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Colloids and Surfaces A: Physicochem. Eng. Aspects 422 (2013) 1– 9
Contents lists available at SciVerse ScienceDirect
Colloids and Surfaces A: Physicochemical andEngineering Aspects
jo ur nal homep a ge: www.elsev ier .com/ locate /co lsur fa
iO2 nanoparticle assisted solid phase photocatalytic degradation of polythenelm: A mechanistic investigation
eny Thankam Thomas1, Vaishakh Nair1,2, N. Sandhyarani ∗
anoscience Research Laboratory, School of Nano Science and Technology, National Institute of Technology, Calicut, Kerala-673 601, India
i g h l i g h t s
Photocatalytic degradation of poly-ethylene was studied with two sizedTiO2 particles under UV radiation.Degradation efficiency of TiO2-50was 56.20% and TiO2-200 was 27.78%on UV exposure of Congo red.We report effective degradationof polyethylene film using 0.1 wt%TiO2 confirmed from FTIR, SEM andweight loss studies.Weight loss was 18% for TiO2-50 onUV irradiation.A possible mechanism of degrada-tion is proposed.
g r a p h i c a l a b s t r a c t
A comparative study on the photodegradation of two different sized TiO2 incorporated LDPE under UVradiation was carried out. Polyethylene film incorporated with TiO2 nanoparticle of size 50 nm showed18% degradation under UV radiation.
r t i c l e i n f o
rticle history:eceived 1 November 2012eceived in revised form 10 January 2013ccepted 13 January 2013vailable online 23 January 2013
a b s t r a c t
The solid-phase photocatalytic degradation of low density polyethylene (LDPE) with sol–gel synthesizedTiO2 nanoparticles as photocatalyst was investigated under ultraviolet (UV) irradiation in ambient airconditions. TiO2 nanoparticles were synthesized by optimizing various parameters and the TiO2 nanopar-ticles were dispersed in LDPE using cyclohexane solution. This TiO2–PE nanocomposite was made inthe form of thin films of 40 �m size by facile solution casting method and studied photodegradation
eywords:itania nanoparticlesolyethylene degradationhotocatalytic degradationolythene–titania composite film
of these films. A comparative study on the photodegradation of two different sized TiO2 incorporatedLDPE under UV radiation was carried out. Polyethylene film incorporated with TiO2 nanoparticles ofsize 50 nm showed higher degradation rate under UV radiation. Partial oxidation was confirmed fromthe IR spectrum of the TiO2 incorporated polyethylene film after radiation exposure. SEM analysis andAFM nanoindentation measurements confirm the degradation. A possible mechanism of TiO2 assisted
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ongo red degradation of the polyet. Introduction
Environmental remediation is one of most crucial area ofesearches at the present time [1]. The environment gets con-aminated by various pollutants. Among the solid pollutants,
∗ Corresponding author. Tel.: +91 495 2286537; fax: +91 495 2287250.E-mail address: [email protected] (N. Sandhyarani).
1 The authors contributed equally to this work.2 Present address: Indian Institute of Technology, Madras, Chennai-36,
amilnadu, India.
927-7757/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.colsurfa.2013.01.017
e matrix has also been proposed.© 2013 Elsevier B.V. All rights reserved.
polyethylene contributes to a major extent due to its wider usage,durability and non degradability. Low density polyethylene (LDPE)in the form of films are the common form of polyethylene (PE), usedin a variety of applications including carrying, storing and packingof food product [2]. In spite of all these utility, the usage of poly-ethylene has to be constrained due to its resistance to degradationwhen disposed to the environment. If burnt, polyethylene infusesthe air with toxic compounds such as methane, ethane, aldehydes,
ketones and acrolein which causes serious problems of pollution[3,4]. Since the usage of plastics has become an integral part of thesociety, new technologies have to be implemented to eradicateits harmful effects. Prasun et al. have recently reviewed whether
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R.T. Thomas et al. / Colloids and Surfac
he degradation of polyethylene is a fantasy or reality. They haveiscussed in detail different degradation mechanisms of PE and thearious degradation products, its impact on the environment andiodegradation. They concluded that the fate of the degradationroducts and its entry into the eco-cycle is a matter of concernence long term studies are essential. They have highlightedhe demand for developing protocols to quantify the effect andhe nontoxicity on to the environment [5]. Many researchersave been working on the biodegradability of polyethylene withiopolymers, microorganisms, fungus etc. It was observed thatolyethylene resists biodegradation initially [6,7]. Thermoxidativeegradation of polyethylene films under different temperaturessing pro-oxidant additives have also been reported where in theorrelation between temperature, oxygen content, and the timeeeded for the formation of biodegradable low molecular massxidation products were evaluated [8]. Another area of degradationhich is being researched is photocatalytic degradation. Titaniumioxide (TiO2) nanoparticles have been employed as a suitableandidate for environmental application due to its non-toxicity,trong oxidizing power, chemical inertness, and low cost [9]. TiO2as been used for water purification and for treatment of indus-rial wastes [10] like nitrobenzene [11] dyes, [12] phenol and itserivatives [13,14], industrial waste gas [15] and pesticides [16,17].
