Investigation of Mechanical and Thermal Stabilities of Tamarind Seed-and Peanut Shell Powder-Reinforced Vinyl Ester Composite

Efcient exploitation of agricultural waste results in a more sustainable and ecofriendly environment since it lessens the burden of their disposal, which has become increasingly important in recent times. Due to their high mechanical strength and high thermal stability


Introduction
Te existence of humanity is contingent on maintaining a pristine environment at all times.As a result, material scientists and technologists are working to develop cuttingedge commercial and environmentally friendly products that are both sustainable and biodegradable.Te utilization of ecologically safe components contributes to the preservation of the ecosystem, and the speed with which these materials break down in the natural setting helps to promote this purpose.As an outcome, the number of items made from renewable resources has risen rapidly in recent years [1].Natural wastes are by far the most prevalent material to be utilized in producing ecofriendly composites.Waste products derived from natural processes are both cost-efective and renewable.One of the most important aspects of natural waste is that biological processes can break it down.Tese wastes can potentially increase the biodegradability of the composite while improving its strength [2].Terefore, the need to utilize such materials in the composite industry is inevitable.Natural fllers are renewable resources that can serve as reinforcing agents for various polymer matrices and are versatile enough to be utilized in diferent felds related to transport, construction, aviation, toy making, defense, sporting goods, and electronic industries [3].Tese agrowastes are abundant in the form of kernels and shells.After being ground and sieved, they can be used as cellulosic biofuels or inexpensive polymer composite additives [4].Adding fllers is the most efective strategy for increasing polymeric materials' mechanical and thermal aspects when these capabilities are not adequate for a particular application.Improved adhesion behavior between hydrophilic fbers and hydrophobic matrices can be attained through fllers.In situations where biocomposites are required, natural fllers are the better option.Tese composites are known for their little impact on the environment and their ability to be renewed.Te natural fllers will produce satisfactory outcomes up to the optimal weight percentage, after which adding more could cause the composites' qualities to deteriorate [5].
Using these natural fllers in a polymer matrix helps reduce the manufacturing cost of the composites by minimizing resin requirements [6].However, increased moisture absorption, low strength, uneven surface quality, and limited thermal stability are some of the critical challenges researchers face when working with these natural fller/fber waste materials.Such challenges can be overcome by hybridization [7].Hybrid composites show better tensile and fexural properties, improving their load-carrying capacity [8].
Tamarind is a massively produced agricultural commodity throughout the majority of the tropical nations of Asia, Africa, and Central America.Te tamarind tree can fourish even on soil lacking fertility, has a shallow water requirement for its growth, and does not require any human labor for its care.With an annual output of 45,000 metric tons, Tamil Nadu is the top producer of tamarind among all Indian states.Tis estimate may account for about 98,000 metric tonnes (45.4% of the total subcontinent share).Te fruit of the tamarind tree is the most cherished and costly part of the plant.Te seed, which accounts for most of the fruit, namely, 25-40%, is thrown away as trash [9].Similarly, like most other agricultural leftovers, peanut shells are produced in vast numbers each year and either dumped into the environment without the appropriate treatment or generally utilized to feed animals [10].Prabhakar et al. experimentally explored whether or not the powder from peanut shells might be used to produce composite materials and found it feasible.Te fndings of the experiments demonstrated that it is possible to manufacture composites by employing peanut shell powder (PNS) as the reinforcement material.Te incorporation of PNS signifcantly enhanced the thermal and mechanical characteristics.Despite the diversity of countries that produce groundnuts, utilizing waste products, such as shells, in manufacturing valuable components would appeal to the economy.To produce composites at an afordable cost, PNS-reinforced composites are a viable option, which may also lead to an increase in the scope of their application [11].Hence, utilizing this agrowaste as hybrid reinforcement in a polymer matrix has much content in structural and other applications.
Te most popular composite matrices are epoxies, unsaturated polyesters, and vinyl esters.Epoxies fnd use in high-performance applications, although unsaturated polyesters are the industry's leaders owing to their lower cost and greater ease of processing.However, they have low UV and temperature resistance.Due to its higher mechanical qualities and temperature resistance, epoxy is typically utilized when unsaturated polyesters no longer work.Epoxies are employed in high-cost areas because of their improved characteristics.Vinyl esters (VE) are chemically similar to unsaturated polyesters and epoxies and are frequently a compromise between the two.Epoxy has outstanding properties when it comes to mechanical or thermal stability.Tese properties were combined with the speed and ease of crosslinking of unsaturated polyesters to make this resin.Using fllers to reinforce the vinyl ester resin enhances the polymer composite's performance while decreasing production costs.Particulate fllers are the most signifcant way to support the vinyl ester resin in cast structural products [12].
By altering the percentage of fller addition in the polyester resin matrix, Jeyaprakash et al. created a composite out of powdered hybrid particulate reinforcing particles of tamarind seed (TS) and palm fber (PF).Te researchers demonstrated that the composite's maximum hardness in the Rockwell scale of about 90.2% and maximum impact resistance (1.066 J) could be achieved by using a 25 wt.%TS, 15 wt.%PF powders, and 60 wt.% polyester resin mix.Te composite attained its maximum tensile strength of 18.3 MPa when 18 wt.%TS, 22 wt.%PF powder, and 60 wt.% polyester resin were combined [13].Te properties of epoxy composites made from groundnut shell powder (60 wt.%) and tamarind shell powder (60 wt.%) were studied by Santosh and Shetty.Tey also studied that tamarind shell fragments were tougher and brittler when compared to groundnut shell fragments and had better mechanical properties when added with epoxy [14].Nagaprasad et al. fabricated hybrid fller-reinforced vinyl ester composites from tamarind seed and date seed wastes and then examined the mechanical properties after being altered.Mechanical tests (tensile, fexural, and impact) and Barcol hardness tests reveal that the best strength of the composites is achieved at a fller content of 10 wt.%.Tey claimed that hybrid fller composites are suited for use in the production of end products because the composite material has a low impact on the environment and can be applied to a variety of industrial applications as well as home applications [15].Aradhyula et al. reinforced polypropylene (PP) biomaterials with biowaste catla fsh scale (CFS) and proved that adding CFS content increased the fexural strength by 5%, density by 1%, and hardness by 11% of the PP/CFS composite.Also, CFS loading improved the composite's impact strength and melt fow index [16].

