Mechanical and thermal properties of a nanocomposite made of a polymer matrix reinforced by a binary nanoparticle TiO2 - SiO2 produced by sol-gel method

doi:10.21203/rs.3.rs-2574529/v1

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Mechanical and thermal properties of a nanocomposite made of a polymer matrix reinforced by a binary nanoparticle TiO2 - SiO2 produced by sol-gel method

https://doi.org/10.21203/rs.3.rs-2574529/v1

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published 05 Apr, 2023

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This study investigated the effect of adding 5% wt of SiO₂-TiO₂nanoparticles to polyester-fiberglass on the structural, mechanical and thermal behaviours of the nanocomposite. For this purpose, scanning electron microscopy (SEM) and a Fourier transform infrared spectroscopy (FTIR) were used to examine the surface modification and morphology of the nanocomposites. After the heat treatment of this materialat different compositions, it was observed that its crystalline state was changed and a rutile structure appeared in the treated nanofillers. However, the presence of SiO2 seemed to prevent the complete conversion to this structure. Hence, this change in the microstate affected the mechanical and behavior of the nanocomposite. Indeed, theaddition of 5% wt divided in 75%SiO2-25%TiO2 to the nanocomposite increasedits Young’s modulus by 15.15% and its microhardness by 14%. Furthermore, in terms of thermal behaviour, the addition of 5% wt divided in 75%SiO2-25%TiO2 yieldeda thermal resistance of TG = 49.66 °C.

These results would imply the production of nanocomposite with a specific high resistance, a high modulus and a good fatigue resistance which would present a potential replacement for other materials in various industrial applications.

Nano-powders

TiO2-SiO2

Sol-Gel

Polymer-matrix

nanocomposites

VARTM process.

Organic matrix composites (OMC) have attracted a lot of interest as an alternative to conventional structural materials such as steel and wood. For instance, Varga et al. [1] reported potential that glass fiber–reinforced polymer (GFRP)wasan alternative material in automotive, marine, aircraft manufacturing, wind power plants, boats and ships. Similarly, fiber reinforced plastic (FRP) composites have been appreciated for their excellent mechanical and chemical properties, including high specific strength and modulus, good fatigue and corrosion resistance. In this context, Seshanandan et al. [2] showed that the stiffness and strength of these polymers were improved by adding stiffer and stronger fibres to the matrix composite. These materials presented more industrial advantages in terms of their balanced mechanical properties, lighter weight and lower costs Of more relevance to this work, Kumar et al.[3].Examined the effect of glass fibre hybridization on the mechanical properties of the best fibre-based hybrid polymer composites such as jute, hemp, kenaf and flax. These scholars concluded that fibreglass acted as a barrier against the unfavourable environment to prevented the degradation of natural fibres and increased the strength of the material [3]. Yet, the glass fiber itself as well as the unsaturated polymers needed to be get their mechanical and thermal properties enhanced.

Hence, researchers turned the nanofillers as a solution to improve the mechanical properties of these materials. Within this context, Nayak et al. [4] and Patel and Dhnola [5] recommended the addition of different nano-powders due to their enhancement of the mechanical properties of the polymer matrix. In addition, Bazrgari et al. [6] reported that a wide range of inorganic nanofillers such as 3D rigid spherical nanoparticles prepared through the sol-gel method had a positive effect on the mechanical properties of the composites. Vives and Meunier [7] reported that these nanoparticles proved to be more adequate due to the efficiency of the elaboration method. Nevertheless, as was rightly observed by Wetchakun et al. [8], nanoparticles sometimes presented shortcomings that reduced their mechanical properties. Indeed these scholars reported that when the dispersion of the nanoparticles in the polymer matrix was not homogeneous, the nanocomposites flexural strength, stiffness, toughness and strain at break were not improved. Goyat [9] confirmed this observation when they reported that TiO2 nonoparticles showed a tendency to agglomerate due to their large surface-to-volume ratio. In addition, this macroscopic reinforcement approach resulted in materials that were not isotropic with a weaker interface/interphase.