Nano-size TiO2 when used, provide the advantage of highurface area thereby increasing degradation process [18]. The pho-ocatalytic mechanism has already been discussed in literature [1].riefly, TiO2 generates the highly reactive electron–hole pairs (exci-ons) on absorption of suitable energy. These electrons and holeseact with the adsorbed molecules on the surface and produceeactive free radicals. These free radicals in turn react with theolecules or compounds and degrade them. Both modified and
nmodified TiO2 has been investigated as a photocatalyst for theegradation of polystyrene [19,20]. Another work reported in thiseld is the solid phase photocatalytic degradation of polyethylenesing P25 type TiO2 particles under solar and UV-radiation [21,22].hey have discussed the mechanism of degradation.
In this work photocatalytic degradation of polyethylene haseen investigated using semi crystalline anatase type TiO2anoparticles synthesized using sol–gel method. Photocatalyticegradation of polyethylene was compared using commerciallyroduced crystalline anatase TiO2 powder having size around00 nm and sol gel synthesized TiO2 nanoparticles (50 nm). Thesere described later as TiO2-200 and TiO2-50 respectively. Evenhough few works on the photocatalytic degradation of polyeth-lene using commercially available P-25 Degussa TiO2 has beeneported, the sol–gel synthesized and size dependant comparisonf the degradation property has not been reported so far. Here weeport effective degradation of polymer film using 0.1 wt% TiO2nder two 15 W UV lamps which is cost effective compared to thearlier reports. Interestingly, we found that the degradation is sizeependent and a higher degradation rate of PE film was observedith TiO2-50 under UV radiation. The possible mechanism of degra-ation of the polyethylene matrix has also been explained. Weompared the effect of size by taking only two types of titania par-icles, as intermediate size will not show a drastic difference in theegradation of PE. Higher sizes than 200 nm are not studied as thisill not show a good photocatalytic activity in the UV light and iteviates from the nanosize.
. Experimental
.1. Synthesis of TiO2nanoparticles
Titanium(IV) isopropoxide (TTIP) purity 98% (Sigma–Aldrich),olyoxyethylene sorbitan monolaurate – Tween 20 (Merck), cyclo-exane (Fischer Scientific), TiO2-200 anatase 97.5% (Travancore
hysicochem. Eng. Aspects 422 (2013) 1– 9
Titanium Products Ltd., India) Congo red (CR) (Spectrum chemicals,India) ethanol (absolute grade purity 99.8%) (Merck, India) wereused as received. Ultrapure water obtained using an ultrafil-tration system (Milli-Q, Millipore) with a measured resistivityabove18 M� cm at 25 ◦C was used for all the experiments.
TiO2 nanoparticles were synthesized after optimizing variousparameters such as pH, solvent, stabilizer concentration, temper-ature and stirring time. (See supporting information Fig. S1–S5).Briefly TiO2 nanoparticles were synthesized by the following pro-cedure. 0.2 ml Titanium(IV) isopropoxide was dissolved in 100 ml1:1 ethanol water mixture and 4% Tween 20 was added as stabilizer.Synthesis was done at different pH (supporting information Table1) and it was observed from the zeta potential that the particleswere stable at pH 4 than at lower or higher and hence the pH of thesolution was maintained at 4 and reaction temperature at 50 ◦C.The mixture was stirred for 3 h and centrifuged at 8000 rpm andwashed thrice with distilled water to remove the unreacted mate-rials. Purified nanoparticles were collected by centrifugation anddried. These nanoparticles were further used for characterizationsand incorporation into the PE films.