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Advances in Materials Science and Engineering Abhishek et al. developed a hybrid epoxy composite from fsh bone-derived nanofllers and Phoenix pusilla natural fber.Tey identifed a 22.5% rise in tensile strength and a 20% rise in fexural strength, and a 15.2% rise in hardness was achievable by incorporating bio-nanofllers into hybrid polymer composites [17].According to the research of Olumuyiwa et al., a polymer composite can gain its hardness by including coconut shell particles in a low-density polyethylene matrix, which is a crucial property requirement in making automobile interior panels [18].Studies conducted by Jagadeesh et al. examined the usage of corn husk four, an agricultural byproduct, as reinforcement for thermoplastic polymers (polylactic acid).Tey proved this by adding the biofller fexural modulus enhanced with increasing fller loading (10,20,30, and 40 wt.%) and mesh size (50∼100, 100, and 300).Tey concluded that using materials derived from agrowaste as reinforcement in the manufacture of ecologically friendly composites is an attractive trend from the perspective of mechanical properties [19].Saba et al. developed a kenaf/ epoxy hybrid nanocomposite by dispersing the nanofller comprising an empty fruit cluster of the nano-oil palm fbers, a material composed of layers of silicate called montmorillonite and biologically modifed montmorillonite nanoclay.Mechanical testing revealed that compared to traditional kenaf fbers-reinforced epoxy composites, the nano-oil palm fller-reinforced composite showed a hike in tensile strength, impact strength, and elongation [20].
Research performed in the past makes it abundantly clear that incorporating a fller into a polymer matrix composite improves its mechanical and thermal properties.To utilize agricultural wastes efciently to minimize the efort required to dispose of them, this work uses tamarind seed and peanut shell biosolid wastes as hybrid fller particle reinforcement in a vinyl ester matrix.Tis study explores the enhancement of vinyl ester composites' mechanical and thermal properties by incorporating tamarind seed and peanut shell powder as hybrid natural fllers.Additionally, SEM analysis was performed, providing information about the microstructural integrity of the composite and how it interacts with the matrix.

