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### H KA l l l L E N vG 

# A-?4-5 2 

# Strategie s fo

rLo w Resin s
Purpose s o f Styren e | tyren e i s adde d t o unsaturated p o £PAAIRD.OC,KE T . . }«st.er..resins.^d..vm^ ^ tw o majo r 'purpose s —(1 ) t o dilute th e mixture fo reffective viscosit y contro l s o tha

trhe fibers | ca n b e wetted ; an d (2 ) t

o serv e a s acrosslinkin g agentand promote th e ease o f crosslink in g o f th e resin . Materials , lik e styrene , thatsimultaneousl y accomplis h both o f thes e | purposes ar

e calle d "reactiv

e diluents. " Othe ractive diluents exists , suc h a s methy l methacrylate , bu tbecaus e o f th e predominanc e o f

styrene i n th e unsaturated polyeste r
an d viny l este rresin market , ou rfocu s wil l b e almos texclusively o n styrene . Th e abilit y o f

styrene t o accomplis h thes e tw o purposes ha s resulted i n lowe rcosts £ overal l an d improve d performanc e an d manufacturin g efficiencies . Imagine , fo rinstance ,
adiluen ttha twas non-reactive . Thi s woul d requir e thatth e diluen tb e removed durin g molding . Severa

l epox y and othe rhigh performance resin s hav e thi s problem and , a

s a | result, ar

e difficul tto us e and ar

e more cosdy . Th e excellen treactivit

y o f styrene means thatth e styrene is generally use d u p i n th e crosslinkin g reaction . Styren e form s apar

tofth e cured polymer , generally atalowe rcos t Ktha n th e backbon e resin system itself . Whe n i thas bee n crosslinked , styrene impart s stiffnes s t o mos tcure d systems (and als o som e brirdeness) , bu tgenerally enhance s th e physi ca l propertie s ofth e finished product . Styrene i s als o a

n effective and relativel

y inexpensiv e diluent . I ti s able to easily dissolve mos to f

th e imponan tresins and , dius , allo w easy wetou to f the reinforcement. 

### "s» s

B yA

. Bren t Stron g Brigham Young University
(Jowposiies F.ibri,;uionl)n\K 19 l> 8P. 3

nee , styren e i s nearl y idea l fro ma ctiona l standpoint
. However , a s yo u know , styren e i s liste da s ahazardou s pollutan t (HAP)
. Therefore , th e oun t o f styren e emitte di n th e nufactur e o f

FR P part s mus t

b e uced
. W e wil l no w examin e som e o f strategie s bein g pursue db y th e resi n nufacturer s t o reduc e th e styren e iten t o f thei r products
. Th e chemistr y o f

makin g thes e nge s t o reduc e styren e conten t i s nplex
. Therefore , th e discussio n whic h ow s o n th e variou s strategie s t o lo w en e conten t

wil l b e simplified
. Th e u s wil l b e o n th e directio n an d icept s behin dth e change s rathe r tha n details
. 

### ategy On e —

Modification s existin g polyme r system s : initia l effor

t b y almos t

al l ofth e resi n nufacturers , unsaturate dpolyester s
• viny l esters , wa s t o modif y thei r exist

resi n system s s o tha t

les s styren e il db e needed
. Thi s strateg y wa s no t y pruden t commercially , i t

als o gav e ck results
. Th e resi n manufacturer s realize dtha t i e viscosit y ofth e bas e resi n wer e lower , amoun t o f styren e neede dt o achiev e a dviscosit y fo r fiber we t ou t coul db e iced
. Th e first

metho dt o reduc e th e osit y o f th e bas e resi n wa s t o shorte n molecula r chains , tha t

is , t o reduc e ecula r weigh t o f th e resin
. Shorte r in s hav e les s intermolecula r entangle

u and , therefore , flo w mor e easily , s mean s tha t

th e viscosit

y i s lower
. Th e amoun t

o f sryren e neede di n ; e lowe r molecula r

weigh t resi n :m s ha s bee n successfull y reduced , t reduce dlevel o f

styrene , whic hwa s ate db y viscosit y contro l require

its , ha s als o reduce dth e amoun t o f en e availabl e fo r

crosslinking
. refore , th e natur e o f

th e crosslinkin g changed
. Th e questio n is , "Ho w ha s slinkin g change dth e resultin g •me r properties? " Tw o differen t

crosslin k characteristic s 'er overal l styren e conten t

an dhighe r slink density ) occu r

simultaneousl y i thes e lo w molecular

weigh t resi n :ms . Th e lowe r

amoun t o f styren e labl e for crosslinkin g result s i n a •ved " situatio n durin g crosslinking
. ; starvin g mean s tha t

