Study of the interdiffusion of epoxy binder components

Polymer Science U.S.S.R. Vol. 20, pp. 2897-2903. ~) Pergamon Press Ltd. 1979. Printed in Poland

0032-3950/78/1101-2S97507.50/0

STUDY OF THE INTERDIFFUSION OF EPOXY BINDER COMPONENTS * N . Y E . SHUBIN, A . Y E . CHALYKH, A . ~4I. POIMANOV a n d YE. V. TROSTYANSKAYA I n s t i t u t e of Physmal Chemistry, U.S.S.R. A c a d e m y of Sciences Scientific Industrial Associatmn " P o l y m e r "

(Received 24 January

1978)

A s t u d y was made of the diffusion of an anhydride hardener into oligo-oxyester based on triglyeidylisocyanurate a n d products of solidification. The investigations were carried out in the temperature and time interval corresponding to the chemmal rateraction of the diffusion agent with oligo-oxyester. Coefficients of diffusmn were calculated within the diffusion range of displacement of components. I t was s h o ~ n t h a t an increase in the degree of hardening of oligo-oxyester reduces the dLffusion coefflcmnts of components of the e p o x y binder. The diffusion mobility of binder components into sohdified oligo-oxyester was determined and an assumption p u t forward concermng the appearance of optical and concentration heterogeneities in compositions. THIS s t u d y w a s c a r r i e d o u t t o e s t a b l i s h c a u s e s o f f o r m a t i o n o f c o n c e n t r a t i o n a n d o p t i c a l h e t e r o g e n e i t i e s i n a l l a r d e n e r - o l i g o m e r - f i l l e r s y s t e m . T h e filler w a s a solidified polymer of the same composition as the binder. The following were used for the investigation: m e t h y l t e t r a h y d r o p h t h a h c a n h y d r i d e (MTHPA) (m.p. 66°), ohgo-oxyester of M ~ 800 and a softening point of 70 to 75 °, b i n d e r oligo-oxyester-MTHPA alloy and a sohdffied binder. Oligo-oxyester was obtained b y prepolymerizatlon of triglycidylisocyanurate (m.p. 154°t with diphenylolpropane (m.p. 157 °) a t 160 ° for 20 rain with a 2 : 1 molar ratio of components; t h e binder was prepared b y melting 100 parts b y weight oligo-oxyester with 80 parts b y weight M T H P A a t 120--130 ° for 20-25 min to an acid numl)er of 180-200 mg KOH/g. The filler was obtained b y changing the binder to the three dimensional state a t 160 ° . Diffusion in b i n a r y systems (MTHPA-oligo-oxyester, M T H P A - b i n d e r , MTHPA-solidified binder and oligo-oxyester-solidified binder) was examined b y micro-interferometry [ 1, 2], which enables the variation of refractive index in the zone of interaction of components to be recorded with a m i n i m u m accuracy of 10 -~. Methods of experiments, analysis of interferograms a n d calculations of diffusion coefficients corresponded to a previous description [1]. Diffusion was investigated in the temperature range of 120-160 °, where epoxy resins are n o r m a l l y solidified with anhydride solidifiers.

Diffusion in the oligo-oxyester-solidifier system. F i g u r e s 1 a n d 2 s h o w i n t e r ference patterns typical of this system and corresponding curves of concentration d i s t r i b u t i o n o f t h e h a r d e n e r @1 a t d i s t a n c e x i n t h e r e g i o n o f i n t e r d i f f u s i o n o f * V y s o k o m o l . s o y e d . A20: N o . 11, 2581-2586, 2897

1978.

2898

N. YE. S m ~ 1 ~ et al.

components. Two time segments may be distinguished, in which reaction kinetics vary. With short times (t
F I a . 1. Interferograms of the range of interdiffusion: a--ohgo-oxyester-solidifier-- i0 min, 160°; b - - b i n d e r - s o h d i f i e r - - 1 5 min, 140°; c--filler of low network dens,ty-sohdifier--10 rain, 160°; d--filler of high network .density-solidffier-- 60 rain, 160 °.

Interdiffusion of e p o x y binder components

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diffusion Dr were determined within the range of this time interval using the Matano-Boltzmann method. Concentration dependences of coeffÉcients of ~ffusion are shown in Fig, 4a. I t can be seen t h a t Dr increases in proportion to the increase of MTHPA content in the zone of interdiffusion according to a steady continuous curve. The overall variation of Dr on transition from oligo-oxyester to a hardener reaches 1-5 orders of magnitude. A lower variation of Dr was recorded at 160 °, which is due to a slighter difference in the viscosity of oligo-oxyester and MTHPA at 160 °, compared with other temperatures. .2:~/T/n7

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FIG. 2. Curves of concentration distribution for an oligo-oxyester-solidifier system, 160% Time of diffusion, mln: 1--0"5, 2--4.5, 3--6, 4--8, 5--12, 6 - - 2 0 and 7--45. FiG. 3. Relation of x-t* for an oligo-oxyester-solidffier system, 160 °. Values of ~: 1 - - 0 , 2--0.1; 3--0.2; 4--0.3; 5--0.4; 6--0"5; 7--0"6; 8--0.7; 9--0.75; •0--0.8; 11--0.9 a n d 12--1.0.

