Nanoparticles and Nanowires of ZnO with Organophilic Surfaces and their Nanocompo sites with Poly(methyl methacrylate)

The Subject of the Invention

The subject of the invention is nanoparticles and nanowires of zinc (II) oxide - ZnO with organophilic surfaces, synthesized in various diols in the presence of para-toluene sulfonic acid (p-TsOH) and their nanocomposites with polymethyl methacrylate (PMMA), prepared without additional surface modification of ZnO particles. ZnO nanoparticles and nanowires are useful as: semiconductive additives in PMMA for various electronic applications, light and UV transformers in nanocomposites with a PMMA matrix for solar techniques, UV absorbers and light stabilizers in plexiglass for outdoor applications, in nontransparent nanocomposites with PMMA for outdoor applications, and in coating systems that contain PMMA or its copolymers as binders where methacrylic or acrylic polymers are the prevailing components.

State of the Art

Over the past few years, research activities have been oriented towards the environmentally acceptable synthesis of nanoparticles and other types of nanostructures, as well as towards the synthesis of nanocomposites composed of nanoparticles and various matrixes using procedures that are acceptable for industrial application. One of the environmentally acceptable ways to synthesize ZnO nanoparticles is hydrolysis in various diols. Patent application KR20050043442 describes the synthesis on ZnO powder in glycol. The scientific literature, quoted under consecutive numbers from 1 to 6, describes the synthesis of ZnO in various alcohols. In the majority of cases it describes the synthetic procedures of ZnO in various mono and diols with no additives or with the addition of an acid or base as a catalyst. The disadvantage of ZnO synthesized in monoalcohols is the rather poor organophilicity of their surface, creating the need for additional surface modification for their application in nanocomposites. Additional surface modification increases the price of such nanofillers and can also cause the deterioration of some mechanical properties of the nanocomposite. The disadvantage of the synthesis of ZnO in monoalcohols and in diols without the addition of p-

TsOH is the low concentration of precursor, if the targeted particle size of ZnO is below 100 nm. The low concentration of precursors causes high consumption of solvents in the synthesis of nanoparticles, which again increases the price of such nanoadditives.

There is no literature source describing the synthesis of ZnO in diols with the addition of p- TsOH as a catalyst. The literature, under consecutive numbers from 7 to 13, describes procedures for the preparation of nanocomposites with ZnO synthesized in various monoalcohols. In all cases additional surface modification is used to achieve homogeneous distribution of ZnO in the PMMA matrix. Additional surface modification usually deteriorates thermal stability, as, for example, in literature source 13, and it also deteriorates the mechanical properties of nanocomposites because most of the surface modifiers have a softening side effect. There is no information in the literature about the application of ZnO synthesized in diols for the preparation of nanocomposites with PMMA.

Literature:

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9. M.M. Demir, K. Koynov, U. Akbey, C. Burbeck, I. Park, I. Lieberwirth, G. Wegner, Macromolecules, 40, 2007, 1089-1100

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11. E. Tang, G. Cheng, X. Pang, X. Ma, F. Xing, Colloid Polym. Sci., 284, 2006, 422-428

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13. P. Liu, Z. Su, J. Macromol. Sci. Part B, Physics, 45, 2006, 131-138

The Aim of the Invention

The aim of the invention is the synthesis of a filler on the basis of ZnO nanoparticles with a narrow average particle distribution below 100 nm and with a defined shape (e.g. spheres, wires, etc.), which have organophilic surfaces, prepared by a procedure which makes feasible the synthesis of nano ZnO with average particle size under 100 nm at precursor concentrations of at least 0.1 mol/L. The aim of the invention is also to synthesize homogeneous nanocomposites of methacrylates or acrylates and the stated filler on the basis of ZnO with enhanced UV, light and thermal stability, and predominantly unchanged mechanical properties, as well as the simple preparation procedure of such nanocomposites by polymerization of methacrylic and acrylic monomers in bulk or by casting the solution of methacrylic or acrylic polymer, which can be transparent, if there is such a necessity.

