Extraction and characterization of nano-silica particles to enhance mechanical properties of general-purpose unsaturated polyester resin

: Unsaturated polyester resin (UPR) is the most versatile liquid polymer with a wide range of applications in every aspect of the industry but it has low impact strength, low elongation at break, and low toughness. Its mechanical properties can be enhanced with the addition of an optimum percentage of nano-silica ﬁ llers by using ASTM polymer test standards, which have been followed by various research groups. For this research, enhanced mechanical properties of the resin have been tested for 0.5, 1, 2, 3, and 4% amount by weight fraction of the nano-silica as ﬁ ber nanomaterial. The sugar cane bagasse ash was collected from the Wenji Sugar Factory and extracted with the required size of the particle, which is 10 nm. The ability of extraction is used to manipulate the particle size as the researcher needs. The aim is to determine the enhanced mechanical properties of the UPR by the addition of optimum nano-silica particles. Nanoparticles have the e ﬀ ect of ﬁ lling porous regions, crack path de ﬂ ection, and crack bridging capability of the material, which provides good adhesion with the matrix to increase the mechanical properties of composite materials. Experimental result dictates that 0.5% nano-silica addition with 10 nm particle size performs best by enhancing the mechanical properties of composite material up to 30.45% for tensile, 33% for compression, 17.8% for ﬂ exural, a slightly 10% improvement for impact test and it shows an overall 27% better performance than the pure UPR. Thermal stability and glass transition temperature were not in ﬂ uenced by the addition of nano-silica.


