A process for preparation of nanocrystalline cellulose and application thereof

Abstract

The present invention provides a continuous mechano-chemical synchronization process designed to enhance the yield of acid hydrolysis of cellulose, specifically targeting the production of nanocrystalline cellulose (NCC). The process employs a two-stage controlled acid hydrolysis of Micro Crystalline Cellulose (MCC), utilizing a uniquely tailored reactor configuration to control morphology and optimize process efficiency. Additionally, it outlines advanced downstream operations for product neutralization and purification through tubular centrifuge and nano-pores membranes. The present invention also explores the potential for resource recovery for sustainability approach in this extraction process and demonstrates applications on biodegradable packaging, reinforced plastics and as absorbent materials for hygiene products.

Description

[0001] PJN105187

[0002] A PROCESS FOR PREPARATION OF NANOCRYSTALLINE CELLULOSE AND APPLICATION THEREOF

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a method for the preparation of nanocrystalline cellulose (NCC) with continuous mechano-chemical synchronization. Particularly, the present invention relates to a continuous mechano-chemical synchronization process, which focuses on an enhancement in the acid hydrolysis route by involving the two-stage controlled acid hydrolysis of cellulose source (Micro crystalline cellulose (MCC)) to produce nanocrystalline cellulose (NCC) with unique and specifically tailored reactor configuration and its downstream operation for product neutralization and purification.

[0005] BACKGROUND OF THE INVENTION

[0006] Cellulose is the most abundant and sustainable material on planet Earth. Besides its relative abundance, it is inexpensive, non-toxic, biodegradable, renewable, reusable, and environmentally friendly. The cellulose can be used to prepare the next generation of nanomaterials, nanocrystalline cellulose (NCC) which has attracted great attention in recent years. The NCC has a "rod-like" structure, short, and stiff, with length from 100 nm to several microns. The NCC can be extracted from cellulosic sources such as pulp and microcrystalline cellulose (MCC) through various treatments or techniques. During such treatment, the amorphous section in the cellulose chain is digested to obtain a highly crystalline and light-denser material that has excellent mechanical properties, a large specific surface area, and biodegradability making it with potential application in biodegradable and allied industries. NCC also finds application in various industries that including in emulsions, foams, optical devices, adhesives, composites, packaging, oil and gas (drilling), non-woven, textile and green chemicals.

[0007] The cellulose is well known to its strong hydrogen bonding force in the intramolecular and intermolecular phases. The chemical structure of cellulose has always been a problem in extracting NCC in uniform size nanocrystals with high stability and large-scale industrial production. There are various methods for extraction through mechanical route likePJN105187

[0008] physical ball milling and ultra- sonication, chemical route like acid hydrolysis, TEMPO-oxidation and enzymatic hydrolysis.

[0009] Reference may be made to the patent application “CN106220904” which discloses a method for preparing NCC with its application in modified sodium alginate degradable composite film. It further discusses the use MCC as the starting material which undergoes acid hydrolysis at 45 DEG C for 2-3h for the preparation of degradable composite membrane having good biodegradable and biocompatibility.

[0010] Reference may be made to the patent application “CN109776883” which discloses a preparation method of an NCC / modified konjac glucomannan degradable film by acid hydrolysis of microcrystalline cellulose with sulfuric acid to obtain NCC and further discusses the compounding of NCC in biodegradable film by modifying konjac glucomannan with chloroacetic acid. The film prepared reported that it has the advantages of good flexibility, high mechanical strength, degradability, high thermal stability and environmentally friendly.

[0011] Reference may be made to the patent application “IN202241064456” which discloses the synthesis of cellulose nano crystals (CNC) through mechanical route by hybrid hydrodynamic cavitation-assisted acid hydrolysis of micro-crystalline cellulose (MCC) for the development of cellulose nano crystals wherein 39% for the particles range from 23 nm to 100 nm and 57.6% of the particle possess a size below 500 nm.

[0012] Reference may be made to the Journal “Int. J. Mol. Sci. 2022, 23(18), 10764” which discloses a study on pretreatment effects on the properties of spherical CNC produced from MCC by mixed acid hydrolysis. They achieved spherical CNC with an average size of around 10 nm were formed economically, and reported great mechanical properties, good biocompatibility, a high specific surface area, biodegradability, and a low thermal expansion coefficient for usage in biomedicine, food packaging, and energy storage.