Similarly, Younis, Oleiwi and Mohammed.[10] who studied the mechanical properties of unsaturated polyester resin reinforced with 1%wt, 3%wt and 5%wt SiO2 to make glass fibres, revealed that only the SiO2 at 5%wt yielded satisfactory mechanical properties of the unsaturated polyester resin. This finding implied that other contents of nanocomposite failed to improve the mechanical properties of the pure polyster because of their faulty distribution in the matrix. Equally, Ahmadizadegan and Esmaielzadeh[11] produced PE/SiO2 hybrids, and reported that the Young's moduli (E) of the hybrid films increased with the increase of SiO2 content. Uddin and Sun [40] reported a 40%- increase in the Young’s modulus of glass/polypropylene composites when the SiO2 content was 15 wt. %. Bracho et al.[12] found that the effect of silica nanoparticles on the composite mechanical behavior depended on both particle size and surface modifications. In their study, the optimum particlesize that improved the mechanical properties was 20 nm.. Ahmad, Mamat& Ahmad. [41]andLandowski and Imielińska [13]found that the addition of 15 wt% SiO2 into epoxy resin increased the Young’s modulus of the composite because at this amount, the nanoparticles were homogenously dispersed in the epoxy resin. Luo et al. [42] and Zahrouni, Bendaoued&Salhi [14] reported that the incorporation of modified TiO2 nanoparticles into polymer matrix at 1.5 wt. %, the mechanical and thermal properties of polymer were improved remarkably.

As can be seen through this brief review of the different studies aiming to improve the mechanical, structural and thermal properties of the unsaturated polymers through the addition of nanoparticles, the results were discrepancies on the type of nanoparticles to beaded, on the amount of the filler and on the obtained results. For this reason, this work attempted to investigate mechanical and thermal properties of a nanocomposite made ofa polymer matrix reinforced by a binary nanoparticle TiO2 - SiO2 produced by sol-gel method.

II.1. Matrials

The composites were made from ortho polyester resin, a thixotropic polyester resin with moderate reactivity for general use and good mechanical properties, manufactured by PolikorBoyaVeKimya with hardener. Figure 1 shows the five main steps of reinforcing the resin was with an E-glass fiber star cloth to prepare the nanocomposite.

Following Zahrouni, Bendaoued & Salhi’s [14] step approach, step 1 illustrates the elaboration of TiO₂ and SiO₂nanopowders by sol-gel method. Step 2 presents the preparation of TiO₂-SiO₂ system at different percentages; Step 3 shows the heat treatment of TiO₂-SiO₂ system at 1000°C and 1200°C. Step 4 illustrates the dispersion of the nanopowder in the polyester resin by mechanical and ultrasonic agitation methods. Finally, Step 5 shows the production of the nanocomposite plate by vacuum assisted resin transfer molding (VARTM).

II.2. Synthesis of the nanopowders

Initially, each ceramic powder was synthesized by a sol-gel process using supercritical drying of ethanol. The starting solution of SiO2 was prepared by dissolving Tetraethyl-orthosilicate (TEOS) in ethanol and distilled water (H2O). Then, the mixture was stirred for 30 min until a transparent sol was obtained. Finally, a given volume of hydrofluoric acid (HF) was added. In order to synthesize TiO2nanopowder, methanol and acetic acid (CH3COOH) used as catalysts and titanium tetra isopropoxide (TTIP) precursor were mixed in the order shown in Fig. 1. Following Bendaoued et al. [15], the mixture was stirred for 30 minutes at a constant speed to obtain the TiO2 sol .The Silica and Titania sols were synthesized individually to get the formation of a homogeneous structure due to the different kinetic parameters, hydrolysis and polymerization rate of corresponding precursor. Then, the resulting sols were introduced into an autoclave heated up to 243°C and pressurized to overcome the critical point of ethanol (Tc = 243°C, Pc = 63bar). After maintaining temperature at 243°C for 1h, gelation of the sol occurred. To evacuate the interstitial solvent, a depressurization for 1 h down to room temperature was conducted with nitrogen gas. To avoid cracking of the sample due to thermal strain, the autoclave was opened after 24 h to slowly achieve thermal equilibrium. Finally, TiO2 and SiO2 aerogels were obtained and then annealed in air at 500°C for 1 h. The powder mixtures were dispersed in ethanol using an ultrasound probe then dried at 80°C for 24 h.

