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Table of Contentslntroduction
Evaluatin g Unsaturated Polyesters
Level of Unsaturation
Three lsomers of Phthalic Acid
Modification with Aliphatic Acids
Glycols
Unsaturated Goreactants
Glossary
A Summary of Trends
Health and Safety Information
On the cover: A Fisher-Hirschfelder-Taylor model of anisopolyester molecule illustrates the space filled by thecovalent bonds. This model represents a polyesterwith a 1 :1 ratio isophthalic acid to maleic anhydridecondensed with propylene glycol and crosslinkedwith three moles of styrene per mole of maleateunsaturation. Light blue represents oxygen, orange ishydrogen, and black is carbon. Study of the modelsprovides a useful intuitive feeling for the sterichindrances that may increase corrosion resistanceand for the changes in resin density,'flexibility andcrystallinity produced by various combinations ofpo lyeste r i ng red i ents.
2
lntroduction I
2 Fiber reinforced polyester composites have achieved 1
. fabricate. This makes isopolyesters the preferred" choice in gel coats, pipes and tanks, structuralg molding, and automotive appearance parts.
The remarkable versatility of fiber reinforced12 isopolyesters is largely derived from the almost
ro unlimited possibility for easy modification of the basic'! polymer structure. Major variables include selection of
20 glycols, the choice of unsaturated coreactant,proportions of these ingredients used, and processing.
23 As manufacturer and marketer of three basicchemicals for isopolyesters-isophtha I ic acid, ma leic26 anhydride, and siyrene monomer-Amoco Chemical
26 has actively.monitored trends and developments in theunsaturated polyester i ndustry.
27 This brochure outlines the information Amoco hascollected on the effect of ingredients on unsaturatedpolyester properties and performance. Most of thedata is from work conducted by Amoco laboratories.Some information comes from the laboratories ofaffiliated companies as well as from recognizedindustry and academic sources. This compilation isintended as a guide to available information. Amocowelcomes dialogue with manufacturers and users ofpolyesters about issues that this work may engender.
The Ghemistry ofU nsatu rated PolyestersUnsaturated polyesters are the product of acondensation reaction between difunctional acids andalcohols one of which (generally the acid) contributesolefinic unsaturation. This polymer is dissolved instyrene or other monomeric material containing vinylunsaturation. With heat and,/or free radical initiation,the polyester and reactive diluent crosslink into asolid, non-melting network. The photos show asimplified model of the basic materials required toform a thermoset polyester.
With this picture in mind, the methods of varying thepolyester to tailor it to specific applicationrequirements are readily apparent. The principalpolyester variations effected by constituent changesare the frequency of crosslinking sites (crosslinkdensity), the degree of steric protection afforded tovulnerable functional groups and the rotationalfreedom within the polymer chains.
Additional effects on properties are produced bypolyester molecular size - a joint function of theratio of ingredients and processing variables - andby coreactant selection and concentration.
Even this brief overview of polyesters indicates thatseveral routes are usually available to achieve aparticular property. A goal of this brochure is tosuggest usef ul paths of investigation to resinformulators seeking cost effective resins to meetspecific end use requirements. While the particularemphasis will be on the role of ingredients inpolyesters based on isophthalic acid, many of thetrends observed in our laboratory can be extrapolatedto other types of unsaturated polyesters.
lllustrationl PolyesterReactants
F-=aAmoco Maleic Anhydride (MAN)
.WxAmoco lsophthalic Acid flpA)
lllustration 3 Cured lsopolyester - The same model as on the cover. Oxygen is light gray, hydrogen is dark gray, and carbon is btack. Theball and'stick diagrams omit hydrogen; black circles represent carbon and open circles are oxygen.
lllustration 2 Liquid Polyester With Styrene Monomer
ffWr
v
Processing AffectsPolyester PropertiesThe brief description of processing included here isintended only as a basis for the discussion ofprocessing's influence on properties. A morecomplete review of Amoco's recommendations forunsaturated isopolyester processing is available inother publications.
Equipment for processing good quality unsaturatedpolyesters includes: a heated kettle with agitator,temperature measurement devices, reactant additionand sampling ports; an overhead system withefficient fractionating and total condensers; andapparatus for safely diluting the polyester withmonomer.
Good quality unsaturated polyesters are processed bya two stage reaction in which aromatic and saturatedacids are reacted with all the glycol until at least onefunctional group of all diacid has reacted. The resinmixture is then cooled, maleic anhydride added andprocessing continued to f inal properties asdetermined by test methods, such as acid number orviscosity, that reflect polymer size.
Esterifying the slower reacting acids with asubstantial glycol excess produces low molecularweight. hydroxyl terminated oligomers that react inthe second stage to more evenly distributeunsaturated f unctionality throughout the polymer.
The esterification reaction is accelerated by efficientlyremoving the water of reaction (hence the need foran efficient partial condenser), higher thanatmospheric pressure and/ or certain catalysts.
The polyester chain grows as acid and hydroxylgroups combine and release water. Unreacted acidand hydroxyl groups left in the reaction mixture canbe monitored by conventional wet chemicaltechniques to indicate the course of the reaction.
Figure 1 illustrates the growth of polymer size andincrease in viscosity as the available end groups areconsumed. Because virtually all isopolyesters areformulated with a hydroxyl excess, acid number iscommonly used to quickly indicate the remaininglevel of reactive material. Excessive residual carboxylfunctionality contributes to viscosity drift and greatervulnerability to chemical attack in end useapplications. Therefore. the preferred method forcontrolling polyester molecular weight is to adjustinitial hydroxyl excess, rather than prematurely endthe esterification reaction.
Figure 1 Molecular Weight lncreases AsEnd Groups Disappear
During Esterification
Mn byVapor PhaseOsmometry
TotalEnd Grouo 'Number ' 150
Gardner-Hd!y'Viscosity
(60% NVM)in Styrene
Acid 50
100
30Number
^\
Evaluating theUnsaturated PolyesterA variety of tests are available for determining theidentity and properties of polyester resins as solutionsand as cured solids. Tests used in process qualitycontrol must give quick, accurate results, beconvenient to perform, and be low in cost whenperformed frequently. Other tests are used to predictlong term performance in actual use.
Tests of the wet or uncured resin and knowledge of theresin formulation and ingredients can tell themolecular weight, level of unsaturation, probablethickening rate and cure response. Conventional testsof uncured resin and their implication for the resinformulator and user are shown in Table 1.
The focus of this brochure is on unsaturated resinsthemselves; however, in most applications the resinsare combined with fibrous reinforcement or fillers. Theuser of the final product is most concerned with theproperties of the composite which are affected by boththe resin and the reinforcement.
Certain properties are dominated by reinforcement andthe contribution of the cured resin is masked. Figure 2illustrates the correlation of cured resin and compositetensile elongation for most of the resins studied byAmoco Chemical. Untilthe sample is elongated about2.5 percent the tensile elongation of the composite isinfluenced by resin. Thereafter, it is determined by thestiffness of the reinforcement.
Other composite properties, such as flexural strength(stress perpendicular to the orientation of most of thereinforcement), are largely determined by the resin.Corrosion resistance is amont the properties that relateto the interaction between reinforcement and resin and
that is best determined by testing a laminate.