Starting from a given moment of time, which agrees with gel formation of oligo-oxyester, the diffusion zone changes. 'In the region of contact of components a maximum appears, while straight lines x - t ~ (Fig. 3) change their gradient and the process is discontinued. Using the Matano-Boltzmann method for long periods of interaction, we calculated the effective coefficient of diffusion Deft. A study of concentration dependence (Fig. 4b) shows that diffusion slows down in the region of MTHPA compositions with a m a x i m u m product of concentrations of reacting substances and this is obviously due to the high rate of formation of the polymer, preventing the diffusion of the solidifier into oligo-oxyester. Furthermore, the reduction of the diffusion coefficient observed is due to a reduction in the concentration of MTHPA as a consequence of its reaction with oligo:oxyester. On the curve of concentration distribution along the coordinate (Fig. 4b) this is shown by the

2900

N. Y~. SaUBIN e t a / .

formation of a section, of which the slope is lower t h a n for end sections of branches of the concentration profile. The structure formed is characterized by the existence of a region with high internal stress which in some cases produces rupture in the mass of the polymer solidified at the boundary of contact with non-solidified oligo-oxyester. The probability of this rupture increases with a rise in temperature.

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FIG. 4. Dependence of log Dv (a) and log De~ (b) on the composition of the oligo-oxyestersolidffier system at 120 (1), 140 (2) and 160°. (3,3").Time of dtffusion, mm: a: 1--4, 2--5, 3--1; b: 1--25, 2--15, 3--12 and 3'--45. The hardener does not, subsequently, undergo diffusion through the zone of increased density. This m a y be due to the fact t h a t at temperatures of 120-160 ° the solidified polymer is in the glassy state (with a stoichiometrie ratio of oligo-oxyester and MTHPA Tg~ 150-155°). Diffusion in a binder-solidifier system. During interdiffusion of the solidifier and polymer at the stage preceding solidification (i.e. binder model) interference patterns are similar to interference patterns for an oligo-oxyester-MTHPA system (Fig. lb). Diffusion coefficients increase in the initial stages, compared with the previous case: when ql -~ 0 the value of Do is extrapolated to 5 × 10 -9 cm2/sec at 140 and 160 ° and 10 -1° 'cm~/sec at 120 °, followed by a reduction to 5× 10-1° and 8× 10 -11 cm2/sec, respectively (Fig. 5). The initial increase in diffusion coefficients is due to a fairly high mobility of binder molecules by the moment of contact with the solidifier as a consequence of the plasticizing action of the still' unreacted solidificr. As in the first system, at given stages of solidification of the binder the x-t t relation deviates from the linear, which is due to the transition of the binder into gel (Fig. 6). _Filler-solidifier. I t m a y be assumed t h a t for a polymer of low network density the diffusion coefficient differs slightly from diffusion coefficients in a solidifierbinder system at the intermediate stage of solidification. This was confirmed by a study of molecular diffusion of the solidifier into the polymer network with a

Interdiffusion of epoxy binder components

2901

considerable shortage of hardener, compared with the calculated amount--0.25. mole solidifier per 1 epoxy gro up. Diffusion of the solidifier was carried out from the moment of gel formation of the model filler. X~ n7m 12

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FIG. 5. Dependence of log Do on the composition of the binder-solidifier system: 1, 2-- 120 °, 2 and 12 mln; 3, 4--140 °, 2 and 24 rain, 5, 6--160 °, 1 and 10 rain; 2, 4 and 6 correspond to Dell. FIG. 6. Relation of x - t ~ for a binder-solidlfier system a t 140 °. Values of ~: •--0; 2--0.1; 3--0.2; 4--0.3; 5--0.4; 6 - - 0 . 5 ; 7--0"6: 8--0.7; 9--0.8; 10--0.9; 1 1 - - 1 . 0 .

As shown b y Fig. lb a smooth transition from the filler to the hardener is observed on the interferograms and when ~ -, 0, diffusion coefficients have about the same values as for the binder (Fig. 7). Polymers of high network density, obtained with a stoichiometric proportion of hardener had lower diffdsion coefficients (Fig. 7) and interferograms clearly indicate the phase interface between th~ solidifier and filler (Fig. ld). The diffusion coefficient varies during diffusion: some time after contact has been established the diffusion coefficient increases which is, evidently, due to an increase in segmental mobility of the three dimensional polymer network as a consequence of the plasticizing action of hardener molecules. Subsequently, the network swells, chain mobility is reduced and the diffusion coefficient decreases accordingly. It is also essential to bear in mind the possibility of contraction o f the three dimensional network as a consequence of the interaction of unreacted epoxy or secondary alcoholic groups contained in the solidified polymer with

1~. YE. SHUBIN •$ al.

