Influence of Ozone as an Air Pollutant on Polypropylene Fiber Properties

Abstract

Ever increasing ozone concentrations in the earth's atmosphere polluted by photochemical smog raise the question of possible ageing of fibers in such an environment. This paper investigates polypropylene fibers characterized by pronounced ageing in the natural environment under the impact of sunlight. Fibers are exposed to ozone for varying times and temperatures in a concentration range that can be expected in a heavily polluted urban industrial environment. Changes in the level of chemical composition and molecular configuration are investigated, together with morphological characteristics and end-use properties. Results indicate that, even under relatively mild ozone conditions, hydroperoxide groups are created, morphological surface changes occur, fibers become more brittle and lose strength, and the isotacticity of the configuration is pronounced, but there are some rather positive effects as well. I The investigation described in this paper is primarily aimed at determining the possibly detrimental influence of ozone on polypropylene (PP) fibers. These fibers are highly sensitive to atmospheric factors, especially ultraviolet rays [3, 4, 11 ], so the question arises whether (and if so, how much) the increased amount of ozone in the troposphere influences the problem of PP fiber ageing in atmospheric conditions. The literature on the subject indicates a lack of research on this topic, especially where fibers, as a specific form of the material, are concerned.Oueslati et al. have made some interesting investigations of the impact of ozone on chemical and morphological changes in PP fibers [8, 9, 101, which were exposed to ozone concentrations of -4.5 x 106 pphm, a very intensive treatment. This amount of ozone is a few thousand times higher than the average concentrations in polluted environments registered for a number of years in various parts of the world (Los Angeles, California; Arkon, Germany; Basel, Switzerland; Sydney, Australia). All the concentrations registered were in the range between 1.5 and 4 pphm [ 12], while occasional peaks of pollution reached-115 pphm (Los Angeles) or -75 pphm (Zurich). Using IR-and ESR spectroscopy, the authors investigated chemical changes in PP macromolecules [9, 10], and with electronic microscopy, they showed what this level of &dquo;ozonization&dquo; does to the core/sheath structure of PP fibers [8]. Similar morphological changes were also observed by Catoire et al.[2] at somewhat milder, but still highly intensive, ozone treatments (3.1 x 105 pphm).The literature does not offer proof of the impact of ozone on other relevant physicomechanical properties of the fibers, which is important for assessing ageing during use in real conditions of air pollution with ozone. For this reason, our investigation deals with ozone concentrations slightly higher than peak values in polluted urban environments. We focus on end-use properties, but we also consider other relevant properties for a complete overview of the problem.. MethodologyAll the tests involved undyed PP filaments...

Polymeric Materials for Membrane Contactor Devices Applied to Water Treatment by Ozonation

“…Appearance of a band in 1708 cm -1 , region of ketone carboxyl groups (C=O), also reflects changes occurring in the polymer structure. Although Cataldo 12 had observed that materials with single bonds showed great resistance to ozone attack, in the present work two polymeric materials, PP and PDMS, have suffered break of the single bonds due to ozone attack at high concentrations used, as observed in the literature [13][14][15] . Similar modifications were also observed for PDMS membranes (Figure 5b), moreover for prolonged exposition to ozone it was observed changes in the spectral region 2990-2855 cm -1 and 1485-1415 cm -1 of alkyl groups (-CH 3 ) from long chain with stretching vibration (symmetric and asymmetric) and asymmetric bending vibration, respectively 32 .…”

“…Nevertheless, some authors proposed a simple mechanism of initiation and propagation for ozone attack of single bonds structures where various groups, as carboxyl, ketone, etc., are created with elevated ozone concentrations [13][14][15] . Goto et al 16 evaluated the chemical reactivity between ozone and different polymers through material thickness reduction.…”

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“…It is also essential to know that the higher the energy of the UVR, the greater the degradation will be since it will more easily break the chemical bonds of the textile fibers [189]. These modifications are not immediately observable but develop over time, dependent on the radiation exposure conditions [189,191].…”

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