Nondestructive testing of defects in adhesive joints

processing variables on the adhesion strength of substrates bonded with these PSAs - the results of
which are reported in this paper.
O
HO OH
P
O
( CH2)7 CH CH CH2 CH CH CH2
(I)
Prepolymer of PCNSL
Materials & Methods
(
CH CH2 )
n
n = 2 to 4
Polychloroprene rubber (CR) (Skyprene Y-30H, Toyo Soda Co.) was supplied by M/s. Jeni
Polyplast, Ahmedabad, Gujarat, India. CNSL conforming to Indian Standards IS: 840 - 1964 was
supplied by M/s. Adarsh Industrial Chemicals, Sanoor, Mangalore, India. Commercial sample of PSA
(Fevicol SR 998) was manufactured by M/s. Pidilite Industries Pvt. Ltd., Mumbai, India.
PCNSL was synthesized (at 20 kg level) by the simultaneous esterification and oligomerization of
CNSL using o-phosphoric acid at controlled temperature, time and vacuum conditions in a Multi
Purpose Reactor (Pyrodevices) supplied by M/s. Thermosystems, Veli, Thiruvananthapuram.
Blends of NR, CR and PCNSL (in various proportions) were prepared by mixing on an open two
roll mill (6” X 12”) for 5 minutes followed by homogenization and sheeting out. The sheets were cut
to small pieces and weighed amounts of the same were kept immersed in requisite amount of
dichloromethane for 24 h, stirred there-after for homogeneity and kept in air-tight containers.
The viscosity of the PSAs was measured on a rheometer (Anton Paar Physica, Austria, model
MCR-150) by parallel plate method, at 28°C over the shear rate range from 0.1 s 1 to 100 s 1 . T-peel
test specimens were prepared from rexin sheet cut to size (75 mm X 25 mm). Two coats of the PSA
were applied manually on an area of 50 mm X 25 mm from one end of the fabric surface, an open
tack time of 2 minutes was given and bonded together under hand pressure. The test specimens were
kept pressed between two flat sheets under a load of 10 kg, applied uniformly for a period of 24 h or
168 h. The T-peel adhesion strength of the specimens was measured on a Universal Tensile testing
Machine (Hounsfield, H5KS) at a cross head speed of 100 mm/min. The optical micro photographs
of the failure surfaces were obtained using a stereo microscope (Leica MZ 16A / DC Twain) at a
magnification of X 11.
RESULTS AND DISCUSSION
Effect of type of PCNSL and storage time of bonded specimens on adhesion strength
The results on T-peel strength of rexin specimens bonded with the PCNSL based PSAs are given
in Table 1. It shows a general increase in the T-peel strength with the change in type of PCNSL from
2