-2902

an excess of hardener, which also reduces the coefficient diffusion. I n contrast with t h e previous two cases, during the interaction of the hardener with a polymer o f high network density, an optical boundary is maintained between t h e m which corresponds to the interface of t w o phases: the solidifier and the polymer.

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log Do -9

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/.0~

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"FIG. 7. Dependence of log D on the concentration of the solidifier for a filler-solidifier system: 1, 2--2 and 12 rain, 140°; 3, 4--1 and 7 rain, 160°; 5, 6, 7--1, 7 and 21 min, 140°. The filler was obtained by solidification of oligo-oxyester using 0.25 (1-4) and 1.00 mole solidlfier per epoxy equivalent. FIG. 8. Dependence of log Do on the amount of solidifier incorporated in the three dimensional network of the filler at 140 (1) and 160° (2). Results obtained for Do with different polymer network densities are of interest (Fig. 8): with an increase of ~sol to the equimolecular value, D Odecreases, which reflects an increase of steric hindrances with an increase of chemical network density. I t m a y also be noted t h a t these results of M T H P A diffusion in a binder and filler only represent a particular case of interaction in an oligo-oxyester-MTHPA system and therefore supplement results characterizing t e m p o r a r y changes of compositions examined. I n contrast with the hardener, oligo-oxyester obtained by melting triglycidyl iso'cyanurate and diphenylolpropane, has lower mobility: during interaction with a model filler for 1 hr the width of the region of interdiffusion has a minimum value of the systems examined and covers less t h a n 60/tm. This means t h a t -hardener molecules having a high rate of diffusion not only in the monomer-oli-

Diffusive flame of solidified epoxy resin

2903

gomer system, but also during interaction with an unsolidified binder and a three dimensional filler network, have the main rule during the interaction of components of the binder with the solidified polymer. Therefore analysing processes t a k i n g place in t h e systems studied it m a y b e n o t e d t h a t t h e y are more complex, c o m p a r e d with p o l y m e r n e t w o r k s o b t a i n e d b y a radical m e c h a n i s m o f p o l y m e r i z a t i o n [3]. The heterogeneous s t r u c t u r e of binders near the interface w i t h the mineral filler [4], as a consequence of selective a d s o r p t i o n o f c o m p o n e n t s in the case o f s y s t e m s w i t h a p o l y m e r filler, is f o r m e d as a result of diffusion of low molecular weight c o m p o n e n t s of the binder (solidifier) into a three dimensional-crosslinked filler n e t w o r k a n d increases with the increase of the c o n c e n t r a t i o n of the solidifier, increase of the d u r a t i o n o f c o n t a c t a n d with the increase of m o b i l i t y of t h e t h r e e dimensional polymer network.

Transla~d by E. S ~ m ~ REFERENCES

1. 2. 3. 4.

A. Ye. CHALYKH and R. M. VASENIN, Nauchnyye trudy MTILP, 1964 Yu. V. KOLOMIITSEV, Interferometry (Interferometers). Mashinostroyeniye, 1976 Yu. S. LIPATOV and A. M. SERGEYEVA, Uspekhi khimii 45: 138, 1976 Ye. B. TROSTYANSKAYA, V Sb. Napolniteli polimernykh materialov (Polymer Fill.ers). Izd. MDNTP, 1969

Polymer Science U.S.S.R. Vol. 20, pp. 2903-2908. ~ ) Pergamon Press Ltd. 1979. Printed in Poland

0032-3950/78/1101-2903507.50/@

MASS SPECTROSCOPIC EXAMINATION OF THE DIFFUSIVE FLAME OF SOLIDIFIED EPOXY RESIN* V. L. YEFREMOV,B. YA. KOLESNIKOVand G. I. KSANDOPULO S. M. Klrov State Umversity, Kazakhstan

(Received 26 January 1978) A study was made of the dflYusion flame of ED-20 sohdffied epoxy ream. Cylindrical samples were burnt in a mixture of oxygen and argon with a hne~r flow velocity of 5 cm/sec. Products of combustion were sampled from the flame usmg a quartz microprobe and analysed in an MI-1305 mass spectrometer. The presence of oxygen, carbon monoxide and dioxide and several other intermediate combustion products in the flame was established. It was shown that the introduction of a probe into th6 * Vysokomol. soyed. A20: No. 11, 2587-2591, 1978.