Sustainable development of fibrous cocoon waste of Antheraea proylei and Bombyx mori as a sorbent for purification of various oil spills from water

Introduction

Silk is considered as natural protein polymer and known as "Queen of fibers". Silkworm larvae spin silk, which is widely used in textiles. During spinning of cocoon, silkworm larvae produce silk to form a protective shell for the delicate caterpillar. The Pupal stage is pass inside the cocoon and metamorphose into the adult stage (Bentley & Auldridge, 2017) [2] . These cocoons are considered as commercial sources of silk material. Silk materials have outstanding mechanical strength and toughness. Silk is considered bio-compatible and biodegradable. Silkworm evolved cocoon for protection against various threats and to regulate gaseous exchange for pupa development. Silkworm cocoon is a non-woven structure, and it is made up of continuous silk fibers joined together by sericin matrix. For commercial purpose these silkworm cocoons are cultivated to yield silk fibers in apparel and biomedical applications (Bucciarelli & Motta, 2022) [3] . In India, commonly two types of silkworms are cultivated, namely A. proylei and B. mori. Release of oil spills into water continuously affects the aquatic ecosystem; oil spills have various hazardous compounds which enters by means of food chains, leading to severe health issues in humans. Now a days biodegradable cocoon waste acts as oil sorbent gaining too much attention due to their ecofriendly nature. Recently many researchers investigated the unique property of silk fibers for oil water separation (Gore et al. 2020; Yin et al. 2022) [7,6] . Sorbents have the ability to concentrate and alter them into semisolid state, and spilled oil can be easily removed by convenient methods (Moriwaki et al. 2009) [8] . Presently many natural biodegradable sorbents such as wool fibers, cotton fibers, collagen fibers and kapok fibers have been used as sorbent to clean up leaked oil (Moriwaki et al. 2009; Subramoniapillai & Thilagavathi, 2022) [8,10] . These sorbents have good sorption capacity, low cost, renewable and biodegradable. Soil and silicates are also currently used to clean up various oil spills, but it takes a lot of energy and cost to clean up leaked or spilled oil. To solve this problem this study used sorbents derived from fibrous cocoon waste. Application of natural silk fibroin waste is very important to study (DeBari et al. 2021; Nogueira et al. 2010) [4,9] . Hydrolyzed fibroin (HF) from the fibrous silkworm cocoon waste can be used as an efficient sorbent for the purification of various oils in automobile industries, food industries, in pharmacy and textile industries (Viscusi, 2023) [14] . During the extraction of silk fiber from the silkworm cocoons (reeling) up to 28% of silk fibers are converted into waste (depends upon the silk spinning mill). In terms of quality and mechanical properties silk fiber waste is considered as inefficient for textile industries. Whereas chemical properties of both silk fibers and fibrous waste are the same. That is why hydrolyzed silk fibroin has excellent sorption property, this property can solve various problems practically. Silk fibers consist of fibroin and sericin proteins, the amount of these proteins in the silk fibers depends upon the quality of diet and living conditions of worms. The present study aims to investigate the potential application of fibrous cocoon waste, a byproduct remaining after the reeling process, as a sorbent material for various types of oils. Emphasis is placed on evaluating the oil sorption behavior of this fibrous waste, with the objective of exploring its effectiveness and suitability as a sustainable and low-cost sorbent for oil spill remediation and related environmental applications.

