Description:FIELD OF THE INVENTION
[0001] The present disclosure relates to a field of nanocomposites. Particularly, the present disclosure provides natural rubber-lignin nanocomposites. Further, the present disclosure also provides a green method for synthesis of natural rubber-lignin nanocomposites.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Recently, the biomaterials have garnered tremendous interest in research and industry due to the increasing problems associated with the usage of non-renewable materials. Natural rubber latex is a biopolymer, primarily consisting of cis-1,4-poly (isoprene) along with carbohydrates, lipids, proteins, etc. Given its excellent elasticity, tensile strength, flexibility, elongation, resilience and inhibition to water and acid, NR is regarded a valuable elastomer [Sethulekshmi et al., Int J Biol Macromol, 2022, 194, 819–842]. NR exhibits less heat-build up and better electrical insulating characteristics upon dynamic stress. Apart from these advantages, NR also shows some disadvantages such as failure to endure high temperatures and comparatively less weather, ozone, and oil inhibition. Incorporation of various nanofillers can enhance the mechanical, barrier, electrical, thermal, antimicrobial, and other characteristics of NR to a great extent. Therefore, NR-based nanocomposites are considered to be excellent candidates for numerous industrial and day-to-day applications includes aerospace [Zhao et al., Polym Test, 2018, 70, 396–402], automotive [Yaragalla et al., Ind Crops Prod., 2015, 74, 792–802; Cao wt al., Compos Part B Eng., 2019, 161, 667–676; Liu et al., Compos Part A Appl Sci Manuf., 2015, 70, 35–44], healthcare [Sukumar et al., ACS Biomater Sci Eng., 2020, 6, 2007–2019; Sethulekshmi et al., Int J Biol Macromol, 2023, 225, 351–360; Yin et al., Carbohydr Polym, 2019, 207, 555–562], electronics [parvathi et al., J Appl Polym Sci., 2022, 139, e53120], sensors [ Yin et al., Carbohydr Polym, 2019, 207, 555–562, Liu et al., Compos Part B Eng., 2019, 171, 138–145], oil sorbent [Songsaeng et al., J Adv Res., 2019, 20, 79–89], electromagnetic interference shielding [Zhan et al., Chem Eng J., 2018, 344, 184–193], supercapacitors, [Suriani et al., Mater Lett., 2015, 161, 665–668], etc.
[0004] Lignin stands as an organic complex biopolymer and is the biopolymer with the second-highest prevalence. Lignin can be extracted from wood residues, black liquor, and agricultural residues [Naseer et al., Zeitschrift für Phys Chemie, 2019, 233, 315–345; Parvathy et al., Process Saf Environ Prot, 2021, 145, 395–410]. Lignin exists in various types, including kraft lignin, hardwood lignin, soft wood lignin, lignosulfonate lignin, alkaline oxidation lignin, organosolv lignin, etc., based on their origin and extraction technique. Possessing a cross-linked structure and a diverse array of functional moieties such as carboxyl, methoxyl, carbonyl and hydroxyl and cross-linked structure, lignin exhibits numerous distinctive properties [Espinoza-Acosta et al., BioResources, 2016, 11, 5452–5481] including antimicrobial [Guo et al., Appl Biochem Biotechnol., 2018, 184, 350–365; Ndaba et al., Sustain Chem Pharm, 2020, 18, 100342], biodegradability [Sahoo et al., Compos Part A Appl Sci Manuf., 2011, 42, 1710–1718], biocompatibility [Rocca et al., RSC Adv, 2018, 8, 40454–40463], antioxidant [Barclay et al., J Wood Chem Technol, 1997, 17, 73–90], UV absorption [Wang et al., Ind Eng Chem Res, 207, 56, 11133–11141], adhesive properties [Ghorbani et al., BioResources, 2016, 11, 6727–6741], thermal stability [Li et al., Int J Biol Macromol, 2013, 62, 663–669], stabilizing effect [Gregorova et al., Polym Degrad Stab, 2006, 91, 229–233], reinforcing ability [Espinosa et al., Int J Biol Macromol, 2019, 141, 197–206; Cui et al., Compos Part B Eng, 2021, 225, 109316], etc. Considering all these properties, its availability and cost effective production, vast range of works have been carried out in lignin [Kumar et al., Bioresour Bioprocess, 2017, 4, 1–19].
[0005] Converting lignin from its micro size into nano form yields enhanced properties, opening up new possibilities for applications. Lignin nanoparticle synthesis has been reported by numerous researchers [Frangville et al., ChemPhysChem, 2012, 13, 4235–4243; Gilca et al., Ultrason Sonochem, 2015, 23, 369–375 ]. Temperature, concentration, pH, solvent/antisolvent, etc are some of the factors that can tune the shape of the lignin nanoparticle [Zhang et al., Nanomaterials, 2021, 11, 1336]. Mechanical procedures, anti-solvent precipitation, self-assembly, and stand out as extensively used approaches for lignin nanoparticle synthesis. Use of excessive organic solvents, lengthy and complicated procedures, etc. are some of the drawbacks associated with lignin nanoparticle synthesis and researchers are trying to find green, simple, and safe methods. Nair et al. [ChemSusChem, 2014, 7, 3513–3520] described the LNP synthesis using kraft lignin through a simple 4 h shear homogenization method. The nano lignin thus obtained exhibited no difference in the molecular weight distribution, chemical structure, and polydispersity when contrasted with bulk lignin.
