Hansen Solubility Parameter-Guided Binary Solvent Extraction of Sugarcane Wax from Agro-Industrial Byproducts: A Sustainable Biomass Valorization Approach

Abstract

Here, we report a comprehensive study on the extraction and characterization of sugarcane wax obtained from sugar industry byproducts, primarily bagasse and press mud. These agro-residues represent a renewable and sustainable source of natural wax with significant industrial potential. Sugarcane wax is a high-value bioproduct with versatile applications in food, pharmaceuticals, cosmetics, and biodegradable coatings. The extraction process was optimized using Hansen solubility parameters to identify efficient single and binary solvent systems. Among the studied feedstocks, press mud consistently produced higher wax yields than bagasse. Toluene alone yielded 7.45 ± 0.29% wax, whereas a mixture of turpentine oil (TO):Toluene (20:80 v/v) significantly enhanced extraction efficiency, providing 11.98 ± 0.32% crude at a 1:20 sample-to-solvent ratio with 3 h of extraction time. FTIR showed a strong ester carbonyl band at 1735 cm^–1, while GC–MS confirmed the presence of octacosanol, β-sitosterol, n-hexadecenoic acid, and cuminaldehyde. XRD displayed a semicrystalline peak at 2θ (21.5°), verifying ordered hydrocarbon chains. TGA analysis indicated improved stability, with binary extracts retaining 9.2% residue at 600 °C. Physicochemical evaluation showed a reduced acid value (12.5 mg KOH g^–1) and enhanced wettability. Greenness assessments reinforced the eco-friendly nature of the process, yielding an analytical eco-scale score of 79. Collectively, these results establish TO:Toluene binary extraction as a high-efficiency and environmentally friendly approach for producing high-quality sugarcane wax with strong potential in edible coatings, biodegradable packaging, and other industrial applications.

1. Introduction

In recent decades, significant advancements in extraction and sample preparation methods have been developed in the scope of green analytical chemistry, focusing on enhancing extraction efficiencies and minimizing environmental impact. In response to growing environmental concerns and resource scarcity, biobased solvents have emerged as sustainable substitutes for petroleum-based solvents, which discharge over 20 million tons of volatile compounds annually from industrial processes. The 12 principles of green chemistry address critical environmental challenges such as pollution, waste, energy demand, and workplace safety. Green solvents, including ionic liquids, supercritical CO₂, biosolvents, organic carbonates, deep eutectic solvents, and terpenoid-based solvents like limonene and turpentine oil (TO), have been proved to be alternatives to the use of petroleum-based solvents in extraction of bioactive compounds, with comparable efficiency but less toxicity. TO, a renewable byproduct of pine trees, is primarily composed of terpenes and terpenoids (C₁₀H₁₆) and has proven to be a potential alternative to n-hexane, aligning with green chemistry principles and supporting sustainable industrial practices. In the food industry, the recovery of natural compounds is increasingly being evaluated using tools such as the Analytical Greenness Metric (AGREE), the National Environmental Methods Index (NEMI), and the Analytical Eco Scale (AES). Considering advancements in green extraction techniques, Hansen Solubility Parameters (HSPs) are particularly notable for their ability to predict solvent–solute interactions in a wide range of applications. The HSP theory estimates solubility and compatibility by analyzing their atomic dispersion forces (δ_D), molecular dipolar interactions (δ_P), and hydrogen-bonding forces (δ_H). Based on these parameters, the compatibility of a solvent can be calculated by using the Relative Energy Difference (RED) value, which represents the distance between the solvent and solute in Hansen solubility space and distinguishes incompatible solvents from compatible ones. According to HSP theory, a solvent is considered “good” when RED < 1, while solvents with RED ≥ 1 are considered “poor”. This approach is particularly useful in selecting optimal solvent mixtures for natural product extraction. HSPs have been applied to a diverse range across multiple fields, including pharmaceuticals, corrosion inhibitors, predicting green solvents for organic photovoltaics, and the extraction of phytochemicals. Their use has also been reported in determining HSPs of natural waxes and oils such as rice bran wax, sugarcane wax (SCW), and sugarcane oil. Recent studies have further demonstrated the applicability of HSP theory in the determination of HSPs of refined SCW and the interpretation of extraction behavior using ethanol as solvent.

The sugarcane agro-industry is of prime importance in Pakistan, with an estimated production of approximately 87.60 million metric tons in 2023–2024. Large quantities of byproducts are produced during sugar processing, primarily bagasse (BG) and press mud (PM). BG is a fibrous residue often used for the production of electricity, while PM is collected during juice clarification processes and is mainly used as a soil conditioner for agricultural lands. , The unprocessed disposal of these byproducts has substantial adverse impacts on the air (e.g., emissions from open burning and decomposition), water, and soil ecosystems. SCW, a value-added product obtained from sugar industry byproducts, holds significant commercial potential with diverse applications in pharmaceuticals, agriculture, food, and cosmetics, contributing to Pakistan’s bioeconomy. Its hydrophobic and barrier properties, i.e., resistance to moisture transfer and gas permeability, like other natural waxes, further enhance its suitability for industrial uses such as edible coatings and protective formulations. − SCW is a mixture of fatty acids, alcohols, aldehydes, sterols, and esters, including long-chain aliphatic primary alcohols (policosanols), known to reduce cholesterol levels, inhibit platelet aggregation, protect against osteoporosis, and exhibit anti-inflammatory and antiviral actions. With several phytochemicals of nutritional and functional value, SCW is considered a viable alternative to carnauba wax and candelilla wax in edible coatings, which enhance the postharvest quality of fruits and vegetables. The protective properties of these coatings can be further enhanced by incorporating additives such as antioxidants. A literature survey reveals that SCW has been extracted using a wide range of polar and nonpolar solvents, with reported yields of 0.5–4.1% from BG, 3.8–87.3% from PM, 64.45% from peels, and 16–25% from oilcane waste (Table ). The variation in reported yields could be attributed to differences in feedstock composition, solvent type, and extraction technique. Some studies reported extremely high recoveries of SCW; the value often represents crude wax yield obtained and may include large components of coextracted lipophilic molecules along with the targeted SCW. For instance, Mtolo et al. reported crude wax yields of 80–87% using solvent extraction; however, an additional purification step is required to obtain refined wax. Although many researchers have calculated HSP values for various solvent systems, only a few have applied these beyond theoretical predictions. The use of binary solvent systems can improve selectivity and efficiency since green solvents often possess distinct properties that enhance the solubility of specific compounds. Despite these advancements, most studies rely on theoretical predictions of HSPs or focus on extraction using single solvent systems. The practical application of HSP-guided binary solvent systems for the selective extraction of SCW remains largely unexplored. Limited studies have been conducted on HSP-based solvent screening with experimental validation using single and binary green and nongreen solvent systems for SCW extraction from both feedstocks. This gap is addressed in the present work through systematic HSP-guided solvent design and experimental validation.

