1. INTRODUCTION:

The increasing environmental awareness and the exhaustion of fossil fuel reserves have initiated a paradigm shift in favour of renewable and biodegradable substitutes of petrochemical surfactants and solvents. Some of the possible promising renewable feedstocks include vegetable oils and their derivatives which are biodegradable, low in volatility, less toxic and have higher flash points, which can be used in home care, cosmetics, agrochemicals, and fuel systems.^1-3

The Jatropha oil is one of the non-edible sources that have been found to contain a sustainable raw material that is rich in long-chain triglycerides which are converted into fatty acid methyl esters (FAMEs) and bio-based surfactants. FAMEs is a product that is formed after the transesterification process and has recently been considered as the green solvents due to low volatile organic compounds (VOC) emissions, biodegradation and good solvency in relation to the traditional aromatic hydrocarbons.^4-6 Their ester functionality and hydrophobic tail make them highly compatible with surfactant systems and active ingredients in multifaceted formulations.⁷

Microemulsions are thermodynamically stable, clear, and isotropic combinations of oil, water, surfactant than co-surfactant. They have unparalleled solubilization, cleaning and delivery properties due to their ultralow interfacial tension and nanometric sized droplets which have been utilized in home-care cleaners, agrochemical emulsions and cosmetic formulations.^11-13 However, the conventional microemulsion systems are more based on the use of petroleum-based surfactants and hydrocarbon solvents, which make them toxic and poorly biodegradable to the environment. The recent evidence has shown the practicability of vegetable oil-based microemulsions which makes use of methyl ester sulfonates (MES), fatty alcohol ethoxylates, and long surfactants with propoxy or ethoxy linker which improves the solubilization of polar and non-polar domain.^2,3,9,14 These bio-based surfactants permit the creation of stable and clear microemulsions between renewable oil phases, and generate cleaner and carrier alternatives to the petrochemical. These formulations have very good interfacial tension reduction and rheological properties can be tuned; therefore, they can be used in any industry. In addition, they are biodegradable and have low toxicity profiles that are in line with strict environmental standards. Ongoing studies are aimed at developing the maximum optimization of the structure of surfactants to provide better performance, and remain sustainable. The latest development in vegetable oil based microemulsions has taken advantage of methyl ester sulfonates (MES) and fatty alcohol ethoxylates and extended surfactants with propoxy or ethoxy linkers to obtain superior solubilization in both polar and non-polar phases.^15-16 The resulting bio-based surfactants enable the development of clear and stable microemulsions containing renewable oil phases, which makes them potential straight replacements of cleaners and carriers based on petrochemicals in terms of sustainability. Their capacity to greatly minimize interfacial tension and provide adjustable rheological characteristics highlights the versatility of these formulations and their adaptation to the desired needs of different industrial applications including home care and agrochemical usage.^17-20 Besides their functional performance, these microemulsions have desirable environmental properties, such as biodegradability and low toxicity, which matches the continually high regulatory requirements to reduce the ecological impact. Current studies are also focused on the fine tuning of the surfactant molecular structures to achieve better performance features without compromising on the sustainability properties. This involves the investigation of new linker chemistry and surfactant structures that improve the stability of microemulsions and efficacy without sacrificing biodegradability, which will advance the design of green solvent systems that are consistent with the global trends toward environmentally friendly formulation technologies. Methyl esters have been developed in the home and institutional cleaning industries as a green solvent in degreasers, surface cleaners, and rinse-aids as co-emulsifiers. The combination of palm- or Jatropha-derived MES and FAMEs (vegetable oil-based) has proven to be very detergent, fast in eliminating soil, and with fewer environmental impacts.^2,3,8 Researchers that followed e.g. Ismail et al. (2011) and Sailah et al. (2021) validated that palm methyl ester-based microemulsions exhibit good emulsification capabilities and cleaning efficacy in comparison to hydrocarbon-based systems.^2,3 These bio-based solvents can also lead to a better biodegradation and reduce toxicity, which are in favour of more environmentally sustainable solvents. Their affinity with different surfactant systems allows them to be formulated into stable microemulsions that can be utilized under a range of different conditions. Therefore, these innovations enable the substitution of the traditional petrochemical solvents in cleaning products with more sustainable ones.

