WO2025073772A1

WO2025073772A1 - Biochar-containing polymer composites

Info

Publication number: WO2025073772A1
Application number: PCT/EP2024/077760
Authority: WO
Inventors: Hossein BANIASADI; Jukka Seppälä
Original assignee: Aalto Korkeakoulusaatio sr
Current assignee: Aalto Korkeakoulusaatio sr
Priority date: 2023-10-02
Filing date: 2024-10-02
Publication date: 2025-04-10
Anticipated expiration: 2026-04-02

Abstract

The invention relates to processes for producing a polymer composite The process comprises providing a mixture comprising biochar and one or more monomers, and polymerizing said one or more monomers in situ in the presence of said biochar to produce said polymer composite. The invention further relates to polymer composites comprising one or more polymers and biochar. The biochar and polymer chains of the one or more polymers are mechanically interlocked.

Description

Biochar-containing polymer composites

Technical field

The field of the invention involves the incorporation of pyrolyzed biomass, specifically biochar, into polymers, which represents a sustainable approach to reducing bio-waste. This innovation focuses on the integration of various concentrations of biochar into a polymer matrix through in situ polymerization.

Background

In recent years, there has been a significant effort to find alternatives to petroleum-based plastics. This is driven not only by the depletion of oil sources but also by the increasing demand for environmentally sustainable consumer products. One well-established approach to developing more sustainable materials is the integration of biomass with conventional synthetic polymers, leading to the exploration of eco-sustainable and biobased composite materials. Renewable resources and agricultural waste, such as sugar palm, coconut shell, cashew shell, com husk, rice husk, and orange peel, have demonstrated significant potential. A viable method to transform these waste materials into value-added fillers is thermal conversion, which produces biochar. Biochar is a stable and carbon-rich material (comprising more than 70 wt-% carbon) generated through biomass pyrolysis in the absence of oxygen. When biomass, the precursor to biochar, decomposes through microbial activity in the soil, it releases CO2 into the atmosphere. However, the carbon present in biomass undergoes limited decomposition during pyrolysis under oxygen-limited conditions, leading to its retention in the soil and subsequently reducing CO2 emissions into the atmosphere. Therefore, biochar can be regarded as a carbon-negative material.

Biochar has been utilized in various applications, such as carbon capture, soil remediation, air filtering, and water treatment, for numerous years. However, advancements in controlled pyrolysis methods for biomass carbonization and a better understanding of carbonaceous structural evolution during biochar production have unveiled new possibilities for functional applications, including sensors, energy storage, and composite reinforcement. Biochar exhibits intriguing characteristics, including high specific surface area, elevated carbon content, strong thermal stability, porosity, and hydrophobic nature. Moreover, it is more cost-effective compared to most other available carbon-based fillers. Consequently, biochar emerges as an ideal filler for developing polymer composites, effectively enhancing their physical, mechanical, and thermal properties. Incorporating biochar as a filler in composites also has the potential to reduce the overall product cost.

Thus far, biochar has been incorporated into various thermoplastic matrices, such as polyamide, polypropylene, polyethylene, and polylactic acid. Conventionally used incorporation methods include, e.g., melt compounding and solvent blending. Melt compounded biochar-polymer composites, however, suffer from poor mechanical and morphological properties (e.g., cracking) at high biochar concentrations (above 20-30 wt-%).

Thus, improved methods for incorporating biochar in polymer matrices, even in high concentrations, are needed.

Summary

An object of the invention is to overcome the drawbacks associated with the conventional solutions.

Particularly, an object of the invention is to provide processes for preparing biochar-containing polymer composites with improved mechanical properties compared to conventional methods, especially in high biochar concentrations.

The invention is defined by what is stated in the independent claims. Some advantageous embodiments are presented in the dependent claims.

The features recited in the dependent claims and the embodiments in the description are mutually freely combinable unless otherwise explicitly stated. The exemplary embodiments presented in this text and their advantages relate by applicable parts to all aspects of the invention, both to the process and to the polymer composite, even though this is not always explicitly mentioned.

A process for producing a polymer composite is presented. The process comprises providing a mixture comprising biochar and one or more monomers, and polymerizing said one or more monomers in situ in the presence of said biochar to produce said polymer composite.

Employing the in situ polymerization eliminates the need for additional processing steps like melt compounding. Being able to avoid energy- intensive processing steps like melt compounding, the presented invention has the advantage of improved energy efficiency.

A polymer composite is correspondingly presented. The polymer composite comprises one or more polymers and biochar. In the polymer composite, the biochar and polymer chains of the one or more polymers are mechanically interlocked.

