A process for preparation of lignin-reinforced natural rubber (NR) latex composite

Abstract

The present invention discloses a process for preparation of lignin-reinforced natural rubber (NR) latex composite. The present invention is particularly related to a process for preparation of lignin-reinforced natural rubber (NR) latex composite; wherein said natural rubber (NR) latex is selected from Hevea brasiliensis, Parthenium argentatum (Guayule) and Taraxacum kok-saghyz (TK). Furthermore, the present invention is related to a process for preparation of lignin-reinforced natural rubber (NR) latex composite for providing enhance thermal stability, mechanical strength and antimicrobial properties.

Description

[0001] A PROCESS FOR PREPARATION OF LIGNIN-REINFORCED NATURAL RUBBER (NR) LATEX COMPOSITE FIELD OF THE INVENTION

[0002] The present invention is related to a process for preparation of lignin-reinforced natural rubber (NR) latex composite. The present invention is particularly related to a process for preparation of lignin-reinforced natural rubber (NR) latex composite; wherein said natural rubber (NR) latex is selected from Hevea brasiliensis, Parthenium argentatum (Guayule) and Taraxacum kok-saghyz (TK).

[0003] BACKGROUND OF THE INVENTION

[0004] Rubber compounding is crucial in industries like tire manufacturing, automotive, aerospace, medical, and industrial goods. Rubber compounding is the process of mixing raw rubber with various ingredients to achieve desired properties for specific applications. The main goal of rubber compounding is to enhance properties such as elasticity, durability, chemical resistance, thermal stability, mechanical strength and processability.

[0005] Many synthetic additives in rubber compounding, such as nitrosamine-forming accelerators, phthalates, carbon black, and PAH-rich oils, pose health and environmental risks, including carcinogenicity, respiratory issues, and aquatic toxicity. Other harmful compounds include halogenated flame retardants, phenolic antioxidants, and VOC-emitting resins. Safer alternatives like low-PAH oils, phosphorus-based flame retardants, and bio-based plasticizers can reduce these hazards, promoting eco-friendly rubber manufacturing.

[0006] Lignin is a natural biopolymer and byproduct of the pulping and biorefinery industries, has gained significant attention as a sustainable reinforcing filler for natural rubber (NR) latex composites. It offers several advantages, such as biodegradability, thermal stability, and potential for improved mechanicalproperties. However, lignin agglomerates due to its polar nature, while NR latex is non-polar, causing weak adhesion.

[0007] Soda lignin, a renewable byproduct of soda pulping, enhances the mechanical strength, thermal stability, and biodegradability of natural rubber (NR) latex composites. However, its dispersion in NR is challenging due to polarity differences. Surface modifications may improve compatibility. Optimized filler loading (5-20 wt%) balances reinforcement and processability. Applications include tires, gloves, coatings, and packaging, offering a sustainable alternative to petroleum-based fillers.

[0008] Prior art S. H. Botros et al. (2004) discloses thermal stability and dielectric relaxation of natural rubber / soda lignin and natural rubber / thiolignin composites. The influence of soda lignin(20 phr) on the mechanical properties (tensile strength is around 5 to 12 and elongation at rupture is around 1000 to 1200 %). Incorporation of either soda lignin into NR mixes results in composites with shorter cure time 15 (tc90, min).

[0009] Prior art F. J. Tibenham et al. (1954) discloses compounding natural rubber with lignin and humic acid. The process involved grinding lignin and water in a ball mill for 2 hours, adding caustic soda, and mixing with concentrated latex. The mixture was then mixed with diluted formic acid, resulting in a filterable crumb with 36 parts of lignin per 100 parts of rubber.

[0010] As mentioned in above prior art, there are several drawback such as the material's low tensile strength limits load-bearing applications, while its high elongation reduces stiffness and shape retention. Incorporating soda lignin shortens cure time, potentially causing processing challenges like premature vulcanization, reduced durability, and altered viscoelastic properties, affecting long-term performance and flexibility.Furthermore, the process as described in prior art is time-consuming due ball milling and requires careful handling of caustic soda and formic acid. Filterable crumbs may leave residues, needing extra processing. High lignin content reduces elasticity, weakens tensile strength, and stiffens the rubber. Additionally, uneven lignin dispersion can lead to inconsistent material properties, affecting rubber homogeneity and overall performance and durability.