Materials and Methods
2.1.Materials.Te primary raw materials used in this research are tamarind seed, peanut shell, and vinyl ester resin.Tamarind seeds and peanut shells were purchased from local sources, such as farmers from the nearby area.By using distilled water, they are cleaned to get rid of pulp, dust, and soluble impurities.Water droplets settled on the top surfaces of the objects were wiped with the help of a tissue paper.After that, they were baked in an electrical furnace in the 60 °C heat range for one whole day.A pebble mill was used to grind up dried tamarind seeds with peanut shells to 30 and 60 μm particle sizes.HORIBA SZ100 particle analyzer was used to determine the average grain size of crushed tamarind seeds and peanut shells.
In this study, in addition to the untreated vinyl ester resin, the matrix was formed of bisphenol-A-epoxy-derived resin (styrene-45%), which is nothing but a vinyl ester.It measured 400 cps in viscosity and 1.09 in specifc gravity, and its density was 1.145 g/cm 3 .In addition, it had a promoter called N,N-dimethylaniline (C 8 H 11 N), a catalyst called methyl ethyl ketone peroxide (C 8 H 18 O 6 ), and the element cobalt.Sathyam Fibertex, Coimbatore, India, supplied these chemicals for the study.
Table 1 summarizes the properties of the materials used in the study.Te particle size of both tamarind seed powder and peanut shell powder was taken in the range of 30 μm-60 μm and measured using a HORIBA SZ100 particle analyzer.Te tamarind seed powder and peanut shell powder were prepared by cleaning, baking, and grinding.Te vinyl ester resin, a bisphenol-A-epoxy-derived resin, was used with a density of 1.145 g/cm³ and a viscosity of 400 cps.Tese properties are integral to understanding the behavior of the composite materials studied.

Material Preparation.
Te usual method of compression molding is utilized during the fabrication of hybrid fllers in addition to VE resin.In this research, tamarind seed and peanut shell additives are blended as a mixed type of fller with a combined percentage of weight.To prepare vinyl ester specimens with variable fller loadings ranging from 5% to 30%, a specifc mold is designed (200 × 200 × 3 mm).Carbon black-made mold release wax was initially applied on the surface of the mold and on the cover plate to make it easier to remove the plates, which are cured as soon as they achieve their fnal state [15].Ten, the promoter (10% N,Ndimethylaniline) of about 1.5 wt% was added to a known volume of VE resin.To remove any air bubbles that had crept in during the stirring process, the liquid was made to pass through a vacuum chamber to remove gases after being stirred for an additional 2 minutes.After adding an equal amount of accelerator and catalyst (1.5 wt.%), the mixture was stirred for two minutes before degassing in a vacuum chamber [21].Te catalyst is methyl ethyl ketone peroxide with a wt.% of 50, while the accelerator is 3 wt.%cobalt naphthenate.Te use of methyl ethyl ketone peroxide (MEKP) at 50 wt.%as a catalyst is chosen to efectively initiate the curing process in vinyl ester resins, balancing safety and reactivity.Cobalt naphthenate is used as an accelerator at 3 wt.% to enhance the curing rate without compromising the composite's properties.Tis combination is standard in the industry for efcient and reliable curing of vinyl ester resins.
After that, the prepared mixture was put into the mold, which was then secured using a cover plate.After curing the sample for 24 hours at room temperature, it was taken out of the mold for postcuring of about 2 hours at 80 °C.After the composite plate had utterly hardened, the mold was split loose and removed.Similarly, the hybrid composite consisting of variable fller loadings has been synthesized.

