cure by copolymerization of the vinyl monomer with the unsaturated groups in the polyester to yield a cross-linked or three-dimensional structure. The ability to cure or polymerize without evolution of volatile byproducts is their outstanding characteristic. Principal applications and uses are in laminating, casting, and molding.
ESATURATED polyesters are fundamentally no more than a natural evolutionary development of the rapidly growing alkyd or polyester chemistry field, which had its origin in the early part of the twentieth century. They could be classified w B natural result of a combination of knowledge of polyester chemistry and polymerization. Although they vary considerably in type and composition, they are generally solutions of unsaturated polyesters made from difunctional glycols and acids in a vinyl monomer such as styrene. When catalyzed with a free radical catalyst such as benzoyl peroxide, they cure by copolymerization of the vinyl monomer with the unsaturated groups in the polyester to yield a crosslinked or three-dimensional structure (Figures 1and 2). CHARACTER1 STICS
Properties of unsaturated polyesters can be varied from strong rigid resins to tough flexible ones. This is accomplished by any of the following variables: 1. Type of dihydric alcohol used 2. Type of dibasic acid used 3. Ratio of unsaturated to saturated dibasic acid 4. Type and quantity of vinyl monomer used
Special characteristics can be bull‘ them by combinations of these variables. Figure 3 shows the widely varying rigidity which is possible in this class of resins. If we were to list the physical properties of a typical rigid resin, we would see that although it had good strength properties, electrical properties, and chemical resistance, none could explain the rapid growth of this industry. What then is the underlying reason for this grov, th? It is the fact that they are 100% reactive, usually liquid resins, which cure rapidly by polymerization to their final. stage without the evolution of any volatile reaction by-products. This is the characteristic that forms the basis of their wide usefulness. Yet this is not new, this same characteristic has been known to polymerization chemistry for over 50 years. In order to save unnecessary repetition let us call this “characteristic A”;the ability to cure or polymerize n-ithout the evolution of volatile by-products. Besides giving the resins favorable properties, characteristic A has also posed severe problems in their application. This is one reason why applications were slow to develop during the early 1940’s. Entirely new handling techniques had to be developed and mastered in the fabrication industry to deal rrith these sticky liquid resins. It was not until these new techniques
G -
-G
A
G
G
A
G
p
f G
G
--.-.---=--.---I---.,=:-
Figure 1. Unsaturated Polyester Resin before Curve G.
A.
August 1954
Glycol Saturated acid
Figure 2. Unsaturated Polyester Resin after Curve - Unsaturated acid M.
Monomer
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Figure 3.
Special Characteristics Can Be Built Into the Resins
were developccl that J,&J noniically sound applications resulted. It was I I Q \ , ~ A, 5 years after their introduction, that applicafiont were sufficiently well established that continued grox t h of this industry was ensured, and development had been helped along during this period by .iT-artinic economv and urgency. The Society of Plastics Industry reports the following production figures for unsaturated polyester resins: 1948 1950 1951 1952 1953 1954 1955
L\lillion Pounds 2 7 14 19 27 (est.) 38 (est.) 50 (est.)