1. Reported Yields of SCW from Sugar Industry By-Products Using Single and Binary Solvent Systems.

Extraction technique	Solvent(s)	% Yield	Year	ref
Bagasse (BG)
Soxhlet	Acetone	0.9	2015
	Hexane	1.69	2021
		0.6
		0.5	2015
	Ethanol:Petroleum Ether (1:1)	1.20	2016
	Methanol:Benzene (1:2)	4.1	2019
Soxtec	Acetone	1.0	2022
	Ethanol	1.97
	Dichloromethane	1.14
	Ethyl acetate	1.0
Press mud (PM)
Soxhlet	Toluene	4.79	2020
		85.0	2022
		5.4–5.6	2012
		14.55	1984
		5.5	2002
	Hexane	41.3	2002
		5.4–5.6	2021
		2.52	2020
		9.03	2016
	Dichloromethane	7.67	2020
	Ethanol	4.81
	Turpentine oil	81.	2022
	Butanol	87.3
	2-Butanone	85.
	Benzene	6.9–7.4	2012
		5.5	2002
	Isopropyl alcohol	4.76	1948
	Carbon tetrachloride	5.2	2002
	Refined alcohol	12.65	1984
	Gasoline	13.05
	Gasoline fraction	13.06
	Naphthalene	14.05
	Denatured alcohol	13.09
Soxtec	Ethanol	16.7	2023
	Ethanol:Water (1:1)	3.83
Accelerated Solvent Extraction (ASE)	Ethanol	13.32	2016
Supercritical Fluid Extraction (SFE)	Ethanol	5.46	2016
		4.75	2019
Melt extraction	-	56.0	2022
Sugarcane Peels
Soxhlet	Limonene	64.45	2022
Oilcane waste mud
Soxhlet	Hexane	25.6 ± 0.2	2024
	Ethyl acetate	16.6 ± 0.4

This study, therefore, aims to determine the HSP and RED values of commonly used nongreen solvents and evaluate their suitability for the growing need for an economically viable SCW extraction. The best-performing nongreen solvents were then combined with the green solvent “TO” to form a binary solvent system, leading to a more selective and efficient process with reduced environmental impact. The HSP-guided solvent design was further validated experimentally using both single and binary solvent systems for the extraction of SCW from both feedstocks. This provides a practical framework for selective and sustainable SCW recovery. Although TO is classified as an irritant, it is widely used in food and cosmetic formulations, and its biobased origin and relatively low environmental persistence contribute to reduced environmental impact. Moreover, the International Agency for Research on Cancer (IARC) classifies TO as “not classifiable as to its carcinogenicity to humans” (Group 3), indicating limited evidence of harmful long-term effects. Together, these attributes and favorable solubility behavior guided by HSPs demonstrate the potential of binary extraction systems as a sustainable approach for SCW recovery, particularly for edible coating applications. This study aligns with three United Nations Sustainable Development Goals (SDGs): Good Health and Well-Being (SDG 3), Industry, Innovation and Infrastructure (SDG 9), and Responsible Consumption and Production (SDG 12).

2. Experimental Section

2.1. Chemicals and Reagents

The solvents and reagents used in the study were of analytical grade. Chloroform (99.8%, CAS No. 67-66-3, CHCl₃) and methanol (99%, CAS No. 67-56-1) were purchased from Merck (Germany). Isopropyl alcohol (98%, CAS No. 67-63-0), ethanol (98%, CAS No. 64-17-5), carbon tetrachloride (98%, CAS No. 56-23-5, CCl₄), hexane (98%, CAS No. 110-54-3), activated charcoal (98%, CAS No. 7440-44-0), hydrochloric acid (37%, CAS No. 7647-01-0), and potassium hydroxide (CAS No. 1310-58-3) were procured from Lab Chem (USA). Toluene (98%, CAS No. 108-88-3) and dichloromethane (99.9%, CAS No. 75-09-2) were sourced from Sigma-Aldrich (USA). Commercial sugarcane wax (CSCW, CAS No. 91722-22-4), used as a reference standard for comparison with the extracted wax, was procured from Cinobee (China). Turpentine oil (99%, CAS No. 8006-64-2) was purchased from Lab Chem (China) and used without further purification.

2.1.1. Feedstock and Pretreatment of Sugar Industry Byproducts

BG and PM were kindly provided by Shakarganj Mill and Miran Sugar Mill (Zamand, Dera Ismail Khan, KPK) during the sugar manufacturing season (December–February). The samples were air-dried, ground using a high-speed laboratory grinder (BIOBASE HC-2000Y), and sieved through a 50-mesh screen (aperture size ≈ 300 μm) to obtain a uniform particle size. The processed feedstock was then sealed in polyethylene bags and stored in a cool, dry place until further use.

2.2. Determination of HSPs and Construction of HSS for Single and Binary Solvent System Optimization

The HSPs (δ_D, δ_P, δ_H) for each solvent were calculated using standard HSP relationships, considering dispersion, polar, and hydrogen-bonding contributions to cohesive energy. The concept of the Hansen Solubility Sphere (HSS) represents solvent–solute interactions in a three-dimensional space and enables classification of solvents as “good” or “bad” based on their position relative to the sphere.

$${\delta }_{\mathrm{T}}^2={\delta }_{\mathrm{D}}^2+{\delta }_{\mathrm{P}}^2+{\delta }_{\mathrm{H}}^2$$ 1

where δ_T is the total solubility parameter, δ_D represents the dispersion component, δ_P is the polar component, and δ_H is the hydrogen-bonding component of the HSPs. These parameters collectively describe the intermolecular interactions contributing to the cohesive energy of the system. The distance (Rs) between a solute and solvent in Hansen’s three-dimensional space depends on their respective partial solubility parameters and is calculated using eq .

$$\mathrm{Rs}={[4{(\delta {\mathrm{D}}_{\mathrm{wax}}-\delta {\mathrm{D}}_{\mathrm{mixture}})}^2+{(\delta {\mathrm{P}}_{\mathrm{wax}}-\delta {\mathrm{P}}_{\mathrm{mixture}})}^2+{(\delta {\mathrm{H}}_{\mathrm{wax}}-\delta {\mathrm{H}}_{\mathrm{mixture}})}^2]}^{1/2}$$ 2

For binary solvent systems, the overall solubility parameters were calculated by volume-fraction weighting of δ_D, δ_P, and δ_H (eq ). The required δ values were obtained from the Hansen Solubility Parameters in Practice (HSPiP) database and applied for solvent screening (Table ). When parameters were not available in standard databases, they were estimated using the group contribution calculator provided within the HSPiP online platform and were compared with literature data where available. All subsequent calculations, including mixture parameters, solvent–solute distances (Rs), and RED values, were performed using eqs –. The determination of HSPs and Hansen sphere radius was supported using the solver add-in, following established methodologies reported in the literature,

$${\delta }_{i\mathrm{mixture}}=\frac{\%\mathrm{Volume\; of\; Solvent\; A}}{100}\times {\delta }_i\mathrm{of\; Solvent\; A}+\frac{\%\mathrm{Volume\; of\; Solvent\; B}}{100}\times {\delta }_i\mathrm{of\; Solvent\; B}$$ 3

where i represents the contribution of HSP parameters: dispersion (D), polar (P), or hydrogen-bonding (H) accordingly.

