Nondestructive testing of defects in adhesive joints

NR / CR
TSC (%)
100 / 0 75 / 25 50 / 50 25 / 75
Mean T-peel 15 2.4 3.3 4.9 3.7
strength (N/25mm) 20 2.8 3.6 4.5 4.8
Table 2. T-peel strength of rexin / rexin bonded with unmodified NR/CR based PSAs
In the former, the lower segmental mobility of the elastomeric chains in the absence of PCNSL may
reduce the flow and wetting of the substrates, essential for development of a high value of adhesion
strength. It is expected that the plasticizing and softening effect of PCNSL in NR 5 and CR 6 as
reported earlier facilitates the built up of adhesive tack in the PCNSL modified PSAs.
Effect of solids content of PSA on adhesion characteristics
The optical micro-photographs of the failure surfaces of rubber specimens bonded with Fevicol
SR 998 and PCNSL based PSAs are given as Figure 2.
(a) (b)
Fig.2.T-peel failure surface of rubber / rubber bonded with (a) Fevicol and (b) PCNSL based PSA,
(TSC – 30%)
Figure 2(a) shows almost uniform and complete wetting of the substrate with a layer of the adhesive.
A similar morphology was observed for the PCNSL based adhesive at 30% solids content (Fig.2(b)).
This was reflected in the increase in T-peel adhesion strength from 10% to 30% solids content, as
given in Table 3. Also, the nature of adhesion failure changed from ‘adhesive’ to ‘cohesive’ type with
PSA TSC (%) Mean T-peel strength (N/25mm)
Fevicol SR 998 - 39.5
NR/CR/PCNSL 10 15.8
20 25.9
30 45.5
Table 3.T-peel strength of rubber / rubber bonded with Fevicol and PCNSL based PSA
the increase in solids content.
Effect of proportion of CR and type of PCNSL on adhesion strength
Table 2 gives the T- peel adhesion strength of rexin specimens bonded with PSAs based on
blends of NR and CR at two different solids contents. It can be noted that irrespective of the content
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