Fillers and Reinforcements for Plastics

19 Corrosion Engineering in Reinforced Plastics

Downloaded by UNIV OF CINCINNATI on February 18, 2015 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch019

OTTO H. FENNER Monsanto Co., 800 N. L i n d b e r g h B l v d . , St. Louis, M o . 63166

Reinforced plastics provide the materials engineer with a solution to the economic dilemma arising from the current prohibitive cost of exotic alloy construction. They are serving in highly corrosive environments as materials for many major pieces of process equipment, auxiliaries, and structural members. The excellent chemical resistance properties of FRP, epoxy, furan, phenolic, and polyester resins make each a premium performer in specific services. "One-side" panel testing, along with changes in residual flexural strength of "dunk" test strips, appears to be the best way to evaluate the performance of plastics. Failures in laminated plastics are readily solved with the electron scanning microscope through plastographic analysis tech niques and infrared spectroscopy.

C u c c e s s f u l c o r r o s i o n e n g i n e e r i n g d e p e n d s to a great d e a l o n a n i n - d e p t h ^

knowledge

o f c h e m i s t r y a n d c h e m i c a l reactions.

T h e chemist or

process engineer e n g a g e d i n m a t e r i a l s selection f o r c o n s t r u c t i o n of e q u i p m e n t d e s t i n e d f o r use i n h i g h l y aggressive e n v i r o n m e n t s m u s t first b e w e l l f o u n d e d i n b o t h i n o r g a n i c a n d o r g a n i c c h e m i s t r y . T h i s is p a r t i c u l a r l y true w h e n i t becomes necessary

to u s e a n i n t u i t i v e c h o i c e of a

m a t e r i a l of c o n s t r u c t i o n f o r l a c k of specific c o r r o s i o n resistance d a t a . T h e c h e m i c a l resistance a n d p r o b a b l e p e r f o r m a n c e o f n o n - m e t a l l i c m a t e rials u n d e r s u c h c o n d i t i o n s m a y b e r e a d i l y a n d often a c c u r a t e l y p r e d i c t e d b y c o n s i d e r i n g t h e c h e m i c a l s t r u c t u r e of t h e c o m p o u n d s encountered

i n the environment.

I t is because of h i s extensive,

to b e spe-

c i a l i z e d t r a i n i n g i n the fields o f i n o r g a n i c , o r g a n i c , a n d p h y s i c a l c h e m i s t r y 195 In Fillers and Reinforcements for Plastics; Deanin, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

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FILLERS A N D R E I N F O R C E M E N T S FOR PLASTICS

t h a t w e find the c h e m i s t is often successful i n i n d u s t r y as a c o r r o s i o n engineer. D u r i n g the past 20 years there has b e e n a t r e m e n d o u s g r o w t h i n the use of r e i n f o r c e d plastics for f a b r i c a t i n g process e q u i p m e n t .

T h e i r fine

p e r f o r m a n c e , w i t h i n the l i m i t s of t h e i r t e m p e r a t u r e a n d p h y s i c a l p r o p erties, has b e e n d e m o n s t r a t e d

repeatedly

in application.

Plastics

no

longer n e e d to be r e g a r d e d w i t h h e s i t a n c y or t r e p i d a t i o n w h e n c o n s i d e r e d w i t h respect to the costly exotic alloys a n d metals. T h e y h a v e e x p e r i e n c e d


e x t r e m e l y satisfactory service i n m a n y h i g h l y corrosive e n v i r o n m e n t s . T h r o u g h t h e i n g e n u i t y of the p o l y m e r chemist t h e p r o p e r t i e s

of

plastics c a n b e a l t e r e d t h r o u g h f o r m u l a t i o n a n d the i n c o r p o r a t i o n

of

specific

fillers

a n d reinforcements

to o b t a i n m o d i f i c a t i o n s

approaching

the s t r e n g t h of steel, the lightness of a l u m i n u m , a n d a c h e m i c a l resistance better t h a n some of the super alloys. T h i s is a p r i m e reason for t h e i r phenomenal acceptance i n chemical processing equipment. P l a s t i c m a t e r i a l s are h i g h l y i m p o r t a n t to the cost-conscious m a i n t e n a n c e a n d d e s i g n engineer.

G e n e r a l l y they h a v e r e l a t i v e l y l o w

initial

costs, are l i g h t w e i g h t a n d e a s i l y i n s t a l l e d i n h a r d - t o - r e a c h areas, a n d c a n often be r e p a i r e d i n p l a c e w i t h o u t the p r o h i b i t i v e costs of s h u t t i n g d o w n adjacent e q u i p m e n t .

I n most instances the expense of p o s t - f a b r i c a t i o n

stress-relieving heat treatments, often associated w i t h the c o n s t r u c t i o n of a l l o y e q u i p m e n t , is unnecessary. E x c e p t for s p e c i f i c a l l y f o r m u l a t e d a n d c o m p o u n d e d plastics or r e s i n systems, these materials d o n o t c o n d u c t e l e c t r i c a l current. T h u s , one of the c h i e f concerns of the c o r r o s i o n e n g i n e e r — g a l v a n i c a n d stray c u r r e n t c o r r o s i o n — i s non-existent w h e n s u c h m a t e r i a l s are u s e d . C o l o r p i g m e n t a t i o n d u r i n g the f a b r i c a t i o n of a r e i n f o r c e d p l a s t i c u n i t p e r m i t s a n extra aesthetic p r e m i u m not a v a i l a b l e i n m e t a l l i c s t r u c tures r e q u i r i n g p o s t - c o n s t r u c t i o n

painting.

Quite frequently metal-ion

c o n t a m i n a t i o n leads to serious color a n d taste p r o b l e m s d u r i n g t h e m a n u f a c t u r e of p h a r m a c e u t i c a l or f o o d g r a d e c o m p o u n d s i n m e t a l or a l l o y equipment.