[0013] Reference may be made to the Journal “Enzyme Microb. Technol, 2013, 52 (1), 20-25” which discloses the synthesis of spherical nanocellulose by controlled hydrolysis of microcrystalline cellulose using anaerobic microbial consortium and purified through differential centrifugal technique to achieve size distribution of width in 43 ± 13 and length in 119 ± 9 nm for biomedical application.PJN105187

[0014] Reference may be made to the Journal “Carbohydr. Polym, 2021, 251, 117094” which discloses reported a preparation method of nanocellulose in high yield via chemomechanical synergy in an autoclave followed through ultrasonication to achieve a diameter and length 16 to 45 nm and 150 to 600 nm, respectively.

[0015] Reference may be made to the patent application “CN114345129” which discloses a deacidification method for directly separating acid from a hydrolysate in the process of preparing cellulose nanocrystals using ultrafiltration membrane separation system and ceramic membrane with plate-type or tubular membrane for large-scale production and industrial application.

[0016] However, the above investigations and inventions are restricted to batch processes that lack control over the hydrolysis rate and report a maximum yield of only 20-25%. The reactors used are conventional batch reactors without any process intensification. The neutralization steps are cumbersome and time-consuming, especially during lyophilization or dialysis. Additionally, there is no recovery of spent acid, and the recovery of glucose and inorganic salts has not been addressed. Furthermore, detailed product specifications are not provided in other studies. Scalability is another issue, with difficulties in maintaining efficiency and cost-effectiveness at larger scales.

[0017] In contrast, continuous mechano-chemical synchronization with two-stage hydrolysis along with down-streaming represents a novel and promising approach to produce NCC efficiently and sustainably. This method of producing NCC involves the simultaneous application of mechanical forces (such as grinding, milling, or shearing) and chemical treatments (such as acid hydrolysis or oxidation) to cellulose. The synergistic effect of mechanical agitation and chemical reactions allows for enhanced breakdown of cellulose crystallites size into nanoscale dimension with defined stage of hydrolysis. This synchronization not only accelerates the process but also facilitates better control over the size, morphology, crystallinity and yield of the resulting nanocrystals.

[0018] The advantage of the present invention is that the effectiveness of the continuous mechanochemical synchronization will further destroy the hierarchical structure and digest the amorphous region of the cellulose, thereby increasing the reaction area, and reducing the excessive digestion and successfully preparing the NCC with higher yield. The presentPJN105187

[0019] invention also discloses resource recovery and its application in biodegradable packaging, reinforced plastic and absorbing material for hygiene products.

[0020] OBJECTS OF THE INVENTION

[0021] Main object of the present invention is to provide a process for the preparation of nanocrystalline cellulose (NCC) using mechano-chemical synchronization.

[0022] Yet another object of the present invention is to provide a continuous reactor configuration and optimize the process parameters for controlling the size, morphology, crystallinity of nanocrystalline cellulose particles, enhancing their functional properties and ensuring reproducibility and scalability.

[0023] Another object of the present invention is to provide a continuous mechano-chemical process to overcome commercial gaps in NCC preparation.

[0024] Yet another object of the present invention is to explore and validate reinforcement of NCC in biodegradable products and durable plastic applications, showcasing its potential in enhancing the performance and sustainability in the product.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the schematic diagram of a process for preparation of NCC from MCC (a) conventional batch process (b) present invention’s continuous process.

[0026] FIG. 2 illustrates the schematic diagram of continuous downstream of hydrolyzed suspension (a) Quenched using neutral solution (b) Quenched using base solution.

[0027] FIG. 3 illustrates the schematic diagram of down streaming of centrifuged supernatant (a) Quenched using neutral solution (b) Quenched using base solution.

[0028] FIG. 4 illustrates the process scheme of the tailored reactor for the continuously controlled acid hydrolysis (a) perforated basket (b) twin-screw extruder (c) CSTR (continuous stirred tank reactor) 3 -phase pitch blade.

[0029] FIG. 5 illustrates the geometrical sketch and design details of the R2 reactor configuration (a) perforated basket (b) twin-screw extruder (c) 3-phase pitch blade.PJN105187

[0030] FIG. 6 illustrates the process scheme for mechano-chemical mild hydrolysis and neutralization.

[0031] FIG. 7 illustrates the morphology of NCC prepared from Example 2 with neutral quenching solution (a) transmission electron microscope image (TEM) and (b) particle size distribution.

