croindentation of elastomers. In introduction part the principle of compliance method has been presented and compared to ISO standards on the determina­

Dariusz M. Bieliński*

Microindentation of elastomers. Case studies

The paper summarizes above 8 years of the author’s experience with mi­

croindentation of elastomers. In introduction part the principle of compliance method has been presented and compared to ISO standards on the determina­

tion of rubber hardness. The advantages and the limitations of microindenta­

tion have been discussed.

Experimental results demonstrate application of the technique to study surface segregation in elastomer-plastomer blends, blooming of low molecular weight substances in rubber, gradient of crosslink density and structure in vulcanizates, effects of chemical and physical modifications, aging and stress relaxation in elastomers. Case examples are presented and discussed in terms of the potential influence on exploitation characteristics of the materials.

K e y w o r d s :

elastomers, surface layer, microindentation, composition and structure, modification

Badania elastomerów metodą mikroin­

dentacji. Wybrane przykłady

Artykuł stanowi podsumowanie ponad 8-letnich doświadczeń autora

w

dziedzinie mikroindentacji elastomerów. We wstępie przedstawiono ideę po­

miaru twardości opierając się na metodzie „compliance” (ang. podatność me­

chaniczna), porównując ją do standardowych oznaczeń twardości, ujętych

w

normach ISO. Przedyskutowano zalety i wskazano na ograniczenia, jakim podlega mikroindentacja.

Wyniki badań świadczą o możliwości zastosowania tej techniki do jakoś­

ciowych i ilościowych oznaczeń segregacji powierzchniowej

mieszaninach elastomerówo-plastomerowych, badania zjawiska wykwitania substancji mało- cząsteczkowych

gumie, gradientu gęstości usieciowania i struktury węzłów sieci w wulkanizatach, efektów chemicznej i fizycznej modyfikacji, starzenia i relaksacji naprężeń

elastomerach. Wybrane przykłady przedyskutowano z punktu widzenia potencjalnego wpływu zmian budowy i struktury na charak­

terystykę eksploatacyjną materiałów.

S ło w a k lu c z o w e :

elastomery, warstwa wierzchnia, mikroindentacja, budowa i struktura, modyfikacja

1. Introduction

H ard n ess and m e c h a n ic a l m o d u lu s are th e m o s t im ­ portant m e c h a n ic a l p aram eters o f m ateria ls. T h eir v a ­ lu es are u se d fo r c a lc u la tio n s o f m e c h a n ic a l stren gth , d u rab ility or w ea r r e s is ta n c e [1].

A c c o r d in g to th e H o o k e ’s la w th e m e c h a n ic a l m o d u lu s o f m aterial is d e fin e d as a p ro p o rtio n a lity c o n ­ stant b e tw e e n stress and strain. T h is g en era l rule h o w ­ e v er d o e s n o t in c lu d e e la s to m e r s fo r w h ic h stress is n ot

* Institute of Polymer & Dye Technology, Technical Univer­

sity of Łódź, Łódź, Poland

Rubber Research Institute “STOMIL”, Piastów, Poland The work is dedicated to the 10lh anniversary of the ELAS­

TOMERY journal. Paper based on the lecture given at the Micro Materials European Users’ Meeting, Darmstadt (Ger­

many) 15-16.11.2006.

d irectly , p ro p o rtio n a l to strain. It m a k es P N -IS O 37 to d e fin e th e s o - c a lle d m o d u li at e x te n s io n o f 100% , 20 0 % and 3 0 0 % .

E la s to p la s tic b e h a v io u r is a lso r e sp o n s ib le fo r d if­

feren t stan d ard p ro ced u res se r v in g th e d eterm in a tio n o f h a rd n ess. T ra d itio n a l d e fin itio n o f h a rd n ess g iv e n as a ratio o f lo a d to th e su rfa ce o f in d en t o f certain g eo m etry , a g a in d o e s n o t a p p ly to e la s to m e r s w h ic h e x h ib it h ig h v a lu e o f th e e la s tic c o m p o n e n t o f d efo rm a tio n . T h is is w h y IS O 4 8 p r o p o se s to d e fin e the h ard n ess o f rubber as stress g en e r a te d in th e sp rin g o f d u rom eter durin g p u sh in g the in d en ter o f c o n ic a l g e o m e tr y in to the m a te ­ rial. F ro m th e th eo retica l p o in t o f v ie w su ch a m ea su re­

m e n t c a n n o t b e c o n s id e r as u n ifo rm , b e c a u s e it p r o v id e s e x p e r im e n ta l data on th e d ifferen t d eg ree o f d efo rm a ­ tio n , v a ried a c c o r d in g to m e c h a n ic a l ch a ra cteristics o f e la s to m e r s stu d ied . M o reo v er, a p p lica tio n o f a S h o re d u ro m eter lim its in fo rm a tio n to th e b u lk o f m aterial, w h e r e a s in th e lig h t o f recen t in v e s tig a tio n s th e ro le

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technika mikroindentacji

F ig . 1. In flu en ce o f a n in d e n te r g e o m e tr y o n th e d e g r e e o f d e fo r m a tio n o f m a te r ia l s tu d ie d R ys. 1. W p ły w g e o m e tr ii p e n e tr a to r a n a s to p ie ń o d k s z ta łc e n ia b a d a n e g o m a te r ia łu

p la y e d b y the su rfa ce la y er in e x p lo ita tio n p er fo r m a n c e o f rubber is v ery im p ortan t [2 ]. It s e e m s u n r e a so n a b le w h y this m atter o f c o u r s e is o ften u n d e r e stim a te d or e v e n n e g le c te d b y rubber in dustry.