T h i s is a v e r y m i l d type of attack r e f e r r e d to as " m i c r o - m i l "

c o r r o s i o n . Stainless steel alloys h a v e b e e n u s e d i n m a n y instances w h e r e s u c h c o n t a m i n a t i o n or q u a l i t y c o n t r o l is the p r o b l e m r a t h e r t h a n severe, p r o h i b i t i v e corrosion.

O f t e n even stainless steel is i n a d e q u a t e , a n d r e -

i n f o r c e d plastics h a v e b e e n r e q u i r e d as substitutes. B e c a u s e of the serious q u a l i t y p r o b l e m s a r i s i n g f r o m this m i n i s c u l e a m o u n t of c o r r o s i o n , the m a t e r i a l s or c o r r o s i o n engineer often is c a l l e d u p o n to assist the p r o d u c t i o n s u p e r v i s o r i n r e c o m m e n d i n g a n a l t e r n a t i v e m a t e r i a l of

construction.

A l t h o u g h this m i n u t e attack w i l l

introduce

m e t a l ions i n parts p e r m i l l i o n i n t o the p r o d u c t , this is f r e q u e n t l y s i g nificant e n o u g h to i m p a r t adverse color effects or u n d e s i r a b l e tastes to

In Fillers and Reinforcements for Plastics; Deanin, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

19.

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FENNER

197

Engineering

not o n l y t h e m a i n c o m p o u n d b u t subsequent p r o d u c t s .

T h e use of r e -

i n f o r c e d plastics often has s o l v e d the p r o b l e m . I n m a n y instances no m e t a l o r a l l o y is either p r a c t i c a l or e c o n o m i c a l to use f o r f a b r i c a t i n g a c u s t o m - b u i l t p i e c e of e q u i p m e n t w h i c h w i l l b e exposed to a h i g h l y c o r r o s i v e e n v i r o n m e n t .

T h i s is c e r t a i n l y true i n

m a n y a p p l i c a t i o n s d e a l i n g w i t h strong o x i d i z i n g acids, w i d e ranges of p H , a n d a c i d i c salt solutions. I n these a p p l i c a t i o n s , specific r e i n f o r c e d plastics are i n v a l u a b l e . B y u s i n g p l a s t i c structures w i t h a h i g h d e g r e e of t r a n s l u c e n c y , safer Downloaded by UNIV OF CINCINNATI on February 18, 2015 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch019

a n d easier operations are e n c o u n t e r e d , as w e l l as savings of

thousands

of dollars for l i q u i d l e v e l - m e a s u r i n g auxilliaries. T h e a b i l i t y to d e t e r m i n e v i s u a l l y the h e i g h t of a l i q u i d i n a t a n k at a glance lessens the h a z a r d of spillovers i n t o a n o p e r a t i n g area. O n e p r o p e r t y of p l a s t i c m a t e r i a l s of c o n s t r u c t i o n w h i c h m u s t

be

c o n s i d e r e d f r o m a safety v i e w p o i n t is t h e i r a b i l i t y to b u i l d u p a static charge.

R a p i d bleed-off

around

flammable

procedures

and sparking can be

particularly hazardous

l i q u i d s or d r y dust e n v i r o n m e n t s .

Suitable grounding

or n e u t r a l i z i n g m e d i a m u s t b e u s e d i n these situations to

guarantee safe w o r k i n g c o n d i t i o n s . resins w i l l b u r n ,

fire-retardant

S i n c e m a n y plastics a n d r e i n f o r c e d

steps are necessary w h e n e v e r the q u e s t i o n

of safety arises f r o m this source.

G e n e r a l l y the s o l u t i o n is s i m p l y t h e

m o d i f i c a t i o n of the r e s i n f o r m u l a t i o n b y the a d d i t i o n of

fire-retardant

c o m p o u n d s or b y the i n t e r n a l m o d i f i c a t i o n of the r e s i n m o l e c u l e itself. F r o m a n e n g i n e e r i n g s t a n d p o i n t , the most i m p o r t a n t d e s i g n c o n s i d eration is the s t r u c t u r a l soundness

of t h e u n i t .

T h i s means

that the

l a y - u p a n d thickness of the l a m i n a t e m u s t b e e v a l u a t e d to m a k e c e r t a i n that not o n l y w i l l the s t r u c t u r e w i t h s t a n d a l l of the h y d r a u l i c or static l o a d pressure i m p r e s s e d u p o n i t b u t also t h a t a n y p r o p o s e d v a c u u m or pressure service conditions w i l l b e c o n s i d e r e d .

T h e u n i t should be f a b r i -

c a t e d to w i t h s t a n d a n y v i b r a t i o n a l f a t i g u e a r i s i n g f r o m a g i t a t i o n of

fluids

or h e a v y slurries w i t h i n the tank. A n y a g i t a t o r d r i v e a s s e m b l y m u s t b e t a k e n i n t o c o n s i d e r a t i o n . T h i s s h o u l d b e externally s e l f - s u p p o r t e d w h e n the t a n k w a l l s are not sufficiendy s t r o n g a n d t h i c k e n o u g h to

support

the a d d e d w e i g h t . I n the m a j o r i t y of cases, f a i l u r e s i n glass fiber r e i n f o r c e d plastics are physical-mechanical i n nature.

