Bonding Rubber to Metal

There is a stronger case for using polyurethane adhesives to bond rubber to metal than metal to metal. It is reported that an observation made during investigation of the isocyanates as vulcanizing agents. leads to their examination in bonding rubber to metal. When the new technique became known in 1945 it was considered to be an important advance, but time has since shown it to be only limited industrial value. There are today a number of adhesive capable of bonding rubber to metal satisfactory, for example, some epoxy resins and some of the two-polymer adhesives. But there is one important difference; the polyisocyanates are capable of satisfactorily bonding unvulcanized rubber, whereas the other adhesives are not. Polyisocyanates can therefore to be used to bond rubber to metal, as can also be done in the brass plating method during the process of vulcanisation. The reactivity of the rubber composition usually makes the addition of a crosslinking agent unecessary.

The most satisfactory results are obtained with aluminum and magnesium alloys and with steel, the preferred isocyanate being triphenylmethane triisocyanate. The rubber to metal bond strength has been claimed to be of the same order as that obtained by the brass plating method. The compatibility of the isocyanates with certain rubber has enabled involved polyurethane adhesives to be formulated by the incorporation of a proportion of rubber.

Gluing Metal to Metal

As metal to metal glues the polyurethanes are inferior to epoxy resin adhesives and to the best two polymer adhesives. Test on aluminum alloy using a number of polyurethane systems based on tolylene diisocyanate and saturated polyesters have shown the highest tensile shear strength that can be obtained is less than half that given by the best epoxy resin and two polymer adhesives when cured at 150oC. The strength of hot-cured metal to metal joints can be markedly improved by incorporating a relatively high proportion (up to 25%) of polyvinyl butyral, or formal, with which tolylene diisocyanate is compatible; peel strength, not usually very good is polyurethane adhesives is also substantially increased by such an addition. Increasing the proportion of polyester, thereby again increasing the flexibility also improves peel strength, but at a point where the gain becomes worthwhile a decrease in shear strength inevitably follows.

In examining as an adhesive for aluminum a polyurethane based on a triisocyanate and hydroxylated polyesters, it was found that the polyester having the lowest hydroxyl content gave the strongest bonds. This is rather surprising, but since the bonds were also reported to lack water resistance, it is interesting to consider whether the adhesive system contained hydroxyl groups in excess of the isocyanate requirement.

In a study of the effect of the ratio of molecular weight to isocyanate and others compared the adhesive strength of MDI and TDI. Using the same polyol mixture, it was bound that at room temperature (about 24oC) both systems had approximately equal maximum tensile shear strengths of about 5,300 psi, which is quite surprisingly high. But below this temperature the MDI system was considerably better (test made on aluminum): at -730C, for example, the MDI system had strength of 5,100 psi as against 3,900 psi for the TDI.

Because the polyurethane resins can be foamed in situ and adhere to metal their use as the core material in sandwich construction is of possible interest. Fabrication is not difficult, but the polyurethane having low moduli of elasticity compare unfavorably, for example, with aluminum honeycomb as a sandwich core material.

See the different adhesive Resin and Plastic.

Superglue Accidentally Founded

More sticky material. This one is famous for its high adhesive power, not like Post-It Notes. Super strong glue was created in 1942 when Dr. Harry Coover was trying to isolate a clear plastic material to make up the firearm. While he was working with chemicals cyanoacrylates, immediately after the polymerized materials exposed to moisture makes all the chemicals in the experiment bound together. Coover on this experiments was failed, but the research goes on.

Six years later, Coover worked at a chemical plant in Tennessee, and realize the potential of a substance when they were testing the heat resistance of cyanoacrylates, known in advance that the glue does not require heat and pressure to form a strong bond. So, after a certain amount of commercial improvement, Superglue or "Alcohol-Catalyzed Cyanoacrylate Adhesive Composition" (composition of materials Cyanoacrylate glue catalyzed by alcohol) was born.

The glue that is used later to treat wounded soldiers in the Vietnam War - the glue can be sprayed on open wounds, to stem the bleeding and facilitate transportation of soldiers. This glue has a lot of saving lives of the victims injured by firearms.