Natural weathering of polypropylene in a tropical zone

Abstract

Natural weathering of isotactic polypropylene (PP) plates (2 mm in thickness) was conducted for 15 months in the Philippines. Optical microscopy, scanning electron microscopy, and atomic force microscopy revealed that the surface layer (200 -300 nm in thickness) was affected in the first month, and cracks are formed toward the deeper layer. On the basis of the microscopic observations along with FTIR, DSC, GPC, and tensile strength measurements, the following degradation mechanism of PP was proposed. At first, through oxygen introduced into the PP, only the surface layer seems to be affected. Gradually, the surface layer may be removed, exposing the inner layer. Then, molecular chains of the inner layer start to be degraded, accompanying a significant loss of tensile properties. Part of the degraded materials seems to be eroded, leading to the formation of cracks on the surface of the uncovered inner layer. Finally, the original surface layer may be totally eroded, making the structure of the inner layer (which should reflect the spherulitic texture) evident.

The effect of natural weathering on the mechanical, morphological and thermal properties of high impact polystyrene (HIPS)

“…Qayyum and White [18], Bedia et al [12], Sing et al [19], Baum et al [20], Van Krevelen and Hoftyzer [21], Ragab et al [22], Uzomah and Onuoha [23], Schoolenberg [24], Sharbel et al [25], Kalfoglou [26], Sınmazçelik [27] investigated the effects of natural weathering on the polymers. The objective of this study is investigating the effect of natural weathering and cold drawing on HIPS.…”

“…Natural weathering gives the most practical and the faithful data regarding the variation of the performance of the products in use [12]. Natural weathering of polymer refers to the exposure of polymers to natural outdoor conditions where direct or indirect sunlight, heat, oxygen, moisture and other factors contribute to the degradation of materials properties.…”

Data on Specific Polymers

“…749 Carbonyl index determined by FTIR is thus a very good indicator of the weather- m ing progress. 749,750 Density and crystallinity of PP increase with degradation time and the radiation energy delivered to the samples. 753,760 Molecular weight of PP decreases on exposure to UV radiation due to the chain scissions in surface layers.…”

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

“…Its further application, however, has been considerably restricted due to the poor weatherability of PP material which is vulnerable to the effect of sunlight and thermal oxidation and consequently easy to degrade. Therefore, many studies have been conducted to investigate the degradation of PP material in natural and artificial accelerated weathering conditions [1][2][3][4][5][6][7][8]. Natural weathering can give the most practical and faithful data regarding the variation of the properties of the material used in a given natural environment.…”