Effect of Addition of Various Acrylates on the Performance of Ethyl Cyanoacrylate Adhesive

This article was downloaded by:[CDL Journals Account] On: 17 September 2007 Access Details: [subscription number 780222585] Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Polymer-Plastics Technology and Engineering Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713925971 EFFECT OF ADDITION OF VARIOUS ACRYLATES ON THE PERFORMANCE OF ETHYL CYANOACRYLATE ADHESIVE P. Samatha a; T. Thimma Reddy a; P. V. S. S. Srinivas a; N. Krishnamurti a a Organic Coatings and Polymers Division, Indian Institute of Chemical Technology, Hyderabad, India Online Publication Date: 04 May 2000 To cite this Article: Samatha, P., Reddy, T. Thimma, Srinivas, P. V. S. S. and Krishnamurti, N. (2000) 'EFFECT OF ADDITION OF VARIOUS ACRYLATES ON THE PERFORMANCE OF ETHYL CYANOACRYLATE ADHESIVE', Polymer-Plastics Technology and Engineering, 39:2, 381 - 392 To link to this article: DOI: 10.1081/PPT-100100036 URL: http://dx.doi.org/10.1081/PPT-100100036 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 POLYM.–PLAST. TECHNOL. ENG., 39(2), 381–392 (2000) EFFECT OF ADDITION OF VARIOUS ACRYLATES ON THE PERFORMANCE OF ETHYL CYANOACRYLATE ADHESIVE P. SAMATHA, T. THIMMA REDDY, P. V. S. S. SRINIVAS, and N. KRISHNAMURTI* Organic Coatings and Polymers Division Indian Institute of Chemical Technology Hyderabad-500 007, India Abstract Polyalkyl 2-cyanoacrylates begin to retropolymerize and deteriorate dramatically at temperatures above 80°C. They bond rapidly to the metal surfaces and readily lose strength even at ambient temperatures. These two drawbacks of the cyanoacrylates have made this class of adhesives unpopular as structural adhesives. Several attempts have been made to increase the thermal stability and the stability of the bond between the metal surfaces by adding chemicals like cyclopentadienoates and anhydrides to the cyanoacrylates. Cyclopentadienoates are not available commercially, and, therefore, in this study, we have selected various acrylates and methacrylates in the cyanoacrylate formulation and these were tested to various temperatures. Interesting results have been obtained and reported. Key Words: Cyanoacrylate; Adhesives; Temperature resistance; Tensile strength; Alkyl acrylates and methacylates. * To whom correspondence should be sent. 381 Copyright © 2000 by Marcel Dekker, Inc. www.dekker.com Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER REPRINTS 382 SAMATHA ET AL. INTRODUCTION Alkyl 2-cyanoacrylates are enjoying increased popularity as instant and speciality adhesives in industrial and consumer markets. Cyanoacrylates, which could be classified as speciality structural adhesives, are known to be useful in bonding operations involving a wide variety of substrates. These adhesives require no heat, pressure, or addition of catalysts to cure. Adhesive action is a result of exothermal anionic polymerization by water molecules adsorbed on the substrate (1,2). The cyanoacrylate esters are distinguished from the other olefinic monomers by their ability to undergo rapid anionic polymerization initiated by mild nucleophiles, even in the presence of contaminants like water and oxygen, which efficiently inhibit most other anionic polymerizations (3). One of the properties of a cyanoacrylate adhesive bond is its low heat resistance (80°C) due to both the low glass transition temperature of the polymer and also the low onset of the thermal degradation. It is of practical interest to overcome, at least to some degree, this disadvantage to increase the versatility of the cyanoacrylate adhesives. In an attempt to cope with this problem, some cyanoacrylates containing an unsaturated bond in the ester radical of the molecule were synthesized recently (4). There are some general ways to increase the heat resistance of polymers (5–7). There are many theories as to the preferential reactions that might occur that are influenced by the addition of acrylic monomers. It is apparent that the