Biochar is a promising filler for polymer composites. Biochar may be produced from non-food biomass, whereby the CO2 emissions of the composites may be drastically decreased compared to fossil-based polymers without compounding. Moreover, biochar addition has shown to improve the mechanical properties of the polymers. For example, polymer composites may have a higher tensile modulus and tensile strength compared to pristine polymers, at least up to a certain biochar concentration. Thus, these composites have the potential to contribute to CO2 emission reduction by utilizing non-food biomass biochar fillers. Biochar is present in the inventions as particles.

In the course of this application, the expressions ‘mechanically interlocked’ and ‘mechanical interlocking’ refer to structural integration between the biochar particles and the polymer chains at the microscopic level. Integration in the microscopic level should be understood as being obtainable only through the so-called in situ polymerization. In situ polymerization refers to a process of producing a composite of a polymer and a filler, e.g., biochar, nanoparticles, silicates (clay), or carbon nanotubes. The composite forms in the polymerization mixture during polymerization. In situ polymerization processes comprise an initiation step followed by a series of polymerization steps, which results in the formation of a hybrid between polymer molecules and the filler.

The biochar used in the present invention possesses a certain level of porosity. Without being bound to any theory, the polymer chains are believed to form around the biochar particles and/or within the porous structure of the biochar particles during the in situ polymerization process. This creates a physical entanglement, or interlocking, between the two components.

The mechanical interlocking, which can be achieved by in situ polymerization, i.e. , monomer penetration and/or chemical bonding, ensures that the biochar is embedded within the polymer matrix in a way that enhances the load transfer between the biochar filler and the polymer. This interlocking significantly improves the mechanical properties of the composite, such as tensile strength and stiffness, by allowing the stress to be distributed more evenly across both the biochar and polymer phases. Mixing the biochar with one or more small-molecule monomers during in situ polymerization rather than a molten polymer enables fundamentally different compatibility of the components and phases. Viscosity of the mixture of the one or more monomers and the biochar is remarkably lower than viscosity of a molten polymer. Therefore, the biochar particles are well dispersed and wetted by the one or more monomers. Further, the small monomer molecules can penetrate and wet the microscopical pores of the biochar particles. Polymerization of this well-dispersed mixture of the one or more monomers and the biochar particles will result in a composite structure fundamentally different from conventional melt-compounded biochar-polymer composites. The biochar particles and the polymer chains are entangled and integrated within each other in a microscopic level, i.e., mechanically interlocked. The mechanical interlocking creates the unique properties of the biocharcontaining polymer composites, such as the improved tensile strength and modulus. The structural definition of mechanical interlocking goes beyond the polymerization method itself, focusing on the resulting composite structure, where biochar serves as more than a passive filler. The porous nature of biochar allows polymer chains to penetrate its structure, creating a robust composite material with superior mechanical and thermal characteristics compared to those produced through traditional blending methods.

In this invention, a novel approach was undertaken to synthesize biocharcontaining polymer composites through in situ polymerization.

The invention utilizes biochar, a carbon-negative material, as a filler for polymer composites.

Unlike traditional methods, the invention employs in situ polymerization, ensuring excellent filler-polymer compatibility and reducing energy consumption.

The developed composites exhibit improved physical, structural, and thermal properties compared to pristine polymers. The presented polymer composites show excellent rheology (i.e., melt flow) characteristics, low viscosity, and an excellent balance of toughness and stiffness. Polymer composites comprising biochar in concentrations of up to 70 wt-% may be prepared while maintaining the excellent mechanical and morphological properties of the polymer composites.

The composite materials allow for the creation of uniform filaments suitable for 3D printing, offering high dimensional accuracy and structural integrity.

The high-performance composites can be used to manufacture lightweight and durable automotive components, reducing vehicle weight and improving fuel efficiency.

The invention enables 3D printing of complex structures with precision, making it valuable for additive manufacturing applications in various industries. The use of non-food biomass fillers and the elimination of energy-intensive processes contribute to CO2 emission reduction, making the composites environmentally friendly.

The invention has the potential to reduce the overall production cost of polymer composites, making them more economically viable.

The invention addresses the need for sustainable materials by utilizing biomass-derived biochar and an environmentally friendly polymerization process.

The composites exhibit improved mechanical, thermal, and viscoelastic properties, expanding their potential applications.

By retaining carbon and eliminating energy-intensive processes, the invention contributes to reducing CO2 emissions.

The composites can be used in various industries, including automotive, manufacturing, and environmental technologies.

By reducing production costs, the invention promotes the economic feasibility of sustainable composite materials.

The presented polymer composites may be usable in any applications that require reinforced polymer composites or polymers comprising fillers.

The presented process enables to manufacture polymer composites at higher biochar concentrations compared to conventional methods, while still maintaining excellent mechanical and morphological properties of the polymer composites.

The high biochar concentrations contribute to a smaller material usage in producing polymer composites, thus decreasing an environmental impact of the polymer composites and their manufacturing process.