To most clearly focus on resin contribution to laminateperformance and avoid the scatter of test resultsinevitable with composite testing, most propertiesdiscussed in this brochure are based on testing of clearor unreinforced castings of resins. Laminate testing isused only for corrosion resistance and flexural fatigueevaluations that are functions of resin/reinforcementinteraction.
Figure 2 Reinforcement Masks ResinTensile Elongation PropertiesLaminate
TensileElongation
o/o
2.5
2461020Clear Casting Tensile Elongation, %
Table I LaboratoryTests of Uncured Resin
Property Test method Predictive Significance
HydroxylnumberAcid numberAcid numberGel
Molecular weight
Molecular weight
Composition
Composition
Non volatilematerial.Viscosity
ASTM E222ASTM Dl639ASTM Dl639SPltestVapor phase osmometry
G e I pe rm eati o n ch ro m atog ra phy
I nf ra - red s pectro sco py
NMR spectroscopy
SPltest
ASTM D1824, D2196, SPI test
Corrosion resistance and thickening rate, indirectlyindicates molecu lar weight,Same as hydroxyl number.Reactivity and demolding time.Number average MW, used to calibrate gelpermeation ch romatography.Number and weight average MW as well asdistribution.Can be run on styrenated resin and cured resin,qualitative test.Sample must be dry and monomer-free bothqualitative and quantitative.
Monomer content. With viscosity it indicatesmolecular weight.Handling and thixotropic properties Also indicatesmolecular weight.
^\
3lResin Properties are lntertwinedChange in one property usually causes a change insome other property. The properties most desired bythe end user are frequently inferred from severalmeasurable variables.
For example, toughness, a most desirable property, isoften defied as the area under the tensile stress/straincurve. Figure 3 depicts a hypothetical charting ofdestructive tensile stress of a clear resin casting. Thearea of the roughly triangular figure formed under thecurve is proportional to the toughness of the testedresin. This property will be affected by changes ineither ultimate tensile elongation or ultimate tensilestrength. lf each component of a multivariateproperty, such as toughness, changes slightly in thesame direction, the cumulative change is muchgreaterthan each individual change. For instance, a
Figure 3 Tensile Stress/Strain AreaDefines Toughness
lncreasing Strain
Data obtained by ASTM D638 using lnstron tester,
30 percent increase in both tensile elongation andtensile strength will result in a 70 percent increase intoughness.
Similarly, a difference in destructive stress testing oflaminates can reflect a more substantial difference innon-destructive, cyclic stress. Table ll shows that aclear cast isopolyester has 34 percent greater flexuralstrength than an orthopolyester. When reinforced, the
Figure 4
Strengthpsi MPa
20,000
15,000
10,000
Strengths Are Maximizedat lntermediate Flexibility
vqa0)
ac'6G
O:
'610Tensile Elongation, %
5020
ii, Flexural
Strength
'!.,.
I 1r I ::'r.1rir::allll:ll:rij.:lrt.,.irir:t 1l:l:iji::l:lili.rr :ll t:.rililLliiiiilir
' r;ir, r:ijrii.,,ia:r::arrtr:
'. rr .l ia.:::.i11r:.)jujrr:''irlitiiiiiiiiii.i:;
'rlrlfr:r::rlr:r'l,:tlii::._:r:;
,:,:l:r,.
t... t:t.:;:r
..::...::::.r::i:i:::i:*
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FO ..:=i='
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Tensile
Strength
r.i:4b
Table ll FlexuralStrenqth and Fatique TestinglsopolyesterResin
131 MPa19,000 psi
221MPa32,000 psi
80 MPa1 1,600 psi
98 MPa14,200 psi
201 MPa29,100 psi
66 MPa9,600 psi
Orthopolyester lso AdvantageResin Over Ortho
Clear cast flexural strength(ASTM D79O)
Laminate flexural strength(ASTM D7e0)
Flexural load sustainablefor 1 million cycles bylaminate(ASTM D671)
34Y"
1Oo/o
21% v
A\
difference falls to 10 percent. However, when thelaminate is subjected to flexural fatigue load testing,the difference is again apparent. (For details of thetest and resin see Figure 22 on page 16.)
Flexibility, which underlies many physical propertiesof resins, is usually closely correlated with tensileelongation. Figures 4 through 6 show the relationshipbetween tensile elongation and flexural strength,tensile strength, stiffness (flexural and tensilemodulus), and heat deflection temperature forpolyesters studied in Amoco's laboratories. Thegraphs indicate relatively invariable relationships
Figure 5 Glear Gasting Stiffness Gorrelateswith Tensile ElongationTensile
Modulus106 psi MPa
0.60
Tensile Elongation, %
between some properties: heat deflection resistanceand high elongation are not compatible combinationsof properties in the same class of resin. On the otherhand, toughness can be increased in resins with lowflexibility by increasing tensile elongation, while invery flexible resins toughness will be improved byreducing elongation.
Table lll summarizes the physical tests andinstrumental analyses that indicate resincharacteristics and usefulness for variousapplications.
Figure 6 Heat Deflection Temperature Versus
Heat Deftecrion Clear Gasting Tensile ElongationTemperature
oc
41020Tensile Elongation, %
Table lll Laboratory Tests of Cured Resins and LaminatesPropertv Test Method SisnificanceTensile strengthTensile elongation
Flexural modulus
Heat deflection temp.
Permeability
Glass transition temp.
ASTM D638
ASTM D638
ASTM D79O
ASTM D648
ASTM D2684 Dl653 (modified)
Th e rm a I g ravi metric a na lysi s
Determine required part thickness
Flexibility
Stiffness, required part thickness
Service temperature, warp tendency
Dual laminate construction
Electrical service tem peratu re-\
Determination of Corrosion Resistance
Even in applications not normally referred to ascorrosion resistant, the ability of reinforcedisopolyesters to resist conditions that would causedeterioration in other materials is a valued attribute.ln normal fabrication of corrosion resistant laminates,the surface is fiber free. Still, liquids may permeatepolyester to some extent, making the laminatevulnerable to attack of the resin, the glass fibers or thei nterface between them. Conseq uently, Amoco'spreference is for corrosion testing of completelaminates with edges protested from exposure. TablelV shows some common corrosion resistance testswhich are conducted in Amoco laboratories.
Most of Amoco's testing has been conducted onlaminates constructed and exposed in corrosivemedia by the procedures outlined in ASTM C581.Analysis of flexural properties and hardness at one,three, six and twelve months can be plotted onlog-log graphs to project ten year performance. Anexample of such projections is shown in Figure 7. lfthe best straight line through the one year dataindicates 50 percent or more retnetion of properties atten years, the laminate is considered acceptable forcommercial service in that media. Advantages of thistest method are that its acceleration is throughtwo-sided exposure, not heat which can distortresults. The test evaluates the resistance of the totallaminate and is reliable. ln Amoco's tests propertyretentions have been reproducible to within 5 percentfor flexural modulus and 10 percent for hardness andflexural strength,
Figure 7
Retention ofProperties
Loss of Propefties During One YearPredicts Long Term Resistance
jr
v70
60
40
30
20 T
60
I
36
I
o
I
12
I
120
lmmersion Time, Months
o
Table lV Gommon corrosion resistance testsPropertyStain corrosion
Pi pe stiff ness retention
Single-sided exposure
Totalimmersion
Test MethodASTM D3262
ASTM D2412
ASTM D4398
ASTM D581
SignificanceMeasures properties of FRP pipe.
