SynopsisPolyethylene, polypropylene, poly(viny1 fluoride) (Tedlar), polystyrene, nylon 6, poly(ethy1ene terephthalate) (Mylar), polycarbonate, cellulose acetate butyrate, and a poly(oxymethy1ene) copolymer were treated with activated helium and with activated oxygen. Mechanical strengths of adhesive-bonded specimens prepared from treated and from untreated coupons were compared. Polyet.hylene (PE) and polypropylene (PP) showed the greatest increases in bond strength. Oxygen and helium were both effective with polyethylene, but polypropylene showed no improvement when treated with activated helium. The results with excited helium parallel the effects of ionizing radiation on these two polymers, as does the appearance of unsaturation bands in the infrared (965 cm-' in PE, and 887 and 910 cm-1 in PP). Active nitrogen produced excellent bond strength with polyethylene but not with polypropylene. Of the remaining polymers examined, Tedlar, polystyrene, and nylon 6 showed the greatest improvement in bondability after treatment, and Mylar showed moderate improvement. Polycarbonate, cellulose acetate butyrate, and the poly(oxymethy1ene) copolymer gave approximately two-fold increases in lap-shear bond strength. I n several cases, significant differences in response to time of treatment and type of excited gas were found.
synopsisThe bondability of the following polymers as a function of length of exposure to excited helium or oxygen was investigated: lowdensity polyethylene, highdensity polyethylene (two types), poly(4methyl-l-pentene), poly(viny1 fluoride), poly(vinylidene fluoride), FEP Teflon, poly(oxymethy1ene) copolymer, nylon 6, nylon 66, poly(ethy1ene terephthalate), and polystyrene. Generally, the bond strength increases rapidly initially and then remains nearly constant, perhaps decreasing in some cases a t long exposure times. A method is presented for calculating bond strength-versusexposure time curves. The calculated curves generally fit the data reasonably well. Polypropylene showed a rapid increase in bondability with exposure to excited oxygen. Helium was ineffective toward this polymer under normal conditions, but could produce good bond strength at higher temperatures.
Poly‐(2,6‐dimethyl)‐1,4‐phenylene oxides and related copolymers have been evaluated for high temperature adhesive applications. Because of the high‐melting character of these polymers, proper wetting was found to be difficult to achieve. Where such conditions can be obtained, good tensile strength values have been reached up to 600°F. The introduction of allyl group and epoxy group into such polymers provides sites for thermosetting. The fast setting rate of these groups, however, introduces difficulty in bonding procedure. Problems and ways to improve the initial bonding of specimens are discussed.
The effect of varying the molecular structure of epoxy resins on their mechanical properties when used as adhesives was studied. The work was directed toward preparation of bisphenols of the general formula HOϕCR(R′)ϕOH where R and R′ are either alkyl or alicylic substituents, in which case the benzhydryl carbon is incorporated in a cyclopentane or cyclohexane ring for use in the preparation of glycidyl polyethers having the formula:
where B is the divalent hydrocarbon radical of the bisphenol and n is an integer of the series 0, 1, 2, 3… Preparation of 13 epoxy resins which are liquids at room temperature is described. The effect of varying the structure of the dihydric phenol in the epoxy resin on the strength of adhesive‐bonded joints was determined. The results indicate that relative bonding strengths of epoxy resins synthesized from various bisphenols can probably be attributed to the symmetry and chain length of the substituents attached to the carbon atom connecting the two aromatic nuclei. There is a high correlation between adhesive properties and steric influence of a substituted methyl group. Although the qualitative features of substitution on the central carbon atom are shown to be fairly well understood, there are a number of points that still require clarification. For instance, a more conclusive picture of the effect of branching is desirable. Also, there are uncertainties about the magnitude of the temperature effect and the influence of the substituent on the impact values.
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