Thermoplastic fiber-reinforced composite containing basalt fibers and modified lignin

Abstract

The present invention relates to a thermoplastic fiber-reinforced composite comprising basalt fibers and modified lignin, and more specifically, to a thermoplastic fiber-reinforced composite comprising 100 parts by weight of a thermoplastic resin composite comprising basalt fibers and 10 to 20 parts by weight of lignin modified with fatty acids relative to 100 parts by weight of the composite, wherein the modified lignin has compatibility with the thermoplastic resin and the basalt fibers, thereby being dispersed within the thermoplastic resin composite to improve impact resistance. According to the thermoplastic fiber-reinforced composite material comprising basalt fibers and modified lignin of the present invention, lignin modified by an esterification reaction with an anhydrous fatty acid having 2 to 4 carbon atoms has minimized polarity and improved thermal stability, so when the modified lignin is added to a thermoplastic resin containing basalt fibers, it has the effect of improving the impact resistance of the composite. Therefore, it is expected that the modified lignin can be utilized for the commercialization of fiber-reinforced composite materials.

Description

Technology Field

[0001] The present invention relates to a thermoplastic fiber-reinforced composite comprising basalt fibers and modified lignin, and more specifically, to a thermoplastic resin composite in which both impact strength and tensile strength are improved by further including basalt fibers and lignin modified with fatty acids as a compatibilizer. Background Technology

[0002] Interest in plastic recycling is increasing due to rising environmental pollution. These recycling methods include mechanical and chemical recycling. While mechanical recycling involves changing only the physical form of the plastic without altering its original properties, chemical recycling refers to the process of completely reverting polymeric plastic back to its original raw material form, the monomer, through chemical reactions. Therefore, it is desirable to develop products based on chemical recycling—specifically, products based on thermoplastic resins.

[0003] Furthermore, fiber-reinforced composites are formed by combining high-strength fibers with thermosetting or thermoplastic polymer resins. Based on their excellent mechanical and thermal properties, they are utilized in various fields. In particular, thermosetting resins have the advantage of allowing the use of various fiber types due to their high impregnation properties for reinforcing fibers resulting from their low viscosity before curing. However, as mentioned above, thermosetting resins have the problem of being non-recyclable, and the requirement for a curing reaction leads to increased molding cycle times and reduced productivity.

[0004] Accordingly, technology development utilizing recyclable thermoplastic resins that do not require a curing reaction and offer high productivity is currently underway. In particular, ABS resin, a type of thermoplastic resin, can be used as a matrix for fiber-reinforced composites as it possesses excellent physical properties—such as thermal stability, chemical resistance, rigidity, aging resistance, toughness, impact resistance, low-temperature resistance, and processability—by varying the chemical composition ratios of acrylonitrile, butadiene, and styrene. However, ABS resin has the problem of low miscibility and impregnation with reinforcing fibers due to its high melt viscosity. Specifically, this leads to uneven distribution, uneven impregnation, and / or porosity of the reinforcing fibers; these fibers act as stress concentration points, thereby reducing impact strength. Furthermore, this can ultimately result in the deterioration of the mechanical properties of the resulting products.

[0005] Meanwhile, basalt fiber, one of the natural inorganic fibers, is an industrial fiber produced by melting basalt at 1,500°C and spinning it using centrifugal force. While fibers and carbon fibers are produced by melting raw materials at high temperatures and releasing liquefied material through nozzle pipes, basalt fiber has the relative advantage of lower energy consumption. Basalt fiber possesses high tensile strength and elastic modulus, and because it is environmentally friendly, non-toxic, and relatively inexpensive, it is utilized in various application fields.

[0006] Furthermore, compatibilizers are thermodynamic surfactants that enhance adhesion to polymers, form stable structures, and ensure uniformity between the dispersed and continuous phases. Therefore, to prevent the reduction of mechanical and thermal properties caused by reinforcing fibers in fiber-reinforced composites, it is important to improve the compatibility between the reinforcing fibers and the polymer resin through the addition of appropriate compatibilizers.