Conducted on stoppered pipe sections filled withchemical reagents.
Measures time to blistering for marine gel coatsand laminates.
Measures retention of flexural strength andhardness after one year. Compares resins onability to protect glass fibers.
-\ Level of UnsaturationThe essential ingredient for an unsaturated polyesteris the carbon-carbon double bond or olef inicunsaturation that will subsequently crosslink with thereactive diluent. ln virtually all commercial resinsunsaturation is provided by maleic anhydride orfumaric acid. As shown by the molecular models,they are very similar in the esterified form, and theirdifferences are minor compared with the effect oftheir use level in the polyester (lllustration 4).
lllustration 4 Maleate Versus Fumarate Unsaturation
The ratio of maleic or f umaric unsaturation to thetotal ingredients of the polyester is the primarydeterminant of reactive double bond f requency in thepolymer. This frequency in turn determines theamount of crosslinking that can occur with a reactivediluent, such as styrene, and thus, stronglyinfluences cured resin properties.
An unsaturated polyester could be made with onlythe unsaturated acid or anhydride and a glycol oroxide. As saturated acid replaces unsaturated, thefrequency of double bonds in the polymer willdecrease causing an increase in flexibility asreflected by tensile elongation (Figure 8). The sametrend is displaced, but still true, for resins made withquite different glycols. Figure 9 shows the increasedtensile elongation associated with higher aromaticacid content in resins made with diethylene glycol.
Figure ITensile
Elongation
2.
Figure 9Tensile
Elongation%
125
Unsaturation Level AffectsTensile Elongation
1:2 1:1
IPA:MAN Ratio
Tensile Elongation lncreasesas Reactivity Drops
2:1
IPA:MAN Ratio
Propyleneglycol reslns
aI 45ok stvrene
q3:1
Figure l0
Heat DeflectionTemperature
'c
Heat deflection temperature, as expected, decreasesas crosslink density is reduced (Figure 10). However,as noted in the previous section, the effect of crosslinkdensity on flexural and tensile strengths depends onresin flexibility. A rigid propylene glycol polyester
becomes stronger and more flexible by increasing thearomatic acid content (Figure 11), while a very flexiblediethylene glycol polyester exhibits lower strength asit is made more flexible by increasing aromatic acidcontent. (Figure 12).
Figure 12 Strength of Flexible Resins Fallsat Lower Unsaturation
TensileStrength
psi MPa
10.000
1 :1 2'.1 3:1 4:1 5: 1
IPA:MAN Ratio
lf the formulation of a polyester is known, the degreeof unsaturation can be readily calculated in moles perunit mass (mol/kg), Table V shows a samplecalculation for a polyester with two moles ofunsaturation in 968 grams of polyester or a degree ofunsaturation of 2.07 mol/kg.
Table V Example of Polyester Material BalanceReactant mol kq
Heat Reflection Fallsat Lower Unsaturation
Strength of Rigid Resins Risesat Lower Unsaturation
1:2 1:1
IPA:MAN Ratio
Amoco isophthalicacid
Amoco maleicanhydride
propylene glycolless water
yield
u nsatu ration : 2.0/0,968 : 2.07 mol/kg
U
v
130
Figure l1
pst
20,000
18,000
't6,000
14,000
12,000
10,000
8,000
6,000
3.0 0.498
2.0 0.196
5.5 0.418- 8.0 -0.144
IPA:MAN Ratio
MPa
10
0.968
-\
These polyester double bonds react with the doublebonds in styrene or other coreactant though afree-radical mechanism. This exothermic reaction isusually initiated by a peroxide or other free-radicalsource. Propagation time (a measure of the in-moldcure time) and peak exotherm as determined by theSPI gel test correlate well with the amount ofunsaturation in the polyester, if all other factors areconstant. Figures 13 and 14 illustrate these trends fora series of resins made with propylene glycol andcrosslinked with 45 percent styrene. Generally, higherpolyester unsaturation levels will rsult in faster cureand higher temperatures.
Figure l3 Unsaturation Level AffectsPropagation TimeReaction
Time,Minutes4
Propyleneglycol resins
aI 45ok styrene
I1:4 1:2 1:1
IPA:MAN Ratio
Other Effects of Crosslink Densitylmpact resistance is positively associated withflexibility, Thus, decreasing unsaturation will increaseimpact resistance, reducing molded part damageduring fabrication and shipping.Resins with higher unsaturation levels can toleratemore inert filler because the crosslink density remainssufficiently high to provide good strength as the resinportion of compound volume is reduced,
The higher heat deflection temperatures of morehighly unsaturated resins allows service at highertemperatures.
Sources of UnsaturationWhile theoretically a great variety of unsaturateddifunctional acids and anhydrides could be used toprovide the required double bonds in the polyester,vi rtua I ly a I I com merci a I u nsatu rated polyestersincorporate maleic anhydride (cis configuration) orfumaric acid (trans configuration),
Maleic anhydride is usually less expensive thanfumaric acid. lt can be reaily melted and handled asa liquid. The anhydride form reacts faster than theacid and one less mole of esterification water isreleased du ring processing.
Maleic acid readily isomerizes to form fumaric acid.During esterification the maleate structure canrearrange into the fumarate configuration. The extentof isomerization is reported to be dependent on thetype of glycol used. Table Vl shows the amount ofisomerization observed.
GlycolAmountlsomerized
propylene glycolneopentylglycolethylene glycoldiethylene glycol
From Curtis, et al., 19th Annual SPI RP/Cconference
The advantage of total trans configuration (fumaricacid) was reported to be typical of a more linear andcrystalline polymer: greater hardness, high moduli orstiffness, lower elongation, higher heat distortiontemperature, reduced gel and propagation times, andhigher exotherms. The trend of these differences is tomake the polyer more rigid.
tt2:1 4:1
Table Vl lsomerization of Maleic to Fumaric DuringPolyesterificationFigure 14
PeakTemperature
"c
Unsaturation Level AffectsPeak Exotherm
240
220
200
95%727065
I1:4
tt1:2 1 :1
T
2:1I
4:1
11
-r
IPA:MAN Ratio
Three lsomers ofPhthalic AcidThere are three isomers of phthalic acid: orthophthalicacid (1,2-benzenedicarboxylic acid), isophthalic acid(1,3-), and terephthalic acid (1,4-). Orthophthalic acid,the only one of the three that can form an anhydride, isnormally used in that form.
Each phthalic isomer has particular advantages andliabilities when used in polyester production. Researchby Amoco Chemical indicates that polyesters madefrom isohthalic acid (lPA) offers substantially betterproperties than equivalent formulations made withphthalic anhydride (PAN ).
