Ultrasonic investigation of interpenetrating networks of poly(methyl methacrylate) and polyurethane

Abstract

Interpenetrating networks are the most recent development in polymeric blend materials. Due to the crosslinking of both the continuous and dispersed phases, a high degree of molecular mixing is achieved in these materials. Notwithstanding that poly(methyl methacrylate)-polyurethane (PMMA-PUR) interpenetrating and semi-interpenetrating networks have been extensively investigated by Meyer et al., ultrasonic relaxation technique has been applied here for the first time. These materials were found to be highly ultrasound absorbing.It is observed that ultrasonic absorption has a peak at a particular composition of PMMA-PUR interpenetrating network. The absorption coefficient c< increases with frequency f The absorption is of relaxational nature and is not due to the scattering of ultrasonic waves by the domains of the dispersed phase. At every composition of the interpenetrating network, the c~/f 2 vs. f curve indicates the presence of a relaxation frequency below 2 MHz and that the absorption increases with the temperature at some compositions which indicates the presence of thermal relaxation. An attempt is made to relate the absorption with the relaxation of pendent groups of polyurethane in the continuous phase.

Ultrasonic studies on polystyrene/styrene butadiene rubber polymer blends filled with glass fiber and talc

“…As they shifted mostly to higher temperatures with increasing frequency, it is natural to attempt an interpretation of these losses in terms of relaxation type process which can be attributed to standard linear solid type behavior with low dispersion and Arrhenius type relaxation times of the form s = s 0 exp(U/KT), where U is the average activation energy. Sudhakar and Singh [13] concluded that the absorption in polymer blends is of relaxation nature and not due to scattering of ultrasonic waves by domains of the dispersed phase. A comparatively big shift of peak temperature for some samples are observed, for example specimen 10% SBR shows a shift in peak temperature T p (taking for example the second peak loss) from 363 to 380 K while the frequency changes from 1 to 5 MHz and as the same attitude for specimen 40% SBR shows a shift in peak temperature from 320 to 338 K. The ultrasonic absorption at peak temperature increases rapidly with the frequency that could be observed for all samples especially for 10 and 40 wt% of SBR.…”

“…They concluded that in compatible blends the ultrasonic velocity varies linearly with composition while it deviates from linearity in incompatible polymer blends. It is also, known that [12] the ultrasonic absorption in heterogeneous medium may be caused by dispassion of the particles of the medium, however Sudhakar and Singh [13] reported that the absorption is of relaxation nature and not due to scattering of ultrasonic waves by the domains of the dispersed phase. It has been also concluded that the ultrasonic absorption increased with temperature at some compositions which indicates the presence of thermal relaxation.…”