2.2. Characterization
The particle size and morphology of the nanoparticles and thecomposite films were characterized using scanning electron micro-scope (FESEM) Hitachi SU6600 Variable Pressure Field Emission.Energy dispersive X-ray analysis (EDX) studies were carried outwith the same system for analyzing the elemental composition.The mode of degradation of polyethylene titania composite filmsbefore and after irradiation was monitored using Fourier transforminfrared spectrometer (FTIR) Thermo Nicolet, Avatar 370 IR. Thedegradation studies of Congo red were done using Schimadzu 1800UV–vis spectrophotometer. The measurements were done at roomtemperature with distilled water as the reference solution usinga pair of quartz cuvette with path length of 1 cm. X-ray diffractionstudies were done using Bruker AXS D8 Advance diffractometer (CuK� radiation � = 1. 5406 Å). UV–vis diffuse reflectance spectra wereperformed on Thermoscientific evolution 600. Differential scanningcalorimetric analysis of the samples were done to study the phasetransition of the sample using DSC 4000 PerkinElmer. The mechani-cal properties of the films were investigated using nanoindentationtechnique in Park XE-100 Atomic force microscopy.
2.3. Preparation of low density poly ethylene–titania compositefilm
About 0.5 gm of polyethylene was added to 40 ml cyclohexaneand vigorously stirred for one hour at 70 ◦C. Later 0.1 wt % of TiO2was added and uniformly dispersed using a magnetic stirrer whilemaintaining the temperature at 70 ◦C. About 10 ml of the PE–TiO2solution was poured into a petri dish of about 4 cm radius. Thissolution was dried for 20 min at 70 ◦C and then kept at room tem-perature to obtain a thin film of PE–TiO2 composite. This methodwas used to prepare the two types of PE–TiO2 films using TiO2-200and TiO2-50.
2.4. Photocatalytic degradation of the films
The UV degradation study of PE–TiO2 films was performedin a designed chamber containing two 15 W UV tubes (365 nm).The chamber contains one common inlet and outlet for keep-ing the samples. The photodegradation reaction was conducted
under ambient air at around 25 ◦C in a lamp housing box(55 cm × 35 cm × 30 cm) reactor with ultraviolet lamp as shown inScheme 1. In all the experiments the samples were placed 20 cmaway from the lamp unless otherwise stated. The samples were
R.T. Thomas et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 422 (2013) 1– 9 3
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Scheme 1. Schematic of the preparation PE–TiO2 films and photocatalytic
ept for 300 h in the chamber continuously. Sampling was carriedut by withdrawing the film from the chamber at regular inter-als of time and monitored the degradation using the techniquesescribed. The degradation study of films under solar radiation wasone by keeping the samples in a petri dish and exposed to sunaily from 9 am to 4 pm with measured intensity between 75000nd 95000 luxes. The size effect of TiO2 on the degradation processas studied using TiO2-200 and TiO2-50 particles. Degradation wasonitored at regular interval of time.
.5. Photocatalytic degradation of Congo red
Congo red (CR) dye was used as a model contaminant. Thehotocatalytic activity of TiO2 nanoparticles were investigated byonitoring the degradation of aqueous CR solutions. 100 �l of CR
ye was added to 20 ml aqueous solution of titania photocatalyst0.1 mg/ml) and stirred well. The solution was kept in the degrada-ion chamber and reaction was carried out under stirring. At variousime intervals 2 ml of solution was withdrawn and the photocat-lytic decomposition of the dye was monitored by recording theV–vis absorption spectra.
. Results and discussion
.1. Synthesis and characterization of titania nanoparticles
Titanium dioxide nanoparticles were synthesized using sol–gelethod in ethanol–water mixture at 50 ◦C at the solution pH 4. Var-
ous solvents such as ethanol, water and ethanol–water mixtureere used for the synthesis and it was observed in UV–vis spec-
rum that the ethanol–water mixture gave a single narrow peakompared to that of water and ethanol solvents. It was observed
r setup with (1) UV tubes (15 W) (2) sample (3) Common Inlet and Outlet.
that monodispersed nanoparticles of TiO2 were obtained when thereaction was done in 1:1 water–ethanol mixture with 4% Tween 20as the stabilizer at a temperature of 50 ◦C and at pH 4. The particlesize and morphology was confirmed by SEM analysis (Fig. 1a). TheSEM images showed that the particles were spherical in shape andhad a mean size of 50 nm. The energy dispersive spectra showed thepresence of Ti (28.43 at.%) and O (71.57 at.%) in the sample (Fig. 1b)which confirmed the elemental composition and the absence ofother elements showed that the TiO2 prepared was pure. The dif-fuse reflectance spectra (DRS) of the TiO2-50 showed absorptionaround 280 nm and TiO2-200 around 350 nm (Fig. 1c). The indirectband gap of TiO2 nanoparticles was determined from the UV–DRSspectra. The band gap was estimated by plotting hv versus (˛hv)1/2.The absorption coefficient ˛ is related to the bandgap Eg as
˛h� = A(h� − Eg)1/2,
where hv is the incident photon energy and A is a constant. Theband gap of the TiO2-50 was determined to be 3.17 eV and that ofTiO2-200 was 3.08 eV.