Being lightweight yet strong and stiff materials, the presented polymer composites show optimized weight / performance characteristics. Brief of the drawinqs

Figure 1. SEM images of a) biochar, b) plain PA11 matrix, c) PABC10, d) PABC20, e) PABC30, and f) PABC50. The imaging was done at 5 kV.

Figure 2. a) Typical stress-strain curves and b) The comparison of different mechanical properties of the composites with different biochar loading, c) Storage modulus and d) loss factor versus temperature. The temperature ramp was performed from 0 °C to 190 °c with a rate of 5 °C/min.

Figure 3. Rheology results for plain PA11 matrix and composites, a) storage and loss moduli versus shear strain rate, b) storage and loss moduli versus angular frequency, and c) complex viscosity at 220 °C. The strain sweep test was performed at a fixed angular frequency of 10 rad/s from 0.01 % to 100%. The frequency sweep test was conducted at a fixed shear strain rate of 1 % from 0.01 rad/s to 628 rad/s. The solid and blank symbols represent the shear storage modulus (G¹) and shear loss modulus (G"), respectively.

Figure 4. SEM image from the surface of the fabricated filament a) and b) before and c) and d) after extruding from the printer feeder, c) and d) are with higher magnification, e) the CAD model and f) the digital photograph of the 3D-printed sample.

Detailed

The presented process may comprise providing a mixture comprising biochar and one or more monomers. Providing the mixture comprising biochar and one or more monomers may comprise physically mixing the biochar with the one or more monomers.

The mixture may further comprise one or more selected from the group comprising solvents, catalysts, initiators, and any combination thereof.

Suitable solvents may be selected from the group comprising, water, aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, and any combination thereof.

RECTIFIED SHEET (RULE 91) ISA/EP Suitable catalysts may be selected from the group comprising heterogeneous catalysts, homogeneous catalysts, and any combination thereof, such as cationic catalysts, anionic catalysts, metal-organic coordination catalysts, preferably Ziegler-Natta catalysts, metallocene catalysts, phosphites, peroxides, alum inoxanes, mercaptans, and any combination thereof.

Free radical polymerizations and chain growth polymerizations typically require the use of initiators. Suitable initiators include, e.g., organic peroxides.

The mixture may comprise the biochar in an amount of 0.1-70 weight-%, preferably 1-60 weight-%, more preferably 5-50 weight-% of the total weight of said biochar and said one or more monomers. Too high biochar concentrations may lead to poor mechanical properties and poor morphology of the polymer composite. Too low biochar concentrations, on the other hand, diminish the environmental advantages achieved by the biochar addition. Also, the mechanical properties of the polymer alone or a composite with a very low biochar content are inferior to composites with the biochar amounts as presented herein. The mixture may comprise the biochar in an amount of equal to or greater than 0.1 wt-%, 1 wt-%, 5 wt-%, 10 wt-%, 15 wt-%, 20 wt-%, 25 wt%, 30 wt-%, or 35 wt-% of the total weight of said biochar and said one or more monomers. The mixture may comprise the biochar in an amount equal to or smaller than 70 wt-%, 65 wt-%, 60 wt-%, 55 wt-%, 50 wt-%, 45 wt-%, 40 wt-%, or 35 wt-% of the total weight of said biochar and said one or more monomers.

The biochar in the process as presented herein may have a particle size in the range of 1-200 pm. The biochar particles may show large variations in the particle size. Therefore, the particle sizes as defined here should be understood as lower and upper limits of individual particle sizes found in a collection of biochar particles, measured as a largest linear dimension in an individual biochar particle.

Biochar suitable for the presented process may show some porosity. The mechanical interlocking, i.e., the entanglement of the polymer chains between and/or around the biochar particles and pores is stronger if the biochar shows some porosity. Like the particle size, also the pore size in the biochar may have large variations. The biochar may have porosity in the range of 10 nm-200 pm. As the pore size may largely vary within a certain specimen of biochar, the pore sizes as defined here should be understood as lower and upper limits of individual pore sizes found in a collection of biochar particles. The pores spanning from micropores to macropores, showcasing varied sizes and distributions, thereby offer an extensive surface area and an intricate network conducive to facilitating the diffusion of monomers and the growth of polymer chains within the biochar matrix.

The biochar remains essentially inert during the polymerization reaction. Thus, the biochar in the presented polymer composite may correspondingly be in the range of 1-200 pm, and/or the porosity of the biochar in the presented polymer composite may be in the range of 10 nm-200 pm.