[0011] Therefore, to overcome these challenges, it is essential to develop a process that optimizes mixing to reduce processing time. Using milder alkalis and avoiding synthetic additives that enhances safety and improves crumb quality. Additionally, better lignin dispersion prevents stiffening, while reducing lignin content balances reinforcement and flexibility, ensuring improved rubber homogeneity, mechanical properties, tensile strength and thermal stability.

[0012] Hence, the inventors of the present invention have developed process for preparation of lignin-reinforced natural rubber (NR) latex composite by controlling pH and temperature. This ensures effective lignin dispersion, prevents early coagulation, improves solubility, compatibility, and homogeneity, while also enhancing thermal stability and mechanical strength.

[0013] OBJECTIVE OF THE INVENTION

[0014] The main objective of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite.

[0015] Another objective of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite to enhance thermal stability, mechanical strength and having antimicrobial properties.

[0016] Another objective of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite for preventing early coagulation and providing effective lignin dispersion.Another objective of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite under controlled conditions and showing with no surface cracks.

[0017] Another objective of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite for increase in tensile strength, better retention while elongation at break, improved flexibility, homogeneity and compatibility.

[0018] Another objective of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite for increased durability and environmental resilience, helping to improve eco-friendly rubber-based products.

[0019] SUMMARY OF THE INVENTION

[0020] The main aspect of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite.

[0021] One more aspect of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite; wherein said natural rubber (NR) latex is selected from Hevea brasiliensis, Parthenium argentatum (Guayule) and Taraxacum kok-saghyz (TK).

[0022] One another aspect of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite for the enhancement of thermal stability, mechanical strength and antimicrobial properties.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1: TGA(Thermogravimetric Analysis) of Marketed NR latex sheet, 5 PHR and 10 PHR added lignin composite.Figure 2: TGA of marketed NR sheet

[0025] Figure 3: TGA of 5 PHR lignin NR sheet

[0026] Figure 4: TGA of 10 PHR lignin NR sheet

[0027] DESCRIPTION OF THE INVENTION

[0028] The detailed description set forth below is intended as a description of exemplary embodiments and is not intended to represent the only forms in which the exemplary embodiments may be constructed and / or utilized. The description sets forth the functions and the sequence of steps for constructing and / or operating the exemplary embodiments. However, it is to be understood that the same or equivalent functions and sequences which may be accomplished by different exemplary methods are also intended to be encompassed within the scope of the invention.

[0029] As defined herein, all scientific and technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs.

[0030] Although any process and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described.

[0031] As stated in the present invention herein, the singular forms “a,” “an” and “the” specifically also encompass the plural forms of the terms to which they refer, unless the content clearly dictates otherwise. The term “about” is used herein to means approximately, in the region of, roughly, or around.

[0032] As stated herein, that it follows in a transitional phrase or in the body of a claim, the terms “comprise(s)” and “comprising” are to be interpreted as having an open-ended meaning. That is, the terms are to be interpreted synonymously with the phrases “having at least” or “including at least”. When used in the context of aprocess, the term “comprising” means that the process includes at least the recited steps but may include additional steps. When used in the context of a composition, the term “comprising” means that the composition includes at least the recited features or components but may also include additional features or components.

[0033] The term used herein, “lignin” refers to a complex organic polymer found in the cell walls of plants, particularly in wood and bark. It provides structural support, rigidity, and resistance to decay, making it essential for plant strength and water transport. Lignin is the second most abundant biopolymer on Earth, after cellulose.

[0034] The term used herein, “natural rubber (NR)” refers to a naturally occurring elastomer, and is known for its high elasticity and resilience.

[0035] The term used herein, “natural rubber (NR)” is refers to a dry material, while “natural rubber latex” is refers to a liquid form of rubber.

[0036] The term used herein “lignin-reinforced natural rubber (NR) latex composite” is refers to a green composite material made by incorporating lignin into natural rubber latex (NRL). This composite has improved mechanical properties, and biodegradability.

