Effect of polarity of bisphenol a epoxy resins on adhesion at cryogenic and elevated temperatures

Abstract

synopsisSubstituted bisphenol A epoxy resins have been prepared with substituents on the aromatic ring varying in polarity. The substituent effect on adhesion at cryogenic and elevated t,emperatures has been determined and shown to be of minor importance as compared to the epoxy content. The adhesives were evaluated on aluminum and stainless steel for tensile shear strength over the temperature range of -320' to +400"F. and in one case at -453°F. INTRODUCTIONDuring the course of investigating epoxy resins for their effectiveness as cryogenic adhesives which also show good elevated temperature properties, it was of interest to explore the use of substituted bisphenol epoxy resins for this purpose.In the literature there appeared no systematic study of bisphenol epoxy resins as cryogenic adhesives. However, Erich and Bodnar' had reported a preliminary investigation of the effect of molecular structure on the mechanical properties of epoxy resins which left many questions unanswered. It was not clear from their work what the epoxy content of each material was. In addition the adhesives were tested only at 73.5 and 160°F.; nevertheless, Erich and Bodnar showed that a decrease in shear strength is obtained at 160°F. when the methyl groups in bisphenol A are replaced by increasingly longer aliphatic chains. These correlations would have been more meaningful had they all been related in some way to their epoxy content.The object of this investigation was to compare the effect of polarity of substituted bisphenol epoxy resins with the epoxy content of these resins as factors in adhesion to aluminum over the temperature range from -320°F. to +400"F. The curing agent used was 4,4'-diaminodiphenylmethane. EXPERIMENTAL SynthesisEpoxy resins were prepared by a procedure2 known to produce compounds of low molecular weight and high epoxy content. 3707 IThe bisphenol compound (1.0 mole), epichlorohydrin (10.0 mole), and 5 ml. of water were mixed in a resin kettle fitted with a stirrer, condenser, and thermome'ter. Solid NaOH (2.05 mole) was added in six or seven small portions. After the first addition, the flask was heated and cooled alternately as required, while the NaOH additions were made, the pot temperature being maintained between 95 and 100°C. After the final addition, no further cooling was applied. When the exotherm had subsided, the epichlorohydrin was distilled off under vacuum (50 mm.) until the temperature in the flask reached 150°C. To the residue, cooled to 70"C., was added 50 ml. of benzene. The precipitated salt was filtered out and washed with 50 ml. of benzene. The benzene solutions were distilled until the temperature in the flask reached 125°C. and then the distillation was continued at 5 mm. until the temperature reached 170°C.The results are summarized in Table I. Bisphenols were prepared by the reaction of the ketone with phenol according to the procedure described by Erich and Bodnar' from aliphatic ketones.A typical preparation is the synthesis of 1 ,l-bis(4-hydroxyphenyl)-4-methylcyclohexane starti...

Tough Structural Adhesives with Ultra-Resistance to Both High and Cryogenic Temperature

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“…( c ) Measured steel bonding strengths at different temperatures. ( d ) Comparison of bonding strengths between MX/MXU resins and the structural adhesives in the literature and commercial products (Key: CP2050 [ 25 ] and E2534 [ 26 ] represent commercial Epoxy-Phenolic and Two-Component Epoxy adhesives, respectively; PU-10 [ 14 ], PU-11 [ 14 ] represent different polyurethane adhesives; EP-7 [ 27 ] represents Bisphenol A epoxy adhesives; BSA [ 28 ], PC10 [ 29 ] represent supramolecular adhesive; TPBC represents TPBC-toughened epoxy adhesive [ 12 ]).…”

Mechanical characterization of different epoxy resins enhanced with carbon nanofibers

“…Normally, strong polar attractions or direct bonds that can be formed between reactive sites in the resin and polar sites on the surface of the filler. Most inorganic materials (metals, minerals, glasses, ceramics) have some polarity so they have high surface energy, whereas organic polymer surfaces are generally less polar (more covalent) and lower surface energy [32,33]. In a very wide range of epoxy resins, polarity varies depending the molecules and curing conditions involved.…”

Versatile Epoxidized Soybean Oil-Based Resin with Excellent Adhesion and Film-Forming Property

“…As shown in Figure d, for bonding steel-involved hybrid substrates, 15–18 MPa shear strength was obtained. Moreover, the overall bonding performance of the MHE-1.0 resin is competitive to some high-performance petroleum-derived epoxy resins which are currently the most important structural adhesives and exhibit bonding strength for metals (steel and Al) of 4.45–19.65 MPa …”

“…Moreover, the overall bonding performance of the MHE-1.0 resin is competitive to some high-performance petroleum-derived epoxy resins which are currently the most important structural adhesives and 65 MPa. 28 To estimate the water resistance of the MHE-1.0 resin, the wet bonding strengths were tracked during 72 h by soaking the bonded steel specimens in cold water. The results in Figure 7e shows that the bonding strength remained in the range of 18− 20 MPa which is 75−83% of the original strength, indicating the adhesive can be used in a humid environment relying on its excellent stability toward hydrolysis.…”