The heat treatment of the TiO2-SiO2 nano-systems (Fig. 2) was conducted at temperatures ranging from 1000°C to 1200°C. The effects of temperature on the structure, the stress at break, Young’s modulus and the shear modulus of the products produced were examined. This cycle consisted of a three-step heat treatment: An increase in temperature at a rate of 2.5°C/min up to the desired temperature (lower than the sintering temperature), followed by stabilization at this temperature for 2 hours to allow the chemical reaction, then a decrease in temperature to room temperature.

II.3. Preparation of the nanocomposites

At this stage, nanocomposite plates were obtained by using the vacuum forming process where the polyester matrix reinforced by glass fibers was filled with 5 wt% of TiO2-SiO2system nanopowdersas shown in Fig. 1, Step4. Table 1 illustrates the composition of the nanocomposites studied in this work.

Table 1

The composition of the nanocomposites
Composition	Designation
Polyester 85 Wt% + 15 Wt % Glass Fiber	COMP
Polyester 85% + 15 Wt% Glass Fiber + 5 Wt % (25Wt%TiO₂-75Wt%SiO₂)	COMP + 5 Wt% 25Ti-75Si
Polyester 85% + 15 Wt% Glass Fiber + 5 Wt % (50Wt%TiO₂-50Wt%SiO₂)	COMP + 5 Wt% 50Si-50Ti
Polyester 85% + 15 Wt% Glass Fiber + 5 Wt % (75Wt%TiO₂-25Wt%SiO₂)	COMP + 5 Wt% 75Si-25Ti

The VARTM process was applied through the following steps. In the first step, the mold was placed in a black bag and its surface was covered with a bagging film to obtain a smooth mold surface. In the second step, the molding agent was added and the mixture was formed by overlapped layers of resin and a reinforcement structure formed by tissue-like fibers of glass. Using a spiked roller or a brush, a first layer of reinforcement was laid while avoiding air pockets followed by a second layer of resin.Finally, the mold was the black bag was closed to suck out all the air inside the mold for 20 h under vacuum allowing the resin to toughen. The obtained samples were parallelepiped in shape with 180 mm*180 mm*3 mm sides similar to those observed by Karnati et al. [16] and Bose et al. [17].

II.4. Characterization of the nanofillers

The samples were submitted to Infrared Fourier Transform spectrometer (FTS165) with a resolution of 4 cm^− 1. The phase identification of nanopowders was accomplished using PAN analytical X’Pert Pro MPD with CuKα radiation for X-ray diffraction (XRD) measurements recorded in the 20–85 range with an incidence angle of 0.05°.

To investigate the mechanical properties of the prepared samples, the experimental set up was arranged as follows: The uniaxial compression test (F = 47.1 KN; V = 5mm/min) specimens were cylindrical in shape with a diameter of 20 mm and a thickness of approximately 5 mm. Then, the pellets were subjected to heat treatment at 1000°C and 1200°C for 2hrs, respectively. To study the response of each nanomaterial to linear strain and uniform pressure and the shear modulus (G), Young’s modulus (E) and the response of the materialsto hearing strains were used respectively. Finally, following Daniyal,Akhtar&Azam [18] who showed that the ultrasonic technique was a basic non-destructive testing (NDT) method to evaluate materials and some of their mechanical properties, ultrasonic test was adopte because of the fragility and the shape of the samples.

II.5. Characterization of the nanocomposites

The hardness tests were conducted on the section of the nanocomposites specimens by using Vickers microhardness tester at different composition of nanocomposites. Each sample was loaded with a force of 200 gf and the measurements were taken at 8 points along the section to assess the influence of TiO2 nanoparticles inside the nanocomposites. The prior tensile tests were conducted to determine the Young's modulus.

