DESC:Field of invention
The present invention relates to an efficient, easily scalable method for surface modification of natural fibres making them super active leading to enhanced interaction/adhesion with polymers resulting in significantly improved mechanical properties of the composites.
Background of the invention
The use of natural fibres as reinforcers in polymer composites to develop biodegradable composites at reduced cost has increased tremendously over the last decade. In general, the natural fibres are made up of cellulose, hemicellulose, lignin pectin and wax with varying concentrations. The presence of polysaccharides and wax over the fibre surface makes the surface smooth and presence of hemicellulose and lignin is the major cause of hydrophilicity which results in reduced mechanical properties and early failure of such polymer composites.
These fibres are often treated with various chemical agents to remove hemicellulose, lignin, and wax from the surface to create a rough hydrophobic surface for an enhanced fibre-matrix interaction to achieve higher mechanical properties. Along with the chemical treatments, the physical treatments for natural fibers have also been developed which do not lead to any toxic effluents and are therefore preferred over chemical treatments, though using such treatments presents several challenges along with operational risks/hazards while scaling up for industrial processes.
Chemical and Physical treatments of natural fibres have been known in the art for decades however chemical treatments of natural fibres involve treating with a combination of multiple chemicals often involving strong alkali or chemicals such as glutaraldehyde which when used in large amounts on an industrial scale possess operational risks due to their toxicity and adverse effects, also disposing of these chemicals requires immense purifications adding to the cost and energy requirement for the process. There have a few attempts to treat natural fibres using green processes such as supercritical CO2 and other non-toxic chemicals though such established treatment processes are often time-consuming for example, the treatment using chemical agents such as amine containing polymers, generally requires the fibres to be soaked in the solution for longer periods of time, such as 48 hours. Some of these processes though often suitable for lab-scale treatment pose severe operational risks considering the required safety norms making them unsuitable for large scale applications.
Accordingly, there exists a need of an efficient and scalable green fibre treatment process that is capable of treating the fibres on a large scale and subsequently improving the mechanical properties of the composites being prepared using said fibres.
Summary of the invention
The present invention provides a process for surface modification of natural fibre and utilization thereof in development of polymer composites. The process of the present invention comprising of treating natural fibres in a reaction chamber at a temperature in the range of 30°C to 140 °C and at a pressure in the range of 2-20 bar. The reaction chamber is supplied with water through a liquid supply line connected thereto. Preferably, the water is supplied to the reaction chamber at a room temperature followed by an elevated temperature in the range of 30°C to 140°C. The reaction chamber is also supplied with pressurized gaseous CO2 through a gas supply line connected thereto. A chemical supply line is connected to the reaction chamber to supply an optimized amine compound prepared using a combination of simple amines (PNH2). The said presence of water and CO2 along with PNH2 under specific conditions facilitates the removal of hemicellulose and lignin from said natural fibres thereby roughening the surface of said natural fibres and reducing the water attracting groups from the surface thereby adding functionalities such as carboxylic, ketone and amino groups, which enhance interactions with the polymer matrix which lead to an overall stronger polymer-fibre interaction. In next step, the super active natural fibre is obtained with enhanced inherent properties along a product line and residual water is collected along a residual water stream. In further step, the residual water stream is subjected to a filtration through a filter for obtaining sub-micron lignin removed along separate line. In next step, the super active fibres of earlier step are processed through a twin-screw extruder along with a polymer or bio-polymer matrix in order to obtain a polymer-fibre composite material.
In accordance with an embodiment of the present invention, the process facilitates treatment and activation of the surface of said natural fibres to increase the polymer-fibre interaction thereby improving load transfer resulting in enhanced mechanical properties while avoiding the use of any toxic chemical. In the context of the present invention, extraction of sub-micron lignin which is a high impact filler material for polymer composites is of high commercial value.
In accordance with an embodiment, the polymer-fibre composite of the present invention utilizes super active fibres that facilitate an increased tensile strength, an increased tensile modulus, an increased impact strength, an increased flexural modulus and an increased heat distortion temperature up to 150.1 ºC to the polymer-fibre composite. The polymer-fibre composite has an increased thermal stability due to removal of hemicellulose and lignin therefrom.