addition of an acrylic monomer will alter the stoichiometry during the adhesive bond formation. The motivated assumption behind the present work is that after the typical anionic curing of the resin, the adhesive bond would be able to undergo heat-initiated cross-linking, due to the presence of an acrylic monomer, thus yielding a three-dimensional structure with improved thermal properties. EXPERIMENT Materials The monomers methyl acrylate (MA), methyl methacrylate (MMA), and hydroxy ethyl methacrylate (HEMA) (E. Merck, Germany) were used as-received. Diethylene glycol diacrylate (DEGDA), triethyleneglycol diacrylate (TEGDA), polyethyleneglycol(200)dimethacrylate [PEG(200)DMA], trimethylolpropanetri methacrylate (TMPTMA) (8), and ethyl cyanoacrylate (ECA) (9,10) were prepared in our laboratory. Adhesive Formulations Adhesive formulations were made by mixing different percentages of different monomers as shown in Table 1 and were left for 24 h to obtain clear and Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER REPRINTS PERFORMANCE OF ETHYL CYANOACRYLATE 383 TABLE 1 Ethyl Cyanoacrylate with Comonomers (Formulations) Sample No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Code No. Comonomer Monomer in the mixture IA IB IC ID IIA IIB IIC IID IIIA IIIB IIIC IIID IVA IVB IVC IVD VA VB VC VD VIA VIB VIC VID VIIA VIIB VIIC VIID Methyl acrylate Methyl acrylate Methyl acrylate Methyl acrylate Methylmethacrylate Methylmethacrylate Methylmethacrylate Methylmethacrylate Hydroxyethyl methacrylate Hydroxyethyl methacrylate Hydroxyethyl methacrylate Hydroxyethyl methacrylate Polyethyleneglycol(200)dimethacrylate Polyethyleneglycol(200)dimethacrylate Polyethyleneglycol(200)dimethacrylate Polyethyleneglycol(200)dimethacrylate Triethyleneglycol diacrylate Triethyleneglycol diacrylate Triethyleneglycol diacrylate Triethyleneglycol diacrylate Diethyleneglycol diacrylate Diethyleneglycol diacrylate Diethyleneglycol diacrylate Diethyleneglycol diacrylate Trimethylol propane trimethacrylate Trimethylol propane trimethacrylate Trimethylol propane trimethacrylate Trimethylol propane trimethacrylate 5% 10% 15% 20% 5% 10% 15% 20% 5% 10% 15% 20% 5% 10% 15% 20% 5% 10% 15% 20% 5% 10% 15% 20% 5% 10% 15% 20% homogeneous solutions. They were used for bonding mild-steel substrates and then bond strengths were determined. Tensile Bond Strength at Different Temperatures The tensile bond strength at different temperatures were determined according to the ASTM D-987-78 procedure, using ␲-test specimens and a Mikrotech Tensometer (India). Surface cleaning is the vital step in the bond- Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER REPRINTS 384 SAMATHA ET AL. TABLE 2 Tensile Bond Strengths of Pure Ethyl Cyanoacrylate Sample Bond strength No. Temp. (°C) (MPa) 1 2 3 4 5 6 7 30 50 75 100 125 150 175 18.2 21.55 11.39 6.07 3.03 1.59 0.30 ing process, as the adhesive bonds are extremely sensitive to surface contamination. Therefore, the ␲-specimens were cleaned with fine emery paper (No. 120) and then wiped with dry acetone. ECA adhesive compositions (0.03 mL) containing different acrylates were placed on one of the ␲-specimens and another ␲-specimen was placed on top of it to spread the adhesive in a thin film. The glued specimens were kept for 24 h at various temperatures from 25°C to 175°C, cooled to room temperature, and thereafter tested for resistance to a uniform direct pull. Bond strengths are shown in Tables 2–6. TABLE 3 Tensile Bond Strengths (MPa) with 5% Acrylic Comonomer Sample No. 1 2 3 4 5 6 7 Code No. 30°C 50°C 75°C 100°C 125°C 150°C 175°C IA IIA IIIA IVA VA VIA VIIA 7.74 13.6 18.83 7.97 9.87 21.55 Ͼ30 5.6 10.4 15.34 5.6 9.87 21.55 Ͼ30 10.2 15.9 7.2 4.17 8.35 10.2 16.7 2.43 6.9 3.03 1.36 7.9 9.11 14.4 2.65 2.58 2.2 1.36 3.03 3.03 3.36 1.57 2.27 1.36 0.78 1.57 1.57 0.91 0.37 0.37 0.45 0.53 0.45 0.53 0.15 Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER REPRINTS PERFORMANCE OF ETHYL CYANOACRYLATE 385 TABLE 4 Tensile Bond Strength (MPa) with 10% Acrylic Comonomer