ester resin. This is an unusually good example of an applicatioi] which utilizes, besides characteristic A, tlie inherent permanerive, corrosion resistance, high strength, and high yield point of gl fiher-reinforced unsaturated polyester resins. Casting and potting arc grouped because of their similarit\-. Vnsaturat,ed polyester resins are today being cast into thermo sheet which forms the basis for many useful products. They arc also being used for encapsulation of electronic circuits, for potting of electrical components, coils, etc. Thcy provide a good protective moisture-resistant barrier for these applications. This can he accomplished by various materials, but, it is charactcrist,ic 11 that, provides the basis for tlieir use in this industry. “Molding” is a rather broad category that covers a host of uses and applications for unsaturated polyester resins. I n almost all instances, combinations with glass fibers render unusual strength to the resulting product. llolding as a field of applicat’ion m s slow to catch on because of the really different techniques required by characteristic A . It was necessary to learn to handle the \vet sticky mass which resulted when reinforcing fiber8 were saturated with resins which did not require evaporation of solvent. Molding techniques that have been developed have circumvented this problem by introducing the glass fiber material into the mold separately and subsequently effecting sahration with the liquid resin and curing in the same step. Although the control of this step is most, important and often leaves something to be desired, the method has caught on rapidly for many items, including: 1. Tote boxes and trays having high strength Keight’ ratio yielding high pay loads 2. Containers having high strength and valuable nondenting properties 3. Various housings and parts for the household appliance field: here corrosion resizt,ance and sound-deadening propcrties have been important
APFLICATION S
hpplicatioiie and uses of unsaturated polyest,er resins can be divided roughly into three fields: 1. Laminating 2. Casting or potting 3. Molding One of the earliest uses of these resins was in glaeE fiber-rrinforced laminates for fuel cell backing board in aircraft. This application gave birth to a nerv industry--continuous laniinating, xhich expanded into laminates for other industrial uses in the electrical and engineering fields, and decorative laminates for consumer use. This whole industry, which enables production oi continuous lengths of thermoset material with excellent thickness tolerance, depends wholly on characteristic A. Il-it’houtit, such a process would not be possible. A closely related use for these resins is that of glass-reinforced corrugated sheet (Figure 4). This currently constitutes one of the most important uses of unsaturated polyester resins. This industry was born using the simplest of equipment and process but, today utilizes continuous or semicontinuous processes for large scale production. Characteristic A \%-asnecessary to both the birth of this industry, with its simple equipment and process, and contemporary continuous processes that yield efficient economical production. The nianufacture of glass-reinforced pipe by several different processes similarly relies heavily on characteristic A. This product is finding application in many places where the combination of corrosion reskta,nce and high strength are required. Every sporting goods &ore in America shows the modern line of fishing rods which arc practically indestructible. Most of these so-called glass rods are composed of glass fibers firmly bound together with 30 to 60% by \?eight of unsaturat,ed poly-
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Figure 4. Use of Glass-Reinforced Corrugated Sheet
In all these uses, however, last,ing applications that t,hn-art duplication with other materials, utilize characteristic .i in some degree. Large complex shapes are now fabricated because of lower pressures possible in molding: 1. Aircraft pa,rtrsJsuch as duct y o r k matic a t eswitially no pressure, and large radar housings, with compIes aerodynamic shapes, are made a t bag moldin pressuree. These also utilizc t,he excellent electrical properties o f the resins. 2. Rosts, up to 1 G feet long, are being produced by scveral manufact,urers; many are one-piece sbructures. New highly functional designs are possible utilizing the unique qualities of reinforced unsaturated polycstcrs. 3. There is considerable interest in the automotiva induutry in glass fiber-reinforced polyesters for use in bodies. Some model.+ are already in trial production .il-ith plans x~ellunder way for fuller
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 46, No. 8
-Unsaturated scale production. Eager and watchful eyes are beamed on this development, and there are almost as many opinions regarding its probable course as there are eyes. Production methods certainly need improvement. It is generally agreed that there is a place for reinforced polyesters in the automotive field. It remains to be seen where it will be-whether it is best suited for prototype and sports models only or whether larger scale production will be economically realized. If in this development top consideration is given to the unique properties of reinforced polyesters (strength weight ratio, nondenting properties, noncorrosiveness, and ability to be formed a t low working pressures), the right answer will certainly be found quickly.
Polyesters-
Again, all these parts in these three fields lean heavily on characteristic A to make them practical as this enables production of large shapes at lowpressures* I n any consideration of applications, numerous flat sheet materials made by standard press methods must be included; these are finding wide utility in electrical and mechanical products. A180 growing rapidly are the alkyd molding resins and various reinforced “premix” compounds. RECEIVED for review December 7, 1953.
