Introduction

Silicone rubber, known as polysiloxane, is one of the most common elastomer polymers. It contains silicon, carbon, hydrogen, and oxygen atoms, where the siloxane functional group (Si–O–Si) is present in the elastomer backbone [1,2,3]. Different types of silicone rubber, e.g., polydimethyl, polyvinylacetate, polyvinylacetate-co-methyl methacrylate, polyvinylmethyl, polydimethyl-vinylmethyl, polymethyl-vinyl-phenol, and other co-elastomers, are used commercially [4,5,6]. Versatile properties, such as flexibility, permeability, elasticity, biocompatibility, corrosion resistance, ease of manufacturing and shaping, self-plasticizing effect, translucent, odorless, tasteless, etc., enrich the application of silicone rubber in coating, lubricants, automobile, building, pharmaceutical, electronics insulators, aerospace, fire-retardancy, and optical instrument [7,8,9,10,11,12,13]. Commercial silicone rubbers may contain additional side groups attached to silicon atom, which can promote the process of crosslinking. The crosslinking can be performed via vulcanization and catalyzation curing. The reaction is usually performed by platinum complex, peroxide, and condensation. A condensation reaction is occurred through one-part system (room-temperature vulcanizing) where a hydrolysis is performed by crosslinker, such as silane, alkoxy, and ester, at room temperature to form hydroxyl or silanol groups, which are condensed later. Also, the two-part system condensation can take place by mixing the condensation catalyst and crosslinker with the silicone rubber base [14,15,16,17].

Many additives are emblended in silicone rubber to reduce its cost and to achieve the desired characteristics, regarding physical and mechanical properties. A nanocomposite based on epoxy/silane-modified silica nanoparticles was used to support silicone rubber with high strength and strong adhesion [18]. Usage of SiO2 nanospherical particles in silicon rubber microsphere matrix with 30% concentration was stated to enhance the surface hydrophobicity [19]. The interfacial thermal resistance and optical properties were studied after loading the rubber base with Al2O3 with modification with polycatechol polyamine and electroless plating of silver particles [20]. Another silicon rubber matrix was filled by poly(2-hydroxyethylmethacrylate)-methacrylic acid as co-polymer and polymethacrylic acid as hydrogel material. It was found that the permeation rates to water-soluble organic compounds and drugs are high while the mechanical properties are fair [21]. The solution casting technique was processed to silicon rubber specimens incorporated with carbon nanotubes, titanium dioxide, and their hybrid via room-temperature vulcanization process; the nanomaterials enhanced the tensile strength and compressive modulus. For the potential application in piezoelectric actuation, the actuation displacement was also improved with increasing input voltage for the prepared nanocomposite [22]. The influence of graphene and graphene-metallic oxides hybrid on the properties of silicone rubber and silicone resin was studied in detail. In particular, the composites based on graphene and silicone rubber or silicone resin provided significant mechanical, electrical, and thermal properties compared with the blank polymers. The ultimate investigations are attributed to the combination of functionalized nanocarbon materials. The mentioned composites could be applied to wearable electronics, sensors, and microwave absorption materials, in addition to antifouling, antibacterial, and anticorrosion coatings. Another type of silicone rubber was loaded with few-layer graphene, iron oxide, and TiO2 nanofillers. The results indicated the successful formation of the final nanocomposite, where the mechanical properties were improved by all fillers. Furthermore, it was found that the actuation displacement depends on the type of nanofiller and the applied voltage [23, 24].

Other silicone rubber compounds were tested with different types of synthetic fillers, e.g., aramid fiber, glass fiber, carbon black, and graphene. Different types of silicone rubbers were used and can be categorized into mercapto hyperbranched polysiloxane, polydimethylsiloxane, polyethylene glycol/urethane-interpenetrated polysilsesquioxane, and platinum-catalyzed silicone matrices. As investigated, the interfacial adhesion at the rubber-aramid surface was promoted by the in-situ growing of hyperbranched polysiloxane and aramid fiber throughout the polydopamine precursor and the condensation between silane coupling agents [25]. Another study characterized the flexibility of glass fiber-polydimethylsiloxane composites via newly developed testing device in consideration of fiber direction, with modification of the step-cycle testing under viscoelastic tensile loading [26]. An interpenetrated polymer network was designed based on rigid polysilsesquioxane/styrene and flexible polyhexamethylene diisocyanate/polyethylene glycol to get maximum flexural strength, with adding fiber component to promote the fire-retardancy and the dielectric properties [27]. A new silicone rubber-carbon black-graphene-conductive composite network was fabricated for large strain sensors. The results indicated that the electromechanical response of network has highly reversible and durable behavior, with strain up to 300% [28].