[0006] Recently, bio-based reinforcing fillers are gaining more research interest due to its biocompatibility, biodegradability, easy availability, eco-friendly nature, etc. Among various bio-nanofillers, lignin nanoparticles are excellent reinforcing agents for various polymers like rubber [Parvathy et al., Process Saf Environ Prot, 2021, 145, 395–410], epoxy [Behin et al., Korean J Chem Eng, 2018, 35, 602–612], polylactic acid [Shojaeiarani et al., Ind Crops Prod, 2022, 183, 114904], polyvinyl alcohol [He et al., Int J Biol Macromol, 2019, 127, 665–676], polyethylene [Wang et al., Polym Adv Technol, 2016, 27, 1351–1354], and poly(methyl methacrylate) [Yang et al., Compos Part A Appl Sci Manuf, 2018, 107, 61–69]. Tailoring to specific applications, insertion of lignin into polymers can be done with or without chemical modifications. The introduction of lignin into rubber produces less dense, non-conducting, and light-coloured material. In non-polar rubbers, lignin exhibits less reinforcement. Incorporating bio-based nanofillers into a bio-polymer like NR leads to the development of environment-friendly NR nanocomposites with exciting properties. In 2013, Jiang et al. [ Express Polym Lett, 2017, 7] detailed the synthesis of NR nanocomposites incorporating nano lignin, where nano lignin was prepared with the help of Poly (diallyldimethylammonium chloride) (PDADMAC) complex. PDADMAC, having a structure akin to NR, facilitated the improvement of compatibility between lignin-PDADMAC complexes (LPCs) and NR compared to NR/lignin composites. Homogeneous distribution of LPCs within NR leads to improved mechanical strength, thermal stability, and thermo-oxidative properties in NR/LPC nanocomposites. The tensile stress of NR improved with the increase in sodium lignosulfonate addition as reported by Ikeda and team [Ikeda et al., RSC Adv, 2017, 7, 5222–5231] in 2017. Moreover, the rise in lignin loading helped to increase the storage modulus and reduce the dissipative loss with less glass transition temperature. Recently, Hosseinmardi and co-workers [Hosseinmardi et al., Ind Crops Prod, 2021, 159, 113063] demonstrated the synthesis of nanoscale organosolv lignin incorporated NR nanocomposites with improved mechanical properties. The effect of the leaching process on mechanical and thermo-oxidative stability was also studied by them. Excess chemicals such as stabilizers, dispersing agents, and proteins of the NR were removed during the leaching process thereby establishing excellent crosslinking and inter-particle attraction. In 2023, Qui et al. [Int J Biol Macromol, 2023, 233, 123547] prepared lignin/silicon dioxide nano-hybrid and the insertion of 10 phr of this nanohybrid, along with 40 phr of carbon black (CB) into NR, showed comparable mechanical properties and a reduction in rolling resistance compared to NR with only CB.
[0007] The intricate structure and greater molecular weight of lignin pose challenges in the synthesis of lignin-based nanocomposites. Studies based on LNP-reinforced NR matrices are very less. In those reported works, the focus was solely evaluating the thermal or mechanical characteristics of the NR nanocomposites. No work has been reported on evaluating the biodegradability, antimicrobial, and UV blocking ability of NR after LNP addition. Moreover, no research has been reported based on the incorporation of LNP synthesized via the homogenization method into NRL.
[0008] Thus, there is a need to develop a novel nanocomposite which can overcome the drawbacks of the prior arts and is economic and environment friendly process.

OBJECTS OF THE INVENTION
[0009] An object of the present disclosure is to provide natural rubber-lignin nanocomposites.
[0010] Another object of the present disclosure is to provide a novel composite having excellent mechanical, thermal, biodegradation, antibacterial, and UV-blocking properties.
[0011] Still another object of the present disclosure is to provide a green method for synthesis of natural rubber-lignin nanocomposites.
[0012] Yet another object of the present disclosure is to provide a method to utilize the lignin waste from the paper and pulp industry, ethanol plants, and biorefineries and to provide an environmentally friendly material.

SUMMARY OF THE INVENTION
[0013] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0014] An aspect of the present disclosure is to provide a natural rubber-lignin nanocomposites comprising a lignin nanoparticle dispersion, and a natural rubber latex.
[0015] Another aspect of the present disclosure is to provide a green method for synthesis of natural rubber-lignin nanocomposites comprising: a) treating an aqueous dispersion of kraft lignin with a high shear homogenizer under condition to obtain lignin nanoparticle dispersion; b) mixing of 0.1 to 10 phr of lignin nanoparticle dispersion with 30 to 70 DRC of a natural rubber latex via probe sonication in an ice bath to obtain a natural rubber latex/lignin nanoparticle (NRL/LNP) dispersion; c) dipping the molds into the natural rubber latex/lignin nanoparticle (NRL/LNP) dispersion of step b) to fabricate a thin film followed by withdrawing the glass molds from the latex compound, and the molds are dried under condition to obtain a dried film; d) cooling the dried film under condition, followed by second dipping and subsequent drying to obtain a second thin film; e) processing the second thin film of step d) by vulcanization under condition to obtain a vulcanized thin film; f) removing the vulcanized thin film from the molds using silica powder to obtain a vulcanized sample; g) casting the remaining NRL/LNP dispersion onto a glass plate, dried and vulcanized to obtain a vulcanized sample; and h) allowing all the vulcanized samples to mature under condition to obtain the natural rubber-lignin nanocomposites.
[0016] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The following drawings form part of the present specification and are included to further illustrate aspects of the present invention. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[0018] Figure 1 illustrates A) Preparation of NR/LNP compound. B) Preparation of NR/LNP nanocomposite films - a, b and c-first dipping, d and e-second dipping, f-vulcanized samples.
[0019] Figure 2 illustrates FT-IR spectrum of Lignin and LNP.
[0020] Figure 3 illustrates XRD of Lignin and LNP.
[0021] Figure 4 illustrates Particle size distribution of LNP.
[0022] Figure 5 illustrates SEM images of a) and c) lignin and b) and d) LNP.
[0023] Figure 6 illustrates TEM images of (a) lignin and (b) LNP.
[0024] Figure 7 illustrates Antibacterial action of lignin (A) and LNP (B) on E. coli (left) and S. aureus (right).
[0025] Figure 8 illustrates FT-IR spectra of NR/LNP nanocomposites.
[0026] Figure 9 illustrates XRD of NR/LNP nanocomposites.
[0027] Figure 10 illustrates Optical microscopy images of NR/LNP nanocomposites, A-NR, B-NRL1, C-NRL3, D-NRL5 and E-NRL7.
[0028] Figure 11 illustrates TEM images of pure NR (A and C) and NRL7 (B and D).
[0029] Figure 12 illustrates Mechanical analysis of NR/LNP nanocomposites.
[0030] Figure 13 illustrates A-TGA thermograms and B- DTG of NR and nanocomposites.
[0031] Figure 14 illustrates DSC thermograms of NR and NR/LNP nanocomposites.
[0032] Figure 15 illustrates Antibacterial studies NR/LNP nanocomposites, 1-NR, 2-NRL1, 3-NRL3, 4-NRL5 and 5-NRL7.
[0033] Figure 16 illustrates Biodegradation results of NR and NR/LNP nanocomposites.
[0034] Figure 17 illustrates NR/LNP nanocomposites before and after biodegradation study (From left to right-NR, NRL1, NRL3, NRL5 and NRL7).
[0035] Figure 18 illustrates SEM images of NR (a-d) and NRL7 (e-h) before and after biodegradation.
