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Understanding When Things Go Wrong

January 29, 2020

Of course, life is much easier when things go right where using adhesive is concerned. Sometimes though, things go wrong and there is just nothing you can do about it. What we can do though, is learn from those occasions. Understanding when things go wrong is a vital part of ensuring that future work goes to plan.

With that in mind, we have put together this helpful article explaining various types of failures when using adhesives.

 

Adhesive Failure

Adhesives failure occurs when forces that are applied to the substrates to pull them apart, results in the failure of the bond at the interface between the adhesive and the substrate. So adhesive is seen on one of the substrates but not on the other. This is due to surface contamination of the substrate(s), poor surface preparation of the substrate(s), or the adhesive being unable to wet and form a good bond with the substrate(s). This latter point could also be due to the wrong choice of adhesive to bond the substrates.

 

Cohesive Failure

This occurs within the body of the adhesive and is seen when there is adhesive present on both surfaces of the two substrates, when the bond has failed. The failure maybe in the main body of the adhesive, resulting in a similar amount of adhesive seen on both substrate surfaces, near the interface of the adhesive and the substrate or a mixture of both. This is observed when the adhesive has adhered well to the substrate, but the internal strength of the adhesive is less than the forces holding the adhesive to the substrate(s), or if the adhesive hasn’t fully cured (or still wet). This can also occur if too much adhesive has been applied when making the bond allowing movement within the adhesive film when forces are applied causing separation of the substrates.

 

Non-Coalescence

This occurs when the adhesive has been coated on both substrates and allowed to dry. The bond is then made by bringing the two surfaces together. The bond that is formed maybe weak or non-existent. If there is a bond formed but when external forces are applied to the bond to separate the two substrates, causing the bond to fail, non-coalescence can be part or all of the cause. This type of failure is seen when the adhesive has remained coated on each substrate, but the adhesive seems to have failed to bond with itself on the other substrate. The cause for this is due to the films being unable to coalesce. This can be due to the films being too hard to adhere to each other. The reasons could be due to lack of tack within the adhesive, the adhesive has cured before bringing the adhesive films together or the adhesive has been left too long before bringing the two surfaces together e.g. several hours or days.

Sometimes this can be rectified by activating the surface of the adhesive before the surfaces of the adhesive are brought together. One way to do this is by solvent reactivation, where the surfaces of the adhesive are wiped with a suitable solvent to make the films tacky. Another way is to heat reactivate the adhesive films so that they become soft and will coalesce or join with each other to form a bond. One final way is to reapply a thin coat of adhesive and make the bond before the adhesive is completely dry.

 

Substrate Failure

There is a further type of failure, but this is not down to the adhesive but the substrate. This is where the bond formed by the adhesive is stronger than the internal forces within the substrate(s) itself. So when the bond fails, the site where the two substrates are bonded is still intact but the substrate itself has broken. This is common when using a PVA adhesive to bond wood, some ceramic tile adhesives, or a two-part reactive adhesive used to form the bond. The bond itself is said to be stronger than the substrate(s) that it is bonding.

 

Bonds can fail due to any number of reasons and here we have mentioned just a few. Other common causes include temperature and human error. It is also possible that the failure is a combination of all of these.

 

Our experienced Technical team at Anglo, are just a quick call or email away if ever you need assistance with a failed adhesion of any kind.

 

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You can contact our team on +44 (0) 1664 480866 or email sales@angloadhesives.co.uk

 

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