The properties of terepolyesters are generally betterthan orthopolyesters and are often quite similar to thoseof isopolyesters. Terepolyesters generally have a higherheat deflection temperatures but offer less aromaticsolvent resistance and less UV stability.
lllustration 6 Cured Orthopolyester
vrlllustration 5 Cured lsopolyester
lllustration 7 Cured Terepolyester
-\
{a\
Cost Differences
A resin manufacturer's cost analysis includes rawmaterial costs, processing costs and ancillary costsassociated with special handling of any product. Suchan analysis is an overly simple view of the real costand value of the user. Customer oriented cost analysismust include not only resin purchase price andfabrication costs, but life-cycle cost factors such asmaintenance, useful life before replacement andperformance in multiple environments. The manu-factuer producing high quality resins can offer thesavings of longer service life in more variedconditions.
The combination of better physical properties andsuperior corrosion resistance reported for isophthalicpolyesters in this section can be exploited in severalways:
o thinner laminates can match performance oflower quality resins at lower cost and lessweight;
. the safety margin for catastrophic stress can beincreased.
o useful product life can be extended;o maintenance costs can be reduced;o product defect incidence caused by nnanu-
facturing stresses can be reduced.
Differences in Material Handlingand Processing
The ortho isomer is normally used as the anhydridewhich reacts faster initially and releases one, ratherthan two, moles of esterification water. Phthalicanhydride can be melted, providing someconvenience for plants equipped to pump hot liquidsto storage and process units.
Terephthalic acid is the slowest reacting of the threephthalic acids. catalysts or pressure are required toesterify TA within a reasonable time period.
lsophthalic acid reacts more readily than TA, but itsinitial rate is slower than phthalic anhydride. Theesterification of isophthalic acid can be catalyzed toprovide reaction times approximating those ofanhydride esterification. A summary of typicalprocessing time with and without catalysts andpressure is shown in Table Vll.
Table Vll Processing Time Variation of lsomers ofPhthalic Acid
First Second Total Finalstage stage time viscosityhr hr hr at60 NVM
200'C peaktemp., no catalyst, no pressurePhthalic
anhydride 24.0 24.0 T
232'C peak, no cat., no pres.Phthalic
anhydride 5.5lsophthalic acid 9.0Terephthalic acid 48.7
232'C peak, no cat., w/pres.lsophthalic acid 4.5 10.0Terephthalic acid 14.0 10.0
9.5 15.0 T-U10.0 19,0 v9.5 58.2 V
14.5 V-W24.0 V
232'C peak, with cat.*, no pres.lsophthalic acid 4.3 1 1.0 15.3 U-VTerephthalic acid 8.5 7.5 16.0 V
Data are averages from many cooks of 1 :1 ratio aromatic acid andmaleic anhydri-de condensed with propylene glycol. Times willvarydepending on equipment.*Fascat 4100, hydrated monobutyltirr oxide, a product of M&TChemical, lnc.
The Kr reported in Table Vlllfor orthophthalic acid isnot indicative of the initial reaction rate of theanhydride. Note the significantly lower K2 of orthoversus iso. The practical implication of this low K2 is amuch slower reaction rate for the second acid groupof orthophthalic acid based polyesters, Consequently,it is much more difficult to obtain high polyestermolecular weight with phthalic anhydride than withthe sio or tere conformations. Efforts to pushorthopolyester to high molecular weight increase therisk of gelation and aggravate the sublimation rate ofphthalic anhydride. These efforts also negate theinherent advantages of ortho resins-fast reactiontimes and light color.
Table Vlll Properties of Phthalic Acids andAnhydrides
Solubility lonizationGonstantin Water in Waterat 20'C K1 K2
PAN 131
oPA 231tPA 348,5TA 300*
*Sublimes
Data from Kirk-Othmer, Encyclopedia of Chemical Technology,2nd ed.
M.P.oc
0.70.010.002
io*to-, o6x1o-,33x'tr0-5 3.2x10-u31x10-5 1 .5x10-u
I
^
13
s
The sublimation tendency of phthalic anhydriderequires caution during processing and can indirectlyinfluence cured properties. Sublimed phthalicanhydride fumes are flammable and can causefractionator and condenser plugging. Condensedphthalic anhydride and low molecular weight phthalicesters can drip back into the resin kettle during finalstages of processing and after the reaction iscomplete. These low molecular weight materials haverelatively high water solubility, act as plasticizers ofthe cured resin and reduce corrosion resistance.
Because terephthalic acid requires catalysis foreff icient processing, the consequences of residualcatalyst in cured resin must be evaluated in end useapplications. Amoco's experience indicates thatcertain catalysts may be detrimental to corrosionresistance properties and unacceptable for foodcontact applications. TA resins cooked with catalystsgenerally have dark color and poor shelf life. Gelcharacteristics can also be affected.
Liquid Resin Properties
Equivalent formulations made with the differentphthalic isomers will have somewhat different liquidproperties resulting from the different target endproperties. Resins based on isophthalic or tere-phthalic acid will normally be processed to highermolecular weights and will show higher viscositiesand lower end group counts (acid numbers andhydroxyl nurnbers) than equivalent phthalic anhydrideformulations. To obtain proper solution viscosity forparticular end uses, such as spray application,somewhat more styrene dilution or relatively moreglycol may be required with IPA than with phthalicanhydride. Stopping the isopolyesterification reactionat a lower molecular weight (higher acid number) isgenerally not recommended as many of the curedresin advantages will be lost.
Terephthalic polyesters made with primary glycolssuch as neopentyl have poor solubility in styrenecompared with ortho and isopolyesters. Blends ofglycols and highly branched or cyclic glycols havebeen suggested to improve TA resin solubility.
Cured Resin Differences
The magnitude of the differences caused by thevarious phthalic isomers depends on the selectionand proportion of other ingredients in the polyester.High reactivity resins designed for SMQ applicationcontain only 10 to 15 percent aromatic acid in thecured polymer whereas the aromatic acid can be wellover 30 percent of some flexible resins.
14
Comparing equivalent formulations based on differentaromatic acids is complicated by the differencescaused by processing parameters. As indicated above,orthophthalic resins are rarely processed to the samemolecular weight as iso- and tere-based resins.Orthophthalic resins that are specially processed tothe molecular weight range easily attained withisophthalic acid are susceptible to premature gelationand may contain low molecular weight species.
To demonstrate the differences attributable solely tothe isomeric structure, most of the comparisonsreported here are with very high quality, laboratory-prepared orthophthalic resins that are unmatched bycommercial phthalic resins. The greater advantage ofcommercial iso resins over commercial orthophthalicpolyesters is evident in comparing the differencesshown in Figure 15 to Figures 16 and 17. Anisophthalic high reactivity resin prepared in Amoco'slaboratory showed about 5 to 10 percent higherphysical properties than a comparable orthophthalicpolyester made to the same standards. Tensiletoughness, a multivariate property, is more than 20percent better with the isopolyester. ln contrast, highreactivity commercial isopolyesters are at least twiceas tough as equivalent commercial orthopolyesters.
Figure l5 Toughness of Rigid LaboratoryHigh Reactivity Resins
TensileStrength
psi MPa
5,000
2,500
0.5
Elongation, o/o
v
I
N
1
J
30
20
F]iiirlliiJi:::iili,.!,j6ffiffi
6riiitil$ti$$ffiffi0.0 1.0
v
I
I
A,
,
Figure l6Tensile
Strengthpsi MPa
Figure l7Tensile
Strengthpsi MPa
Toughness of RigidCommercial High Reactivity Resins
1.0Elongation, o/o
Toughness of Resilient GommercialHigh Reactivity Resins
Formulations with a high ratio of aromatic tounsaturated acids amplify the difference IPA canmake. Figure 18 shows tensile stress,/strain datafrom a series of flexible resins made with diethyleneglycol. For these formulations, at equivalent ultimatetensile elongation, the iso resins have 65 to 75percent higher tensile strength.