Although most of the related works achieved improved major characteristics, the included synthetic or industrial fillers can be harmful to the environment. Hence, the use of natural materials, safe nano-oxides, and waste fillers, alternative to the synthetic types, is aimed in elastomer-based materials and other modern composites. Properties like ecofriendly, low density, low cost, facile preparation, low carbon footprint, and environmental nature encourage to develop such composite types in different sectors such as thermoplastic and thermosetting composites, construction, building blocks, and environmental-friendly polymers [29,30,31,32]. The surface, mechanical, and physical characteristics of silicone rubber-Arenga pinnata sugar palm biocomposites were studied. It was found that the sugar palm modified the values of uniaxial tensile and modulus, due to the dispersed interface. The density, swelling, and water absorption were increased with the higher concentrations as well [33]. Another natural fiber, flax type, was modified with vinyl groups for effective filling to silicone rubber elastomer with high fiber-matrix adhesion [34]. High-performance continuous thermal-conductive composite based on silicon rubber and high-load branched Al2O3 was performed. The thermal decomposition, tensile, and modulus were improved simultaneously [35].

The literature focusing on silicone compounds/natural fiber/chromium oxide composites was reported. For example, the chromium oxide filler succeeded in improving the thermal stability of cold-cured silicone rubber compositions that support high-performance operational characteristics [36]. The sealing performance was studied for a composite gasket made of silicone rubber and ramie natural fibers applied in bolted joint connection. The proposed composite presented better sealing performance, compared with blank silicone rubber, up to five times [37]. In other trial, the addition of bamboo cellulosic filler to the silicone rubber matrix, in terms of compressive properties in different immersion medium, was investigated. The results indicated that the higher concentration of bamboo has improved the compression strength and stiffness [38].

The previous work studied the properties obtained after using one filler type without focusing on the effect of exposure to accelerated conditions. In this research, the dual effect of natural and safe fillers on silicone rubber is studied. The related physical and mechanical properties are investigated. In particular, improved environmental-friendly silicone rubber-waste natural fiber/chromium oxide nanocomposites are prepared and characterized. Also, the investigation against accelerating conditions, which is missed in related work, was performed. The proposed composite can serve as partially environmental nature, in addition to the expected improvement in the properties of silicone rubber for repair materials, electronics, hidden lamination, and indoor rubber-like materials applications.

Materials and methods

Materials

The used matrix is Ruisil RJL-101-30 T silicone rubber (S), manufactured by Hangzhou Ruijiang Co., with a dynamic viscosity of 27,500 mPa.s and 3% mixing ratio of hardener. Natural fiber waste, mainly corncob, was used as natural filler and obtained from local source as agricultural residue. Sodium hydroxide and sulforic acid (Merck KGaA, Germany) were used for treatment of fiber. Chromium sulfate (Cr2(SO4)3) and ammonia solution (25% NH4OH), Sigma-Aldrich Shanghai Trading Co., were used for synthesis of chromium oxide nanoparticles.

Treatment of natural fiber

Firstly, the used waste of natural fiber was dried at 70 °C for 3 h and then sieved for 10 min using the 200 mesh size using an electrical sieving machine. The treatment process was performed as follows: With the help of vigorous stirring, the taken amount of natural fiber waste was distributed in a solution of 5% NaOH, and then few drops of sulfuric acid were added to the solution. After 20 min, the obtained paste was washed several times with distilled water and dried for 3 h at 70 °C, getting the treated microfiber filler (Fiber).

Synthesis of chromium oxide nanoparticles

In a system equipped with 1000-ml round flask and mechanical stirring, 500 ml of 0.1 mol Cr2(SO4)3 solution was prepared, and then about 150 ml of ammonia solution was added slowly under the same mechanical stirring until reaching the pH 10. The obtained precipitate was filtered, washed several times with distilled water, and dried at 70 °C for 24 h giving 60% yield. The precipitate was finally calcined at 600 °C for 6 h. The obtained green powder is chromium oxide (Cr2O3) nanoparticles, abbreviated as (Cr).