The anatase form of titania was confirmed from XRD. The XRDstudies revealed that the crystalline nature of the TiO2 depend onthe pH. It was seen that as the pH reached the optimum value, peaksrelated to the anatase phase at 2� = 25◦ was well resolved (Fig. 2).Since in this study we are focusing on the size effect of anatase TiO2,we used the particles synthesized at pH 4 for further investigations.
3.2. Photocatalytic degradation of Congo red
Congo red (CR) in distilled water exhibits three characteristicbands at 497, 347 and 237 nm at pH 5. In order to evaluate theefficiency of the TiO2 nanoparticles (TiO2-50) photocatalyticdegradation of Congo red was investigated by the absorbance
4 R.T. Thomas et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 422 (2013) 1– 9
2-200
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Fig. 1. (a) SEM image, (b) EDAX spectra (c) UV–DRS spectra of TiO
ecay of the characteristic peaks. This was monitored by UV–vispectrum at different time intervals during the course of theeaction. TiO2-50 nanoparticle was added to the CR solution at
pH 5. The resulting solution was exposed to UV light in theeaction chamber described earlier. Fig. 3a shows the UV–vispectra of CR at different time intervals of UV exposure. It islear from the spectra that the absorbance of CR decreases afterxposing to the UV radiation at different time intervals for 14 h.he kinetics of degradation is analyzed by plotting ln[A] vs time
here A is the absorbance (Fig. 3b) and the linear fit indicateshe first order kinetics of degradation. The rate of the reaction is.34 × 10−3 min−1. Fig. 3c represents the exponential decay of the
ig. 2. XRD pattern of TiO2 nanoparticles synthesized at various pH values (a) 4 (b) and (c) 2 respectively.
and TiO2-50 (d) Band gap determination of TiO2-200 and TiO2-50.
dye with time by plotting [A]/[A0] vs time where A0 is the initialabsorbance and A the final absorbance at time t. Fig. 3d shows thephotodegradation efficiency of the titania particles which can becalculated from the following equation. � = [(A0 − At)/A0] × 100%,where, Ao is the absorbance at time zero and At at time t, respec-tively. The degradation efficiency of TiO2-50 after 10 h was foundto be 56.20% and that of TiO2-200 was 27.78%.The degradationefficiencies of TiO2 nanoparticles synthesized at different pH isshown in Fig. S6 which was lesser than TiO2-50.
3.3. Photocatalytic degradation of PE, PE–TiO2 films under UVirradiation
Photocatalytic degradation of pure polythene film and PE–TiO2nanocomposite films were monitored by analyzing the weightloss measurements, SEM and FTIR. It is seen that the PE filmcontaining the TiO2-50 particles showed enhanced weight lossthan the pure PE film and PE film containing the TiO2-200 particlesunder UV radiation (Fig. 4). The films were exposed to sunlight also(supplementary information). The PE film containing the TiO2-200particles showed more weight loss under solar radiation than thePE film containing the TiO2-50 particles (Fig. S7). The weight lossrates were significantly higher in the composite films than the purepolythene films which showed only 0.5% weight loss under UVirradiation. After 300 h of UV exposure, 18.1% weight loss was seenin PE film containing TiO2-50 and the TiO2-200 showed only 7.5%weight loss. The effect of light intensity on the degradation of the
polymer was also studied (Fig. S8). It was observed that when thedistance between the light source and sample were reduced (i.e.at a higher light intensity) the rate of degradation also increased.Since efficient weight loss was observed for polyethylene films
R.T. Thomas et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 422 (2013) 1– 9 5
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ig. 3. (a) UV–Vis spectra of CR degradation using TiO2-50 nm (b) Plot ln[A] vs timehe exponential decay of CR (d) Photodegradation efficiency of TiO2-50 and TiO2-20
ncorporated with TiO2-50 with optimum conditions under UVxposure, these samples were further characterized.