[0007] Accordingly, the inventors of the present invention, in order to manufacture a thermoplastic resin-based fiber-reinforced composite using basalt fiber as a reinforcing fiber, made efforts to develop a naturally derived material capable of improving the compatibility between the natural basalt fiber and the thermoplastic resin. As a result, they confirmed that lignin can be modified with fatty acids using an esterification reaction and utilized as a compatibilizer, thereby completing the present invention. Prior art literature

[0008] Republic of Korea Open Public Notice No. 2015-0123369 Republic of Korea Open Public Notice No. 2014-0158109 The problem to be solved

[0009] Therefore, the present invention has as its technical problem to provide a thermoplastic fiber-reinforced composite material comprising lignin modified with fatty acids using an esterification reaction and basalt fibers. means of solving the problem

[0010] In order to solve the above technical problem, the present invention,

[0011] 100 parts by weight of a thermoplastic resin composite containing basalt fibers, and

[0012] The above complex further comprises 10 to 20 parts by weight of fatty acid-modified lignin per 100 parts by weight,

[0013] The present invention provides a thermoplastic fiber-reinforced composite comprising basalt fibers and modified lignin, characterized in that the modified lignin has compatibility with the thermoplastic resin and the basalt fibers, thereby being dispersed within the thermoplastic resin composite to improve impact resistance.

[0014] In the present invention, the thermoplastic resin and basalt fiber are included in a weight ratio of 70:30 to 90:10.

[0015] In the present invention, the modified lignin is modified by an esterification reaction with an anhydrous fatty acid having 2 to 4 carbon atoms, and is characterized by being represented by Chemical Formula 1.

[0016] The present invention provides a thermoplastic fiber-reinforced composite comprising basalt fibers and modified lignin, characterized in that the modified lignin is prepared by the following steps: mixing an anhydrous fatty acid having 2 to 4 carbon atoms with an organic solvent to prepare an anhydrous fatty acid solution; adding and mixing lignin to the anhydrous fatty acid solution to perform an esterification reaction; and precipitating and filtering the mixture in which the esterification reaction is completed in an alcohol solvent and drying to obtain fatty acid-modified lignin.

[0017] In the present invention, the modified lignin is at a thermal decomposition temperature T d.5% It is characterized by being at least 250°C.

[0018] In the present invention, the thermoplastic resin is acrylonitrile butadiene styrene resin (ABS resin), styrene-acrylonitrile copolymer (AS resin), polylactic acid (PLA), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polycaprolactone (PCL), polybutylene succinate (PBS), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyvinylidene chloride, polystyrene (PS), polyvinyl acetate (PVAc), polytetrafluoroethylene (PTFE), acrylic resin (PMMA), polyamide (PA), polyacetal (POM), polycarbonate (PC), modified polyphenylene ether (m-PPE, modified PPE, PPO), polybutylene terephthalate (PBT), cyclic polyolefin (COP), It is characterized by being selected from the group consisting of polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polysulfone (PSF), polyethersulfone (PES), amorphous polyarylate (PAR), polyetheretherketone (PEEK), polyimide (PI), and polyamideimide (PAI). Effects of the invention

[0019] According to the thermoplastic fiber-reinforced composite material comprising basalt fibers and modified lignin of the present invention, lignin modified by an esterification reaction with an anhydrous fatty acid having 2 to 4 carbon atoms has minimized polarity and improved thermal stability, so when the modified lignin is added to a thermoplastic resin containing basalt fibers, it has the effect of improving the impact resistance of the composite. Therefore, it is expected that the modified lignin can be utilized for the commercialization of fiber-reinforced composite materials. Brief explanation of the drawing

[0021] Figure 1 shows a GPC graph of modified lignin according to the present invention. Figure 2 shows the tensile strength of ABS / BF and ABS / BF / KL ​​composites according to one embodiment of the present invention. Figure 3 shows the impact strength of ABS / BF and ABS / BF / KL ​​composites according to one embodiment of the present invention. Figure 4 shows SEM images of ABS / BF and ABS / BF / KL ​​composites according to one embodiment of the present invention. Specific details for implementing the invention

[0022] The present invention will be described in detail below.

[0023] The present invention is susceptible to various modifications and may take various forms, and embodiments are described in detail in the text. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention encompasses all modifications that fall within the spirit and scope of the invention.