Materials and Methods

Silkworm cocoon waste of Antheraea proylei was procured from the Sericulture Research Extension Center, Chauntra, Mandi, Himachal Pradesh, India, while cocoon waste of Bombyx mori was obtained from the Silkworm Seed Production Center, Palampur, Himachal Pradesh, India. Six different oil samples, namely mustard oil, petrol, diesel, crude oil, motor oil, and lubricant oil, were used in this study and were purchased from the local market. The density and viscosity of the oils were measured at room temperature. The density of mustard oil was 0.92 g/mL, with a viscosity ranging from 60 to 70 mm²/s. Petrol exhibited a density between 0.72587 and 0.7429 g/mL and a viscosity of 0.88 mm²/s. Diesel had a density range of 0.83 to 0.86 g/mL and a viscosity range of 2.0 to 4.5 mm²/s. Crude oil displayed a density between 0.70 and 0.99 g/mL, with viscosity ranging from 2 to 10 mm²/s. The density of motor oil ranged from 0.866 to 0.89 g/mL, with viscosity values between 43 and 60 mm²/s. Lubricant oil showed a density of 0.866 g/mL and a viscosity range of 55 to 70 mm²/s.  Sorption analysis: Six samples of oil were used for the experiment namely motor oil, vegetable oil, mustard oil, petrol, diesel, crude oil, and lubricant oil. One gram of oil in a Petri dish was placed for 24 hours and 10 days at room temperature. Then, the weight of oil loss was measured by an analytical balance.  For oil sorption and retention capacity 10 gm of motor and vegetable oil were added to the beaker containing 100 mL of distilled water for the sorption experiment. Therefore, after 10 minutes, 0.1 g of the SCWS was generously applied to the oil surface. The material was then removed using forceps and allowed to drain for one minute. Oil-sorbed material was placed on a petri plate. In comparison to that dried for 10 days at room temperature, drying for 24 hours had no effect. So, a 24-hour drying window was established as shown in Figure 1. The oil-sorbed material was weighed using an analytical balance after drying. The testing was done both with and without stirring (S Viju et al. 2019) [11] .  Reusability test analysis: For the material's reusability test, 10 gm of motor and vegetable oil were added to a beaker with 100 ml of distilled water, and 0.1 gm of SCWS was then sprinkled on top of oil. For each sample, the Sorption process was run five times. The material was weighed and squeezed in between each cycle. The amount of oil recovered was determined by dividing the difference between the material that had been squeezed and that which had been previously sorbed with oil.  Statistical analysis: Statistical analysis and plotting of graphs were done using Origin Pro 2025 (graphing and analysis) and Microsoft Excel.

Results

For oil spill clean-ups, it is crucial to consider the sorbent material's oil sorption and oil retention capabilities throughout field application, handling, and transfer. The sorbent material made of silkworm cocoon waste was water repellent. The oil sorption and oil retention performance of the sorbent immediately and after 24 hours is shown in Figure 1 (a & b). Calculating the oil sorption capacity of sorbent material is considered as one of the important criteria for oil spill cleanup. The oil sorption capacity needle punched sorbent material produced from A. proylei and B. mori silkworm cocoon waste was calculated and compared presented in Table 1.

(a) (b)

[11] , mentioned in their research that high viscous oil showed higher adsorption than low viscous oils. Similarly present research also concludes that motor oil and crude oil are highly absorbed by needle punched fibers of silkworm cocoon wastes than vegetable oil and petrol. The reason could be higher viscosity of motor oil and crude oil than vegetable oil and petrol. In general, high viscous oils show higher adsorption capacity than low viscous oils because of capillary diffusion of oils into the pores present in the fiber's structures leading to the higher adsorption capacity (S. Viju et al. 2019) [11] . Hydrophobic amino acid such as alanine, phenylalanine, tryptophan, valine, methionine and proline are mainly present in silk, mainly responsible for hydrophobicoleophilic nature of the silk. (Aftabuddin & Kundu, 2007; Gore et al. 2019) [6] reported that silkworm raw silk fibers composed of 70% to 80% fibroin, 20-30% sericin, 1.2% to 1.65% carbohydrates, 0.4% to 0.8% waxy matter, 0.7% inorganic matter, and 0.2% pigment. SEM micrographs of A. proylei and B. mori cocoon structure displayed in Figure 2 (a & b). [5] ) discussed in their research that desorption of oils in needle punched sorbent material of cocoon waste is slower in case of high viscous oil as compared to low viscous oil. According to the results crude oil showed a slower desorption process due to its higher viscous nature.