Preparation of silicon rubber nanocomposites

The proposed nanocomposites were prepared by filling the silicon rubber matrix with the treated natural fiber and chromium oxide nanoparticles fillers. The filling percentages are 0.25 wt.%, 0.50 wt.%, 0.75 wt.%, and 1 wt.%. Fiber and Cr fillers have been mixed individually with the base of silicon rubber through vigorous mechanical mixing for 20 min, followed by ultrasonic mixing for 5 min in an ice-bath. The latter process is necessary for better distribution of nanofillers into matrix where the well-distributed filler supports the final composite with the expected properties. After addition of the hardener, the obtained composites were charged in Teflon molds. Finally, the prepared silicon rubber composites were left overnight at room temperature for the crosslinking. After some performed characterizations which are mentioned in Section of Results and Discussion, an overall concentration based on 1 wt.% hybrid fillers was prepared using the same technique. This hybrid is taken as optimized formula and named as (Mix) nanocomposite.

Characterizations

PANalytical-X’Pert-PRO was used to detect the X-ray diffraction of prepared samples using 1.54-Å wavelength, 40-kV voltage, 40-mA current, and 10–80° 2θ range with the rate of 1°/min. Nicolet IS-10 FTIR spectrophotometer-Thermo Fisher Scientific was used for detecting the spectra of Fourier transform-infrared (FTIR). The surface morphology was examined by transmission electron microscopy (TEM) using high-resolution JEOL-2100F TEM at 200 kV. Specimens of cured nanocomposites were subjected to weathering conditions using the Haida UV-Accelerated Aging Chamber following ASTM G154. Samples with 22 mm length, 10 mm width, and 1.5 mm thickness were aged for 200 h at 254-nm wavelength, 95% humidity, and 60 °C. The analysis was performed to the prepared samples for detecting their stability. The dielectric properties were examined by the Novocontrol high-resolution ALPHA analyzer (Montabaur) at room temperature. Two parallel gold-coated brass electrodes were used in a circular form for measuring. The relative complex permittivity (ε*) of the specimen is identified by Eq. 1, where (ε′, real part) is the dielectric constant and (ε″, imaginary part) is the dielectric loss.

$$\varepsilon * \, = \, \varepsilon^{\prime } \, {-} \, i\varepsilon^{\prime \prime }$$
(1)

Dynamic mechanical analysis (DMA, Triton Instruments) was used to investigate the modulus of prepared composites. Three specimens of each composite of dimensions of 22 mm length, 10 mm width, and 1.5 mm thickness were tested, and then the standard deviation was calculated. The DMA operated in the tension mode at 1-Hz frequency and room temperature (25 °C) for a fixed time for determination of results. The contact angle of prepared composites was identified by One-Attension tensiometer-Biolin Scientific. The sessile drop method was performed by applying drops of distilled water over the tested composite surface and measuring the contact angle obtained at the “solid–liquid–gas” interface. The contact angles were evaluated at two positions per specimen using the related software package where the measurements were taken every 0.2 s.

Results and discussion

Characterization of fillers

For chromium oxide, its formation is confirmed by the XRD analysis as shown in Fig. 1a. The diffraction peaks at 2θ of 24.49°, 33.60°, 36.21°, 41.49°, 50.23°, 54.86°, 58.40°, 63.48°, 65.13°, 72.91°, and 76.83° correspond the chromium oxide nanoparticles as rhombohedral phase (JCPDS no. 38–1479) [39, 40]. The morphology was evaluated by the TEM micrograph in Fig. 1b. It was successfully obtained as separated nanoparticles with mean particle size of 40 nm.

Fig. 1
figure 1

XRD (a) and TEM (b) of chromium oxide nanoparticles

Full size image

For natural fiber, the crystalline lattice structure and morphology are investigated as represented in Fig. 2. Figure 2a shows the XRD patterns characteristic to the cellulose phase: the strong peak at 2θ 22° and the other two small peaks near 2θ 16° and 35°. These peaks are attributed to the obtained cellulosic material with more ordered structure due to the performed treatment [41]. This reveals the disposal of non-cellulosic materials from natural fiber without destruction of cellulosic units. The micrograph in Fig. 2b shows the needles shape of the treated natural fiber used, like these microfibers indicate the obtained main cellulose.