The process of the present invention utilizes water and CO2 along with a simple functionalized non-toxic material under specific conditions with temperatures of 30 °C to 140 °C and pressure as low as 2-20 bar which facilitates scalability to an industrial level without any major operational risks as being not involving high pressures, high temperatures or toxic chemicals. Further, the process of the present invention utilizes CO2 in gaseous state which results in the decrease in CO2 concentration in the environment. In addition, water in combination with CO2 can be filtered and reused for multiple cycles as not involving any toxic chemicals or producing any toxic affluents.
Brief Description of Drawings
FIG. 1 is an illustrative representation of a process for preparing super active natural fibres for polymer and biopolymer composites development in accordance with the present invention;
FIG. 2 shows FTIR analysis of fibers after being treated through the process of the present invention;
FIG. 3 is an illustrative representation of addition of functional groups on a fibre surface during the process of the present invention;
FIG. 4 shows SEM images of the fibres after treatment through the process of the present invention;
FIG. 5 shows the lignin particles extracted from the fibers using the process of the present invention;
FIG. 6 shows SEM images of the treated fibers incorporated in the composite in accordance with the present invention;
FIG. 7 shows a graphical representation of Tensile Strength property of the polymer fibre composite upon treatment using the process of the present invention;
FIG. 8 shows a graphical representation of Tensile Modulus property of the polymer fibre composite upon treatment using the process of the present invention;
FIG. 9 shows a graphical representation of Impact Strength property of the polymer fibre composite upon treatment using the process of the present invention;
FIG. 10 shows a graphical representation of Flexural Strength property of the polymer fibre composite upon treatment using the process of the present invention;
FIG. 11 shows a graphical representation of Flexural Modulus property of the polymer fibre composite upon treatment using the process of the present invention; and
FIG. 12 shows a graphical representation of Tensile Strength property of the polymer fibre composite upon treatment using the process of the present invention.
Detailed Description of the invention
The invention described herein is explained using specific exemplary details for better understanding. However, the invention disclosed can be worked on by a person skilled in the art without the use of these specific details.
References in the specification to "one embodiment" or " an embodiment" means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment. References in the specification to "preferred embodiment" means that a particular feature, structure, characteristic, or function described in detail thereby omitting known constructions and functions for clear description of the present invention.
Referring to FIG. 1, the present invention provides a process (100) for preparing super active natural fibres for polymer and biopolymer composites development that begins with treatment of natural fibres in a reaction chamber (102). The reaction chamber is configured to carry out fibre treatment process (100) at a predefined temperature and pressure conditions. The predefined temperature in accordance with the present invention is in the range of 30°C to 140 °C and the pressure for the treatment covers a range of 2-20 bar. The temperature and pressure are correlated for a right tradeoff for the better output.
The reaction chamber (102) is filled with a feedstock containing natural fibres. A liquid supply line (104) is connected to the reaction chamber (102) to supply water to the reaction chamber (102). A gas supply line (106) is connected to the reaction chamber (102) to supply CO2 in gaseous state to the reaction chamber (102). A chemical supply line (108) is connected to the reaction chamber (102) to supply an optimized amine compound prepared using a combination of simple amines (PNH2). Accordingly, the process (100) of the present invention is designed to carry out treatments of the natural fibres in the reaction chamber (102) in presence of water and CO2 along with PNH2 under specific conditions to accelerate and enhance the natural fibre treatment thereby obtaining surface modified natural fibre with enhanced inherent properties along a product line (110).
In particular, the natural fibres are treated physically using pressurized gaseous CO2 which has the capability to dissolve and can also be removed easily in gaseous state, along with PNH2 under specific conditions where the temperature and reaction pressure are controlled simultaneously while maintaining a direct relation between them, this removes hemicellulose and lignin thus roughening the fibre surface and reducing the water attracting groups from the surface while at the same time adding functionalities such as carboxylic, ketone and amino groups, which enhance interactions with the polymer matrix which lead to an overall stronger polymer-fibre interaction. The utilization of PNH2 in the process is at a very low concentration and does not require or produce any additional or produce toxic affluents. The treatment also results in conversion of lignin present in the fibres into sub-micron particles which are further obtained along a line (116) through filtration of the residual water stream (112) via a filter (114). It is understood here that sub-micron lignin is an equally important product. Further, it is understood here that the residual water obtained from the reaction chamber (102) contains a mixture of hemicellulose, pectin, and wax in dispersed form.