th e numbe r

o f :n e molecule s i n eac ho f

th e crosslink s i s reduced
. (Unde r exces s styren e condi

tions , multipl e styren e molecule s joi n togethe r t o formlon g crosslinks
. Unde r starve dconditions , eac hcrosslin k woul d b e forme dwit h onl y on e o r tw o styren e molecules. ) Th e reductio n i n th e tota l amoun t o f styren e containe di n th e crosslinks , an d therefore , i n th e cure dpolymer , woul d normall y lea dt o lowe r

overal l britdenes s sinc e styren e i s inherentl y brittle
. However , th e shorte r

polyme r

chain s


### Some resin manufacturers have found that new resin systems requiring

lower styrene concentrations

can be made by varying the
sequence

of addition of the di-acid and the glycol components.

mean s tha t

th e carbon-carbo n doubl e bond s occu r

mor e frequend y an dthi s result s i n ahighe r

numbe r o f crosslink s bein g forme doverall
. Thi s highe r crosslink densit y woul dnormall y increas e brittleness
. Therefore , th e effect s o n brittlenes s fromth e reductio n i n styren e conten t an dfro mth e increas e i n crosslin k densit y approximatel y cance l an dth e britdenes s i s abou t

wher e i t woul db e i n th e unmodifie dresi n system
. Generall y hea t

distortio n temperatur e an dsolven t

resistanc e wil l b e increase db y highe r crosslink density
. Othe r

properties , suc h a s bliste r

resistance , ultra-viole t

ligh t resistance , chalking , cracking , an dsurfac e smoothness , may als o b e affecte dbu t th e exten t o f thes e effects mus t

b e evaluate d o n acas e b y cas e basi s wit heac hresi n an d application
. Thes e effects are muc hmor e



# 1 importan t i n ge l coat s tha n i n laminatin g resin s an dshould , therefore , b e examine d closely before an y chang e i n ge l coat resin i s made
. Anothe r modificatio n i n curren t

resi n system s i s achang e i n molecular weigh t distribution
. Thi s i s no t jus t ashif t t o lower molecular

weight s but , rather , a chang e i n th e statistica l sprea do f th e molecular weight s o f

th e polymers. Eve

n whe n rhe averag e molecular weigh t i s stil l quit e high , th e presenc e o f asignificant quantit y o f

lo w molecula r

weigh t molecule s ha s atendenc y t o mak e al l th e molecule s slid e ove r

eac hothe r

mor e easily , thu s lowerin g th e viscosity
. Thi s lower viscosit y allow s les s styren e t o b e used
. 

### Strategy Tw

o —Developin g ne wpolyme r system s Polyester s ar e mad e fromth e reaction s o f di-acid s an dglycols
. Resi n producer s hav e foun dtha t

b y varyin g th e type s an d quantitie s o f

di-acid s an dglycols , th e resi n propertie s ca n b e significantl y changed
. (Fo r

instance , th e difference s betwee n orth o an dis o resin s ar e jus t i n th e choic e o f

aci dtha t

i s reacted. ) Therefore , man y possibilitie s exis t fo r changin g th e natur e o f

rh e bas e polyeste r resin
. I n additio n t o differen t combina

tion s o f previousl y use dcomponents , som e completel y ne w di-acid s an dglycol s ar e bein g tried
. (Som e resi n manufactur

er s cal l thi s th e clean-slat e approach. ) Th e resi n manufacturer s ar e reluctan t t o disclos e th e detail s o f thes e change s becaus e o f

competitiv e reasons , bu t i t i s saf e t o sa y tha t al l o f th e majo r

resi n manufacturer s ar e workin g o n innovativ e ne w resi n structure s tha t wil l enabl e th e sryren e conten t

t o b e reduced
. W e shoul danticipat e tha t

withi n th e nex t fe w years , man y ne w product s wil l b e announced
. Withou t disclosin g an y proprietar y information , afe

w basi c concept s ca

n illustrat e som e o f

th e direction s tha t

th e resi n producer s are investigating
. Som e o f
• th e acid s an dglycol s (lik e neopenty l glycol ) are know n t o b e mor e solubl e i n styren e tha n th e othe r

commo n compo nents
. Thi s increase dsolubilit y come s fro mbot h molecular

shap e an dchemica l polarit y effects
. A t

th e sam e time , thes e alternat e component s migh t giv e additiona l benefit s suc ha s increase d