Fig. 2
figure 2

XRD (a) and SEM (b) of fiber

Full size image

Contact angle of composites

Increasing the hydrophobicity of polymers is important to improve the physical properties, due to the accepted water and dust repellence [42, 43]. The hydrophobic surface is known to have a contact angle greater than 90° [44, 45]. The neat silicon rubber and its composites are considered to be hydrophobic materials, in case of filling with hydrophobic fillers. As illustrated in Table 1, because of the hydrophilic nature of natural fiber, their related composites exhibit lower contact angles compared with the blank S. The 1% Fiber composite, as the maximum fiber concentration, has a more hydrophilic surface due to the least contact angle (82.8°). However, the reducing in contact angle is not that large (maximum 8.3%), reflecting the good physical properties. For chromium oxide nanoparticles-filled rubber in Table 2, the contact angle has increased by increasing the concentration of chromium oxide nanoparticles. All nanocomposites have more hydrophobic property. Respectively, the 0.25% Cr, 0.5% Cr, 0.75% Cr, and 1% Cr recorded 93.2°, 105.1°, 107.4°, and 108.2°, compared with 90.3° for blank S. The increased surface area of Cr nanofillers which make them rougher [46] may increase the hydrophobicity of final nanocomposite due to the nature of nanoparticles. Consequently, the composite surface became more porous and rougher. This lets more air pockets to be trapped between the nanocomposite surface and the water droplet, which decreases the contact area between surface and water, and increases contact angle. For a better understanding of this phenomenon, examples of surface tension are given to ensure the given data. For the highest concentration, addition of Cr nanoparticles decreased the surface tension of blank S from 24 to 21 mN/m, which increases the hydrophobicity of silicon rubber. However, in case of Fiber, the value increased to 26 mN/m. It can be concluded that the fillers used have altered the hydrophobicity of the silicone matrix. The Cr nanoparticles supported the nanocomposite surface with hydrophobicity, while the Fiber increased hydrophilicity due to the differentiation of nature.

Table 1 Contact angle of silicone rubber composites loaded with different concentrations of fiber
Full size table
Table 2 Contact angle of silicone rubber composites loaded with different concentrations of chromium oxide nanoparticles
Full size table

Dielectric properties of composites

Figure 3a and b collects the dielectric constant and dielectric loss of Si-rubber loaded with different concentrations of Cr and natural fiber and the Mix nanocomposite, respectively. The dielectric constant of composites loaded with natural fiber decreases as the loading of fiber rises, while composites loaded with chromium oxide exhibit an increase in the dielectric constant. The blank S sample demonstrates the relativity-low dielectric constant value as a result of the lack of permanent dipoles. The observed change in the dielectric constant and dielectric loss in the fiber-based composites can be attributed to the reduction in orientation polarization. This reduction is a result of the increased hydrophilicity of alkali-treated fibers. The application of treatment on fibers results in the disruption of hydrogen bonds, leading to the increased reactivity of the fibers. The application of this treatment induces the dissolution and leaching of fatty acids and lignin, which serve as the cementing or binding agents. Consequently, this process enhances the interlocking between fiber and the rubber matrix, leading to the production of composites with enhanced strength; furthermore, the hydrophilic properties of the fibers are changed as a result of the treatment, leading to a subsequent decrease in orientation polarization [47, 48]. As a result, fibrous composites treated with alkali demonstrate a little decrease in dielectric constant values in comparison with blank silicone rubber. Conversely, the dielectric constants of blank Si-rubber samples, with a dielectric constant of 4.68, changed to 4.09, 4.96, 5.44, 5.99, and 6.96 for 0.25% Cr, 0.5% Cr, 0.75% Cr, 1% Cr, and Mix (Cr and Fiber) nanocomposite silicone rubber, respectively. The increased dielectric constant observed in composites containing chromium oxide, as compared to blank Si-rubber and composites including natural fiber, can be related to the phenomenon of interfacial polarization (IP) or Maxwell–Wagner (M-W) polarization. The emergence of these phenomena can be attributed to the existence of electrically diverse materials [49]. Interfacial polarization arises within these systems as a result of the dispersion of conductive filler inside the insulating polymer matrix. The presence of permanent dipoles generated by chromium at the interfaces of the polymer and filler materials leads to an augmentation of polarization, resulting in an enhancement of the dielectric constant. The presence of these dipoles, which are comparatively larger in size than orientation, ionic, and electronic dipoles, plays a role in the creation of an interface between inorganic and organic components. This contact leads to an augmentation of polarization and an elevation of the dielectric constant [50].