In agrochemical industry, FAMEs have also been used as carrier solvents in emulsifiable concentrate (EC) pesticides preparations in place of dangerous aromatic solvents such as xylene and naphtha.¹⁰ Tran et al. (2021) prepared cypermethrin EC with the help of methyl esters, and the emulsion level and storage characteristics were excellent. It has been verified in the study that methyl esters enhance dispersion and wetting properties and reduce environmental toxicity. On the same note, Zaratti et al. (2024) showed that FAMEs may be assumed to be applied as a replacement of mineral spirits and ligroin in cleaning and conservation, as they tend to be as solvency-wise like these two solvents and are, in fact, non-toxic.^10-11 In more recent times, studies in green chemistry have focused on the development of microemulsions systems based on bio-derived surfactants and renewable solvents such as FAMEs to create fully biobased microemulsions to use as surface care, Agro formulations and fuel emulsions. Such systems are consistent with the UN Sustainable Development Goals (SDG 12: Responsible Consumption and Production) and the EU Green Deal, in the context of which the product innovation of the circular economy is supported.^11-12 Although there have been major advancements in the use of palm-based fatty acid methyl esters (FAMEs), minimal studies have been channeled at Jatropha oil-based surfactants and Jatropha oil-based methyl esters to be used in designing renewable microemulsions. Jatropha products, which are non-edible, and which are abundant in the region, provide a viable and sustainable feedstock. It has a distinctive fatty acid composition, making it possible to produce tunable HLB surfactants with a high interfacial activity, which when combined with the vegetable oil methyl esters as the oil phase can produce microemulsions with improved solubilization and phase stability and environmental compatibility.^23-25

In this paper, the design and total characterization of renewable microemulsion systems working with ethoxylated surfactants made of Jatropha oil and vegetable oil methyl esters, i.e. the ones obtained as a result of the Jatropha and Karanja oils, are considered. The study will involve physicochemical characterization of the methyl esters to determine their appropriateness as renewable oil phases, analysis of Jatropha ethoxylates with different hydrophilic-lipophilic balance (HLB) values as bio-based emulsifiers, and pseudo-ternary phase diagrams to map the area of microemulsions formation. The designed systems are also described based on droplet size, pH, conductivity, and density and then long-term stability is evaluated using centrifugation and storage test.

2. MATERIALS AND METHODS:

2.1. Materials:

Jatropha oil derived surfactants, namely Jatropha oil ethoxylate-15EO (HLB = 9.7) and Jatropha oil ethoxylate-20EO (HLB = 11.7). The oil phase used in the study comprised Jatropha oil methyl ester and Karanja oil methyl ester gifted by Rossari Biotech Ltd., Mumbai, India all obtained from Analytical-grade reagents were procured from standard suppliers and used as received. All materials were of analytical reagent (AR) grade unless stated otherwise.

2.2. Methods:

2.2.1. Characterization of Vegetable Oil Methyl Esters:

The physicochemical properties of Jatropha oil methyl ester and Karanja oil methyl ester were determined using standard AOAC and AOCS procedures. Parameters such as acid value, saponification value, iodine value, and specific gravity were evaluated to assess purity and oxidative stability. The fatty acid composition was analysed using gas chromatography (GC-FID).

2.2.2. Characterization of Jatropha Oil Derived Surfactants:

The synthesized Jatropha oil ethoxylates (15EO and 20EO) were characterized to confirm their suitability as emulsifiers. Appearance, specific gravity, and HLB values were determined following standard non-ionic surfactant characterization protocols, Surface tension was measured at 25±1°C using a Du Noüy ring tensiometer These measurements provided insights into the emulsification capacity, surface activity, and compatibility of the surfactants with the selected oil phases.

