Bonding, adhesive good bond, basic requirements

The strength of a bonded joint will be determined by the strength of its weakest component, whieh is generally designed to be the adhesive. It follows that the requirements for satisfactory joint performance eu-e (a) good contact between the adhesive and substrate (b) absenee of weak layers in the joint (e) that the adhesive should possess appropriate mechanical properties. These basic requirements are implieit in the essential elements of bonding, and are related to many faetors which affect the performance of bonded assemblies as summarised in Table 4.2. 

The basic requirements for a good bond to plastic substrates are surface cleanliness, wetting of the surface by the adhesive, solidification of the adhesive, and proper selection of adhesive and joint design. These requirements are briefly defined here and then more thoroughly discussed in following sections. 

Various theories attempt to describe the phenomena of adhesion. No single theory explains adhesion in a general way. However, knowledge of adhesion theories can assist in understanding the basic requirements for a good bond. 

The basic requirements for a good adhesive bond are cleanhness, wetting, sohdification, and proper selection of adhesive and joint design. 

The objective of any surface treatment method is to enhance the adhesive bond strength and durability when it is exposed to environmental factors of service. There are, however, other considerations for the formation of an adequate adhesive bond. The basic requirements for a good adhesive bond are the following ... 

To try and summarize these discussions, then there is no single readily identifiable mechanism. It is obvious that any weak boundary layer must be removed prior to adhesive bonding but it is not well established that such layers are commonly found on most grades of polyolefins. Further, even if such layers are present and then removed, good adhesion to the polyolefin will not automatically follow unless the surface has been chemically modified, typically by oxidizing the surface regions. Hence, the essential basic mechanism appears to be one of chemical modification, but with some polyolefins the removal of a weak boundary layer may be a necessary first step. As mentioned earlier, the type of adhesive employed will play a role in influencing the exact mechanisms which will operate, and hence the exact details of the pretreatment which will be required. 

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