Description of the Invention

The invention will be described by the following figures and embodiments:

Figure 1 : Transmission electron micrographs (TEM) of ZnO nanoparticles, synthesized by the polyol procedure with no addition of p-toluene sulfonic acid (p-TsOH) in: a) di(ethylene glycol) (DEG), b) tetra(ethylene glycol) (TEG).

Figure 2: X-ray diffractogram of a ZnO sample synthesized by the polyol procedure with no p-

TsOH.

Figure 3: Fourier transform infrared spectrum (FTIR) of a ZnO sample synthesized by the polyol procedure with no p-TsOH.

Figure 4: TEM micrographs of ZnO nanoparticles, synthesized by the polyol procedure with the addition of p-toulen sulfonic acid (p-TsOH) in various diols: a) 1,4 - butane diol (BD), b)

TEG, c) DEG, d) ethylene glycol (EG), e) 1,2 -propane diol (PD).

Figure 5: X-ray diffractogram of ZnO sample synthesized by the polyol procedure with addition of p-TsOH.

Figure 6: FTIR spectrum of ZnO sample synthesized by the polyol procedure with addition of p-TsOH.

Figure 7: TEM micrographs of PMMA/ZnO nanocomposites - ZnO synthesized in DEG.

Figure 8: Ultraviolet- visible light (UV-vis) spectra of PMMA/ZnO nanocomposites with various weight fractions of ZnO: A) 1 %, B) 0.1 %, C) 0.01 %, D) 0.001 %, E) 0 %.

Figure 9: Differential thermogravimetry (DTG) curves of PMMA/ZnO nanocomposites with various weight fractions of ZnO.

Figure 10: TEM micrographs of PMMA/ZnO nanocomposites - ZnO synthesized in TEG.

Figure 11 : TEM micrographs of PMMA/ZnO nanocomposites - ZnO synthesized in various diols: a) BD, b) TEG, c) DEG, d) EG.

Figure 12: UV-vis spectra of PMMA/ZnO nanocomposites (ZnO synthesized in various diols in the presence of p-TsOH): A) 0.01%, B) 0.1%, C) 1.0%, D) 0%.

Figure 13: DTG curves of PMMA/ZnO nanocomposites (ZnO synthesized in the presence of p-

TsOH) in various concentrations of ZnO.

Figure 14: TEM micrographs of PMMA/ZnO nanocomposites (ZnO synthesized in PD in the presence of p-TsOH) prepared by the prepolymer procedure (procedure B).

Figure 15: UV-vis spectra of PMMA/ZnO nanocomposites (cone. ZnO = 0.1 %) under various preparation procedures: A) prepared directly from monomer (Procedure A), B) prepared by the prepolymer procedure (Procedure B), C) sample without ZnO.

Figure 16: UV-vis spectra of PMMA/ZnO nanocomposites (ZnO synthesized in EG) dependent on the concentration of ZnO: A) commercial plexiglass, B) PMMA/ZnO nanocomposite (0.05% of ZnO synthesized in EG) prepared by procedure C, C) sample without ZnO.

Figure 17: TEM micrograph of PMMA/ZnO nanocomposite prepared by casting from solution.

Figure 18: UV-vis spectra of PMMA/ZnO nanocomposites prepared by casting from solution:

A) PMMA/ZnO nanocomposite (0.1% ZnO), B) sample with no ZnO.

The subject of the invention are nanoparticles of ZnO, with particle sizes between 20 and 300 nm and with organophilic surfaces, synthesized in various diols, as well as their transparent and nontransparent nanocomposites with methacrylic or acrylic polymers, prepared by the polymerization of methacrylic or acrylic monomers in bulk or by casting the polymer solutions.