[0036] Figure 19 illustrates a) UV-Visible transmittance spectra b) digital photographs of NR and NR/LNP nanocomposites show the optical transparency (NR, NRL1, NRL3, NRL5 and NRL7 from top to bottom).

DETAILED DESCRIPTION OF THE INVENTION
[0037] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0038] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0039] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[0040] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0041] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it is individually recited herein.
[0042] All processes described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0043] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0044] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0045] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0046] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description that follows, and the embodiments described herein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[0047] It should also be appreciated that the present invention can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.
[0048] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0049] The NR/LNP nanocomposites are prepared via the double dipping method and analyzed the mechanical, thermal, antibacterial, biodegradation, and UV-blocking characteristics of the nanocomposites. Therefore, this is the first study, concentrating on the multifunctional analysis of NR/LNP nanocomposites. The entire work was carried out using water as a solvent and is free of toxic solvents; therefore, this method is environmentally friendly for fabricating NR/LNP nanocomposites with excellent mechanical, thermal, biodegradation, antibacterial, and UV-blocking properties. Lignin is one of the abundant wastes generated from several sources such as paper and pulp industry, cellulose extraction, biorefineries and crop production. Properly separating lignin from these waste sources and converting it into nanolignin allows its use as nanofiller for NR, thereby actively mitigating the waste issues associated with lignin. Additionally, the insertion of lignin not only addresses waste problems linked to lignin but also augments the biodegradability of NR, promoting environmentally friendly material fabrication practices. Consequently, this work establishes a sustainable pathway for disposal of biomedical devices based on NR nanocomposites, such as surgical gloves, condoms, catheters, and surgical tubing.
[0050] An embodiment of the present disclosure provides natural rubber-lignin nanocomposites comprising: a lignin nanoparticle dispersion; and a natural rubber latex.
[0051] In an embodiment, the lignin nanoparticle dispersion having an amount in the range of 0.1 to 10 phr (parts per hundred rubber) of the total weight of the nanocomposite. Preferably, the amount of lignin nanoparticle is in the range of 1 to 7 phr of the total weight of the nanocomposite. The lignin nanoparticle dispersion is prepared by using kraft lignin without any purification.
[0052] In an embodiment, the natural rubber latex having DRC (Dry Rubber Content) in the range of 30 to 70. Preferably, the DRC of natural rubber latex is 60 DRC.
[0053] Another embodiment of the present disclosure provides a green method for synthesis of a natural rubber-lignin nanocomposites comprising: a) treating an aqueous dispersion of kraft lignin with a high shear homogenizer under condition to obtain lignin nanoparticle dispersion; b) mixing of 0.1 to 10 phr of lignin nanoparticle dispersion with 30 to 70 DRC of a natural rubber latex via probe sonication in an ice bath to obtain a natural rubber latex/lignin nanoparticle (NRL/LNP) dispersion; c) dipping the molds into natural rubber latex/lignin nanoparticle (NRL/LNP) dispersion of step b) to fabricate a thin film followed by withdrawing the glass molds from the latex compound, and the molds are dried under condition to obtain a dried film; d) cooling the dried film under condition, followed by second dipping and subsequent drying to obtain a second thin film; e) processing the second thin film of step d) by vulcanization under condition to obtain a vulcanized thin film; f) removing the vulcanized thin film from the molds using silica powder to obtain a vulcanized sample; g) casting the remaining NRL/LNP dispersion onto a glass plate, dried and vulcanized to obtain a vulcanized sample; and h) allowing all the vulcanized samples to mature under condition to obtain the natural rubber-lignin nanocomposites.
[0054] In an embodiment, the condition in step a) is carried out at a speed in the range of 10000 to 20000 rpm for a period in the range of 5 to 15 hrs. Preferably, condition in step a) is carried out at a speed of 15000 rpm for a period of 10 hrs.
[0055] In an embodiment, the mold in step c) is washed and dried at a temperature in the range of 60 to 80 °C before dipping the latex compound. Preferably, drying is carried out at the temperature of 70 °C.
[0056] In an embodiment, the dipping speed in step c) ranging from 0.5 to 2 cm/sec. Preferably, the dipping speed ranging from 1 to 1.5 cm/sec.
[0057] In an embodiment, the condition includes in step c) includes drying the molds at a temperature in the range of 50 to 70 °C. Preferably, the temperature is 60 °C.
[0058] In an embodiment, the cooling in step d) is carried out at a temperature in the range of 15 to 30 °C. Preferably, the cooling temperature is in the range of 20 to 25 °C.
[0059] In an embodiment, the drying in step d) is carried out at a temperature in the range of 50 to 70 °C. Preferably, the drying temperature is 60°C.
[0060] In an embodiment, the vulcanization of step e) is carried out at a temperature in the range of 70 to 90 °C for a period in the range of 30 min to 60 min. Preferably, the vulcanization temperature in step e) is 80 °C for a period of 45 min.
[0061] In an embodiment, the vulcanization of step g) is carried out at a temperature in the range of 90 to 110 °C for a period in the range of 30 min to 90 min. Preferably, the vulcanization temperature in step g) is 100 °C for a period of 60 min.
[0062] In an embodiment, the mature condition in step h) includes temperature in the range of 15 to 30 °C for a period of at least 3 days. Preferably, the temperature is in the range of 20 to 25 °C for a period of at least 3 days.
[0063] Recently, biomaterials have garnered tremendous interest in research and industry due to the increasing problems associated with the usage of non-renewable materials. Natural rubber latex (NRL) is a biopolymer, primarily consisting of cis-1,4-poly (isoprene) along with carbohydrates, lipids, proteins, etc. Given its excellent elasticity, tensile strength, flexibility, elongation, resilience and inhibition to water and acid, natural rubber (NR) is regarded a valuable elastomer. NR exhibits less heat-build up and better electrical insulating characteristics upon dynamic stress. Incorporation of various nanofillers can enhance the mechanical, barrier, electrical, thermal, antimicrobial, and other characteristics of NR to a great extent. Therefore, NR-based nanocomposites are considered to be excellent candidates for numerous industrial and day-to-day applications includes aerospace, automotive, healthcare, electronics, sensors, oil sorbent, electromagnetic interference shielding, supercapacitors, etc.
