Effect of Green Hybrid Fillers Loading on Mechanical and Thermal Properties of Vinyl Ester Composites

The need of eco-friendly materials has been attracted due to renewability, abundance availability, low cost, and so on. Therefore, the search for bio llers for the production of bio-based composite materials is gaining more and more attention in both academic and industry circles because it promotes sustainability. The present study represents the utilization of biomass solid waste in the hybrid form of tamarind seed and date seed powder into polymer reinforced composite which has been explored for the rst time by a compression molding technique. These llers are bio-waste that can be obtained at a minimal cost from renewable sources. An attempt has been made to use these hybrid llers to reinforce with the matrix ranging from 0 to 50 wt.%, and their physical, mechanical, and thermal properties were investigated. In general, the inclusion of hybrid llers increases mechanical properties, although the addition of hybrid llers had only a minor impact on thermal properties. When compared to the pure vinyl ester resin, the hybrid llers reinforced composites revealed a signicant improvement in tensile, exural, impact, and hardness properties, with improvements of 1.51 times, 1.44 times, 1.87 times, and 1.46 times respectively, at 10 wt.% ller loading. Filler matrix interaction of fractured mechanical testing samples was analyzed by scanning electron microscope. Based on the ndings, hybrid ller reinforced composites may be suitable for applications where cost is a consideration and where minor compromises in thermal qualities are acceptable. llers ller mechanical ller DSF) The knowledge gaps properties hybrid ller lled tensile, exural, impact, well, as hardness, on wide range underlying parameters in for their practical application to feasible. the ndings a of llers seed ller DSF) civil physical, mechanical, thermal properties of hybrid llers DSF) reinforced vinyl ester hybrid composites tested


Introduction
Researchers all across the world are attempting to achieve an ambitious objective is to the production of highperformance engineered materials using renewable resources. Due to environmental restrictions as well as new recycling laws for composite materials, manufacturers have been forced into developing innovative new materials derived from renewable resources 1 . Because of their abundant availability and low cost of production, agricultural bio-waste llers serve a critical and signi cant role in reducing environmental restraints while also serving as an outstanding possible replacement for synthetic bre polymer goods 2 . There are more than 50 countries around the world, including India, Bangladesh, Sri Lanka, Thailand, and Indonesia, as well as the Gulf countries, tamarind (Tamarindusindica L.) seeds and date seeds (Phoenix dactylifera L.) seeds are grown. The seeds are underutilized in the majority of regions, despite the fact that there is potential to make them more helpful 3 . We are investigating the possibility of using them as llers in polymer composites as part of our ongoing attempt to increase their monetary value. Among the bene ts of employing these materials are their low density, sustainability (since they are natural renewable resources), biodegradability, and lack of toxicity, making them more environmentally sustainable in terms of recycling and less hazardous to users and consumers 4 . In the early stages of ller reinforced composites research and development, inorganic llers predominated in the majority of the studies and developments. However, while inorganic ller composite materials such as silicon carbide, talc, and calcium carbonate are high-performance materials, they are non-biodegradable. They are derived from non-renewable resources than natural llers. As a result, the usage of natural llers may provide environmental bene ts, in addition to cost bene ts in some cases 5 . Acosta et al. 6 investigated the mechanical and thermal characteristics of the Pecan Nutshell reinforced Poly(lactic acid) composites and found that in comparison to the clean resin, the biocomposites exhibited improved mechanical characteristics such as tensile and exural modulus, as well as fracture toughness.In accordance with the results of the dynamic mechanical study, it has been established that the stiffness of the biocomposites is enhanced when Pecan Nutshell is used.Mittal et al. 7 investigated the Mechanical, Thermal, and Degradation characteristics of the Date Seed llers (DSF) reinforced poly-L-lactide composites. The ndings reveal that the tensile modulus of the DSFbased composites was increased by more than 300 percent in the composite with 40 percent ller content as compared to the composite with neat resin.Rheological characteristics demonstrated that the polymer retained its viscosity behaviour even when added a high quantity of ller.Hybrid composites were materials that comprise two or even more reinforcement components in a single matrix, which is referred to as a matrix composite. The reinforcement may be two separate bres, two distinct ller particles, or bres plus ller particles. These ller and particulate reinforcements with in polymer offer excellent mechanical qualities. Hybrid composites with bio waste and natural ller reinforcement provide two important bene ts: rst, bio waste may be reduced and utilised in a productive way; secondly, good mechanical qualities can be attained through the use of natural ller materials 8 . Nagaraja et al. 9 studied the Physical, mechanical, moisture absorption properties of the Limoniaacidissima shell powder loaded vinyl ester composites and observed the alkaline treated llers with 15 wt.% of ller loading produced better strength. In previous studies, researchers have used various natural llers, i.e., from Rice Husk 10 , walnut shell powders 11 , Thymus moroderi 12 , Walnut shell, Pinewood and Black rice husk 13 , Peanut Shell Powder 14 , Betel Nut Husk 15 , Polyalthialongifolia seed 16 to enhance the mechanical and thermal properties of the polymer composites. A detailed investigation of the impacts of multiple parameters on the mechanical characteristics of hybrid ller composites clearly lacks in the literature, and the mechanical and thermal characteristics of hybrid ller (TSF & DSF) have not yet been explored. The knowledge gaps indicated above demonstrate that the mechanical properties of hybrid ller lled with vinyl ester resin, such as tensile, exural, impact, as well, as hardness, must be evaluated based on a wide range of underlying parameters in order for their practical application to be feasible. We predict that the ndings will provide valuable design inputs for developing a newer generation of hybrid llers (tamarind seed ller (TSF) and DSF) that will be suited for industrial and vehicle applications as well as structural loading applications in civil engineering. The physical, mechanical, and thermal properties of hybrid llers (TSF and DSF) reinforced vinyl ester hybrid composites were explored in the present study. We demonstrated the fabrication of natural llers reinforced hybrid composites and subsequently tested various properties hardness, tensile, exural, and impact properties of the composites. To establish the sustainability of the hybrid composites in various distinct aquatic environments, the moisture absorption characteristics of the composites were investigated as well. Vinyl ester resin was adopted as the matrix material as it is commonly utilized to build hybrid composites and provides high dispersion of reinforcement particles.