[0024] Furthermore, throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0026] The present invention utilizes lignin modified with fatty acids as a compatibilizer to improve interfacial adhesion between a thermoplastic resin and basalt fibers. According to one embodiment of the present invention, the invention relates to a thermoplastic fiber-reinforced composite comprising basalt fibers and modified lignin, wherein the composite comprises 100 parts by weight of a thermoplastic resin composite containing basalt fibers and 10 to 20 parts by weight of lignin modified with fatty acids relative to 100 parts by weight of the composite, and wherein the modified lignin is dispersed within the thermoplastic resin composite to improve impact resistance by having compatibility with the thermoplastic resin and the basalt fibers. Preferably, the composition may consist of 100 parts by weight of a thermoplastic resin composite and 10 to 15 parts by weight of modified lignin.

[0027] In the present invention, the basalt fibers are dispersed within a thermoplastic resin matrix to form a composite, thereby improving mechanical properties. Preferably, the thermoplastic resin and basalt fibers are included in a weight ratio of 70:30 to 90:10. This is because if the content of the thermoplastic resin is too low and the content of the basalt fibers is too high, mechanical properties such as tensile strength and elongation at break may actually decrease, and if the content of the thermoplastic resin is too high and the content of the basalt fibers is too low, the effect of improving mechanical properties by the basalt fibers is negligible. More preferably, the composition may consist of 70 parts by weight of the thermoplastic resin and 30 parts by weight of the basalt fibers.

[0028] In addition, the thermoplastic fiber-reinforced composite is characterized by including modified lignin as a compatibilizer when forming a thermoplastic resin composite in which basalt fibers are dispersed within a thermoplastic resin matrix.

[0029] At this time, the lignin is a fat-soluble phenolic polymer that constitutes wood along with wood. As a byproduct produced in large quantities during the wood pulping process, it is difficult to thermoform and has limited applications. According to the prior art, it is known that adding lignin to a polymer resin reduces mechanical properties. This is because a large number of hydroxyl groups within the structure of lignin increase polarity, thereby lowering compatibility with polymer resins that are close to non-polar. Accordingly, in the present invention, compatibility between the lignin and the thermoplastic polymer resin is improved through a modification reaction to increase compatibility. In particular, by modifying using an ester reaction, the lignin is made to be effectively compatible with the thermoplastic resin matrix.

[0030] In particular, the present invention is characterized in that the lignin is lignin modified into fatty acids by the esterification reaction.

[0031] The above fatty acid-modified lignin enhances interfacial adhesion by increasing the contact area with basalt fibers through the various chains of fatty acids, thereby increasing compatibility with thermoplastic resins and forming a stable structure through the removal of hydroxyl groups within the lignin structure via esterification. Consequently, the fatty acid-modified lignin improves adhesion to both thermoplastic resins and basalt fibers, forms a stable structure, and creates a uniform dispersion and continuous phase. This prevents stress concentration caused by the uneven distribution of basalt fibers, which would otherwise reduce the impact strength of the fiber-reinforced composite, and instead improves both impact strength and tensile strength.

[0032] More preferably, the fatty acid modified lignin is modified by an esterification reaction with an anhydrous fatty acid having 2 to 4 carbon atoms, and is characterized by being represented by the following chemical formula 1.

[0033] [Chemical Formula 1]

[0034] (In the above formula, R is a fatty acid of acetate, propionate, and butyrate, respectively, but is not limited thereto.)

[0035] More preferably, the modified lignin is characterized by being prepared by the following steps: mixing an anhydrous fatty acid having 2 to 4 carbon atoms with an organic solvent to prepare an anhydrous fatty acid solution; adding and mixing lignin to the anhydrous fatty acid solution to perform an esterification reaction; and precipitating and filtering the mixture in which the esterification reaction is completed in an alcohol solvent and drying to obtain fatty acid-modified lignin.

[0036] According to a preferred embodiment of the present invention, the esterification reaction of lignin is carried out at 70°C by adding lignin to a mixture of acid anhydride and pyridine. At this time, the reaction temperature is preferably 70°C, and the reaction time can be adjusted according to the functional group conversion rate and can be 12 to 24 hours. Preferably, it is 24 hours. The mixture after the reaction is completed is precipitated in methanol, and modified lignin is obtained using a filtration device.

[0037] In this regard, Figure 1 shows the GPC curve of lignin and lignin modified by an esterification reaction, and it can be confirmed that the modification and purification process was successfully carried out as the lignin modified by the esterification reaction shows a single peak.