The biochar may be generated through pyrolysis of biomass in the absence of oxygen at a temperature in the range of 300-1000°C, preferably in the range of 300-600°C. Higher temperatures render the biochar surface smoother and less porous, whereby the pore sizes decrease and the physical entanglement between the polymer chains and the biochar particles gets weaker. Furthermore, pyrolysis at higher temperatures reduces the yield of solid biochar and shifts the pyrolysis reaction balance towards gaseous and liquid components. Thus, the pyrolysis temperatures as defined here may increase the yield of solid biochar obtainable from the biomass. Biochar prepared in temperatures as defined here may have functional groups, e.g., hydroxyls, present on the surface of the biochar particles. Without being bound to any theory, these functional groups may aid in the physical entanglement between the polymer chains and the biochar particles, thereby strengthening of the mechanical interlocking in the composite. Preferably, the biochar is generated using a heating rate of 0.1-5°C/min, preferably 0.2- 2°C/min. A heating ramp of the presented heating rate may be followed by an isotherm at a temperature in the range of 300-1000°C, preferably in the range of 300-600°C for 0.5-10 h, preferably for 1-5 h. In other words, after the heating ramp, the temperature is kept constant at the temperature in the range of 300-1000°C, preferably in the range of 300-600°C for 0.5-10 h, preferably for 1-5 h. Preferably, the biochar is generated in the presence of an inert gas selected from the group comprising nitrogen, helium, neon, argon, krypton, xenon, radon, and any combination thereof. Flow rate of the inert gas may be in the range of 1-100 ml/min, preferably 10-50 ml/min. The slow heating ramp may provide a porous structure to the biochar, facilitating efficient entanglement between the polymer chains and the biochar particles, leading to a strong mechanical interlocking in the polymer composite.

Suitable sources for the biomass used for the biochar production may be selected from virgin biomass or recycled biomass, such as agricultural waste or side streams of cellulose industry. The biomass may be selected from the group comprising cellulose-containing biomass, lignin-containing biomass, non-cellulose-containing biomass, non-lignin-containing biomass, and any combination thereof, such as wood, hardwood, softwood, wood chips, lignin, sawdust, bark, agricultural waste biomass, grass, bagasse, sugarcane, corn, rapeseed, palm, straw, and any combination thereof. The agricultural waste biomass may be selected from grass, bagasse, sugarcane, corn, rapeseed, palm, straw, sugar palm, coconut shell, cashew shell, corn husk, rice husk, orange peel, and any combination thereof.

The process may comprise polymerizing said one or more monomers in situ in the presence of said biochar to produce said polymer composite. In comparison to conventional composite development methods, in situ polymerization offers distinct advantages. It ensures excellent miscibility between fillers and polymers, facilitating uniform dispersion of fillers within the polymer matrix. Additionally, when dealing with porous fillers like biochar, the monomer precursor can penetrate the porous structure during the in situ polymerization process, leading to a compatible and intimate interface between filler particles and polymer chains formed by mechanical interlocking of the filler particles and the polymer chains. This mechanically interlocked interface is crucial for improved mechanical properties of the polymer composite. Most importantly, in situ polymerization enables a more environmentally friendly process by eliminating further process steps, such as energy-intensive melt compounding, thus enhancing sustainability.

In the presented composites, the mechanical interlocking may be obtainable through the in situ polymerization of one or more monomers in the presence of said biochar. The presented polymer composites may be obtainable by the presented process.

The one or more monomers for the polymerization should be compatible with the biochar. In other words, the one or more monomers should selected in such a way that the biochar evenly disperses with the monomer when physically mixing the biochar and the one or more monomers. The one or more monomers should be able to penetrate in the pores of the biochar particles for efficient mechanical interlocking. The one or more monomers may be selected from the group comprising amino acids, diamines, diacids, diols, alkenes, amides, and any combination thereof. Preferably, the one or more monomers are selected from the group comprising linear, branched or cyclic amino acids, diamines, diacids, diols, alkenes, amides, and any combination thereof. More preferably, the one or more polymers are selected from the group comprising 11-aminoundecanoic acid, 12-aminolauric acid, 1 ,12-diaminododecane, hexamethylenediamine, 1 ,4-phenylenediamine, 1 ,2- ethanediol, 1 ,4-butanediol, 1 ,12-dodecanedioic acid, 1 ,18-octadecanedioic acid, adipic acid, terephthalic acid, 2-hydroxypropanoic acid, caprolactam, ethylene, propylene, vinyl chloride, and any combination thereof.

The one or more monomers may comprise 12-aminolauric acid in combination with another monomer. For example, the one or more monomers may comprise a combination of 12-aminolauric acid with 11- aminoundecanoic acid, 1 ,12-diaminododecane, hexamethylenediamine, 1 ,4- phenylenediamine, 1 ,2-ethanediol, 1 ,4-butanediol, 1 ,12-dodecanedioic acid, 1 ,18-octadecanedioic acid, adipic acid, terephthalic acid, 2-hydroxypropanoic acid, caprolactam, ethylene, propylene, vinyl chloride, or any combination thereof.