[0037] The term used herein “PHR” refers to "parts per hundred rubber". It's a unit of measurement used by rubber chemists to express the weight of ingredients in a rubber compound.

[0038] The main embodiment of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite.Another main embodiment of the present invention is to provide a process for preparation of lignin-reinforced natural rubber (NR) latex composite comprises the steps of:

[0039] a) Measuring 1600 ml of natural rubber (NR) latex from Hevea brasiliensis into a beaker;

[0040] b) Adding ammonia to the step (a) for preventing coagulation and covering the beaker for preventing ammonia evaporation;

[0041] c) Stirring continuously the solution of step (b) and gradually adding the soda lignin dispersion to the NR latex;

[0042] d) Maintaining and ensuring the homogeneity, viscosity, and pH of the mixture of step (c) between 8 and 10;

[0043] e) Adding a 5N organic acid solution in the mixture of step (d) to start coagulation of NR composite at room temperature;

[0044] f) Removing the coagulated rubber mass after 15 to 20 minutes from step (e) and draining the excess of water;

[0045] g) Placing this coagulated mass of step (f) in an oven at 100 ± 5°C for 30 minutes for drying and eliminating all water content to obtain lignin- reinforced natural rubber (NR) latex composite.

[0046] As per one embodiment of the present invention, natural rubber (NR) latex is 100% dry rubber base comprises Hevea brasiliensis, Parthenium argentatum (Guayule) and Taraxacum kok-saghyz (TK).

[0047] As per one embodiment, natural rubber (NR) latex is collected from Kerala kottayyam.

[0048] As per one wmbodiment of the present invention, wherein said natural rubber (NR) latex is high ammonia centrifuged latex with 60% hydrocarbon content.As per prefered embodiment, the said ammonia in a process for preparation of lignin-reinforced natural rubber (NR) latex composite is used in the range of 0.1 to 50 ml, preferably 1 to 20 ml, more preferably 5 ml.

[0049] As per another embodiment of the present invention, process for preparation of said soda lignin dispersion comprises the steps of:

[0050] a) Making alkaline solution while keeping its pH between 12 and 13; b) Adding 50 to 100g of soda lignin in step (a) to get final 5 to 10 PHR soda lignin dispersion.

[0051] As per one embodiment, using NaOH or KOH for making an alkaline solution while keeping its pH between 12 and 13 to get a final 5 to 10 PHR soda lignin dispersion.

[0052] As per one embodiment of present invention, wherein adding the soda lignin dispersion to the NR latex by maintaining the pH between 8 and 10.

[0053] As per one embodiment of the present invention, lignin is commercially provided by Chem Process Systems Pvt Ltd.

[0054] As per another prefered embodiment, wherein said organic acid used in process for preparation can be selected from acetic acid, formic acid, lactic acid, citric acid and calcium chloride.

[0055] As per preferred embodiment of the present invention formic acid or acetic acid can be used as an organic acid.

[0056] As per one embodiment of the present invention, the coagulated rubber mass to obtain a lignin-reinforced natural rubber (NR) latex composite can be further processed and converted into the coagulated sheet.As per one embodiment of present invention, lignin-reinforced natural rubber (NR) latex composite has 12-28% of tensile strength.

[0057] As per one embodiment of present invention, lignin-reinforced natural rubber (NR) latex composite has 425-500 % of elongation at break.

[0058] As per one embodiment of present invention, lignin-reinforced natural rubber (NR) latex composite has 45-55 Shore A of hardness.

[0059] As per one other embodiment of present invention, lignin-reinforced natural rubber (NR) latex composite exhibits thermal stability, with the residual mass at 600°C-900°C rising from 16.9% to 24.7% upon the incorporation of lignin.

[0060] As per one embodiment, the present invention is relates to a process for the preparation of lignin-reinforced natural rubber (NR) latex composite for enhanced thermal stability, mechanical strength, and antimicrobial properties; increased tensile strength; better retention while elongating at break; and improved flexibility, homogeneity, and compatibility for increased durability and environmental resilience, helping to improve eco-friendly rubber-based production.

[0061] The invention is further illustrated by the following examples, which are provided to be exemplary of the invention and do not limit the scope of the invention. While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.

