The design and fabrication of polymer/metal oxide nanocomposite films have gained considerable interest in recent years, owing to their novel optical, electrical, magnetic, and mechanical properties, as well as their widespread applications in the scientific, industrial, and medical fields [1, 2]. The consistent distribution of nanofillers across the matrix, their enlarged interfacial area, and their interfacial interaction with the matrix materials can change these properties of the polymer nanocomposite films [3]. The homogeneous dispersion of nanofillers in the polymer matrix enhances loading efficiency and lowers local stress [4]. Furthermore, the particle size, shape, and concentration of nanofillers influence the properties of matrix material [5]. The concentration of nanofillers can have a significant impact on the various properties of nanocomposite films, including optical and mechanical properties. At higher nanofiller concentrations, the agglomeration/aggregation of nanofillers in the polymer matrix alters mechanical properties like low hardness, tensile modulus, and yield strength [6]. The addition of nanofillers generates new energy states in the matrix band gap, leading to an intriguing optical properties [7].
Polymers, namely polyaniline (PANI), polyvinylchloride (PVC), polythiophene (PTh), polycarbazole (PCz) and poly(methyl methacrylate) (PMMA) are being studied extensively for a wide range of applications including fuel cells, rechargeable batteries, corrosion resistance, optoelectronic devices, drug delivery, and medical applications [8–11]. PMMA is more popular than other organic polymers due to its superior properties such as, good electrical insulators, good chemical resistance, high optical transparency, good weather ability and thermal stability [12, 13]. It also has exceptional mechanical properties such as dimensional stability, impact resistance, flexural strength, and fracture toughness, making it better material for denture-based applications [14, 15]. In denture based application, the optical and mechanical properties play an important role. The addition of nanofillers such as metal, metal oxide, and carbon nanomaterials to polymer matrices can alter the opto-mechanical properties [16]. The series of metal oxides like SnO2, TiO2, MnO2 and ZrO2 have been used as filler materials in the polymer matrices due to their superior opto-mechanical properties [17, 18]. Among the numerous metal oxides, ZrO2 is an unique choice due to its outstanding properties such as good ionic conductivity, high optical transparency, high facture toughness, good mechanical strength and wideband gap of > 5 eV[19, 20]. Because of these properties, ZrO2 is a suitable filler material for the PMMA matrix to improve its optical and mechanical properties. Therefore, the fabrication of PMMA/ZrO2 nanocomposite films using different fabrication techniques such as sol-gel[21], spin coating[22], spray pyrolysis[23],magnetron sputtering[24], solution casting[25] were reported. Solution casting technique has several advantages over the other methods mentioned above, including its simplicity, low cost, and low operating temperature.
Until now, numerous studies on the optical and mechanical properties of PMMA films with different types of nanofillers have been reported. They indicate the distinctive optical properties due to the formation of new states within the band gap of matrix material, as well as the enhancement/reduction of mechanical strength [26, 27]. Sengwa and Dhatarwal[28] used a solution casting technique with tetrahydrofuran as a solvent media to fabricate PMMA nanocomposite films with various nano-fillers (ZnO, SnO2 and TiO2). Because of the formation of certain localized states in the PMMA forbidden energy gap caused by the generation of structural defects, they exhibited a shift in the absorption edge towards a longer wavelength and a decrease in the value of the energy band gap as the concentration of nano-filler increased. Tekin et al [29] utilized a simple spin coating technique to fabricate PMMA/ZrO2 and PMMA/WOxZrO2 nano-comoposite films. They have observed the decrease in band gap of nanocomposite films as concentration of ZrO2 nanoparticles increased due to increased carrier-carrier interaction, band levels approach of one another. By dissolving methyl methacrylate in chloroform and benzyl peroxide as a catalyst, a new spin casting technique was used to fabricate ZnO/PMMA nanocomposite films reported by Singh et al. [30]. The presence of intrinsic vacancies, such as Zn ions and oxygen vacancies, has been observed to produce blue-green emission peaks at 434 and 500 nm. The photoluminescence peak of ZnO/PMMA nanocomposite films has not significantly shifted due to the near band edge emission caused by band edge transitions or exciton recombination. Bay et al. [31] have reported the fabrication of PMMA/silica nanocomposite films by spin coting technique and examined the effects of free surfaces and internal interfaces on the mechanical properties of PMMA/silica nanocomposite films. As the thickness of the films increased, they observed a decrease in the stress value of PMMA films. However, there was no discernible change in the elastic modulus of the films when the concentration of nanoparticles loading increased. Martínez et al [32] reported the mechanical and optical properties of PMMA-GPTMS-ZrO2 hybrid thin films were fabricated through a sol-gel route. They elaborated the improvement in hardness of the PMMA-GPTMS-ZrO2 hybrid films with ZrO2 content due to the strong chemical bond between PMMA and ZrO2 nanoparticles. The synthesis of PMMA-ZnO nanocomposites with different weight percent of ZnO nanoparticles (2–5%) is reported by Ahmad et al [33]. In their investigation, they observed the enhancement in absorption intensity of PMMA-ZnO nanocomposites with weight percent of ZnO nanoparticles and the better antifungal efficacy against various candida species, indicating that this material could be a smart choice for denture application. Very recently, Kumari et al [34] developed the denture based PMMA and PMMA-ZrO2 nanocomposites with different ZrO2 content (2% -10%) using heat cure technique. They observed reduction of band gap as ZrO2 content increases with the enhancement of mechanical properties for 5 wt % of ZrO2 in PMMA including the maximum compressive strength (76.6 MPa) and fracture toughness (6.58 MPa-m1/2). Based on these results, they came to the conclusion that the 5 wt % of ZrO2 nanoparticles loaded PMMA/ZrO2 nanocomposite is the better material for denture applications. A few studies on optical properties of PMMA/ZrO2 nanocomposite films have been reported in literature, however the variation in mechanical properties of PMMA/ZrO2 nanocomposite films with different concentration of ZrO2 nanofillers have not been thoroughly investigated. The novelty of the present work involves PMMA a thermoplastic polymer that exhibits low mechanical strength and brittle on impact. Furthermore, the reinforcement of ZrO2 nanofillers in PMMA matrix improves the mechanical rigidity and strength of the pure PMMA, rendering it a better alternative material for denture based applications. Therefore, in this work, we have fabricated PMMA/ZrO2 nanocomposite films using a solution casting method. The effect of varying concentrations of ZrO2 nanofiller on the structural, optical and mechanical properties of PMMA/ZrO2 nanocomposite films is investigated.