Sample No. 1 2 3 4 5 6 7 Code No. 30°C 50°C 75°C 100°C 125°C 150°C 175°C IB IIB IIIB IVB VB VIB VIIB 13.6 16.7 18.2 3.03 6.07 18.99 11.39 21.32 24.75 12.77 3.03 6.07 15.9 8.54 2.96 5.77 7.9 2.8 5.3 15.9 7.9 1.82 4.33 6.07 3.03 4.2 10.6 8.35 1.59 1.3 2.27 0.75 2.65 3.03 4.55 1.59 0.785 1.29 1.59 1.59 2.27 0.45 0.30 0.45 0.37 0.53 0.37 0.53 0.22 TABLE 5 Tensile Bond Strengths (MPa) with 15% Acrylic Comonomer Sample No. 1 2 3 4 5 6 7 Code No. 30°C 50°C 75°C 100°C 125°C 150°C 175°C IC IIC IIIC IVC VC VIC VIIC 26.58 30.03 15.90 2.27 9.87 18.90 11.39 12.91 22.79 21.27 1.59 9.11 24.75 9.11 6.45 12.15 7.21 3.03 7.21 9.87 7.21 3.03 3.03 5.69 3.42 5.69 7.90 5.30 3.41 5.08 1.59 2.27 5.08 4.55 4.55 1.89 2.12 0.78 0.30 2.17 2.59 2.57 0.30 0.22 0.30 0.22 0.30 0.15 0.30 TABLE 6 Tensile Bond Strength (MPa) with 20% Acrylic Comonomer Sample No. 1 2 3 4 5 6 7 Code No. 30°C 50°C 75°C 100°C 125°C 150°C 175°C ID IID IIID IVD VD VID VIID 18.7 21.27 4.17 2.05 6.07 9.49 3.79 9.87 17.1 4.4 2.27 5.3 7.2 3.03 4.55 3.03 4.55 2.27 6.07 9.87 2.65 4.93 4.55 2.65 1.59 3.19 2.65 4.71 2.27 4.17 2.27 1.59 3.79 4.71 4.55 2.27 2.65 2.27 0.6 1.59 1.59 2.27 0.30 0.45 0.22 0.15 0.3 0.6 0.45 Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER REPRINTS 386 SAMATHA ET AL. RESULTS AND DISCUSSIONS It is important to note the influence of the acrylic monomer in the adhesive mixture on the bond strength. The addition of the monomer enhanced the time of setting of ECA. This may be due to the increased solubility of ECA in the monomer. This is confirmed by the theoretical calculation of the solubility parameter (11) (Table 7), which shows that all the monomers used and ECA fall in the same solubility range and they are highly miscible. This causes the decreased availability of the anion, which can initiate the polymerization and results in the adhesive bond. The rate of reaction is low when the monomer is added to ECA. This is observed by the calculation of ⌬GLC values for hypothetical polymer structures. Tensile Strength The tensile strength of all the formulations were tested above their glass transition temperature (Tg ), so that the crystallinity will not become a problem. As all polymers are glassy, the internal stresses will be high when they are tested for tensile strength. The bond strengths obtained from different adhesive formulations are reported in Tables 2–6. These results are discussed in three groups: 1. 2. 3. Effect of monomer concentration Effect of substituent groups in the monomer Effect of temperature TABLE 7 Solubility Parameter of Monomers and Polymers by Fedor’s Method Monomer Sample No. Polymer ECoh V ␦ ECoh V ␦ MA MMA HEMA PEG(200)DMA TEGDA DEGDA TMPTMA ECA 1 2 3 4 5 6 7 8 Monomer Polymer 31,330 36,040 71,010 112,230 58,250 45,020 119,930 61,800 59.5 93 101.7 259.2 156.2 120.2 257.2 99.6 22.95 19.7 26.4 20.8 19.3 19.35 21.6 24.9 31,080 33,830 68,800 107,810 58,000 44,770 122,720 59,590 66.6 81.9 90.6 237 170.4 134.4 223.9 88.5 22.6 20.3 27.5 21.3 18.4 18.25 23.4 26.0 Note: ECoh ϭ cohesive energy (J/mol); V ϭ volume (cm3/mol); ␦ ϭ solubility parameter (J /cm3/2). 1/2 Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER REPRINTS PERFORMANCE OF ETHYL CYANOACRYLATE 387 TABLE 8 Copolymer Tg (K) in Different Wt% of Comonomer on ECA % of Monomer Sample No. 1 2 3 4 5 6 7 Comonomer 5 10 15 20 MA MMA HEMA PEG(22)DMA TEGDA DEGDA TMPTMA 399 406 403 403 400 402 409 390 405 398 399 393 396 410 382 403 393.6 394 386 390 411 373 401 389 389 378 384 412 Note: Theoretical calculation based on group contribution (11). Effect of Monomer Concentration It is seen that the tensile strength increased with the increase of the monomer (MA and MMA) content at room temperature (30°C). At a level of 5–15% monomer on the ECA, the tensile bond strength reached maximum (Tables 3–6). But above 15% monomer, the tensile bond strength reduced rapidly due to the reduced degree of cross-linking. In the case of MA, the thermal stability decreased as the monomer concentration increased. This can be explained on