2. HSPs and RED Values of Single Solvents and Binary Solvent Systems for SCW Extraction .

Solvent	Ratio of solvents (v/v)	δD (MPa1/2)	δP (MPa1/2)	δH (MPa1/2)	Rs	Boiling points (°C)	RED values	Nature of system
Single solvent systems
Carbon tetrachloride	–	17.80	0.0	0.60	3.13	76.7	0.83	Good
Chloroform		17.80	3.10	5.70	3.70	61.2	0.98
Toluene		18.00	1.40	2.00	1.54	110.6	0.41
Turpentine Oil (TO)		16.90	1.90	2.00	1.75	154.0	0.46
Isopropyl alcohol		15.80	6.10	16.40	15.22	82.3	4.02	Bad
Methanol		14.70	12.30	22.30	23.17	64.7	6.11
Ethanol		15.80	8.80	19.40	18.77	78.4	4.95
Dichloromethane		17.00	7.30	7.10	6.93	40.0	1.83
Binary solvent systems with TO as a green cosolvent
TO:CCl4	10:90	17.71	0.19	0.74	2.89	–	0.76	Good
TO:CHCl3	10:90	17.71	2.98	5.33	3.32		0.88
TO:Toluene	20:80	17.78	1.50	2.00	1.30		0.34
TO:Isopropyl alcohol	20:80	16.68	2.74	4.88	3.46		0.91
TO:Methanol	90:10	16.68	2.94	4.03	2.81		0.74
TO:Ethanol	90:10	16.70	2.59	3.74	2.58		0.68
TO:Dichloromethane	50:50	16.95	4.60	4.55	3.42		0.90

^a Reference solute: (SCW) (δ_D = 17.66, δ_P = 2.78, δ_H = 2.02 MPa^1/2, R _o = 3.79).

Construction of HSS was carried out using HSPs (δ_D, δ_P, and δ_H), where the RED value was determined by the ratio of the solute–solvent distance in Hansen space (R_s) to the solute’s HSP sphere radius (R _o), as expressed in eq .

$$\mathrm{RED}={\mathrm{R}}_{\mathrm{s}}/{\mathit{R}}_{\mathrm{o}}$$ 4

2.3. Method of Wax Extraction and Recovery of Solvent

Soxhlet extraction is a well-known and effective method for solid–liquid extraction as it allows continuous solvent circulation and effective solute–solvent interaction. It is a simple, cost-effective, and energy-efficient extraction method, but it requires larger volumes of solvent and longer processing time and offers lower extraction efficiency. − In this study, the Soxhlet method was used because it enables thorough extraction of nonpolar compounds with high reproducibility and simple operation and is suitable for the extraction of nonpolar compounds such as waxes. Although several advanced extraction techniques, such as supercritical fluid extraction, ultrasound, and microwave-assisted extraction, have emerged in recent years, Soxhlet extraction remains a preferred choice for wax recovery due to its ability to provide exhaustive extraction using conventional laboratory equipment.

Wax recovery from BG and PM was carried out using various solvent systems, including both single and binary solvent mixtures. For the single-solvent extraction, solvents such as carbon tetrachloride, chloroform, dichloromethane, ethanol, isopropanol, methanol, and toluene were used. A 1:20 sample-to-solvent ratio was employed, where 20 g of samples were loaded with 400 mL of the respective solvent for effective solute–solvent interaction and efficient extraction, as reported by Teixeira et al. The extraction was performed in a batch-type Soxhlet extractor for approximately 3 h, until the siphon solvent became nearly colorless. Similar extraction approaches and time ranges have been reported for the extraction of SCW. Since Soxhlet extraction functions under the principle of solvent reflux, the temperature was set at the boiling point of each solvent. As a result, the comparison mostly represents solvent–solute affinity under practical operating conditions. Binary solvent extractions were then conducted using TO in combination with toluene, chloroform, and carbon tetrachloride. In these systems, extraction was carried out under reflux conditions of the solvent mixture. Although all the studied binary solvent systems exhibited RED values <1, only TO:Toluene, TO:CHCl₃, and TO:CCl₄ were selected for the extraction of SCW due to their nonpolar nature, high selectivity, and minimal coextraction of polar impurities. Other combinations, despite theoretical compatibility, were excluded due to their tendency to extract nonwax (polar) components, which were partially removed during purification (Table ). After extraction, the solvents were recovered using a rotary evaporator (Heidolph, G3) to concentrate the wax extracts. The recovered solvents were stored and reused in subsequent extractions to minimize solvent loss and environmental impact. The concentrated extracts were then transferred to Petri dishes and dried in the open air, after which the wax yield was calculated using eq .

$$\mathrm{Crude\; wax\; yield}(\%)=\frac{\mathrm{Mass\; of\; crude\; wax}(\mathrm{g})}{\mathrm{Mass\; of\; BG\; or\; PM}(\mathrm{g})}\times 100$$ 5

3. Yields of Crude and Purified SCW Extracted from Both Feedstocks Using Single and Binary Solvent Systems with Relative Purification .

Single solvent systems
	Crude wax yield (%)		Purified wax yield (%)		Relative purification of wax (%)
Solvent system	(BG)	(PM)	(BG)	(PM)	(BG)	(PM)
Carbon tetrachloride	1.79 ± 0.12 k	6.36 ± 0.43fg	1.06 ± 0.16	4.19 ± 0.49	59.5	65.9
Chloroform	1.82 ± 0.12k	6.40 ± 0.39fg	1.04 ± 0.16	4.20 ± 0.46	57.0	65.6
Toluene	4.46 ± 0.49hi	7.45 ± 0.29def	2.67 ± 0.33	5.30 ± 0.25	59.8	71.12
Isopropyl alcohol	3.85 ± 0.51ij	7.42 ± 0.51def	2.01 ± 0.15	5.31 ± 0.46	52.3	71.5
Methanol	3.38 ± 0.41ij	7.19 ± 0.25ef	1.16 ± 0.44	5.14 ± 0.26	34.3	71.5
Ethanol	3.05 ± 0.15j	9.15 ± 0.20 bc	1.64 ± 0.37	6.61 ± 0.49	53.8	72.3
Dichloromethane	1.29 ± 0.13k	5.80 ± 0.36g	0.49 ± 0.10	3.82 ± 0.60	38.0	65.8
Binary solvent systems
TO:CCl4 (1:9)	5.26 ± 0.30 gh	8.53 ± 0.38cd	3.04 ± 0.24	6.60 ± 0.40	57.9	77.4
TO:CHCl3 (1:9)	5.61 ± 0.20 gh	9.87 ± 0.15 b	3.84 ± 0.16	7.57 ± 0.22	68.5	76.7
TO:Toluene (2:8)	7.85 ± 0.17de	11.98 ± 0.32a	5.99 ± 0.31	9.34 ± 0.39	76.4	78.0

^aNote: Mean values with the same alphabet in each column do not have a significant difference (p < 0.05).