I n the c o n s t r u c t i o n of s u c h e q u i p m e n t ,

the f o l l o w i n g cause the most f r e q u e n t p r o b l e m s : ( 1 ) I n a d e q u a t e w e t t i n g of the glass fibers b y the r e s i n , r e s u l t i n g i n d r y spots a n d d e l a m i n a t i o n s ( 2 ) E n t r a p p e d a i r , r e s u l t i n g i n subsurface air b u b b l e s a n d blisters or craters ( 3 ) N o n - u n i f o r m i t y of l a m i n a i c o n s t r u c t i o n , s u c h as fold-overs a n d i r r e g u l a r i t i e s of l a m i n a l thickness


198

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REINFORCEMENTS FOR

PLASTICS

( 4 ) P r o h i b i t i v e p o r o s i t y a n d crevices at junctures of nozzles a n d tank w a l l (5)

I n a d e q u a t e r e i n f o r c e m e n t a n d / o r s u p p o r t of nozzles a n d t a n k

walls ( 6 ) E x p o s e d glass fibers of the r e i n f o r c i n g m a t to the e n v i r o n m e n t b e c a u s e of m i s s i n g s u r f a c i n g w a l l (7)

corrosive

Insufficient thickness i n p r o t e c t i v e surface g e l coat

( 8 ) A p p l i c a t i o n of g e l c o a t i n g over a p a r a f f i n - w a x e d surface, r e sulting i n poor adhesion


( 9 ) E x c e s s i v e l y r i c h r e s i n areas w h i c h p r o d u c e s h r i n k a g e cracks, a n d h i g h t e m p e r a t u r e exotherms

b r i t t l e sections,

( 10 ) I n t e r n a l stress c r a c k i n g (11)

U n f i n i s h e d sections, u n r e i n f o r c e d areas, a n d careless w o r k m a n -

ship (12) tortion

Prohibitively thin

flanges,

l e a d i n g to w a r p e d faces a n d d i s -

( 1 3 ) C o n t a m i n a t i o n f r o m f o r e i g n m a t e r i a l s i n the w o r k i n g area, e m b e d d i n g w i t h i n or u p o n surface of r e s i n I n a d d i t i o n to the a b o v e , the c u r i n g p r o c e d u r e m u s t b e s t u d i e d to d e t e r m i n e w h e t h e r i t is a d e q u a t e or not. A n i m p r o p e r l y c u r e d u n i t c a n g i v e disastrous results i n service. Reinforced

Plastics

Epoxy. T h e r e a c t i o n p r o d u c t s of b i s p h e n o l A a n d e p i c h l o r o h y d r i n , k n o w n as e p o x y resins, h a v e excellent a d h e s i v e q u a l i t i e s a n d e x h i b i t g o o d c h e m i c a l resistance.

T h e y c a n b e r e a d i l y c u r e d b y catalysts a n d a c c e l -

erators at a m b i e n t temperatures, w h i c h m a k e s t h e m e x t r e m e l y w o r t h w h i l e i n p a t c h i n g process e q u i p m e n t or r e i n f o r c i n g f r a g i l e m a t e r i a l s . G e n e r a l l y r e i n f o r c e d w i t h glass fibers, the epoxies s h o w v e r y g o o d r e sistance to w a t e r , sour c r u d e s , salt w a t e r , strong a l k a l i n e solutions, n o n o x i d i z i n g a c i d s , jet fuels, a l i p h a t i c s , a n d some a r o m a t i c c o m p o u n d s . generally recommended 250°F.

H o w e v e r , g o o d results h a v e b e e n e x p e r i e n c e d

fiber-reinforced

The

t e m p e r a t u r e for m a x i m u m operations is a b o u t w i t h the glass

e p o x y as h i g h as 350° F i n a c i d i c v a p o r s of p H 3.

T h e epoxies h a v e b e e n u s e d for glass

fiber-reinforced

storage tanks,

receivers, f e e d t a n k s , c o l u m n s , scrubbers, a n d ducts f o r h a n d l i n g h i g h l y corrosive l i q u i d s a n d v a p o r s ; p r o t e c t i o n of f r a g i l e m a t e r i a l s s u c h as glass p i p i n g , c e r a m i c s , stoneware, c a r b o n , a n d g r a p h i t e f r o m b r e a k a g e u n d e r tensile stresses t h r o u g h a r m o u r i n g w i t h glass t a p e a n d e p o x y r e s i n a d h e s i v e o v e r l a y ; p r o t e c t i v e coatings a n d l i n i n g s for tanks, storage b i n s , h o p p e r s , a n d c h u t e - h a n d l i n g w e t crystals a n d d r y p o w d e r s ;

monolithic

floor t o p p i n g s to p r o m o t e acid-resistant floors a n d m o r t a r s for a c i d - p r o o f brick

floor.


19.

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Engineering

F u r a n . T h e f u l l y c u r e d f u r a n resins h a v e excellent c h e m i c a l resistance to strong acids, c o n c e n t r a t e d

alkalies, c h l o r i n a t e d solvents,

and

m o i s t u r e . T h e y are not resistant to s u c h o x i d i z i n g agents as n i t r i c a c i d , chromic

a c i d , concentrated

sulfuric acid, chlorine, and

T h e i r h i g h degree of c h e m i c a l resistance to c h l o r i n a t e d s u c h as c h l o r o f o r m ,

chlorobenzene,

hypochlorites. hydrocarbons

and dinitrochlorobenze

has

the furans a p r e m i u m m a t e r i a l for p r o t e c t i o n of e q u i p m e n t w h e r e other materials are unaffected.

A l t h o u g h the r e c o m m e n d e d

o p e r a t i n g t e m p e r a t u r e for the glass

fiber-reinforced

few

continuous

furans is 2 8 0 ° F ,

successful a p p l i c a t i o n s as h i g h as 350° F h a v e b e e n r e p o r t e d . Downloaded by UNIV OF CINCINNATI on February 18, 2015 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch019

made

The furan

resins h a v e b e e n u s e d extensively for t h e m a n u f a c t u r e of p i p e s , ducts, valves, p u m p s , b l o w e r s , jets, exhaust a n d v e n t stacks, s c r u b b i n g towers, receivers,

distillation

exchangers,

filters,

towers,

tanks, mist e l i m i n a t o r s , absorbers,

heat

presses, pressure filter tanks, t a n k l i n i n g s , a n d a c i d -

proof b r i c k mortars. Phenolics.

T h e p h e n o l i c s h a v e b e e n p e r f o r m i n g y e o m a n chores i n

p r o t e c t i n g c h e m i c a l e q u i p m e n t for n e a r l y 50 years.