Mechanical Testing.
Assorted test specimens' composite plates were trimmed to the required size with the help of a saw cutter.At room temperature, tensile and fexural Advances in Materials Science and Engineering tests were performed on a (Tinius Olsen H50K) universal testing machine.Tree samples were analyzed for each wt.% of body weight to provide consistent results.Crosshead with the speed setting of 1 mm/min was set and employed in tensile tests to ensure compliance with the requirements of the ASTM D638 standard with a specimen size of about 165 mm × 10 mm × 3 mm [22].Te fexural test is performed on specimens (127 × 12.7 × 3 mm) according to the ASTM D790-10 standard.Te three-point bending method was applied with a 50 kN capacity with a crosshead speed of 2 mm/min [23].Later, the impact strength test results evaluated (Charpy approach) as per the standards of ASTM D256 using a specimen size of 65 × 13 × 3 mm 3 were analyzed.

Heat Defection Temperature
Test.An HDT-TSP type analyzer (60 × 12 × 3 mm 3 ) was used to test HDT for composites with a hybrid fller loading of 0 to 30 wt.% as specifed by ASTM D648 (60 × 12 × 3 mm 3 ).Te constant temperature range in this experiment was 2 °C/min, and the loading pressure was 455 kPa.Te HDT was measured after the deformation of the test specimen under fexural force, which is a typical behavior [24].

Tensile Test.
In terms of its tensile properties, the behavior of a material is determined by three diferent elements.Tese are the material's tensile strength, the elongation of the material at the point of the break, and its tensile modulus.Figures 1 and 2 show how increasing the fller quantity changes the concentration of hybrid fller reinforcement, which directly afects the tensile properties of the vinyl ester composite.Figure 1 depicts such efects that the factor had on the tensile strength property, and Figure 2 illustrates what efect the factor had on the tensile modulus.Pure vinyl ester resin has a tensile strength of 26.5 MPa, so its tensile modulus is 1.17 GPa.In the tensile test, the composite showed an interesting trend.Te tensile strength peaked at 40.3 MPa at 20 wt% fller content, indicating improved stress distribution and load-bearing capacity at this concentration.Concurrently, the tensile modulus, which refects the material's stifness, achieved its maximum value of 2.14 GPa at a slightly higher fller concentration of 25 wt%.Tis difference illustrates how the composite's fexibility and rigidity balance varies with fller content, highlighting the tradeof between strength and stifness in composite materials.At 20 wt% fller, the tensile strength increases due to optimal fller dispersion and stress distribution.In contrast, the tensile modulus decreases because the natural fllers add fexibility to the composite, reducing its stifness.Te tensile property of the composite material falls when an extra hybrid fller is introduced to the mixture of materials [15,21,[25][26][27][28]. Tis is because the mixed fller has a lower tensile modulus.Also, this is due to the TMS/PNS fller concentration in the composite being higher than 10 wt.%, which caused the surface contact of the fllers to begin getting structured.As a result of this, the composite exhibited the characteristics described above.Te SEM images in Figure 3 provide a microstructural perspective of the tensile fracture surfaces of the TMS/PNS-reinforced vinyl ester composites.Tese images reveal crucial details about the fller distribution and interfacial bonding quality at varying fller contents.At the optimal 20 wt% fller concentration, where the tensile strength peaked at 40.3 MPa, the SEM image in Figure 3(a) shows an even distribution of fllers with minimal evidence of fller pull-out or voids.Tis suggests a strong fller-matrix adhesion, contributing to the improved stress distribution and load-bearing capacity.In contrast, at a higher fller concentration of 25%, the image in Figure 3(b) shows increased instances of voids and fller pull-out, indicating weaker interfacial bonding and explaining the observed decrease in tensile strength beyond the 20 wt% fller content.Tese microstructural observations correlate well with the mechanical test results, highlighting the importance of optimal fller content for maximizing tensile strength.Te development of connections became noticeably more extensive if the TMS/PNS fller addition was higher than 20 wt.%.It was discovered that the TMS/PNS hybrid fllerreinforced composites saw a considerable drop in their strength and stifness when they were treated to a concentration of fller equivalent to or higher than 25 wt.%.Te clustering of hybrid fllers, which are prone to be easily removed by an applied force and ultimately result in the failure of the material, was the primary cause of this phenomenon.In Figure 4, the elongation at the break of the vinyl ester composite shows a continuously rising trend until 15 wt.% of fller loading, after which it starts to drop and stays at that level until 25 wt.%.However, the maximum allowable 3.9% was reached when the hybrid fller loading was 30 wt.%.

