Nondestructive testing of defects in adhesive joints

Effect of Plasticizer
The polyurethane elastomers resulted from prepolymers A and B with curative X3 are blended
with varying levels (10phr, 30phr and 50phr) of plasticizer are studied. The incorporation of plasticizer
influences the properties of elastomer. The increase in level of plasticizer decreases the mechanical
characteristics of polyurethane elastomer. For example, the hardness of the elastomer product AX3 falls
from 53 to 37 by increasing the concentration of plasticizer from 0% to 50%. Similarly the hardness of
product BX3 falls from 53 to 27 for the same level of plasticizer concentration. The plot of varying
concentration of plasticizer against hardness of the polyurethane elastomer (AX3 and BX3) is given in
figure 1. The hardness decreases with increase in plasticizer level.
Tensile strength, density, modulus and tear strength are also in the same trend as shown in figures
2, 3, 6 and 7. The strength, modulus and density decreases with increase in plasticizer concentration. The
increase in the plasticizer level influences the pot life of the products. The plot of varying level of
plasticizer against pot life of the polyurethane elastomer (AX3 and BX3) is given in Figure 4. The pot life
increases with increase in plasticizer concentration. The increase in plasticizer concentration influences
the elongation for the product of BX3, but it is reversible for the product of AX3 (Figure 5). This is due to
the nature of prepolymer A and this behavior may be explained due to the anti-plasticization effect
observed with the reactants involved. Generally 30 phr plasticized polyurethane elastomer gives higher
solvent resistance than 10phr and 50phr plasticizer concentration.
Properties of Filler on Plasticized Polyurethane Elastomer
Polyurethane elastomers resulted from prepolymers A, B, and C with curatives X3 are
incorporated separately with 30phr and 50phr plasticizers and 60phr filler, in order to improve their
performance characteristics. The hardness, tensile strength, tear strength, density, elongation and solvent
resistant characteristics of additive blended polyurethane elastomers are studied. The incorporation of
filler in the plasticized polyurethane enhances the hardness, tensile strength, modulus, density, tear
strength and solvent resistance. For a particular level of prepolymer the pot life increases, when additives
are added. For example the pot life for unfilled product from AX3 is 45 minutes. Whereas the same
product filled with 60 phr filler and 50 phr plasticizer gives 85 minutes. The enhancement of pot life is
due to retardation of reactive functional groups.
The addition of filler (60phr) to the product AX3 increases the hardness from 43 to 61, whereas
the same product with 60 phr filler and 50 phr plasticizer enhances hardness from 37 to 52. The strength
properties (tensile strength, modulus, tear strength ) of plasticized (30 phr) elastomer, namely for the
product from AX3, the tensile strength increases from 7.6 kg/cm 2 to 22.1 kg/cm 2 , modulus increased from
7.2 kg/cm 2 to 18.2 kg/cm 2 , and tear strength from 4.18 kg/cm to 8.41 kg/cm respectively.
The increase in strength properties is due to the reinforcement effect of filler and the formation of
secondary bonding with polar groups of polyurethane elastomers. The results obtained from the solvent
treatment reveals that the incorporation of filler improves the solvent resistant characteristics. For
example 30phr plasticized product AX3, the swelling in ethyl acetate for 7 days gives 128% whereas the
same product filled with 60phr filler in the same solvent for the same period gives swelling of 69%.
Conclusions
The different combinations of polyurethane elastomers are prepared using prepolymers A, B and
C with curatives X1, X2, X3 and X4. In order to utilize the product for the print roller applications, the
properties i.e., hardness, pot life, tensile strength, modulus, tear strength, elongation, density, compression
set and solvent resistance are studied by standard methods. The polyurethane elastomer obtained from
5