Figure 18
TensileStrengthpsi MPa
Tensile Stress of FlexibilizedUnsaturated Polyesteru
2.0
8,000
6,000
4,000
2,000
0
I
Elongation, %
A\
15
Figure 20Heat DeflectionTemperature
'c
Heat Deflection Temperatureof 1:1 Polyesters
At a 1 :1 ratio of aromatic is unsaturated acids,isopolyesters offer 15 to 20 percent better strengths,ultimate elongation (Figure 19)and heat deflectiontemperatu re ( Figu re 20) tha n orthopolyesters.. Theisopolyesters are more than 40 percent tougher thanthe ortho resins.
lsopolyesters can endure substantially higher loadthan orthopolyesters in laminate flexural fatigue testsof medium reactivity resins (1 :1 and 3:2 ratios ofaromatic to unsaturated acids). This series of tests(Figure 22ltollow ASTM method D 671; non-destructive loads were applied cyclically until stressrelaxed to half of original. The orthopolyestersincluded a commercial resin whose fatigue resistancewas significantly lowerthan that of the laboratory-prepared resins.
Most physical properties of 1 :1 terephthalatepolyesters are not substantially different than 1 :1isopolyesters. The most dramatic differences are thehigher heat deflection temperature (Figure 20)andlower hardness (Figure 21 ) of the terephthalatepolyesters. lsopolyesters are about 15 percenttougher than equivalent terepolyesters (Figure 19).
Figure 19
TensileStress
psi MPa
Toughness of 1:1
Polyesters in Tensile Stress /Strain
7,500
5,000
120
Figure 21
BarcolHardness
Figure 22FlexuralStresspsi MPa
16,000
14,000
12,000
10,000
8.000
\r/
110
100
35
30
IPA TA PANAromatic acid
Hardness of 1:1 Polyesters45olo Styrene
TA PANAromatic acid
Flexural Fatigue of Laminates
10s
Cycles
45
40
IPA
Ortho \z'"\\ -':::
16
lsopolyester Offer Balance of Properties
Many applications for unsaturated polyesters dependto some extent on the resistance of these resins toattack by environments that corrode metals. Resinswith equimolar ratios of unsaturated to aromaticacids generally exhibit the best balance of corrosionresistant properties.
The traditional preference for isopolyesters overorthophthalates for corrosion resistance is dramati-cally illustrated by the results of laminate immersionin representative media (Figures 23,24 and 25). Evenwhen a phthalic anhydride resin is processed in twostages to a very low acid number and high molecularweight (HMW), its ten-year projected properties dropto unacceptable levels. A lower molecular weight(LMW) orthopolyester processed to more typicalcommercial properties deteriorated to unacceptablelevels within the year of immersion.
Several factors may cause the lower resistance oforthopolyesters to attack by aqueous solutions. Asevident in the molecular models (lllustration 6),orthophthalate ester linkages are more visible, henceare more susceptible to attack than the ester linkagesof isopolyesters. The hydrolytic stability of ortho-polyesters is far inferior to that of isopolyesters asshown by clear castings after six days boiling waterimmersion (lllustration 8). A further vulnerability isthe possibility of free phthalic anhydride or lowmolecular weight phthalate esters that may drop intothe orthopolyester resin near the end of processing.
lllustration I
After six days in boiling water, orthopolyester (on left) has becomecloudy and opaque while isopolyester is still clear.
35o/o HCI at 4'9oC
lsopolyester
llll12 36 60 120
Months
25olo Ethanol at 71oC
Figure 23Retention ofProperties
o//o
/-\ 99
90
80
70
60
50
40
30
I6
Figure 24Retention ofProperties
0/6
99
80
70
60
50
40
30
20
W .*,* ls??o,lyester
I
I
t
I
I
12
Months60 120
1 N NH4OH at 38oC
36
Figure 25Retention oiProperties
%
9080
70
60
50
40
12Months
120
-\30
36 60
17
Figure 27
Retention ofProperties
Benzene at 23oC
v
v
Terepthalate Gorrosion Resistance
Amoco's immersion studies showed no advantage forterephthalate polyesters at temperatures up to 93'C(Figures 26,27, and 28). lsopolyesters demonstratedbetter resistance to dilute acids and bases thanterepolyesters. The TA resins failed in benzene whilethe iso resin softened, but maintained strength andmodulus.
Figure 26
Retention ofProperties
oh
25% H2SO4 at93oC
lsopolyester
Tere
I12
Months
lsopolyester
Tere
I12
Months
1009080
10
40
30
20
100
90
80
70
60
50
40
30
20
tt36 60
ll36
I120
Figure 28
Retention ofProperties
5olo NaOH at 23oC
tll36 60 120
tl36
912 18
Months
(,18
24
Modification withAliphatic AcidsAliphatic acids, particularly adipic acid, can replacepart of the aromatic portion of an unsaturatedpolyester to offer higher tensile elongation withoutdrastically reducing heat distortion temperature.The aliphatic chain is more flexible than the aromaticring; thus the effects shown in Figures 29 and 30 arenot surprising. Adipic acid in the polyester backboneacts as a flexibilizer, lowering stiffness andincreasing elongation. Because crosslink density isessentially constant, the reduction in heat distortiontemperature is modest up to the 50 percentreplacement level. Above this level heat distortiontemperature drops rapidly.
Figure 29Moduli
106psi GPa
Adipic Acid Reduces Stiffness
0.60
0.55
0.50
0.45
0.lm
0
Figure 30
10 20 30 40 50Mole % Adipic Acid (Substitution for IPA)
30% Styrene
Adipic Acid Substitutionlncreases Tensile Elongation
TensileElongation
o/o
5
10 20 30 40Mole % Adipic Acid (Substitution for IPA)
30% Stvrene
The steric hindrance protecting the ester linkage ismuch lower with aliphatic acids than with isophthalicacid. Therefore. polyesters containing a substantialfraction of adipic acid suffer severe loss of corrosionresistance and hydrolytic stability.
The degree of property degradation is partiallydependent on glycol. Polyesters with about 20percent molar substitution of adipic acid forisophthalic acid that are condensed with a highly-branched glycol such as neopentyl glycol, offer agood balance of flexibility and toughness withacceptable corrosion resistance for many appli-cations. Adipic-modified polyesters made with etherglycols are readily susceptible to corrosion by manycommon media.
Figure 3/ Adipic Acid Substitution Slightly Decreases
Heat Defrection "eat Deflection Temperature
Temperature'c
95
85
80
75
01020304QMole % Adipic Acid (Substitution for IPA)
30% Styrene
50
lllustration 9
Adipate (upper section) versus isophthalate structure.
A\
GlycolsAs partner in every ester linkage, glycols areimportant determinants of polyester properties.Amoco is not a manufacturer of glycols, therefore wehave looked primarily at glycols as coreactants withisophthalic acid and maleic anhydride withoutattempting to exhaustively investigate the full rangeof available materials. The trends described are bothwhat we have observed and what has been reportedby generally available trade and academic sources.
