Journal of Adhesion Science and Technology, Vol.14, No.8, 999-1019, 2000
Evaluation of the polymer-nonpolymer adhesion in particle-filled polymers with the acoustic emission method
The acoustic emission (AE) test was employed to study the debonding of glass beads from a polystyrene (PS) matrix for uniaxially loaded specimens of composites with a different adhesion level between the glass surface and PS. The adhesion was varied by tailoring the interface with end-functionalized PS or polystyrene-block-poly-(2-vinylpyridine) copolymers adsorbed onto the glass surface. The number of beads was about 30 000 per specimen, which allowed good statistics to be obtained in the experimental data. The number of AE events, the debonding stress, the AE amplitude (AEA) for every signal, and the elongation of the specimen were recorded in the test. The experimental distribution of the number of AE signals per stress unit was fitted with a Weibull function and the maximum of the function was associated with the average debonding stress (ADS). The distribution of AE signals via AEA was also fitted with a Weibull function and the amplitude that corresponded to the maximum of the function was used as a parameter to characterize the AE energy released. All the parameters were used for the analysis of the failure mechanism of the composites. The ADS increases as the interface strength increases. The AEA measurement data usually should be fitted by two Weibull functions with two AEAs of relatively small and large energy (I and II, respectively). Both AEA-I and AEA-II decrease as the adhesion increases. These two maxima are assumed to characterize two different microdefects at the interface. AEA-I is caused by the propagation of the microdefects that were formed at the interface during the material preparation. The dewetting of the glass beads at larger stress affects the AE signals with larger AEA-II. It is suggested that the decrease in AEA with adhesion is caused by the propagation of microdefects towards the matrix. Simultaneous consideration of ADS and AEA allows the interfacial strength and location of the microcracks to be evaluated. The polydispersity of the PS matrix, the duration of sample preparation (melting under pressure), the rate of specimen deformation in the test, and the volume fraction of the filler within the range 2-15 vol.% have very slight effects on the results.