Discussion

One of the key characteristics of oil sorbent material is its capacity to be reused. The price of managing oil pollution can be decreased by using materials that can be recycled frequently. Figures 3 and4 display the oil sorption performance of silk cocoon waste for five cycles of sorption and desorption cycles for both species of cocoon waste samples. After five sorption-desorption cycles the oil sorption capacity sorbent material of A. proylei cocoon waste after five sorption-desorption cycles were 4.0 g/g, 2.0 g/g and 8.0 g/g against crude oil, mustard oil and lubricant oil. The oil sorption capacity sorbent material of B. mori cocoon waste after five sorption-desorption cycles were 8.0 g/g, 8.0 g/g and 7.0 g/g against mustard oil, crude oil and motor oil. The oil sorption capacity of needle punched sorbent material continuously decreases with every cycle. The reason could be tightening of inter fiber spaces, irreversible deformation of few fiber structures or incidence of residual oils. (S. Viju et al. 2019) [11] proved in their research that after each cycle, the oil sorption ability of silkworm cocoon waste continues to decline. (Wang et al.

2012) [15] has also discussed in their research that, presence of residual oil in nonwoven fabrics, irreversible deformation of partial fiber structure, and tightening between inter fiber gaps are few potential causes for the decrease in oil sorption capacity with every cycle. The sorbent material was made from residual silkworm cocoons (SCWS), and the SCWS greatly varies from how quickly it absorbed different oils. By subtracting the starting sorbent weight from the total weight of the wet sorbent, the amount of oil that was absorbed was calculated. The porosity, specific surface area, and pore estimate of the sorbents were strongly correlated with differences in oil sorption capacity. As oil consistency increases, sorption capacity rises. The variation in oil viscosities was primarily responsible for the variation in adhesiveness. High-viscous oils desorb from nonwoven textiles more slowly than lowviscous oils during the draining stage (Dong et al. 2015) [5] . It is evident that after each cycle, the silk non-woven fabric's ability to absorb oil continues to decline. this may be caused by a number of things, such as the presence of residual oil in nonwoven fabrics, tightening of inter-fiber gaps, and irreversible deformation of partial fiber structure (Wang et al. 2012) [15] . In order to assess the material's oil sorption capability, oil retention capacity, and reusability silkworm cocoon waste was used as a sorbent material. B. mori has a lower oil sorption capacity than A. proylei, indicating that the latter is preferable in terms of sorption capacity, albeit each oil sample's effect on each cocoon's oil retention capacity will vary. Continuously using the cocoon waste sample for five cycles reveals a consistent decline in oil sorption capacity for both cocoons. There is no residue of silk cocoon waste found after 100 days of burial in soil (S. Viju et al. 2022) [13] . According to the results of this study, the silk cocoon waste from A. proylei has greater sorbent activity than B. mori. The silk cocoon waste with good sorption capacity can be used for the solution of two problems, i.e., purification of oils and reducing oil pollution in natural waters.

Conclusion

In conclusion, this research shows that silk cocoon waste from Antheraea proylei and Bombyx mori exhibits effective oil sorption, retention, and reusability characteristics. A. proylei showed better sorption capacity, specifically with high-viscosity oils like motor oil, because of its beneficial fiber structure. Crude and motor oils were more efficiently absorbed and retained than low-viscosity oils such as petrol. Amino acid composition played an important role in oil affinity, and it is attributed to the hydrophobic-oleophilic nature of silk. Reusability analysis showed a gradual decline in performance over 5 cycles which may be due to residual oil accumulation and fiber structure changes. A 24-hour drying period was found adequate, with no negative impact on sorption ability. Notably, B. mori exhibited slightly better oil retention in crude oil, although it was found that overall, A. proylei was more efficient. The SCWS was also confirmed to be biodegradable, which left no residue after International Journal of Advanced Biochemistry Research https://www.biochemjournal.com 100 days of burial in the soil. Therefore, SCWS, particularly from A. proylei, is a promising, eco-friendly, and reusable material for oil spill remediation and purification applications.