the lower Tg of MA (i.e., 276 K). As the concentration of the monomer (MA) is increased, the resultant Tg of the copolymer formed is decreased (Table 8); thus, the onset of degradation also decreased accordingly. The same pattern of degradation of the copolymer was noticed with MMA. However, the bond strengths of MMA formulations are higher than those obtained from MA copolymers, up to 150°C. This is due to the fact that the Tg of PMMA (378 K) is much higher than that of PMA (276 K). In case of DEGDA- and TMPTMA-based copolymers, the tensile strength decreased from 5% to 10%. This is due to the solvency effect. The bond strength remained constant from 10% to 15% and decreased thereafter. In the case of PEG(200)DMA, a constant decrease was observed. This may be the result of the plasticizing effect of the polyethylene glycol moiety present in PEGDMA. A typical differential scanning calorimetric (DSC) curve for DEGDA and ECA is shown in Fig 1. This emphasizes the two peaks present in the degradation curve. This imparts the evidence of forming a block copolymer rather than alternating. DSC curve of DEGDMA ϩ ECA film. 388 FIG. 1. Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER REPRINTS SAMATHA ET AL. Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER REPRINTS PERFORMANCE OF ETHYL CYANOACRYLATE 389 The two blocks have their own Tg and neither of the two matches with the homopolymer. This is because of the formation of the microdomain (i.e., in the block copolymer); the blocks of different chemical constituents have segregated into their own microdomains. The change in Tg may be due to the strain imparted by the block junction placed at the microdomain boundaries or from the partial intermixing of the different types of blocks into the microdomains of other types (12). Effect of Substituent Groups in the Monomer The effect of substituent groups plays a major role in controlling the polymerization. In the case of methyl methacrylate, when compared to methyl acrylate, the ␣-methyl protons increase the reactivity of the monomer (13); hence, the polymerization is faster than the mixture containing methyl acrylate. This is inferred by fast setting of the adhesive formulation. This is further supported by the free enthalpy (⌬H ) of the reaction calculated by the theoretical consideration of a hypothetical polymer molecule (11). In the case of PEG(200)DMA, DEGDA, and TEGDA, the internal plasticization decreased from PEG to TEG. The effect of this plasticization on bond strength is greater compared to the ␣methyl group in PEG(200)DMA. Compositions having DEGDA have higher bond strengths than those having PEG(200)DMA and TEGDA copolymers. When DEGDA (V), TEGDA (VI), and TMPTMA (VII) monomers are added to ECA, the bond strengths have considerably improved over the rest of the formulations and the bonds formed between stainless-steel surfaces have withstood temperatures moderately well up to 125°C (Tables 3–6). This is due to the fact that the diacrylates cross-link more effectively than the monoacrylates. Therefore, TMPTMA (VII), which is a trifunctional monomer, is expected to give highly cross-linked polymers with the increase in temperature. Because of this, the TMPTMA cyanoacrylate copolymers gave the highest tensile bond strengths, as expected. For example, even the 5% addition of TMPTMA in ECA gave bond strengths above 30 MPa at 30°C and this reduced to 14.4 MPa at 100°C. However, when we increased the monomer, Tg played an important role. At 20% of TMPTMA, the Tg of the resultant copolymer is about 139°C; below this temperature, it is a very brittle polymer and bond strengths decreased considerably from 5% to 20%. The addition of the HEMA monomer to ECA also improved the bond strength satisfactorily although it is a monoacrylate. However, the higher bond strengths were obtained because the hydroxyl group of HEMA initiated the anionic polymerization of ECA; this is evidenced by the infrared (IR) spectrum shown in Fig 2. At the same time, the cross-linking of the methacrylate group with ECA took place. FIG. 2. IR spectrum of HEMA ϩ ECA film. 390 CM-1 Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER REPRINTS SAMATHA ET AL. Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER REPRINTS PERFORMANCE OF ETHYL CYANOACRYLATE 391 Effect of Temperature The effect of temperature on the adhesive bond is dependent on both the Tg of the polymer and also on the degradation temperature of the copolymer. During the degradation, the polyethyl cyanoacrylate is supposed to liberate high yields of monomer rather than oligomers because of the tertiary carbon atom (14) present in the polymer backbone and also because of the blocking of chain transfer by the group at the ␣-position (11). The overall view of the effect of temperature on bond strength is that as the temperature increased, the bond strength decreased. At higher temperatures, the bond strengths obtained from copolymers are more than the values obtained from pure ECA. This may be due to the copolymerization of the acrylic monomer at higher temperatures and also the increase of the onset of the degradation temperature. At higher temperatures, the bond strength is greater in the formulations containing DEGDA than PEG(200)DMA and TEGDA. This can be explained by the fact that the PEGDMA is a more flexible polymer than the other two, as it contained a greater number of ethylene glycol moieties. However, in this series, as the temperature increased, the bond strength decreased. CONCLUSIONS The information and results reported in this work are with the objective of projecting the ECA performance by the addition of various acrylates to it, so that they can be used for higher-temperature applications. Among the formulations developed and studied, the tensile strength properties of the formulation containing trimethylol propane trimethacrylate (code No. VIIA) is found to be the best for its application at room temperature (30°C) and at 50°C. The formulation containing diethylene glycol diacrylate (code No. VIB) is giving appreciable tensile bond strength compared to ECA at 75°C and 100°C. In an overall view, formulation with 15% MMA (code No. IIC) has a better tensile bond strength at all ranges of temperatures compared to ECA alone. This study also accounts in effectively reducing the cost, as the monomer can be added as an additive. These formulations have good storage stability at 25°C. REFERENCES 1. H. W. Coover, Jr. and J. M. Mclntire, in HandBook of Adhesives, 2nd ed. (K. I. Skiest, ed.), Van Nostrand Reinhold, New York, 1976. 2. K. L. Shantha, S. Thennarasu, and N. Krishnamurti, J. Adhes. Sci. Technol., 3, 237 (1989). Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 ORDER 392 REPRINTS SAMATHA ET AL. 3. D. C. Pepper J. Polym. Sci. Polym. Sympos., 62, 65 (1978). 4. D. L. Kotzev, C. Konstantinov, P. C. Novakov, and V. S. Kabhinov, Bulgarian Patent 23, 321 (1997). 5. Z. Z. Denchev and V. S. 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Shershnew The Chemistry and Physics of Polymers, Mir Publishers, Moscow, 1990, p. 246. Downloaded By: [CDL Journals Account] At: 21:40 17 September 2007 Request Permission or Order Reprints Instantly! Interested in copying and sharing this article? In most cases, U.S. Copyright Law requires that you get permission from the article’s rightsholder before using copyrighted content. All information and materials found in this article, including but not limited to text, trademarks, patents, logos, graphics and images (the "Materials"), are the copyrighted works and other forms of intellectual property of Marcel Dekker, Inc., or its licensors. All rights not expressly granted are reserved. Get permission to lawfully reproduce and distribute the Materials or order reprints quickly and painlessly. Simply click on the "Request Permission/Reprints Here" link below and follow the instructions. Visit the U.S. Copyright Office for information on Fair Use limitations of U.S. copyright law. 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