A p p lic a tio n o f c o n v e n tio n a l “im p rin t” m e th o d to d eterm in e h a rd n ess o f th e su r fa c e layer, e v e n in the m ic r o sc a le , is n ot a b le to b rin g g o o d r e su lts d u e to in ­ s ig n ific a n t co n trib u tio n o f p la s tic d e fo r m a tio n in s h a l­

lo w d epth in d en ta tio n .

V ery p r o m isin g s e e m s to b e m ic r o in d e n ta tio n o f ela sto m e r s b a sed o n c o m p lia n c e m e th o d [3 ], e s p e c ia lly w h en sp h erica l in d en ter and lo a d - partial u n lo a d ap ­ p roach w ill b e a p p lied [4 ]. S p h erica l g e o m e tr y m a k e s p o s s ib le to vary th e d e g r e e o f d e fo r m a tio n o f m ateria l, o w in g to the in c r e a s e o f th e a n g le b e tw e e n ta n g en t to the co n to u r o f in d en ter and th e su r fa c e o f ela sto m er.

T h is is n o t a c h ie v a b le fo r c o n ic a l or p y ra m id a l in d e n ta ­ tio n s - F ig u re 1.

2. Experimental

2.1. Materials

•

B l e n d s o f e t h y l e n e - p r o p y l e n e - d i e n e r u b b e r (E P D M ) and lo w d e n sity p o ly e t h y le n e (L D P E ) w ere p rep ared w ith a tw o -r o lls m ill. T h e m a c h in e o p erated at tem p eratu re o f 1 3 0 °C , w e ll a b o v e the m e ltin g tem p era ­ ture o f th e c r y sta llin e p h a se o f p o ly e th y le n e , in order to fa c ilita te b len d in g . In the s e c o n d sta g e th e ro lls w ere c o o le d d o w n to 4 0 °C and d ic u m y l p e r o x id e (D C P ), as a c r o s s lin k in g a g en t, w a s in tr o d u c e d to th e sy s te m . C o m p o s itio n s o f the b len d s, to g eth er w ith c o n d itio n s o f th eir v u lc a n iz a tio n (P N -I S O 3 4 1 7 ) are g iv e n in T ab le 1.

B le n d s o f natural rubber (N R ) and tr a n s - 1 ,4 - p o ly - o cten a m er (T O R ) w e r e prep ared in an in tern al m ixer. In

T ab le 1. C o m p o s itio n s o f th e L D P E /E P D M b le n d s s tu d ie d T ab ela 1. S k ła d b a d a n y c h m ie s z a n in P E - L D /E P D M

No. Component Content [phr]

1.

Low density polyethylene (LDPE) 15

2. Ethylene-propylene-diene rubber (EPDM) 2) 100

3. Dicumyl peroxide (DCP) 3) 0.6

1)

Conditions of vulcanization (ISO 3417):

Poly­

ethylene Mw(GPC) Mw/Mn

Degree of crystallinity (WAXS), Xc [%]

Density, d Ig/cm3]

Degree of branching (FUR)

[CH

/IOO °C]

Melting temp. (DSC),

Tm f°C]

LDPE 1 15,000 2.32 47.3 0.930 3.8

LDPE 2 35,000 2.56 30.6 0.906

90

Ethylene-propylene- -diene rubber

; v //Density, t l d (g/cm3)

Ethylene content [%]

Mooney viscosity, M L (1+4)125 (C

Physical structure (DSC)

EPDM 1 0.860 71±4 59±5 block Xc = 3.9 %

EPDM 2 0.860 48±4 28±5 statistic Xc = 0 %

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technika mikroindentacji

th e s e c o n d sta g e a tw o -r o lle r m ill w a s a p p lied to in tro ­ d u ce D C P to th e m a teria ls. C o m p o s itio n s o f the b len d s, to g eth er w ith c o n d itio n s o f th eir v u lc a n iz a tio n (P N -IS O 3 4 1 7 ) are g iv e n in T a b le 2.

T ab le 2. C o m p o s itio n s o f th e T O R /N R b le n d s s tu d ie d T ab ela 2. S k ła d b a d a n y c h m ie s z a n in T O R /N R

Component Content [phr]

Natural rubber (NR) 100

t r a n s - 1 ,

4-polyoctenamer (TOR) 0-100

Dicumyl peroxide (DCP) 2) 0.6

^

C o n d i t i o n s o f v u l c a n i z a t i o n ( I S O 3 4 1 7 ) : 1 6 0 ° C , To.9

•

M ix e s o f s ty r e n e -b u ta d ie n e rubber (S B R ) co n ta in ­ in g 5 phr o f c a r b o x y lic a c id s o f v a rio u s len g th o f m a c ­ r o m o le c u le s ( C l 1- C l 7 ), p rep ared w ith a tw o -r o lls m ill, w e r e c r o s s lin k e d w ith 0 .6 phr o f D C P. C o m p o s itio n o f the b le n d s , to g e th e r w ith c o n d itio n s o f th eir v u lc a n iz a ­ tion (P N -I S O 3 4 1 7 ) , are g iv e n in T ab le 3. •

T ab le 3. C o m p o s itio n s o f th e n - c a r b o x y lic a c id s /S B R m ix e s s tu d ie d

T ab ela 3. S k ła d b a d a n y c h m ie s z a n in n -k w a s k a r b o k s y - lo w y /S B R

Component Content [phr]

Styrene-butadiene rubber (SBR) 100 n-carboxylic acid (SC 11 - SC 18) 5

Dicumyl peroxide (DCP) 0.6

Merck-Schuhardt (92 wt % o f purity), Germany

C o n d i t i o n s o f v u l c a n i z a t i o n

(

•

P e r o x id e (D C P ) v u lc a n iz a te s o f c / s - 1,4 -p o ly is o - p ren e (IR ) w e r e p rep ared in a ste e l m o u ld , un d er c o n d i­

tio n s d e te r m in e d r h e o m e tr ic a lly (P N -IS O 3 4 1 7 ). C o m ­ p o s itio n s o f th e m ix e s , to g e th e r w ith c o n d itio n s o f their v u lc a n iz a tio n , are g iv e n in T a b le 4.

