Polyester adhesive shear strength

The lap shear test involves measuring the adhesive shear strength between two surface fluorinated polyolefin sheet tokens that are adhesively secured with a reinforcement resin. The tokens are individually reinforced with steel backing plates to eliminate flexural distortion in the shear joint. Lap shear tests carried out with various reinforcing polyester-type resins, contrasting fluorination and oxyfluorination as surface treatment, are shown in Table 16.8. 

Table 3.4 Adhesive shear strengths (thermoset polyesters)...

The reinforcing fabrics used were aramid (Kevlar DuPont) and poly(p-pheny-lene-2,6-benzobisoxazole) (PBO) (Zylon Toyobo). The fabrics were first treated with a 1.5% solution of HB PAMAM (AD-102), dried, then interleaved with an epoxy film structural adhesive (epoxy stage B on polyester net), and compression-molded for 90 min at 120 °C. For the aramid-based composite, FM-73 (Cy-tec) was used as the matrix. For the PBO-based composite, AF-191 (3M) was used as the matrix. The laminates were cut into strips and tested for interlaminar shear strength (ASTM D-2344) using a three-point bending instrament. 

P(2) Epoxy resins should be considered where higher shear strength than is available with polyester resins is required and the application requires good mechanical properties at elevated temperatures or durability. Epoxies occur in many varieties, feature high strength properties (as seen in some of the most effective engineering adhesives) and have been developed for water resistant coatings. 

Epoxies, isocyanate cured polyester, and cyanoacrylates are used to bond acetal copolymer. Generally, the surface is treated with a sulfuric-chromic acid treatment. Epoxies have shown 150 to 500 psi shear strength on sanded surfaces and 500 to 1000 psi on chemically treated surfaces. Plasma treatment has also been shown to be effective on acetal substrates. Acetal homopolymer surfaces should be chemically treated prior to bonding. This is accomplished with a sulfuric-chromic acid treatment followed by a solvent wipe. Epoxies, nitrile, and nitrile-phenolics can be used as adhesives. 

Effect of fiber treatments Alkali treatment on OPFs significantly improved its interfacial shear strength in polyester matrix [14]. Alkali treatment washed out the outer skin, better exposing fiber to the polyester matrix, leading to proper interaction between their surfaces. In addition, the fine holes created on alkali treatment allowed the polyester to penetrate into the fiber bundles in a better way. Acetylation treatment to the fibers improved impact strength of OPF-polyester composites due to improved fiber wettability and resulting fewer void spaces [71]. The tensile stress of OPF-polyester composites increased slightly upon both acetylation and silane treatments on fibers and decreased upon titanate treatment [14]. The flexural modulus of OPF-PP composites also increased considerably upon acetylation treatment on fibers. Similarly the abrasion resistance of OPF-polyester composites was enhanced upon alkali treatment to fibers [13]. Treated fibers enhanced the adhesion resistance of polyester resin by 75-85%, while untreated fibers enhanced the abrasion resistance only by 50-60%. 

The ability to control the interface is central to successful application of adhesion in a composite. By modifying or tailoring the interface, the improved fundamental adhesion might result in the improved practical adhesion for example, various surface treatments of ultra-high modulus polyethylene fibres used as reinforcemenf in polyester and epoxy composites that changed the values of both monofilament pull-out adhesion and interlaminar shear strength. ... 

Structural adhesive types recommended are epoxy (up to 71°C), polyester with isocyanate-curing agent (up to 121°C), and cyanoacrylate (up to 82°C). Structural adhesives for bonding acetal copolymer to itself have yielded shear strengths of 4.1—5.5 MPa. Nonstructural adhesives are usually... 

Adhesion is not an intrinsic property of a materials system, but is dependent on many factors. By now it should come as no surprise that the measurement of adhesion is sensitive to both rate and temperature as all of the other mechanical properties have been. In fact, adhesion can often be transformed by the WLF (Williams, Landel, Ferry) equation or Arrhenius transformation in the same maimer as modulus and other properties. Figure 11.7 shows the transformation of isothermal peel data transformed into a master curve along with the polyester adhesive s shear and tensile strength properties. In another study investigating the effect of temperature and surface treatment on the adhesion of carbon fiber/epoxy systan, five epoxy systems were found to fit an overall master curve when corrected for the material T. This result is quite remarkable and is shown in Fignre 11.8. 

Modified processing techniques have been useful for thermoplastic starch polymers. Recent work [45, 46] has examined the use of coextruded sheet processing to produce polyester / thermoplastic wheat starch / polyester multilayer films. They found that adhesion strength between the layers and stability of the interface were crucial properties in controlling the final performance properties of the films. Work by Sousa [47] has examined use of the novel shear controlled orientation injection molding (SCORIM) process to control morpholoiges and provide tensile property increases of thermoplastic starch/synthetic blends. 

Requirements of the adhesive. A full compliance spectrum for steel/concrete bonding has been published by the authors(18) and is reproduced as an Appendix at the end of the book. The purpose of the adhesive is to produce a continuous bond between steel and concrete to ensure that full composite action is developed by the transfer of shear stress across the thickness of the adhesive layer. Experience has shown that the best chance of success is likely to be achieved by using cold-cure epoxy based adhesives which have been specially developed for use in the construction industry. Provided that the surfaces have been prepared properly, these bond well to both steel and concrete and do not suffer shrinkage and cracking problems such as may occur with other systems like polyesters. For these purposes a cold-cure adhesive is defined as one which is capable of curing to the required strength between the... 

Low content of LC polyesters can also be used as a processing aid (lubricant), which effectively reduces the viscosity of the blends [123]. It is found that the LC polyesters domains do not always deform into fibrils during reinforcement for some LC polyesters/ thermoplastic blends. One must provide adequate shear stress and torque to deform it into elongated fibrils. The rule of thumb is to have process conditions which yield the viscosity ratio of the dispersed LC phase to the thermoplastic matrix to be lower than 1 [123]. The blends also suffer from poor adhesion strength between the LC polyesters phase and the thermoplastic matrix. Forming cross-linkable LCP blends is one of the ways to overcome it [124]. LC polyester/ LC polyester blends have also been developed [125] to yield LC polyesters with a better performance. 

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