2.3.1. Purification of Crude Wax

Activated charcoal and isopropyl alcohol were used for the purification of crude SCW in the ratio of 1:4:2 (crude sugarcane wax: isopropyl alcohol: activated charcoal) for the effective removal of colored impurities and polar contaminants due to the high adsorption capacity of activated charcoal, while minimizing wax loss as reported by Mtolo et al. Specifically, 1.0 g of crude wax was dissolved in isopropyl alcohol and refluxed with activated charcoal for a duration of 2 h to eliminate undesirable coloration. After refluxing, the mixture was filtered to remove the solids, and the resulting filtrate was collected, dried, and weighed. The yield of refined wax was then calculated using eq .

$$\mathrm{Yield\; of\; purified\; wax}(\%)=\frac{\mathrm{Mass\; of\; purified\; wax}(\mathrm{g})}{\mathrm{Mass\; of\; BG\; or\; PM}(\mathrm{g})}\times 100$$ 6

The relative purification of wax was calculated as the ratio of purified wax yield to the crude wax yield, expressed as a percentage using eq .

$$\mathrm{Relative\; purification\; of\; wax}(\%)=\frac{\mathrm{Purified\; wax\; yield}(\%)}{\mathrm{Crude\; wax\; yield}(\%)}\times 100$$ 7

2.4. Spectroscopic and Chromatographic Characterization

A (0.1% w/v) wax solution was prepared in hexane for spectroscopic analysis. For UV–vis analysis, the solution was scanned between 200 and 700 nm using a Shimadzu UV-1800 spectrophotometer. FT-IR spectra of the extracted wax were recorded in the range of 4000–450 cm^–1 using a Nicolet iS50 (Thermo Fisher Scientific) spectrophotometer, and the data were processed with OMNIC 9.15 software. Thin-layer chromatography (TLC) was carried out on silica gel plates to separate wax components using toluene:acetic acid (99:1 v/v) as a mobile phase. The developed plates were visualized under UV light at 245 nm.

2.5. Physicochemical Properties

For acid value, 0.1 g of wax was weighed and dissolved completely in 20 mL of hexane with gentle heating and constant stirring. A few drops of phenolphthalein indicator were added, and titration was carried out against 0.1 N KOH solution until a faint pink color end point persisted for 20–30 s. Continuous stirring and mild heating were maintained throughout the procedure to prevent wax solidification and ensure accurate titration. Triplicate analyses were carried out, and the average titer value of KOH was used to calculate the acid value using eq .

$$\mathrm{Acid\; value}({\mathrm{mg\; KOH\; g}}^{-1})=\frac{\mathrm{Volume\; of\; KOH}\times \mathrm{Normality\; of\; KOH}\times \mathrm{Equivalent\; weight\; of\; KOH}}{\mathrm{Weight\; of\; sample\; wax}}$$ 8

Saponification value was calculated using eq by dissolving 0.5 g of wax, which was weighed, in 20 mL of ethanol with constant heat and stirring. To this solution, 15 mL of 0.1 N ethanolic KOH was added, and the mixture was refluxed for 1 h at 80 °C with intermittent shaking to ensure complete saponification. After refluxing, the solution was allowed to cool, and 10 mL aliquots were titrated against 0.5 N HCl using phenolphthalein as an indicator, until the pink endpoint disappeared. All analyses were performed in triplicate. A blank determination was carried out under identical conditions but without the addition of wax.

$$\mathrm{Saponification\; value}({\mathrm{mg\; KOH\; g}}^{-1})=[({\mathrm{Volume}}_{\mathrm{H}\mathrm{C}\mathrm{l}(\mathrm{blank})}-{\mathrm{Volume}}_{\mathrm{H}\mathrm{C}\mathrm{l}(\mathrm{sample})})\times \mathrm{Normality\; of\; HCl}\times \mathrm{Equivalent\; weight\; of\; KOH}]/[\mathrm{Weight\; of\; sample\; wax}]$$ 9

The apparent pH of SCW was measured in hexane using a calibrated (PHS-3C) pH meter, and wettability of extracted SCW from BG and PM was evaluated through contact angle analysis using the sessile drop method. Wax samples were coated onto a precleaned and dried glass substrate by the drop-casting method. To minimize contamination during the coating process, all glass substrates were thoroughly cleaned and dried prior to use. A droplet of distilled water was then placed on the surface, followed by image capture via a digital imaging device. Measurements were performed in triplicate, and the contact angle was determined using ImageJ software.

2.6. Instrumental Characterization Techniques

GC-MS analysis was carried out on a GC System 7890A (Agilent Technologies) coupled with a GC/MS Triple Quad (Agilent Technologies) equipped with an electron multiplier detector. A ZEBRON ZB-5MS capillary column (30 m × 0.25 mm I.D., 0.25 μm film thickness) was used, with helium as the carrier gas. 1 μL of the sample was injected, and the maximum oven temperature was set to 330 °C. The oven temperature was initially ramped at 30 °C min^–1 to reach 200 °C, held for 15 min, and then increased at a rate of 7 °C min^–1 to 300 °C, where it was held for 16 min.

X-ray diffraction (XRD) analysis was performed using an X’PERT PRO diffractometer (Malvern PANalytical, Netherlands) with HighScore Plus software. To prepare the sample, it was placed between Kapton sheets, heated to 553 K, subsequently pressed into a film, and cooled to room temperature. The film was then mounted on a flat silicon zero-background holder (ZBH) (Malvern PANalytical, Netherlands) and analyzed under ambient conditions. ,

Thermogravimetric analysis (TGA) was carried out to evaluate the thermal behavior of CSCW and extracted waxes, including their thermal stability and decomposition patterns, using a TA Instruments SDT Q600 thermogravimetric analyzer (USA). Approximately 2 mg of the sample was placed in an alumina pan and heated from 25 to 600 °C at a heating rate of 10 °C/min under a nitrogen (N₂) purge atmosphere with a flow rate of 50 mL min^–1. Data acquisition and analysis were carried out using TA Instruments Advantage software and Universal Analysis software. The experimental conditions were adapted with minor modifications from previous studies.

2.7. Statistical Analysis

All experiments were carried out in triplicate, and the results are presented as mean ± standard deviation. A two-way ANOVA under the general linear model (GLM) framework was utilized to compare crude wax yields, considering feedstock (BG vs PM) and solvent formulation (single vs binary systems), followed by Tukey’s posthoc test at a 95% confidence level. Statistical analyses were performed using Minitab version 20.3. The entire methodology followed in this study is summarized in Figure , providing a visual overview of the extraction workflow from HSP-based solvent selection to wax characterization and greenness evaluation.

1.

Schematic overview of eco-friendly extraction of SCW from both feedstocks guided by HSPs.