[0062] EXAMPLES EXAMPLE 1: THERMAL STABILITYThermogravimetric analysis (TGA) was done on marketed NR latex sheets, and 5 PHR and 10 PHR lignin-added sheets of present invention are shown in figure 1, figure 2, figure 3, figure 4 and table 1.

[0063] Sr Sample Residual Mass at Major Weight Loss Heating Rate No. 900°C (%) (%) (°C / min) 1. NR 16.9% 83.1% 10 2. 5 PHR 23.3% 76.7% 10 3. 10 PHR 24.7% 75.3% 10

[0064]

[0065] Table 1: Thermal stability

[0066] Result:

[0067] Lignin addition improves thermal stability by increasing residual mass at 600°C- 900°C from 16.9% to 23.3% of 5 PHR and 24.7% of 10 PHR, promoting char formation and protecting the material from degradation. Lignin also reduces decomposition rate, with minimal gains from 5 PHR to 10 PHR.

[0068] EXAMPLE 2: EVALUATION OF LIGNIN-REINFORCED NATURAL RUBBER (NR) LATEX COMPOSITE

[0069] All the testing of the samples of final lignin-reinforced natural rubber (NR) latex composite was done in accordance with ASTM Standards D 5289, D 412-16, D 2240-15, D 297, D 395-18, D 5963-04, D 573-04, and D 1149-2018; the samples are as shown below:

[0070] 1) Sample 1: T1

[0071] T1 is NR rubber (Latex Sheet)

[0072] 2) Sample 2: T2

[0073] T2 is 5 PHR lignin- reinforced NR latex

[0074] 3) Sample 3: T3

[0075] T3 is 10 PHR lignin- reinforced NR LatexEXAMPLE 2.1: Rheometric test

[0076] Sr Rheometric test ASTM. Sample code No. Test condition: 24 °C± 2 Std. Tl T2 T3 1. Minimum torque(ML) D 5289 0.34 0.42 0.50 (dN-m)

[0077] 2. Maximum torque(MH) 9.20 9.15 9.24 (dN-m)

[0078] 3. (MH-ML) Torque 8.86 8.73 8.24 (dN-m)

[0079] 4. Scorch time tS2 0.75 0.84 0.92 (Min)

[0080] 5. Optimum cure time, t90 1.77 1.76 1.73 (Min)

[0081]

[0082] Table 2: Rheometric test

[0083] As shown in Table 2, rheological tests were conducted on all test samples Tl, T2, and T3 using the Moving Die Rheometer (MDR).

[0084] Example 2.2: Properties of stress and strain

[0085] The stress and strain properties were assessed after a 5-minute cure time under 150 °C.

[0086] Sr Stress- strain properties ASTM. Std. Sample code No. Test condition: 24 °C± 2 Tl T2 T3 1. 100% Modulus (MPa) D-412-16 1.5 1.6 1.8 2. 200% Modulus (MPa) 2.8 2.9 3.2 3. 300% Modulus (MPa) 4.7 3.2 3.1 4. Tensile strength (MPa) 12.61 19.6 27.5 5. Elongation at break % 435 495 480 6. Angular tear strength, Die C (KN / m) D 624-2020 32 33 32 7. Hardness (Shore A) D 2240-15 49 49 51 8. Specific Gravity D 297 0.999 0.999 1.002

[0087]

[0088] Table 3: Properties of stress and strain

[0089] Unaged stress- strain properties of test samples Tl, T2 and T3 has shown in table 3. Significant increase in tensile strength from 12.61 MPa (pure NR) to 19.6 MPa (5 PHR lignin) and 27.5 MPa (10 PHR lignin). While the 300% modulus slightly decreased from 4.7 MPa (NR) to 3.2 MPa (5 PHR lignin) and 3.1 MPa (10 PHR lignin), indicating improved flexibility, abrasion resistance significantly improved.

