Adhesive Bond Properties of Ethyl-2-cyanoacrylate Modified with Poly(methylmethacrylate)

J4 Adhesion, W88, Vol. 25. pp. 2A5—Z53 Reprints available directly irom the publisher Photocopying permitted by license only © 1933 Gordon and Breach Science Publishers, Inc. Printed in the United Kingdom Adhesive Bond Properties of Ethyl- 2-cyanoacrylate Modified with Po|y(methy|methacry|ate) C4 PETROV. B. SERAFIMOV and D. KOTZEV Scientific Industrial Centre for Special Polymers, Kliment Ohridski St 4A, 1 155 sorva, Bulgaria (Received June 30, 1987; in fimzlftzrm October 26, I937} The mechanical properties of the adhesively bonded joints with ethyl-2-cyanoacrylate and ethyl-2-cyanoacrylate modified with poly(methy|methacryIaIe) weie determined. The modifier lowers tensile stifiness, increases deformahility and relaxation of the adhesive bond and improves impact resistance. A morphological structure similar to an interpenetrating network system is suggested which arises trom the rapid polymerization or the solvent. The results obtained may he helplul for the design or joints with cyanaacrylate bonding. KEY WORDS Adhesively banded joints‘ cyanaacrylate; ethyl-2-cyanoacrylate; PMMA; mechanical properties; glass transition: interpenetrating network. INTRODUCHON The ability of cyanoacrylates to bond most materials in seconds has produced spectacular growth in their production and application.‘ One of the ways to overcome the poor impact resistance of their adhesive-bonded joints has been the introduction of polymer modifiers into the cyanoacrylate monomer. Poly(methy|meth- acrylate),2 po1y(butadiene-co-acrylonitrilef and copolymers of methyl acrylate and ethylene‘ are some of the polymer modifiers which were found to decrease the brittleness of the resultant bond. 245 246 C. PETROV. B. SERAFIMOV AND K. KOTZEV The aim of this paper is to study the influence of poly(methyl- methacrylate) modifier of ethyl 2-cyanoacrylate on the stiffness, strength, deformation characteristics and relaxation properties of the resultant adhesive bond between steel specimens. EXPERIMENTAL 100% GC pure ethyl 2-cyanoacrylate (ECA) was obtained by distillation of the commercial product Kanokonlit E. It was stabi- lized with 250 ppm hydroquinone and 200 ppm p-toluenesulfonic acid. Modified adhesives were obtained by dissolving specified amounts of poly(methylmethacrylate) into the ethyl 2-cyanoacrylate monomer by mixing at 50°C. The poly(methyl methacrylate) (PMMA) was commercial grade bulk polymer with molecular mass of 1.5 x 10‘. All mechanical tests were performed on steel (0.Z%C content) bonded joints. The surfaces to be bonded were roughened with Igel 400 sandpaper and degreased with trichloroethylene. Chemical treatment or activation were not employed. Universal testing machine Zwick 1474 was used. Tensile shear strength was deter- mined in accordance with ASTM D-1002 on single overlap specim- ens. After adhesive application the joint was clamped and left for 24h at 20—22°C and 55-65% relative humidity. The crosshead speed of testing was 50mm/min. The reported values are the averages of 15 tests. Tensile strength was determined in accordance with ASTM D2095 on cylindrical specimens. No clamping was employed. All other conditions were as specified above. Impact strength was determined in accordance with ASTM 950-72. The test specimen for shear strain determination had dimensions shown on Figure 1.5" The thickness of the glue-line (0.05 mm) was controlled with the use of calibrated copper wire. The test specimen for tensile strain determination is shown on Figure 2.7 This multilayer structure was chosen because it provides a means for increasing the absolute value of deformation within measurable limits. All adhesive layers had a thickness of 0.05 mm controlled with calibrated copper wire. To obtain the necessary co-axiality a specially cut Teflon jacket was used for assembly of the specimens after adhesive application. MODIFIED ETHYL-Z-CYANOACRYLATE ADHESIVES 247 i . I / \\ \i2i FIGURE 1 Test specimens for shear strain determination (Rel. 5,6) (Dimensions in mm) For determination of the real proportionality limit in the stress- strain dependence a cycle of "loading-pause-unloading-pause" was employed. The rate of loading and unloading was 0.025 mm/min. The loaded pause (600 sec) was used as the criterion for appearance of visco-elastic strain. The unloaded pause (600 sec), on the other hand, was a measure of the reversibility of the strain. Strain was measured with an lnstron G-51-11-M extensiometer and the strain/time dependence was recorded with the help of additional Tacussel EPL-2 recorder. Relaxation experiments were conducted on bonded specimens with dimensions according to ASTM D1002. The bonded specimens were loaded in tension with 100 mm/min {.4 FIGURE 2 Test specimens tor tensile strain determination (Ref. 7) (Dimensions in mm) 248 C. PETROV, E. SERAFIMOV