3. Results and Discussion

3.1. Evaluation of RED Values within HSS for Single and Binary Solvent Systems

HSP theory was applied in the proposed study to calculate the RED values of single solvents and binary solvent systems for SCW extraction. It was observed that, among the single solvents screened, carbon tetrachloride (0.83), chloroform (0.98), and toluene (0.41) were classified as “good” solvents, indicating suitable compatibility, particularly for the extraction of SCW, whereas isopropanol (4.02), methanol (6.11), ethanol (4.95), and dichloromethane (1.83) were categorized as “bad” solvents due to their high RED values, showing poor solubility (Table ). Based on HSP criteria, TO with a RED value of 0.46 was also identified as a good solvent. TO and its major constituents have been widely used as terpene-based green alternatives to conventional nonpolar solvents for natural product extraction. ,,, Furthermore, HSP-based studies on extraction support the use of mixed solvent systems for improved extraction performance. , However, the high boiling point (Table ) and low volatility of TO may limit efficient solvent recovery. Therefore, in the present work, TO was utilized as a green cosolvent in binary systems to balance the solvation system, enhance the selective solubilization of wax components, and reduce the environmental impact. The theoretical data were illustrated by plotting HSS for single solvent systems (Figure ) where good solvents lie within the sphere, while poor solvents fall outside the sphere. Furthermore, binary solvent systems incorporating TO as a green cosolvent were developed, and RED values were calculated for each solvent system. It was found that all TO-based binary systems achieved RED < 1, indicating favorable compatibility. The RED values obtained were carbon tetrachloride (0.76), chloroform (0.88), toluene (0.34), isopropyl alcohol (0.91), methanol (0.74), ethanol (0.68), and dichloromethane (0.90). These values displayed good solubility and fell within the HSS for SCW (Figure ). It was observed that the single solvents with poor RED values displayed improved RED values when combined with TO. This improvement may be attributed to enhanced compatibility in the presence of TO, which modified the overall dispersion, polar, and hydrogen-bonding interactions of the binary mixture. Consequently, the solvent blend moved closer to the solubility sphere of SCW, resulting in lower RED values and better extraction suitability. Among the developed binary systems, TO:CCl₄, TO:CHCl₃, and TO:Toluene were selected for extraction because the three nonpolar solvents, including carbon tetrachloride, chloroform, and toluene, exhibited RED < 1 when used individually as solvent systems for extraction and showed strong affinity with the hydrophobic constituents of wax. ,, Since TO has a low evaporation rate at ambient temperature i.e., 154 °C, its proportion in the binary systems was adjusted to ensure efficient solvent recovery. A wide range of binary compositions was first evaluated using HSPs, and the complete set of tested ratios with their RED values is provided in Supporting Information (Table S1). Among the screened optimized ratios of these binary systems, TO:CCl₄ (10:90 v/v), TO:CHCl₃ (10:90 v/v), and TO:Toluene (20:80 v/v) were selected based on low RED values and a high fraction of green solvent. TO:Toluene (20:80 v/v) was selected for further investigation because it exhibited the lowest RED value (0.34), delivered the highest wax yield, and supported efficient solvent recovery due to the reduced fraction of TO relative to toluene.

2.

Hansen solubility sphere showing compatible single solvents for SCW extraction.

3.

Hansen solubility sphere for SCW extraction using TO-based binary solvent systems with different green and hazardous cosolvents.

3.2. Extraction Yields of SCW Using Single and Binary Solvent Systems

In the present study, crude and purified wax yields from BG and PM were determined using both single and binary solvent systems. The extraction yields exhibited significant variations depending on the solvent and feedstock used. It was found that PM produced higher wax yields than BG, consistent with earlier reports of its comparatively richer wax content. , This can be attributed to the processing steps in sugar production, i.e., grinding and milling of sugarcane, where a significant portion of wax transfers into the liquid extract. This juice is then clarified, and the resulting byproduct, PM, possesses a high concentration of wax. Accordingly, extraction results show that among single solvent systems, toluene (4.46 ± 0.49%) and isopropyl alcohol (3.85 ± 0.51%) showed the highest wax yields from BG, while ethanol (9.15 ± 0.20%) and toluene (7.45 ± 0.29%) produced the highest wax yields from PM, as predicted by HSPs. Nonpolar solvents performed better due to their affinity with hydrophobic wax constituents, while polar solvents can extract a broader range of compounds. , For binary solvent systems, the incorporation of TO significantly enhanced wax recoveries from both feedstocks. Table represents wax recoveries from both feedstocks using TO:CCl₄ (10:90 v/v), TO:CHCl₃ (10:90 v/v), and TO:Toluene (20:80 v/v) solvent systems. TO:Toluene (20:80 v/v) produced the highest yields (7.85 ± 0.17%) from BG and (11.98 ± 0.32%) from PM.

The improved wax recovery confirms the advantage of binary systems, which combine the strong hydrophobic affinity of nonpolar solvents with the solvation capacity of TO. The enhanced performance of the binary solvent system can be partly attributed to improved compatibility between the HSPs of the solvent mixture and wax components. The combination of TO and toluene adjusts the combined Hansen parameters toward those of SCW. Toluene provides strong dispersion interactions suitable for dissolving long-chain hydrocarbons and wax-like alkanes, consistent with its high affinity for refined SCW and other long-chain hydrocarbons. In contrast, TO contributes to improved interaction with slightly polar constituents such as alcohols and esters. This interaction may lead to a broader solubility range and suggests improved selectivity toward wax components while limiting the extraction of highly polar impurities. Furthermore, the RED value for TO:Toluene (0.34) indicates close proximity to the solute in Hansen space, which is consistent with the observed extraction efficiency. The results are further supported by statistical data obtained from Tukey’s posthoc test, which showed a significant difference between binary and single solvent systems. A two-way ANOVA was used to evaluate the effects of feedstock type (BG and PM) and solvent systems (single and binary) on % crude wax recovery (Table S2a). The analysis showed that both main factors and their interaction were significant (p < 0.0001), indicating that extraction efficiency depends on both the choice of feedstock and solvent selection (Table S2b). The model demonstrated an excellent fit, with an adjusted R² of 98.05%. The main effects and interaction plots (Figure ) revealed that PM consistently yielded more wax than BG, while nonpolar toluene-based systems including TO:Toluene provided the highest recoveries compared to polar solvents such as methanol and ethanol, which supports the prediction of HSP theory. The interaction plots further highlighted that the yield advantage of PM over BG was distinct with toluene-containing solvents. These findings emphasize that both feedstock composition and solvent polarity jointly determine wax extraction efficiency, with PM and binary toluene mixtures offering favorable outcomes. In addition, purification efficiencies of 65–78% indicate that binary extractions not only enhanced yields but also produced wax fractions with higher purification efficiency, comparable to values reported for oilcane waxes (58–65%). This experimental trend agreed well with the RED-based compatibility assessment. The relationship between crude wax yield (%) extracted from both feedstocks and calculated RED values for single and binary solvent systems is shown in Figure . Solvents located in the favorable region (RED < 1) showed high wax recovery, while those with RED values >1 corresponded to low yields.

4.

(a) The main effects and (b) interaction plots showing the influence of solvent system (single vs binary) and feedstock type (BG vs PM) on the crude wax yield (%).

5.

Correlation between calculated RED values and crude wax yield obtained from BG and PM. The vertical dashed line (RED = 1) separates favorable (green) and unfavorable (red) regions according to Hansen solubility theory.

3.3. UV–Visible Spectroscopic Analysis of Wax Samples

The UV absorption spectra of wax samples extracted from both feedstocks using single and binary solvent systems with TO revealed prominent absorption peaks around 230 and 275 nm (Figure ). These wavelengths may be attributed to π–π* transitions associated with unsaturated or weakly conjugated systems present in the wax components. The spectrum showed no peaks in the 400–700 nm range, suggesting the absence of strongly absorbing chromophores such as pigments. Binary solvent extracts (TO:Toluene) showed spectra similar to CSCW, with reduced visible absorbance, which may suggest improved purity relative to single-solvent extracts. Minor differences observed in absorbance intensity in the UV region may occur due to variations in the concentration of unsaturated or minor components extracted under different solvent conditions. These findings are consistent with earlier reports on sugarcane peel wax by Inarkar and Lele, who observed UV–vis bands at ∼230 and ∼270 nm attributed to lipid absorption and conjugated systems. Comparable UV absorption below 300 nm has also been reported for beeswax and carnauba wax, supporting the presence of low-conjugated systems in natural waxes.

6.

UV–vis spectra of waxes from both feedstocks extracted with toluene and TO:Toluene, compared with CSCW.

