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SYNOPSISNatural and artificially accelerated weathering trials were carried out on low-density polyethylene samples used for agricultural and disposable purposes. Modifications in polymer characteristics were studied using Fourier transform infrared (FTIR) spectroscopy, different scanning calorimetry (DSC), gel permeation chromatography (GPC), scanning electron microscopy (SEM), and mechanical properties testing. The natural exposure trials were conducted at five geographical locations representing varying ambient temperature and humidity conditions and receiving different doses of solar radiation. The artificially accelerated exposure trials were carried out in an Atlas weatherometer for 5,000 hours, whereas the natural exposure was for 24 months. Rates of photo-oxidative and thermal degradation have been determined by measuring the formation of non-volatile carbonyl oxidation products which absorb in the infrared region with a maximum absorbance level at 1710 cm-'. Thermal characteristics were noticed to vary in terms of the shape and size of melting peak for both the natural and artificial weathering. This implies a change in crystallinity, which has indicated an increasing trend with exposure time. The crystalline melting temperature (T,) remains almost steady for both exposure tests. The drop in mechanical properties and the modification in polymer chain length were also monitored. The GPC analysis indicated the change in molecular weight distribution (MWD), which shows the formation of lower molecular-weight species. Surface modifications were revealed in terms of abrasion effects apparent from SEM micrographs. A correlation between natural and artificial weathering was considered for lifetime prediction in a short exposure time. It was found that the confidence level of predicting lifetime on the basis of artificially accelerated exposure trials is dependent on many parameters, which include time, material, equipment, etc.

ABSTRACT:The effect of ethylene, ethylene acrylate and glycidyl methacrylate (EA) terpolymer, and ethylene butyl acrylate (EBA) copolymer on asphalt modification was investigated at 4, 6 and 8% polymer concentrations. Both melt state rheology and asphalt concrete mix (ACM) were investigated. In the melt state analysis, dynamic shear rheology, storage stability, artificial ageing, and performance grading (PG) were studied. The PG grading of polymer modified asphalt (PMA) is correlated to the elastic properties of the polymers. Both resins improved the rheological properties, reduced the temperature susceptibility, showed better storage stability, and increase the upper grading (performance) temperature of the base asphalt. The two polymers showed similar ageing characteristics with little influence on flow activation energy. In asphalt concrete mix analysis, Marshall stability, stripping (durability), resilient modulus, and permanent deformation tests were performed. Polymer-modified asphalt concrete mix (PMACM) has increased percent retained stability and the resilient modulus when compared with ACM. The elastic modulus of PMA and the resilient modulus of their ACM followed the same trend. Weak influence on water sensitivity was observed, but excellent rutting resistance was obtained for PMACM over ACM. EA (much cheaper than EBA) produced satisfactory properties of PMA and superior ACM properties when blended with the high asphaltenes Arabian asphalt.

ABSTRACT:The thermomechanical modification of hydrogenated nitrile butadiene rubbers (HNBR) of different molecular parameters was investigated by rheological and light scattering techniques. The influences of acrylonitrile content, degrees of hydrogenation, and Mooney viscosity were examined. A melt blender with Banbury-type mixing blades was used to condition the rubber samples in the temperature range from 190 to 260°C. Light scattering was used to determine the effect of conditioning on MW and hydrodynamic radius of the rubber molecules. Dynamic viscosity (Ј) and storage modulus (GЈ) were measured for the as-received and conditioned samples. Experimental results showed that degradation in these rubbers occurred through chain scission and crosslinking. Depending on the molecular parameter, it was found that one of these two mechanisms dominated the degradation process in most brands. Addition of adequate amounts of antioxidants (Irganox 1010 and Irgafos 168) was successful only in preventing degradation by crosslinking. Compared to thermal degradation, thermomechanical degradation was found to be much more severe and progressed at much higher rates. Rheology was found to be a very sensitive technique to structural parameters of the polymers and could be used to detect and identify the mechanism of degradation.

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