These

heat-cured

resins are i n s o l u b l e i n most solvents. T h e y h a v e h i g h a c i d resistance a n d are i n e r t to most of the c o m m o n c h e m i c a l s . T h e i r resistance to m o i s t u r e is v e r y g o o d . I n g e n e r a l , the u n m o d i f i e d p h e n o l i c s e x h i b i t p o o r resistance to a l k a l i n e m e d i a as w e l l as to s t r o n g o x i d i z i n g agents.

These materials

h a v e b e e n u s e d at temperatures as h i g h as 3 5 0 ° F for p r o l o n g e d p e r i o d s . T h e i r d i m e n s i o n a l s t a b i l i t y r e m a i n s q u i t e h i g h over a w i d e t e m p e r a t u r e range.

T h e p h e n o l i c s are classified as n o n - f l a m m a b l e materials.

T h e r e i n f o r c e d p h e n o l i c s m a y use c a r b o n or g r a p h i t e , asbestos, glass fiber, or n a t u r a l a n d s y n t h e t i c fibers. T h e y are u s e d to f a b r i c a t e process p i p i n g , valves, p u m p s , b l o w e r s , a n d tanks. T h e i r a p p l i c a t i o n s i n c l u d e asbestos-filled p h e n o l i c r e s i n c r y s t a l l i z e r s , quenchers, b o i l i n g t u b s , h o l d tubs, storage a n d f e e d b i n s , h o p p e r s , stacks, a n d d u c t i n g ; p h e n o l i c r e s i n i m p r e g n a t e d g r a p h i t e valves, p u m p s , jets, heat-exchangers, (bubble-cap

or

packed)

columns,

and

split-flow

distillation

controllers;

filters,

presses, c o a t e d t r a y a n d shelf v a c u u m d r y e r s , r o t a r y d r y e r s , a n d pressure and vacuum

filter

t a n k s ; f u m e a n d a c i d v a p o r s s c r u b b i n g towers

and

exhaust jets. Polyesters. T h e c h e m i c a l - r e s i s t a n t polyesters i n c l u d e the w e l l k n o w n p r o p o x y l a t e d b i s p h e n o l A — f u m a r a t e r e s i n ; one b a s e d u p o n h y d r o g e n a t e d b i s p h e n o l A a n d f u m a r i c a c i d ; the isophthalates; a n d polyesters

made

w i t h c h l o r e n d i c a n h y d r i d e o r t e t r a c h l o r o p h t h a l i c a n h y d r i d e . T h e s e resins h a v e g o o d c h e m i c a l resistance to n o n - o x i d i z i n g a c i d s , corrosive salts, a l i p h a t i c solvents, a r o m a t i c c o m p o u n d s , a n d c h l o r i n a t e d solvents.

They

e x h i b i t f a i r resistance to w e a k bases a n d esters b u t are severely a t t a c k e d b y s t r o n g o x i d i z i n g acids a n d strong bases.


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T h e polyesters are g e n e r a l l y r e i n f o r c e d w i t h glass c l o t h , m a t , r o v ings, c h o p p e d

fibers,

essing e q u i p m e n t . usually employed

or glass flakes i n the f a b r i c a t i o n of c h e m i c a l p r o c A l t h o u g h the glass

fiber-reinforced

polyesters

at c o n t i n u o u s o p e r a t i o n t e m p e r a t u r e s b e l o w

t h e y h a v e b e e n successfully a p p l i e d i n s t r o n g l y c o r r o s i v e

are

212 ° F ,

environments

as h i g h as 250 ° F .

S p e c i a l modifications w i t h r e a c t i v e d i l u e n t s or cross-

linking monomers

s u c h as t r i a l l y l c y a n u r a t e have b e e n r e p o r t e d

with

heat s t a b i l i t y at temperatures as h i g h as 500 ° F . T h e glass

fiber-reinforced

polyesters h a v e e x h i b i t e d a v e r s a t i l i t y of


use w h i c h ranges f r o m parts of the l u n a r e x c u r s i o n m o d u l e

to

mine

sweepers i n V i e t n a m waters. T h e i r a p p l i c a t i o n i n the c h e m i c a l i n d u s t r y i n c l u d e s reactors, storage tanks, c a t c h tanks, b o i l i n g tubs, g r o u n d tanks, receivers, a n d separators; r e c l a i m e d w a t e r sumps, funnels,

laboratory

sinks; ducts, hoods, a n d v e n t stacks; d i p p i p e s , process p i p i n g , sewers; dry powder troughs,

b i n s , feeders,

conveyor

covers;

chutes, carts; w e t c a k e h o p p e r s , chlorine

absorbers,

off-gas

screw-feed

scrubbers,

mist

e l i m i n a t o r s , a n d c o l u m n s ; doors, w i n d o w s , canopies, p a n e l i n g , s t r u c t u r a l m e m b e r s ; e q u i p m e n t safety shields, m o t o r covers; fans, b l o w e r s , eductors, jets, exhausters; filter press frames, s l i d e blast gates, c h e c k v a l v e s ; waste d i s p o s a l troughs, s e t t l i n g basins, c o o l i n g towers, g u t t e r i n g , d o w n s p o u t s ; c h o p p e d fiber s p r a y a n d glass flake l i n i n g s for i n - p l a c e r e h a b i l i t a t i o n of process e q u i p m e n t . Testing T h e testing of glass

fiber-reinforced

plastics either i n t h e l a b o r a t o r y

or u n d e r a c t u a l p l a n t operations b y the s i m p l e i m m e r s i o n m e t h o d is often sufficient to d e t e r m i n e a c c e p t a b i l i t y b y t h e e n v i r o n m e n t .