3.4. FT-IR Characterization of SCW Extracted Using Single and Binary Solvent Systems

FT-IR analysis was conducted to identify the functional groups in SCW isolated from BG and PM using single (toluene) and binary (TO:Toluene) solvent systems. The FT-IR spectra of all samples (Figure ) with differences in band intensities and resolution show similar functional group characteristics compared to CSCW, as summarized in Table . A broad O–H stretching band in the region of 3415–3420 cm^–1 is observed, indicating the presence of hydroxyl-containing compounds. In the region of 2920–2850 cm^–1, the aliphatic C–H stretching vibration characteristics are clearly observed in all samples, indicating the presence of long-chain hydrocarbons. A distinct absorption band at 1735–1740 cm^–1 corresponds to carbonyl ester (CO) stretching vibration, which is found to be consistent in all the extracted wax samples, suggesting ester linkages as a major component of the wax structure. In the fingerprint region, a band near 1460 cm^–1 assigned to CH₂ bending is observed in CSCW and most extracted samples, while CH₃ bending at 1375 cm^–1 appears with low intensity. C–O–C and C–O stretching vibrations occur in the region of 1200–1000 cm^–1 and are found in most of the wax samples. The CH₂ rocking band at 720 cm^–1 is clearly observed in all spectra, further supporting the presence of long aliphatic chain characteristics of waxes. In general, the FT-IR spectra indicate the retention of hydrocarbons, esters, alcohols, and other oxygenated functionalities in the extracted SCWs. The spectra indicate that waxes recovered using different solvents exhibit similar functional groups; however, differences in band intensity and slight peak shifts suggest some compositional variation. These results are consistent with previous studies on plant-derived waxes, where comparable absorption bands at about 3395–3420 cm^–1 region (O–H), 2918–2850 cm^–1 (C–H stretching), 1735 cm^–1 (CO), and 1170 cm^–1 (C–O–C) were reported. ,

7.

FTIR spectra of waxes from both feedstocks obtained using single (toluene) and binary (TO:Toluene) systems, compared with CSCW.

4. FTIR Absorption Bands (cm^–1) of SCW from Both Feedstocks Extracted with Toluene and TO:Toluene, Compared with CSCW .

	Observed Peak (cm –1 ) of Wax Samples
	CSCW	Toluene		TO:Toluene
Assignment	(reference)	(BG)	(PM)	(BG)	(PM)
O–H stretching (hydroxyl)	3415	3415–3420	3415	3420	3420
C–H asymmetric stretching (CH2)	2920	2920	2920	2920	2917
C–H symmetric stretching (CH2)	2850	2850	2850	2851	2852
CO stretching (ester)	1735	1735–1740	1735–1740	1735–1740	1735–1740
CH2 bending (scissoring)	1460	1460	-	1460	1460
CH3 bending	1375	-	-	1375	1375
C–O–C stretching (ester linkage)	1172	-	-	1170	-
C–O stretching	1100	-	-	1100	-
CH2 rocking	720	720	720	720	720

^aNote: Peak positions are approximate (±2–3 cm^–1) and were determined from the FTIR spectra; minor variations may occur due to baseline correction and peak broadening.

3.5. Analysis of TLC Profiles of Wax Samples

The retention factor (R_f) values obtained through TLC analysis provided a qualitative comparison of the separation of various compounds present in the extracted wax and the effect of the solvent on their isolation. TLC analysis of SCW extracted from BG and PM in toluene alone and in a binary solvent system of TO:Toluene was performed in toluene:acetic acid (99:1 v/v) solvent system. For BG, the R_f values obtained for toluene-extracted wax were 0.113 and 0.931, while with the binary solvent system of TO:Toluene, they were 0.116 and 0.931, respectively. Similarly, for PM, the values with the single solvent and with the binary solvent system were 0.113 and 0.954 and 0.090 and 0.931, respectively. These results, depicted in Supporting Information (Figure S1), revealed the presence of polar and nonpolar compounds such as hydroxyl or ester groups, which is comparable with the TLC profile of CSCW studied in the same solvent system, i.e., 0.090 and 0.931. Furthermore, the findings from TLC were consistent with literature-reported R_f values of other natural waxes (0.29 and 0.85 for alcohol and hydrocarbon fractions, respectively). Subsequently, the findings of the TLC of the extracted SCW were further confirmed by GC–MS analysis.

3.6. Physicochemical Characterization of SCW Samples

The physicochemical parameters of crude SCW extracted from both feedstocks using optimized single (toluene) and binary (TO:Toluene) solvent systems were evaluated through acid, saponification, apparent pH, and contact angle values and were compared with CSCW as a reference (Figure ). The acid value, which reflects the free fatty acid content and stability of waxes, was found to be highest in PM wax extracted with toluene, indicating a larger number of fatty acids and reduced stability. In contrast, the binary system lowered the acidity in both feedstocks, reflecting improved quality. The analysis of the saponification value disclosed that TO:Toluene (PM) was closely comparable to CSCW, demonstrating a similar saponifiable content, including ester and fatty acid components. These results are consistent with earlier literature, where higher saponification values were associated with greater ester content, while lower values indicated higher nonsaponifiable matter. With respect to apparent pH, all waxes exhibited slightly acidic pH, consistent with earlier reports on natural waxes, while the binary TO:Toluene system yielded comparatively higher apparent pH values, indicating reduced acidity and improved quality. The contact angle measurements confirmed the hydrophobic nature of the SCW. Single solvent extracts exhibited comparatively lower angles, while the binary system yielded values closer to the CSCW reference, particularly for PM. Table shows sessile drop images corresponding to the contact angles of all wax samples. The contact angle values of the extracted waxes were found to be comparable to those of CSCW, indicating similar surface wettability. The observed hydrophobic nature suggests the use of SCW in edible coatings to reduce moisture loss and extend shelf life as higher contact angles are generally associated with improved barrier properties.

8.

Physicochemical parameters of CSCW and waxes from both feedstocks under toluene single and TO:Toluene binary systems.

5. Physicochemical Parameters and Wettability of CSCW and Extracted Crude Waxes from Both Feedstocks under Toluene-Based Single and Binary Solvent Systems.

3.7. Gas Chromatography–Mass Spectrometry Profiling

GC–MS analysis (Figure ) provided detailed information regarding the chemical composition of SCW extracted from both feedstocks using the TO:Toluene solvent system. The chromatogram showed the presence of o-Cymene, β-terpinyl acetate, 2-carene, fenchone, carveol, fenchol, borneol, α-terpineol, cuminaldehyde, longifolene, caryophyllene, and caryophyllene oxide among the low-molecular-weight constituents. Since TO was used as a cosolvent for extraction, the presence of certain terpenoid compounds may be associated with residual traces of the cosolvent in the binary solvent system. However, the solvent was removed prior to the characterization of the extracted wax samples; therefore, the presence of residual solvent compounds is expected to be minimal. The chromatogram also exhibited the characteristic peaks of lipophilic compounds, including long-chain hydrocarbons and fatty acids. These compounds include n-hexadecenoic acid as the major fatty acid, while tetracosane, pentacosane, hexacosane, heptacosane, octacosane, and nonacosane represent a predominant hydrocarbon fraction. These long-chain alkanes contribute to the hydrophobicity, barrier properties, and structural stability of the wax matrix. Furthermore, long-chain fatty alcohols, particularly 1-octacosanol, were detected, confirming the presence of policosanol-rich fractions that are widely recognized as characteristic constituents of SCW. It further showed the presence of phytosterol-derived compounds such as stigmasta-3,5-dien-7-one, commonly reported in SCW and related plant waxes. The reported literature reveals the availability of most of the extracted compounds in SCW obtained from different feedstocks and using different solvents. , This might be due to HSP-guided binary solvent extraction as a greener and effective approach for wax production. The abundance of a comparatively greater number of compounds using TO:Toluene indicates that the binary solvent system and feedstock contribute to selective solubilization. Table represents detailed peak identification, retention time, and percent peak area data for the representative PM-extracted wax.