The essential element of preparation of nanoparticles and nanowires of zinc (II) oxide - ZnO is the hydrolysis of the zinc compound comprising: Zn(CH ₃ COO) ₂ x2H ₂ O, Zn(C ₅ H ₇ O ₂ )XH ₂ O, ZnC ₂ O ₄ XH ₂ O, ZnSO ₄ x7H ₂ O, Zn(NO ₃ ) ₂ x6H ₂ O, Zn(PO ₄ ) ₂ , ZnCl ₂ , ZnBr ₂ in the presence of the

catalyst, para toluene sulfonic acid (p-TsOH), in various diols comprising: ethylene glycol - EG, 1,2 - propane diol - PD, 1,4 - butane diol - BD, di(ethylene glycol) - DEG and tetra(ethylene glycol) - TEG at temperatures between 100 and 300 ⁰ C. The calculated amount, in the concentration range from 0.005 to 5 mol, of the zinc compound, the calculated amount of deionized water (from 0.5 to 4 mol H ₂ O per mole of Zn), and the p-TsOH in the concentration range from 0.001 to 2 mol/L are mixed with the diol. The mixture is sonicated from 5 to 60 min. and heated from 30 to 90 min. at a temperature between 100 and 300 ⁰ C with constant mixing. After one hour the resulting suspension of ZnO is transferred to a beaker and it is left over night to sediment. If the suspension is stable, it is centrifuged. The product is sonicated and washed twice with ethanol and subsequently centrifuged. Washed ZnO is air-dried.

The essential element of the preparation procedure for PMMA or other methacrylic or acrylic polymers/ZnO nanocomposites is that unmodified ZnO, prepared by hydrolysis in diols, is used for their preparation according to procedures A, B and C described in the embodiments below. The results of all procedures are nanocomposites with predominantly homogeneous particle distribution in the PMMA matrix. In a beaker, a calculated quantity of MMA and/or other monomer from the group of methacrylic or acrylic monomers comprising: methyl, ethyl, isopropyl, n-propyl, n-butyl, n-pentyl, n-hexyl, phenyl, naphtyl, ethylhexyl, oleyl, palmityl, stearyl methacrylate or acrylate, an initiator (concentration from 0.01 to 1 %) and nano ZnO at concentrations from 0.0001 to 10 weight % are mixed. The mixture is sonicated from 5 to 60 min. and is subsequently either transferred directly into the glass mold where the polymerization is carried out until the completion of the reaction at temperatures between 35 and 90 °C from 1 to 24 hours or it is transferred into a glass reactor where partial polymerization of MMA is carried out at temperatures between 35 and 80 °C from 1 to 2 hours either without sonication or with constant sonication. 20 % initiator is added to the resulting prepolymer and the mixture is transferred into a glass mold. The mixture in the mold in sonicated again from 5 to 60 min. and the mold is subsequently placed into a water bath where the monomer is polymerized until completion at temperatures between 35 and 90 ⁰ C from 1 to 24 hours. After the polymerization is finished the mold is cooled and the formed nanocomposite is separated from the mold.

For the preparation of nanocomposites from a solution of methacrylic or acrylic polymer (Procedure D - embodiments), the solution of PMMA and/or other methacrylic or acrylic polymer from the group comprising: methyl, ethyl, isopropyl, n-propyl, n-butyl, n-pentyl, n- hexyl, phenyl, naphtyl, ethylhexyl, oleyl, palmityl, stearyl methacrylate or acrylate in organic solvent is mixed with nano ZnO prepared according to claim 2 at a concentration from 0.00001 to 10 weight % and the mixture is subsequently dispersed with a dispersion mixer between 200 and 20000 RPMs for a time period from 20 - 600 s with subsequent sonication of the mixture for 5 to 60 min., and the resulting mixture is then cast into the mold or it is sprayed onto a suitable substrate and it is finally dried.

The synthesized nanocomposites have outstanding UV absorption properties from 280 to 380 run and they can be, if properly prepared, transparent for visible light. PMMA nanocomposites with 0.1 % to 1.0 % of ZnO absorb from 95 to 99.5 % of incident UV light, while those with 0.01 % of ZnO absorb from 80 to 95 % of incident UV light. The synthesized nanocomposites also have enhanced thermal stability since the onset of thermal degradation is shifted towards higher temperatures by 30 - 40 ⁰ C if the material contains 1 % nano ZnO. By adding nano ZnO at a concentration of 0.1 % the impact resistance is increased by 5 to 10 %. Very low concentrations of ZnO significantly enhance the resistance to sunlight reducing δE from 10-1 1 for pure PMMA, to values between 1 and 6 for PMMA/ZnO nanocomposites.