The breaking strength of the materials was tested by using a Hounsfield (H25KS) Universal Testing Machine (UTM) at a crosshead speed of 2 mm/min. Tensile test pieces were conducted following the ASTM D638 standard. Differential Scanning Calorimetry (DSC, TA Instruments model Q200) was used to measure the effect of the nanofiller on the thermal properties of the composite (polyester-15% fiberglass) such as melting temperature and crystallization at low temperature. The molten state of the different phases was considered in function of the thermal heat of the TiO2-SiO2 nano-system.

The DSC analyzes were carried out in a temperature range of 60°C to 160°C in two cycles (heating rate of 10° C/min and a cooling rate of 20° C/min). The thermal analyzes of the various nanocomposites were subjected to a thermogravimetric analysis (TGA, TA Instruments Model TGA 500). The TGA analyzes were conducted from room temperature to 650°C with a heating rate of 10°C/min. The stability and degradation mechanisms of nanocomposites were considered important properties for various fields of application due to changes in viscoelastic behavior. In this study, the thermal properties of nanocomposites were investigated using TGA/DTG. The TGA data was investigated to know the decomposition characteristic and thermal stability under a wide temperature range. In these methods, the changes in thermal stability were represented as percent weight loss as a function of the temperature. The DTG data were characterized by the maximum temperature (Tmax) and the setpoint temperature (Te). The morphological observation of the samples (surface and cross-section) was studied by using Scanning Electron Microscopy (SEM) with an accelerating voltage of 15 KV. Dynamic Mechanical Properties (DMA) was determined by the Q800 Dynamic Mechanical Analyzer (TA Instruments, Dual Cantilever) at temperatures ranging from 20°C to 180 ° with a fixed frequency of 1 Hz.

III.1.Characterization of the nanopowders

III.1.1.Infrared analysis of the nanocomposites

Figure 3 shows the FTIR spectra of thenanocompositescalcinated at 1000 °C and 1200 °C for 2hours. Figure 3a presents FTIR spectra the composite with 25 % Si-75 % Ti.The bands around 1086cm-1and 1049cm-1would confirm the presence of Si-O-Si bound. The absorption band around 2850-3640cm-1would correspond to the fundamental stretching vibration of hydroxyl O-H groups caused by the presence of H₂O completely evaporated.This band would be further confirmed by the weak band at 1634 cm-1 as was rightly demonstrated by Arun Kumar,Merline-Shyla& Xavier [19]. Figure 3b exhibits the FTIR spectra of the composite with 50 % Si-50 % Ti nanocomposite. The bands appearing at 1100 and918cm^-1 would be associated with asymmetric Si-O-Si stretching vibration and Si-O-Ti vibration, respectively. The band centered at 1600 cm^-1would correspond to the vibration of hydroxyl groups. These findings would confirm previous results reported by Aziz, Asyikin and Sopyan [43] and Quyen et al. [20] who agreed on the fact that the band at around 2490-3650 cm^-1 observed before heat treatment was due to the presence of O–Hstretching and bending vibrations. Figure3c shows the FTIR spectra of the composite with 75 % Si-25 % Ti. Three characteristic bands appeared at around 2486-3589 cm-1, 1100 cm-1, and 940 cm-1. The peak from 1100 cm-1could bean indication of the presence of asymmetric stretching vibrations of Si-O-Si bond as Du et al. [44] explained. Moreover, in line with Quyen et al. [20], the small peak observed at 940 cm-1 could be attributed to Ti-O-Si linkages affirming the bonding between Ti and Si At 1200°C.Thus, the Ti-O-Si bond would improve the thermal stability of TiO2 and suppress the phase transformation from anatase to rutile. In addition, the FTIR measurements correlated with Yu et al.[21] who argued that the presence of a peak at 650 cm-1 indicated the vibration absorption of the Ti-O-Ti bond, Furthermore, in line with Quyen et al. [20],the broad band located between 2486-3589 cm-1could be assigned to the feature stretching vibration of hydroxyl O-H groups. However, the band intensity of hydroxyl groups at around 2600-3660 cm-1 increased with the increase of TiO2 mass fraction and disappeared after calcination. This would confirms the control of the synthesis method based on the sol-gel process.