The effects of glycols are analogous to those ofacids: bulkier, more branched or cyclic glycols offermore ester protection and less rotational freedom;longer chains offer more flexibility; larger glycolsreduce unsaturation level modestly with associatedchanges of properties.
Types of GlycolsThe common glycols used in unsaturated polyestersynthesis can be classified as aliphatic, branched,and etheric. Typical examples of each type areethylene glycol, propylene glycol and diethyleneglycol. Each class of glycol has advantages andliabilities for unsaturated polyester application.Within each class increasing molecular weightcauses reduced polymer unsaturation level whichgenerally correlates with changes in resin properties.
Manufacturers considering any specific glycol shouldobtain f ull handling and safety information from theirglycol supplier. Many glycols require special storage,handling and processing precautions to avoiddegradation or excessive sublimation.
Characteristics of Aliphatic GlycolsStraight-chain glycols. such as ethylene glycol and1,4 butane diol, are not as commonly used asbranched or ether glycols. Ethylene glycol esters havepoor styrene solubility; 1,6 hexane diol is a solid atroom temperature and its initial reaction product withIPA is quite waxy. Higher molecular weight aliphaticglycols should impart flexibility comparable to that ofadipic and other aliphatic acids.
Branched GlycolsThe lowest molecular weight member of the class -propylene glycol - is the base point for most of thecomparisons in this brochure. The branched glycolstend to be low boiling (propylene glycol). easilysublimed (neopentyl glycol) or heat sensitive (1,3butane diol and trimethylpentanediol). Branchedglycols offer excellent protection to ester linkages andthus have outstanding corrosion resistance. Thependant methyl groups restrict rotation;, thereforecured resins based on branched glycols are morerigid than resins using aliphatic or ether glycols ofequivalent molecular size.
20
lllustration 1 O lsopolyester Made With Propylene Glycol
lllusttation I I lsopolyester Made With Neopentyl Glycol
Ether GlycolsThe common ether glycols combine the goodflexibility offered by longer aliphatics with styrenesolubility and useful resin viscosity. The most obviousdrawback to ether glycols is the lack of stericprotection given the ester linkages. Ether glycols aregenerally unacceptable for corrosion resistantapplications.
V
v
lllustration 1 2 lsopolyester Made With Diethylene Glycol
Other Hydroxyl SourcesA partial list of alternatives to glycols includesalcohols, oxides and polyhydric materials.
Alcohols are polyester chain terminators and act tolimit polymer growth. They cannot be the sole sourceof hydroxyl functionality in polyesters. lf introduced tothe reaction mixture before all dibasic acids arepartially reacted, alcohols can esterify with free acidto form non-reactive. plasticizing species.
Ethylene and propylene oxides can be substituted forthe equivalent glycols. When used with anhydrides,oxides esterify without producing water; the reactioncan be explosively exothermic and is often doneunder pressure in continuous reactors.
Polyols, such as trimethylolethane and pentaeryth-ritol, introduce branching to the basic polyesterchain. Caution must be exercised to avoid gelationduring processing with polyols and viscosity instyrene is generally higher than with comparablelinear polyesters.
The Effects of lncreasingGlycol Molecular Size
A Within a given class of glycol the effects on curingand cured resin properties relate well to the changein unsaturation level caused by varying glycolmolecular size. lf all else is constant, as glycol sizeincreases, the unsaturation level of the polymer isreduced; exotherm during cure drops (Figure 32) andpropagation time is extended (Figure 33). Curedresins based on larger glycols are less stiff (Figure34), have higher ultimate tensile elongations (Figure35) and lower heat deflection temperatures (Figure 36).
Figure 32
PeakTemperature
'c
Glycol Effects on Peak Exotherm
450
400
Figure 33
ReactionTime,
Minutes
10:00
7;00
4:00
1:00
Figure 34FlexuralModulus
103 psi GPa
500
Figure 35 Glycol Effects on Tensile Elongation
DEGA
A TMPD
Glycol Eflects on Propagation Time
TMPD 11:45 A
A DEG
lncreasing Glycol Molecular Size
Glycol Effects on Flexural Modulus
450
TensileElongation
7o8
21
lncreasing Glycol Molecular Size
lncreasing Glycol Molecular Size
.q
lncreasing Glycol Molecular Size
Figure 36
Heat DeflectionTemperature
"c
Glycol Effects onHeat Deflection Temperature
v
v
Glycol Excesses During ProcessingSome glycol is volatilized and carried through thefractionation column with water evolved duringpolyesterification. The rate of loss depends on factorsincluding the efficiency of the fractionator, heat inputrates and the nature of the glycol. The sixth coiumnof Table lX reports the glycol excess typically used inpilot plant synthesis of unsaturated polyesters. Theseexcesses should be modified to match experiencewith particular reactors or to meet the requirementsof specif ic formulations.
lncreasing Glycol Molecular Size
Table lX A Synopsis of Glycol Considerations
Glycol Classif ication
Number ofPendant MolecularMethyls Weight
BoilingPoint, oC
Typical Processing andEquivalent Liquid Resin Effects on CuredExcess, % Effects Resin Properties
Ethyle ne
P ropylen e
Aliphatic
B ra nched
197.5
187.3
204 0
Sublimes 213
14tr F
231 .9
11F
228
o 62
-t6 10
10
2
I
2
causes incom Magnifies influences of acidspatibility withstyre n e
Good corrosion resislanceand structural properties.
heat sensitive
lmproves corrosion and weatherresista nce.
Excellent f lexibility, poorcorrosron resistance.
Compromise of f lexibility withcorrosion resistance.
heat sensitive Good corrosion resistance, embrittlesresin. Slow to f ully cure.
Excessive flexibility, poor corrosionresista nce.
1,3 Butylene Branched
Neopentyl Branched
D i ethylene Aliphatic Ether
Dipropylene Branched Ether
Trimethyl Bra nc hedpentanediol (TMPD)
Trrethylene Alipharic Ether
22
90
104
106
134
14E
150
v
U nsaturated CoreactantsThe most widely used reactive diluent for unsaturatedpolyesters is styrene. Styrene has low viscosity andhigh solvency, is widely available, and is low cost. ltsdrawbacks are flammability and potential healthhazards at high emissions. Some alternatives tostyrene are listed in Table X. Material safety datasheets (MSDS) should be obtained from suppliersbefore evaluating any reactive monomer.