Nanocomposites prepared by the polymerization of methacrylic and acrylic monomers in bulk can be used as UV and visible light stabilized transparent and nontransparent materials, including plexiglass for solar techniques, in glazing applications, for facade linings, for safety railings along highways, and in various applications with UV and visible light as well as thermal loads. Nanocomposites prepared by casting from solution of methacrylic or acrylic polymers can be used in UV and visible light stabilized transparent and nontransparent coatings where the material is exposed to high UV and visible light as well as thermal loads.

The invention covers the preparation of undefined and defined ID and 3D forms of ZnO, nanospheres and nanowires of variable degrees of crystallinity with an organophilic layer on the particle surface, synthesized by the polyol procedure in various diols with the addition of p- TsOH as the catalyst. The advantage of the addition of p-TsOH is in the enhanced repeatability of the synthesis, i.e. the average particle size and particle shape of ZnO nanoparticles. By

adding p-TsOH we obtain a repeatable synthesis of ZnO particles with defined particle size between 20 and 50 nm having an increased degree of crystallinity compared to ZnO synthesized in the absence of p-TsOH. With the addition of p-TsOH the synthesis of 20 - 50 nm ZnO particles can realized at a precursor concentration up to 5 mol/L and this allows a substantial savings in the volume of solvents and energy consumption. The advantages of using diols over monoalcohols are higher viscosity of medium, thus reducing particle agglomeration, and higher boiling points, allowing the synthesis of particles with a higher degree of crystallinity. Due to the organophilic surface layer, ZnO particles are homogeneously dispersed in the polymethacrylic and in the acrylic matrix, allowing the preparation of homogeneous PMMA/ZnO nanocomposites without additional surface modification. Surface modification substantially increases the price of nanoparticles, which is relatively high by itself and thus significantly reduces their potential applicability. Nano ZnO, synthesized by the polyol procedure, can be homogeneously dispersed in the PMMA matrix without surface modification at concentrations up to 10 %.

Nano ZnO particles in the form of nano wires with a length between 30 and 500 nm and with a diameter from 5 to 30 nm, synthesized by the polyol procedure with the addition of p-TsOH at high precursor concentrations (0.1 - 5 mol/L), are a novelty. Nanowires also have an organophilic surface layer that enables the preparation of homogeneous nanocomposites without additional surface modification.

Transparent nanocomposites of polymethacrylates or polyacrylates with ZnO with enhanced UV and visible light stability, such as visible and UV light resistant plexiglass and also nontransparent composites on the basis of methacrylic or acrylic, prepared by polymerization in bulk or by casting from polymethacrylate or acrylate solution according to procedures described in realization examples, are also a novelty. The organophilic layer on the particle surface is an effective dispersing agent. Synthesized nano ZnO is a very effective UV absorber, namely, the addition 0.05 % of ZnO quantitatively absorbs UV light from 290 to 370 nm, which is much better than the published data where it was reported that they achieved 60-70 % absorption of UV light by adding from 10 to 30 % of ZnO. The addition of nano ZnO, synthesized by the polyol procedure, in concentrations from 0.05 to 0.1%, substantially enhances the resistance to sunlight (sun test) because the color change (δE) is reduced from 10 - 11 for pure PMMA to 1 to 5. Besides this, the addition of 0.1 to 1 % nano ZnO increases the

thermal degradation onset temperature by 20 to 40 °C, which also increases the temperature range of application of these materials, and the addition of unmodified ZnO doesn't deteriorate but rather enhances the impact resistance of composites by 5 to 10%.

Embodiments

Realization examples do not constrain the patent, but they only help to explain it.