Flexural Test.
Te material demonstrated its capacity to withstand bending loads during the fexural test.Te fexural strength of the composite increased signifcantly, reaching 142 MPa at 20 wt% fller content, which is 1.69 times higher than that of pure vinyl ester resin.Te infuence of fller loading on the fexural strength of the TMS/PNS-VE composite is depicted in Figure 5. Tis increase is attributed to this concentration's enhanced bonding and load transfer capabilities.Regarding fexural modulus, which indicates the rigidity under bending, the composite also showed improved performance, correlating with the increase in strength.Tis simultaneous enhancement in both fexural strength and modulus underscores the efcacy of the TMS/PNS hybrid fller in reinforcing the composite for structural applications.Tis is because the hybrid fller has a larger elasticity modulus than pure resin [29][30][31][32][33][34].Te fexural resistance of the material improves when there is excellent adhesion between the fller and the resin at the interface.Further addition of fller particles increases void content due to particle agglomeration, which reduces the dispersion of particles, creating weak interfacial bonding.An increase in  Advances in Materials Science and Engineering particle reduces matrix weight, afecting the stress distribution rate between the matrix and fller [35].Te SEM images in Figure 6 examining the fexural fracture surfaces provide insights into the composite's ability to withstand bending loads.At 20 wt% fller content, where the fexural strength reached its maximum (142 MPa), the SEM micrograph in Figure 6(a) shows a cohesive and well-bonded fller-matrix interface.Te absence of signifcant voids or debonding at this concentration underscores the efcacy of the TMS/PNS hybrid fller in the composite.Tis is refected in the enhanced bonding and load transfer capabilities, as observed in the mechanical test results.However, with further increase in fller content, the SEM image in Figure 6(b) reveals more pronounced voids and poor interfacial bonding, contributing to a decrease in fexural strength.Tis observation supports the fndings that beyond 25% fller concentration, the mechanical properties tend to deteriorate due to factors such as particle agglomeration and reduced matrix weight, afecting stress distribution between the matrix and fller.