Fig. 3
figure 3

Dielectric constant (a) and dielectric loss (b) of Si-rubber loaded with different concentrations of Cr and natural fiber

Full size image

Mechanical properties and weathering effect

Figure 4a and b collects the storage modulus and loss modulus of Si-rubber loaded with different concentrations of Cr and natural fiber and Mix nanocomposite, respectively, before weathering. In Fig. 4a for Si-fiber composites, it is clear that the 0.25% and 0.5% concentrations achieved higher modulus (0.97 MPa and 0.99 MPa), compared with 0.77 MPa for blank. The higher concentrations have no more obvious effect on modulus, due to the effective filling around these concentrations. The highest value is 1.1 MPa for 1% Si-fiber composite. However, with Si-Cr nanocomposites, the first three concentrations, i.e., 0.25%, 0.5%, and 0.75%, affect slightly on the modulus of rubber matrix. Only the 1% Si-Cr nanocomposite has improved the modulus by more than 65%, compared with Si-rubber blank. As given in Sect. “Contact angle of composites,” the Si-fiber suffers from less hydrophobicity with 82.8° contact angle, compared with the 90.3° for blank Si-rubber, due to the hydrophilic nature of natural fiber [51]. On the other hand, the Si-Cr specimen is the most improved one among all composites because of its higher values of modulus and thermal stability. Moreover, it presents more hydrophobic character after increasing the contact angle from 90.3° to 108.2°. An optimized nanocomposite, based on silicon rubber matrix, 1% microfiber, and 1% chromium oxide nanoparticles (Mix), is hybridized to maximize the improved mechanical, thermal, and hydrophobic properties, in addition to the environmental-friendly effect. The Mix nanocomposite achieved the highest modulus (1.43 MPa) over all composites; it has the improved mechanical properties in addition to the expected improved hydrophobic behavior. For the values of loss modulus presented in Fig. 4b, the improved loss modulus is obtained by 1% of each Si-Cr and Si-fiber composites. Although there is a large difference between Si-Cr and Si-fiber composites, the Mix nanocomposite has an overall loss modulus of 0.044 MPa, compared with 0.021 for blank silicon rubber. It is noticed that Mix has a dual effect of both Cr and fiber fillers. The artificial weathering was performed to investigate the stability of composites. The weathering factors including UV radiation, aging time, wavelength, humidity, and temperature were fixed during exposure, and then the mechanical performance was checked before and after this weathering for clear comparison. The tested modulus for Si-Cr and Si-fiber composites is given, respectively, in Fig. 5a and b. The two groups of composites show similar behavior regarding the lower modulus after weathering due to the exposure to radiation in the humid, warm environment. The change in modulus of composites was reported to be attributed to the factors of artificial weathering that alter the surface properties [52]. However, the proposed Mix nanocomposite presents higher modulus at normal conditions, compared with all composites, due to the dual effect of the two fillers. With weathering conditions, the Mix nanocomposite recorded fewer values, however still higher than blank S. The Mix recorded modulus of 0.64 MPa after weathering, compared with the 0.45 MPa for the blank. The reason for the decrease in modulus is the deterioration of S matrix caused by weathering; the given data show that the single fillers failed to protect the matrix. However, the Mix concentration shows some enhancement; therefore, it was proposed as the optimized concentration. Although the weathering for 200 h is not that long time, this time was able to decrease the mechanical characteristics of single composites (Cr- and Fiber-based composites), by the gathered effect of factors of radiation, humidity, and high temperature. However, the Mix composite was stable against all of these factors in normal conditions. Thus, this kind of composites is more suitable for indoor applications.