1) Synthesis of nano ZnO with the addition of deionized water

A calculated quantity (0.005 - 5 mol/L) of Zn(CH ₃ COO) ₂ XH ₂ O and a calculated quantity of deionized water (0.05 - 4 mol of H ₂ O per 1 mol of Zn) are mixed with di(ethylene glycol) - DEG or in tetra(ethylene glycol) - TEG. The mixture is sonicated from 5 to 60 min. and is heated during constant mixing for 30 to 90 min. at temperatures between 100 and 300 °C. After one hour, the suspension of ZnO is transferred into a beaker and it is left for 24 hours to sediment. If the suspension is stable it is centrifuged between 3000 and 12000 RPMs from 1 to 24 hours. The product is sonicated twice in ethanol (washing) and centrifuged at between 3000 and 12000 RPMs from 1 to 24 hours. The washed product is air-dried.

2) Synthesis of nano ZnO with the addition of deionized water and p-TsOH

A calculated quantity (0.005 - 5 mol/L) of Zn(CH ₃ COO) ₂ XH ₂ O and a calculated quantity of deionized water (0.05 - 4 mol of H ₂ O per 1 mol of Zn) as well as p-TsOH at a concentration between 0.001 and 2 mol/L are mixed with various diols (ethylene glycol - EG, 1,2 - propane diol - PD, 1,4-butane diol - BD, DEG and TEG). The mixture is sonicated from 5 to 60 min. and is heated during constant mixing at temperatures between 100 and 300 ⁰ C from 30 to 90 minutes. After one hour, the ZnO suspension is transferred into a beaker and is left for 24 hours to sediment. If the suspension is stable it is centrifuged between 3000 and 12000 RPMs from 1 to 24 hours. The product is sonicated twice in ethanol (washing) and it is centrifuged at RPM between 3000 and 12000 from 1 to 24 hours. The washed product is air-dried.

3) Preparation of methacrylic or acrylic nanocomposite with ZnO by bulk polymerization between two glass plates (Procedure A)

A calculated quantity of methyl methacrylate (MMA), initiator (concentration from 0.001 to 1%) AICN, and nano ZnO at a concentration between 0.0001 and 10 % are mixed in a beaker. The mixture is sonicated from 5 to 60 min and it is subsequently transferred into a glass plate mold. The mixture in the mold is som ^' cated sonicated again from 25 to 60 min. and the mold is subsequently placed into a temperature controlled water bath where the monomer is polymerized until completion of the reaction at temperatures between 35 and 90 ⁰ C for 20 hours. After the polymerization is finished, the mold is cooled down and the nanocomposite is separated from the mold.

4) Preparation of methacrylic or acrylic nanocomposite with ZnO by prepolymer synthesis and by subsequent bulk polymerization between two glass plates (Procedure B)

A calculated quantity of methyl methacrylate (MMA), initiator (concentration from 0.001 to 1%) AICN, and nano ZnO at a concentration between 0.0001 and 10 % are mixed in a beaker. The mixture is sonicated from 5 to 60 min and it is subsequently transferred into a glass reactor and partial polymerization of the monomer is carried out at temperatures between 35 and 80°C for 1 to 2 hours. Subsequently, an additional 20 % of initiator is added and the mixture is transferred into the glass plate mold. The mixture is sonicated again from 25 to 60 min. and the mold is subsequently placed into a temperature controlled water bath where the monomer is polymerized until completion of the reaction at temperatures between 35 and 90 ⁰ C from 1 to 24 hours. After the polymerization is finished, the mold is cooled down and the nanocomposite is separated from the mold.

5) Preparation of methacrylic or acrylic nanocomposite with ZnO by prepolymer synthesis accompanied by constant sonication and by subsequent bulk polymerization between two glass plates (Procedure C)

A calculated quantity of methyl methacrylate (MMA), initiator (concentration from 0.001 to 1%) AICN, and nano ZnO at a concentration between 0.0001 and 10 % are mixed in a beaker. The mixture is sonicated from 5 to 60 min and it is subsequently transferred into a glass reactor and partial polymerization of the monomer is carried out at temperatures between 35 and 80°C for 1 to 2 hours accompanied by constant sonication. Subsequently, an additional 20% of the initiator is added and the mixture is transferred into a glass plate mold. The mixture is sonicated again from 25 to 60 min. and the mold is subsequently placed into a temperature

controlled water bath where the monomer is polymerized till completion of the reaction at temperatures between 35 and 90 ⁰ C from 1 to 24 hours. After the polymerization is finished, the mold is cooled down and the nanocomposite is separated from the mold.