III.1.2. XRD analysis of the nanocomposites

Figure 4 shows the XRD spectra of the nanocomposites before and after annealing at 1000°C and 1200°C for.2 hours. Considering all nanocomposites, at 243°C, anatase structure was identified in accordance with the JCPDS files NO. 00-004-0477. Moreover, in line with (2015).Hui et al.[22], the small peak at around 2θ=13° would reveal the presence of amorphous SiO₂. The transition from anatase to rutile structure was observed forpure TiO₂ at 1000°C.Nonetheless, this phase transformation was not observed for the TiO₂-SiO₂ nanocomposites treated at the same temperature. It would be worth mentioning that the crystallinity of amorphous SiO₂ increased with calcination temperature and that the addition of silica to TiO₂nanopoudres did not have an impact on the crystalline structure of anatase TiO₂. These results correlated with Pakdeland.Daoud’s [23] previous findings.Additionally, the anatase-rutile transformation with calcination at 1000°C and 1200 °C was highly delayed in the TiO₂-SiO₂ nanocomposites. This phenomenon was also observed even at low Si:Ti ratioss can be observed in figure 4,.Moreno et al. [24] explained this by the fact that the formation of this amorphous SiO₂ phase was considered to be important in retarding the anatase-to-rutile phase transition because the aerogels synthesized with ethyl orthosilicate (TEOS) and acetic acid had a good thermal stability at high-temperature of anatase. Finally, the amorphous SiO₂was concluded to be a stronger inhibitor of the phase transformation of TiO₂nanopowders at temperatures greater than 1200°C which wouldaffect the mechanical properties of the resulting nanocomposites as was rightly explained by Vega, Olaya, and Ruiz [25].

III. 1.3. Mechanical characterization of the nanocomposites

the structural results represent changes in the chemical composition and structure of materials, in this test we can see the influence of this nanometric change on the macro or mechanical behavior. As can be seen in figures 5a and 5b, there was a clear drop of the Young’s modulus and shear modulus at 1200°C. This can be explained by the presence of water filling the micro-pores and forming a film of water inside them. Hence, the presence of water in the pores would lead to a low contribution and a relaxation of the' Stress Ground-frost. Que et al.[26] explained this by the fact that after filling the pores by capillary condensation, E and G would decrease because the pores of different sizes would undergo the capillary condensation one after the other. Therefore, they would have a nano-indenter and would show a dependence on the heat-treatment temperature. Figure 5c shows the Poisson’s Ratio of the nanocomposites at different temperatures. The values of Poisson’s Ratio had an inverse trend to that of the modules of elasticity. This can be explained by the different behaviors of the physical and chemical properties of the different aerogels used in this study. Indeed, these aerogels would have pores and defects accompanied by the formation of some cracks. However, after heat treatment at 1200°C, there was not a very large difference knowing that the values vary within the same error range. These findings would confirm the findings reported in section III.1.1 above about the FTIR analysis.

III.2. Thermal properties of the nanocomposites

III.2.1.DSC analysis

Figure 6a shows the DSC scans of polyester composite. As can be seen in figure 6a, the values provided by the differential scanning calorimetry of the polymer composite having 15% fiberglass were clear in the temperature range between 25 and 160°C. The vitreous transmission temperature Tg of the respective compositions and states of the nanocomposites can be clearly determined through the curves in figures 6 b, 6c and 6d. The Tg started with the state of polyester/fiberglass composite at 42.8°C. With the addition of TiO₂-SiO₂ system of 5%wt, a relatively small increase was observed depending on the composition of this system. This increase in Tg was of a maximum value of 45.11°C for the 75%TiO₂-25%SiO₂nanofiller. This finding correlated very well with Nayak, Mahato, and Ray [27]. As can be seen in figure.6, theaddition of the TiO₂-SiO₂ nanofillers seemed to affect the value of Tg of the composite with 75%TiO₂-25%SiO₂at a heat treatment of 1000°C. Indeed, this value rose to 49.66°C; i.e. an increase of 15.6% in the state not loaded. Hence, it can be said that the Tg depends directly on the property of themolecular motion. This would obviously indicate that the molecular chain of nanocomposites needs a higher temperature to undergo the glass transition process. This would be explained by the fact that the movement of the molecular chains was inhibited by the addition of the functionalized nano-system .Hence, it can be induced that the TiO2 nanofiller of this composition with a rutile structure increased the internal lassion of the composite notes. In contrast, the presence of SiO2 weakened this behavior.