9.

GC–MS chromatogram of (a) CSCW, benchmarked against waxes extracted using the TO:Toluene binary solvent system from (b) BG and (c) PM.

6. GC–MS Profiling of Wax Extracted Using the TO:Toluene Binary Solvent System .

S.No.	Class	Compound Name	RT (min)	Area Sum (%)
1	Acid	Cyclopropanecarboxylic acid, 2,2-dimethyl-3-cis-[α-(carboxymethyl)-allyl]	16.7	0.36
2		n-Hexadecenoic acid	28.2	1.54
3	Aldehyde	Cuminaldehyde	15.8	0.18
4		2-Isopropyl-5-methyl-6-oxabicyclo[3.1.0]hexane-1-carboxaldehyde	19.3	1.64
5	Alcohol	Cyclohexanol	13.4	1.09
6		Dimethylhexynediol	16.5	0.81
7		Dimethylhexynediol	16.9	1.90
8		6-Methyl-cyclodec-5-enol	17.1	1.18
9		2-cis-9-Octadecenyloxyethanol	52.5	0.58
10		2-cis-9-Octadecenyloxyethanol	53.7	0.77
11		2-cis-9-Octadecenyloxyethanol	54.8	5.37
12		1-Octacosanol	55.5	4.24
13		1-Octacosanol	56.0	3.68
14		2-cis-9-Octadecenyloxyethanol	57.0	3.11
15	Alkane/Hydrocarbon	Tetracosane	44.5	0.99
16		2,6,10-Trimethyltetradecane	44.5	0.99
17		Pentacosane	47.2	1.37
18		Hexacosane	49.1	2.67
19		Heptacosane	50.7	10.62
20		Octacosane	52.1	1.25
21		Nonacosane	53.3	5.63
22		Heptacosane	55.4	1.76
23		17-Pentatriacontene	56.6	1.80
24		Heptacosane	57.6	1.92
25	Ester	β-Terpinyl acetate	10.6	0.11
26	Sterol	Tremulone (Stigmasta-3,5-dien-7-one)	58.9	2.75
27	Terpenoid	o-Cymene	10.4	2.20
28		2-Carene	11.3	0.13
29		2-Carene	12.0	0.13
30		Fenchone	12.1	0.34
31		p-Isopropenyl toluene	12.2	0.48
32		Carveol	12.8	0.28
33		Fenchol	12.9	0.81
34		1-Isopropenyl-4-methyl-1,2-cyclohexanediol	13.6	0.48
35		1-Methyl-4-isopropylcyclohexane-8-ol	13.7	1.04
36		Borneol	14.2	0.14
37		p-Cymen-8-ol	14.6	9.03
38		α-Terpineol	14.7	2.46
39		5-Isopropenyl-2-methyl-7-oxabicyclo[4.1.0]heptan-2-ol	17.7	0.61
40		α-Longipinene	17.7	0.61
41		Dihydroumbellulone	18.0	1.13
42		6-(Hydroxymethyl)-1,4,4-trimethylbicyclo[3.1.0]hexan-2-ol	18.1	0.45
43		7-Oxo-2-oxa-7-thiatricyclo[4.4.0.0(3,8)]decan-4-ol	18.4	0.19
44		α-Himachalene	18.4	0.32
45		6-(Hydroxymethyl)-1,4,4-trimethylbicyclo[3.1.0]hexan-2-ol	18.6	0.31
46		D-Longifolene	19.1	6.68
47		Caryophyllene	19.3	0.16
48		(2,2,6-Trimethyl-bicyclo[4.1.0]hept-1-yl)-methanol	19.4	0.45
49		1,2-cis-1,5-trans-2,5-dihydroxy-4-methyl-1-(1-hydroxy-1-isopropyl)cyclohex-3-ene	19.5	2.27
50		6-Isopropyl-3-methyl-7-oxabicyclo[4.1.0]heptan-2-one	19.9	0.46
51		1-Hydroxybicyclo[2.2.2]oct-5-en-2-yl, methyl ketone	20.2	2.94
52		2-Bornanol, 2-methyl	20.4	1.87
53		5-Isopropenyl-2-methyl-7-oxabicyclo[4.1.0]heptan-2-ol	20.7	2.41
54		1,2-Cyclohexanediol, 1-methyl-4-(1-methylethenyl)-	21.0	0.45
55		4-(1,3,3-Trimethyl-7-oxabicyclo[4.1.0]hept-2-yl)-2-pentanone	22.0	0.47
56		Caryophyllene oxide	22.2	1.37
57		Isoaromadendrene epoxide	23.6	0.41

^aWax extracted from PM.

^bThe identified compounds accounted for 99.4% of the total chromatographic area; the remaining fraction corresponds to minor unidentified peaks and/or rounding errors.

3.8. Evaluation of X-ray Diffraction Characterization of CSCW and Binary Solvent-Extracted Waxes

X-ray diffraction (XRD) analysis was carried out to evaluate the crystallinity of SCW extracted from feedstocks using the TO:Toluene solvent system. The XRD patterns of the extracted waxes displayed distinct orthorhombic crystalline reflections at approximately 2θ = 21.4° and 23.7°, comparable to CSCW (reference), which exhibited sharp reflections at 21.5° and 23.8° (Figure ). These peaks can be assigned to the (110) and (200) planes of an orthorhombic crystal structure, indicating the presence of crystalline domains typically associated with long-chain aliphatic compounds in natural waxes. , However, the peak intensities of BG-extracted wax were lower than those of PM-extracted wax, indicating reduced crystallinity, which is consistent with reports that higher proportions of amorphous constituents (resins, gums, and minor polysaccharides) diminish the crystallinity of natural waxes. In addition, weaker diffraction features observed at higher angles (35–45° and above) may be attributed to secondary reflections of long-chain hydrocarbon structures, further supporting the semicrystalline nature of the samples.

10.

XRD patterns of (a) CSCW, benchmarked against waxes extracted using the TO:Toluene binary solvent system from (b) BG and (c) PM.

3.9. Thermogravimetric Analysis of CSCW and Binary Solvent-Extracted Waxes

The thermal stability of CSCW and TO:Toluene-extracted waxes from each feedstock was evaluated by TGA (Figure ). All wax samples showed a minor weight loss below 150 °C, related to residual moisture evaporation, which remained limited because SCW and its solvent-extracted fractions are inherently hydrophobic. For CSCW, the first major decomposition was observed around 182 °C and extended to 450 °C, reflecting volatilization and bond cleavage of low- to mid-molecular-weight esters and hydrocarbons. The degradation extended up to 551 °C, reflecting the gradual decomposition of more thermally stable and oxygenated constituents, leaving 3.8% residue at 600 °C, indicating near-complete volatilization. In contrast, both BG and PM waxes showed earlier onset (100–110 °C), which may be attributed to the presence of residual moisture or low-molecular-weight volatile components, but continued to degrade over a broader temperature range (Table ). The higher residues (13.9% for BG and 9.2% for PM) are indicative of refractory components and thermally stable fractions enriched by binary solvent extraction. , These results indicate that the thermal stability of the extracted waxes, particularly the TO:Toluene PM sample, is comparable to CSCW, supporting their potential use in thermally processed applications such as edible coatings and food packaging.

