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A Novel Polymethyl Methacrylate (PMMA).

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  WU NS uhan University Journal of Natural Sciences Vo1.11 No.2 2006 415 418 Article ID 1007-1202 2006)02 0415-04 A Novel Polymethyl Methacrylate PMMA). Ti02 Nanocomposite and Its Thermal and Photic Stability [] ZAN Ling LIU Zhongshi FA Wenjun PENG Tianyou College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, Hubei, China Abstract. A new kind of polymethyl methacrylate (PM- MA)-TiO2 nanocomposite was synthesized through polymeri zation. The thermal and photic stability of this PMMA-TiO2 nanocomposites were investigated. The as-prepared samples were characterized by scanning electron microscopy (SEM), UV-Vis spectroscopy, differential thermal analysis (DTA) and the photo-induced weight loss. The results show that the photostability of the PMMA-TiOz nanocomposite is higher than that of the pure PMMA under UV-light irradiation. The weight-loss of the pure PMMA reaches 30~ after 300 h UV irradiation, while the composite only 0.3~ under the identical experimental condition. The glass transition temper- ature (T,) of pure PMMA is only 80 'C, while the T, of the composite reaches 258 C. Compared with pure PMMA, the thermal stability of the composite is greatly enhanced. Key words polymethyl methacrylate ( PMMA ) TiOz nanocomposite; polymerization; thermal and photic stability CLC number O 643 Received date: 2005 03 13 Foundation item: Supported by the Natural Science Foundation of Hubei Province (203130835) Biography ZAN Ling(1963-), female, Professor, Ph. D., research direction= photocatalytic of Ti()2 nanoparticle. E-mail: rlab @ whu. edu. cn Introduction p olymethyl methacrylate (PMMA) is an important ther- moplastic material. It is widely used as a sheet glazing material, optical lenses and fluorescent solar collections be- cause of its optical clarity. However, the stability of PMMA under UV-irradiation is poor, which results in the decrease of PMMA transparency under sunlight irradiation. The thermal stability of PMMA is not very well, it is usually used under 80 ~ El?. If the temperature is above 80 ~ PMMA will be- come tender and metamorphose. Rutile TiO2 is excellent in shielding ultraviolet E2-4~. It has been used in polymeric pig- ment to improve its photic stability E5 6~. To author s best knowledge, there has not been any research group reported the PMMA-TiO2 nanocomposite and its thermal and photic stability yet. It is well known that TiO2 particle will aggregate badly in the low polarity medium, if there is no enough steric hin- drance T s? . The Ti()2 nanoparticles in polymer usually incor- porate into the polymer matrix in the form of huge agglomer- ates, whose size is extended up to a few micrometers. Due to the high reflecting of these micrometer-sized agglomerates, the transparency of polymeric material is decreased obviously. In order to keep the transparency of PMMA-Ti02 nanocompos- ite, it is important to solve the agglomerate of TiOz particles in PMMA. Our former experiment has proved that the grafted Ti()~ nanoparticles can be dispersed better in polymer c9~ , which will decrease the effect of agglomerate to polymeric transparency. 415  In this paper, the rutile TiOz nanopartides were modified by polymer firstly, and then the grafted TiOe particles were involved in the methyl methacrylate (MMA) monomers to prepare PMMA-TiO2 nanocom- posite by polymerization. The thermal and photic stabili- ty of the composite were investigated by UV-Vis spec- trometer, differential thermal analysis (DTA), SEM and photo-induce weight-loss. Experimental 1.1 Regents Ruffle TiO2 nanoparticles were prepared in author's laboratory with 40-60 nm primary particle diameters. The WD-70 coupling agent was supplied by Wuhan Uni- versity Chemical ~ Material Co Ltd, and its formula is as follows: (CH3 CH2 O) 3--Si--CHz CH2 CHz --O--C(O)--C(CH3 )=CH2 Methal methacrylate was washed by 10 ~ NaOH so- lution and distilled by decompressing before it was used. AIBN (2, 2-Azo-Bis-iso-butyronitrile) was supplied by Shanghai Chemical Reagent Co Ltd. The AIBN was re- crystallized from methanol. 1.2 Preparation of the PMMA TiOz Nanocomposite The experiment procedure of grafting TiO2 particles refers to the Ref. ]-10~. The G-TiO2 particles were dis- persed into MMA monomers by ultrasonic vibration for 20 min, and the weight concentration of Ti()2 was 0.01}/0, 0.05~, 0. 10 respectively. AIBN was cast into the suspension with the 0. 