Shear adhesion

Fig. I. Comparison of unprimed and eleetroprimed single lap-shear adhesive joint strengths for steel coupons bonded with imidazole-cured epoxy [43].

There is second shear adhesion test that is now being reported with increasing frequency, the so-called SAFT, or shear adhesion failure temperature test. It is particularly popular among block copolymer PSA developers. In this test [15], a shear specimen with an overlap area of 2.54 cm x 2.54 cm is prepared and suspended in a circulating air oven. A 1-kg weight is attached to the tape and the oven temperature is raised continuously 5.5°C per 15 min until failure. An industry wide standard has not yet been written for this test. 

Fr is the radial die wall force that develops because the powder is in a confined environment (i.e., not able to spread outward as pressure is applied down upon it because it is residing within the die). The coefficient of friction at the die wall, iw, is due to the shearing adhesion that occurs along the die a as the powder is made more dense and compressed. The following relationship between and FD, iw, and Fr is found to exist ... 

In essence, the durability of metal/adhesive joints is governed primarily by the combination of substrate, surface preparation, environmental exposure and choice of adhesive. As stated earlier, the choice of the two-part nitrile rubber modified epoxy system (Hughes Chem - PPG) was a fixed variable, meeting the requirement of initial joint strength and cure cycle and was not, at this time, examined as a reason for joint failure. Durability, as influenced by substrate, surface preparation, and environmental exposure were examined in this study using results obtained from accelerated exposure of single lap shear adhesive joints. 

The aging environments in which cured lap shear adhesive bonds were exposed included ... 

Another type of shear test involves testing under heated conditions. The shear adhesion failure test (SAFT) (FINAT FTM 8, PSTC-7) is a static shear test administered to a PSA sample under increasing temperature at a rate typically of 1 or 2°C per minute. The recorded SAFT value is the temperature at which the adhesive bond fails. 

Table III. Tensile Shear Adhesive Strength of Ozonized Lignin/Epoxy Resins. (Normal Test)...

Entry Holding Power 10N (ambient temperature) (min) Shear Adhesive Failure Temperature Bond Strength to Polyethylene (N/cm)... 

These standards now also include the method for measuring shear adhesion, which is essentially the same as for shear but the test piece is strained at 50 mm/min and the force at break recorded. 

Yoon TH, Arnold CA, McGrath JE (1989) Titanium 6/4 single lap shear adhesive performance of polyimide homopolymers and poly(siloxane imide) segmented copolymers. Mater Res Soc Symp Proc 153 (Interfaces Polym Met Ceram) 211... 

Berger EJ(1991)A method of determining the surface acidity of polymeric and metallic materials and its application to lap shear adhesion. 

D 3528 Test Method for Strength Properties of Double Lap Shear Adhesive Joints by... 

Shear adhesion studies In this Laboratory have been made on... 

Shear Adhesion—(Also called creep resistance) The force required to pull a gasket from a standard surface in a direction parallel to that surface. 

PA-6 (80) / PS (10-16) / SMA (2% MA) (4-10) internal mixer at 240°C / torque rheometry / SEM / selective solvent extraction / DSC / morphological stability to annealing / lap shear adhesion / comparison to PA-PS block copolymer compatibilized blends Park et at., 1992... 

PA/PS blends have been compatibilized through block copolymer formation between amine-terminated PA and anhydride-terminated PS. Anhydride end-groups were introduced into PS through reaction of either anion-terminated PS or hydroxy-terminated PS with trimeUitic anhydride chloride. Park et al. [1992] blended 80 parts PA-6 with 10-16 parts PS and 4-10 parts anhydride-terminated PS in an internal mixer at 240°C. The blends were characterized by torque rheometry, SEM, selective solvent extraction, DSC, morphological stability to annealing, and lap shear adhesion. The effect... 

Dharmarajan et al. [1995] have prepared com-patibilized blends of PO/PP/styrene copolymer. Blends of 100-0 parts PP, 0-100 parts SMA, 0-15 parts EP-g-l° amine (0.3 mol % amine), and 0-5 parts PP-2° amine (0.4 wt% amine) were combined in an internal mixer at 220°C. Blends were characterized by FTIR, DMTA, TEM, rheology, mechanical properties, lap shear adhesion, and paint adhesion. Properties were compared for blends containing either of the two amine-functionalized polymers alone. 

EMAc (100-0) / vinyl-functionaUzed PDMS (3.8% vinyl) (0-100) LDPE (50) / EMAc (0-10) / vinyl-functionalized PDMS (3.8% vinyl) (50) internal mixer at 85-180°C / capillary rheometry / DMA/FTIR internal mixer at 180°C / mechanical properties / DMA / FTIR / SEM / WAXS / X-ray diffraction / lap shear adhesion Bhattacharya Cl/., 1995 SaatraetaL, 1993a Santra et aL, 1993b... 

The shear adhesion strength of the PU formulations was tested by single lap shear joints, according to ASTM D 1002-94 (at a rate of 1.3mmmin ). Peel strength was evaluated by T-Peel (ASTM 1876-95) (at a rate of 254 mm min ). 

EHA), vinyl acetate (VAc) and acrylic acid (AA), and with varying contents of 2-hydroxyefhyl methacrylate (2-HEMA) and an unsaturated benzophenone derivative (P-36). The UV-crosslinking behavior of the PSAs was monitored by FTIR-ATR and PSA performance was evaluated by probe tack, peel strength, and shear adhesion failure temperature (SAFT) after exposure to various UV doses. 

---