Table X Crosslinking Solvents for Unsaturated PolyestersM.W. B.P.
ocDensity Unsat. Liquid prop. Cured prop.at 20'C mol/kg (styrene is the basis for comparisons)
t-Butylstyrene* 160
Chlorostyrenex 138.5
Styrene
Vinyltoluene
Divinylbenzenex
Alpha-
145
168
219
177-185
200
165
M.P.:57
77
82 atSmm Hg
77
0.929
0.911
0.998 at60'c
0.806
1.104
1.056
104
118
131
118
0.906
0.897
0.884
1.984
9.61
8.47
6.25
7.22
7.63
8.47
5.91
18.86
8.62
7.69
11.62
10.00
low viscosityhigh solvencygood reactivity
higher viscosityslightly shorter cure
higher viscosity
higher viscosityshorter cure
higher viscosityfaster cure
lower emissionslower exothermlonger cure
much higher viscositymuch longer cure
lower viscositylonger curelower exotherm
higher viscosityslightly longer,cooler cure
similarto hyroxethylacrylate
lower viscositylower exotherm
lower viicosity
high strengthhigh modulus
lower elongationslightly higher heatdeflection temp.less shrinkage
better weathering
good weatheringhigher heatdeflection temp.some flame retardancy
harderhigher HDT
lower physical prop,
higher heatdeflection temp.
lower strengthbetter weathering
better weatheringsofter, less stifflower shrinkage
better weathering,weaker, less stiffbetter clarity
better weatheringless odormore claritymore shrinkage
methylstyrene*
Diacetoneacryl- 169amide*
Acrylonitrile* 53
Hydroxyethylacrylate*
Hydroxypropyl 130acrylate*
Methyl acrylate*86
Methyl 100methacrylate*
70 at 0.956608mm Hg
100
116
0.9u14
*Generally used in combination with other coreactants
Awide range of vinyl compounds can be used alone or incombination to dissolve and crosslink polyester resins.Typical effects that can be obtained from coreactantmodifications i nclude viscosity control, lower exotherm,improved UV stability, lower emissions, higher elongation,different cure temperatures, and better optical clarity. The
best balance of cost and performance is frequently reportedwith blends of styrene with one or two other vinylcompou nds. Resi n formu lators i nvestigatin g any coreactantshould obtain and follow the manufacturer's precautionaryinformation.
23
The dual f unction of coreactants is to dissolve thepolymer for ease of handling and application and tocrosslink the polyester chains to form a thermoset,solid plastic.
Most effects of increasing resin dilution on liquidresin properties are self-evident: easier handling andapplication, faster wetting of reinforcement and fillers,but increased emission of vapors from the solution.
The effects of styrene to polyester ratio on cured resinproperties are more complex. Sufficient coreactant isneeded to bridge the gap between unsaturation sitesof adjacent polyester chains during crosslinking. Toobtain good aging properties, all polyester unsatu-ration should react with monomer. Additionalmonomer will react with itself to form longer sidechains or bridges between the polyester chains.Excessive monomer self-polymerization will tend toforce cured resin properties more toward polystyrenethan polyester properties.
Amoco's investigations indicate that cured resinproperties are optimized within a fairly narrow rangeof polyester dilution with monomer. This range is specif icto the resin formulation, but with most commonformulations a strikingly consistent ratio of monomerto polyester unsaturation optimizes most properties.
The ratio of monomer to polyester unsaturation canbe determined by dividing the moles of monomerunsaturation per 1O0O g (9.6 for styrene) by themoles of maleic anhydride land/or other unsaturationcontributor) per 1O00 g of polyester a.nd multiplyingby the ratio of monomer to polyester in the final resinsolution.
moles monomer unsaturation,zl000 o Yo monomer; *
"t"-'Potv"tt"..
An example of calculating polyester unsaturationlevel is shown on page 10.
Because styrene has more unsaturation per unitweight than polyesters, more styrene in the resinsolution increases the total amount of unsaturation.Consequently the total exotherm is higher (Figure 37).Propagation time is longer (Figure 38) with morestyrene. The peak exotherm temperature drops atvery high styrene levels because heat is dissipatedduring the long propagation time.
StyreneContentAffects Peak Exother- VFigure 37
PeakTemperature
'c
12345678Molar Ratio of Styrene to Polyester Unsaturation
Figure 38 Styrene Content Affects Propagation Time
ReactionTime
Min:Sec3:30
2:00
123456189Molar Ratio of Styrene to Polyester Unsaturation
24
Fully cured resin properties indicate a pattern ofdifference as styrene level is changed. With the samepolyester, higher styrene levels will tend to increasethe space between sites of crosslinking, thus thestiffness of the cured resin is reduced. Figure 39shows lower flexural and tensile moduli as morestyrene is introduced into the polyester. The curvesfor strengths and heat distortion temperature indicatethat these properties are maximized at anintermediate level of styrene.
This information indicates that polyesters should bereacted with sufficient styrene to obtain somewhatover three moles of monomer unsaturation for eachmole of polyester unsaturation. Styrene dilutionbeyond this point tends to cause polystyrene-likeproperties to dominate the cured polyester.
With very strong resins, such as the example used forFigures 3-7 to 41, the introduction of styrene abovethe 3.6 unsaturation ratio will tend to degradestrengths. However, with a very flexible resin such asthose reported in Figure 18, more styrene willstrengthen the resin because the flexible resin is notas strong as polystyrene. Tensile elongation of thisresin would, of course, be lower with more styrene.
The optimum level of styrene indicated byunsaturation ratio may differ f rom the level requiredfor easy handling of the liquid resin and thoroughwetting of reinforcement and fillers. Resinmanufacturers may be able to resolve suchdiscrepancies by caref ul polyester processing todifferent endpoints (see page 4), by reformulating todifferent polyester molecular weights or by usingblends of lower viscosity coreactants with styrene.
Figure 39 Styrene Gontent Affects Stiffness
Moduli106psi GPa
0.55
Figure 40
Strengthspsi MPa
20,000
16,000
123Molar Ratio of
Figure 41
Heat DeflectionTemperature
'c
Styrene Content Affects Strengths
456789Styrene to Polyester Unsaturation
Styrene Content AffeetsHeat Def lection Temperature
3,8.li::li::air'r.......
;.,r, j ji:.:...i.,t:iri.:r:.r:,r-ril,...'.:r i,:,i::-r::i1i.rr)::i:ti,.1i:j::::;:iil._ ."'.''.r,.:,ri::::.:,:::iirl,l....:,,,,...,...
-r::: j.t: :::.;:i i::::ai.t::iri:''|r'i.: :::a ;:::!: iir_: i:rrr :i:.: "':t:.':.;
1.-
3.6 ''"'::i.ia.].:l:.:ri::.::r::,-:t ,,.,,....
r].],::,':,::lt,,t.::... Flexural '"'"iiii:::'i:j:j:..1:ii5. ;
. f :::j..:,::t;rjtrj:' .r:.,i,ar-:,1r:i:a..rjitr::.:r., -..r:il:: ::ltlr.:i:.:ti::t:tl.::.r't;1it...-
.
3.4 ":'l:i.t:.:Llii.,,::l:ii
-:',..:il:i:r:,tl':l:.::1:'.':-' :',..Tensile''':'::r'':::',.,..:":ri::::l:r:':-'
,:,1
3.2
0.
115
110
IY
I1
fq
I1
rttt2345
Molar Ratio of Styrene to
tlf678
Polyester U nsaturation
ttt234
Molar Ratio of Styrene
tttl5678to Polyester Unsaturation
105
25
G lossary
Aromatic acid Generally carboxyl {unclionalgroups on benzene ring. ln thisbulletin benzene dicarboxylicacids are lrequently termedaromatic acids.
BMC Bulk Molding Compound. A resin-ous mixture o{ short reinforce-ment libers, f illers, thermoplasticadditive and high reactivity resindesigned for compression molding
cis configuration Functional groups attached toolefinic unsaturalion located onthe same side of the bond axis.Also see trans conliguration.