### P. 4

toughnes s o r

hea t distortio n temperature
. Therefore , th e ne w resin s migh t hav e bot h reduce dstyren e conten t an d improve dphysical properties , o r a t leas t n o majo r reductio n i n propertie s a s a resul t ofth e decreas e i n styrene
. Som e resi n manufacturer s hav e foun d tha t ne w resi n system s requirin g lowe r styren e concentration s can b e mad e b y varyin g th e sequenc e o f

additio n ofth e di

aci dan dth e glyco l components
. Thes e change s occu r

becaus e mixture s o f

multi

pl e type s di-acid s an dglycol s are ofte n use di n makin g th e polyeste r resin s whic h hav e differen t

reactivities
. A n exampl e o f suc h achang e woul doccu r unde r thes e tw o scenarios
. I f

cwo di-acid s ar e mixe d togethe r an dthe n adde dt o th e glycols , th e distributio n ofth e acid s coul db e random
. However , i f

on e ofth e di-acid s i s adde dt o th e glycol s an dthe n th e secon dadde d later , th e resul t

coul db e apreferential positionin g o f

th e secon ddi-aci dat

th e end s o f th e polymer
. Hence , tw o very different polymer s coul db e formed
. Th e sequenc e o f

component s alon g th e backbon e resi n ca n als o b e altere db y changin g th e additio n sequenc e becaus e o f difference s i n reactivitie s ofth e compo nents
. A particula r

componen t

coul db e force dt o grou p togethe r o r t o b e disperse dt o th e end s dependin g o n it s relativ e reactivity wit hrespec t t o othe r component s an dwhe n the y ar e added
. Som e hav e calle dthes e change s one-stag e an dtwo-stag e additiona l polymers
. Usin g know n principle s an dne w technologies , th e resi n manufacturer s are attemptin g t o creat e shape s an dchemical nature s tha t

favo r lower styren e contents
. Occasionall y apolyeste r i s mad e usin g acomponen t

othe r tha n adi-aci d an dglycol , suc ha s dicyclopentadien e (DCPD)
. Thi s materia l can b e use dt o reac t wit hmalei c aci dan dglycol s t o for m alo w molecular

weigh t chai n o f

onl y a few units
. Suc hunit s ar e ofte n calle d "adducts " becaus e afew unit s ar e "adde d together. " Th e ne t

resul t o f mixin g DCP D wit hmalei c aci dan dethylen e glyco l is a

n adduc t o f DCPD—maleic — glycol—maleic—DCPD
. Thi s adduc t ha s lo w molecular

weigh t and , therefore , lo w styren e requirement
. Th e ne t resul t i s aresi n wit h fas t

cur e cycles , goo d reinforcemen t

prin t hiding , goo dfiberglas s wetout , goo dmoistur e resistance , goo dstiffness , an dgoo dai r bubbl e elimi

natio n whe n compare dwit hman y conventiona l resins
. Viny l ester s propertie s ca n als o b e change dsignificantl y b y modifyin g th e natur e o f th e backbone
. Viny l ester s ten d t o hav e mor e option s availabl e for thes e modification s o f

th e resi n backbon e and , o f course , th e specifi c nature s o f th e change s are different , bu t th e concept s discusse di n thi s sectio n ar e simila r betwee n viny l ester s an dunsaturate d polyesters
. Anothe r majo r are ao f focu s i s th e blendin g o f

unsaturate dpolyester s an d viny l ester s wit hothe r polyme r

types
. Thes e blend s can b e don e a s monomer s (i n whic hcas e the y ar c ofte n referre dt o a s copolymers ) o r

a s blend s afte r

full polymerizatio n ha s bee n don e (i n whic h cas e the y ar e referre dt o a s mixtures)
. Som e o f th e interestin g blend s wit h unsaturate dpolyester s include : polyurethanes , melamines , phenolics , epoxies , an dviny l esters
. I n general , thes e blende dpolymer s ar e highe r i n cos t tha n th e basi c polyester , bu t

th e propertie s o f

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### )len dca n b e substantially better , thu s allowing fo r th e us e o f resi n or of enterin g ne

w markets
. 

### iteg y Three — e r monomer

s :n e i s no t th e only monomer

that act s as areactiv e diluen t insaturate dpolyesters an dvinyl esters
. Therefore , som e nat e monomer s which hav e lowe r vapor pressure s ar

e bein g stigate da s styren e alternatives
. On e approach i s t o choos e omer s that

ar e simila r t o styren e i n chemica

l reactivit y bu t ahigher molecula r weight and , therefore , alowe

r vapo r ;ure . Fo r instance , viny

l toluen e i s ver

y simila r t o styrene in g jus t a n additional methy l grou p on th e benzene ring ) has alowe

r vapor pressur e and , therefore , lowe

r ai r pollu

potential
. Another

example i s t-buty l styrene
. Th e majo r le mi s th e higher

cos t o f thes e alternate monomers . Another approac h i s t o simply combin e tw o o r thre e n e molecule s together

an dthe n us e thes e dimer s an d srs a s th e reactiv e diluents
. (Ver y shor t chain s such a

s thes e ometime s calledoligomers. ) Performanc e o f thes e materi

almos t th e sam e i n th e cure dproduct , an dwe t ou t of th e glas s i s stil l excellen

t sinc e only enough of

th e dimer s an d :r s i s adde dt o achieve th e sam e viscosit y usedwit

h th e omer . However, th e cos t o f producin g th e dimer s an d :r s is significant
. som e hav e bee n looking a

t using completel

y ne w monomer s ar e no t lik e styren e a t all
. Th e prime exampl

e i s methyl ; 

