Adhesive systems do not work in isolation. For a correct adhesive bond of the required strength and the right physical, chemical properties it's important to factor in the physical and chemical factors at play. At a glance the factors affecting the bond are:
?Chemical and physical nature of the materials to be joined (the substrates)
?Quality of the substrate surfaces (e.g. roughness, any surface treatment)
?Environment in which the joint will be operating (e.g. temperature, humidity)
?Required durability of the joint (its required lifetime)
?Application/process factors (e.g. cure time, volume used, dispensing systems)
Chemical and physical nature of the substrates or the adherents with respect to adhesive has to be taken care of. They also need to be compatible with each other to allow successful adhesion. At times the adhesive is corroded through and through due to the incompatibility of the adherents and adhesive for e.g. Acid etching, chromic acid is used to surface treat polyolefin's, and anodizing. Materials like caustic soda, oxidizing agents can cause high damage to the substrates rendering them useless.
Surface of the substrates have to pretreat for the adhesives. Methods to prepare the surface are degreasing (through detergent cleansing, alkaline degreasing) and chemical pretreatments (metals need to be activated to accept the adhesive). Whatever the pretreatment procedure used, it is good practice to bond the surfaces as soon as possible after completion of the pretreatment - i.e. when the chances of contamination are lowest and when surface properties are at their best. Treated surfaces are easier to bond because of the property that smooth surfaces bond quickly, strongly and require less pressure whereas pressure is required to bond rough and(or) untreated surfaces.
Physical environment of operation such as the temperature, humidity, surface tension etc. also are equally responsible for the successful adhesion. Many adhesives do not work with the right industrial adhesive equipment because they are not compatible with the adhesive.
The flowability and viscosity of the adhesive is highly dependent on the temperature of operation. This further affects the thickness of the adhesive film application. Too thick a film will cause voids and bond will be weakened, too thin an adhesive will result in run off rendering adhesive useless. Adhesive application equipment can only work with the right adhesive when the properties of the adhesive are taken into account i.e. the pressure, temperature of application, application module, and type of adhesive being used.
Factors of tensile strength (maximum stress that a material can withstand while being stretched or pulled before failing or breaking), compressive strength (opposite of tensile strength) and shear strength also decide how the adhesive will perform under given set of conditions.
Other chemical factors affecting the adhesion are degree of polymerization and effect of pH. Strong acid and alkaline affects the bond negatively.
Thus, the environment of the adhesives and adherents play an important role as the physical and chemical nature of the substrates. Also correct adhesive application equipment can be chosen only when the factors at play are clearly understood.