Fig. 4
figure 4

Storage modulus (a) and loss modulus (b) of Si-rubber loaded with different concentrations of Cr and natural fiber, before weathering

Full size image
Fig. 5
figure 5

Effect of weathering conditions on modulus of Si-rubber loaded with different concentrations of Cr (a) and natural fiber (b)

Full size image

Optimization effect

The Mix nanocomposite was proposed as optimization formula based on the curried dielectric and mechanical testing. The improved dielectric properties of Mix composite and the enhanced storage and loss moduli after adding 1 wt.% of Cr and Fiber put the Mix nanocomposite as optimized concentration. In this section, IR, contact angle, and morphological characterizations were carried out to ensure the stability of the proposed Mix nanocomposite. Figure 6 indicates the infrared spectra of the optimized Mix nanocomposite and blank S. The observed characteristic peaks of silicone rubber are present in all samples as follows: The absorption peak at 2960 cm−1 is for stretching vibration of methyl groups. The peak at 1260 cm−1 corresponds to the Si-CH3 bond, the peaks at the range of 1000–1100 cm−1 are attributed to the existence of Si–O-Si, and the strong absorption peak near 790 cm−1 results from the stretching vibration of Si-(CH3)2 [53]. The Mix nanocomposite specimen contains similar characteristic peaks, with lower intensity. This confirms the reaction occurred between all components, keeping the silicone rubber backbone covering all fillers. The overall composite has improved characteristics as well, as discussed previously.

Fig. 6
figure 6

Infrared spectra for the optimized Mix nanocomposite and blank S

Full size image

Furthermore, Table 3 illustrates the contact angle of the optimized formula before and after weathering aging. In comparison with blank S, the Mix nanocomposite is still hydrophobic where the contact angle is 108.8°. The good dispersion of Cr in silicon rubber basically supports the composite with hydrophobicity. Although being less hydrophobic, the used fiber fillers do not reduce the overall hydrophobicity of nanocomposite. This may be because of good attachment and wetting of fibers with the segments of silicon rubber matrix. After weathering condition occurred, the contact angle of Mix nanocomposite recorded 108.1°. So after weathering, the gained hydrophobicity is almost similar to that of unconditioned specimen due to its stability. As a result, both of the used fillers have increased the overall surface character, compared with blank polymer.

Table 3 Contact angle of optimized nanocomposite before and after weathering aging
Full size table

Additionally, the morphology of the Mix nanocomposite was investigated. The morphological captures in Fig. 7a indicate two clear distinct phases of natural fiber and chromium oxide, over the silicone rubber matrix. The matrix attaches with both fillers smoothly; there are no gaps or voids at polymer/fiber/chromium oxide interfaces. Such conditions allow more compatible mixing and distribution among all phases, which lead to improved composite. After weathering conditions, the photographs in Fig. 7b display morphological features similar to that of unconditioned specimen in Fig. 7a. The polymer surface is still stable even after weathering without failure; only the microfiber has shorter length. It was reported that many kinds of natural fibers are unstable against weathering due do some degradation in the cellulosic skeleton [54]. But in general, the overall composite is uniform and shows stable profile with no etching.

Fig. 7
figure 7

Morphology of the optimized Mix nanocomposite before (a) and after (b) subjecting to weathering aging

Full size image

In summary, the given data reveal the interaction of chromium oxide nanoparticles and natural fiber with silicone rubber matrix; the overall properties of the optimized nanocomposite have been amended.

Conclusion

  • New environmentally friendly polymer nanocomposites, based on silicone rubber matrix loaded with waste fiber and chromium oxide nanoparticles, were successfully prepared.

  • The microstructural characterizations confirmed the obtaining of the crystalline and separated chromium oxide nanoparticles and the natural microfiber fillers, in addition to the formation of overall composite that keeps silicone rubber backbone covering all fillers.

  • The prepared waste fiber-silicone rubber composites have more hydrophilic surfaces, but with a limited value; however, all chromium oxide nanocomposites have more hydrophobic properties due to the increased surface area, which reflects the improved surface properties.

  • The dielectric properties showed a slight decrease with fiber-based composites and a good increase with chromium oxide-based composites. However, the optimized composite has a sharp improvement in its dielectric properties.

  • The optimized concentration, based on 1 wt.% filler hybrid, achieved the highest modulus, dielectric constant, and hydrophobicity compared with blank silicone rubber and other composites. The morphologies show smooth and clear phases of fillers and matrix even after weathering conditions, with no gaps or etchings, which reflect the improved properties.

  • The recommended nanocomposite improved the physical, surface, and mechanical properties of silicone rubber due to the wetting of the matrix with all the distributed filling materials, resulting in a uniformly stable final composite. Such nanocomposite is recommended for laminations and indoor applications.