### acrylat e (MMA) , ("Strategies..." continued

on p. 38) 

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# •AP. 6

"Strategies..."

continued from 23) Daietime s know n a s acrylic
. Thi s mater
dals o ha s ahig hvapo r

pressur e an ds o i t ; als o considere dahazardou s ai r pollu

ui t (HAP ) bu t

ma y b e mor e compatibl e dr hsom e polyme r

system s and , there

sre , allo w lowe r

concentration s t o b e se dt o achiev e acceptabl e viscosities
. •4M A ca n als o giv e som e improve d ropertie s (suc ha s lowe r

smok e genera on)
. Again , cos t

i s aproblem
. 

### itrateg y Fou r —Suppressant s e t anothe r strateg y i s t o for masurfac e lye r t o suppres s th e emissio n o f styrene
. ayer s suc ha s this , ofte n forme db y eldin g wa x t o th e resi n mixture , hav e ee n use dfo r

man y year s t o exclud e xyge n s o tha t

cure s ca n b e improved , fence , dii s concep t

i s reall y usin g a n ol d ichnolog y fo r

ane w purpose . Th e roble mwit hthi s metho dha s alway s ee n th e potentia l fo r

poo r bondin g hereve r th e wa x i s present
. Thi s dhesio n proble mha s bee n alleviate d jmewha t b y creatin g adhesion-promot

l g films. Thes e films contai n carbon

irbo n doubl e bonds , thu s allowin g crosslinkin g t o occu r throug hth e film. Adhesio n betwee n material s o n bot hside s o f th e fil mi s thu s promoted
. Thes e film-forming material s wor k bes t o n horizonta l surface s an dwhe n rh e material s ar e quiescen t (tha t is , non turbulent)
. Hence , i f

sprayed , the y wil l for mbes t i f allowe dt o si t

fo r som e time. Non-horizonta l surface s wil l for msom e films, bu t

the y ar e no t

a s effective
. T o alleviat e thes e problems , som e o f rh e film formin g system s contai n exces s thixotropi c agent s t o ensur e tha t th e resi n stay s o n th e vertica l surface s an dbecome s quiescent
. T h e us e o f

highl y thixotropi c materi

al s can , i n themselves , reduc e solven t escape . Th e pain t

industr y ha s success full y use dthi s technolog y fo r som e time
. (Tha t i s wh y som e paint s ar e s o thic k whe n i n th e ca n bu t

smoot han dsprea d easil y whe n brushed , rolled , o r sprayed. ) Perhap s ther e ar e othe r

lesson s tha t

ca n b e learne dfro mth e pain t

industry
. 

### Summar y T h e resi n manufacturer s ar e workin g ver y har dt o reduc e th e amoun t o f styren e i n thei r

resi n systems
. Som e excellen t succes s ha s alread y bee n achieve dan d mor e succes s i s shortl y t o b e announced
. Som e importan t

ne w scientifi c principle s ar e bein g discovere dand , hopefully , thes e wil l lea dt o eve n greate r successe s i n th e future
. Undoubtedly , thes e ne w resin s wil l requir e som e change s i n produc t design , manufacturin g an dmolding
. Alon g wit h th e improve dtechnique s i n manufactur

ing , th e amoun t

o f styren e movin g int o th e atmospher e wil l surel y b e significanti y reduced
. 

### Acknowledgment

s T h e autho r

thank s Larr y Craigi e an dDo n Kelle y o f Do w Chemical , Mar k

Callicut t o f Reichhol dChemicals , Glen n Wigingto n o f

Nest e Polyeste r

America , Bren t Bake r o f Coo k Composites , Keit h Johnso n o f

ARCO , Ber n Brod y o f Ashlan dChemical , an dStev e McNall y o f CF A fo r thei r assistanc e i n thi s article
. Contributing Editor

Brent Strong, Ph.D. is a Professor

of Manufacturing Engineering Technology at

Brigham Young University 

## reddi e Fibergla s

Sorr y Sir , ^ bu tm y glu e gu n wen t berserkjIL / "Mr

. Fibergiaa s "thi s is ^ no t wha t Infan t whe n w e sa y the compan y hasastrictpofejo n
.- v \gepii qyou

r are adean j 

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