[0032] FIG. 8 illustrates the NCC prepared from Example 2 with base quenching solution (NH3) by (a) transmission electron microscope (TEM) image and (b) particle size distribution.

[0033] FIG. 9 illustrates the morphology of NCC prepared from Example 2 with base quenching solution (NaOH) by (a) transmission electron microscope (TEM) image and (b) particle size distribution.

[0034] FIG. 10 illustrates the crystallinity index by X-ray diffraction analysis graph (a) cellulose source MCC (b) NCC - neutral quenching solution (c) NCC - base (NH3) quenching solution (d) NCC - base (NaOH) quenching solution.

[0035] FIG. 11 illustrates the surface morphology and purity of NCC prepared from Example 3 by field emission scanning electron microscopy (Fe-SEM) image and energy dispersive X-ray (EDX) of (a) NCC with neutral quenching solution (b) NCC with base quenching solution (NH3) and (c) NCC with base quenching solution (NaOH).

[0036] FIG. 12 illustrates the atomic force microscopy (AFM) of (a) NCC with neutral quenching solution (b) NCC with base quenching solution.

[0037] SUMMARY OF THE INVENTION

[0038] Accordingly, the present invention provides a process for the preparation of nanocrystalline cellulose (NCC) in aqueous suspension and powder form with continuous mechano-chemical synchronization comprising the steps of:

[0039] a) mixing a cellulose source and a hydrolysis agent continuously in a homogenizer reactor (Rl, FIG. 4) to obtain a homogenized suspension;PJN105187

[0040] b) overflowing the homogenized suspension obtained in step (a) into a reactor (R2, FIG. 4 and FIG. 5) followed by controlled acid hydrolysis at a temperature in the range of 45°C to 60°C to obtain a hydrolyzed suspension;

[0041] c) quenching the hydrolyzed suspension as obtained in step (b) with a controlled flow of neutral or basic solution in a reactor (R3, FIG. 4) maintained at a temperature in the range of 5°C tolO°C at an atmospheric pressure followed by constant mixing to obtain a partially quenched suspension by using a neutral solution and a totally quenched suspension by using a basic solution respectively;

[0042] d) centrifuging the partially or totally quenched hydrolyzed suspension obtained in step c) in a centrifuge operated at 10000 to 15000 rpm to obtain NCC cake and a supernatant;

[0043] e) re-dispersing the NCC cake obtained in step d) in a pitch-blade stirrer rotating at a rate of 375 rpm to 450 rpm assisted by a series of membranes adjusted to maintain the pH of the suspension in the range of 5.5-7.5 with conductivity of in the range of 768 - 1200 pS to obtain a neutralized NCC suspension;

[0044] f) washing the totally quenched suspension as obtained in step c) in the pH range of 5.5-7.5 to obtain a neutralized NCC suspension and a supernatant;

[0045] g) spray drying the neutralized NCC suspensions as obtained in steps e) and f) at an inlet temperature in the range of 190°C to 210°C with an atomizer speed in the range of 1850 rpm to 2000 rpm in constant compressed gas flow to obtain NCC powder;

[0046] h) electrodialysis of the supernatant from partially quenched suspension as obtained in step d) to recover inorganic acid followed by reverse osmosis to recover glucose and water;

[0047] i) filtering supernatant obtained in step f) by the use of a bipolar membrane or reverse osmosis to obtain inorganic salts and glucose.PJN105187

[0048] In an embodiment of the present invention, the hydrolysis agent is selected from the group consisting of sulphuric acid (H2SO4), Hydrochloric acid (HC1), Phosphoric acid (H3PO4) and Nitric acid (HNO3) or water.

[0049] In another embodiment of the present invention, the reactor configuration (R2, FIG. 5) is selected from the group consisting of a perforated basket, a twin-Screw extruder or a 3-phase pitch blade impeller.

[0050] In yet another embodiment of the present invention, step (b) is carried out with solid’s content of MCC is at least 5-10% by weight of overall homogenized suspension.

[0051] In yet another embodiment of the present invention, the centrifuge in step f) is selected from the group consisting of a tubular bowl centrifuge or screw centrifuge.

[0052] In still another embodiment of the present invention, the reverse osmosis in step h) has pure water as permeate and inorganic salts with glucose solution the reject.

[0053] In another embodiment of the present invention, the spray drying in step g) of the process is assisted by ultrasonication, freeze drying or lyophilization.

[0054] In still another embodiment of the present invention, the NCC has a particle size in the range of 95-145 nm and 5- 45 pm in suspension and powder form, respectively.