[0064] Lignin stands as an organic complex biopolymer and is the biopolymer with the second-highest prevalence. Lignin can be extracted from wood residues, black liquor, and agricultural residues. Lignin exists in various types, including kraft lignin, hardwood lignin, soft wood lignin, lignosulfonate lignin, alkaline oxidation lignin, organosolv lignin, etc., based on their origin and extraction technique. Possessing a cross-linked structure and a diverse array of functional moieties such as carboxyl, methoxyl, carbonyl and hydroxyl and cross-linked structure, lignin exhibits numerous distinctive properties including antimicrobial, biodegradability, biocompatibility, antioxidant, ultraviolet (UV) absorption, adhesive properties, thermal stability, stabilizing effect, reinforcing ability, etc. Considering all these properties, its availability and cost-effective production, vast range of works have been carried out in lignin. Converting lignin from its micro size into nano form yields enhanced properties, opening up new possibilities for applications. Lignin nanoparticle (LNP) synthesis has been reported by numerous researchers. Temperature, concentration, pH, solvent/antisolvent, etc. are some of the factors that can tune the shape of the lignin nanoparticle. Mechanical procedures, anti-solvent precipitation, self-assembly, and stand out as extensively used approaches for lignin nanoparticle synthesis. Use of excessive organic solvents, lengthy and complicated procedures, etc. are some of the drawbacks associated with lignin nanoparticle synthesis and researchers are trying to find green, simple, and safe methods.
[0065] Recently, bio-based reinforcing fillers are gaining more research interest due to its biocompatibility, biodegradability, easy availability, eco-friendly nature, etc. Among various bio-nanofillers, lignin nanoparticles are excellent reinforcing agents for various polymers. Tailoring to specific applications, insertion of lignin into polymers can be done with or without chemical modifications. The introduction of lignin into rubber produces less dense, non-conducting, and light-coloured material. Incorporating bio-based nanofillers into a bio-polymer like NR leads to the development of environment-friendly NR nanocomposites with exciting properties. In the present disclosure, LNP synthesized via the homogenization method was incorporated into NRL using probe sonication, and NR/Lignin nanocomposites (NR/LNP) were fabricated using latex dipping method. The addition of LNP resulted in significant enhancements in mechanical and antibacterial properties, biodegradability, and UV blocking capabilities with the addition of 7 parts per hundred rubber (phr) of LNP, due to the uniform dispersion and effective interaction between NR and LNP. This research demonstrates a versatile pathway for integrating LNP into NR through a green method, enabling the production of eco-friendly NR nanocomposites for multifunctional applications. This pathway contributes to a safe disposal of NR based products.
[0066] Lignin, a valuable biomaterial having an array of exciting properties is increasingly favoured as a reinforcement material in the fabrication of green composites. Reinforcement in biopolymers like NR using LNP is considered a hotspot today. The intricate structure and greater molecular weight of lignin pose challenges in the synthesis of lignin-based nanocomposites. Studies based on LNP- reinforced NR matrices are very less. In the prior arts, the focus was solely evaluating the thermal or mechanical characteristics of the NR nanocomposites. No work has been reported on evaluating the biodegradability, antimicrobial, and UV blocking ability of NR after LNP addition. Moreover, no research has been reported based on the LNP synthesized via the homogenization method NRL. In the present disclosure, NR/LNP nanocomposites are prepared via the double dipping method and analyzed the mechanical, thermal, antibacterial, biodegradation, and UV-blocking characteristics of the nanocomposites. Therefore, this is the first study, concentrating on the multifunctional analysis of NR/LNP nanocomposites. The entire work was carried out using water as a solvent and is free of toxic solvents; therefore, this method is environmentally friendly for fabricating NR/LNP nanocomposites with excellent mechanical, thermal, biodegradation, antibacterial, and UV-blocking properties. Lignin is one of the abundant wastes generated from several sources such as paper and pulp industry, cellulose extraction, biorefineries and crop production. Properly separating lignin from these waste sources and converting it into nanolignin allows its use as nanofiller for NR, thereby actively mitigating the waste issues associated with lignin. Additionally, the insertion of lignin not only addresses waste problems linked to lignin but also augments the biodegradability of NR, promoting environmentally friendly material fabrication practices. Consequently, this work establishes a sustainable pathway for disposal of biomedical devices based on NR nanocomposites, such as surgical gloves, condoms, catheters, and surgical tubing. Moreover, the efficient UV blocking property exhibited by these nanocomposites can be effectively used in the fabrication of protective clothing.
[0067] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

EXAMPLES
[0068] The present disclosure is further explained in the form of following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the disclosure.
Example 1
(A) Materials
[0069] Kraft Lignin (Low sulfonate content, average Mw ~10,000, particle size ~ 6 µm, 99 % purity) for the synthesis of nanoparticle was purchased from Sigma Aldrich and used as received. Distilled water was employed for the synthesis of LNP. Prevulcanized latex was produced using double-centrifuged latex (DRC- 60%). Centrifuged NRL was preheated to 550C before compounding process. The compounding process occurred in a compounding tank with slow (15-20 rpm) and continuous stirring with compounding materials such as vulcanizing agent (1.0 phr), primary accelerator (0.5 phr), secondary accelerator (0.2 phr), activator (0.9 phr), antioxidant (0.5 phr), dispersing agents and stabilizer. After adding these chemicals, the mixture was stirred continuously for about 1 h. The prevulcanization of the latex was then carried out by heating the compounded NRL in a SS tank jacketed with hot water at 550C for eight to ten hours until a proper state of cure was attained.
(B) Lignin nanoparticle synthesis
[0070] Lignin nanoparticle dispersion was synthesized as follows: obtained kraft lignin was used without any purification. 30% of LNP was prepared by homogenization method by using a 10 hrs high shear homogenizer (Heidolph, Silentcrusher M) at 15000 rpm. During the homogenization process, the homogenizer was operated for 60 min period, and 10 min was allowed to cool down the temperature and mass of bubbles to settle down.
(C) Fabrication of NR/LNP Nanocomposites
[0071] NR/LNP nanocomposites were fabricated using latex double-dipping method, which involves mold pre-treatment, latex double dipping, vulcanization and stripping. Initially, a 30% LNP dispersion was mixed with NRL via probe sonication (750 W, 3 min at 20% amplitude) in an ice bath. From the 30% LNP dispersion, volumes corresponding to 1, 3, 5, and 7 phr of LNP dispersion were taken for 300 mL latex. The dipping process was conducted using a semi-automatic dipping machine (PLASTOMEK Private Ltd. India). Thin films were fabricated by dipping the molds, after washing and drying at 70°C, into the latex compound at a dipping speed ranging from 1-1.5 cm/sec. After the initial dipping and withdrawal of the glass molds from the latex, the molds were dried at 60°C in an oven. The films were then cooled at room temperature, followed by a second dipping and subsequent drying at 60°C. Vulcanization was then carried out for 45 min at 80°C. The final thin films were removed from the molds using silica power. The residual latex was cast onto a glass plate with dimensions of 15 × 15 cm and vulcanized at 100°C for 1 h. The vulcanized samples were then allowed to mature at room temperature for a minimum 3 days. NR nanocomposites containing 1, 3, 5, and 7 phr nanocomposites are represented by NRL1, NRL3, NRL5, and NRL7. Figure 1 illustrates the fabrication of NR/LNP nanocomposites.