Introduction
Unsaturated polyester (USP) is a versatile and low-cost condensation resin formed generally by the reaction of polyols (polyhydric alcohols) with unsaturated dibasic acids whose production started in the year 1930 [1].These resins are generally pale-yellow oligomers with a low degree of polymerization and are viscous liquids depending on their chemical composition and molecular weight.Unsaturated polyester resins (UPRs) are one among the many thermosetting resins and belong to the family of esters [2].It has excellent corrosion resistance, chemical resistance, fire resistance, rapid crosslinking, dimensional stability, design flexibility, and processing properties [3][4][5][6][7].They find application in sanitary wares, matrix for composite materials, storage tank construction, sealant, pipes, gratings, and high-performance components for the marine and transportation industry (closure, body panels, fenders, boat hulls, decks, etc.).Unfortunately, UPRs are brittle, just like other thermo-setting resins of epoxy, phenolics, and vinyl esters [8][9][10][11][12][13][14][15][16].Relatively poor mechanical and thermal properties of pure unsaturated polyester epoxy (UPe) limit their use in advanced composites, and their performances could be improved by designing macromolecules' chemical constitution, configuration, and conformation, changing the degree of material crystallinity, and phase formation/segregation.The performances of UPe resins may be improved by the addition of inorganic fillers, especially nano-filler with controllable size, shape, and textural properties, which improves rheological, optical, electrical, mechanical, and thermal properties, enhances fire resistance, and decreases the shrinkage effect of the neat UPe [8,[16][17][18].Embirsh et al. [19] reported that by using biobased unsaturated polyester resin (b-UPR), synthesized from waste polyethylene terephthalate (PET) glycosylate and renewable origin maleic anhydride (MAnh), propylene glycol (PG) was reinforced with unmodified and vinyl-modified biosilica nanoparticles obtained from rice husk had given 88% increase of tensile strength upon addition of 2.5 wt% biosilica modified with vinyl silane.Soleyman et al. [20] reported that using highly controllable self-coiling and tensile shape memory behaviors of the 3D printed poly-ethylene terephthalate glycol (PETG) thermoplastic structures as a novel shape memory polymer (SMP) obtained a maximum printing-induced prestrain of the PETG stored in the first printed layer and a 20-fold increase in the deformation speed for the warm programming condition resulted in a doubled gentler undesired self-bending and a 14.3% higher shape recovery.Soleyman et al. [21] reported that using the 4D printing capability and shape memory effect of PETG as a novel shape memory thermoplastic with an option of emerging tailor-made excess curved third shape during the shape recovery step and obtained shape memory effect behavior with higher than 96% total shape recovery.Karimi et al. [22] also investigated that on plastic recycling, especially biodegradable plastics of polybutylene adipate-co-terephthalate (PBAT) for direct pellet printing, which eliminates the need for filament conversion and obtained SEM results as nozzle temperature increases, print quality improved and avoids micro holes and layered structure formation at 200°C.Nagendra et al. [23] reported from their review of the impact of machining, tools, monitoring, and cooling techniques on carbon-fiber-reinforced polymer (CFRP) composites to achieve sustainable manufacturing processes while maintaining the desirable properties of CFRP composites.The objective was to meet diverse application needs and enhance CFRP machining processes, highlighting the importance of sustainable practices in shaping composite materials of the future; utilization of coating on the tool has enhanced tool life and drill hole quality as a review conclusion.Adin [24] reported that the effect of total accumulated weld volumes (TAWVs) and different groove angles (45°, 60°, 75°, and 90°) on the mechanical properties of AISI 1040 and AISI 8620 cylindrical steel joints was investigated experimentally.The result was observed that ultimate tensile strength (UTS) values of the dissimilar material joints were positively affected by the increase in TAWV.The UTS value of the 90°groove-angled joint was found to be 40.25%higher than the UTS value of the 45°groove-angled joint.Saraç et al. [25] investigated that using single lap joints and adding nano-Al 2 O 3 , nano-TiO 2 , and nano-Al 2 O 3 powders in various proportions to the epoxy adhesive (DP460), and using the pure additive-free epoxy adhesive, the mechanical properties of the connections were experimentally investigated at 20, 25, 30, 50, and 70 mm overlap lengths under shear load for AISI 304 stainless steel plate as an adherent material.They obtained that the effective nanoparticle in increasing the failure strength of the adhesive joints is nano-Al 2 O 3 particles, and the maximum failure strength increase rate was 20 mm in overlap length and 97% in 4 wt% nano-Al 2 O 3 -reinforced specimens.Elongation at break also increases as the nanoparticles incorporated into the epoxy adhesive.Adin and Adin [26] investigated the mechanical properties of composite materials from woven jute produced in the form of epoxy adhesive layers using the hand lay-up method.Aluminum, mica, and ceramic particles were added into the epoxy as structural adhesive as 2, 4, and 6 wt% as fiber of the composite.They obtained that tensile and bending failure loads of the composite materials using particle reinforced adhesive were increased.Enhanced tensile strength was achieved via aluminum particles with 4 wt%, and enhanced bending strength was found at aluminum particles of 2 wt%.
Huang et al. [27] reported that using reactive nanosilica coated with a silage coupling containing epoxy group (E-Sio 2 ) and dimer fatty acids (DFA) were allowed to participate in the polycondensation reaction of UPR and they obtained E-Sio 2 /DFA/UPR hybrid composite material.They studied the influence of E-Sio 2 on the mechanical performance of the composite material in comparison with pure USP.Finally, the 0.8 wt% E-Sio 2 shows improved mechanical properties of the composite material as tensile strength, Young's modulus, flexural strength, elongation at break, and shore a hardness enhanced by 37.03, 69.18, 86.81, 14.0, and 14.71%, respectively, compared with DFA/UPR.Similarly, the addition of E-Sio 2 also enhances the water resistance of hybrid materials.
Gumus et al. [28] investigated the effect of nano/inorganic fillers on USP thermal, mechanical, and physical properties.UPR reinforced with nanoparticles showed better properties than the pure USP polymer, and the fillers were used in a polymeric matrix to enhance the thermal, mechanical, and physical properties.Their novelty was the use of boron nitride and silica particles with different weight ratios.Un-modified UPRs are not preferred in applications like construction and transportation due to their low impact strength, low elongation at break, resistance to crack propagation, and low toughness.Thus, their application is limited as the polymer matrix in the fiber-reinforced composite products.Hence, there is a need to enhance the mechanical properties and toughening of UPR to increase its scope of applications using different elastomers, thermoplastics, and fillers in the USP matrix [2,19].Even though the reported literature above stated mechanical property enhancements, they did not address the issue of mechanical property enhancement as a function of smaller particle size using sugar cane bagasse ash (SCBA) with UPR till now.This research is different from the literature's investigated result stated above since it uses a very small silica particle size (10 nm) extracted locally from SCBA at the Wenji Sugar Factory for structural application.The aim of this research is to enhance the mechanical properties of the UPR by adding silica particles for structural and industrial application which increases its scope of application.The materials have been determined from the literature and a detailed flow chart of the research is explained as shown in Figure 1.

Matrix resin
The matrix material used for this research is UPR, which was bought from World Fiber Glass and Water Proofing Engineering Company, Addis Ababa, Ethiopia.The polyester resin is cured by hardener HY-951, which facilitates the chemical reaction between matrix and fiber without changing its own properties and composition was bought there.The density of the polyester is 1.103 g/cm 3 , and its dynamic viscosity is 11.789 Pa s.The matrix material was prepared using resin and hardener in a ratio of 10:1, as recommended in the study of Zhu and Joyce [3].