T ab le 4 . C o m p o s itio n s o f th e p e r o x id e IR v u lc a n iz a te s s tu d ie d

T ab ela 4 . S k ła d b a d a n y c h w u lk a n iz a tó w n a d tle n k o w y c h IR

Component j Content [phr]

c is -

1,4-isoprene rubber (IR)1} 100

Dicumyl peroxide 2) 0.2-0.8

0 Cariflex IR 305 - Shell Int., U K

2) Merck-Schuhardt (92 w t % o f purity), Germany

C o n d i t i o n s o f v u l c a n i z a t i o n ( I S O 3 4 1 7 ) : 160 °C, T0 .9

S u lp h u r v u lc a n iz a te s o f sty ren e-b u ta d ien e rubber (S B R ) w e r e p rep ared in a ste e l m o u ld under c o n d itio n s d e te r m in e d r h e o m e t r ic a lly (P N -I S O 3 4 1 7 ) . V a rio u s c r o s s lin k in g s y s te m s c o n ta in in g su lp h u r (S^), su lp h u r d o n o rs (tetra m eth y lth iu ra m d is u lp h id e - T M T D ) or a c­

c e le ra to rs (m e r c a p to b e n z o th ia z o le - M B T , or d ip h e n y l- g u a n id in e - D P G ), w e r e p r o p o se d to g e t d ifferen t stru c­

ture o f c r o s s lin k s - T a b le 5 [5 ].

T ab le 5. C o m p o s itio n s o f th e s u lp h u r IR v u lc a n iz a te s s tu d ie d

,

T a b ela 5. S k ła d b a d a n y c h w u lk a n iz a tó w s ia r k o w y c h IR w r a z z e s k ła d e m i b u d o w ą c h e m ic z n ą w ę z łó w ich s ie c i p r z e s tr z e n n e j [ 5 ]

rl[ Component •. ’• •• Content ipbrj Styrene-butadiene rubber

(SBR) 11

crosslinking agent /system 2) 3)

!) Ker 1500 (Z. Chem. D wory S.A ., Poland) 2) DCP, TM TD , Ss+M B T or Sg+DPG

^

C o n d i t i o n s o f v u l c a n i z a t i o n ( I S O 3 4 1 7 ) : 160 °C, T0 .9

C o rin g a g e n t / s y s te m

Crosslinks structure Dicumyl peroxide (DCP) -c-c-

100%

Tetramethylthiuram disulphide (TMTD)

-C-C-, -c -s -c -

altogether

-C-S2-C- =22%

S8 + Mercaptobenzothiazole (Ss+MBT)

-C-C-, -C-S-C- altogether =5%

-C-S

-C- =74%

-C-Sx-C-x>3 -21%

S8 + Diphenylguanidine (Ss+DPG)

-C-C-, -C-S-C- altogether =2%

-C-S

-C- =8%

-C-Sx-C-x>3 =90%

C o m p o s itio n o f c r o s s lin k in g s y s te m w a s ad ju sted in d iv id u a lly in ord er to a ssu re sim ila r d eg ree o f the c r o s s lin k in g o f v u lc a n iz a te s.

•

C o m m e r c ia l p e r o x id e (D C P ) v u lc a n iz a te s o f a cry ­ lo n itr ile -b u t a d ie n e rubber (N B R ) fille d w ith carb on b la c k (C B ) w e r e su b je c te d to io d in a tio n rea liz e d b y e x p o s u r e o f th e su rfa ce to io d in e fro m eith er liq u id or g a s p h a se . T h e fo rm er to o k p la c e in L u g o l’s so lu tio n [8]

(L S ), w h e r e a s io d in e v a p o u rs (IS ) w ere u sed fo r the latter.

B ath ch lo rin a tio n o f co m m ercia l rubber for w in d ­ s h ie ld w ip ers w a s rea lized in th e solu tio n co n tain in g 1.7 - 2 .2 g o f C l/d m 3. R u b b er sa m p les b ased on natural rub­

ber (N R ) fille d w ith carbon b la ck (C B ) w ere im m ersed in fo the m o d ify in g m ed iu m for 2 3 or 4 6 m in., then taken o u t and w a sh e d w ith th e stream o f w ater to stop ch lorin e actio n , and fin a lly dried. D u e to their co m m ercia l appli-

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technika mikroindentacji

t e c h n i k a mikroi

Fig. 2. Determination o f the bloom thickness o f low molecular weight substances from the load-partial unload characteristics o f rubber:

- tangent to the load curve in the bloom layer,

- tangent to the load curve in the rubber substrate, 3 - the unload curve

Rys. 2. Wyznaczanie grubości wykwitów substancji malocząsteczkowych na podstawie charakterystyk obciążenie- częściowe odciążenie gumy:

- styczna do krzywej obciążania w warstwie wykwitu,

- styczna do krzywej obciążania w podłożu gumowym, 3 - krzywa odciążania

cation the recipes of the rubber mixes and details on the modifications have not been provided.

• Physical modification and exploitation aging The same NR vulcanizates filled with CB ware subjected to UV treatment in order to accelerate aging and modify the material. The home-made ozone cham­

ber contained UV source, multiple sample holder, air ventilators and 30 cm spherical mirror [9]. Rubber sam­

ples were exposed to the light of UV mercury lamp of 125 W (line 257 nm UVB) from the distance of 100 mm for 0.5 - 72 hrs. During experiments the chamber was intensively ventilated to prevent the modified surface from overheating.

