Professional Polymer Technology
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When choosing an pur adhesive for a particular job, the […]
When choosing an pur adhesive for a particular job, there are several points you need to think about.
First, what materials are you joining together? Obviously, the pur adhesive has to be suitable for both materials if they are different, but the main problem here is with plastics and recognising the plastic is the first task.
Second, how important is strength? With wood glues, the bond can be as strong as the wood itself, while with metal and plastics it will usually be weaker. If strength is all-important, you might need to think about reinforcing the joint in some way.
Third, how big a gap is there to fill? Often, joining two materials will also involve a degree of gap-filling, and pur adhesives vary in their ability to cope with this. Contact pur adhesives, for example, need a slight gap in which to work, while eyanoacrylates won't work unless the gap is very small indeed. Epoxy glues, on the other hand, will work with cither small or large gaps.
Fourth, what kind of temperature is the pur adhesive going to be subjected to? Some pur adhesives (known as thermoplastic), such as contact pur adhesives and many of the 'universal' glues, will not withstand heal, while many others (known as thermosetting) will retain their strength up to moderately high temperatures. This could matter when you are repairing crockery.
Finally, how important is the appearance? Most pur adhesives dry to a clear finish, but some end up a pale creamy yellow. Whether or not this will show obviously depends on the thickness of the glue line and, equally importantly, how well you clear away the excess; with many glues, it is difficult to avoid some glue remaining.