6) Preparation of methacrylic or acrylic nanocomposite with ZnO by casting from the solution (Procedure D)

Nano ZnO prepared according to the claim 2 is added to the PMMA solution at a concentration between 0.0001 and 10% and the mixture is homogenized by a dispersion mixer between 200 and 20000 RPMs for 20 to 360 seconds. The mixture is sonicated for 5 to 60 min. and is subsequently cast into a petri dish or is sprayed onto a suitable substrate and is then dried.

Results of testing

Synthesis of nano ZnO

SEM micrograph (Fig. 1) shows nanoparticles of ZnO with an average particle size of 100 run, synthesized by the polyol procedure in DEG with the addition of 0.05 to 4 mol of deionized water per mol of Zn. Particles have an irregular spherical shape, narrow particle size distribution and are weakly agglomerated. SEM micrograph (Fig. 2) shows nanoparticles of ZnO with average particle size between 300 and 400 nm, synthesized in TEG. XRD diffractograms of particles show typical ZnO diffraction maxima at 2θ values of: 31,8; 34.5; 36,2; 47,6; 56.6; 62,9; 66,4; 67,9; 69,1; 72,6; 76,9. Relatively broad diffraction maxima indicate rather small crystallite size. IR spectra of both samples show a well-expressed characteristic absorption band of ZnO in the wave number range from 420 and 480 cm ^'1 (Fig. 3). Relatively strong absorption bands around 1000 CπL ¹ and in the wave number range between from 1300 to 1650 cm ^"1 indicate that samples contain a substantial quantity of organic components — the remains of solvents and/or their degradation products.

Nanoparticles of ZnO synthesized in BD, TEG, DEG, EG and in PD with the addition of deionized water and p-TsOH, which acts as a catalyst, are shown on Fig. 4. Particles are mostly crystallites with sizes between 20 to 60 nm and they are more agglomerated than those synthesized without p-TsOF (Fig. 1). The TEM micrograph in Fig. 4c shows nanowires of ZnO

with lengths between 40 and 150 ran and width between 10 and 39 nm, synthesized in DEG. The degree of agglomeration in nanowires is even more expressed than in other samples, most probably due to higher contact surfaces between particles. The widths of diffraction maxima in XRD diffractograms of particles synthesized in the presence of p-TsOH are very narrow indicating the high degree of crystallinity of synthesized ZnO particles. IR spectra of particles show a well-expressed characteristic absorption band of ZnO in the wave number range between 420 and 480 cm ^"1 , while the absorption bands of organic compounds are much less intense than in samples synthesized without p-TsOH.

Preparation of nanocomposites with polymerization in bulk (Procedure A)

TEM micrographs in Fig. 7 show the distribution of ZnO particles, synthesized in DEG without p-TsOH, in the PMMA matrix of PMMA/ZnO nanocomposite. Figure 7a shows, that ZnO is homogeneously distributed in the polymer matrix but it is partially agglomerated (Fig. 7b). Fig. 8 shows UV-VIS spectra of PMMA/ZnO nanocomposites with various concentrations of nano ZnO. The addition of 0.1 or 1 % of nano ZnO in PMMA absorbs more than 98 % of the incident UV light, while the absorption in nanocomposites with ZnO concentrations of 0.01 and 0.001% is still above 80% of incident UV light. Absorption of visible light is also high, meaning that these materials are only partially transparent, i.e. translucent. DTG curves of PMMA/ZnO nanocomposites with various concentrations of nano ZnO show that the addition of 0.1% of nano ZnO increases the thermal degradation onset temperature by 20 ⁰ C, while the addition of 1 % of ZnO increases it by 35 ⁰ C (Fig. 9). Such materials are potentially useful as UV stabilized plexiglass with enhanced durability.