[0055] In still another embodiment of the present invention, the NCC has a yield in the range of 26% - 33% and a high aspect ratio with diameter in the range of 21 nm - 28 nm and length in the range of 112 nm - 130nm.

[0056] In another embodiment of the present invention, the produced NCC compounded as a reinforcement material with thermoplastic starch through extrusion to enhance the thermal and mechanical barrier of the compostable / biodegradable bags.

[0057] In yet another embodiment of the present invention, the NCC obtained co-extrude as a filler with fossil-derived polymer not limited to PE, PP, PU, and PS to enhance its mechanical properties in moulded automotive parts.PJN105187

[0058] In still another embodiment of the present invention, the NCC obtained is used as an absorbent for the application of hygiene products to enhance fluid retention and absorption capacity of the adsorbent core.

[0059] DETAILED DESCRIPTION OF THE INVENTION

[0060] The present invention provides a continuous mechano-chemical synchronization process, which focuses on an enhancement in the acid hydrolysis route by involving the two-stage controlled acid hydrolysis of cellulose source (Micro Crystalline Cellulose (MCC)) to produce nanocrystalline cellulose (NCC) with unique and specifically tailored reactor configuration and its downstream operation for product neutralization and purification.

[0061] The present invention relates to a process for the preparation of nanocrystalline cellulose (NCC) with continuous mechano-chemical synchronization comprising the following steps:

[0062] (a) mixing the MCC (25 - 200 pm) with a hydrolyzing acid agent in a specialized reactor at a temperature of at least about 45 to 60 °C and at a hydrolyzing agent concentration ranging from about 35 to about 65 wt% based on the initial particle size and purity in the modified perforated basket reactor and a twin-screw extruder reactor;

[0063] (b) quenching the acid hydrolyzed suspension in the mean of neutral or a base solution;

[0064] (c) recovering a quenched acid hydrolyzed cake comprising NCC from acid hydrolysis agent through continuous centrifugation;

[0065] (d) mechano-chemical mild hydrolysis neutralization of suspension in pH range 5.5 - 7.5;

[0066] (e) recovering sugars from spent liquor and recovered inorganic acid from spent liquor for reuse in the system or to produce inorganic salts;

[0067] (f) spray drying of neutralized suspension undergoes dilution / ultrasonication to avoid aggregation to get the desired morphology.PJN105187

[0068] The cascade configurations of the present invention are used for the controlled acid hydrolysis of MCC to NCC with scalable downstream and effluent treatment for recovery of acid and sugar as shown in FIG. lb.

[0069] Initially, water and acid are pumped through the inline dosage pump at different retention times in the reactor with MCC feed through the gravimetric feeder system continuously at optimized flow rate. This configuration has reactors Rl, R2 (FIG. 5a, 5b, 5c), and R3 which are temperature-controlled vessels with different temperature profiles in operation. A feed of MCC and acid solution in Rl is controlled to achieve a definite residence time distribution (RTD). The first stage / reactor, Rl (FIG. 4a, 4b, 4c) controls the addition exothermicity of the continuous feed system and initiates the mild hydrolysis under cooling conditions to attain homogeneity in the mixture, then it passes continuously to R2. In the second stage / reactor, R2 (FIG. 4a, 4b, 4c) comprises different tailored reactor configurations that the homogenized suspension from Rl will undergo controlled hydrolysis at a fixed temperature based on the feed particle morphology to obtain hydrolyzed suspension within a fixed desired residence time to pass into the next reactor R3. Wherein the stage / reactor R3 (FIG. 4a, 4b, 4c) initiates quenching of hydrolyzed suspension under cooling conditions through neutral / base solution as illustrated in FIG. 2. The continuous quenched hydrolyzed suspension will pass to downstream operation as in FIG. 6.

[0070] In one instance, the quenched material in R3 passes to the semi-continuous centrifuge, where acidic or neutralized spent is removed as supernatant and passed to a membrane-assisted electrodialysis (E.D) unit to recover acid for reuse or to remove produced inorganic salts and aqueous glucose which is concentrated through a reverse osmosis (R.O) system as shown in FIG. 3. Then the hydrolyzed cake obtained through continuous centrifuge comprising NCC is re-suspended to neutralize or purify through a series of nano-filtration / diafiltration membranes to obtain suspension of NCC in the pH range of 5.5-7.5. The continuously obtained neutralized suspension of NCC is dispersed continuously before being fed to the spray drier to obtain the desired morphology of NCC.