Materials
In order to conduct this experimental investigation, a total of 3 kg of date seeds and tamarind seeds were obtained from Manidharma Biotech dealers in Chennai, Tamil Nadu, India. The seeds were cleaned with distilled water to eliminate any excess fruit pulp that had become stuck to them throughout the cleaning process. Tissue paper was then used to wipe away any extra water that had collected on their surfaces. Finally, they were dried for 24 hours at 60°C in an oven. Following milling in a ball mill, a good morphology of 30-60 μm was achieved, making the llers ready to be employed as reinforcement. GSRR Resins And Polymers, Madurai, Tamilnadu, provided the industrial bisphenol-A-epoxy vinyl ester resin (styrene -45 percent), which had a density of 1.145 g/cm 3 , viscosity of 400 cps, and speci c gravity of 1.09, as well as N-dimethylaniline (C 8 H 11 N -promoter), methyl ethyl ketone peroxide (C 8 H 18 O 6 -catalyst) and cobalt 6% naphthenate (C 20 H 34 CoO 4 -accelerator) was employed for curing purposes in accordance with the supplier's recommended ratio. Table 1 shows the chemical composition of TSF and DSF with various llers and bres.

Fabrication of Composites
The compounding of hybrid llers and vinyl ester has been accomplished in this current study using a typical compression molding approach. For specimen manufacturing, different ller loadings ranging between 5 to 50 wt.% were adopted with mould speci cations of approximately 200 mm long, 200 mm wide, and 3 mm thickness. The phases of preparation of the date seed ller are displayed in Fig. 1. Initially, mold removal wax (provided by Carbon black) was added to the inside surface of the mould as well as the covering plate to facilitate the removal of the cured composite plates once they had been cured. And then, a measured quantity of vinyl ester resin was Placed in a container, and 1.5 wt.% of the promoter (10 percent, N-dimethylaniline) was included in the beaker. The beaker was then agitated for another 2 minutes, and the mixture was degassed in a vacuum chamber to eliminate any air bubbles that had penetrated on where stirring procedure. A mixture of equal amounts (1.5 wt.%) of accelerator (3 wt.% Cobalt naphthenate) and catalyst (50 wt.%methyl ethyl ketone peroxide) were introduced one at a time and mixed for 2 minutes before being degassed in a vacuum chamber every after the introduction of accelerator and catalyst. The testing samples are cut from the composite plates that had been produced in accordance with the ASTM D570-99 standard. Rectangular samples with dimensions of 39 x 10 x 3 mm 3 were used in this study. The materials were dried for 24 hours at 105 degrees Celsius in an oven. Following that, they were submerged in water that was at normal temperature. In each sample, three samples were immersed in four distinct watery environments, namely warm water, cold water, seawater, and normal water. The results were compared. Each of the specimens was immersed in water for two hours, twenty-four hours, twenty-four hours, and twenty-four hours at atmospheric temperature, respectively.
Utilizing an electronic weighing balance with a precision of up to 10 -4 g, the weight of every specimen previously they were immersed in water was measured. Before every examination, a wiping cloth was utilized to wipe away the water droplets from the surfaces of all of the specimens once they were removed from the water 20 .
The absorbed water content of each of the specimens was determined using Eq. (1).
Where W t indicates the weight of the sample after a speci c soaking period and W o means the weight of the specimen after being oven-dried.

