Thermo-oxidative stability of polyamide 6 films

Matrix-assisted laser desorption/ionization time-of-flight investigation of Nylon 6 and Nylon 66 thermo-oxidation products

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) was used to determine the structure of the molecules produced in the thermo-oxidative degradation of Nylon 6 and Nylon 66, at 180 degrees C and 250 degrees C in air. The MALDI spectra of the thermo-oxidized nylons provide information on the structure and end groups of the oligomers produced in the oxidation process. Our results show that the thermo-oxidation of both Ny6 and Ny66 proceeds through a hydrogen abstraction and subsequent formation of hydroperoxide intermediates. The latter decompose, yielding oligomers containing aldehydes, amides and methyl terminal groups. The aldehydes undergo further oxidation to produce carboxylic end groups. The formation of cyclopentanone terminal groups is also observed in the case of Nylon 66. Oligomers with structures deriving from Norrish-type degradation processes were not detected here for either Ny6 or Ny66.

Use of isothermal heat-conduction microcalorimetry (IHCMC) for the evaluation of synthetic biomaterials

Isothermal heat-conduction microcalorimetry (IHCMC) allows measurement of extremely small rates of heat flow-on the order of 0.1 microwatt. This provides, for example, the ability to directly observe-and quantitate in a few days-rates of degradation as low as 1% per year at body temperature, in solid material samples of a few grams. Also, one method of IHCMC data analysis allows direct determination of the reaction-rate constant at the temperature of interest, thereby avoiding possible errors due to rate mechanism changes with temperature, an issue that needs to be considered when the Arrhenius method is used. IHCMC can also be used to measure transient phenomena, such as heat of adsorption, and initial metabolic responses of cellular entities to biomaterials. The purposes of this review article are to (a) explain the basic principles, attractive features, limitations, and methods of IHCMC; (b) describe biomaterials applications to date--including studies of the stability of ultra-high-molecular-weight polyethylene and implant-grade calcium sulfate, setting reactions of dental adhesives, and macrophage response to biomaterial particles; (c) provide a discussion of issues and concerns that should be addressed in order to maximize the utility of IHCMC in biomaterials studies; and (d) suggest a number of possible future biomaterials applications for this technique.