[0071] In the present invention, the reactor R2 is configured as a perforated basket illustrated in FIG. 5a. This comprises L / D of 1 perforated basket made up of stainless steel (SS316L, EN2348) configured in reactor R2 has counterclockwise rotation in 200-800rpm whichPJN105187

[0072] consist of outer ring, center piece and filter mesh of 2 micron. The homogenized suspension from reactor R1 enters to R2 in continuous mode where the basket is in rotation motion in variable speed, this rotation phenomenon increase the contact time of acid and cellulose which results in effective size reduction with limited glucose formation and the filter mesh only allows the desired particle out of the basket. This has increased the potential of acid hydrolysis in mean of selective particle size passage from the basket.

[0073] The reactor R2 is tailored as a twin-screw extruder illustrated in FIG. 5b. The present invention comprises twin-screw extruder as reactor R2 which consist of 1320mm length including metering and mixing zones with 22mm screw diameter and 24 mm barrels having 7 heating zones. The homogenized suspension from reactor R1 enters to R2 in continuous mode where the screw is rotated at variable speed (6-10) rpm throughout feeding zone to metering zone has maintained in the same temperature between 45 to 50 °C and it undergoes acid hydrolysis and forms NCC. This has increased the potential of acid hydrolysis in mean of shear by compression ratio of 3: 1 to 5: 1 between feeder to metering zone which effectively reduce particle size.

[0074] All three reactors are configured as a CSTR-pitch blade illustrated in FIG. 5c. The present invention provides a continuous process in conventional jacketed reactor CSTR with 3-phase pitch blade impellers in Rl, R2, R3 to perform continuous operation of NCC. This blade is configured in L / D of 1.25 to provide continuous operation in NCC preparation by means of agitation as mechanical phenomena. The homogenized suspension from reactor Rl enters R2 where the agitation at a constant speed with 3 -phase pitch-blade impeller at the temperature in the range of 45-50°C is maintained in R2. This has increased the potential of acid hydrolysis in mean of severe agitation that breaks the particle with the help of acid as a catalyst which effectively reduce particle size.

[0075] The present invention comprises the mechanical assisted downstream to promote further size reduction by mild hydrolysis in the preparation process that overcomes the challenges in the neutralization and drying process. The quenched suspension from R3 is sent to a centrifuge that separates cake comprised of NCC and supernatant in pH (0.8-7.5) depending upon the quenching agent. The recovered cake is re-suspended in the agitation tank assisted by nano- porous membrane in series with porosity of 30 nm. This process neutralizes and reduces the conductivity of the suspension ranging from 450-750 pS whichPJN105187

[0076] is preferred for a NCC suspension by limited aggregation of particles and attainment of the particle size of 95-145nm in suspension. The obtained suspension is further centrifuged to remove unhydrolyzed particles and off-spec materials. The centrifuged suspension is transferred to an agitation tank that washes the suspension until the suspension attains 3wt.% (solid content) with conductivity around 100-175 pS. This results in the formation of clean NCC suspension subjected to well dispersed by dilution / ultrasonication, that makes 0.3wt.% suspension which is suitable for spray drying in a desired flow rate at 170-210°C to get a desired NCC with particle size of 5-45 pm.

[0077] In the present invention, two forms of nanocrystalline cellulose (NCC) are produced: one in an aqueous suspension and the other in powder form. Comprehensive characterization of NCC is crucial to assess its purity, morphology, and chemical and physical properties. Various state of art characterization techniques, as detailed in Table 9, are employed to identify key parameters that enhance the commercial viability and application potential of the produced NCC and its developed product specification is mentioned in Table 10.

[0078] The most commonly known process for preparing nanocellulose through the acid hydrolysis is shown in FIG. la. The acid hydrolysis method operates by the infiltration of the amorphous cellulose region via hydronium ions in strong acids, thereby catalyzing cellulose hydrolysis and facilitating the isolation of the crystalline cellulose fraction to yield nanocellulose. However, despite its industrial adoption, this method is plagued by notable limitations. These encompass prolonged processing durations, substantial wastewater generation, equipment susceptibility to corrosion induced by the strong acidic environment, and diminished yields attributable to extensive cellulose degradation.

