NSF Award
0105622
This award is directed to the study of polymer degradation due to UV irradiation and thermal treatment in the presence of air and ozone/air mixtures. The proposed studies will be performed on polymers containing hindered amine stabilizers (HAS) as protecting additives. The main method of study is electron spin resonance imaging (ESRI) of nitroxides and other radical intermediates formed in the degradation process. Spatial information will be encoded in the spectroscopy by collecting ESR spectra in the presence of magnetic field gradients. 1D ESRI will provide the spatial distribution of the radical intensity, and 2D spatial-spectral ESRI will allow visualization of the line shapes along the sample depth. The experiments will be performed as a function of treatment time, wavelength of the UV source, and temperature in thermal degradation. Additional information will be obtained by spin probe ESR, UV, FTIR, and differential scanning calorimetry (DSC). Photo- and thermal degradation will be performed on two classes of polymers: 1. Polymers based on styrene, acrylonitrile and butadiene, as homopolymers and in different combinations as copolymers. This group will include the copolymers poly(styrene-co-butadiene), poly(acrylonitrile-co-butadiene) and poly(styrene-co-acrylonitrile), and poly(acrylonitrile-butadiene-styrene) (ABS). 2. Copolymers of polypropylene and ethylene prepared by sequential polymerization. These polymers consist of a semicrystalline polypropylene (PP) matrix and a dispersed amorphous elastomeric component, and have a phase-separated morphology; the study of these systems will benefit from the rich literature available on polypropylene degradation, but will present the challenge and advantage of properties modification by addition of the elastomer phase. The ability to perform nondestructive profiling via ESRI is an important advantage compared to other (destructive) methods now in use for probing the spatial dimension.<br/>%%%<br/>The proposed research is expected to: identify specific morphological domains where the degradation process is accelerated; map the consumption of the stabilizer within the sample depth on the scale of mm, and within the morphological domains on the scale of micrometers, contribute to the understanding of environmental factors, for instance the effect of irradiation wavelength and ozone; and lead to nondestructive spectral profiling as a method for the detection of early events in polymer degradation and stabilization.