(D) Characterization of LNP and NR/ LNP Nanocomposites
i) FT-IR
[0072] The Infrared spectrum of lignin and LNP is depicted in Figure 2. Presence of various vibration modes of chemical bonds in the lignin makes the IR spectrum complex in nature. The large broad band seen at 3500-3100 cm-1 is associated with the phenolic and alcoholic hydroxyl functionalities, whereas the peak at 2945 and 2838 cm-1 is because of the C-H stretching vibrations of the methoxy group. The stretching vibration of C=O is viewed at 1725 and distinctive vibrations from the aromatic rings are at 1600, 1518, and 1462 cm-1. IR spectra of both bulk and LNP exhibit a similar structure with slight shift in peaks towards longer wavelengths, indicating that the chemical structure of lignin remains unaltered and is unaffected by the formation of LNP. The homogenization process conserved the functional groups in the bulk lignin, and there were no significant changes observed in the core of the lignin structure. Both the lignin and nanolignin have the same structure, resulting in no significant differences in their FT-IR spectra.
ii) XRD
[0073] Figure 3 represents the XRD profiles of lignin and LNP. Both lignin and LNP show a broad area in the diffractograms which proves the amorphous behavior of both the materials. However, the peak intensity of LNP was reduced in comparison to lignin. Lignin shows a maximum 2Ѳ value at 300, whereas LNP is at 23.40. The diffraction peaks at 30.470 and 320 in bulk lignin disappeared in LNP which shows the change in the crystallinity in LNP after the homogenization process. Moreover, the peak at 39.250 in lignin is shifted to a lower angle (34.770) in LNP. The crystallinity of LNP was found to be small with a broad amorphous region than the bulk, suggesting that the LNP has lower crystallization degree than bulk lignin.
iii) Particle Size
[0074] Particle size determination of LNP is crucial for its utilization as a reinforcing material in NRL. The size of LNP was analyzed, and the particle size distribution is presented in Figure 4. As shown in Figure 4, the majority of particle sizes of the LNP concentrate are between 130 to 170 nm. Although the size distribution spans a wide range from 20 nm to 205 nm, the average diameter of LNP was 151.1 nm.
iv) Morphological Analysis
[0075] SEM analysis is generally explored to investigate the morphological inspection of materials. Figures 5a and 5b are the high-magnification FE-SEM images of bulk lignin and LNP, respectively whereas Figures 5c and 5d are the low-magnification images of bulk lignin and LNP, respectively. Initially, the lignin existed in an agglomerated form due to strong intermolecular hydrogen bonding between macromolecular lignin. As depicted in Figure 5d, the size of lignin was reduced after the homogenization process. TEM is an efficient tool to study the shape, size and surface analysis of nanoparticles. Figure 6 represents the microstructure and morphological images of bulk lignin and LNP analyzed by TEM. From the TEM, both samples exhibit an irregular shape, but raw lignin has more aggregated structure. The size of LNP is smaller than that of lignin. TEM images of LNP reveal nanosized precipitates, indicating that LNP contains small lignin particles forming aggregate-like structures.
v) Antibacterial Analysis
[0076] Figure 7 and Table 1 depict the antibacterial efficacy of lignin and LNP. The antibacterial actions of lignin are not yet fully understood. Various studies propose different mechanisms. Some studies propose that the antibacterial action of lignin is linked to its ability to induce oxidative stress in bacterial cells through the production of hydrogen peroxide. This antibacterial action is also correlated with the polyphenol’s capability to prevent essential enzymes for bacteria. Moreover, other studies highlight their ability to disrupt the integrity of the bacterial membrane, thereby improving the cell permeability. Here, antibacterial action of LNP is higher than that of bulk lignin. Small size of LNP facilitates easy penetration into the bacterial cell wall. Upon entering the cell, it is believed that small phenolic compounds from lignin, such as cinnamaldehyde, may induce reduction in intracellular pH, resulting in depletion of ATP. The antibacterial action of LNP also involves a rise in oxidative stress by stimulating the production of ROS.
Table 1: Inhibition zone of Lignin and LNP.
No Sample Zone of Inhibition (mm)
E. coli S. aureus
1 Lignin 14 ±0.763 13±1.112
2 LNP 29±1.312 28±1.270

vi) FT-IR of NR/LNP nanocomposites
[0077] FT-IR analysis is essential for examining the chemical and physical interactions occurring in the composite materials. Figure 8 presented the FT-IR spectra of NR and NR/LNP nanocomposites. The NR film showed characteristic peaks at 3038 cm-1 (=CH stretching), 2838-2953 cm-1 (C-H stretching), 1660 cm-1 (C=C stretching), 1366-1460 cm-1 (C-H bending) and 834 cm-1 (C=CH wagging) [68]. Peaks in the range of 3500 cm-1 to 3050 cm-1 corresponded to the O-H group [69]. Additionally, the vibrational band at 1541 cm-1 was associated with amide II, while the band at 1044 cm-1 was linked to C-O stretching.
[0078] As the LNP content increased, the broadening of the O-H peak also intensified, accompanied by a shift of peak center towards higher wavenumber, indicating the formation of hydrogen bonds between the LNP and NR. With the introduction of LNP, the peak observed at 2917 cm-1, corresponding to =CH, lost intensity and showed a reduction in peak area. Additionally, this peak shifted to a higher wavenumber (2941 cm-1) compared to NR.
[0079] Furthermore, the peak at 1541 cm-1 shifted to 1594 cm-1 with increasing LNP content, and its intensity increased, possibly due to interactions between non-rubber components and lignin’s functional groups. The peaks at 1377 cm-1 and 1442 cm-1 shifted to higher wavenumbers (1385 cm-1 and 1450, respectively), and broadened, likely indicating the hydrogen bonding interactions between lignin’s functional groups and NR’s methyl groups. The peak at 1044 cm-1 in NR split into two peaks in NRL5 and NRL7. Lignin exhibited C-O stretching vibrations from ether and alcohol at 1030 cm-1. The peaks in NRL5 and NRL7 at 1040 cm-1 and 1096 cm-1 representing the overlap of lignin’s C-O-C or C-O stretching vibrations with those of NR, resulting in a doublet. The addition of LNP altered the molecular environment within the NR due to interactions between the non-rubber components of NR and lignin’s functional groups. These interactions led to shifts or splitting of vibrational modes in the composite, highlighting lignin’s influence on the properties of the nanocomposite.