2.2.3. Preparation of Microemulsions:

Pseudo-ternary phase diagrams were constructed at ambient temperature (25±1°C) using the aqueous titration method. The oil phase (individual or blended JME and KOME) was combined with the surfactant system at weight ratios ranging from 0:10 to 10:0 (oil: surfactant). Deionized water was added dropwise under gentle stirring until turbidity appeared, indicating the phase boundary. The weight fractions of oil, surfactant, and water at the turbidity point were recorded and plotted on the pseudo-ternary diagram. The microemulsion region was identified as the transparent and isotropic area on the phase diagram. Selected formulations within this region were subjected to detailed physicochemical evaluation.

2.2.4. Characterization of Microemulsion Formulations:

The optimized microemulsions were characterized for physicochemical properties, droplet size, and stability to evaluate their suitability as renewable formulations.^16-17

A) Appearance and Clarity: Visual observation at 25 °C was performed to assess transparency, homogeneity, and absence of phase separation.

B) pH Measurement: The pH of each formulation was determined in triplicate using a digital pH meter (Equiptronics EQ-621, India) calibrated with standard buffer solutions (pH 4.0, 7.0, and 9.0).

C) Particle Size and Polydispersity Index (PDI): Determined by Dynamic Light Scattering (DLS) using a Mastersizer 3000 Hydro (Malvern Panalytical, UK) to evaluate droplet uniformity and stability.

D) Electrical Conductivity: Measured using a conductivity meter (LMCM20, Labman Instruments, India) to distinguish between oil-in-water (O/W) and water-in-oil (W/O) systems.

E) Stability Testing: Microemulsions were stored for 30 days at 25 ± 2 °C and evaluated at regular intervals for changes in pH, particle size, viscosity, and conductivity. Centrifugation at 3,000 rpm for 30 min was carried out to assess thermodynamic stability and resistance to phase separation.

3. RESULTS:

3.1 Characterization of Methyl ester

Table -1: - Physicochemical parameters of methyl ester

Sr.No	Parameter	Jatropha oil methyl ester	Karanja oil methyl ester
1	Physical appearance	Clear Yellow liquid	Clear Yellow liquid
2	Specific Gravity	0.870	0.875
3	Acid Value	0.12	0.16
4	Iodine Value	94	81
5	Saponification value	189	185
6	Viscosity (mm²/s at 40°C)	4.4	4.6

Table -2: - Fatty acid composition of methyl ester

Sr.no	Fatty acid Composition	Jatropha oil methyl ester	Karanja oil methyl ester
1	Palmitic caid	17.717	9.946
2	Stearic acid	3.344	7.170
3	Oleic acid	52.744	57.778
4	Linoleic acid	22.008	3.974

Table -3: - Physicochemical parameters of Surfactant

Sr.no	Parameter	Jatropha oil ethoxylated 15 moles	Jatropha oil ethoxylated 20 moles
1	Physical appearance	Clear yellow Viscous liquid	Clear yellow Viscous liquid
2	pH (5% solution)	6.7	6.9
3	Saponification value	136	105
4	Moisture content	0.5	0.55
5	HLB value	9.7	11.7
6	Surface tension	44.32	41.44