[0038] At this time, the acid anhydride may be one of acetic anhydride, propionic anhydride, and butyric anhydride, and preferably may be acetic anhydride.

[0039] In addition, the fatty acid-modified lignin has reduced hydrophilicity, which prevents self-aggregation caused by hydrogen bonding, allowing it to be applied as a compatibilizer to commercial polymer resins including thermoplastic resins. By controlling polarity through the esterification reaction between lignin and fatty acids, the hydroxyl groups of lignin are replaced with ester groups, thereby improving compatibility with polymer resins. Furthermore, the ester groups inhibit the formation of levoglucosan generated during the thermal decomposition of lignin, thereby improving thermal stability.

[0040] Accordingly, in the present invention, the modified lignin is at a thermal decomposition temperature T d.5% It is characterized by the temperature being at least 250°C. This refers to the T of the lignin before modification. d,5%This represents a significant improvement compared to 215°C, indicating that the thermal stability of fatty acid-modified lignin has been enhanced through esterification reactions. Accordingly, when included in a thermoplastic polymer resin with high melt viscosity, it can exhibit sufficient miscibility with the polymer resin as a compatibilizer while also improving adhesion to basalt fibers.

[0041] In addition, in order to improve the mechanical properties of the fiber-reinforced composite, it is important to include 10 to 20 parts by weight of the fatty acid modified lignin based on 100 parts by weight of the thermoplastic resin composite containing the basalt fiber. If included in an amount less than the above range, the compatibility effect of the fatty acid modified lignin is negligible, and if included in an amount exceeding the above range, the compatibility between the thermoplastic polymer resin and the basalt fiber is low, so perfect adhesion is not formed, resulting in pores, which may instead reduce mechanical properties such as tensile strength and impact strength, and is therefore undesirable.

[0042] FIG. 2 shows the tensile strength of a thermoplastic composite comprising basalt fibers and modified lignin according to a preferred embodiment of the present invention. It can be seen that when the basalt fibers are added, the tensile strength of the thermoplastic composite is improved, and the best tensile strength is exhibited when 15 parts by weight of lignin modified for 24 hours is added compared to lignin. Therefore, more preferably, the best tensile strength and impact strength can be exhibited when 15 parts by weight of the fatty acid modified lignin is included.

[0043] Figure 3 shows the impact strength of a thermoplastic composite comprising basalt fibers and modified lignin according to a preferred embodiment of the present invention. It can be seen that the thermoplastic composite, which has reduced impact strength due to the addition of basalt fibers, exhibits improved impact strength when 15 parts by weight of lignin modified for 24 hours is added to the lignin.

[0044] In addition, in the present invention, the thermoplastic resin is acrylonitrile butadiene styrene resin (ABS resin), styrene acrylonitrile copolymer (AS resin), polylactic acid (PLA), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polycaprolactone (PCL), polybutylene succinate (PBS), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyvinylidene chloride, polystyrene (PS), polyvinyl acetate (PVAc), polytetrafluoroethylene (PTFE), acrylic resin (PMMA), polyamide (PA), polyacetal (POM), polycarbonate (PC), modified polyphenylene ether (m-PPE, modified PPE, PPO), polybutylene terephthalate (PBT), cyclic polyolefin (COP), It is characterized by being selected from the group consisting of polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polysulfone (PSF), polyethersulfone (PES), amorphous polyarylate (PAR), polyetheretherketone (PEEK), polyimide (PI), and polyamideimide (PAI). Preferably, it may be ABS resin.

[0045] As such, the present invention includes the above-mentioned basalt fiber and further includes fatty acid modified lignin fiber, in which polar reactive groups are modified by an esterification reaction as a compatibilizer, thereby increasing the compatibility between the thermoplastic resin and the basalt fiber, so that the thermoplastic fiber-reinforced composite containing the basalt fiber and modified lignin can secure improved impact resistance. Most preferably, the present invention includes 30 parts by weight of the above-mentioned basalt fiber to increase the tensile strength of the thermoplastic resin and lower the impact strength, while adding 15 parts by weight of lignin fiber, in which polar reactive groups are modified by an esterification reaction as a compatibilizer, thereby increasing the compatibility between the thermoplastic resin and the basalt fiber, so that the thermoplastic fiber-reinforced composite containing the basalt fiber and modified lignin can simultaneously secure improved mechanical properties and compatibility.