III.2.2. TGAanalysis

The stability and degradation mechanisms of nanocomposites are an important property for various fields of application due to changes in viscoelastic behavior. In this study, the thermal properties of nanocomposites were investigated using TGA/DTG. The TGA data is investigated to know the decomposition characteristic and thermal stability under a wide temperature range. In these methods, the changes in thermal stability are represented as percent weight loss as a function of the temperature.

The DTG data were characterized by the maximum temperature (T_max) and the setpoint temperature (T_e). The area behind the DTG plot is proportional to the mass change and the height of the peak represents the rate of mass change at that temperature [28].

Figure 8 exhibits the various TGA and DTG curves of the composites.Following Ismail, et al.[28], the area behind the DTG plot would be proportional to the mass change and the height of the peak would represent the rate of mass change at that temperature.

As can be seen in figure 8a, the unfilled composite showed a thermal stability up to about 200°C associated with a low weight loss of 5% above this temperature until a sudden drop towards 280°C. Subsequently, a loss of mass of high amplitude – approximately 90% of the initial mass – wasobserved up to a temperature close to 400°C, this was in line with da Luz et al. [29] who detected a degradation peak at 384.79° in their DTG curve. The TGA curve and the corresponding DTG thermograms of the nanofiller composites with15%wt and with the respective composition of the TiO₂-SiO₂ system, with a variation of the heat treatment temperatures from untreated to 1000°C and 1200°C, are illustrated in figures 8 b-e.The TGA results revealed that there was a variation of the thermal behavior of the compositesshown in the evolution of the temperature of decomposition.

This temperature was almost stable at the maximum value for the composite with 75%TiO₂-25%SiO₂ of heat treatment at 1200°C with a weight loss ratio of 5% .These findings differed withda Luz et al. [29] who revealed that the incorporation of the bagasse fiber nanofillers into a polymer matrix at different compositions and heat treatment temperatures, did not significantly modify the thermal behavior of the composite

2.2. Dynamic mechanical analysis (DMA)

Figure 9 shows the plots of the storage modulus (E'), the loss modulus (E'') and the ratio of the loss and storage modulus (tanδ) of the fiberglass polyester composite with a value of E'= 2.849 GPa, E'' =257 MPa at a room temperature of 27°C and a maximum value of tanδ' of 0.85. Compared to the unfilled composite, the incorporation of 5% nanofillershowed an increase in the storage modulus.Maharramov et al. [30] considered this increase as a contribution to the improvement of the interfacial bond between the nanofillers and the polyester matrix. It can be observed that the highest storage modulus was obtained with 5 %wt of 25%TiO₂-75%SiO₂of untreated composite. The storage modulus of nanocomposites decreased when the temperature increased until the material reached its glass transition temperature of T=44.53°C. This could contribute to the improvement of the thermal stability and the resistance of the treated samples. The thermal capacity would increase by the evolution of the the increase of the Tg value. However, a small reduction would be observed at 1000°C and then a sharp decrease at 1200°C.

Similarly, it was observed that the increase of Tg decreased the storage modulus and caused the transition from glassy state to the rubbery state. Therefore, the molecules would start to lose their packed structure and a rise of vibration al movements would occur leading to a steep loss of storage modulus. Indeed, Bendaoued et al. [31].recommended that a better reinforcing effect in the composites would require a limitation of the amount of vibration occurring within the molecules of a materia to maintain its solid state. Finally, the DMA test coupled with the mechanical and thermal resistance revealed that the most durable compositions would be made of 25% Ti-75% Si and 75% Ti-25Si treated at 1200°C.