The treated fibers are then then fed directly into the twin screw extruder along with the polymer or bio-polymer matrix at predetermined processing conditions and feed rate for the preparation of biocomposites which are obtained along a line (118) with evenly dispersed aligned fibres acting as load bearers in the composite.
As shown in FIGS. 2 and 3, the FT-IR analysis revealed a decrease in peak intensity at around 3200 cm-1 representing OH peaks which indicates removal of hydroxide containing hemicellulose and lignin from the fibres also corroborated from the obtained dark brown color of the residual water. The process is also expected to result in addition of functional groups on the fiber surface which can be inferred from the observation showing extra generated peaks around 1700 and 2800 cm-1 along with the signature Carbon Chain peaks. The use of gaseous CO2 under specific conditions as proven from FT-IR analysis is capable of removing lignin and hemicellulose from the fibres which leads to surface modified fibers that can be seen through scanning electron microscope (SEM) images as shown in FIG. 4. It is observed that increased interaction area leads to enhanced fibre-matrix interaction.
As shown in FIG. 4, the fibres in their natural state are smooth in nature because of which their adhesion with the polymer matrix difficult but after the treatment (as seen in the FIG. 4), the surface becomes highly active due to removal of wax, polysaccharides, hemicellulose and lignin. Increased activity of fibres helps increase the polymer-fibre interaction thus improving load transfer resulting in enhanced mechanical properties while avoiding the use of any toxic chemical. The fiber-matrix adhesion also increases as a result of addition of functional groups following the treatment due to actions of CO2 and PNH2. Increased surface activity of fibers along with increased functionality helps increase the polymer-fiber adhesion thus resulting in enhanced mechanical properties. The same is evident from SEM images of the treated fibers incorporated in the composite as seen in FIG.6. The lignin extracted in the process was observed in the form of particles ranging from nano to micro range dispersed in water with size ranging around 200-300 nm as seen in FIG. 5.
The complete process is also carried out in a much shorter duration compared to most chemical treatments. In the reported process the amine groups tend to react with cellulose in pressurized CO2 through a process that typically involves the functionalization of cellulose in the fluid. In this state, pressurized CO2 acts as a solvent that facilitates the interaction between cellulose and amine groups. The high temperature and pressure of CO2 can enhance the reactivity of the amines, allowing them to form bonds with hydroxyl groups on the cellulose. Pressurized CO2 tends to penetrate the cellulose structure, creating a favorable environment for the reaction. The amine functionalities act as nucleophiles, attacking the electrophilic hydrogen atom of the hydroxyl group (-OH) on cellulose, resulting in the formation of a strong covalent bond (Cellulose-O-NH-). Lignin, when extracted through the process, are also obtained in the form of evenly dispersed sub-micron particles (Ref. FIG. 5).
In the context of the present invention, the process (100) of the present invention advantageously offers increased activity of the fibre surface, the addition of carboxylic, ketone and amino functional groups and defibrillation of fibres, the combined effects of which are expected to increase the fibre-matrix interaction/adhesion and provide enhanced mechanical properties for the prepared composite thereof.
In the context of the present invention, the process (100) of the present invention is designed such that the fibres are subjected to a combination of water and CO2 along with PNH2 under specific conditions wherein the fibres are modified and activated.
In the context of the present invention, the process (100) of the present invention has a great social impact and environmental advantage as it primarily consumes CO2 as inputs becoming carbon-negative with no required or produced chemical affluents compared to traditional methods like alkaline-based treatments. The only output is steam which can be condensed and reused. The process demonstrated the successful use of CO2 present in the gas phase at a lower pressure. The process of the present invention uses CO2 in the gaseous state which is the naturally existing form of carbon dioxide and is thus easily obtainable. The mentioned process involves the usage of carbon dioxide in gaseous state which can be obtained through CO2 capture technology which along with being economic will also result in the decrease in CO2 concentration in the environment making this process a green process.
