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TOLEDO (SPAIN)ANALYTICAL FRACTIONATION TECHNIQUES APPLICATION IN THE
POLYETHYLENE PHOTODEGRADATION PROCESS
M.T. Expósito1, C. Domínguez2, J. Codina3, R.A. García1
1Department of Chemical and Environmental Technology, Rey Juan Carlos University, Móstoles (Madrid), Spain
2Polymer Technology Laboratory (LATEP), Rey Juan Carlos University. Móstoles (Madrid), Spain
3Applus-LGAI Technological Center S.A, Bellaterra (Barcelona), Spaine-mail:teresa.exposito@urjc.esAbstract
The effects of ultraviolet (UV) source on polyethylene (PE) store bag were investigated in this study. The photodegradation
activity on the PE bags was determined by monitoring its molecular weight loss through the Gel Permeation Chromatography(GPC). This degradation process has been analyzed using a novel solution technique, analytical Temperature Rising Elution
Fractionation (TREF), which have allowed to isolate and quantify the evolution of the different families with dissimilarmolecular weight after bag photodegradation. Finally, the chemical modifications were studied by Fourier Transform Infrared(FTIR) spectroscopy.

Keywords: polyethylene bags, photodegradation, TREF

1. Introduction
The wide use of polymers in many industrial anddomestic fields causes ecological problems connectedwith their utilization. Some synthetic plastics including
polyolefins, as low density polyethylene (LDPE), arecharacterized by relatively high stabilities under bothphotochemical and environmental conditions for tens ofyears. In the presence of sunlight LDPE undergoes aseries of reactions such as photolytic, photo-oxidative
and thermo-oxidative, leading to chemical degradation,
and as consequence, its brittleness, loss of brightness,colour change, opacity and crack formation [1]. In thelaboratory, this degradation might be accelerated byultraviolet (UV) irradiation of LDPE. During irradiation
activated molecules are formed, and then processes
such as chain scission, cross-linking and oxidation takeplace [2]. The main process is the reduction in molecularweight, however, the formation of carbonyl, hydroxyl andvinyl groups also take place in the LDPE molecules [3].
The presence of chains with very low molecular weightand functional groups promote and accelerate the LDPE
biodegradation.

techniques have been employed such as FTIR
spectroscopy, to analyze the absorption peak offunctional groups, and GPC to determine the molecularweigh and its distribution. As new, the analyticaltechnique TREF applied to diluted solution, has also
been used to study and quantify the number of chainswith different molecular weight. Finally, standard
biodegradation experiments have been carried out.

3. Results and Conclusions
Simultaneous exposure to UV light and oxygen led to thephoto-oxidative degradation of LDPE films. As aconsequence and it was expected, an increase offunctional groups and a shift in molecular weight
distribution to lower values were observed. TREF results
show three crystallization peaks corresponding to threechain sets with molecular weights which differ in one ormore order of magnitude. Beside this, the ratio amongareas under crystallization peaks indicates the photooxidative degradation is a homogeneous andindependent process of characteristic chain (Figure 1).

2. Materials and Methods
In this study a LDPE film placed in both colored andwhite part of store bags has been analyzed. It is
important to note that this film contains an additive prodegradable, based on metal salts, which combines twodegradation routes, allowing a shorter weathering
degradation time (around three years) compared to otheradditives. These bags have been cut into small pieces.
Then, LDPE is irradiated with a UV source in order tocause an accelerated aging. For evaluation of thesamples before and after treatment different conventional

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6th International Symposium on Feedstock Recycling of Polymeric Materials
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untreated LDPE
Aged LDPE

1644,9 %46,8 %dWt/dT /%∙ºC-1

1429,3 %17,4 %

1210865,9 %
5,0 %414,8 %
30,8 %

202030405060708090100 110 120

T /ºCFig 1. TREF profiles of LDPE film untreated (black color)and after accelerated aging (gray color). Areas undereach crystallization peak are also indicated.

References[1] A.L. Andrady, S.H. Hamid, X. Hu and A.Torikai, J.
Photochem. Photobiol. B, 46 (1998) 96-.
[2] K.C.C. Tse, F.M.F. Ng and K.N. Yu, Polym. Degrad.
Stab., 91 (2006),2380-.
[3] A.R. Sousa, K.L.E. Amorin, E.S. Medeiros, T.J.A.
Melo and M.S. Rabello, Polym. Degrad. Stab., 91(2006),1504-.

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