Oxidative Ageing and Structural Characterization of Naturally Weathered Low Density Polyethylene Films
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EGRADATION OF POLYMERS
Oxidative Ageing and Structural Characterization of Naturally Weathered Low Density Polyethylene Films N. H. Benmilouda,*, S. F. Chabirab, A. H. Bhatc, Y. K. Dasanc, and M. Sebaad aMechanics
Laboratory (lme)-RFME, Faculty of Technology, Amar Telidji University, Laghouat, 03000 Algérie b Engineering Process Department, Mechanics Laboratory (lme)-RFME, Faculty of Technology, Amar Telidji University, Laghouat, 03000 Algérie c Fundamental and Applied Sciences Department, Universiti Teknologi Petronas, Bandar Seri Iskandar, Tronoh Perak, 31750 Malaysia d Mechanical Engineering Department, Mechanics Laboratory (lme)-RFME, Faculty of Technology, Amar Telidji University, Laghouat, 03000 Algérie *e-mail: [email protected] Received November 5, 2019; revised March 8, 2020; accepted March 26, 2020
Abstract—Natural weathering was performed in a Saharan region to characterize its effect on low-density polyethylene (LDPE) films used for greenhouse coverings. The morphological changes, followed by differential scanning calorimetry (DSC), showed that the damages caused by the oxidation of tie molecules increased the lamellae thickness, its distribution and the crystallinity. Wide-angles X-ray diffraction (WAXD) was used to follow both the structural and morphological changes of the film. The WAXD crystallinity increase had the same trend as that determined by DSC. Field emission scanning electron microscopy (FESEM) of the films surfaces and cross-sections showed that the degradability increased with exposure time. Atomic force microscopy (AFM) analysis was used to evaluate changes in the surface morphology and roughness. Ageing caused a change of the surface topography of the LDPE films as observed by the increase of surface roughness which is indicated by the increase of the roughness parameters. Simultaneously the peaks-spacing d decreased. DOI: 10.1134/S1560090420040016
INTRODUCTION Polyolefins have been widely used owing to their high performance such as high modulus, high tensile stiffness, high chemical resistance and low cost for processing. These materials have numerous applications, such as cable and wire insulation, food packaging, medical components and many more [1]. One of the most weight consumption of this type of material is their use for greenhouses coverings. In such an application, the polyethylene film is subjected to weathering agents such as sunlight, thermal cycles, temperature, humidity, rain, atmospheric oxygen, windblown sand and pollutants [2, 3]. These environmental parameters can affect adversely the polymer’s thermal and structural properties. These are due to the microstructural changes undergone by the macromolecular structure, mainly governed by chain scission and cross-linking [4–6]. Knowing that LDPE is a semicrystalline polymer having a glass transition temperature far below ambient temperature, the toughness of the material is controlled by the efficiency of the tie molecules that link neighboring crystallites across the amorphous phase.
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