In the context of the present invention, residual water used in the process (100) is enriched with lignin, which is then filtered and reused, with sub-micron lignin being a byproduct.
The overall treatment conditions being presented here involves treatment using water, CO2 and PNH2 under specific conditions with temperatures around 30°C to 140 °C and pressures as low as 2-20 bar, such treatments can be easily scaled up to an industrial level without any major operational risks as compared to other processes involving high pressures /temperatures or toxic chemicals. The process conditions along with the process requirements are easily achievable making this process relatively economic and thus can also be combined in continuation with other techniques.
The process also uses water in combination with CO2 and low concentration of PNH2 for the treatment which can be filtered and reused for multiple cycles. The process does not involve any toxic chemicals or does not produce any toxic affluents making the water completely safe to be discarded after multiple repeated uses.
In the context of the present invention, separation of residual water via mentioned treatment technique also produces lignin in sub-micron sized particle form dispersed in water as a side product. The obtained sub-micron lignin acts as a reinforcer and will be sold separately as a high impact filler material for polymer composites.
The process of the present invention involves temperatures ranging from 30 ºC to 140 ºC and pressures of 2-20 bar for which the results have been analyzed and optimized for various conditions providing the optimum and most effective results. Accordingly, temperature and pressure beyond the mentioned range are also expected to provide similar results though at the cost of economic aspects and scalability of the process.
EXAMPLES
The following examples and comparative examples are provided to demonstrate particular embodiments of the present invention. It should be appreciated by those skill in the art that the methods disclosed in the examples and comparative examples that follow merely represent exemplary embodiments of the present invention. Those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments described and still obtain a like or similar result without departing from the spirit and scope of the present invention.
In the context of the present invention, a mechanical analysis for the samples was performed to determine the detailed effect of fibres on polymer-fibre composite as discussed below:
Example- 1: Tensile Modulus/Strength Analysis–
A Tensile Modulus/Strength Analysis for the samples was performed to determine the detailed effect of fibres on polymer-fibre composite. As shown in FIG. 7 and FIG. 8, a tensile modulus of a sample represents the stiffness of a material in resistance to tensile force whereas the strength refers to the maximum stress that a material can withstand while being stretched before breaking. Fibres present in the composite acts as load bearing material which increases the strength of the material, although the improvement in load bearing capacity is limited by the efficiency of load transfer between the polymer matrix and the fibre which can be improved with increased fibre-matrix interaction. Treatment of fibres leading to change in cellulose/hemicellulose/lignin combination was expected to improve the individual strength of the fibres along with increased activity of fibres leading to higher fibre-matrix interaction which can be observed using the obtained data as the tensile strength of polymer-fibre composite increased from 24.64 MPa for composites with untreated fibres to 26.05 MPa upon using treated fibres. Treatment of fibres causing a change in cellulose/hemicellulose/lignin combination also results in an increase in the strength of individual fibres which is clearly visible in the results obtained for tensile modulus analysis of composites with treated and untreated fibres which shows a significant increase in modulus from 2402 MPa to 2771 MPa.
Example-2: Impact Strength Analysis –
An Impact strength Analysis for the samples was performed to determine the detailed effect of fibres on polymer-fibre composite As shown in FIG. 9, an impact resistance of a polymer decreases upon incorporation of natural fibres due to the stiffness of fibres making the composite brittle and susceptible to cracking and crack propagation. Increasing the overall strength of individual fibres can help counter the effect and can lead to an increase in impact resistance of the composite making it significantly closer or even higher in some cases than impact strength of neat polymer.
As observed in the current study the impact strength of the composite with untreated fibres was 51.44 J/m which increased to 65.07 J/m for composite with treated fibres. This increase in impact strength of the composite again corroborates the increase in strength of individual fibres upon proposed treatment.
