Spectroscopic Studies of Photodegradation of Polyethylene Films Containing TiO 2 Nanoparticles Rui Yang, 1 Paul A. Christensen, 2 Terry A. Egerton, 2 Jim R. White, 2 Adam Maltby 3 1 Department of Chemical Engineering, Tsinghua University, Beijing 100084, China 2 School of Chemical Engineering and Advanced Materials, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom 3 CRODA Chemicals Europe, Ltd., Oak Road, Hull HU6 7PH, United Kingdom Received 9 July 2009; accepted 27 September 2009 DOI 10.1002/app.31669 Published online 18 August 2010 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: The effect of UV radiation on a family of low density polyethylene films containing different con- centrations of TiO 2 nanoparticles has been studied. The photodegradation was monitored using FTIR measure- ments of carbonyl group development and an in situ FTIR method that tracks the generation of CO 2 as a principal product of degradation. Samples containing dispersant and/or a phenolic antioxidant but free from TiO 2 particles were examined as controls. It was shown that the effects of photodegradation of the polymers could be followed even when these additives were present. The dispersant gave rise to absorption in the carbonyl region of the IR spectrum but meaningful results concerning the progress of photodegradation were obtained using difference spec- tra. Good correlation was found between the carbonyl and the CO 2 measurements of the relative photosensitivities of the films with different compositions, and both methods indicated that addition of the nano-particulate rutile TiO 2 had decreased the film photostability. The decreased photostability inferred from spectroscopic measurements was also observed as a reduction, from  1100 h to 400 h, of the exposure time before film cracking, when samples were exposed to UVA radiation in QUV equip- ment. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 1330– 1338, 2011 Key words: polyolefins; titanium dioxide; nanoparticles; FT-IR; photodegradation INTRODUCTION Commercial polymeric materials usually contain a variety of additives. These include both molecular and particulate antioxidant stabilizers, which are included to protect the material during both process- ing and service. Fibers and particles are often added to improve the material’s mechanical properties, and for the past 20 years, nanoparticles have been increasingly used to enhance these properties at lower mass fractions than are used for macroscopic fibers and particles. 1–9 The introduction of any par- ticulate additive almost inevitably demands the use of a dispersant to prevent particle aggregation. This article is concerned with TiO 2 nanoparticles. Because of their small size, these nanoparticles can be used to modify the film properties without sacri- ficing film transparency but, because TiO 2 is a broad band semi-conductor, they absorb short wavelength light. Consequently, they offer a way to tailor the optical properties of the polymer nanocomposite. For example, packaging film could have sufficient transparency to let the wrapped contents be seen, but still prevent the photochemically active wave- lengths from reaching and spoiling the product. By acting as a UV screen, the TiO 2 may protect the polymer from photochemical degradation and lengthen its lifetime. Conversely, it may instead shorten film lifetime by photocatalyzing polymer degradation. Indeed, photocatalysis has been studied as a method of disposing of used plastics articles, especially for poly(vinyl chloride). 10–12 Aspects of the photoprotection and photosensitization of polyo- lefins by TiO 2 have been discussed by the current authors 13 and by Allen and coworkers. 14–18 The lat- ter workers concluded that nano-particle TiO 2 was generally more active than pigmentary ( 0.3 lm) TiO 2 16,17 and that for polyethylene (PE) filled with 0.5% TiO 2 , the time to reach a carbonyl index of 0.1 was greater for 25 nm rutile than for 20–30 nm ana- tase, and that this time varied with particle size for different nano-anatase powders. 16 However, as the coating applied to TiO 2 pigments strongly influences the balance of photocatalysis and photoprotec- tion, 16,17,19 it is very difficult to decouple any intrin- sic size-related effect from the effect of the coating on the nanoparticles. Zeynalov and Allen showed that nano-titania (and particularly nano-rutile) Correspondence to: T. A. Egerton (T.A.Egerton@ncl.ac.uk). Contract grant sponsors: China Scholarship Council, UK DTI/EPSRC (ACORN Collaborative Project with Croda Chemicals). Journal of Applied Polymer Science, Vol. 119, 1330–1338 (2011) V C 2010 Wiley Periodicals, Inc.