[0090] Example 2.3: Compression set and Din abrasion

[0091] Sr Stress- strain properties ASTM. Std. Sample code No. Test condition: 24 °C± 2 Tl T2 T3 1. Compression set (Strain=25%, Temp D 395-18 29 28 31 = 70 °C, Time 22 hrs)

[0092] 2. Abrasion loss D 5963-04 219 209 198 3. Abrasion Index 52 40 34

[0093]

[0094] Table 4: Compression set and Din abrasion

[0095] As shown in table 4, ASTM D395, Method B is used as a test method to determine the compression set of rubber. Furthermore, ASTM D std. is used to determine abrasion loss and abrasion index. The abrasion index reducing from 52% (NR) to 40% (5 PHR lignin) and 34% (10 PHR lignin), demonstrating enhanced durability.

[0096] EXAMPLE 3: AEROBIC AGED STRESS-STRAIN PROPERTIES

[0097] The aerobic aged stress-strain properties of all test samples were tested under 100°C per 72 hours, the results listed in table 5.

[0098] Sr Rheometric test ASTM. Sample code No. Test condition: 24 °C± 2 Std. Tl T2 T3 1. Change in Tensile strength(%) D 573-04 -15.1 -8.4 -2.2 2. Change in Elongation at break(%) -25 -14 -6 3. Change in Hardness(Shore A) -3 -1 2

[0099]

[0100] Table 5: Aerobic aged stress-strain propertiesResults:

[0101] In aerobic aging studies (100°C, 72 hrs), tensile strength degradation was significantly reduced from -15.1% (NR) to -8.4% (5 PHR lignin) and -2.2% (10 PHR lignin), while elongation at break and hardness was better retained.

[0102] EXAMPLE 4: OZONE TEST

[0103] Ozone testing on all rubber samples was performed under the conditions listed below:

[0104] Test standard: ASTM-D 1149-2018

[0105] Ozone concentration: 50 + 5 pphm

[0106] Test temperature: 40 ± 1 °C

[0107] Total test duration: 72 hours

[0108] Type of strain: Static- 20%

[0109] Test start date: 12-02-2025

[0110] Pretension condition time: 24 hrs

[0111] Sr Time ASTM. Sample code

[0112] No. Test condition: 24 °C± 2 Std. T1 T2 T3

[0113] 1. 24 hours D-412-16 Cracks Cracks not Cracks not Observed observed observed 2. 48 hours Cracks Cracks not Cracks not Observed observed observed 3. 72 hours Cracks Cracks not Cracks not Observed observed observed

[0114]

[0115] Table 6: Ozone test

[0116] Result:

[0117] As shown in table 6, ozone resistance testing on lignin-reinforced rubber exhibits superior performance, with no surface cracks after 72 hours, making it a sustainable, eco-friendly alternative for applications requiring durability, thermal stability, and environmental resistance.

[0118] EXAMPLE 5: ANTIFUNGAL PROPERTYThe tests were conducted at various times by using Gram positive and gram negative bacteria on all the test sample Tl, T2 and T3 as listed below:

[0119] 1) Gram positive bacteria- Staphylococcus aureus (SA)

[0120] (No. S ATCC29213 n=34)

[0121] 2) Gram negative bacteria- Escherichia coli (E.coli)(No. )

[0122] (No. E ATCC25922n=79)

[0123] Test on different hours

[0124] Sr Sample Bacterial strain Control 24th48th72 No. code used cfu / ml cfu / ml cfu / ml 1 Blank Strain (blank) 105cfu / ml 1051051051. Tl Gram Positive 105cfu / ml 85650 60026 1030

[0125] Gram negative 105cfu / ml 85399 55280 858 2. T2 Gram Positive 105cfu / ml 89500 67026 1010

[0126] Gram negative 105cfu / ml 84929 58882 1008 3. T3 Gram Positive 105cfu / ml 99050 63026 1100

[0127] Gram negative 105cfu / ml 87999 54882 862

[0128]

[0129] Table 7: Antifungal property

[0130] EXAMPLE 6: ANTIMICOBIAL TESTING ON SODA LIGNIN

[0131] Effect of lignin concentration on E.coli Growth has shown in below table 8: Sr Lignin concentration (mg) % Growth compared to control no.