Results And Discussions
Tensile properties The tensile properties of a material are comprised of tensile strength, elongation at break, and tensile modulus. respectively. Further addition of hybrid ller results in a reduction of both tensile strength and tensile modulus. The surface contact of llers was started con gured when the ller concentration within the composite was more than 10 wt.%, and this formation of contacts was vigorous when the hybrid ller concentration was more than 25 wt.%. The deterioration of strength and stiffness of the hybrid ller reinforced composites were more pronounced beyond the 25 wt.% of ller concentration. This was majorly due to the agglomeration of hybrid llers, which can be easily disrupted by the applied force and leads to material failure. In addition, the crack was started at the ller/matrix interface, and this is more e cient where the llers formed dense colonies. The SEM images con rmed the accumulation of llers when the ller level reaches 25 wt.% (as shown in Fig. 4). Agglomeration tends to reduce the interfacial contact between matrix and llers. This causes a lack of contribution of polymer chain when subjected to mechanical load and reduces the stiffening of material.
However, the elongation during the break of the vinyl ester composite has reached a maximum at 25 wt.% of hybrid ller concentration (as shown in Fig. 3). The reduced elongation of the hybrid composites owing to higher brittleness of the material when the hybrid ller concentration is below 25 wt.%.

Flexural properties:
The exural strength of the material indicates its ability to withstand against applied bending load. The higher exural strength of the material enables its application in the structural eld. The experimented results of vinyl ester hybrid composites are depicted in Fig. 5. The exural strength of hybrid composites was enhanced when the hybrid ller concentration was less than 10 wt.%. Further addition of llers leads to a strength deterioration.
At low ller concentration, good interface bonding between the hybrid ller and the vinyl ester leads to an increase in exural strength from 78 MPa to 112 MPa, which is 1.4 times higher than the pure vinyl ester. It was visualized that the void formation was under control when the hybrid ller concentration was lower than 10 wt.%, and this helped to obtain good load transfer capacity to the hybrid composites. In contrast, a relatively higher void formation was observed when the ller concentration raiesd from 10 wt.% to 50 wt.%. Apparently, higher ller reinforcement (more than 30 wt.%) has produced a signi cant reduction in exural strength and exural modulus. At higher ller concentration, inevitable factors such as agglomeration of llers and air trapped during fabrication are more cause a large reduction in exural properties. This is con rmed through SEM analysis of fractured surfaces (Fig. 6).

Hardness
The results obtained through the measurements of hardness are presented in Fig. 7 for the neat vinyl ester resin, and hybrid llers reinforced vinyl ester composites. The reinforcement of hybrid llers increased the hardness of the vinyl ester signi cantly. The hardness of the neat vinyl ester resin was 26.3, and it was reached the maximum of 38.3 when the hybrid ller concentration was 15 wt.%. An increase in hardness is evident as the concentration of the hybrid ller increases, especially in the low ller concentration level (20 wt.%) lled composites. This was due to the fact that the lignocellulosic natural llers have noticeably higher hardness compared to the soft polymeric matrix. When assessing the wear qualities of such systems, the hardness of the material should be taken into account. In fact, hardness ratings are a measure of wear resistance because hard materials resist friction and wear better. In contrast, the hardness of the sample started to decrease when the ller concentration crossed more than 20 wt.%, and the reduction was noticeable beyond this level. The major reason for a reduction in hardness is an accumulation of llers.
This causes wide variation in hardness at a different locations. It can be noticed that the hardness of the samples revealed similar increase and decrease behavior compared to tensile and exural tests.