.kCCEPTED
February 3 , 1984.
Physical Properties of Polyester Resins EARL E. PARKER AND E. W. MOFFETT Pittsburgh Plate Glass Co., 235 E. Pittsburgh Ave., Milwaukee 1, Wis.
T h e ratio of unsaturated to saturated dibasic acid was varied i n 10 mole % steps in four series of unsaturated polyesters. One of these was mixed with 20, 30, 40, and 50% styrene, while the others were mixed with 30% styrene. Flexural strength, modulus in flexure, tensile strength, modulus in tension, elongation, water absorption, and heat distortion points were determined on castings prepared from each mixture. The results are discussed.
C
OMMERCIAL interest in the chemistry of linear polyesters was initiated by the work of Carothers. The subsequent development of one branch of this field resulted in the present unsaturated polyester resin industry. Commercial polyester resins usually contain three essential components: polyester, monomer, and inhibitor. Styrene is the most common commercially used monomer and was used exclusively in this work. An inhibitor is necessary in a polyester-styrene resin in order to provide storage life of the product before it is catalyzed and working life of the liquid resin after it is catalyzed. Hydroquinone was used for this purpose in the resins used in this work. The polyester usually constitutes 50 to 85% of a commercial polyester resin. These polyesters are prepared by esterifying one or more dibasic acids with a glycol. One of the dibasic acids must be ethylenically unsaturated and is commonly introduced as maleic anhydride or fumaric acid. A variety of ethylenically saturated acids is used, but phthalic anhydride is the most common. Ethylene, diethylene, and propylene glycols are the most frequently used glycols. The following equation shows the reaction between maleic acid and ethylene glycol to produce the simplest unsaturated polyester, ethylene maleate HOOC-CH=CH-COOH
+ HOCHzCHzOH
H( OCHZ-CHsOOC-CH=CH-CO)x
+
OH
Polyesters of this type are conveniently prepared with a molecular weight of approximately 800 to 2000 representing some 6 to 15 repeating units. Commercial polyester resins are usually sold in the form of sirups, These are converted to the solid form by dissolving a peroxide-type catalyst in the resin and heating the solution for a short time. Combinations exist that will cure in a few hours a t room temperature while others cure in as little a8 ’/z minute a t 110’ C. The chemical reaction that takes place involves a reaction between the double bonds in the unsaturated polyester August 1954
and the vinyl group in the monomer resulting in the polyester becoming cross-linked in a number of places. There is a fairly strong tendency for an alternating-type copolymer to form, but a large excess of styrene can be consumed without the formation of any appreciable amount of polystyrene. This indicates that several monomer units may be consumed in cross-linking two polyester molecules. This paper deals primarily with the relationship between the physical properties of the cured resin and the chemical composition of the uncured material. Three types of variation were studied: 1. The degree of unsaturation of the polyester 2. The ratio of polyester to styrene in the resin 3. The chemical components of the polyester Four series of polyesters were used to study these variables 1. 2. 3. 4.
Propylene maleate phthalate Propylene fumarate phthalate Propylene maleate adipate Diethylene fumarate phthalate
The ratio of ethylenically unsaturated to saturated acid was varied in 10 mole % ’ steps, so that there were 10 numbers of each series. An attempt was made to prepare all of the polyesters so that they had approximately the same viscosity and, therefore, roughly equal molecular weights. Each member of the propylene maleate phthalate series was mixed with 20, 80, 40, and 507, styrene in order to obtain the effect of varying the quantity of styrene as well as the degree of unsaturation of the polyester. EXPERIMENTAL
The polyesters were prepared in 5-liter three-necked flasks equipped with a thermometer, an inlet tube for inert gas, and a device for azeotropic removal of water. I n most cases 20 moles of acid (or anhydride) and 22 moles of glycol were refluxed with xylene as a solvent until the acid number was reduced to approxi-
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