[0132] 1. 10 112 %

[0133] 2. 40 100%

[0134] 3. 80 126%

[0135] 4. 100 86.3%

[0136] 5. 140 80.3%

[0137]

[0138] Table 8: Antimicrobial testing of soda lignin

[0139] Table 8 reveals that increasing soda lignin concentration decreases the percentage growth compared to the control.The process involves dissolving lignin powder in sodium hydroxide, ensuring proper dispersion, and incorporating it into NR latex under controlled conditions. Optimized formulations with 5 PHR and 10 PHR lignin content showed superior performance compared to conventional NR latex sheets.

[0140] The study reveals a significant increase in tensile strength from 12.61 MPa to 19.6 MPa and 27.5 MPa, with a slight decrease in the 300% modulus, indicating improved flexibility. Additionally, the abrasion resistance significantly improved, with the abrasion index reducing from 52% to 40% and 34%, indicating enhanced durability.

[0141] Lignin's char-forming ability increased residual mass at 600°C- 900°C, resulting in a significant increase from 16.9% to 24.7%. Aerobic aging reduced tensile strength degradation from -15.1% to -8.4%, and improved elongation at break retention, indicating improved thermal stability.

[0142] Furthermore, Lignin-reinforced rubber demonstrated superior ozone resistance, showing no surface cracks after 72 hours of exposure, making it a sustainable alternative for applications requiring durability, thermal stability, and environmental resistance, contributing to eco-friendly rubber-based materials.

Claims

Claims,We claim1. A process for preparation of lignin-reinforced natural rubber (NR) latex composite comprises the steps of:a) Measuring 1600 ml of natural rubber (NR) latex from Hevea brasiliensis into a beaker;b) Adding ammonia to the step (a) for preventing coagulation and covering the beaker for preventing ammonia evaporation;c) Stirring continuously the solution of step (b) and gradually adding the soda lignin dispersion to the NR latex;d) Maintaining and ensuring the homogeneity, viscosity, and pH of the mixture of step (c) between 8 and 10;e) Adding a 5N organic acid solution in the mixture of step (d) to start coagulation of NR composite at room temperature;f) Removing the coagulated rubber mass after 15 to 20 minutes from step (e) and draining the excess of water;g) Placing this coagulated mass of step (f) in an oven at 100 ± 5°C for 30 minutes for drying and eliminating all water content to obtain lignin- reinforced natural rubber (NR) latex composite.

2. The process for preparation of lignin-reinforced natural rubber (NR) latex composite as claimed in claim 1, wherein said natural rubber (NR) latex is 100% dry rubber base comprises Hevea brasiliensis, Parthenium argentatum (Guayule) and Taraxacum kok-saghyz (TK).

3. The process for preparation of lignin-reinforced natural rubber (NR) latex composite as claimed in claim 1, wherein said natural rubber (NR) latex is high ammonia centrifuged latex with 60% hydrocarbon content.

4. The process for preparation of lignin-reinforced natural rubber (NR) latex composite as claimed in claim 1, wherein process for preparation of said soda lignin dispersion comprises the steps of:a) Making alkaline solution while keeping its pH between 12 and 13; b) Adding 50 to 100g of soda lignin in step (a) to get final 5 to 10 PHR soda lignin dispersion.

5. The process for preparation of lignin-reinforced natural rubber (NR) latex composite as claimed in claim 1, wherein adding the soda lignin dispersion to the NR latex by maintaining the pH between 8 and 10.

6. The process for preparation of lignin-reinforced natural rubber (NR) latex composite as claimed in claim 1, wherein said organic acid used in the process for preparation can be selected from acetic acid, formic acid, lactic acid, citric acid and calcium chloride.

7. The process for preparation of lignin-reinforced natural rubber (NR) latex composite as claimed in claim 1, wherein said composite has 12-28% of tensile strength.

8. The process for preparation of lignin-reinforced natural rubber (NR) latex composite as claimed in claim 1, wherein said composite has 425-500 % of elongation at break.

9. The process for preparation of lignin-reinforced natural rubber (NR) latex composite as claimed in claim 1, wherein said composite has 45-55 Shore A of hardness.

10. The process for preparation of lignin-reinforced natural rubber (NR) latex composite as claimed in claim 1, wherein said composite exhibits thermalstability, with the residual mass at 600°C-900°C rising from 16.9% to 24.7% upon the incorporation of lignin.

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