Composite An aggregation ol dissimilarmaterials, especially combinations of glass liber and resin.
Corrosion resistance The ability ol a material to resistdegradalion by environmentallactors, especially the ability toresist softening or solvation byliqu ids.
Crosslink density A measure ot the {requency ofcrosslinking sites on thepolyester chains.
Cure time The time required in the SPI geltest to reach peak exotherm from65'C (150oF).
Elongation The maximum extensibility of amaterial without failure.
Ester Any compound containing theester functional groupt O
R-o-c- R'
Esterilication The chemical reaction oI acid oranhydride with alcohol, glycol oroxide that forms an ester.
Exotherm The heat released during chemi-cal reaction, such as duringolefinic and vinyl crosslinking.
Flexural latigue The loss of resistance to flexuralstress that occurs with repeated,nondestructive stress.
Flexural modulus
Flexural strength
Flexural stress
Gel co€t
Gel-coated laminate
Gel time
Gelation
Glycol
Ha rdness
HDT
Heat distortiontemperalure
IPAI so-
lsomer
lsomerization
lsophtha late
lsopolyester
The ratio ol flexural stress. todellection a measure of stillness.The tlexural stress sustainablewithout fracture.Stress applied perpendicular tothe plane of the test sample.
A surlace or appearance layer ofunreinforced resin, often con-taining pigmentation and thixo-tropic additives.A laminate fabricated with a gelcoat on one or both sides.
The time required for a resin tosolidily in the SPI gel test.
The phenomenon of resin solidi-fication through molecular growth.
Any compound containing twohydroxyl functional groups.
The resistance to penetration by themetal stylus oI a Barcol or similarhardness tester. Hardness is usedto follow the development of resincure
Heat distortion lemperalureThe lemperature at which asample coupon is deflected 1 0mils by 182O kPa (264 psi).
Abbreviation for isophthalic acidPrefix designating an isomericstructure especially the '1,3 sub-stitution on a benzene ring orsimple branching at the end ot astraight chain.Compounds with different geo-metry but identical chemicalformulas.Conversion of a compound fromone isomeric form to another.Monomeric or polymeric estersof isophthalic acid.
Polyesters based on isophthalicacid,
La m inate
MAN
Olefinic unsaturation
Ortho-
O rthophtha late
O rthopolyesler
PANPeak exotherm
Po lyeste ril icatio n
Polyol
Polyterephtha late
Propagation time
Reactivity
sMc
Strai n
Stress
vComposite materials especiallysheet and tubes labricated ofthermoset plastic aenerally re-inforced with fibers.Abbreviation for maleica nhydrideReactive carbon-to-carbondouble bond.
A prefix designating 1,2 sub-stitution on an aromatic ring.
Monomeric or polymeric estersof phthalic anhydride.Polyesters based on phthalican hydrideAbbreviation for phthalic anhydrrdeThe highest temperature reachedduring cure in the SPI gel lest.Esterilication of difunctional car-boxyl and hydroxyl-containingmaterials producing a polyester.
Molecules with more than twohydroxyl f unctional groups.
Polyesters based on terephthalicacid; the term includes bolhsalurated polyesters, such asfibers, and unsaturated poly-esters.
The difterence between gel andcure time in the SPI gel test; ameasure ol in-mold set time.A measure of ihe amount ofreactive lunctional groups in amaterial; especially the amounlof maleic unsaturation in a liquidpolyester.
Sheet Molding Compound. Par-tially thickened, compressionmolding compound containingmedium-length reinforcement,
-'filler, and other additives.The physical de{ormalion of amaterial by applied torce.
The lorce applied to a material.
A Summary of TrendsTable Xl summarizes the information given in thisbrochure on how formulation variables affectproperties of unsaturated polyesters. The statements
in this table are necessarily general and assume onlyone variation at a time.
Table Xl How Formulation Variables Affect Properties of Unsaturated Polyesters
FormulationVariables Strengths
Moduli{Stiff ness)
"Flexibility"or TensileElongation Toughness Hardness
Source of unsaturationmaleic vs. f umaric
Level of unsaturalionNo effect Fumaric higherDepends on resin PositiveFlexibility correlation
Maleic higherNegative
correlation
Maleic higherDepends on
f lexibility
Fumaric higherPositivecorrelation
Types of nonolefinic acidslsophthalic Acid versus;Phthalic AnhydrideTerephthalic Acid
Adipic Acid
lso higherlso somewhal
h igherlso higher
lso higherNo trend ofdifference
Adipic higher
lso betterlso somewhat
h igherAdipic higher
No trend of differencelso higher
lso higher
Ortho higherlso usually
h igherlso higher
Type of GlycolStraight chain aliphatic glycolsBranched glycolsEther glycolsMolecular weight
Effect variesEffect variesEffect variesEffect varies
Generally higher
Negative lycorre lated
I ncreasedEffect variesI ncreasedPositivelycorre lated
Generally better
Generally betterPositivelycorre lated
H ig her
Generally no effect
26
Varies Can be optimized Can be optimized Generally no effectLevel of Coreactant Lower on kiolhsides of peak
TA
Tensile modulus
Tensile strength
Tensile stress
Tere-
Terephthal icpolyesterThermoplaslic
Thermoset resin
Tough ness
trans configuration
U nsaturatedpolyester
Vinyl compound
Abbreviation for terephthalicac id
Ratio of stress to strain duringtensile elongation; a measure ofstiffness.The greatest longitudinal stressthat can be survived withoutfracture.Force applied parallel to the planeor length oI a sample coupon.
Prefix denoting benzene ringsubstilution in the 1,4 posrtions.
Polyesters based on terephthalicacid.
Polymers that melt with heat andbecome solid when cooled.Polymers that irreversibly soliditythrough crosslinking whenheated.
Strength withour brittleness; de-fined by classical mechanics asthe area under tensile stress-strain curve.Functional groups attached lo aolefinic group and locateddiagonally across the bond axis.Also see cis.Polyester containing reactive ole-tinic unsaturation usually derivedtrom maleic anhydride.Compound containing carbon-to-carbon double bond as aterminal functional group, es-pecially styrene or other reactivedil uents
HeatDistortion CorrosionTemperature Resistance Shrinkage
Peak Exothermof Curing
Fumaric higher No effectPositive Optimizedcorrelation at 1 :1
No effectPositivecorre I at io n
Fumaric higherPositivecorre I at io n
lso higherTere higher
lso higher
lso betterlso better
lso better
No effectNo effect
No effeclNo effecl
Adipic greater Usually higher
LowerH ig herLowerN egativelycorre lated
LowerBetterLowerEffect
va ries
No effectNo EffectNo EffectNegativelycorre lated
Can lower
Negativelycorre lated
Lower on bothsides of peak
Positivelycorrelatedfor manymedia
Positively Positivelycorrelation correlated
over normalra nge
Health and Safetylnformation
I
The product(s)described herein may requireprecautions in handling and use. Material safety DataSheets (MSDS)for Amoco products are availableupon request from your Amoco sales representativeor by writing the address shown on this brochure.Always consult the Material Safety Data Sheet forproducts you consider using.
27