[0079] EXAMPLES

[0080] Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

[0081] Example 1: Controlled Acid Hydrolysis of MCC

[0082] Example la: Through a perforated basket

[0083] In a cascade setup according to FIG. 4a, industrially available MCC (1000 g of 150-240 microns with 2.45% moisture; procured from Sigachi, Kalyan’s Tulsi Ram Chambers,PJN105187

[0084] Madinaguda, Hyderabad Telangana- 500049) was added to the homogenizer reactor R1 continuously along with the neutral solution and 98% acidic solution to make up 60 wt.% acidic solution for 1: 10 S / L at 10°C in atmospheric pressure and constant mixing to control exothermicity of the reaction. Through the overflow of Rl, the homogenized suspension enters R2 (FIG. 5b) configured by a perforated basket, where controlled acid hydrolysis takes place at 45°C in atm pressure at variable RPM. The hydrolyzed suspension of R2 gets quenched with a controlled flow of base or neutral solution in R3 maintained at 5°C in atmospheric pressure at constant mixing to attain the pH ranges of 0 to 0.2 by using a neutral solution as a partially quenched suspension while the pH range of 5.5-7.5 is achieved by using a base solution to obtain a totally quenched suspension. An aqueous solution of NCC has been obtained; this obtained quenched suspension is sent to the mechano-chemical neutralization process. The particle size reduction of each stage is mentioned in Table 1, estimated based on the Dynamic Light Scattering (DLS) method.

[0085] Example lb: Through twin-screw reactor

[0086] Similar to Example la reaction conditions this example differs in the R2 (FIG. 5b) configuration shown in FIG. 4b, the homogenized suspension from Rl enters R2 (Twin-screw reactor) rotating at 8 rpm to get effectively hydrolyzed with a reduction in particle size that attains high crystallinity index. Followed by quenching in R3 with an analysis similar to the above example.

[0087] Example 1c: Through CSTR- 3 stage pitch blade

[0088] Similar to Example la reaction conditions this example differs in R2 (FIG. 5c) configuration, this example shows cascade setup of CSTR shown in FIG. 4c. The MCC get homogenized in Rl, suspension enters R2 through overflow where controlled hydrolysis at specific 650 rpm. Followed by quenching in R3 with an analysis similar to the above example.

[0089] Table 1: Particle size reduction over the reactors

[0090]

[0091] PJN105187

[0092]

[0093] Example 2: Mechano- Chemical mild hydrolysis and Neutralization

[0094] This example shows the mechano-chemical mild hydrolysis and neutralization of hydrolyzed suspension obtained from above Example 1.

[0095] Example 2a: Partially quenched suspension

[0096] As shown in FIG. 6, the partially quenched hydrolyzed suspension in a pH range of 0-0.2 is sent to semi-continuous tubular centrifugation operated at 15000 rpm to collect NCC cake and supernatant. The obtained cake is re-dispersed at S / L of 1:125 in a pitch-blade stirrer rotating at 375 rpm which is assisted by a series of membranes adjusted to maintain the pH of the suspension in the range of 5.5-7.5 with conductivity of 768 - 1200 pS. The neutralized suspension has a viscosity of 50-1 lOcP, density in the range of 1-1.03 kg / cm3, and particle size less than 130 nm at 3 wt.% of solid.

[0097] In FIG. 7, Transmission Electron Microscopy (TEM) and Particle Size Distribution (PSD) of the NCC prepared in this example, represented a high aspect ratio as the diameter is 21 nm and the length is 112 nm.

[0098] Example 2b: Totally quenched suspension

[0099] Similar to Example 2a, a totally quenched suspension in the pH range of 5.5-7.5 is washed to remove impurities such as sulphate salts. FIG. 8 and 9 represent NCC prepared based on different base solution in this example has a high aspect ratio as the diameter is 28 nm and the length is 130 nm.

[0100] This example shows that this method of preparing NCC has a high aspect ratio. Then the obtained suspension is dried to get NCC powder.

[0101] Example 3: Product DryingPJN105187

[0102] In FIG. 6, neutralized suspension was sent to the spray drying unit to obtain NCC powder. The continuous dilution / ultrasonication is done for well dispersed suspension. The spray drier is operated at an inlet temperature of 190°C with an atomizer speed of 2000 rpm in constant compressed gas flow. NCC powder achieved a crystallinity index between 90-91 % based on the quenching agent as shown in FIG. 10. While the Fe-SEM conforms its particle size between l-45pm depicted in FIG. 11. FIG. 12 shows the obtained topology of the dried NCC based on different quenching agents. This example has provided a 26-33 % yield of NCC respective to initial raw material weight.