Fiber-nano-silica
SCBA, as shown in Figure 2, is collected from the Wenji Sugar Factory and transported to the Ethiopian Biotechnology Institute for extraction with the required nanoparticle size.SCBA is sieved with a 6 mm wire mesh to remove any remaining unknown dust and solid parts.The ash is burned again in the lab using a microwave to remove any unburned organic substances or mixed materials until complete ash is produced.
The SCBA was then washed thoroughly with water to remove the soluble particles, dust, and other contaminants present, whereby heavy impurities such as sand will also be removed.It is then dried in an air oven at about 105°C for 24 h.The dried SCBA refluxed with an acidic solution of HCl for nearly 120 min by stirring frequently.It is then cooled and kept intact for about 12 h.Later, it was decanted and thoroughly washed with warm distilled water until the rinse became free from acid.Finally, the wet SCBA was subsequently dried in an oven at 105°C for 24 h.The washed and dried SCBA is further subject to heat treatment to remove some metallic oxides left inside.Samples were burnt inside a programmable furnace at 950°C with a rate of 6°C/min as indicated in Figure 3.A sample of SCBA was stirred in a 2.5 M sodium hydroxide solution at a solid:solvent ratio of 1:10.The solution was heated in a covered beaker for 2.5 h by constantly stirring using a magnetic stirrer, and then it was filtered; the residue was then washed with the 10-fold original solvent amount by boiling with distilled water.The viscous, transparent, and colorless solution was produced when the solution was cooled at room temperature.Later, 10 M H 2 SO 4 was added under constant stirring under controlled conditions until it reached pH 2. Finally, NH 4 OH was added to reach a pH of 8.5 and allowed to stand at room temperature for 3 h.
-FTIR, XRD, TGA test activity done as to complete full characterization of the enhanced composite material.

Conclusion
Enhanced mechanical properties of USP has been explained qualitatively with enhanced mech.properties

Result and Discussion
Characterized data were interpreted in comparison with results obtained from similar and latest literature findings.Nano-silica particles to enhance mechanical properties of polyester resin  3

Preparation of the composite
Polyester resin (USP) and silica particles assisted with the addition of hardener were used to prepare the composite using the recommended weight ratio for mixing polyester resin with hardener at 10:1 [3].Using the volume of the mold shown in Figure 4(b) as a reference, first of all, the calculated volume of resin was poured into the largest bowl, then the required amount of nano-silica, which also depends on its weight percentage using a digital weight balance shown in Figure 4 The bubbles, which are the source of porosity, are simply avoided via having simple pressure over the composite up to 5 MPa for good bonding and longtime stirring.The curing process was by using open atmospheric air for 3-5 h.After the composite cured good enough, it was released with the help of a mold releaser from the mold and ready for other simple machining operations.A mold releaser agent is good for preventing the composite from sticking to the mold when the molds are apart.It is used depending on the mold material and desired characteristics of the finished parts, such as the common waxing types as in paste wax and polyethylene plastic for better surface finish of the composite.

Experimental apparatus
A computer-controlled small punch creep testing machine with a capacity of up to 200 kN and a load cell of 200 kN has  The impact test was also done using a Charpy Izoid testing machine with a capacity of 90 J in accordance with polymer ASTM D6110.

Tensile characterization test setup and apparatus
For the tensile test of this polyester resin with nano-silica composite material, proportional additives of 0.5, 1, 2, and 4% by weight fraction as fiber to matrix experimental samples have been prepared and tested using a polymer ASTM standard as shown in Figure 5 with an ambient temperature of 23 ± 2°C and an approximate humidity value of 50 ± 5% as per the ASTM D638-14 specification.Strain rate and stress rate are also determined via cross-speed standard values for different mechanical test standards.

Flexural characterization test setup and apparatus
Flexural mechanical property is also another point of interest to be enhanced using the ASTM standards via a UTM machine with a capacity of 100 kN, a load cell of 300 kN, a strain rate of 5 mm/min at an ambient temperature of 25°C with a relative humidity of 62% as per ASTM D-790 + 17 for UPR and nano-silica additive particles as a composite material shown in Figure 6.

Impact characterization test setup and apparatus
The notched Charpy impact test using the Charpy Izoid impact testing machine as shown in Figure 7 with a capacity of 90 J was carried out.In each type, specimens were tested in the ambient condition according to the ASTM D-   [29][30][31], where P is the failure load (N), B is the width of the specimen (mm), H is the thickness of the specimen (mm), and σ t is the tensile strength (MPa).
Nano-silica particles to enhance mechanical properties of polyester resin  5 256 standards with an ambient temperature of 25°C and an approximate humidity value of 50 ± 10%.The average value was noted at the initial load deformation and tabulated as impact strength.

