It is imperative in any industry that uses pressure sensitive adhesive (PSA) tapes to choose the adhesive tape based on the application. There is ‘no one size fits all’ in industrial adhesive tapes. The adhesive tapes are decided upon various factors such as application, interior and exterior conditions, requisite properties required and so on. It is very important to understand such factors and R&D Team at Adhesive Specialities understands the various requirements of clients and accordingly gives suggestions as to which PSA tapes will work efficiently for the required application or if required also carry out specific customisations to fulfils the expectations of the customers. 

So why is it necessary to understand the applications?

There are many factors that can contribute to the degradation of adhesive tapes and thus affect their efficacy.

Exposure to high temperature and environmental stress makes reduction in tack, adhesion and other properties and so choosing the right adhesive tapes widely is based upon the conditions that the tape will experience over its lifetime, proper storage etc. which can reduce the degradation. This process will reduce the adhesive tape degradation and failure occurring during the lifetime of the tape.

Effects of Degradation on Adhesive Tapes

The deterioration of properties due to the uncontrolled change in molecular weight of the polymer is the reason for polymer degradation. The change in the colour of adhesive tapes, reduction of adhesion, tack, shear & other properties are due to the prolonged exposure to sunlight, heat, moisture etc. All these properties change leads to the degradation of adhesives tapes (polymers).

Thermal degradation

Thermal degradation of adhesive tapes occurs due to its exposure to temperature higher than the upper limit of service temperature. At higher temperatures, the long chain carbon–carbon (c-c) backbone undergoes molecular scission (breakdown) and leads to changes in the properties. Thermal degradation mainly depends on the stability of c-c bond. The effect of substituent groups on the backbone reduces the thermal stability, and aromatic groups in the polymer backbone increase the thermal stability. Polypropylene, PVC and polyethylene are highly susceptible to thermal degradation and adding stabilizers is the only way to reduce thermal degradation. Stabilizers can work by interrupting the thermal degradation cycle to slow down or prevent the cycle from completing.

Photo degradation

Photo degradation is the molecular degradation in adhesive tapes via exposure to ultraviolet light.  The yellowing and embrittlement of transparent plastic films is due to the tapes interaction with UV light. During this process free radicles are initiated and the degradation starts. Polymers with high bond energies are stable than lower ones.

The below shown figure is an example for photo degradation. Here PET (Polyethylene terephthalate) film is exposed to sunlight (UV radiation) which led to changes in the molecular structure resulting in degradation.  

Photo stabilizers protect polymers from the deteriorating effects of light to a considerable extent. The function of a photo stabilizers (or photo absorbers) is to absorb the UV radiation and dissipate the energy thus absorbed to the environment in some harmless form. Stabilizer acts as a filter and does not allow the radiation energy to attack the polymer molecules. Photo stabilizers mainly reduce staining of bright colors.

Oxidative Degradation

Oxidative degradation leads to hardening, discoloration as well as surface changes. It primarily affects the structure and mainly attacks the double bond by oxygen. Oxidative degradation leads to the deterioration in the physical and mechanical properties of rubber.  During the oxidative degradation, chain hardening (embrittlement), softening (chain scission), cracking, charring, color fading is visible in adhesive tapes. These results in efficient performance such as reduced adhesion and tack in natural rubber-based PSA tapes.

P    ——————>     P*

P – Represents the polymer chain. Free radicle sites are formed because of the attack of oxygen.

P* + O2   ——————>      POO*

Free radicle reacts with oxygen to form peroxide radicle.

POO* + P       ——————>     POOH +P*

Peroxide radicle attacks the neighbouring segment and forms hydrogen peroxide

POO* + -C=C-        ——————>      Po* + -C-O-O-C-

Hydrogen peroxide attacks the neighbouring double bond.

POOH  ————————————->  PO* + OH*

PO* + POOH   —————————>  PO* +POH

PO* +POOH  ————————————->   POH +POO*

Hydrogen peroxide leads to the formation of new free radicle sites.

2POO*       ————————————->     POOP +O2

2PO*    ————————————->       POOP

P* +O*H   ————————————->   POH

2P   ————————————->    P-P

With the all free radicle formed, there is final termination of chain reaction with different combinations. 

Oxidation can be prevented by incorporating Antioxidants. It suppresses the undesirable reaction fueled either by oxygen or peroxides. The secondary aryl amines and hindered phenols are widely used antioxidants.

Degradation by high energy radiations

X-ray, gamma rays, alpha rays and beta rays are among the well-known high energy radiations. Like UV rays, X-rays and gamma rays are electromagnetic radiations, but their energy level is much higher than that of UV rays. Degradation by high energy radiation is much higher than lower energy (UV) radiations. We can say degradation by high energy leads to breaking of its bonds or scission of its chain to crosslinking. If scission happens, degradation is associated with the reduction in molecular weight. On the other hand, crosslinking results in the building up of polymer network with increased molecular weight. Polyethylene, Polypropylene, Polyisoprene, and Polybutadiene etc. gets cross-linked when subjected to high energy radiations. Many of them exposed to radiations give out gases such as hydrogen, carbon dioxide, ammonia, carbon monoxide, cyanogen etc.  

The R&D team at Adhesive Specialities along with their extensive experience is more than happy to suggest what would be the best tape as per your requirements to ensure that degradation does not affect the efficacy of the tapes. 

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