Figure 10 exhibits the DMA analysis of the composite with different amounts of fillers. As can be seen in figure 10a, the loss modulus (E”) indicated the viscous response of the samples measured and provided information on their tendency to disperse the applied energy. The structural mobility of composite increased with the addition of nanofillers. This phenomenon was explained by Lertwimolnun, and Vergnes’ [32]as a sign of interactions of a high surface area and a higher ratio of nanofiller/polyester.These results were in agreement with Choi, Kim and Laine [33] findings. Figure 10b illustrates the ratio of the loss and storage modulus (tanδ). The loss modulus increased in function of the increase of TiO2 particles because of their thermal resistance and their stability. This observation confirmed previous results by Gonzalez-Calderon et al.[34] who revealed that this effect becomes clearer with the heat treatment at 1200°C. Moreover, in the present study, the nanocomposite (COMP+5 Wt % 75Ti-25Si) treated at 1200°C were the most stable and efficient. From a thermo-mechanical point of view, the increase in the temperature peaks of the loss modulus could be attributed to the improvement in thermal stability and to the segmental immobilization of the polyester chainsreinforced withglassfibersand the nanofillers.Lertwimolnun, and Vergnes’ [32] and Alamri,andLow [35]reported that these mechanical properties were due to the higher tendency of nanocomposites to absorb energy due to the addition of nanofillers. The peak tan (δ) of the nanocomposites decreased despite the improvement of the temperature and the addition of nanofillers. This finding would confirms the high rigidity and the interfacial adhesion with the nanofillers and the polymer matrix. When the temperature was raised, the storage modulus of the nanocomposites increased more than the loss modulus, indicating that the structure was thermally stable. With the addition of nanofillers, there was no longer any change in the Tg of the samples. Finally, the viscoelastic behavior and dynamic mechanical properties of nanocomposites were strongly related to the physical and chemical properties of the aerogels used in this study.

III. 3.Mechanical properties of the composite

III.3.1. Microhardness of the nanocomposite

Figure 12 shows the effect of adding nanopowders on the impact strength of the nanocomposites The addition of nanoparticles seemed to increase the microhardness of the 25 TiO2 %-75 SiO2 % nanocompositemicrohardness to around 26hv at 1200°C. This would represent a 60% increase. However, it seemed that the other compositions did not gain a significant increase in microhardness. Furthermore, the the microhardness of the 75%TiO₂-25%SiO₂nanocomposite (in green) decresed to 21 hv at 1200 °C. This would imply that the more SiO₂ was present in the nanocomposite, the higher its hardness was after undergoing a thermal treatment.

This improvement could be attributed to a low agglomeration of the nanofillers grains presented in the polymer matrix which would lead to a strong polymer-filler interaction, thus yielding an increase in microhardness. Rao, Singh and Dwivedi [36].reported that nanocomposites exhibited an improved microhardness with lower loading rate.

III.3.2. Tensile test of the nanocomposite

Figure 13 presents the stress-strain diagram of the elaborated nanocomposites. These tensile tests were conducted to assess the evolution of the tensility of the nanocomposite in function of the addition of nanofillers at different contents. The curve of the 85% wt polyester 15% wt fiber glass composite showed an elastic behavior. With the addition of nanofillers, a very clear plastic zone was observed with an increase in the ductility of the produced material.

Additionally, the tensile test allowed to determinethe tensile modulus, ultimate tensile strength (UTS) and breaking stress (SB). Figure 14 illustrates the effect of the nanoparticles reinforcements on the tensile strength of the prepared samples. Figure 14a shows the value of Yong's modulus for the deferent compositions. The tensile modulus of the composite made of 85% polyester + 15% fiberglasswas 6.6 GPa.With the addition of 5% weight of System nanoparticles made of 25Ti-75Si, there was an increase of 15.15%, while this increase was of only 4.5%, for the composite + 25 Si -75Ti. Therefore, it seemed that the presence of a higher percentage of Si was responsible for the enhancement of the mechanical properties of the composite This finding correlated with the reported DMA analysis and the microhardness results.

