Analysis of Mechanical Property Degradation of Outdoor Weather-Exposed Polymers.

Sunwoo Kim,Changhwan Kim,Youngmin Lee,Sunwoong Choi

doi:10.3390/polym14020357

Abstract

It is well known that many polymers are prone to outdoor weathering degradation. Therefore, to ensure the safety and integrity of the structural parts and components made from polymers for outdoor use, their weather-affected mechanical behavior needs to be better understood. In this study, the critical mechanical property for degradation was identified and modeled into a usable format for use in the virtual analysis. To achieve this, an extensive 4-year outdoor weathering test was carried out on polycarbonate (PC), polypropylene (PP), polybutylene terephthalate (PBT), and high-density polyethylene (HDPE) polymers up to a total UV irradiation of 1020 MJ/m2 at a 315~400 nm wavelength. In addition, tensile tests were performed by collecting five specimens for each material at every 60 MJ/m2 interval. With the identification of fracture strain retention as the key performance index for mechanical property degradation, a fracture strain retention function was developed using logistic regression analysis for each polymer. In addition, a method for using fracture strain retention function to establish a mechanical property degradation dataset was proposed and successfully tested by performing weathering FE analysis on the virtual automotive collision behavior of a PC part under intermittent UV irradiation doses. This work showed the potential of using fracture strain retention function to predict the performance of polymeric components undergoing mechanical property degradation upon outdoor weathering.

Highlights

When polymeric materials are applied to structural parts and components for outdoor use, material degradation due to prolonged weather exposure must be considered in the design to ensure safe and reliable lifetime performance [1,2]
An extensive 4-year outdoor weathering test on PC, PP, polybutylene terephthalate (PBT), and high-density polyethylene (HDPE) polymers was carried out to provide basic long-term stress–strain data to predict the performance of plastic parts undergoing weathering deterioration
1020 MJ/m2 at 315~400 nm wavelength, and they were tensile tested at every 60 MJ/m2 interval

Summary

Introduction

When polymeric materials are applied to structural parts and components for outdoor use, material degradation due to prolonged weather exposure must be considered in the design to ensure safe and reliable lifetime performance [1,2]. This requires a method to generate appropriate mechanical property degradation data and model it into a format for design analysis in virtual engineering. The long-term outdoor weather-affected mechanical property data of polymers are often not readily available, which are essential for successful design analysis of parts made from polymers. Discoloration, loss of gloss, refractive index and mechanical property reduction, and peeling of the surface coatings are among the changes occurring from photooxidation [11–13]. Molecular weight reduction and crosslinking have been identified as major causes of mechanical property changes [4–9]

Methods

Results

Conclusion