Irradiated polymethylmethacrylate studied by positron annihilation spectroscopy

Abstract

The effect of gamma irradiation dose on microscopic structure of polymethylmethacrylate (PMMA) has been studied using positron annihilation lifetime (PAL) and Doppler broadening of annihilation radiation (DBAR) techniques. The measurements were performed at room temperature as a function of the γ-irradiation doses from 60-1200 kGy. The observed lifetime spectra were resolved into three components. The size and the fraction of the o-Ps hole volume were estimated from the positron annihilation parameters. The effect of γ-irradiation was identified at lower doses to be cross-linking while at higher doses the chemical degradation of the polymer was observed. Moreover, the distribution of the free volume shifts from a large to small size as the irradiation increases and has very similar Gaussian-like distribution. The PAL results were confirmed with X-ray measurement. A correlation between the macroscopic mechanical properties Hv and positron annihilation parameters has been demonstrated.1 Introduction Positron annihilation lifetime spectroscopy has been widely applied to study vacancies in metals and intermolecular spaces in polymers. It is a relatively simple technique which can probe the properties of the free volume holes in a non-destructive way. Radiation methods are successfully used for polymerization, for polymer modification and many other applications [1,2]. The radiation processing is a useful technology to induce suitable modifications of materials. In particular, it is a very important way to generate or to improve new properties in materials as well as new means of production. The radiation damage and the oxidative degradation cause chemical changes in the polymer structure with build up of a variety of new functional groups. These changes cause severe deterioration of the polymers, which shows up very early, with consequent decay of important properties such as electrical insulation power, transparency and hydrorepellency. Polymethylmethacrylate, PMMA is completely amorphous but it has high strength and excellent dimensional stability due to its rigid polymer chains. It has exceptional optical clarity, very good weather-resistance, and impact resistance. The PMMA polymers have many applications; e.g. diffusers, indoor and outdoor lighting, lenses, and contact lenses [3].The aim of the present work is to understand the changes induced by γ-irradiation on the microscopic structure of the PMMA samples using positron annihilation lifetime (PAL) and Doppler broadening of annihilation radiation (DPAR) techniques.

Positron Annihilation Spectroscopy

“…In some blends, however, stronger changes have been observed and attributed to a phase separation during the early aging period (89). Further fields studied by using PALS are the γ-irradiation of polymers (124,125) and cross-linking of rubbers (126,127). Of particular interest are studies of the free volume in permeable membranes (82,102,109,128) and among them in those with high internal microporosity (129).…”

Plug-in vehicles car park photovoltatic farm construction for cost and emission reductions

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Microstructure studies of isotactic polypropylene under natural weathering by positron annihilation lifetime spectroscopy

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