Figure 1 GC Gof Karanja Oil Methyl Ester

Figure 2 GC of Jatropha Oil Methyl Ester

Figure 3 Ternary Diagram JOME HLB 9.7

Figure 4 Ternary Diagram JOME HLB 11.7

Figure 5 Ternary Diagram KOME HLB 9.7

Figure 6 Ternary Diagram KOME HLB 11.7

4. DISCUSSION:

4.1 Physicochemical Properties of Methyl Esters:

The characterization data presented in Tables 1 and 2 reveal that both Jatropha oil methyl ester (JOME) and Karanja oil methyl ester (KOME) exhibit physicochemical properties suitable for use as renewable oil phases in microemulsion formulations. The specific gravity values (0.870 for JOME and 0.875 for KOME) are slightly lower than water, typical of fatty acid methyl esters, and consistent with values reported for other vegetable oil-derived FAMEs. These density characteristics facilitate formulation versatility, allowing both oil-in-water (O/W) and water-in-oil (W/O) microemulsion formation depending on surfactant selection and composition ratios. The low acid values (0.12 and 0.16 mg KOH/g for JOME and KOME respectively) indicate high purity and minimal free fatty acid content, confirming effective transesterification and purification processes. Low acidity is crucial for formulation stability, as free fatty acids can interact adversely with surfactants, particularly cationic species, and may contribute to oxidative degradation during storage. The saponification values (189 and 185 mg KOH/g) are consistent with expected values for C16-C18 fatty acid methyl esters, providing further confirmation of molecular composition. The iodine values differ notably between the two methyl esters, with JOME showing higher unsaturation (IV = 94) compared to KOME (IV = 81). This difference correlates with the fatty acid compositional analysis (Table 2), which reveals that JOME contains higher proportions of polyunsaturated linoleic acid (22.01%) compared to KOME (3.97%). The higher unsaturation in JOME may confer superior solvency characteristics for certain pesticide active ingredients and cleaning agents, as unsaturated bonds increase molecular polarity and electron density. However, this also implies greater susceptibility to oxidative degradation, necessitating consideration of antioxidant addition for long-term storage stability in commercial formulations. Both methyl esters exhibit moderate viscosity (4.4–4.6 mm²/s at 40°C), which is advantageous for processing, pumping, and spray application in agrochemical and cleaning formulations. The similar viscosity profiles suggest comparable flow behavior and droplet formation characteristics during emulsification processes. The fatty acid composition analysis confirms that oleic acid (C18:1) represents the predominant fatty acid in both methyl esters (52.74% in JOME and 57.78% in KOME). This monounsaturated fatty acid provides an optimal balance between oxidative stability and the capacity for solvency. The presence of significant palmitic acid (C16:0) content, especially in JOME (17.72%), contributes to resistance to solidification at lower temperatures, which is important for cold-climate applications.

4.2 Characterization of Jatropha Oil-Derived Surfactants:

The properties of the Jatropha oil ethoxylates characterized in Table 3 are consistent with effective nonionic surfactants for the stabilization of microemulsions. The increased number of ethylene oxide units raises the hydrophilicity, thus increasing the HLB value from 9.7 for 15EO to 11.7 for 20EO. This is a fundamental difference because surfactants with HLB values of about 9-10 usually give W/O microemulsions, while those with HLB > 11 stabilize O/W systems preferably. Surface tension measurements give 44.32 mN/m for 15EO and 41.44mN/m for 20EO, showing good surface activity for both, yet the higher ethoxylate displayed better surface tension reduction. Improved surface activity translates into enhanced interfacial adsorption and, therefore, more efficient reduction of oil-water interfacial tension, which is a critical requirement for microemulsion formation. The recorded surface tension values are comparable or even lower than many commercial non-ionic surfactants; this underlines the possibility to consider ethoxylates derived from Jatropha as a bio-based emulsifier. Saponification values decrease with increasing ethoxylation degree, from 136 for 15EO to 105 for 20EO, corresponding to the dilution effect due to the non-saponifiable ethylene oxide chains. This characteristic represents a useful quality control parameter for assessing the extent of ethoxylation in bio-based surfactant manufacturing.

4.3 Phase Behavior and Pseudo-Ternary Phase Diagrams:

The pseudo-ternary phase diagrams (Figures 3-6) provide important information on the composition windows that give stable microemulsions for each oil-surfactant combination. A number of key observations arise from the phase diagrams:

Influence of Surfactant HLB:

For both the JOME and KOME systems, the higher HLB surfactant at 11.7 generates larger microemulsion regions than that with lower HLB at 9.7. The extended domain of microemulsions means that the more hydrophilic surfactant has greater robustness and flexibility in formulation. The larger microemulsion region observed with HLB 11.7 insinuates better interfacial tension reduction and greater tolerance to compositional variations in practice, which is highly desirable from the perspective of commercial formulation where variability of ingredients cannot be completely avoided.

Oil Phase Comparison:

KOME-based systems appear to exhibit slightly larger and more regularly shaped microemulsion regions compared to JOME systems, particularly with the HLB 11.7 surfactant. This may reflect differences in fatty acid composition, specifically the lower polyunsaturated fatty acid content in KOME, which could influence interfacial packing and curvature. The higher oleic acid proportion in KOME (57.78% versus 52.74%) may also contribute to more favourable surfactant-oil interactions.

