CHARACTERIZATION OF THE WELDLINE STRENGTH IN TERMS OF CRACK-GROWTH RESISTANCE IN INJECTION-MOLDED THERMOPLASTIC ELASTOMERS

The weldline strength of injection-molded thermoplastic elastomers (TP Es) were determined in terms of crack growth resistance. The specimens were injection molded under identical processing conditions except th e cavity surface temperature; one cavity has a cold mold surface of 20 degrees C and the other has a hot mold surface equal to the melt temp erature of the TPE, 189 degrees C. These two conditions were investiga ted simultaneously utilizing a two-cavity mold, where the isothermal c avity is based on low thermal inertia molding (LTIM) using thermoelect ric devices for rapidly heating and cooling this cavity. A single-spec imen, trouser tear test method was employed in determining the crack g rowth resistance curves (R curve) from the load-displacement curves. F or the LTIM specimens the critical J integral value (J(C)) was 6 kJ/m( 2) and the conventional specimens had a Je of 5 kJ/m(2). Both types of specimen exhibited a rising crack growth region, with only the LTIM s pecimens reaching a plateau region equal to the maximum R value of 13 kJ/m(2) whereas the conventional specimens reached a peak R value of 1 4 kJ/m(2) and then steadily decreased to a plateau region of 8 kJ/m(2) .