T h i s is p a r -

t i c u l a r l y true w h e n the p l a s t i c is r e a d i l y a t t a c k e d b y the test s o l u t i o n . H o w e v e r , w h e n there is little v i s i b l e change i n the test s a m p l e , determ i n a t i o n of its c o m p a t i b i l i t y w i t h the p a r t i c u l a r e n v i r o n m e n t b e c o m e s s o m e w h a t m o r e difficult. It is possible, for a n e x a m p l e , that u n d e s i r a b l e trace c o n t a m i n a n t s present i n the process s t r e a m m a y b e a b s o r b e d

over

a p e r i o d of t i m e or p e r m e a t e the r e s i n w i t h no i m m e d i a t e v i s i b l e e v i d e n c e of h a r m f u l effects.

A g r a d u a l d e g r a d a t i o n of t h e p h y s i c a l a n d m e c h a n i -

c a l properties of the p l a s t i c m a y b e d e v e l o p i n g a w e a k e n e d structure. U n d e r those c o n d i t i o n s of n o a p p a r e n t v i s i b l e change, i t is g e n e r a l l y best to m a k e c e r t a i n that no i n s i d i o u s or adverse c o n d i t i o n i n g of the p l a s t i c is o c c u r r i n g w h i c h c o u l d p r o m o t e f u t u r e difficulties. T h u s , p e r f o r m a n c e d a t a b a s e d u p o n changes i n p h y s i c a l a n d m e c h a n i c a l properties are v e r y meaningful

(I).

I n i t i a l l y , testing t e c h n i q u e s s i m i l a r to those u s e d i n e v a l u a t i n g the c o r r o s i o n resistance of metals a n d alloys m a y be u s e d for the glass


fiber-

19.

Corrosion

FENNER

201

Engineering

r e i n f o r c e d resins. T h e specific test coupons are exposed to the e n v i r o n m e n t either i n the l a b o r a t o r y u n d e r as n e a r l y as possible s i m u l a t e d p l a n t c o n d i t i o n s or u n d e r a c t u a l field operations i n the process stream.

The

c o u p o n s are u s u a l l y p o s i t i o n e d to p r o v i d e b o t h l i q u i d - a n d v a p o r - p h a s e environmental

exposures.

W h e n exposure is

finished,

the test coupons are r e m o v e d a n d ex-

a m i n e d for changes i n w e i g h t , d i m e n s i o n , a p p e a r a n c e , hardness, d e l a m i n a t i o n , p h y s i c a l a n d / o r m e c h a n i c a l properties, a n d a c t u a l d i s s o l u t i o n of the p l a s t i c .


Incompatibility

of

a reinforced

plastic w i t h

the

environment

is

v i s u a l l y a p p a r e n t b y s u c h occurrences as those d e s c r i b e d b e l o w . Abnormal Surface Changes.

T h e s e m a y be i d e n t i f i e d b y c h a r r i n g ,

c h a l k i n g , b l i s t e r i n g , c r a c k i n g , a n d c r a z i n g , a l l of w h i c h c a n result i n a weakened

s t r u c t u r e a n d p r o h i b i t the e x t e n d e d

use i n the p a r t i c u l a r

service. Color Changes. W h i l e i n d i c a t i n g some i n t e r a c t i o n of the p l a s t i c a n d the e n v i r o n m e n t , s u c h changes do not necessarily p r o h i b i t t h e use of the plastic. M a n y times this color c h a n g e is l i m i t e d either to the i m m e d i a t e surface or at worst to a f e w m i l s p e n e t r a t i o n . causes the d e v e l o p m e n t

Permeation

sometimes

of a color c h a n g e t h r o u g h o u t t h e b o d y of the

p l a s t i c . H o w e v e r , often the d i s c o l o r e d p l a s t i c w i l l n o t h a v e

experienced

a n y significant d e g r a d a t i o n i n its p h y s i c a l or m e c h a n i c a l properties a n d is e n t i r e l y a c c e p t a b l e i n the p r o p o s e d service. Dimensional Changes.

If s w e l l i n g or s h r i n k a g e is m i n o r , it is no

reason for rejection p r o v i d e d s u c h d i m e n s i o n a l changes do not p r o h i b i t the p l a s t i c f r o m p e r f o r m i n g its f u n c t i o n .

M i n o r s w e l l i n g i n the p l a s t i c

l i n i n g of a t a n k is not sufficient cause for a l a r m or r e p l a c e m e n t as l o n g as its a d h e s i o n to the t a n k w a l l is unaffected.

S w e l l i n g to the same extent

w i t h i n the v o l u t e of a p u m p , b o d y of a v a l v e , or t h r o a t of a flow m e t e r i n g d e v i c e m i g h t b e q u i t e unsatisfactory. P r o h i b i t i v e s w e l l i n g is often o n l y i n t h e eyes of the evaluator a n d q u i t e difficult to define i n terms percentage

g r o w t h as to rejection or acceptance.

of

O n the other h a n d

excessive s h r i n k a g e is m o r e easily defined b y s h r i n k i n g , c r a c k i n g , d i s t o r t i o n , or loss i n a d h e s i v e q u a l i t i e s . Hardness Changes.

T h e s e are not u n c o m m o n .

S o f t e n i n g or h a r d e n -

i n g of a p l a s t i c or r e s i n system exposed to a p a r t i c u l a r e n v i r o n m e n t m a y or m a y not b e e v i d e n c e of p r o h i b i t i v e attack.

Softening, i n m a n y i n -

stances, is solely the result of t h e p e r m e a t i o n of a solvent into the r e s i n w i t h some attendent p l a s t i c i z i n g . U p o n r e m o v a l f r o m exposure to the e n v i r o n m e n t , the solvent m a y evaporate a n d the p l a s t i c m a y r e s u m e its o r i g i n a l hardness. T a c k i n e s s a c c o m p a n y i n g a softening of the r e s i n system g e n e r a l l y denotes its u n a c c e p t a b i l i t y . H o w e v e r , this m a y be o n l y a surface phenomenon

a n d a reasonable, p r a c t i c a l l i f e c o u l d b e e x p e r i e n c e d


by

202

FILLERS

AND

REINFORCEMENTS FOR

PLASTICS

the m a t e r i a l i n the e n v i r o n m e n t . B r i t t l e n e s s a n d losses i n tensile or

flex-

u r a l s t r e n g t h often are associated w i t h surface h a r d e n i n g of t h e p l a s t i c . C e r t a i n m e d i a , s u c h as s t r o n g a c i d s , m a y increase the surface hardness of c a t a l y t i c a l l y c u r e d resins w i t h o u t d e t r i m e n t a l effects. Laminai W a l l A t t a c k .