Compression characterization test setup and apparatus
Compression mechanical property analysis was done using the WDM-100S UTM machine as shown in Figure 8 with a loading velocity of 2 mm/min as a strain rate, a load cell of 300 kN, and test samples were done at a temperature of 23 ± 2°C and a humidity of 55 ± 5% as per ASTM D-695-10 standard.
3 Results and discussion

Tensile characterization of the composite material
NB for Sample Code: From Figure 9, the sample code is understood as TNS0.5%-S1= tensile nano-silica with 0.5% for sample batch one.From Figure 10, the sample code is understood as FNS0.5%-S1= flexural nano-silica with 0.5% for sample batch one, and from Figure 10, the sample code is understood as CNS0.5%-S1= compression nano-silica with 0.5% for sample batch one and F m = failure maximum load.The tensile test result dictates that sample batch (a) with TNS0.5%-S1,TNS0.5%-S2, and TNS0.5%-S3 has stress values of 16 MPa with an F m load of 0.908 kN, 38 MPa with an F m load of 2.108 kN, and 50 MPa with an F m load of 2.77 kN, respectively.TNS0.5%-S3 at 2.77 kN force shows good performance.Tensile sample batch (b) with TNS1%-S1, TNS1%-S2, and TNS1%-S3 has stress values of 31 MPa  h [29][30][31] where IS is the impact strength, A is the energy consumed by the impact specimen (Jm), b is the width (mm) of the specimen from the middle of the notch, h is the thickness (mm) of the specimen from the middle of the notch.Tensile sample batch (d) with TNS4%-S1, TNS4%-S2, and TNS4%-S3 has stress values of 18 MPa with an F m load of 1.024 kN, 37 MPa with an F m load of 2.096 kN, and 31 MPa with an F m load of 1.718 kN, respectively, and TNS4%-S2 shows good performance.From the result, the composite material shows overall good tensile strength at TNS0.5%-S3 compared with all silica by weight proportion test scenarios.The 0.5% addition of silica nano-filler has 50 MPa tensile strength, and this is compared with pure UPR tensile strength of 38.33 MPa tested primarily and has a 30.45% improvement on the overall strength of the composite material.

Compression characterization of the composite material
The  From these tabulated results, sample batch (a) with CNS0.5%-S3 nano-silica gives a good compression strength value of 141.4 MPa.This value was compared with the tested pure UPR compression strength value of 120 MPa and showed that the addition of 0.5% fraction by weight of silica particle enhances the compression strength of the UPR composite material by 17.8% of performance.

Impact characterization of the composite material
The mean value for 2% silica by weight is 4.7 J with a standard deviation of 0.2, the mean value for 3% silica by weight is 4.6 J with a standard deviation of 0.1, and the mean value for 4% silica by weight is 4.6 J with a standard deviation of 0.2 values.For this test, the machine considers mean values at different proportions of the silica particles, which also indicates that as the proportion of silica content increases, the impact strength value is not influenced too much.The UPR composite (USP + silica particles) shows a slightly enhanced impact strength than the pure UPR compared to the literature [26,30] with a value of 10% enhancement.

X-ray powder diffraction of the nanosilica
Nano-cellulose X-ray diffraction analysis is used for phase identification of a crystalline material and provides a good understanding of the unit cell dimension of the powder.The sample is exposed to an X-ray, which irradiates through a material and then measures the intensities and scattering angles of the X-ray that leave the material.The average crystalline size of the nano-particles was calculated using the Debye-Scherrer diffraction equation [31], as shown in Figure 11a.This has been done using miniflex 600, powder XRD machine, and upon calculation, the nano-silica particle size is about 10 nm on an average calculation using peak values, as shown in Figure 12b.This X-ray measurement is used to determine the size of the particle.