In certain processes, the one or more monomers do not comprise 12- aminolauric acid.

In the presented process, the mixture comprising biochar and one or more monomers is fed into a reactor for the in situ polymerization reaction. The polymerization reaction may be carried out at a reaction temperature in the range of 50-300°C. The reaction temperature may be selected according to the used monomers. For example, for polyolefines, the reaction temperature may be in the range of 70-300°C. For polyesters, the reaction temperature may be in the range of 160-300°C. For polyamides, the reaction temperature may be in the range of 200-300°C. The in situ polymerization reaction may be carried out in an inert atmosphere. Thus, the reactor may be arranged under a flow of an inert gas selected from the group comprising nitrogen, helium, neon, argon, krypton, xenon, radon, and any combination thereof. Flow rate of the inert gas may be in the range of 1-100 ml/min, preferably 10-60 ml/min.

The in situ polymerization reaction is allowed to proceed for a predetermined reaction time. The predetermined reaction time may be in the range of 0.5- 10 h, preferably 1-5 h. A reaction system comprising biochar, the one or more monomers, and the resulting polymer composite may be stirred at a rate of 1-30 rpm, such as 5-20 rpm. After the polymerization reaction, the reactor may be cooled, and the polymer composite may be collected from the reactor.

The presented polymer composite may comprise one or more polymers and biochar, wherein the biochar and polymer chains of the one or more polymers are mechanically interlocked. The mechanical interlocking ensures a strong coupling between the polymer chains and the biochar particles, whereby the mechanical properties of the biochar-containing polymer composites may increase compared to pristine polymers. For biocharcontaining polyamide composites, for example, tensile modulus and tensile strength improve compared to pristine polymer. Morphology of the presented composites may increase compared to conventional, e.g., melt-compounded composites. For example for polyamides, polymer composites with no signs of phase separation, particle agglomeration, or crack formation may be prepared.

The one or more polymers in the presented polymer composite may be selected from the group comprising polyamides, polyesters, and polyolefines, and any combination thereof. Preferably, the one or more polymers are selected from the group comprising polyamide 6, polyamide 66, polyamide 11 , polyamide 12, poly(ethylene terephthalate), poly(butylene terephthalate), poly (p-phenylene terephthalamide), polyethylene, polypropylene, polyvinyl chloride, and any combination thereof. The one or more polymers may comprise a homopolymer. Alternatively, the one or more polymers may comprise a copolymer. A homopolymer is a polymer consisting of one monomer species, whereas a copolymer is a polymer derived from more than one monomer species.

The one or more polymers may comprise polyamide 12 acid in combination with another polymer, i.e., in a copolymer. For example, the one or more polymers may comprise a combination or a copolymer of polyamide 12 with polyamide 6, polyamide 66, polyamide 11 , poly(ethylene terephthalate), poly(butylene terephthalate), poly (p-phenylene terephthalamide), polyethylene, polypropylene, polyvinyl chloride, or any combination thereof.

Certain composites are free of polyamide 12. In other words, the one or more polymers in these composites do not comprise polyamide 12.

The polymer composite may comprise the biochar in an amount of 0.1-70 weight-%, preferably 1-60 weight-%, more preferably 5-50 weight-% of the total weight of said biochar one or more monomers prior to polymerization that produces said polymer composite. The polymer composite may comprise the biochar in an amount of equal to or greater than 0.1 wt-%, 1 wt-%, 5 wt-%, 10 wt-%, 15 wt-%, 20 wt-%, 25 wt%, 30 wt-%, or 35 wt-% of the total weight of said biochar and said one or more monomers prior to polymerization that produces said polymer composite. The polymer composite may comprise the biochar in an amount equal to or smaller than 70 wt-%, 65 wt-%, 60 wt-%, 55 wt-%, 50 wt-%, 45 wt-%, 40 wt-%, or 35 wt-% of the total weight of said biochar and said one or more monomers prior to polymerization that produces said polymer composite. In other words, the polymer composite may comprise the biochar in an amount of 0.1- 70 weight-%, preferably 1-60 weight-%, more preferably 5-50 weight-% of the total weight of the reaction mixture after polymerization. The polymer composite may comprise the biochar in an amount of equal to or greater than 0.1 wt-%, 1 wt-%, 5 wt-%, 10 wt-%, 15 wt-%, 20 wt-%, 25 wt%, 30 wt-%, or 35 wt-% of the total weight of the reaction mixture after polymerization. The polymer composite may comprise the biochar in an amount equal to or smaller than 70 wt-%, 65 wt-%, 60 wt-%, 55 wt-%, 50 wt-%, 45 wt-%, 40 wt-%, or 35 wt-% of the total weight of the reaction mixture after polymerization. For example for condensation polymers, weight of the smallmolecule byproduct (e.g., water or methanol depending on the monomers) is included in the total weight of the reaction mixture after polymerization.