The “fresh” vulcanizates were compared to the modified ones and additionally to the material of wind­

shield wipers after 2 years of service.

• Stress relaxation infilled rubber

Sulphur vulcanizates of solution styrene-butadiene rubber (s-SBR) filled with 50 phr of N234 carbon black were made of the mixes of different degree of filler agglomeration [10]. The dispersion index (DI) [11] for the samples varied from 2.6 (very poor) to 6.8 (good).

Due to the agreement on confidentiality within the RO­

TOR consortium [12], compositions of the rubber mixes studied have not been published.

3. Techniques

3.1. Spherical indentation

Microindentation experiments were carried out with a Nano Test 600 instrument (Micro Materials Ltd.,

UK) equipped with a 5 pm spherical indenter made of stainless steel. Elastomers studied were loaded with the speed of dP/dt = 0.03 mN/s up to the maximum value Pmax, which varied from sample to sample. Load - 90%

partial unload procedure from Spherical Indentation package [4] was applied for identation and data calcula­

tions. The software allows corrections for the “sink-in”

and “pile-up” effects.

Calculations on stress relaxation in CB filled s-SBR vulcanizates are based on creep data at Pmax, collected for 30 min.

Low molecular weight bloom thickness on rubber was estimated from the deflection point on the load-par­

tial unload characteristics of the systems - Figure 2.

4. Results & Discussion

4.1. E la sto m er-p la sto m er blends

Microindentation study confirms possibility of the surface segregation in LDPE/EPDM blends, suggested in the previous publications [13, 14]. Negative gradient of hardness can be associated with low molecular weight fractions of polyethylene being present in ex­

cess in the surface layer. Hardness profiles of the blends studied vary, depending on molecular weight and macromolecular structure of the both components:

plastomer and elastomer - Figure 3.

Simular conclussion can be drawn from microin­

dentation data of TOR/NR system - Figure 4.

Sta&fotH&iy nr 6 listopad - grudzień 2006 r. TOM 10

F ig . 3. H a r d n e s s p r o f ile o f th e L D P E /E P D M b le n d s s tu d ie d

A ) B le n d s o f s e q u e n c e d (E P D M 1) m a trix , B ) B le n d s o f a m o r p h o u s ( E P D M 2 ) m a tr ix R ys. 3. P r o fil tw a r d o ś c i b a d a n y c h m ie s z a n in P E - L D /E P D M

A ) M ie s z a n in y o m a tr y c y s e k w e n c y jn e j (E P D M 1), B ) M ie s z a n in y o m a tr y c y a m o r fic z n e j (E P D M 2 )

A ls o th is tim e , h a rd n ess p r o file fits in terp retation on the in c r e a s e d th erm al sta b ility o f rubber d u e to the a d d ition o f p o ly o c te n a m e r [1 5 ]. L o w m o d ecu la r w e ig h t fraction o f T O R , m ig r a tin g to th e su rfa ce p rotects N R , but a ls o s w e lls s im u lta n e o u s ly the su rfa ce la y er o f the b len d stu d ied .

M ic r o in d e n ta tio n d a ta sta y s in g o o d a g r e e m e n t w ith in v e s tig a tio n s o n m o r p h o lo g y (A F M ), structure (W A X S ) and c o m p o s itio n (F T IR , X P S ) o f th e su rfa ce la y er o f th e m a te r ia ls stu d ie d , p u b lish e d p rev io u sly . T h e resu lts c o n fir m p o s s ib ilit y o f se g r e g a tio n in p o ly ­ m er b le n d s , w h ic h is n o t o n ly lim ite d to th eir lo w m o ­ lecu la r w e ig h t c o m p o n e n ts . T h is fa ct is o f great im p o r­

ta n ce fro m th e p o in t o f v ie w o f u n d ersta n d in g and ta i­

lo rin g p ro p erties o f p o ly m e r m a teria ls to d ed ica ted e n ­ g in e e r in g a p p lic a tio n s.

4.2. Blooming of low molecular weight components

D e s p it e th e b lo o m in g o f lo w m o le c u la r w e ig h t c o m p o n e n ts in rubber is w e ll k n o w n , q u a n tita tiv e an a­

ly s is o f th e p h e n o m e n o n still le a v e s m u ch to b e d esired . D ir e c t m ic r o s c o p ic e x a m in a tio n s p ro v id e in fo rm a tio n o n ly on th e m o r p h o lo g y o f b lo o m , w h erea s its sp ectral a n a ly s is still req u ires th e te d io u s p ro ced u re o f c o lle c t ­ in g s a m p le m a teria l, w h a t is a d d itio n a lly a ss o c ia te d w ith a s ig n ific a n t error [1 6 ].

M ic r o in d e n ta tio n p r o v id e s d irect p o s s ib ility o f the e s tim a tio n o f b lo o m th ic k n e ss, to g eth er w ith their hard­

n e s s and th e su r fa c e to p o g r a p h y [1 7 ]. E x p erim en ta l data, c a lc u la te d fro m load -p a rtia l u n lo a d ch a ra cteristics

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technika mihroindentacii

technika mikroindentacji

F ig . 4 . H a r d n e s s p r o f ile o f th e T O R /N R b le n d s s tu d ie d R y s. 4 . P r o f il tw a r d o ś c i b a d a n y c h m ie s z a n in T O R /N R

o f the n -c a r b o x y lic a c id /S B R s y s te m s are g iv e n in Ta­

b le 6, to g eth er w ith oth er su r fa c e p a ra m eters o f the b lo o m s .