Example-3: Flexural Modulus/Strength Analysis –
A Flexural Modulus/Strength Analysis for the samples was performed to determine the detailed effect of fibres on polymer-fibre composite. As shown in FIG. 10 and FIG. 11, the results obtained from flexural tests which displays the resistance and ability to withstand the bending stress also displays a similar pattern as observed for tensile properties where the modulus increased from 1790 MPa to 2273 MPa while the strength increased from 31.41 MPa to 34.49 MPa. Improvement in flexural properties and in a similar pattern as observed for tensile properties infers more aligned fibres in the polymer matrix in case of composite containing treated fibres during injection molding for sample preparation. This increase in fibre alignment of fibres with the matrix flow upon treatment is the result and also signifies enhanced fibre-matrix interaction obtained upon CO2 treatment of fibres.
Example-4: Heat Distortion Analysis-
A Heat Distortion Analysis for the samples was performed to determine the detailed effect of fibres on polymer-fibre composite. As shown in FIG. 12, in addition to mechanical properties, an increase in heat distortion temperature was also observed from 141.8 ºC to 150.1 ºC, which signifies increased thermal stability of the fibres due to the removal of hemicellulose and lignin making the material more suitable for outdoor applications.
In the context of the present invention, morphological analysis of the fibres showed a change in surface activity with variations in temperatures. Fibres treated at 30°C to 140°C showed a drastic increase in surface activity as compared to pristine hemp fibres as also concluded from the FT-IR analysis, which would lead to enhanced fibre matrix adhesion. The reduction of lignin and polysaccharides percentage was found and can be related to a decrease in OH groups during FT-IR analysis. It can be observed that the addition of functional groups is resulting from the combined action of CO2 and PNH2 under specific conditions in the process. The presence of ketone, amine, carboxylic groups would lead to more interaction with a compatibilizer and polymer matrix thus enhancing the fibre-matrix adhesion in the composite.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

,CLAIMS:WE CLAIM:
1. A process for process for preparing super active natural fibres for polymer and biopolymer composites development, said process comprising the steps of:
a) treating natural fibres in a reaction chamber (102) at a temperature in the range of 30°C to 140 °C and at a pressure in the range of 2-20 bar;
b) supplying water to the reaction chamber (102) through a liquid supply line (104) connected thereto;
c) supplying pressurized gaseous CO2 to the reaction chamber (102) through a gas supply line (106) along with PNH2 through a supply line (108) connected thereto, said combination of pressurized gaseous CO2 and PNH2 facilitating removal of hemicellulose and lignin from said natural fibres thereby modifying surface of said natural fibres and reducing the water attracting groups from the surface thereby adding functional groups for enhancing interaction with a polymer matrix;
d) obtaining surface modified natural fibre with enhanced inherent properties along a product line (110) and residual water along a residual water stream (112);
e) facilitating filtration of the residual water stream (112) through a filter (114) for obtaining sub-micron lignin removed of step c) along a line (116); and
f) processing the surface modified fibres of step d) through a twin-screw extruder along with the polymer matrix of step c) for obtaining a polymer-fibre composite along a line (118).
2. The process as claimed in claim 1, wherein increasing surface activity of said natural fibres in step c) increases the polymer-fibre interaction thus improving load transfer resulting in enhanced mechanical properties while avoiding the use of any toxic chemical.
3. The process as claimed in claim 1, wherein water supplied to the reaction chamber (102) in step b) is at a room temperature followed by an elevated temperature in the range of 30°C to 140°C.
4. The process as claimed in claim 1, wherein the polymer-fiber composite utilizing surface treated fibres have an increased tensile strength, an increased tensile modulus, an increased impact strength, an increased flexural modulus and an increased heat distortion temperature signifying increased thermal stability.
5. The process as claimed in claim 1, wherein treatment using water and CO2 with temperatures and pressures as low as 30ºC-140ºC and 2-20 bar facilitates scalability to an industrial level without any major operational risks as being not involving high pressures, high temperatures or toxic chemicals.
6. The process as claimed in claim 1, wherein usage of CO2 in gaseous state can results in the decrease in CO2 concentration in the environment.
7. The process as claimed in claim 1, wherein water in combination with CO2 is filtered and reused for multiple cycles as not involving any toxic chemicals or producing any toxic affluents.
Dated this 28th day of September 2023.

For DWARKA GROWTH PRIVATE LIMITED
Pallavi Padia
[IN/PA-3096]
(Agent for Applicant)