[0080] The small shifts found in many wavenumbers suggested interactions between the aromatic C–H groups of lignin and NR. The FT-IR spectra confirmed that NR and lignin interactions were not merely physical but involved chemical changes. Both the polyisoprene chain, and non-rubber components contributed to bond formation with LNP, as evidenced by the appearance of new peaks, shifts in existing peaks, and changes in intensity.
vii) XRD of NR/LNP nanocomposites
[0081] XRD analysis of the nanocomposites was conducted to evaluate the crystallinity of NR after incorporating LNP. Figure 9 showed the diffraction patterns of NR and nanocomposites. NR did not exhibit any sharp peaks, but displayed a broad bump at 19.37°, confirming its amorphous nature. LNP displayed peaks at 2Ѳ value of 23.4°, 34.77°, yet no additional LNP peaks appeared in the XRD patterns of NR nanocomposites. Moreover, the intensity of the broad NR peak reduced with increasing LNP content, indicating interactions between NR and LNP. The nanoscale dispersion of LNP within the NR layers masked the LNP peaks, forming a network with non-rubber components and crosslinking agents. Similar behavior was observed in NR nanocomposites with nanocellulose, where Zn/cellulose complex network formed between the NR matrix layers. The complete absence of LNP peaks in the composites indicated efficient dispersion of LNP in NR. In another study, the crystalline peaks corresponding to cellulose nanofibres were completely absent in NR nanocomposites due to chemical interactions between NR, crosslinking agents and nanocellulose.
viii) Morphological Analysis
[0082] Optical microscopy analysis was captured at 40x magnifications to examine the distribution of LNP in the NR and the images are shown in Figure 10. For, NRL1 and NRL3, the mode of dispersion of LNP is not uniform due to the insufficient loading of LNP particles for the interaction between NR and LNP. Compared to NRL1 and NRL3, a moderate uniform LNP dispersion was attained in NRL5, however, the transparency of the nanocomposite was reduced. In NRL7, LNP particles are homogeneously distributed in the NR. Compared to all other samples, the transparency of the NRL7 is very low; due to the increased LNP loading.
[0083] TEM studies of nanocomposites provide detailed information regarding the dispersion of LNP during nanocomposite preparation. The TEM images of thin sections of NR and NRL7, showcased in Figure 11. Different black spots in NR (Figure 11A) are identified as compounding ingredients. In NRL7, LNPs are uniformly distributed within the NR. Figure 11B shows the development of a continuous LNP network within the NR. LNPs surround NR particles and react with NR through its non-rubber components such as lipid, proteins, fatty acids, etc. This interaction leads to the creation of a network-like lignin structure, where NR acts as a template for the development of the LNP network. In NRL7, high surface area of LNPs facilitates closer and more intimate interaction with NR.
ix) Crosslink Density
[0084] Elastomers are useful only when they are properly cross-linked. The swelling of elastomers reduces as the νe increases. The νe and swelling ratios of the samples attained by the swelling method are shown in Table 2. With an increase in LNP loading, the νe was increased due to the improved interaction between NR and LNP. NRL7 demonstrated highest the crosslink density. The addition of 7 phr nanolignin gave the highest crosslink density. An 8.42% increase in crosslink density was observed for NR with 7 phr of nanolignin, whereas a 59.55% improvement in crosslink density was observed in our system.
Table 2: Swelling ratio and υe of NR and NR/LNP nanocomposites.
No Sample Swelling ratio Crosslink density (10-4 mol/cm3)
1 NR 5.388 0.89
2 NRL1 4.891 1.12
3 NRL3 4.594 1.22
4 NRL5 4.345 1.31
5 NRL7 4.114 1.42

x) Mechanical Properties
[0085] The results of the mechanical analysis for the composites are illustrated in Figure 12 and summarized in Table 3. The tensile strength of NR nanocomposites demonstrated a gradual rise with an increase in LNP loading. Insertion of 7 phr LNP dispersion showed the highest improvement in tensile strength (33.3%), at this loading LNPs were uniformly dispersed in the NR medium, which has been disclosed by optical microscopy images. The modulus of elasticity of nanocomposites is increased from 1.12 to 1.29 MPa with the insertion of LNP. This improved modulus indicates that the nanocomposites have higher stiffness. The modulus of elasticity and tensile strength increment with LNP addition is attributed to the reduced NR chain motion. The interfacial interaction between NR and LNP increases with rising LNP concentrations due to the reduced spaces between NR and LNP, which enhanced their contact. Considering all these, nanoscale lignin was effectively dispersed in the NR and consequently stresses were transferred to LNP from soft polyisoprene matrix resulting in the enhancement in tensile strength. However, elongation at break decreases with the introduction of LNP due to the rise in chain immobilization with nanofiller loading. It can be concluded that a combination of NR-NR, LNP-LNP, and NR-LNP interactions provide excellent mechanical properties to the NR/LNP nanocomposites.
Table 3: Mechanical properties of NR and NR/LNP nanocomposites.