TEM micrographs in Figures 1 Oa and 1 Ob show the distribution of ZnO nanoparticles in the matrix of the PMMA/ZnO nanocomposite synthesized in TEG. Particles of nano ZnO are homogeneously distributed in the PMMA matrix and agglomeration is also minimal (Figure 10 b). Adsorbed molecules on the surface of ZnO particles enable their homogeneous dispersion in PMMA despite high particle dimensions.

Nanocomposites PMMA/ZnO - ZnO synthesized with p-TsOH (Procedure A)

TEM micrographs in Figure 11 show the distribution of ZnO nanoparticles, synthesized in various diols in the presence of p-TsOH. Particles of ZnO, synthesized in the presence of p- TsOH (Figure 1 Ia), are to a small extent more agglomerated than those synthesized without it, (Fig 7 and 10) although they are nevertheless homogenously distributed in the PMMA matrix.

UV absorption is very high in the UV region between 280 and 380 run, because ZnO in concentration between 0.1 and 1 % absorbs more than 98 % of the incident UV light and even at a ZnO concentration of 0.01 % absorption is still between 70 and 90 % of the incident UV light (Figure 12). Such a nanocomposite has a potential application as UV stabilized plexiglass with enhanced thermal stability.

Nano ZnO, synthesized in the presence of p-TsOH, thermally stabilizes the PMMA matrix. The stabilizing effect is most expressed at concentrations of 0.1 and 1 % shifting the onset temperature of thermal degradation towards higher temperatures by tens of degrees centigrade (Figure 13). PMMA with the addition of 0.1% of ZnO or higher has a potential application as PMMA material with enhanced thermal stability.

Preparation of PMMA/ZnO nanocomposites by synthesis via prepolymers (Procedure B)

Preparation of nanocomposites PMMA/ZnO in such a way that MMA is first partially polymerized, i.e. that a prepolymer is prepared, enables the preparation of PMMA/ZnO nanocomposites with higher transparency for visible light (Figure 14). Figure 15 shows the UV - VIS spectrum of PMMA/ZnO nanocomposites prepared by direct polymerization of MMA (A) and by polymerization via prepolymer (B). We can see that the nanocomposite, prepared via the prepolymer is much more transparent to visible light, while the absorption in the UV region (between 280 and 360 nm) is in both cases greater than 98% of the incident UV light (Figure 15). The addition of nano ZnO enhances the impact resistance of these materials by 3 to 5 % at ZnO concentration of 0.05 % and by 8 to 10 % at a ZnO concentration of 0.1%.

Sunlight durability (Sun test) was measured for nanocomposites prepared by procedure B, using nano ZnO synthesized in PD, EG and DEG. Results show significant enhancement of

sunlight durability independent of the ZnO sample and its concentration. This indicates a high potential of PMMA/ZnO nanocomposites for applications with high sunlight exposures, such as facade plates or linings, noise reducing protective highway fences, thermal solar systems, and for acrylic metal and wood coatings, etc.

Table 1 : Results of sunlight durability measurements for PMMA/ZnO nanocomposites - ZnO synthesized in various diols and at various nano ZnO concentrations

Diol ZnO concentration (%) δE ^a

Reference sample - PMMA O 10,6 - 10,8

PD 0,05 1,0 - 1,3

PD 0,1 3,1 - 4,6

EG 0,05 4,1 - 4,3

EG 0,1 1,7 - 2,1

DEG 0,05 1,8 - 2,4

DEG 0,1 4,6 - 6,1 aδE is the color change measured by the colorimeter relative to the unexposed sample

Preparation of PMMA/ZnO nanocomposites by synthesis via prepolymers (Procedure C)

By sonicating the reaction mixture throughout the complete synthesis of the prepolymer (Procedure C), the optical properties of the nanocomposite become close to those of commercial UV stabilized plexiglass (Fig. 16).

Preparation of PMMA/ZnO nanocomposites by casting from solution (Procedure D)

Homogeneous nanocomposites can also be prepared from a solution of PMMA in ethyl methyl ketone (Figure 17). The nanocomposites prepared according to this procedure have UV absorption from 50 to 80 % in the UV region from 290 to 360 nm (Figure 18). Because of this they can be used as coatings in applications with high UV and visible light exposure.