The presented polymer composites may be used in any applications requiring reinforced composites or polymers comprising fillers. The polymer composites may be processed using conventional polymer processing methods, such as injection molding, thermoforming, extrusion, etc. Novel additive manufacturing methods, such as 3D printing e.g. using fused deposition modeling may be used.

The presented polymer composites may be used as filaments in additive manufacturing, i.e., 3D printing. Therefore, a 3D printing filament is presented. The 3D printing filament may comprise the polymer composite presented herein.

The 3D printing filament may be prepared using conventional filament preparation methods and apparatuses, such as a micro-compounder. The 3D printing filament may be prepared at a temperature in the range of 150- 300°C, preferably in the range of 180-250°C.

Examples

Example 1 . Polyamide 11 - biochar composites

Biochar was polymerized with 11-aminoundecanoic acid monomer, derived from natural castor, via a straightforward polycondensation process, allowing for the incorporation of up to 50 wt.% biochar. A comprehensive investigation and discussion were conducted on various properties of the developed composites, including microstructure, crystallinity, thermal stability, mechanical properties, thermomechanical performance, and viscoelastic characteristics. Furthermore, these composites have the potential to contribute to CO2 emission reduction by utilizing non-food biomass fillers (biochar) and employing in situ polymerization, which eliminates the need for additional processing steps like melt compounding. However, it is important to note that a comprehensive life cycle assessment is necessary to fully evaluate the environmental impacts of the developed composites.

Through the use of scanning electron microscopy (SEM), it has been demonstrated that biochar can be uniformly dispersed within the PA11 matrix at concentrations of up to 50 wt.%, without any signs of phase separation, particle agglomeration, or crack formation. This achievement leads to significant improvements in mechanical and thermal properties. Notably, the tensile strength and modulus increase by 35% and 72%, respectively, and the thermal decomposition process is notably delayed when biochar particles are incorporated.

The in situ polymerized composites exhibited significant improvements in physical and structural properties compared to neat PA11 , rendering them highly promising for a wide range of applications, including additive manufacturing and automotive parts. Furthermore, the viscoelastic performance of the PA11 matrix improves substantially with the addition of biochar filler particles. These results highlight the excellent interfacial compatibility between the PA11 matrix and biochar, which is achieved through in situ polymerization.

This innovation not only emphasizes the sustainable use of biochar as a filler but also underscores the effectiveness of in situ polymerization in creating high-performance PA11 /biochar composites suitable for a wide range of demanding applications. Importantly, these composites have the potential to contribute to CO2 emission reduction by utilizing non-food biomass fillers (biochar) and eliminating the need for additional processing steps like melt compounding, thereby reducing the overall cost of PA11 production.

The PA11 polymerization was done through a polycondensation process. Namely, 11-aminoundecanoic acid was mixed physically with different amounts of biochar and was fed into a stainless steel reactor equipped with a mixer and heating jacket. The reactor was heated up to 240 °C under a nitrogen flow (50 ml/min). The system was stirred at 15 rpm for 4 h. After that, the reactor was cooled down, and the product was collected. The weight ratios between PA11 and biochar were selected as 100/0, 90/10, 80/20, 70/30, and 50/50 and the samples were coded as PABC0, PABC10, PABC20, PABC30, and PABC50, respectively. It should be mentioned that the mass of the side product, i.e., water, was taken into account in the calculations. Furthermore, the yield of polymerization was assumed to be 98%, which was achieved experimentally by monitoring the mass of the product for at least four times PA11 polymerization.

The big chunks obtained from the polymerization step were milled by a Retsch SM 300 Cutting Mill. The milled sample was hot-pressed with a Fontijne Lab Press-TP 400 at 220 °C with a static pressure of 150 kPa to get a thin film (approximately 400 pm). Furthermore, a bar-shape specimen with a dimension of 55 mm x 10 mm x 5 mm (L xw x t) was prepared by the press for impact testing. A V-notch with 2 mm depth and a tip radius of 0.25 mm machined on one face. Moreover, dog-bone pieces (3.2 mm x 2 mm x 2.2 mm, L xw x t) were prepared for tensile testing by injection molding of the milled flakes. The injection molding was performed by a tabletop injection molding device (Babyplast 6/12, England).

Mechanical properties of the polyamide 11 - biochar composites are presented in Figure 2. Figure 2a presents stress-strain curves for pristine polyamide 11 and the polymer composites. Figure 2b presents the tensile modulus, tensile strength, tensile strain, tensile toughness and impact strength values for pristine polyamide 11 and the polymer composites. Figure 2c presents storage modulus as a function of temperature for pristine polyamide 11 and the polymer composites. Figure 2d presents loss factor values as a function of temperature for polyamide 11 and the polymer composites. As can be observed especially in Figure 2b, the tensile modulus and tensile strength values show a considerable increase in the PA11 composites compared to polyamide 11 alone.