Figure 14 shows the effects of heat treatment on the mechanical properties of the composite. Hence, figure 14a shows the composition+5 % wt (25%TiO₂-75SiO₂₎hadthe highest Young's modulus value after heat treatment or internal structural modification of r. However, the strain to break test and the UTS shown in figures 13 b and 13 c, respectively revealed that the composition having 75 %TiO₂ exhibited the highest elasticity values. Therefore, SiO₂enhanced the rigidity and TiO₂enhanced the plasticity of the nanocomposite.

III.4. Morphological analysis through SEM observations

Figure 15 shows the SEM micrographs of the composites. The SEM images of the fracture surface of the tested samples showed the deformation mechanisms that occurred after performing the tensile tests on the prepared nanocomposites. As can be seen in figure 15a, the unfilled sample showed a failure section across the matrix surface and the glass fibers orientation with noticeable porosity which could explain the fragility and low mechanical resistance of the composite. Behera et al. [37] rightly explainedthis behavior bythe existence of potholes, fractures and fiber detachment among the failure mechanisms of composites. In addition, in this study, the close inspection of the interface between the glass fabric and the polyester matrix revealed a weak fiber-matrix adhesion. Figures 15b, 15c and 15d show the presence of slightly agglomerated nanofillers proving the importance of the dispersion methods to distribute the nanoparticles TiO₂andSiO₂homogenously in the polyester matrix. This observation correlates well with Saberianet al.’s[38] finding. Indeed, these scholars reported that the well-dispersed TiO₂-SiO₂ system nanoparticles were attributed to better dispersion of the nanoparticles that would improve the interface area leading to a good creation of matrix/fiber interface bonds. Figure 15d shows a visible agglomeration of the nanoparticles. In total agreement with Sahnesarayi, Sarpoolaky, and Rastegari [39], it can be concluded that under these conditions, the dispersion became more difficult to reach a very high concentrations of nanoparticles. These agglomerates caused defects in the nanocomposites and acted as stress concentration sites, generating early cracks and fractures. With the heat treatment,the problem improved. The comparison between the mechanical performances obtained for the different nanocomposites would indicate that the use of 5% wt of nanofillers with the heat treatment, a more resistant fibre-polyester matrix interface was created. As a result, the glass fibers could transfer their reinforcing potential to the nanocomposites and fiber pull-out would be reduced

This work attempted to demonstrate the effective role of a binary filler made of TiO2-SiO2 in the manufacture of polyester-fiberglass composites with improved physical and mechanical properties. It built on previous works, Zahrouni, Bendaoued, and Salhi [14] and Bendaoued et al. [15], on the fabrication protocol of an organic matrix nanocomposite with inorganic composite fillers in treated and untreated states. It described how to produce the nanocomposites. Then, the produced nanocomposites were tested under tensile, impact and microhardness loads by thermal analysis and SEM analysis. The first finding of this work obtained from a DMA test coupled with the mechanical and thermal resistance revealed that the most durable compositions would be made of 25 % Ti-75 % Si and 75% Ti-25Si treated at 1200 °C. Therefore it can be induced that SiO₂ enhanced the rigidity and TiO₂enhanced the plasticity of the nanocomposite Secondly, the nano filler of composition 75% TiO2-25 SiO2 had a good stability and thermal resistance. While the composition 75% SiO2-25 % TiO2 showed a better mechanical resistance. The third result was that heat treatment yielded the best results at 1000°C and 1200°C. Thirdly, it seemed that the dispersion methods was very important to guarantee a homogenous distribution of TiO₂and SiO₂ in the polyester matrix and therefore enhance its mechanical and morphological properties. In conclusion, with such enhanced properties, the obtained composition may be a potential eligible material with various industrial applications.

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Mechanical and thermal properties of a nanocomposite made of a polymer matrix reinforced by a binary nanoparticle TiO2 - SiO2 produced by sol-gel method

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Abstract

Figures

I. Introduction

Ii. Experimental Procedure

II.1. Matrials

II.2. Synthesis of the nanopowders

II.3. Preparation of the nanocomposites

II.4. Characterization of the nanofillers

II.5. Characterization of the nanocomposites

Iii. Results And Discussion

III.1.Characterization of the nanopowders

III.2. Thermal properties of the nanocomposites

Conclusion

References

Additional Declarations

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