03~ (weight) and poly- merized at 75 ~ to get the composite. Then 30 g com- posite was dissolved in 100 mL chloroform to obtain the suspension. The composite film was prepared by sprea- ding the suspension on a slide glass and dried in airtight system for two days. 1.3 UV Irradiation and Characterization of the Composite All samples were irradiated under the 30 W ultravio- let lamp (X--254 nm). The films were characterized by the photo-induced weight-loss, SEM, UV-Vis spectros- copy and DTA (Shimadzu DT40). 2 Results and Discussion 2.1 Weight Loss of the PMMA Ti02 Composite Film Figure 1 shows the photic stabitility of pure PMMA 4 6 sample and PMMA-TiOz composite samples with the dif- ferent Ti02 concentration in air under ultraviolet irradia- tion. The weight loss rate of pure PMMA film reached 30~ after 300 h UV-irradiation. The weight loss might be attributed to the photodegradation which resulted in the chain scission of polymer with COz and CO evolution cu?. While the weight loss of the PMMA-TiO2 composite film (TiOz 0.1 }/0) only reached 0.3 ~ under the identical experimental condition. The photic stability of PMMA-TiOe composite is much higher than pure PMMA. Fig. 1 also shows that the weight loss of the PMMA-TiOe composite film is less yet, even if TiO2 concentration in PMMA is very low (0. 01~ This re- sult indicates that a few rutile TiOe nanoparticles can pre- vent the PMMA from photo&gradation because of its good shielding property. 30 25 20 15 .7= g: io 9 Pure PMMA / --e- PMMA-TiO, TiO~ 0.01%) a~ PMMA-TiO~ TiO~ o.t)5 %) S v PMMA-TiO~ TiO 0 I0 )//= / r 0 50 100 150 200 250 300 Irradiation time / h Fig. 1 Weight oss of pure PMMA and PMMA-TiOz composite films during UV irradiation 2.2 Surface Morphology of Samples The morphologies of the pure PMMA film and the composite film before and after 72 h UV-irradiation are shown in Fig. 2. It can be seen that the surfaces of both pure sample (Fig. 2A) and the composite sample (Fig. 2C) are smooth before irradation. It means that G-TiO2 nanoparticles are dispersed well in the polymer matrix. After irradation for 72 h, the chalking phenomenon took place on the surface of the pure PMMA film (Fig. 2B), but that of the composite film kept smooth besides of a few small holes around the TiOz particles (Fig. 2D). The results are in agreement on the weight loss. The forma- tion of small hole is due to the photodegradation of the composite film under the UV-irradiation. 2.3 Spectra Characterization Figure 3 shows UV-Vis spectra of pure PMMA and PMMA-TiOz composite film before and after UV-irradia-  [] 9 n B ,if 'ql, r k. \~',, ', ', , ;'[I ,,r , ,,X \ t' ~'{]LHt Fig. 2 The morphologies of pure film and PMMA-TiOz composite film before and after UV-irradiation A. pure PMMA film before irradiation; B. pure PMMA film irradiated for 72 h; C. the composite film before irradiation; D. the composite film irradiated for 72 h tion. The transparency of pure PMMA film reached 92 before UV-irradiation, but decreased to 67 with 72 h UV-irradiation, as shown in Fig. 3A. The transparency of the composite film (TiO2 0. 05 ) (Fig. 3B) reached 900/00 and reduced to 85 after 7 h UV-irradiation. Comparing with pure PMMA film, the transparency of PMMA-TiO2 composite film was decreased in some sort before UV-irradiation; it indicated that grafted TiOz nan- oparticles were dispersed well in PMMA. But the trans- parency of composite film after UV-irradiation was im- proved obviously. When the TiO2 content of composite film was increased (Ti()z 0.10~) (Fig. 3C), the trans- parency was decreased evidently in the range 300-600 nm; it implied the TiOz nanoparticles in polymer agglom- erated with the increasing of TiOz content; the dispersing of Ti()2 nanoparticles needed to improve farther. Howev- er the transparency of the composite film (TiOz 0.10 ) was hardly affected by UV-irradiation. The results indi- cate that the rutile TiOz nanoparticles in PMMA can effi- ciently screen the ultraviolet light; the photostability of the PMMA-TiOz composite is higher than that of the pure PMMA under UV-light irradiation. 