T h i s is suffered b y

fiber-reinforced

resin

structures i n e n v i r o n m e n t s i n w h i c h the r e s i n is u n a c c e p t a b l e ( J ) .

How-

ever, s h o u l d the r e s i n system not h a v e b e e n p r o p e r l y c u r e d p r i o r to exposure, failures m i g h t o c c u r i n a n o t h e r w i s e a c c e p t a b l e

environment.

I n other instances, d e l a m i n a t i o n occurs because there is i n a d e q u a t e w e t -


t i n g of the glass, r e s u l t i n g i n p o o r a d h e s i o n . paraffin w a x f r o m the s u r f a c e of a glass

T h e f a i l u r e to

fiber-reinforced

remove

polyester l a m i n a t e

p r i o r to the a d d i t i o n of a n y o v e r l a y c a n cause d e l a m i n a t i o n too.

Expo-

sure of glass fibers to e n v i r o n m e n t s s u c h as strong bases or h y d r o f l u o r i c a c i d w h i c h are i n c o m p a t i b l e w i t h glass c a n cause r a p i d d e t e r i o r a t i o n of the glass r e i n f o r c e m e n t a n d d e l a m i n a t i o n . Weight Changes. T h e s e are u s e d b y m a n y laboratories i n r e p o r t i n g the p e r f o r m a n c e of plastics. T h e s e w e i g h t changes r e s u l t f r o m the a b s o r p t i o n of l i q u i d s , p r o d u c t i o n of c o r r o s i o n p r o d u c t s , l e a c h i n g of r e s i n , erosion, c o r r o s i o n , or other m e c h a n i c a l effects, d e t e r i o r a t i o n of r e i n f o r c i n g fiber t h r o u g h c h e m i c a l attack, o r a c o m b i n a t i o n of these. O f t e n a single w e i g h t m e a s u r e m e n t at the e n d of the exposure p e r i o d is sufficient for e v a l u a t i n g the p l a s t i c f o r the specified e n v i r o n m e n t . H o w e v e r , false or q u e s t i o n a b l e conclusions or inferences m a y result f r o m r e l y i n g solely o n s u c h measurements. T o a v o i d this, a series of p h y s i c a l / m e c h a n i c a l p r o p e r t y tests a n d w e i g h t c h a n g e evaluations s h o u l d be m a d e o n e a c h p l a s t i c at definite t i m e i n t e r v a l d u r i n g the exposure p e r i o d .

These

measure-

ments are p l o t t e d so t h a t a p r o j e c t e d p e r f o r m a n c e l i f e m a y b e p r e d i c t e d f r o m the curves.

A f a i r l y satisfactory t e c h n i q u e plots t h e a c c u m u l a t e d

p e r c e n t a g e w e i g h t c h a n g e f r o m i n i t i a l w e i g h t a l o n g w i t h the d i f f e r e n t i a l percentage w e i g h t c h a n g e b e t w e e n successive w e i g h i n g s . T h i s c o m b i n a t i o n w i l l i n d i c a t e w h e t h e r t h e rate of c h a n g e is i n c r e a s i n g , d e c r e a s i n g , o r r e m a i n i n g constant for a n y i n c r e m e n t of t i m e d u r i n g exposure to the aggressive e n v i r o n m e n t . Residual Physical Properties Method.

T h i s is p r o b a b l y the

i m p o r t a n t c o n s i d e r a t i o n i n t h e e v a l u a t i o n of glass

fiber-reinforced

most

plastic

l a m i n a t e s w h i c h h a v e b e e n s u b j e c t e d to severely c o r r o s i v e e n v i r o n m e n t s . W h e t h e r t h e y h a v e r e t a i n e d sufficient amounts of t h e i r o r i g i n a l pressive,

flexural,

com-

a n d tensile strengths to p r o v i d e a s t r u c t u r a l l y s o u n d

u n i t over a reasonable service l i f e is of p a r a m o u n t i m p o r t a n c e . R e v i e w of m a n y test exposures of glass

fiber-reinforced

r e s i n samples

discloses that b o t h i n i t i a l loss or g a i n i n w e i g h t , or e v e n a decrease i n flexural

s t r e n g t h or m o d u l u s is o n l y p a r t of the p e r f o r m a n c e

picture.

R a t e of c h a n g e or e v e n s t a b i l i t y of these w i t h a d d i t i o n a l exposure is


19.

Corrosion

FENNER

203

Engineering

m u c h m o r e a c r i t e r i o n for acceptance.

M a n y investigations d i s c l o s e d

r a p i d loss i n p h y s i c a l properties the first f e w hours or days of exposure, w i t h a subsequent

flattening

out of the curves w h i c h i n d i c a t e n o a p p r e -

c i a b l e f u r t h e r l o w e r i n g of the s t r e n g t h of the l a m i n a t e . T h e s e studies l e a d to the c o n c l u s i o n t h a t changes i n flexural s t r e n g t h and

flexural

m o d u l u s are the best c r i t e r i a for e v a l u a t i n g the c h e m i c a l

resistance of glass t o r y exposures.