Impact strength
The impact test was carried out until the impact samples were broken. resin. This could be due to the low quantity of ller is added to the composites. The impact strength is low 17,21 . For 10 wt.% ller content, the strength of TSF/DSF-VE composites is increased when compared to 5 wt.%. Signi cantly, the ultimate impact strength of PLSF-VE composites exhibited 22 KJ/m 2 at a higher TSF/DSF-VE weight content of 10 wt.%, due to high load transferred between ller and vinyl ester matrix. The impact strength increases 1.87 times when the resin is pure to an increase of 10 wt.% of TSF/DSF. Furthermore, when the ller content is raised from 10 to 20 weight percent, the impact strength of a TSF/DSF-VE composite materials is moderately reduced from 22 KJ/m 2 to 19 KJ/m 2 , indicating a slight reduction in performance. Impact strength of PLSF-VE composites has been reduced by up to 10 KJ/m 2 once the ller volume fraction is raised from 20 to 50 wt. percent, as has been demonstrated previously. That might be due to an irregular dispersion of the ller between the matrix.

Heat De ection Temperature Tests
HDT is a critical parameter for a material's ability to be able to resist extreme conditions ambient temperatures without de ection. The heat de ection temperature of the TSF/DSF-VE composites at different weight percentages are illustrated in Fig. 8; from the results of the graph, demonstrates that clear resin has an HDT value of 53℃. The result shows that in addition to the pure resin to TSF/DSF, the HDT values are improved. The value was then increased to 68°C, which is 1.28 times more than the performance of virgin vinyl ester resins while adding ller content to 15 wt.%. These results clearly show that TSF/DSF ller has good thermal characteristics among different natural llers. Moreover, after 15wt.% to 50wt.% ller weight the hardness value was decreased from 65 0 C to 40°C. The Heat de ection temperature of the TSF/DSF ller composite is superior to the Banana Ribbon Rope Straight Mat strengthened polyester, tamarind seed ller loaded vinyl ester and Date palm ller reinforced vinyl ester composites 21 , 18 . Water absorption behavior Figure 9 depicts the percentage of moisture absorption curves for hybrid ller-loaded vinyl ester composites. Each data point re ects the mean value of three specimens with varying ller loadings after soaking in normal, cold, salt hot water. The observed result of increasing the hybrid ller loading resulted in an increase in the water absorption percentage because of the hydrophilic character of the ller material, as shown in Figure 9. A similar trend was seen in tamarind seed ller/vinyl ester composite 2 , and date seed ller/vinyl ester reinforced composites 3 . Because of the hydrophobic characteristic of the resin, there was 0% water absorption for the neat vinyl ester resin in the four different environments indicated above. The hot water atmosphere absorbed higher moisture than the other three conditions. The hot water enhanced the hybrid ller/vinyl ester composites diffusivity. As a result, micro-cracks formed in the ller-matrix interface area. For the above 35 wt.% of ller loading, the water absorption rises at times, most likely due to the hydrophilic nature of the bio-based llers. However, due to the presence of big salt (particularly sodium chloride) molecules in seawater, the saltwater environment had lower moisture absorption relative to the other three environments. Because of the delayed penetration of big molecules into the composites, the moisture absorption percentage was the lowest.

Conclusion
In this research work, waste hybrid ller reinforced vinyl ester composites were fabricated and analyzed their mechanical properties. The following conclusions were drawn based on experimental outcomes.
The mechanical property results like tensile, exural, impact, Barcol hardness of the composites show an optimal strength at 10wt.% of ller content.
The Barcol hardness and HDT of the composites show an optimal strength at 15 wt.% of ller content.
The highest tensile strength of a material is 37 MPa occurs at 10 wt.% of the hybrid ller added comparatively higher than TSF/VE composites.     Fractured surface morphology of tensile tested sample contain 25 wt.% hybrid ller.     Heat de ection temperature against % of TSF/DSF loaded VE composite.

Figure 9
The effect of processing on moisture absorption vs ller quantity in TSF/DSF-lled VE composites.