M e c h a n ic a l p ro p erties, to g e th e r w ith th ic k n e s s and c h e m ic a l in tera ctio n w ith rubber su b stra te d e c id e ab o u t the d u rab ility o f b lo o m and th e e f f e c t iv e n e s s o f its p ro ­ tectio n actio n [1 8 ].

4.3. Surface gradient of cross­

link density and structure

C r o sslin k in g o f IR w ith D C P p r o d u c e s th e su rfa ce g ra d ien t o f h a rd n ess, w h ic h d e p e n d s on the a m o u n t o f th e c r o ss lin k in g a g en t - F ig u r e 5.

T h e h ig h er th e a m o u n t o f d ic u m y l p e r o x id e a d d ed th e h ig h er th e s lo p e o f g ra d ien t trend.

T h e su rfa ce g ra d ien t o f h a rd n ess w a s a ls o c o n ­ firm ed fo r su lp h u r v u lc a n iz a te s o f IR - F ig u r e 6.

T ab le 6 C h a r a c te r is tic s o f th e b lo o m o f n -c a r b o x y lic a c id s , g e n e r a te d in th e S B R v u lc a n iz a te s s tu d ie d T ab ela 6 C h a r a k te r y s ty k a w y k w itó w n -k w a s ó w k a r b o ­ k s y l o w y c h p o w s t a j ą c y c h n a p o w i e r z c h n i b a d a n y c h w u lk a n iz a tó w S B R

Sample SBR ATg [°C]

Bloom thickness,

[pm]

Bloom roughness

Rms (nmj

Bloom bearing area [%]

SC — — 6 98

SC 11 15.6 0.02 8 71

SC 12 13.8 0.20 35 25

SC 16 7.7 4.74 227 52

SC 17 11.6 4.47 129 44

SC 18 7.7 3.42 256 71

SC - unmodified SBR

SC 11-S C 18 - SB R m odified with n-carboxylic acid con­

taining 11-18 carbon atoms in a m olecule

F ig . 5. In flu e n c e o f th e a m o u n t o f D C P o n th e s u r fa c e g r a d ie n t o f h a r d n e s s o f IR v u lc a n iz a te s R y s. 5. W p ły w ilo ś c i D C P n a p o w ie r z c h n io w y g r a d ie n t tw a r d o ś c i w u lk a n iz a tó w IR

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F ig . 6. I n f l u e n c e o f c r o s s l i n k i n g s y s t e m o n t h e s u r f a c e g r a d i e n t o f h a r d n e s s o f I R v u l c a n i z a t e s . V u l c a n i z a t e s c r o s s l i n k e d t o t h e s i m i l a r d e g r e e o f c a . 7 . 8 x l O ' 5 mo l / c m ^

R y s. ^{6 . W p t y w} z e s p o ł u s i e c i u j ą c e g o n a p o w i e r z c h n i o wy g r a d i e n t t wa r d o ś c i w u l k a n i z a t ó w I R . V u l k a n i z a t y p o s i a d a ł y z b l i ż o n ą g ę s t o ś ć u s i e c i o wa n i a o k . 7 , 8 x 1 0 ' 5 m o l / c m3

H o w e v e r th is tim e , apart fro m th e v u lc a n iz a te s o f m o n o s u lp h id e c r o s s lin k s (T M T D ), th e gra d ien t o f hard­

n e ss is n o t linear.

G e n e r a lly p o ly m e r s e x h ib it v ery p o o r h eat c o n d u c ­ tiv ity [1 9 ], w h a t m e a n s that v u lc a n iz a tio n in th e su rfa ce la y er ta k es p la c e at h ig h e r tem p eratu re in c o m p a r iso n to th e b u lk o f rubber. T o g e th e r w ith th e p o s s ib le su rfa ce m ig r a tio n o f lo w m o le c u la r w e ig h t c o m p o n e n t s o f c r o s s lin k in g s y s te m , it s e e m s v ery lik e ly to b e r e s p o n s i­

b le for th e m ic r o m e c h a n ic a l p r o file s d etected . T h is fa ct is very im p o rta n t fro m th e p o in t o f v ie w o f th e e x p lo i­

tation o f rubber g o o d s . T h e su rfa ce gra d ien t o f hard­

n ess, b e in g a c o n s e q u e n c e o f c h a n g e s to the a m o u n t and stru ctu re o f c r o s s lin k s , can in f lu e n c e fr ic tio n , w ear, th erm al and a g in g r e sista n c e o f rubber.

T h e e ff e c ts d e sc r ib e d a b o v e h a v e b een c o n fir m e d fo r th e S B R m ix e s (T a b le 5 ), v u lc a n iz e d in th e g rad ien t o f tem p eratu re. T h e ex p e r im e n ta l setu p to g eth er w ith an e x is tin g tem p eratu re g rad ien t, are d em o n stra ted in F ig u re 7.

P r o file s o f th e c o m p o s itio n o f c r o ss lin k s and their stru ctu re a lo n g th e h e ig h t o f v u lc a n iz a te , p resen ted in ou r p r e v io u s w o r k [2 0 ], are r e fle c te d by m icro in d en ta ­ tio n - F ig u r e 8.

T h e d ata p o in t on th e s ig n ific a n t in h o m o g e n e ity o f v u lc a n iz a te s , b e in g p ro n o u n ced already w h en the d is ­ ta n ce b e tw e e n s h e lv e s in a h ea tin g p ress is h ig h e n o u g h to crea te th e tem p eratu re gra d ien t alread y o f ca. 10 d e ­ g ree. It is a c h a lle n g e fo r te c h n o lo g is ts d e s ig n in g rubber m ix e s fo r th ick er g o o d s .