FTIR of nano-silica with resin
These measurements were carried out to identify the functional groups present on the silica and polyester resin during mixture formation.The measuring device thermo scientific Nicolet is50 FTIR shown in Figure 13, with a range of 12,000-50 cm −1 and a resolution of 0.125 cm −1 has been used.The FTIR result for nano-silica particles shows several peaks and functional groups, as shown in the figure.
Carboxylic groups normally exist in a diametric form with very strong hydrogen bonds between the carbonyl and hydroxyl groups.This association results in the very broad, unusual −OH stretching absorption, which occurs from about 3,100 to 2,200 cm −1 , as shown in Figure 14.Nano-silica particles to enhance mechanical properties of polyester resin  9

Thermo gravimetric (TGA) analysis of nano-cellulose with resin
HCT_1 is a compressive thermal analyzer that is considered for the measurement of the thermal characteristics of the composite material.The decomposition of the composite was investigated as the temperature varied between 24 and 900°C using a heating rate of 20°C per minute in a nitrogen environment.The measurement shows the composite material is able to withstand a temperature of up to 420°C as shown in Figure 15(a) and (b), and it is stable under all circumstances.This test needs mass as a function of time or temperature to predict the thermal stability of the composite polymer under dynamic TGA and to measure filler content.

Conclusion
Mechanical property characterization of 0.5% nano-silica by weight addition with pure UPR shows an overall 30.45% enhancement compared with the literature tensile strength value of pure UPR.The flexural properties of the composite UPR have been improved by about 33.9% up on the addition of 0.5% nano-silica particle with 10 nm size, and this has a fragile nature of failure, which can be more improved with the addition of liquid rubber elastomer compared with literature flexural value of pure UPR, whereas compression strength is enhanced well compared to pure UPR material.Pure UPR material has relatively good compression strength, and this has also been enhanced more by the addition of 0.5% nano-silica by weight up to 17.8% enhancement compared with literature and pure UPR test results.The impact strength was not much influenced by the addition of the nano-silica.The size of the nano-silica particle was also determined by the XRD powder diffraction method as 10 nm.The combination of 0.5% nano-silica by weight with UPR shows optimum and good mechanical property enhancement compared with literature values [32][33][34][35].
Systematic literature review to obtain research gap [USP with Silica Nano-particle for Mechanical Property enhancement] Materials [Literature based] and Methods used -USP -Bought from world fiber glass and water proofing Engineering Company -Silica Nano Particle with 10nm size-Extracted from SCBA in Ethiopia as shown in figure [02 and 03] below.

Figure 1 :
Figure 1: Detailed flowchart of the study.
(b), was added into the resin which is now ready to stir manually by hand, and then, it was stirred by a stirrer machine at 660 rpm vigorously for 6 min, and hardener has been added slowly.Stir for 2 min with the hardener and pour into the waxy-ready mold faster.The size of the mold is 170 mm × 265 mm × 4 mm for tensile and compression, as well as 170 mm × 35 mm × 10 mm for compression and impact.The unwanted amount of resin was disposed of simply by overflow before the reaction to cure started.

Figure 3 :
Figure 3: Procedures for production of sodium silicate using 2.5 mol of sodium hydroxide solution and burning of sugar cane bagasse with digital furnace to remove some metallic oxides.Section (a) Burned sodium silicate solution, (b) sodium silicate solution, (c) filtered viscous solution, (d) sodium hydroxide solution, and (e) furnace.

Figure 4 :
Figure 4: Composite material preparation setup: (a) digital weight balance and (b) mold made from steel 1045 via welding.

Figure 5 :
Figure 5: Tensile testing machine and specimen failure mode: = σ P bh t

Figure 6 :f 3 2
Figure 6: Three-point flexural testing UTM machine setup: = σ PL bh f 3 2 [29-31], where P is the maximum load (N), L is the span length of the specimen (mm), b is the width of the specimen (mm), h is the thickness of the specimen (mm), and σ f is the flexural strength (MPa).

Figure 8 :
Figure 8: Compression testing machine setup: = σ P bh C [29-31], where P is the failure load (N), b is the width of the specimen (mm), h is the
compression test result shows that sample batch (a) with CNS0.5%-S1 has a maximum compression strength of 141.4 MPa at 35.35 kN failure load, sample batch (b) with CNS1%-S1 has a maximum compression strength of 103.28 MPa at 25.82 kN failure load, sample batch (c) with CNS2%-S3 has a maximum compression strength of 122.4 MPa at 30.6 kN failure load, and sample batch (d) with CNS4%-S2 has a maximum compression strength of 139.76 MPa at 34.94 kN failure load.

Figure 14 :
Figure 14: FTIR spectra of 0.5% silica nanoparticles with USP as a composite material.

Figure 15 :
Figure 15: (a) TGA plot of pure resin (PR) and 0.5% silica modified composite resin (CR) thermo gravimetric analysis (TG) vs temperature and (b) TGA plot of pure resin and 0.5% silica modified composite resin differential thermal analysis (DTA]) vs temperature.