.4. Morphological characterization
The surface morphology of the irradiated polymer compositelms was studied using SEM. The SEM images of polyethylenelm, polyethylene film with TiO2 particles (nano size and microize) before and after UV irradiation are shown in Fig. 5. Under UV
ig. 4. Percentage weight loss studies of polyethylene: PE–TiO2 films under UVadiation.
sents the kinetics of degradation of Congo red (c) Plot of [A]/[A0] vs time representsifferent irradiation time.
irradiation for 200 h formation of cavities were observed on thepolyethylene film containing TiO2-50. Large cavities were seen inPE containing TiO2-50 film exposed to UV radiation while com-paratively fewer cavities were seen in the PE containing TiO2-200film exposed to solar radiation. One of the reasons for this modeof activity is that the TiO2-50 has higher band gap energy and theyabsorb mostly in the UV region and the specific surface area of theparticles enhances the rate of photocatalytic reaction. TiO2-200 haslower band gap energy and thereby limited absorption in the UVregion. The distribution of titania nanoparticles was clearly seen inSEM image (see supporting information Fig. S9a and b). The TiO2nanoparticles could be evidently seen after the degradation of thepolymer matrix. This also suggests that the degradation was initi-ated at the surface of the nanoparticles (AFM images of the polymerfilms before and after TiO2 incorporation is shown in Fig. S9c and drespectively, which clearly indicated the presence of nanotitania).It is implied that the reactive oxygen species generated on the TiO2surface causes random breakage of the bonds that hold the atomsof the polymer together and etch out the polymer matrix.
3.5. FT-IR spectra
The photocatalytic degradation of PE–TiO2 films were examinedusing FT-IR spectroscopy. Fig. 6 shows the FT-IR spectra of the PEand composite films before and after UV irradiation for 300 h. The
IR spectra of films treated under solar radiation are shown in Fig.S10. It was observed that the untreated PE–TiO2 composite filmshowed the characteristic absorption in the region 2920 cm−1,2850 cm−1, 1460 cm−1 and 719 cm−1 which corresponds to CH2
6 R.T. Thomas et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 422 (2013) 1– 9
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ig. 5. SEM images of the PE, PE–TiO2 (50 nm) and PE–TiO2 (200 nm) composite fiample before irradiation (d) PE–TiO2-50 sample UV-irradiated for 200 h (e) PE–TiO
tretching and bending vibrations. These peaks were the sames that in pure PE film showing that the chemical characteristicsf the polymeric matrix was not affected by the incorporation ofiO2 particles. The degradation of the polyethylene matrix was
ig. 6. FT-IR spectra of films: before and after exposure under UV radiation (1) PEare (2) PE–TiO2-50 before exposure (3) PE–TiO2-50 after exposure.
a) PE film before irradiation (b) PE sample UV-irradiated for 200 h (c) PE–TiO2-50 sample before irradiation (f) PE–TiO2-200 sample UV-irradiated for 200 h.
confirmed by the formation of carbonyl groups due to the partialoxidation of PE (See the proposed mechanism below). The spectraof the UV treated film showed a new peak around 1720 cm−1,which is assigned to C O stretching vibrations which is the char-acteristic absorption of carbonyl group [23]. Also a broadening ofthe peak was observed for the CH2 stretching vibrations after theexposure. The broadening is attributed to the less ordered alkylchain [24]. These variations in the spectra indicate the structuralchanges in the polythene film during the degradation.
3.6. Differential scanning calorimetry (DSC)
Phase changes of the composites during the degradation werestudied using a DSC analyzer. Samples were held at 35 ◦C for 5 minand then heated from 35 ◦C to 375 ◦C at a rate of 10 ◦C min−1 undernitrogen atmosphere. Fig. 7(c) shows a sharp endothermic peak at110.10 ◦C which indicates the melting temperature of PE. There wasno significant shift in the peak for PE–TiO2-50 composite (Fig. 7(b))
which was observed at 110.56 ◦C. The UV treated PE–TiO2-50 com-posite sample (Fig. 7(a)) showed a slight increase in the peaktemperature to 112.94 ◦C indicating the increase in crystallinity ofthe sample. This may be attributed to the formation of the carbonyl
R.T. Thomas et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 422 (2013) 1– 9 7
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ig. 7. DSC curves of (a) PE–TiO2-50 UV treated (b) PE bare (c) PE–TiO2-50 beforeV treatment.
roup in the polythene film during the oxidation, which leads to anncrease in crystallinity [25].