100 IOC 100 80 6O ~4o I I 1 I 400 500 600 700 800 Wavelength / nm 8C 6 3 4~ 20 200 20 200 300 48h 300 400 500 600 700 800 Wavelength /nm 80 60 40 20 200 Oh 4h / 48 h 72 h C) 300 400 500 600 700 800 Wavelength / nm Fig 3 UV-Vis spectra of pure PMMA and the PMMA-TiO2 composite film before and after UV-irradiation A) pure PMMA; B) the composite film Ti )~ O. 05~) ~ C) the composite film Ti )z 0.10~) 2 4 Thermal Analysis The DTA curve of the pure PMMA film in the air is shown in Fig. 4. It can be seen that the glass transition temperature (T~) of pure PMMA film appears at 80 ~ and the melting endothermic peak is around 373 ~ The DTA curve of the pure PMMA appears the exothermic peak at 425 ~ Manring E122 suggested that the thermal- degradation of PMMA around 350-400 ~ would be at- tributed to the random scission of PMMA matrix. The DTA curve of the PMMA-TiO~ composite in the air is different from pure PMMA as shown in Fig. 5. The Tg of the composite film appears at 258 ~ Compa- ring with the PMMA, the Tg of the composite increases greatly. It was due to the effect of the G-TiOz embedded in the polymer E13~. The melting endothermic peak of the composite film was separated into two peaks at 321 ~ and 390 ~ respectively. The polymer chain grafted on TiO2 surface could entwist with the chain of PMMA ma- trix, and the physical intercross was formed. ()n the oth- er side, the polymer chain grafted on the Ti()z surface could co-polymerize with the polymer matrix chain, which caused chemical intercross. The polymer chain around TiO2 particles was affected by these intercrosses; the polymer chain far away from the Ti()~ particles was 4 7  less affected so that the melting temperatures were differ- ent. Due to the intercross effect of G-TiO2 particles, the exothermic peak of the composite film appeared at 460 ~C, and the temperature was higher than that of the pure PMMA. Ordinary PMMA are usually used under 80 C. The embedded TiO2 particles can dramatically en- hance the using temperature of PMMA. 30 t 180 330 480 630 T / ~ Fig. 4 DTA curve of pure PMMA T n~ 30 Fig. 5 180 330 480 630 T/~ DTA curve of PMMA TiO~ composite film Conclusion PMMA-TiO2 nanocomposite was prepared by poly- merization; the grafted TiO2 nanoparticles were dispersed well in the PMMA polymer matrix. The thermal stability and photic stability of the PMMA-TiO2 nanocomposite were enhanced greatly. The transparency decreased less in the PMMA-Ti()e nanocomposite film comparing with pure PMMA. The glass transition temperature (T g) of the PMMA-Ti()z nanocomposite reached 258 ~ which meant the PMMA-TiO2 nanocomposite could be used in much higher temperature. References [1] Ma Zhanbiao. Methyl Methacrylate Resins and Application [M]. Beijing: Chemistry Industry Press, 2002(Ch). [2] Guo Gang, Cao Jianjun, Duan Xiaoping, et al. Study on Mod- ified Polyester/ TGIC Powder Coating with Nano-Rutile Ti()2 [J]. Modern Chemical Industry, 2004,24(5): 38-40(Ch). [3] I.aurent D, Florence 13. Solution NMR Characterization of the Preparation of Sol-Gel Derived Si()e/TiO2 and SiO2/ZrOz (;-las- ses [J]. Chemistry of Materials, 1997,9(11 ) : 2385-2394. [-4] Robert J D, I.iu Z F. Titania-Silica: A Model Binary Oxide Catalyst System [J]. Chemistry o J Materials, 1997,9( 11 ) : 2311-2324. [-5] Zhang Y, Zhou G E, Zhang Y H, et al. Preparation and Optical Absorption of Dispersions of Nano-Ti()2/MMA (Methylmethaerylate) and Nano-Ti()2/PMMA (Polymethyl- methacrylate) [J]. Materials Research Bulletin, 1999, 34 (5): 701-709. [6] Nussbaumer R J, Caseri W, Tervoort T, et al. Synthesis and Characterization of Surface-Modified Rutile Nanoparticles and Transparent Polymer Composites Thereof f-J]. J Nanop- article Research, 2002,4(4) :319 323. [7] I.aible R, Hamann K. Formation of Chemically Bound Polymer l.ayers on Oxide Surfaces and Their Role in Colloidal Stability [J] J Adv Colloid Interfilee &'i, 1980,13(1-2) :65-99. [8] Shirai Y , Kawatsura K, Tsubokawa N. Graft Polymeriza- tion of Vinyl Monomers from Initiating Groups Introduced onto Polymethylsiloxane-Coated Titanium Dioxide Modified with Alcoholic Hydroxyl Groups [J]. Progress in Organic Coating, 1999,36(4) :217-224. [9] Zan L, Tian I. H, [.iu Z S, et al. A New Polystyrene-Ti()2 Nanocomposite Film and its Photocatalytic Degradation [J]. ppl Catal A, 2004,264(2) :237-242. [ 10] Zan L, 1.iu Z S, Zhong J S, et al. Organic Modification on TiO2 Nanoparticles by Grafting Polymer [J]. J Mater Sci, 2004,39(9) :3261-3264. [11] Ranby B, Rabek J F. Photodegradation, Photooxidation and Photostabilization of Polymers [M]. New York: John Wiley and Sons, 1975. [12] Manring I. E. Thermal Degradation of Poly(Methyl Methac- rylate): 4. Random Side-Group Scission [J]. Macromole- cules, 1991,24(11) :3304 3309. [13] ()u Yuchun, Yang Feng, Zhuang Yan, et al. Study of the Polymethylmethacrylate/SiOz Nanocomposites by In-Situ Polymerization [J]. Acta Polymerica Sinica, 1997,2: 199- 205 (Ch). ] 4 8

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