Example 2: 3D filament

A uniform diameter filament was extruded from a composite according to Example 1 , the composite containing 50 wt-% biochar together with polyamide 11. A complex structure with high dimensional accuracy and no detectable structural defects was successfully 3D printed.

The filament was fabricated from the composite with the highest biochar loading, e.g., PABC50, using a micro-compounder (DSM, The Netherlands) at 220 °C to investigate the printability of the developed PA11 /biochar composites. The filament was then employed to print a complex geometry using a Lulzbot-mini Desktop FDM printer (USA). The nozzle diameter was 0.25 mm, and the printing conditions, including printing temperature, buildplate temperature, and printing speed, were set as 220 °C, 60 °C, and 60 mm/s, respectively.

Figure 4 presents the structure of the 3D printing filament. Figures 4a and 4b present SEM images of the filament prior to extruding the filament from a 3D printer feeder. Figures 4b and 4c present SEM images of the filament after extruding from the 3D printer feeder. Figure 4e presents a CAD model of an object to be 3D printed. Figure 4f presents a digital photograph of an object 3D printed according to the model presented in Figure 4e. Reproducibility of the model in 3D printing is excellent.

Example 3: Polyamide 12 - biochar composites

A stainless-steel reactor, equipped with an overhead mixer and a heating jacket, facilitated the polymerization process. The monomer, 12-aminolauric acid, was blended with a small quantity of sodium hypophosphite monohydrate catalyst (0.1 wt-%) and heated to 240 °C under a vigorous nitrogen flow for 4 h. Following synthesis, the resultant polymer, PA12, was cooled under a nitrogen atmosphere to prevent oxidation and subsequently extracted from the reactor. The resulting polymer chunk underwent milling into smaller pieces using a Retsch SM 300 Cutting Mill device equipped with a 6 mm bottom sieve. In the case of biochar-containing composites, a predetermined quantity of biochar was initially mixed with the monomer. The subsequent polymerization steps mirrored those outlined for pure PA12. The quantity of side products, such as water vapor, was theoretically determined, assuming a 100 % yield for the polymerization process. A comprehensive structure-property correlation study of biochar-enhanced polyamide composites was conducted. Three different biochar concentrations were selected: 10 wt%, 30 wt%, and 50 wt%, corresponding to low, medium, and high loadings, respectively. The composites were therefore designated as PA12-BC10, PA12-BC30, and PA12-BC50. It should be noted that although increasing the biochar content beyond 50 wt% was considered feasible during polymerization, it was decided not to exceed this limit due to concerns that higher amounts might render the samples excessively brittle, as indicated by mechanical property considerations.

For tensile testing, dog-bone specimens measuring 3.2 mm x 2 mm x 2.2 mm (L x w x T) were fabricated using an injection molding device, specifically the Babyplast 6/12 from England. Additionally, for the rest of the characterizations, hop-pressed films were produced by melting and pressing the samples with a Fontijne TP 400. A force of 150 kN was applied during pressing, followed by cold pressing at approximately 15 °C to achieve uniform film formation.

The mechanical properties of the samples were evaluated through tensile testing conducted on a Universal Tester Instron model 4204 following ASTM D638 Type V standards. Prior to testing, the samples were conditioned for 48 h at 23 °C and 55 % relative humidity. Subsequently, they were subjected to a 5 kN load cell and stretched at a constant rate of 5 mm/s. The resulting stress-strain curves were analyzed to determine key parameters, including tensile modulus (MPa), tensile strength (MPa), and elongation at break (%). At least five samples were subjected to tensile testing, and the mean value ± standard deviation was analyzed. Table 1. Mechanical properties of polyamide 12 and biochar-containing polyamide 12 composites.

Sample Tensile modulus Tensile strength Tensile strain

(MPa) (MPa) (%)

PA12 745 ± 30 38 ± 1 300 ± 10

PA12-BC10 925 ± 35 39 ± 1.1 191 ± 6

PA12-BC30 1515 ± 49 41 ± 1.5 73 ± 2

PA12-BC50 2055 ± 65 54 ± 2 8 ± 0.5

PA12-BC50 1808 ± 53 31 ± 1 3 ± 0.3

As can be observed in Table 1 , the tensile modulus and tensile strength values increase for the polyamide 12-biochar composites compared to PA12 alone.

Claims

Claims:

1. A process for producing a polymer composite, the process comprising providing a mixture comprising biochar and one or more monomers, and polymerizing said one or more monomers in situ in the presence of said biochar to produce said polymer composite.

2. The process according to claim 1 , wherein the mixture comprises the biochar in an amount of 0.1-70 weight-%, preferably 1-60 weight-%, more preferably 5-50 weight-% of the total weight of said biochar and said one or more monomers.