SćaA&wt&iy nr 6

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technika mikroin

F ig . 8. P r o f i l e o f h a r d n e s s a l o n g t h e g r a d i e n t of t e m p e r a t u r e i n a m o u l d f o r t h e S B R v u l c a n i z a t e s s t u d i e d

R y s. 8. ^Pr o f i l t w a r d o ś c i b a d a n y c h w u l k a n i z a t ó w S B R wz d ł u ż g r a d i e n t u t e m p e r a t u r y w f o r m i e

4.4. Chemical modification

T h e su rfa ce m o d ific a tio n o f rubber m a k e s p o s s ib le to tailor p rop erties o f th e m aterial to e x p lo ita tio n e x p e c ­ ta tio n s. T h e m e c h a n is m o f io d in a tio n o f b u ta d ie n e - a cry lo n itry le rubber (N B R ) and a s s o c ia te d structural c h a n g e s h a v e b een d e sc r ib e d p r e v io u s ly [2 1 , 2 2 ]. N o w , m icro in d en ta tio n data p r o v id e d - F ig u r e 9 , ca n c o n tr i­

b u te to th e e x p la n a tio n o n im p r o v e d tr ib o lo g ic a l p ro ­ p erties o f the su rfa ce io d in a te d rubber [2 3 ].

A p p lic a tio n o f L u g o l’s s o lu tio n [8] in in d u strial p ra ctice s e e m s to b e a le s s h arm fu l a ltern a tiv e fo r v a ­ p ou r io d in a tio n .

A n o th er e x a m p le o f in d u stria l p r o c e s s is th e bath c h lo rin a tio n o f w in d s h ie ld w ip e r s. A p p lic a tio n o f m i­

cro in d en ta tio n m a k es p o s s ib le to m o n ito r th e p ro g ress o f c h e m ic a l reaction and to o p tim iz e th e su r fa c e p r o file o f h ard n ess from the p o in t o f v ie w o f th e e x p lo ita tio n

e ff e c tiv e n e s s o f w ater r e m o v a l from a car w in d o w and th e d u rab ility o f a w ip e r b la d e. E v o lu tio n o f the hard­

n e s s o f rubber w ith the tim e o f treatm en t is p resen ted in F ig u re 10.

O n e ca n s e e th e e c o n o m ic a l a d v a n ta g e c o m in g fro m o p tim iz a tio n o f th e tim e o f ch lo rin a tio n .

4.5. Physical modification

U V treatm en t o f th e rubber b la d e s o f w in d s h ie ld w ip e r s in flu e n c e s m e c h a n ic a l p ro p erties o f th eir su rface la y er - T ab le 7.

C ontrary to th e e x is tin g o p in io n , this k in d o f m o d i­

fic a tio n ca n resu lt in a s ig n ific a n t im p r o v e m e n t o f the e x p lo ita tio n ch a ra cteristics o f w ip e r s [2 4 ]. C h e m ic a l c o m p o s itio n o f th e su rfa ce layer, d eterm in ed b y a p p li­

ca tio n o f N u c le a r R e a c tio n A n a ly s is [2 5 ], has r ev ea led g ra p h itiza tio n o f th e m aterial su b je c te d to m o d ific a tio n .

F ig . 9. H a r d n e s s p r o f i l e of t h e c o m m e r c i a l N BR v u l c a n i z a t e s , s u b j e c t e d t o t h e v a r i o u s k i n d s of s u r f a c e i o d i n a t i o n

R y s. 9. P r o f i l t w a r d o ś c i h a n d l o wy c h w u l k a n i z a t ó w N B R , p o d d a n y c h r ó ż n y m z a b i e g o m j o d o w a n i a n a p o w i e r z c h n i

SCa&fottteKty nr 6 listopad - grudzień 2006 r. TOM 10

F ig . 10. I n f l u e n c e o f t h e t i me of c h l o r i n a t i o n o n t h e h a r d n e s s o f r u b b e r f o r t h e b l a d e s o f c a r w i n d s h i e l d w i p e r s

R y s. 10. ^{W p ł y w} c z a s u c h l o r o wa n i a n a t w a r d o ś ć g u m y p i ó r wy c i e r a c z e k s z y b s a m o c h o d o w y c h

T ab le 7. I n f l u e n c e of U V i r r a d i a t i o n o n t h e h a r d n e s s of c o m m e r c i a l r u b b e r b l a d e s f o r c a r wi n d s h i e l d w i p e r s

T ab ela 7. ^{W p ł y w} n a ś w i e t l a n i a p r o m i e n i o wa n i e m U V n a t w a r d o ś ć h a n d l o w y c h pi ó r w y c i e r a c z e k s z y b s a m o c h o d o ­ w y c h w y k o n a n y c h z g u m y

M ech a n ica l property Tim e o f UV trea tm en t

o

15 min 30 min 1 hr 2 hrs 4 hrs 14 hrs

Hardness [MPa] 8.0 7.5 6.5 6.0 4.0 3.0 4.0

Mechanical modulus [MPa] 25.5 28.0 28.5 28.0 17.0 16.0 22.0

F ig . 1 1

.

R ys. 11. W p ł y w c z a s u e k s p l o a t a c j i n a p r o f i l t w a r d o s ' c i g u m y p i ó r wy c i e r a c z e k s z y b s a m o c h o d o w y c h

T h e d ep th o f c h a n g e s is lim ite d to s o m e h u n d red s o f n m , ly in g in th e ra n g e o f th e le n g th o f m a c r o m o le c u le s , w h a t a ssu res v ery g o o d a d h e sio n b e tw e e n th e grap h i- tiz e d sk in and th e rubber su b strate. O uter, g ra p h itized

part o f m a c r o m o le c u le s is lik e ly to root from the rubber su b strate [2 6 ]. T h e v ery thin grap h ite la y er on hard su b strate fa c ilita te s frictio n and red u ces w ea r [2 7 ], b e ­ in g c o m p e t itiv e to c o n v e n tio n a l grap h ite c o a tin g s.