Water incorporation capability:

Phase diagrams show high water incorporation capability for a wide range of oil-surfactant ratios, thus making formulatory attempts for concentrated cleaning products and agrochemical formulations with considerable aqueous phase content possible. This property is important for the potential to reduce volatile organic compound emissions and further improve the environmental profiles of the final products.

Optimal Formulation Zones:

The triangular microemulsion regions suggest optimal formulations at a medium surfactant concentration, typically within the 20-50% by weight range with balanced oil-water ratios. The formulations at the apex (high surfactant concentration) could be economically unviable despite their stability, while the ones in the vicinity of phase boundaries may be unstable under storage conditions or temperature variations.

4.4 Characterization and Performance of Microemulsions:

The results shown in Table 5 indicate the formation of both O/W and W/O microemulsions in all the formulated systems, with clear physicochemical signatures that distinguish both microemulsion types:

Electrical Conductivity as Type Indicator:

The most reliable indicator of microemulsion type is electrical conductivity. O/W microemulsions consistently exhibit high conductivity (244-370 μS/cm) due to continuous aqueous phase enabling ion mobility, while W/O systems show dramatically lower conductivity (89-110 μS/cm) reflecting the insulating nature of the continuous oil phase. This clear conductivity demarcation confirms successful formation of both microemulsion types and validates the HLB-based prediction of preferred emulsion structure.

Particle Size Distribution:

All formulated microemulsions exhibit particle sizes in the 101-178 nm range, characteristic of true microemulsions and substantially smaller than conventional emulsions (typically >500 nm). The nanometric droplet dimensions confirm thermodynamic stability and explain the optical transparency observed in these systems. Notably, KOME-based formulations with HLB 11.7 surfactant produced the smallest droplets (101.2-110.2 nm for O/W systems), suggesting optimal interfacial curvature and packing efficiency. The smaller droplet size correlates with enhanced stability and improved performance in applications requiring deep penetration or rapid spreading.

Influence of HLB on Microemulsion Characteristics: Comparing formulations prepared with different HLB surfactants reveals systematic trends. The HLB 11.7 surfactant consistently produces O/W microemulsions with higher conductivity and smaller particle sizes compared to HLB 9.7 formulations. This reflects the greater hydrophilicity favoring aqueous phase continuity and more efficient interfacial curvature toward oil phases. For agrochemical EC formulations, the O/W microemulsions formed with HLB 11.7 are particularly advantageous as they readily disperse in spray tank water without requiring additional emulsification energy.

4.5 Stability Assessment and Long-Term Performance:

The centrifugation stability of all the formulated microemulsions, as gathered from Table 6, depicts very good thermodynamic stability. The fact that no phase separation was observed upon centrifugation at 3000 rpm for 30 minutes confirms that true microemulsion rather than kinetically stabilized conventional emulsion had been formed. This resistance to mechanical stress is essential in agrochemical formulations that would be subjected to transportation vibration and mixing operations and also in cleaning products that may experience repeated handling. The storage stability over 30 days at ambient temperature (25 ± 2°C) further confirms practical viability of these renewable microemulsion systems. Maintaining stability in the absence of observable phase separation, creaming, or property drift during this period serves as an indication that these formulations would be able to withstand regular storage conditions in commercial practice. This stability performance is remarkable in particular because this is achieved in the absence of conventional petroleum-based cosolvents or stabilizers, attesting that such performance could indeed be matched or bettered with the bio-based components. The stability across both O/W and W/O microemulsion types offers versatility in applicability. O/W microemulsions are specifically suitable for agrochemical EC formulations designed for tank-mix dilution and for water-based cleaning products. W/O microemulsions may find applications in protective coating systems, water-resistant formulations, and specialized cleaning applications requiring water containment within oil-continuous matrices.