[0103] Example 4: Resource Recovery

[0104] This example provides the recovery of resources from the supernatant generated in Example 2. The hydrolyzed suspension from the controlled acid hydrolysis from R3 is sent to a semi-continuous tubular centrifuge, to remove excess or unreacted acid as spent followed by an addition of quenching agent to adjust pH in the range of 0-0.2 for neutral agent (Partially quenched) and 5.5 to 7.5 for basic agent (Totally quenched). This example has shown that the 80% reduction in the consumption of neutral / base agent and process time on mechano-chemical neutralization process embodied in Example 2.

[0105] Example 4a: Partially quenched suspension

[0106] The supernatant from partially quenched suspension is acidic. Supernatant treated by Electrodialysis to recover inorganic acid followed by reverse osmosis for glucose and water recovery as shown in FIG. 5. Table 2 shows the concentration of inorganic acid and glucose.

[0107] Example 4b: Totally quenched suspension

[0108] Similar to the Example 4a operation, the difference is that the supernatant is slightly basic. Here the recovery undergoes through the usage of a bipolar membrane to concentrate sulphate ions and glucose. Alternatively, inorganic salts and glucose will be concentrated in reverse osmosis where the permeate will be pure water and the reject will be salt with glucose solution which gets spray dried to get powder. This obtained powder can be used as fertilizer.

[0109] Table 2: Spent liquor compositionPJN105187

[0110]

[0111] Example 6: Applications

[0112] Case 1: Biodegradable packaging

[0113] The prepared NCC is reinforced in thermoplastic starch (TPS) to make biodegradable packaging and products. The 3-6 wt. % (corresponding to TPS) of NCC powder is compounded to obtain reinforced TPS (r-TPS) through a twin-screw extruder. The obtained r-TPS granules are blown with poly-butylene Adipate terephthalate (PBAT) in the ratio of 40 / 60 (r-TPS+PBAT). The produced bags are tested to its mechanical and physical properties in comparison with neat TPS and TPS with PBAT blend in Table 3.

[0114] Table 3: Mechanical and physical properties of Biodegradable films

[0115]

[0116] PJN105187

[0117] Case 2: Fiber reinforcement

[0118] The prepared NCC are used as a filler for reinforcing polypropylene (PP) composite used to make products for automotive applications. The 5% and 10% NCC powder was compounded with PP through co-rotating twin screw extruder and molded through injection molding. The obtained specimens are checked for its mechanical and thermal properties with comparison of neat PP and commercial MCC as filler shown in Table 4.

[0119] Table 4: Mechanical and physical properties of fiber reinforced plastic

[0120]

[0121] Case 3: Hygiene product

[0122] Prepared 1% of NCC has embedded in the layer of pulp to form the adsorbent core. The core is then formed into sheets through air-laying or wet-laying processes, followed byPJN105187

[0123] drying to remove excess moisture. Once dried, the sheets are cut to the desired shapes and sizes. These sheets are undergone quality checks to ensure the NCC’s absorption and fluid retention capacity meets the necessary standard according to ASTM shown in Table 5.

[0124] Table 5: Specification of NCC embedded absorbent core

[0125]

[0126] Table 9: Techniques for CNC characterization

[0127]

[0128] PJN105187

[0129] & &

[0130]

[0131] Table 10: Developed Product specifications

[0132] (a) Aqueous Product:

[0133]

[0134] (b) Powder Product:

[0135]

[0136] PJN105187

[0137]

[0138] ADVANTAGES OF THE PRESENT INVENTION

[0139] • Main advantage of the present invention is to provide a mechanochemical synchronization method, enhanced by a tailored reactor configuration for producing nanocrystalline cellulose (NCC).

[0140] • The mechanochemical synchronization method of the present invention, by effectively disrupting the cellulose's hierarchical structure, increases the reaction surface area and the crystalline regions' resistance to sulfuric acid digestion compared to traditional acid hydrolysis.

[0141] • The present invention provides a two-stage controlled acid hydrolysis technique assisted by nano-porous membrane downstream manages the intense oxidation and dehydration effects of sulfuric acid, reducing dehydration and preventing yellowing or charring due to incomplete hydrolysis or high solid concentrations during washing.

[0142] • The present invention provides a semi-continuous centrifugation process which efficiently separates NCC from the effluent and reduces the quenching agent usage. Another advantage of the present invention is the use of electrodialysis and ReversePJN105187

[0143] Osmosis emphasizing resource recovery and providing sustainable and economic benefits.