3. The process according to claim 1 or 2, wherein the biochar is generated through pyrolysis of biomass in the absence of oxygen at a temperature in the range of 300-1000°C, preferably in the range of 300-600°C, preferably using a heating rate of 0.1-5°C/min, preferably 0.2-2°C/min, followed by an isotherm at the temperature in the range of 300-1000°C, preferably in the range of 300-600°C for 0.5-10 h, preferably 1-5 h.

4. The process according to claim 3, wherein the biomass is selected from the group comprising cellulose-containing biomass, lignin-containing biomass, non-cellulose-containing biomass, non-lignin-containing biomass, and any combination thereof, such as wood, hardwood, softwood, wood chips, sawdust, bark, agricultural waste biomass, grass, bagasse, sugarcane, corn, rapeseed, palm, straw, and any combination thereof; preferably wherein the agricultural waste biomass is selected from grass, bagasse, sugarcane, com, rapeseed, palm, straw, sugar palm, coconut shell, cashew shell, com husk, rice husk, orange peel, and any combination thereof.

5. The process according to any of the preceding claims, wherein the biochar has a particle size in the range of 50-200 pm, and/or porosity in the range of 10 nm-200 pm.

6. The process according to any of the preceding claims, wherein the one or more monomers are selected from the group comprising amino acids, diamines, diacids, diols, alkenes, amides, and any combination thereof, preferably selected from the group comprising linear, branched or cyclic amino acids, diamines, diacids, diols, alkenes, amides, and any combination thereof; more preferably selected from the group comprising 11- aminoundecanoic acid, 12-aminolauric acid, 1 ,12-diaminododecane, hexamethylenediamine, 1 ,4-phenylenediamine, 1 ,2-ethanediol, 1 ,4- butanediol, 1 ,12-dodecanedioic acid, 1 ,18-octadecanedioic acid, adipic acid, terephthalic acid, 2-hydroxypropanoic acid, caprolactam, ethylene, propylene, vinyl chloride, and any combination thereof.

7. The process according to any of claims 1 to 6, wherein the one or more monomers do not comprise 12-aminolauric acid.

8. A polymer composite, comprising one or more polymers and biochar, wherein the biochar and polymer chains of the one or more polymers are mechanically interlocked.

9. The polymer composite of claim 8, wherein the mechanical interlocking is obtainable through in situ polymerization of one or more monomers in the presence of said biochar.

10. The polymer composite according to claim 8 or 9 obtainable by the process of any of the claims 1 to 7.

11. The polymer composite according to any of claims 8 to 10, wherein the one or more polymers are selected from the group comprising polyamides, polyesters, polyolefines, and ant combination thereof, preferably selected from the group comprising polyamide 6, polyamide 66, polyamide 11 , polyamide 12, polyethylene terephthalate), poly(butylene terephthalate), poly (p-phenylene terephthalamide), polyethylene, polypropylene, polyvinyl chloride, and any combination thereof.

12. The polymer composite according to any of claims 8 to 11 , wherein the one or more polymers do not comprise polyamide 12.

13. The polymer composite according to any of claims 8 to 12, wherein the one or more polymers comprise a homopolymer, or wherein the one or more polymers comprises a copolymer.

14. The polymer composite according to any of claims 8 to 13, wherein the polymer composite comprises the biochar in an amount of 0.1-70 weight-%, preferably 1-60 weight-%, more preferably 5-50 weight-% of the total weight of said biochar and one or more monomers prior to polymerization that produces said polymer composite.

15. The polymer composite according to any of claims 8 to 14, wherein the biochar has a particle size in the range of 1-200 pm, and/or porosity in the range of 10 nm-200 pm.

16. The polymer composite according to any of claims 8 to 15, wherein the biochar is generated through pyrolysis of biomass in the absence of oxygen at a temperature in the range of 300-1000°C, preferably in the range of 300- 600°C, preferably using a heating rate of 0.1-5°C/min, preferably 0.2- 2°C/min, followed by an isotherm at a temperature in the range of 300- 1000°C, preferably in the range of 300-600°C for 0.5-10 h, preferably 1-5 h.

17. The polymer composite according to claim 16, wherein the biomass is selected from the group comprising cellulose-containing biomass, lignincontaining biomass, non-cellulose-containing biomass, non-lignin-containing biomass, and any combination thereof, such as wood, hardwood, softwood, wood chips, sawdust, bark, agricultural waste biomass, grass, bagasse, sugarcane, corn, rapeseed, palm, straw, and any combination thereof; preferably wherein the agricultural waste biomass is selected from grass, bagasse, sugarcane, corn, rapeseed, palm, straw, sugar palm, coconut shell, cashew shell, corn husk, rice husk, orange peel, and any combination thereof.