4.6 Implications for Agrochemical and Home Care Applications:

Throughout this study, renewable JOME and KOME-based microemulsions exhibited excellent stability, nanometric droplet size, near-neutral pH, and high biodegradability, proving their dual potential both in agrochemical and home care applications. In agrochemical formulations, such O/W microemulsions, optimized with an HLB 11.7 surfactant, can be used to replace hazardous aromatic solvents conventionally used in pesticide EC formulations. In this respect, they yield fine spray droplets after proper dilution with superior spreading, adhesion, and foliar uptake, enhancing their biological efficacy, rain fastness, and environmental safety. In home care and cleaning formulations, the methyl ester oil phase provides strong solvency for lipophilic soils, while rapid emulsification and dispersion are favored by the surfactant system. The near-neutral pH ensures compatibility with pH-sensitive actives and offers improved dermatological safety. W/O microemulsions offer opportunities for innovative waterless cleaners and surface treatment products. Fully biodegradable, nontoxic, solvent-free systems based on these microemulsions will be able to make a contribution to sustainable development through the reduction of toxicity and improvement in performance, offering a renewable alternative to petroleum-derived ingredients for both agrochemical and household cleaning formulations.

5. CONCLUSION:

This experiment allowed showing the effective design and characterization of renewable microemulsions systems when Jatropha and Karanja oil methyl esters were used as bio-based oil phases. Physicochemical assessment was used to classify the appropriateness of these ingredients, and the density, viscosity, and fatty acid profiles were found to be appropriate. Well-defined regions of microemulsion were indicated in pseudo-ternary phase diagrams in which the HLB 11.7 surfactant produced larger and more stable zones of formulations. The systems developed had particle sizes of 101-178 nm, almost neutral pH (7.5-7.75) and were very stable in centrifugation and 30 days storage. Microemulsions of KOME surfactant were most effective at HLB 11.7 because this yielded the smallest particle sizes and greatest conductivity, indicating the best interfacial stabilization, especially in oil-in-water emulsions which could be used in agrochemical preparation. These greener microemulsions introduce greener alternatives to petroleum-based solvents, which are in line with green chemistry and circular economy. They have great potential of application in agrochemicals and home care preparations. Temperature stability, compatibility of active ingredients, scale-up and economic assessment should be added to work with in the future. On the whole, the current research confirms a strong model of a high performance and sustainable system development of microemulsions based on non-edible vegetable oil feedstocks contributing to the shift toward the environmentally sound formulation technologies.

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Received on 07.11.2025 Revised on 12.12.2025

Accepted on 09.01.2026 Published on 10.04.2026

Available online from April 13, 2026

Asian J. Research Chem.2026; 19(2):89-96.

DOI: 10.52711/0974-4150.2026.00015

This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License. Creative Commons License.

Sr. No	Formulation	HLB	Type of emulsion	pH	Density	Conductivity	Particle size
1	JOME-1	HLB 9.7	O/W	7.50	0.998	244.10	121.90
2	JOME -2	HLB 9.7	W/O	7.66	0.999	110.11	155.3
3	JOME -3	HLB 9.7	O/W	7.61	0.993	290.20	178.3
4	JOME -4	HLB 9.7	W/O	7.64	0.995	101.25	167.30
5	KOME-1	HLB 11.7	O/W	7.75	0.994	350.25	110.2
6	KOME-2	HLB 11.7	W/O	7.71	0.997	89.34	135.6
7	KOME-3	HLB 11.7	O/W	7.72	0.996	370.31	101.2
8	KOME-4	HLB 11.7	W/O	7.69	0.992	92.34	103.4

Sr. No	Formulation	HLB	Centrifuge stability Before	Centrifuge stability After 30 days
1	JOME-1	HLB 9.7	Stable	Stable
2	JOME -2	HLB 9.7	Stable	Stable
3	JOME -3	HLB 9.7	Stable	Stable
4	JOME -4	HLB 9.7	Stable	Stable
5	KOME-1	HLB 11.7	Stable	Stable
6	KOME-2	HLB 11.7	Stable	Stable
7	KOME-3	HLB 11.7	Stable	Stable
8	KOME-4	HLB 11.7	Stable	Stable