Sample Tensile strength
(MPa) Enhancement
(%) Elongation at
Break (%) Modulus at 300% elongation (MPa)
Control 21.0±2.213 - 768.5±18.070 1.12±0.046
NRL1 22.9±1.467 9.0 741.3±15.989 1.16±0.036
NRL3 24.1±1.736 14.7 727.3±17.725 1.19±0.029
NRL5 25.2±2.896 19.5 718.4±19.326 1.23±0.029
NRL7 28.0±1.575 33.3 702.8±16.234 1.29±0.048
xi) Thermal Analysis
a) TGA
[0086] TGA was performed to explore the influence of LNP addition on the thermal stability of NR. TGA of LNP, neat NR, and its nanocomposites are presented in Figure 13A. Figure 13B shows DTG of NR and its nanocomposites and the related parameters are summarized in Table 4. In LNP, the reduction in mass from 200-600°C happened as a result of the structural decomposition of lignin and the development of new chemical bonds. Hydrogen and carbon elimination as well as partial lignin fragmentation takes place in the range of 650-1000°C. Compared to neat NR, the initial thermal stability of LNP is low. The onset temperature of NR is around 325.2°C and shifts to 327.6°C, 323.8°C, 323.4°C and 317.6°C for all the LNP nanocomposites with 1, 3, 5 and 7 phr of LNP. Thermal degradation of LNP started at 201°C; however, decomposition of NR/LNP nanocomposite happened only after 325°C. The TGA and DTG curves feature a single degradation peak, showing that the thermal degradation of the samples is primarily a one-stage process. Moreover, it also confirms the uniformity of the system. The peak temperature of the DTG curves, or the temperature corresponding to the maximum loss rate, ranges from 379-384°C. The degradation temperature of NRL1 is marginally greater than that of NR. With an increase in LNP, thermal stability was reduced, except for NRL1. The percolation network played a role in the increase in thermal stability at lower loading, even though the thermal stability of LNP is less. The reduced thermal stability at greater LNP loading is ascribed to the lower thermal stability of LNP. A similar trend in thermal stability was observed in NR nanocomposites containing nanocellulose. An initial improvement was noted at 2.5 % nanocellulose, followed by a decline at 5 %, 7.5 %, and 10 % of nanocellulose loadings. The enhanced thermal stability at lower loading was due to the percolation network and Zn/cellulose complex even though nanocellulose has lower thermal properties. However, at higher loadings, the reduced stability was linked to the critical volume fraction and percolation threshold value. Additionally, nanocellulose has lower degradation temperature than NR, further contributed to the decline in thermal stability at higher loadings. The improved thermal stability at 1 phr LNP and the reduction at higher loadings in present study can be attributed to the increased incorporation of thermally less stable LNP, which introduces more organic matters into NR. This makes the composite more susceptible to thermal degradation, despite enhancements in other properties, such as mechanical strength, antibacterial activity, and UV blocking, at higher loadings. Even though the degradation of LNP-containing NR nanocomposites occurred faster, the residual mass at 800°C is higher for these nanocomposites. This residual mass increment with LNP loading was due to the lignin’s carbonaceous composition of the lignin.
Table 4: TGA results of NR and NR/LNP nanocomposites.
Sample Tonset (°C) Residual mass (Wt%) Wt loss (%) Tmax (°C)
NR 325.2 2.14 93.0 379.6
NRL1 327.6 2.73 90.5 384.1
NRL3 323.8 3.18 88.8 382.6
NRL5 323.4 3.56 88.5 381.9
NRL7 317.6 8.65 88.21 380.0

b) DSC
[0087] DSC measurements were conducted to analyze the impact of LNP on Tg of NR and the obtained DSC data are shown in Figure 14. It can be seen that the Tg of NR is about -55.150C, but addition of LNP shifted the Tg into a lower temperature region except in NRL7. The decrease in Tg with increasing LNP loading implies that LNPs can be regarded as functioning like a plasticizer. The presence of LNPs introduces additional free volume between NR chains, promoting increased chain mobility and consequently lowering Tg. However, in case of NRL7, Tg is observed at -54.60C which is much higher than that of all samples, especially the NR. This increase in Tg in NRL7 might be due to the restricted motion of NR chains by the cross-links formed by the LNPs. As LNP content increases and reaches a saturation point, the additional LNPs may contribute to increased interactions, reducing chain mobility. These increased interactions result in a more constrained polymer matrix, making it less flexible and requiring a higher temperature for the transition from a glassy to rubbery state.
(xii) Antibacterial Analysis
[0088] Antibacterial activity resulting from the insertion of LNP into natural rubber was analyzed on S.aureus and E.coli and the images are presented in Figure 15. Zone of inhibition of NR and NR/LNP nanocomposites are listed in Table 5. NR and its nanocomposites showed very good bactericidal action against S. aureus. The antibacterial activity observed in neat NR is attributed to the presence of the compounding agent, ZnO. In addition, the proteins present in NRL also exhibit bactericidal action. The addition of 7 phr LNP into NR led to the highest antibacterial activity on E. coli compared to neat NR and other nanocomposites. Cell wall damage and enzyme inhibition produced by polyphenols cause the death of microorganisms. The presence of methyl groups in the γ position, along with double bonds in α, β locations of the side chain, enhances the phenolic segment’s activity against microorganisms. In addition to this, the reduced size can also play a crucial role in inhibiting bacterial growth. Reduced size of LNP helps easy penetration of LNP into the cell membrane of bacteria when compared to macro-sized lignin. When the nanosized lignin enters inside the bacterial cell wall, mono phenolic compounds derived from lignin may reduce the intracellular pH of bacteria and lead to bacterial death. Similar to lignin, chitin is another biomaterial with antibacterial properties.
Table 5: Inhibition zone of NR and NR/LNP nanocomposites.
No Sample Zone of Inhibition (mm)
E. coli S. aureus
1 NR 16±0.512 17±0.631
2 NRL1 17±0.327 19±3.157
3 NRL3 15±3.112 18±0.789
4 NRL5 15±2.131 17±3.583
5 NRL7 19±0.321 20±0.534

xiii) Biodegradation Studies
[0089] Biodegradability is crucial property for materials intended for use in packaging and medical applications. Biodegradation of NR is a slow process, needs long period for its breakdown.
[0090] This study examined the influence of LNPs on the soil biodegradation of NR, with Figure 16 depicting the biodegradability measured in terms of % weight loss after 4 weeks. Figure 17 represents the images of nanocomposite samples during the biodegradation study. The degradation of polymer is associated with changes in colour, morphology and size. A preliminary indication of degradation is the observed colour variations during the analysis periods, with a reduction in brightness noted for all samples after the fourth week. Figure 16 clearly shows that the presence of LNP in NR promotes the biodegradation of NR in soil. Control NR shows very low degradation; only 3% weight loss. The rate of biodegradation increased with the rise in LNP loading, in which NR with 7 phr LNP exhibited the highest degradation; it exhibited 13.1% degradation after the fourth week. The biodegradation rate is correlated with the amount of LNP, and the heightened degradation is because of the existence of LNP in the NR matrix. Biodegradation of lignin takes place faster than rubber.