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F ig . 12. I n f l u e n c e of t h e d e g r e e o f c a r b o n b l a c k d i s p e r s i o n ( D I ) o n s t r e s s r e l a x a t i o n i n s - S B R v u l c a n i z a t e s

R y s. 12. W p ł y w s t o p n i a d y s p e r s j i ( D I ) s a d z y n a r e l a k s a c j ę n a p r ę ż e ń w g u m i e z s - S B R

A b ra sio n r e sista n c e o f ru b b er is v e r y im p o rta n t fro m the p o in t o f v ie w o f e ff e c t iv e w a ter r e m o v a l fro m a w in d o w b y a w ip er. E d g e s o f a b la d e h a v e to stay sharp, o th e r w is e it le a v e s tra ces o f w a ter b e h in d [2 6 ].

A c tio n o f the rapid a p p lica tio n o f U V m u st d iffer s i g ­ n ific a n tly from e x p lo ita tio n a g in g . H a rd n ess p r o file s o f

“n e w ” and “o ld ” (after 2 y ea rs o f s e r v ic e ) w in d s h ie ld w ip e r b la d e s d em o n stra te rubber h a rd en in g , b e in g a c o n s e q u e n c e o f e n v ir o n m e n ta l a g in g - F ig u r e 11.

H ard and th ick sk in is fra g ile. It cra ck s and d e la m i­

n ates from rubber su b strate e a sily , b e in g r e s p o n s ib le fo r h ig h w ea r o f the m aterial and d eterio ra tio n o f the e x ­ p lo ita tio n b eh a v io u r o f w ip er.

4.6. Stress relaxation in filled rubber

R ubber is a m u ltic o m p o n e n t and a m u ltip h a s e s y s ­ tem . A part from th e k in d o f e la s to m e r m a trix , th e k in d and a m o u n t o f filler, th e d e g r e e and stru ctu re o f c r o s s ­ lin k s, v ery im p ortan t is th e o r g a n iz a tio n (m o r p h o lo g y ) o f s o lid p h ase.

T h e in f lu e n c e o f f ille r d is tr ib u tio n and a g g lo m ­ e ra tio n o n p ro p erties o f ru b b er is c o m m o n ly a c c e p te d b y rubber te c h n o lo g y . T h e e f f e c t ca n b e a ls o r e c o g ­ n iz e d b y m ic r o in d e n ta tio n . T h e in f lu e n c e o f f ille r d is ­ p e r s io n o n s t r e s s r e la x a t io n c a n b e e a s i l y d is t i n ­ g u is h e d b e tw e e n g o o d (D I = 6 .8 ) a n d b a d (D I = 2 .6 ) m ix e s - F ig u r e 12.

A b ility to stress rela x a tio n is o n e o f th e m o s t im ­ portant e x p lo ita tio n p ara m eters, d e te r m in in g e n g in e e r ­ in g a p p lica tio n s o f rubber.

5. Conclusions

T h e paper r e v ie w s p o s s ib ilit y o f th e a p p lic a tio n o f m icro in d en ta tio n to stu d y e la s to m e r s . In fo rm a tio n d e ­

riv ed from h a rd n ess p r o file , apart fro m h ard n ess v a lu e, can p r o v id e a lo t o f other, e v e n m o re v a lu a b le in fo rm a ­ tio n on th e su r fa c e s e g r e g a t io n , stru ctu ral c h a n g e s , c h e m ic a l m o d ific a tio n or a g in g . T h e y can b e u tilized eith er for th e m o n ito rin g o f c h a n g e s or to co rrect the c o m p o s itio n / treatm en t o f m aterial.

T h e m o s t im p ortan t fin d in g s , p r esen ted and d is ­ c u s s e d in th e paper, are su m m a r iz e d b e lo w :

• S e g r e g a tio n in p o ly m e r sy s te m s is n o t o n ly lim ited to th eir lo w m o le c u la r w e ig h t c o m p o n e n t s but tak es p la c e a ls o in p o ly m e r b len d s.

• R u b b er v u lc a n iz a te s e x h ib it th e su rfa ce grad ien t o f h ard n ess, b e in g a c o n s e q u e n c e o f d ifferen t d eg ree and structure o f c r o ss lin k s , crea ted d u rin g v u lc a n i­

za tio n , in th e su rfa ce la y er in co m p a riso n to the b u lk o f m aterial.

• T h e su rfa ce g ra d ien t o f h a rd n ess, crea ted during c h e m ic a l or p h y s ic a l m o d ific a t io n o f rubber, is v ery im p ortan t fro m th e p o in t o f v ie w o f its e x p lo i­

tation p erfo rm a n ce.

• S trees rela x a tio n in ru b b er d e p e n d s on the d eg ree o f fille r d istrib u tio n .

References

1 . H a m r o c k B . J . , J a c o b s o n B . , S c h m i d S . R . : F u n d a ­

me n t a l s o f M a c h i n e E l e m e n t s , W C B M c G r a w - H i l l ,

B o s t o n - L o n d o n - T o r o n t o 1 9 9 9

2. B i e l i ń s k i D . M . : K a u t s c h . G u m m i K u n s t s t . 5 7, 75

( 2 0 0 4 )

3 . O l i v e r W . C . , P h a r r G . M . : J . M a t e r . R e s .