Impact Test.
Te impact test was continued until all of the impact samples were shattered.Te impact strength fndings that were achieved from using diferent fller weight percentages in TMS/PNS-VE composites are depicted in Figure 7.As a result of increased hybrid fller loading, the TMS/PNS-VE specimens' impact strength increased between 12.6 kJ/m 2 and 16 kJ/m 2 , going from 5 to 20 wt.%.Tis increased the value range by varying the fller loading between 0 and 5 wt.%, and there is an increase in the strength from 12.4 kJ/m 2 to 12.6 kJ/m 2 .Compared to the efect of energy caused by pure resin, the impact caused by a composite containing 5 wt.% of hybrid fller vinyl ester increases by 1.02 times.A possible reason for this is that only a tiny amount of the fller was used to make the composites.Compared to the impact strength of the TMS/PNS-VE hybrid composite with a fller content of 5 wt.%, the material's impact strength is somewhat diminished when the fller level is increased to 10 wt.%.If the weight content was increased by about 20 wt.%, the impact resistance of the TMS/PNS-VE composite was measured at 16 kJ/m 2 , owing to the increase in load transfer between the fller and matrix.Compared with the impact strength of pure resin, an increase in TMS/PNS of 20 wt.% resulted in a factor of 1.29 percent increase in impact strength.After increasing the fller percentage load from 20 to 25 wt.%, the resistance to the impact of the TMS/PNS-VE composite material shows a signifcant decline, going from 16 kJ/m 2 to 14 kJ/m 2 , suggesting a drop in performance.Tis decrease can be seen when comparing the two values.When there is a larger 6 Advances in Materials Science and Engineering quantity of the fller, this occurrence will take place.When the volume of fller addition is increased in the range of 25-30 wt.%, the impact strength of the TMS/PNS-VE composite gets lowered by as much as 12.8 kJ/m 2 , depending on the specifc situation.Tis will likely occur if the fller is not dispersed equally throughout the matrix.

Heat Defection Test (HDT).
Te heat defection temperature is an important parameter to consider when determining whether or not a material can withstand high temperatures and conditions without becoming deformed; hence, a heat defection temperature test (HDT) is carried out.Figure 8 illustrates the HDT of the TMS/PNS-VE composites at various weight ranges.Te fndings of the graph demonstrate that the HDT value of transparent resin is 55 °C.Te data also indicate that an increasing concentration of pure resin in TMS/PNS increases HDT values.Tis is shown by the fact that the HDT values have increased, which demonstrates the point.Despite increasing fller content to 25 wt.%, after that, the temperature rose to its actual capacity of 83 °C, which is 1.51 times that of the efciency of pure vinyl ester resin.Tis is the case even though the value had previously decreased.Compared with the performance of unaltered vinyl ester resin, which is only 0.75 times more remarkable, this is a highly signifcant diference.Tese data make it abundantly evident that the TMS/PNS fller possesses the most favorable thermal properties of the numerous natural fllers.Tis is the fller that includes acceptable thermal characteristics.

Conclusion
Waste TMS/PNS fller-reinforced hybrid vinyl ester composites were created as part of this work, and their consequent mechanical properties were studied.Following are the conclusions drawn from the fndings of the experiments as a result of the data collected: (1) According to mechanical test results performed on the specimen, the optimal strength in tensile, fexural, and impact was attained with a fller loading of 20 wt.%.(2) Te SEM analysis confrmed that the optimal fller content not only enhances mechanical properties but also ensures uniform fller distribution and strong fller-matrix bonding, which is critical for the structural integrity of composites.(3) Te HDT of the composites reaches its maximum value when they have a fller content of 25 wt.%.(4) A weight ratio of 20 wt.% of the TMS/PNS hybrid fller to VE composites is the optimal weight ratio, as determined by the peak tensile strength value of 40.3 MPa.(5) Te highest bending stress in the fabricated composite, around 142 MPa, is attained when 20 wt.% of hybrid fller is utilized; similarly, the impact strength reaches its peak at this wt.%,which is 16 kJ/m 2 .
According to these fndings, the hybrid fller composite can fabricate lightweight load-carrying applications in structural and domestic felds.Our fndings demonstrate the efectiveness of tamarind seed and peanut shell powder in enhancing the mechanical and thermal properties of vinyl ester composites and highlight the potential of these biowastes in paving the way for more sustainable and environmentally friendly material solutions in various industrial applications.

Figure 1 :Figure 2 :
Figure 1: Infuence of fller loading on the tensile strength of the TMS/PNS-VE composite.

Table 1 :
Te properties of tamarind seed powder, peanut shell powder, and vinyl ester resin used in the study.