11.

TGA thermograms showing thermal behavior of waxes from both feedstocks extracted with the TO:Toluene binary system, compared with CSCW.

7. Thermogravimetric Analysis of CSCW and Waxes Extracted from Both Feedstocks Using the TO:Toluene Binary Solvent System.

	CSCW	TO:Toluene
	(reference)	(BG)	(PM)
T onset (°C)	182.3	100.1	109.3
T max (°C)	425.4	365.2	410.5
T end (°C)	551.0	507.0	518.3
% Total weight loss	96.2	86.1	90.8
% Residue at 600 °C	3.8	13.9	9.2
No. of degradation steps	1	1	1

The derivative thermogravimetric (DTG) curves (Figure ) show a major degradation peak for all samples within 350–450 °C, corresponding to the primary decomposition stage of wax components, as commonly reported for natural waxes, edible oils, and lipid-based materials, which typically exhibit mass loss between 180 and 480 °C. CSCW exhibits a sharp intense peak at 420–430 °C, indicating rapid and uniform degradation. The TO:Toluene (PM) wax shows a slightly broader peak in a similar region (400–420 °C), suggesting moderate compositional heterogeneity comparable to blended or composite wax systems that display broadened DTG maxima. In contrast, TO:Toluene (BG) wax displays a broader and less intense peak shifted to lower temperatures (350–380 °C), indicating lower thermal stability and a broader degradation profile. Minor fluctuations below 150 °C are attributed to moisture loss, which is typically observed in the thermogravimetric analysis of hydrophobic materials.

12.

DTG curves of CSCW (reference), TO:Toluene (BG) wax, and TO:Toluene (PM) wax showing thermal degradation behavior.

3.10. Environmental and Safety Comparison of Soxhlet Extraction Using Toluene and TO:Toluene

The environmental and safety performance of Soxhlet extraction using (toluene) and (TO:Toluene) solvent systems was evaluated with three greenness tools: NEMI, AGREE, and AES. NEMI assessment (Figure a) showed that both methods fulfilled the criteria for noncorrosiveness, waste minimization, and absence of persistent, bioaccumulative, and toxic (PBT) substances. Each method scored three green quadrants, corresponding to 75% greenness. AGREE analysis (Figure b) supported this, with the binary system (0.59) outperforming toluene alone (0.53), particularly in safer solvent use, lower energy needs, and improved waste management. AES evaluation (Table , Figure c) gave a higher score to the single system, i.e., 81, compared with the binary system, i.e., 79, primarily due to the higher number of hazard pictograms and the signal word associated with TO. While petroleum-derived toluene is hazardous and regulated under RCRA, the inclusion of a renewable and biodegradable solvent, TO, reduces dependence on fossil resources and lowers the overall environmental footprint as per the solvent’s life cycle. Despite hazard pictograms related to flammability and volatility, TO generally has a milder long-term toxicological profile than toluene, making the binary system more sustainable under green chemistry principles. In conclusion, although the binary (TO:Toluene) system scores slightly lower in AES due to hazard labeling, but TO aligns better with green chemistry principles, making it the more sustainable choice. The combination of NEMI, AES, and AGREE metrics consistently supports that adding TO improves the environmental profile of Soxhlet extraction without compromising analytical performance. Detailed methodology and scoring criteria for all three assessment tools are provided in the Supporting Information (Tables S3–S5).

13.

Comparative greenness evaluation of SCW extraction using toluene and the TO:Toluene binary system based on (a) NEMI pictograms, (b) AGREE metrics, and (c) analytical eco-scale score.

8. Analytical Eco-Scale Assessment of Soxhlet Extraction Using Toluene and TO:Toluene Systems.

4. Conclusion

The present study demonstrates a sustainable and efficient approach for recovering SCW from sugar industry byproducts, specifically from BG and PM. The process not only promotes waste valorization but also contributes to environmental protection by reducing the impact of agro-industrial residues. Extraction driven by HSPs, TO:Toluene (20:80 v/v) binary solvent system was identified as the most effective combination, which exhibited the highest wax yield (11.98 ± 0.32%) and improved wax purity compared to single solvents. The enhanced extraction performance is attributed to improved solvent–solute compatibility, enabling selective solubilization of wax constituents. FTIR analysis verified the presence of ester and hydroxyl functionalities, while GC–MS revealed key components such as octacosanol, cuminaldehyde, fatty acid esters, n-hexadecenoic acid, and phytosterols. XRD analysis demonstrated semicrystalline patterns comparable to CSCW. Thermal analysis further indicated improved stability of binary solvent extracts, and physicochemical properties validated their functional suitability through lower acidity and enhanced wettability in binary solvent extracts. This study demonstrates the novelty of applying an HSP-guided design approach for the selective extraction of SCW from byproducts of the sugar industry, bridging the gap between theoretical prediction and experimental validation. The reuse of solvents and incorporation of biobased solvent TO further reduced solvent loss and minimized the ecological footprint, supporting the green and sustainable nature of the process. Greenness metrics reinforced the eco-friendly profile of the process, with eco-scale scoring indicative of sustainable practice. Together, these findings present an economically viable strategy for producing good-quality SCW suitable for edible coatings, biodegradable packaging, and pharmaceutical applications. It also represents the principles of a circular bioeconomy, where renewable agro-industrial byproducts are resourcefully utilized and reintegrated into sustainable productions. Future studies can focus on the formulation of edible coatings using the extracted wax and evaluate its application in fruit preservation trials. In addition, advanced extraction techniques such as supercritical fluid extraction, ultrasound, or microwave-assisted methods may be utilized to further improve extraction efficiency and reduce solvent use.

Glossary

Abbreviations

SCW

Sugarcane wax

CSCW

Commercial Sugarcane wax

BG

Bagasse

PM

Press mud

TO

Turpentine oil

HSP

Hansen Solubility Parameter

HSS

Hansen Solubility Sphere

RED

Relative energy difference

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.6c00219.

• Optimization of binary solvent systems and RED values (Table S1); general linear model parameters and two-way ANOVA results (Tables S2a and S2b); TLC analysis of extracted waxes (Figure S1); NEMI evaluation of Soxhlet extraction methods (Table S3); AGREE scoring for Soxhlet extraction methods (Table S4); Analytical Eco-Scale (AES) assessment of Soxhlet extraction (Table S5) (PDF)

S.Z.methodology, experiments, software, data curation, analysis, writing (original draft), figure preparation, and funding acquisition. S.N.A.conceptualization, supervision, formal analysis, funding acquisition, resources, and writing (review and editing). P.D.conceptualization, supervision, and manuscript reviewing. O.M.T.formal analysis.

The authors would like to acknowledge the Higher Education Commission, Pakistan, for the award of a research grant under the NRPU program, Grant Ref. No. 20-17065/NRPU/R&D/HEC/2021–2020, awarded to Dr. Saeeda Nadir Ali, and the NED University of Engineering and Technology for the award of research grant No. Acad/50(48)/77410/13114, awarded to Sameera Zaki.

The authors declare no competing financial interest.