[0091] Consistent with previous studies, the biodegradation process initiates with LNP and then extends to NR, which take a longer time to degrade. The degradation of LNP commences with the accumulation of microbes on the LNP. Microorganisms can easily consume the lignin in NR, leading to enhanced porosity, formation of void, and deterioration of rubber integrity. The void formation resulting from LNP biodegradation helps the breakdown of NR into small pieces. SEM images of control and NRL7 samples before and after the biodegradation process is shown in Figure 18. The voids in the control sample after degradation are of small size whereas the voids in NRL7 are of larger size. Figure 18g and 18h clearly prove that the voids in NRL7 are slowly penetrating to nearby spaces leading to further degradation. These findings positively support the biodegradation of NR samples containing lignin nanoparticles.
xiv) UV blocking properties
[0092] A significant disadvantage of NR is its inability to withstand UV irradiation, leading to degradation through a photooxidation process that involves chain scission, crosslinking, and formation of various oxidized products. The lignin is known for its UV absorbing capabilities. Therefore, the effect of LNP insertion on the UV shielding ability of NR was systematically examined, and the results are presented in Figure 19a. The brown coloration observed in the films containing LNP is due to the chromophoric nature of the LNP, and this distinct feature is recognized for its ability to block UV radiation.
[0093] All the NR/LNP systems displayed effective UV blocking even at low loadings of LNP, however, neat NR was unable to show this property, it shows transmittance in the UV range and maintained transparency in the visible range. Notably, the nanocomposites exhibited substantial UVB (280-315 nm) blocking at lower LNP loadings (1 and 3 phr). As LNP loading increased (5 and 7 phr), UV shielding extended to UVA (315-400 nm), albeit with a marginal reduction in visible light transparency. Transmittance values approached zero with increasing LNP content, showing that UV shielding increased with an increase in LNP content. Consequently, NRL7 emerged as the most effective UV blocker among other nanocomposites. In the visible range (400-800 nm), the samples exhibited concentration-dependent optical transmittance. Figure 19b shows that, with increasing the LNP content, the color of the nanocomposites turns darker and thus shows lesser optical transmittance than pure NR.
[0094] The proposed mechanism behind the UV shielding of LNP is that the LNP can block the UV by absorbing photon energy from UV light and transforming it into heat. The hydrophilic chromophores, especially carbonyl, phenolic hydroxyl and carboxyl groups present on the LNP, serving a key role in this process. The absorbed energy may efficiently transform into heat without causing degradation to NR. These findings underscore lignin’s potential as a UV- absorbing material and highlight its role in improving the UV protection in NR nanocomposites. The UV blocking characteristics of NR films makes them appropriate for various applications, including but not limited to medical devices, textiles, apparel, and packaging.
[0095] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.

ADVANTAGES OF THE PRESENT INVENTION
[0096] The present disclosure primarily used a green method, focusing on waste reduction in NR nanocomposites by the incorporation of nanolignin.
[0097] The present approach not only demonstrates the green synthesis of NR thin films through an industrially relevant method but also offers a solution for waste reduction.
[0098] LNP were synthesized through a green method, employing water as the solvent. The incorporation of LNP into NRL using the latex dipping method caused improvements in mechanical strength, thermal stability, antibacterial properties, biodegradability and UV blocking characteristics.
Introduction of 7 phr of LNP shows highest improvement in the properties except thermal properties due to the better NR-LNP interactions and even distribution of LNP in the NR medium. Though, higher amount of LNP did not support the thermal stability of NR/LNP nanocomposites. The study thus depicts the multifarious functions of lignin in the synthesis of biodegradable NR nanocomposites which enhance the utility of NR in the fabrication of biomedical devices and cope up with the menace of their disposal. Moreover, the efficient UV blocking property exhibited by these nanocomposites can be effectively used in the fabrication of protective clothing. The antibacterial action of thin films prepared by this method has been investigated.
, Claims:1. A natural rubber-lignin nanocomposites comprising:
a lignin nanoparticle dispersion; and
a natural rubber latex.
2. The natural rubber-lignin nanocomposites as claimed in claim 1, wherein the lignin nanoparticle dispersion having an amount in the range of 0.1 to 10 phr.
3. The natural rubber-lignin nanocomposites as claimed in claim 1, wherein the lignin nanoparticle dispersion is prepared by using kraft lignin without any purification.
4. The natural rubber-lignin nanocomposites as claimed in claim 1, wherein the natural rubber latex having DRC in the range of 30 to 70.
5. A green method for synthesis of natural rubber-lignin nanocomposites comprising:
a) treating an aqueous dispersion of kraft lignin with a high shear homogenizer under condition to obtain lignin nanoparticle dispersion;
b) mixing of 0.1 to 10 phr of lignin nanoparticle dispersion with 30 to 70 DRC of a natural rubber latex via probe sonication in an ice bath to obtain a natural rubber latex/lignin nanoparticle (NRL/LNP) dispersion;
c) dipping the molds into the natural rubber latex/lignin nanoparticle (NRL/LNP) dispersion of step b) to fabricate a thin film followed by withdrawing the glass molds from the latex compound, and the molds are dried under condition to obtain a dried film;
d) cooling the dried film under condition, followed by second dipping and subsequent drying to obtain a second thin film;
e) processing the second thin film of step d) by vulcanization under condition to obtain a vulcanized thin film;
f) removing the vulcanized thin film from the molds using silica powder to obtain a vulcanized sample;
g) casting the remaining NRL/LNP dispersion onto a glass plate, dried and vulcanized to obtain a vulcanized sample; and
h) allowing all the vulcanized samples to mature under condition to obtain the natural rubber-lignin nanocomposites.
6. The method as claimed in claim 5, wherein the condition in step a) is carried out at a speed in the range of 10000 to 20000 rpm for a period in the range of 5 to 15 hrs.
7. The method as claimed in claim 5, wherein the mold in step c) is washed and dried at a temperature in the range of 60 to 80 °C before dipping the latex compound.
8. The method as claimed in claim 5, wherein the dipping speed in step c) ranging from 0.5 to 2 cm/sec.
9. The method as claimed in claim 5, wherein the condition includes in step c) includes drying the molds at a temperature in the range of 50 to 70 °C.
10. The method as claimed in claim 5, wherein the cooling in step d) is carried out at a temperature in the range of 15 to 30 °C.
11. The method as claimed in claim 5, wherein the drying in step d) is carried out at a temperature in the range of 50 to 70 °C.
12. The method as claimed in claim 5, wherein the vulcanization of step e) is carried out at a temperature in the range of 70 to 90 °C for a period in the range of 30 min to 60 min.
13. The method as claimed in claim 5, wherein the vulcanization of step g) is carried out at a temperature in the range of 90 to 110 °C for a period in the range of 30 min to 90 min.
14. The method as claimed in claim 5, wherein the mature condition in step h) includes temperature in the range of 15 to 30 °C for a period of at least 3 days.