fiber-reinforced

changes i n flexural strength or w i t h respect to t i m e . Downloaded by UNIV OF CINCINNATI on February 18, 2015 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch019

polyesters b o t h i n p l a n t a n d i n l a b o r a -

B r i e f l y , the test p r o c e d u r e is b a s e d o n the e v a l u a t i o n of fluxural

m o d u l u s of the exposed

samples

T h e s e d e t e r m i n a t i o n s are u s e d as the s t a n d a r d

reference b e t w e e n p e r f o r m a n c e of glass

fiber-reinforced

polyesters since

changes i n these p r o p e r t i e s a p p e a r to b e t h e most i n d i c a t i v e c h e c k o n the p h y s i c a l b e h a v i o r of these m a t e r i a l s . D e f l e c t r o n T e s t C e l l . It has b e c o m e q u i t e a p p a r e n t to m a n y r e s e a r c h chemists a n d m a t e r i a l s engineers that the s t a n d a r d " d u n k " test i n t r o d u c e s difficulties i n i n t e r p r e t a t i o n w h e n a t t e m p t i n g to use the d a t a for engineering design.

good

I n c o n s i d e r i n g the effects of c o l d w a l l s u p o n the

p e r f o r m a n c e of m a t e r i a l s , a l m o s t s i m u l t a n e o u s l y , m a n y c o m p a n i e s

Figure 1.

and

Open end test cell

p e r s o n n e l i n t e r e s t e d i n this field h a v e a r r i v e d at the d e c i s i o n t h a t " o n e s i d e " testing of the glass

fiber-reinforced

plastic panel under conditions

s i m u l a t i n g the i n n e r w a l l of a t a n k or d u c t is m o r e d e s i r a b l e . M o n s a n t o C o r p o r a t e E n g i n e e r i n g uses t h e D e f l e c t r o n o p e n e n d test c e l l ( D e f l e c t r o n C o . , St. L o u i s , M o . ) to o b t a i n r e a l i s t i c exposure d a t a i n t h e e v a l u a t i o n of glass

fiber-reinforced

polyesters a n d other sheet plastics.

T h e test a p p a r a t u s ( F i g u r e 1 ) consists of a 4 " - d i a m e t e r X 1 0 " - l o n g glass c y l i n d e r w i t h s e v e r a l ground-glass joint o p e n i n g s p l a c e d i n l i n e p e r p e n -


204

FILLERS

AND

REINFORCEMENTS

FOR

PLASTICS

d i c u l a r to the axis of the c y l i n d e r . T h e ends of t h e glass c y l i n d e r are c l o s e d off w i t h t h e r e s i n glass l a m i n a t e to b e tested a n d sealed

with

s u i t a b l e gaskets, a l l o w i n g one-side exposure o n l y to the p a r t i c u l a r e n v i r o n m e n t . T h e c e l l is h a l f - f i l l e d w i t h the test s o l u t i o n w h i c h p r o v i d e s a n e q u a l l i q u i d p h a s e - v a p o r p h a s e exposure area u p o n e a c h e n d test p a n e l . T h e u n i t c a n be

fitted

w i t h the d e s i r e d a u x i l i a r y e q u i p m e n t s u c h as

reflux condenser, t h e r m o m e t e r , t h e r m o s t a t i c c o n t r o l , a n d agitator.

The

e n v i r o n m e n t a l c e l l is h e a t e d w i t h a n e l e c t r i c h e a t i n g m a n t l e to m a i n t a i n the r e q u i r e d t e m p e r a t u r e .


I n a d d i t i o n to the 6 " χ %"

X 3y2"

the l i q u i d .

X

6" X

V s ^ - t h i c k side test p a n e l , g e n e r a l l y

y 8 " - t h i c k sealed e d g e " d u n k " test strips are i m m e r s e d i n

O n e of these is r e m o v e d after 1, 3, 7, 14, 30, 60, 90, a n d 120

days to o b s e r v e a n y v i s i b l e a t t a c k over t h e p e r i o d of i m m e r s i o n . C h a n g e s i n B a r c o l hardness are d e t e r m i n e d , a n d t h e n r e s i d u a l and

flexural

flexural

modulus

s t r e n g t h d e t e r m i n a t i o n s are m a d e o n e a c h test strip u p o n

its r e m o v a l , a c c o r d i n g to A S T M

D - 7 9 0 , S t a n d a r d M e t h o d for T e s t for

F l e x u r a l P r o p e r t i e s of P l a s t i c s . U p o n c o m p l e t i o n of t h e t e s t i n g p e r i o d , u s u a l l y a 120-day the u n i t is d i s m a n t l e d , a n d t w o % " - w i d e X

exposure,

6 " - l o n g test strips are c u t

f r o m the l i q u i d phase, a n d t w o test strips are c u t f r o m the v a p o r p h a s e of the p a n e l . A s i n g l e y2"-wide X

6 " - l o n g c o n t r o l s a m p l e is c u t f r o m

the u n e x p o s e d p o r t i o n of the p a n e l . T h e s e are t h e n b r o k e n o n a n I n s t r o n i n s t r u m e n t ( I n s t r o n C o r p . , C a n t o n , M a s s . ) to d e t e r m i n e t h e i r r e s i d u a l flexural

modulus and

flexural

strengths.

T h e b r o k e n test strips are r e

a s s e m b l e d i n t o t h e i r f o r m e r p o s i t i o n i n the test p a n e l for f u t u r e reference. T h e fact t h a t c o n t r o l p a n e l s of a specific l a m i n a t e d p l a s t i c s t r u c t u r e m a y b e u s e d w i t h a n u m b e r of D e f l e c t r o n test cells to c o m p a r e c h e m i c a l resistance w i t h those of other r e s i n l a m i n a t e systems is a d e c i d e d a d v a n tage. T h e v a r i a t i o n i n c h e m i c a l resistance t h r o u g h differences i n t r o d u c e d b y v a r i o u s r e i n f o r c i n g fibers s u c h as asbestos, c e r a m i c , n y l o n , a c r y l i c s , polyesters, o r other synthetics is often of i m p o r t a n c e a n d has b e e n e v a l u a t e d b y this t e c h n i q u e . Plastographic Analysis Techniques. tional performance