Acknowledgement

AcknowledgementsWe thank Mr. S.K. Kaul, Mr. Pawan Jhangra and Mr. Durga (Sericulture extension centre, Chauntra, H. P., India) and the state sericulture centre, Palampur, for their kind help in this work.

References

1. Aftabuddin Md, Kundu S. Hydrophobic, hydrophilic and charged amino acid networks within protein. Biophys J. 2007;93(1):225-231.
2. Bentley ML, Auldridge T. Worm spit: integrating curriculum through a study of silk and the amazing silkworm. In: Mueller MP, Tippins DJ, Stewart AJ, editors. Animals and science education: ethics, curriculum and pedagogy. Cham: Springer International Publishing; 2017. p. 1-13.
3. Bucciarelli A, Motta A. Use of Bombyx mori silk fibroin in tissue engineering: from cocoons to medical devices, challenges and future perspectives. Biomater Adv. 2022;139:212982.
4. DeBari MK, King CIII, Altgold TA, Abbott RD. Silk fibroin as a green material. ACS Biomater Sci Eng. 2021;7(8):3530-3544.
5. Dong T, Wang F, Xu G. Sorption kinetics and mechanism of various oils into kapok assembly. Mar Pollut Bull. 2015;91(1):230-237.
6. Gore PM, Naebe M, Wang X, Kandasubramanian B. Progress in silk materials for integrated water treatments: fabrication, modification and applications. Chem Eng J. 2019;374:437-470.
7. Gore PM, Naebe M, Wang X, Kandasubramanian B. Silk fibres exhibiting biodegradability and superhydrophobicity for recovery of petroleum oils from oily wastewater. J Hazard Mater. 2020;389:121823.
8. Moriwaki H, Kitajima S, Kurashima M, Hagiwara A, Haraguchi K, Shirai K, et al. Utilization of silkworm cocoon waste as a sorbent for the removal of oil from water. J Hazard Mater. 2009;165(1):266-270.
9. Nogueira GM, Rodas ACD, Leite CAP, Giles C, Higa OZ, Polakiewicz B, et al. Preparation and characterization of ethanol-treated silk fibroin dense membranes for biomaterials application using waste silk fibers as raw material. Bioresour Technol. 2010;101(21):8446-8451.
10. Subramoniapillai V, Thilagavathi G. Oil spill cleanup by natural fibers: a review. Res J Text Appar. 2022;26(4):390-404.
11. Viju S, Brindha R, Thilagavathi G. Surface modification of nettle fibers by grafting to improve oil sorption capacity. J Ind Text. 2019;50(8):1314-1329.
12. Viju S, Govindarajan T, Brindha R. Oil sorption behavior of acetylated nettle fiber. J Text Inst. 2019;110(10):1415-1423.
13. Viju S, Seenivasan RR, Govindarajan T, Chandra Jeet S, Mohamed HAK. Sustainable development of needlepunched nonwoven fabrics from silkworm cocoon waste for oil spill removal. J Nat Fibers. 2022;19(11):4082-4092.
14. Viscusi G. Advanced fibre materials for environmental applications. In: Aslam J, Verma C, editors. Design, fabrication and applications. Berlin: De Gruyter; 2023. p. 103-148.
15. Wang X, Guo Y, Yang L, Han M, Zhao J, Cheng X. Nanomaterials as sorbents to remove heavy metal ions in wastewater treatment. J Environ Anal Toxicol. 2012;2(7):154-158.
16. Yin C, Qi X, Zhao S, Han X, Guo C, Wu X. Natural silk fibers incorporated aramid nanofiber sponges for efficient oil/water separation. Colloids Surf A Physicochem Eng Asp. 2022;648:129323.