Considerable attention has been given to the general area of adhesion and adhesives [1–3], but a need now exists to review more specific topics in these areas The nature of pressure-sensitive adhesives (PSA's) and the factors contributing to their performance are reviewed here A description for measuring performance of pressure-sensitive adhesives is followed by a treatment of physical and chemical factors that influence adhesive behavior These include surface energetics, rheological behavior, molecular weight, and functional-group contributions

Chemical and physical factors affecting performance of pressure-sensitive adhesives

The effect of polymeric molecular weight and molecular weight distribution on pressure-sensitive adhesive performance was studied in a model system of commercial polyisobutylenes. Molecular weight was characterized by size exclusion chromatography and membrane osmometry. Pressure sensitive adhesive performance was assessed by shear, peel, and probe tack testing based on standardized test methods. Lower molecular weight polyisobutylenes (Mw < 600,000) are successful in peel and probe tack testing due to their ability to flow quickly and wet the substrate test surface. They do not function as well in shear, however, where the polymer must resist flow under a load. High molecular weight species, by contrast, perform well in shear resistance tests and less successfully in peel and probe tack testing. Where high and low molecular weight polyisobutylenes are blended to broaden the molecular weight distribution while maintaining constant weight average molecular weight, adhesive performance in shear, peel, and probe tack are improved. All of the adhesive properties tested were found to have their foundation in some fundamental rheological properties of the polymers (e.g., shear viscosity and tensile creep compliance). This suggests the use of fundamental rheological characterization for screening of adhesive formulations over more empirical adhesive testing methods.

Shear, tack, and peel of polyisobutylene: effect of molecular weight and molecular weight distribution

The properties of asphalt binders strongly influence the overall mechanical response of asphalt mixture composites. A thorough understanding of the mechanistic behavior of asphalt binders is important in order to fully and accurately characterize the behavior of the asphalt mixture. The mechanical properties of the asphalt binder, the matrix in the asphalt mixture composite, are time and temperature dependent and have a lower stiffness compared to the inclusions (aggregate particles). However, computational methods used to model the micromechanics of asphalt mixtures typically assume a constant bulk modulus or Poisson’s ratio for asphalt binders. This research investigates the time-dependence of the bulk modulus of asphalt binders. Several approaches for measuring the bulk modulus were explored and the poker-chip geometry was found to be the most suitable one. The boundary value problem for the poker-chip geometry was solved to determine the bulk modulus and Poisson’s ratio of asphalt binders as a function of time. The findings from this research improve our understanding of the viscoelastic behavior of asphaltic materials, and also guide important assumptions that are typically made during computational modeling of asphaltic materials.

Using the poker-chip test for determining the bulk modulus of asphalt binders

Pressure-sensitive adhesives (PSAs) are materials which in dry form are aggressively and permanently tacky at room temperature and firmly adhere to a variety of dissimilar surfaces upon mere contact without the need of more than finger or hand pressure.1 They are widely used in familiar, everyday products such as masking tapes and office tapes, finger bandages and labels.

Pressure-Sensitive Adhesives for Tapes and Labels

The effects of rubber content, rate of peel and temperature on peel strength of ATBN modified DGEBA based epoxy resin adhesives have been investigated. The fracture surfaces of peel test specimens and the distribution of rubber particles in cured bulk epoxy resin have been observed with SEM and TEM, respectively. The mechanical properties of bulk rubber modified epoxy resin have been also measured. The peel strengths increased with increasing rubber content, peel rate, and decreasing temperature. The peel strengths were superposed as a function of rate and temperature. Plots of the shift factors against temperature gave two straight lines, which followed an Arrhenius relationship. The region of temperature below the intersection of the two straight lines, temperature somewhat lower than Tg of epoxy adhesive, gave markedly high peel strengths and a stick-slip failure due to plastic deformation of the adhesive, and a number of micro holes produced by the rupture of rubber micro particles on the fra...

The Effect of Modification of an Epoxy Resin Adhesive with ATBN on Peel Strength

Effects of molecular weight of adhesive polymer on T peel strength were investigated over a wide range of temperature and peel rate. Polyisobutylene fractions having narrow molecular weight distribution were used as the adhesive, and low-density polyethylene films as the substrate. The peel strengths were found to yield a single master curve with respect to the peel rate and the temperature for both the cohesive and the interfacial failures. It was found that the shift factor aT agrees with that of the Williams-Landel-Ferry (WLF) equation and is almost independent of the molecular weight of the adhesive. Furthermore, the master curves related to the rate-temperature are superimposed by the use of the shift factor aM, to yield a single master curve relation with respect to the molecular weight of the adhesive. In the case the cohesive bond failure, aM is related to the ratio of (M/MO)3.4.

Superposition of Peel Rate, Temperature and Molecular Weight for T Peel Strength of Polyisobutylene

A general formula for the tensile bond strength of a butt joint in the case of internal fracture is given in terms of a simplified model constructed from measurable parameters. The stress distribution under large plastic deformation is obtained from the stress equilibrium on the horizontal symmetry plane of the adhesive film. The yield condition of Mises or Tresca was employed. The theoretical formula shows good agreement with experimental results. The contraction ratio of lateral contractive strain to longitudinal tensile strain at yielding of the adhesive is given as a function of the aspect ratio and is independent of the adhesive materials used. The empirical relation between the bond strength and the contraction ratio is expressed by a single curve and also is independent of the adhesive materials used. The theoretical and empirical equations obtained indicate that the bond strength for the butt joint of internal fracture depends on both the yield strength and the aspect ratio of the adhesive.

Effect of Aspect Ratio on Tensile Bond Strength for Butt Joint of Internal Fracture—Theoretical and Experimental Analysis

The present investigation was undertaken to verify the criterion of the interfacial bond failure. The time-temperature superposition, the failure envelope, the dependence of the tensile bond strength on the degree of crystallinity and the fractography of the interfacial region of the adhesive were observed by the use of steel-nylon 12-steel cross lap joint. The ultimate tensile properties of the joint were found to be associated with the viscoelastic nature of the adhesive rather than with a thermodynamic criterion. The experimental results suggest that the Mises hypothesis can be applied to the tensile adhesive joint as the fracture criterion.

Mineo Masuoka

Papers

Superposition of Peel Rate, Temperature and Molecular Weight for T Peel Strength of Polyisobutylene

Effect of Aspect Ratio on Tensile Bond Strength for Butt Joint of Internal Fracture—Theoretical and Experimental Analysis

Criterion of Interfacial Fracture on Tensile Adhesive Joint