P r o c e d u r e s for o b t a i n i n g a d d i

d a t a after p l a s t i c m a t e r i a l s h a v e b e e n s u b j e c t e d

aggressive e n v i r o n m e n t s , t e r m e d p l a s t o g r a p h i c analysis t e c h n i q u e s

to (2),

are often used. T h e t e c h n i q u e has b e e n e x t r e m e l y h e l p f u l i n p e r f o r m a n c e a n d f a i l u r e analyses studies w h i c h h a v e l e d to the d e v e l o p m e n t of b e t t e r e n g i n e e r i n g m a t e r i a l s of c o n s t r u c t i o n a n d d e s i g n considerations for p l a s t i c a n d r e i n f o r c e d m a t e r i a l s of c o n s t r u c t i o n . I n this p r o c e d u r e

p l a s t i c samples a n d glass

fiber-reinforced

resin

l a m i n a t e s are p r e p a r e d a n d s u b j e c t e d to " k n o w n c o n d i t i o n s " of exposure. W e h a v e u s e d i t most f r e q u e n t l y i n the p e r m a n e n c e studies w i t h

fiber-

r e i n f o r c e d r e s i n m a t e r i a l s . I n these studies t y p i c a l " k n o w n c o n d i t i o n "


19.

FENNER

samples

Corrosion

for c o m p a r i s o n

205

Engineering against S P I s t a n d a r d c o n t r o l l a m i n a t e s

were

p r e p a r e d b y the f o l l o w i n g m e t h o d s : ( a ) P h y s i c a l fractures of the S P I s t a n d a r d c o n t r o l l a m i n a t e t h r o u g h f o l d - o v e r , t o r s i o n a l b r e a k a g e , flexural f a t i g u e c r a c k i n g , a n d h y d r o s t a t i c rupture ( b ) U n d e r c u r e d l a m i n a t e s a r i s i n g f r o m insufficient a d d i t i o n s of catalysts or accelerators, excessively l o w c u r e t e m p e r a t u r e s , air i n h i b i t i o n , or h i g h h u m i d i t y c o n d i t i o n s


( c ) O v e r c u r e d laminates r e s u l t i n g f r o m excessive a d d i t i o n s of catalyst or accelerator, p o o r heat d i s s i p a t i o n , h i g h e x o t h e r m i c c o n d i t i o n s ( d ) I m p r o p e r l y r e s i n - w e t t e d l a m i n a t e s p r o d u c e d as a c o n s e q u e n c e of insufficient m e c h a n i c a l i m p r e g n a t i o n , i n c o m p a t i b i l i t y of s i z i n g a n d fibers, or p r e s e n c e of r e s i n - p h o b i c c o n t a m i n a n t s (e) C h e m i c a l l y degraded S P I standard control laminates i n w h i c h the r e s i n m a t r i x , glass fibers, or b o t h h a v e b e e n a t t a c k e d b y selective solvents, o x i d i z i n g agents, a c i d s , or c a u s t i c c o m p o u n d s . T h e s e a n d s i m i l a r l y p r e p a r e d s p e c i a l samples w e r e t h e n e x a m i n e d under

the

stereomicroscope,

metallographic

s c a n n i n g electron m i c r o s c o p e .

optical

microscope,

A p p r o p r i a t e photographs

were

and

prepared

of e a c h t y p e of f a i l u r e or attack to serve as a set of " k n o w n c o n d i t i o n " c o n t r o l laminates. C o m p a r i s o n w i t h u n k n o w n exposure laminates ferrets out causes for t h e i r q u e s t i o n a b l e or unsatisfactory p e r f o r m a n c e s .

The

e x a m i n a t i o n of these test l a m i n a t e s is d o n e u n d e r magnifications i n the r a n g e of 100-13,000 X a n d h a v e p r o v e d e x t r e m e l y v a l u a b l e i n d e t e r m i n i n g t h e r e s i s t i v i t y of fiber reinforcements a n d the p a r t i c u l a r r e s i n system t o w a r d s the specific e n v i r o n m e n t u n d e r c o n s i d e r a t i o n . I n f r a r e d Spectroscopy.

I d e n t i f i c a t i o n of p l a s t i c materials o f

con-

s t r u c t i o n as to g e n e r i c f a m i l y a n d , w h e r e v e r possible, as to c o m m e r c i a l l y a v a i l a b l e resins or p r o p r i e t a r y plastics is a necessary a d j u n c t to p l a s t i c testing a n d p l a s t o g r a p h i c analysis. It assists i n d e t e r m i n i n g the cause of poor performance

i n f a i l u r e analysis studies, as a n a i d i n e s t a b l i s h i n g

g o o d standards, a n d p r o m o t e s the d e s i g n of better

corrosion-resistant

c h e m i c a l p r o c e s s i n g e q u i p m e n t a n d structures. It is possible b y i n f r a r e d s p e c t r o s c o p y to use a v e r y s m a l l segment of the p l a s t i c or r e s i n m a t e r i a l to i d e n t i f y r a p i d l y a n d a c c u r a t e l y specific p o l y m e r s i n the u n i t u n d e r examination. Conclusion It is necessary

to use i n g e n u i t y i n s e l e c t i n g or d e v i s i n g tests

to

d e t e r m i n e the c h e m i c a l r e s i s t i v i t y of a p a r t i c u l a r p l a s t i c or r e s i n e x p o s e d to a specific e n v i r o n m e n t . T h e a p p l i c a t i o n s dictate the testing p r o c e d u r e n e e d e d to guarantee that the e n d results w i l l g i v e m e a n i n g f u l , safe, a n d useful engineering design data.


206

FILLERS AND REINFORCEMENTS FOR PLASTICS

Literature Cited 1. Cass, R. Α., Fenner, Ο. H., "Evaluating the Performance of Fiberglass Laminates," Ind. Eng. Chem. (1964) 56, 29-34. 2. Fenner, Ο. H., "Plastographic Analysis Techniques in the Evaluation of FRP Structures and Equipment," SAMPE Quart. (1970) 1 (3) 26-31.


RECEIVED October 11, 1973.


Fillers and Reinforcements for Plastics

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