[0144] • The present invention provides sulfuric acid hydrolysis introducing sulfonate groups onto the NCC, which ionize and create a negatively charged surface.

[0145] • The method of the present invention enhances the dispersion of NCC in aqueous solutions, improving its suitability for various applications, including biodegradable plastics, durable plastic and as an absorbent in hygiene products.

[0146] • The NCC preparation is economical and commercial due to the effective advantages of this process.

[0147] • The produced NCC is used for the application of biodegradable bags, automotive parts and hygiene applications not limited to other applications that incorporate NCC as a filler, additive and reinforcement.

Claims

PJN105187WE CLAIM1. A process for preparation of nanocrystalline cellulose (NCC) in aqueous suspension and powder form with continuous mechano-chemical synchronization comprising the steps of:a) mixing a cellulose source and a hydrolysis agent continuously in a homogenizer reactor (Rl) to obtain a homogenized suspension;b) overflowing the homogenized suspension obtained in step (a) into a reactor (R2) followed by controlled acid hydrolysis at a temperature in the range of 45 °C to 60 °C to obtain a hydrolyzed suspension;c) quenching the hydrolyzed suspension as obtained in step (b) with a controlled flow of neutral or base solution in a reactor (R3) maintained at a temperature in the range of 5 °C to 10 °C at an atmospheric pressure followed by constant mixing to obtain a partially quenched suspension by a neutral solution and a totally quenched suspension by a base solution, respectively;d) centrifuging the partially or totally quenched hydrolyzed suspension obtained in step (c) in a centrifuge at 10000 rpm to 15000 rpm to obtain a NCC cake and a supernatant;e) re-dispersing the NCC cake obtained in step (d) in a pitch-blade stirrer rotating at a rate of 375 rpm to 450 rpm assisted by a series of membranes adjusted to maintain the pH of the suspension in the range of 5.5-7.5 to obtain a neutralized NCC suspension;f) washing the totally quenched suspension as obtained in step (c) to obtain a neutralized NCC suspension and a supernatant;g) spray drying the neutralized NCC suspensions as obtained in steps (e) and (f) at an inlet temperature in the range of 190 °C to 210 °C with an atomizer speed in the range of 1850 rpm to 2000 rpm in constant compressed gas flow to obtain NCC powder;PJN105187h) electrodialysis of the supernatant from partially quenched suspension as obtained in step (d) to recover inorganic acid followed by reverse osmosis to recover glucose and water;i) filtering supernatant obtained in step (f) by the use of a bipolar membrane or reverse osmosis to obtain inorganic salts and glucose.

2. The process as claimed in claim 1, wherein the partially quenched suspension is obtained by using a neutral solution to attain the pH range of 0 to 0.2 and the totally quenched suspension is obtained by using a base solution to attain the pH range of 5.5 to 7.5.

3. The process as claimed in claim 1, wherein the hydrolysis agent used in step (b) is selected from the group consisting of sulphuric acid (H2SO4), hydrochloric acid (HC1), phosphoric acid (H3PO4), nitric acid (HNO3) or water.

4. The process as claimed in claim 1, wherein the reactor (R2) is selected from the group consisting of a perforated basket, a twin-screw extruder or a 3 -phase pitch blade impeller.

5. The process as claimed in claim 1, wherein the homogenized suspension in step (b) is having a solid content of micro crystalline cellulose (MCC) in the range of 5-10% by weight of the overall homogenized suspension.

6. The process as claimed in claim 1, wherein the centrifuge in step (d) is selected from the group consisting of a tubular bowl centrifuge, a screw centrifuge or a nanopores membrane.

7. The process as claimed in claim 1, wherein the spray drying in step (g) is assisted by ultrasonication, freeze drying or lyophilization.

8. The process as claimed in claim 1, wherein the reverse osmosis in step (h) has pure water as permeate and inorganic salts with glucose solution as the reject.PJN1051879. The process as claimed in claim 1, wherein the NCC suspension as obtained in step (f) has a particle size in the range of 95-145 nm and the NCC powder as obtained in step (g) has a particle size in the range of 5-45 pm.

10. The process as claimed in claim 1, wherein the yield of the NCC is in the range of 26% - 33% and an aspect ratio with diameter in the range of 21 nm - 28 nm and length in the range of 112 nm - 130nm.

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