Z

4 . w ww . m i c r o m a t e r i a l s . c o m

5 . Ś l u s a r s k i L , M i c h a l a k J . : P o l i m e r y 3 Q , 6 2 ( 1 9 8 5 )

6 . F l o r y P . J . : J . C h e m . P h y s . J J _ 5 2 1 ( 1 9 4 3 )

7 . K i r o s k i D . , S i ms J . , P a c k h a m D . E . , Gr e g o r y A . L . :

K a u t s c h . G u m m i K u n s t s t . 5 0 , 7 1 6 ( 1 9 9 7 )

8 . P o l i s h F a r m a k o p e a 4 t h E d . , P o l i s h P h a r m a c e u t i c a l

S o c i e t y , W a r s a w 1 9 9 3 , 2 , 6 3 6

SCa&fortt&iy nr 6 listopad - grudzień 2006 r. TOM 10

technika mikroind

9 . S z a f r a ń s k i P : A t t e m p t s t o P h y s i c a l a n d C h e m i c a l

M o d i f i c a t i o n o f t h e Ru b b e r B l a d e s o f W i n d s h i e l d

W i p e r s , M S c D i s s e r t a t i o n , T e c h n i c a l U n i v e r s i t y of

Ł ó d ź , Ł ó d ź 2 0 0 5

1 0 . B i e l i ń s k i D . M . , G ł ą b P, Do b r o w o l s k i O . , Ś l u s a r s k i

L : E l a s t o m e r y £ ( S p e c i a l I s s u e ) , 4 2 ( 2 0 0 5 )

1 1 . P N - I S O 1 1 3 4 5 : Ru b b e r - A s s e s m e n t of C a r b o n

B l a c k a n d C a r b o n B l a c k / S i l i c a d i s p e r s i o n . R a p i d

c o m p a r a t i v e m e t h o d s .

1 2 . C a n t a l o u b e B. : E l a s t o m e r y £ ( S p e c i a l I s s u e ) , 3

( 2 0 0 5 )

1 3 . B i e l i ń s k i D . M . , Ś l u s a r s k i L . , W l o c h o w i c z A . , D o u i l -

l a r d A . : C o m p o s i t e I n t e r f

5,

1 4 . Bi e l i ń s k i D . M . , K a c z m a r e k L : J . A p p i . P o l y m . S c i .

1 0 0 . 6 2 5 ( 2 0 0 6 )

1 5 . Bi e l i ń s k i D . M . , Ś l u s a r s k i L , K l e p s T , P a r a s i e w i c z

W . : P r ó g . R u b b e r P i a s t . T e c h n o l . I Z 1 2 3 ( 1 9 9 9 )

1 6 . P a r y s T . , P i a s k i e wi c z M . : P r o c . I n t . C o n f e r e n c e

E L A S T O M E R S ’ 9 8 , K - 1 4 . 7 5 , W a r s a w 1 9 9 8

1 7 . B i e l i ń s k i D . M . , Gł ą b P , Ś l u s a r s k i L , B o i t e u x G . ,

C h a n e l J - P . : J . A p p l . P o l y m . S c i . 8 & 3 3 6 8 ( 2 0 0 2 )

1 8 . B i e l i ń s k i D. M . , G ł ą b P , Ś l u s a r s k i L : C o m p o s i t e

I n t e r f . I Z 4 4 5 ( 2 0 0 5 )

1 9 . B r a n d r u p J . , I m m e r g u t E . H . : P o l y m e r H a n d b o o k

3 r d E d . , J o h n W i l e y & S o n s , L o n d o n - Ne w Y o r k 1 9 8 9

2 0 . B i e l i ń s k i D. M . , K a j z e r M. , Ś l u s a r s k i L , K a c z m a r e k

L : P o l i m e r y 5 ( J 2 9 8 ( 2 0 0 4 )

2 1 . Bi e l i ń s k i D . M . , Ś l u s a r s k i L . , A f f r o s s m a n S . , O ’ N e i l

S . , P e t h r i c k R . A . : J . A p p l . P o l y m . S c i . 6 4 , 1 9 2 7

( 1 9 9 7 )

2 2 . Bi e l i ń s k i D . M . , Ś l u s a r s k i L , W ł o c h o wi c z A . , Ś l u ­

s a r c z y k C z . : J . A p p l . P o l y m . S c i . 6 Z 5 0 1 ( 1 9 9 8 )

2 3 . Bi e l i ń s k i D . M . , Ś l u s a r s k i L : P o l i s h P a t e n t 1 8 2 3 7 2

( 1 5 . 0 9 . 1 9 9 7 )

2 4 . Bi e l i ń s k i D . M . , Gł ą b P : P o l i s h P a t e n t D e c l a r a t i o n

P - 3 7 7 4 8 5 ( 0 6 . 1 0 . 2 0 0 5 )

2 5 . N a s t a s i M . , T e s m e r J . : I o n B e a m A n a l y s i s Ha n d ­

b o o k , A c a d e m i c P r e s s , N e w Y o r k 1 9 9 6

2 6 . B i e l i ń s k i D . M . , Gł ą b P . , Ś l u s a r s k i L . : J . A c h i e v . M a ­

t e r . M a n u f a c t . E n g . ( 2 0 0 6 ) , i n P r e s s

2 7 . B o w d e n F . P . , T a b o r D . : A n I n t r o d u c t i o n t o T r i b o ­

l o g y , H e i n e m a n n , L o n d o n 1 9 7 4

ELASTOMERY 2007

„PRZEMYSŁ GUMOWY - NAUKA I PRAKTYKA”

XII Międzynarodowa Konferencja Naukowo-Techniczna organizowana przez

Instytut Przemyślu Gumowego „Stomil”, Stowarzyszenie EKOGUMA i firmę WERBA-CHEM GmbH

Konferencja odbędzie się w dniach 14-16 listopada 2007 r. w Warszawie w Hotelu Gromada Centrum, Plac Powstańców Warszawy 2.

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