Multi scale aging study of copolymer PP/PE matrix in tropical environment.
Abstract
Tropical climate is characterized by high temperatures, high relative humidity and solar irradiation up to 200kWh/m² [1]. Such conditions are extremely aggressive for polymeric materials in terms of aging and durability. Moreover international standards for lifetime prediction of most polymeric materials are developed for continental or temperate regions and therefore, often conduct to underestimate the material lifetime in tropical environment. This misestimation contribute to the high plastic waste generation for the Caribbean region which was estimated to be around 1.5 million tons per year in 2010 [2]. Use of durable materials would contribute to reduce the amount of wastes and therefore would generate savings for local actors. The aim of this study is to develop a fast characterization technique to predict polymers durability using nanomechanical tests. Commercial thick PP/PE copolymer samples were aged using an artificial aging chamber. Chemical degradation was monitored by Infrared Spectrometry and the surface topography was studied by Scanning Electron Microcopy (SEM). Nanomechanical properties were determined by continuous stiffness measurement (CSM) with indentation depths of 2 and 15 µm. Elastic modulus at macroscale was determined by Dynamical Mechanical Analysis (DMA). Oxidation was detected after 3 days of aging process whereas surface cracks were detected between 6 and 10 days of aging. Elastic modulus measured at nanoscale on the exposed faces increased from 1.35±0.04 GPa at 0 days of aging to 3.6±0.2 GPa at 44 days. An exponential decrease of the Young’s modulus with depth was observed at nano scale. The perturbation zone reached a depth of 1300 µm at 44 days of aging. A Voigt model was used to calculate the Young’s modulus of the whole sample. This calculated parameter was then compared to the macro Young’s modulus deduced from DMA tests. A good correlation was observed at macro and nano scales as long as macroscopic defects such as cracks appeared. This work shows that nano indentation is a suitable technique to detect early stage degradation of polymers and therefore a powerful tool to predict durability of materials.
References
[1]. A. Bertin, J.P. Frangi, Contribution to the study of the wind and solar radiation over Guadeloupe, Energy Convers. Manag. 75 (2013) 593–602. doi:10.1016/j.enconman.2013.07.007.
[2].J.R. Jambeck, R. Geyer, The ocean, Clim. Chang. 2014 Impacts, Adapt. Vulnerability Part B. doi:10.1017/CBO9781107415386.010.