.7. Nanoindentation
Nanoindentation was done to evaluate the mechanical prop-rties like hardness at the nanoscale. A three-sided pyramidalingle-crystal natural diamond tip, a Berkovich indenter was used.
ith the help of this sharp tip, force of few micronewtons waspplied with a loading and unloading rate of 0.3 �m s−1 to obtain
force displacement curve. Oliver and Pharr method was adoptedo measure the hardness and elastic modulus from the indenta-ion load-displacement data obtained during one cycle of loadingnd unloading. Hardness is calculated by dividing the loading forcey the projected residual area of the indentation and the Young’sodulus of elasticity can be obtained from the slope of the unload-
ng curve. The hysteresis indicates that the deformation is not fullylastic and partially inelastic [26].
The mechanical strength of the polyethylene film increasedpon incorporation of TiO2 nanoparticles. Fig. 8 represents the typ-
cal loading and unloading curve obtained from nanoindentation.sing Oliver and Pharr model the hardness and elastic modulusas calculated. The hardness and young’s modulus of PE–TiO2 filmsave been increased by 16.4% and 26.55% respectively comparedo the bare polyethylene. Also it was found that the strength ofE–TiO2 films reduced upon exposure to the UV radiation indi-ating the degradation. The percentage decrease in hardness andoung’s modulus is 2.68% and 10.81% respectively for samples irra-iated under UV radiation when compared to untreated PE–TiO2lms. For the indentation measurements the clear portions present
n the UV treated PE–TiO2 film (where no holes) was subjected tondentation.
.8. Mechanism of degradation
The reaction of pure polymer film under UV irradiation occursia the absorption of photons by the PE molecule to create thexcited states which leads to the chain scission. Incorporation ofiO2 nanoparticles facilitates the absorption of photons and gen-ration of electrons and holes there by the formation of reactive
adical species such as hydroxyl radical (OH•) and hydroperoxyadical (HOO•). These radicals then react with the polymer chain toorm the oxidized species [27]. The proposed mechanism followscheme 2.Scheme 2. Possible mechanism of degradation of polyethylene in presence of titaniaand UV light.
The degradation of polyethylene has been enhanced by theaddition of TiO2 nanoparticles. Due to its innate ability to gener-ate electrons and holes, titania nanoparticles upon UV irradiationaids in the degradation of PE matrix. The initiation of degradationoccurs at weak sites [28] or the amorphous regions in the poly-mer and progress via formation of hydroperoxide intermediatesto form carbonyl compounds. Roy et al. has reported that thesecarbonyl groups absorb UV radiation readily and get excited tosinglet and triplet states which further decompose via Norrish reac-tions of type I and II. The formation of carbonyl groups confirms(Confirmed by IR spectrum and DSC) the degradation of the poly-mer through embrittlement of the films and the chain scission canlead to cracking. As evident from DSC the crystallinity of PE hasbeen increased due to scission of the polyethylene molecule in theamorphous region [29]. This leads to the formation of low molec-ular segments making it favourable for biodegradation and loss ofmechanical properties [30]. Once the formation of free radicals is
achieved they can promote the generation of polyethylene macro-radicals which further react with molecular oxygen to degrade thePE matrix [31].
8 R.T. Thomas et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 422 (2013) 1– 9
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Fig. 8. Force displacement curve of PE–TiO2-50 film b
. Conclusion
The photocatalytic degradation of polyethylene was studiedsing titania nanoparticles. Two different sized TiO2 particles weresed viz. TiO2-50,synthesized by sol–gel technique and commer-ially available TiO2-200. We found that the percentage weight lossf PE–TiO2-50 films under UV radiation was higher than that ofE–TiO2-200. This is attributed to the higher band gap in nanopar-icles, which was comparable to that of the incident UV radiation.herefore, TiO2-50 showed better photocatalytic property underV radiation which showed weight loss up to 18% in 300 h. Par-
ial oxidation leads to the formation of carbonyl group which wasonfirmed from the IR spectrum and the carbonyl group inducedrystallinity was observed in DSC. SEM images clearly indicate theormation of cavities in the polymer matrix upon UV irradiation.ll these data confirms the degradation of plastic using titaniaanoparticles. A possible mechanism of degradation is proposedased on the results from IR and DSC. More research has to beocused on the applications and large scale production of suchco friendly materials aiming at the development of completelyegradable plastics.
cknowledgement
The authors acknowledge National Institute of Technology Cali-ut for providing the facility and financial support.
ppendix A. Supplementary data
Supplementary data associated with this article can beound, in the online version, at http://dx.doi.org/10.1016/j.colsurfa.013.01.017.
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