Investigation of humidity and temperature effects on the accelerated photodegradation of polyethylene flimsies using dma

Abstract

Polyethylene (PE) is a polymer of ethylene (ethene) used in the manufacture of packaging bags. The considerable growth in use is due to the beneficial properties it has over other alternatives. These include, extreme versatility, it is light, extreme durability, resistance to chemicals, water and impact, good hygiene properties for food packaging, excellent thermal and electrical insulation properties and relatively inexpensive. However PE disposal is a challenge, resulting in the used products littering almost every place. This creates a menace obscuring the benefits of PE to the society. Knowledge of environmental factors that can accelerate its rate of photodegradation and wavelength sensitivity of its degradation is an essential tool for effective management of its ultimate disposal. This study sought to establish presence of chromophoric sites in PE which dictates susceptibility to natural degradation in the presence of sunlight. The samples were exposed to sunlight at Egerton University Njoro area. The effects of humidity, temperature and radiation wavelength to photodegration of flimsies were carried out. Samples were irradiated with (200-300)nm and (300-400)nm ultraviolet(UV) light ranges for two hours and exposed to environments of varying humidity and temperatures. Temperature was varied from room temperature (≈ 24 ℃) to 40℃ and 55℃ while the relative humidity (RH) was varied from room humidity (25% RH) to 40% RH and 60% RH. Dynamic mechanical analysis was done using DMA-2980 instrument to detect changes in loss factor (δ), storage (E’) and loss (E’’) modulus which implies degradation. This analysis was made after 50 hrs, 150hrs and 350hrs of exposure. Results show that there is a possible existence of hydroxyl, carbonyl, carboxyl, ketonic compounds or amino groups as chromophores. However UV absorption was below 62%. Hence these films were relatively unstable to sunlight UV with a 42.4% drop in storage modulus after 150 days. Irradiation of (300-400)nm UV range accelerated degradation higher than the (200-300)nm range with similar exposure conditions. Degradation was also higher at 55℃ than at 40℃ other conditions similar. The highest observed reduction of storage modulus (aging) of 74.6% occurred at (300-400) nm irradiation and 55℃ temperature treatment. Raising humidity from 25% RH to 60% RH resulted in increase in percentage drop of storage modulus from 41% to 67%. Natural degradation of these products was low and was accelerated as expected by an initial UV irradiation and exposure to high temperature and humidity conditions. PE products should be formulated with more absorption sites. Pre-use UV irradiation especially within (300-400)nm range and enhanced moisture absorption at higher temperature should be employed to accelerate degradation to curb PE products disposal menace.