AND K. KUTZEV crosshead speed at 22 + 1°C to a constant strain and kept there for 60sec. The time required for achievement of stress equilibrium was recorded. The relaxation time was calculated by the following formula: 0 : (10 e'‘’’ (1) where r~relaxation time a.,—initial stress at time t= 0 a—stress after time interval 2 The calorimetric experiments were conducted on a Perkin-Elmer DSC-2C. The samples used were from the adhesive layer, removed after failure of bonded joints. The scanning rate was 20 deg/min. RESULTS AND DISCUSSION Figure 3 shows the stress—strain curves for bonded joints in the shear tensile loading mode. In the case of the bond based on pure ECA 22 \ \ a my H1 ,2 w ~s. sw:mu‘a i FIGURE 3 Stress-strain relationship in shear mode for cyanoaclylaze adhesive hands l—pure ECA 2—ECA containing 4 wI,% PMMA MODIFIED ETHYL-2»CYANOACRYLATE ADHESIVES 249 02 SYFHS5 lNFu‘ \ \n 3 1/ \% 4 . lwr In flantenv oi Dol)‘l’"9"‘:/lmethaer)mtel FIGURE 5 Tensile stillness of bonded joints as function of PMMA content in ECA 4. The linear relationship is maintained until 63% of failure stress is reached for pure ECA bond (curve 1) and 56% of failure stress for the modified ECA bond (curve 2). The visco-elastic strain com- ponent is registered in the stress interval 63-80% of failure for the ECA bond and 56-70% of failure for the modified ECA bond. Creep is registered at stress above 80% and 70% of failure stress, respectively. At failure, the strain for the pure ECA bond is 1.0% and 1.8% for the modified ECA bond. When the data for shear and tension are compared it is evident that the strain of the adhesive bond in the shear mode is one magnitude higher than that in the tensile mode. The incroporation of PMMA into the ECA adhesive increases the susceptibility of the bond to deformation. Figure 5 shows the data for the stiffness or modified and unmodified ECA bonds. The stifiness values were determined from the mid—range of the linear proportionality part of the stress-strain relationship. Tensile stiflness falls by almost half upon modification MODIFIED ETHYL-2-CYANOACRYLATE ADHESIVES 2st TABLE I Physico-mechanical properties ofetltyl 2-cyanoaerylate adhesive bonded joints Strain Strain Tensile at at shear failure Tensile tnitnre Impact Tensile strength (shear) strength (tension) strength stittness Adhesive (MPa) (%) (MPa) (%) (tr!/in‘) (MP2) ECA 19 24 30 1.0 4.3 2400 ECA oontg. 19 30 30 1.3 5.2 I303 4wt.%i>MMA t: q 3 2 mm , at E 4 ~«: 5 ./ ‘s . / um - Q / 2 o 2 / X. 3 2410, I / 3 / «— sci: '49 . 2—££u~mPMMI:' 3— E12/1»/«Z twin :7 I17 20 an m 547 so 70 3 Reialtve strum, 7. ‘M FIGURE 6 Stress relaxation at constant strain of ECA adhesive bonds 252 C. PETROV, B. SERAFIMOV AND K. KOTZEV M:AL/ 5:: § r— ECA 2— ECA . a-/. sum: non 3m 3&0 350 sen Lao an an ass YEMDERMUFE Mi FIGURE 7 Glass-transition of ECA adhesive bonds of the adhesive with PMMA, then levels off and is not further considerably lowered with the increase of polymer modifier quan- titiy above 2 wt.%. The influence of PMMA modifier is demonstrated also by the mechanical properties of the adhesive joint, summarized in Table 1. The introduction of a small amount of PMMA does not reduce the tensile or shear strength but increases the impact strength of the bond and its deforrnability. The data for stress relaxation at constant strain (Fig. 6) show a lower relaxation time for the bond based on modified cyano- acrylate. These results correlate well with the DSC study of adhesive removed from the bond layer (Fig. 7). The glass—transition of the ECA adhesive bond is 127°C. The bond containing 3wt.% PMMA shows a T3 of 111°C. The specific heat of the glass—transition of the modified adhesive is half of that for the ECA. This shows that the incorporation of high molecular mass PMMA into ECA produces a mild plasticization of the adhesive bond. The higher defonnation susceptibility, the lower stiffness, in- creased relaxation ability and single glass-transition point of the t i 1 3 MODIFIED ETI>{YL«2«CYANOACRYLATE ADHESIVES 253 adhesive based on ECA modified with PMMA lead to the assump- tion that a morphological structure, similar to that of an inter- penetrating network system may be formed, as a result of the rapid polymerization of the PMM’s solvent. The data obtained in this study provide the necessary information for practical stress determination in designing cyanocrylate bonded joints bearing statis loads. Relovanees . Japan /wt. Ind, Book (Tokyo, was), p.57. . D. L. Kotzev and L. B. Diclteva, 1:1 Nat. can/. Chemistry (Sofia. 1955), p. 415. . v. Kabaivanov, D. Kotzev er n!., Bulgarian Pntertt 29, 439, (1979). . .l. 1. O'Connor. US Patent 4, 440, 910, (1954). A t. P. Jeandrau, Int. 1. Adh Adhesives o(4), 229431 (1986). . w. Altltofarvd w. Brockntann, Adh. Age zttm), 27 (1977). . A. E. Freidin, Strength and Durability nfAdIte.n'v: Jairtt: (Hintia, Moscow, 1981), pp. ll3—ll4. ~to»tnA(»--—-