[0047] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

[0049] Ingredients

[0050] The ABS used was MP211 provided by LG Chemical LTD, and the basalt fiber (BF, Basalt Fiber, fiber length 3 mm) was provided by 3D Factory Ltd (Korea). The lignin (KL, Kraft Lignin) was provided by Murim P&P (Korea), which is lignin for hardwood crafts recovered from the black liquid of the pulp process. Acetic anhydride, propionic anhydride, butyric anhydride and pyridine were purchased from Tokyo Chemical Industry Co., Ltd (Japan) and used.

[0052] <Example 1> Modification of Lignin

[0053] Lignin was vacuum dried in a 60°C oven for 24 hours to completely remove moisture. 30 g of lignin was added to a mixture of 300 mL of acid atomizer and 300 mL of pyridine, and the reaction was carried out at 70°C. At this time, the reaction time was adjusted to 12, 24, and 48 hours, respectively, to control the functional group conversion rate of lignin. After the reaction was completed, the mixture was precipitated in 2 L of methanol, and modified lignin was obtained using a filtration device. The modified lignin powder was dried in a vacuum oven at 70°C for 24 hours and used for analysis and complex preparation.

[0054] As a comparative example, the raw material lignin (KL, Kraft Lignin) was analyzed, and the modified lignin resulting from the reaction between lignin and acid was named AcKL or AKL (Acetated Kraft Lignin), PrKL or PKL (Propionated Kraft Lignin), and BuKL or BKL (Butyrated Kraft Lignin).

[0055] UV-Vis analysis

[0056] Since it is difficult to accurately analyze the degree of hydroxyl group substitution due to the unclear structure of lignin, quantitative analysis of phenol groups was performed based on the difference in absorbance between neutral lignin solutions and alkaline lignin solutions via UV-Vis measurements. The functional group conversion rate due to lignin modification was analyzed by measuring in the 200–500 nm range using a Japanese UV-Visible spectrometer (UV-2600, Shimadzu). The analytical sample was prepared by dissolving 0.01 g of the sample in dioxane / water (1 mL, 9 / 1 v / v%) and adding a certain amount to neutral and alkaline solutions. The prepared solutions were measured using a 10 mm quartz cell, and the functional group conversion rate of lignin was calculated based on the following formula and is shown in Table 1.

[0057] [Mathematical Formula 1]

[0058] [Mathematical Formula 2]

[0059] [Mathematical Formula 3]

[0060] Here, [OH] λ% ε₀ is the UV-Vis absorbance of phenol hydroxyl groups at different wavelengths, ΔD is the specific difference in sensitivity, and D is the absorbance (L / g -1 cm -1 ), D ionized ε is the absorbance of the sample in an alkaline solution, Dneutral ε is the absorbance of the sample in a neutral solution. A is absorbance, c is concentration (g / L), b is the light path (cm; thickness of the fuvette wall), Δε is the difference in molar absorbance, and v is the wavelength (cm²). -1 It represents ).

[0062] GPC analysis

[0063] To determine the molecular weight distribution of lignin and modified lignin, 1 mg of each sample was dissolved in 1 ml of tetrahydrofuran and analyzed using gel permeation chromatography (GPC, 1260 series, Agilent Technologies, USA) at a rate of 1 ml / min. Polystyrene standard was used as the standard sample, and the molecular weight distribution of each lignin was determined using a calibration curve to determine the number average molecular weight (M n ), weight-average molecular weight (M w The values ​​of polyvariance (PDI) were analyzed.

[0065] SEM analysis

[0066] To observe the thermal stability characteristics of lignin before and after esterification, thermogravimetric analysis (TGA, Q500, TA instrument, USA) was performed under a nitrogen atmosphere in the range of 25–800°C at an isothermal rate of 20°C / min, and T d,5% , T max The results were summarized.

[0068] The results of UV-Vis analysis, GPC analysis, and SEM analysis are shown in Table 1 below.

[0069] [Table 1]

[0070]

[0071] Referring to Table 1 above, the conversion rates, which indicate the degree of substitution of hydroxyl groups in lignin, were 64.9% (12h), 98.7% (24h), and 98.8% (48h) for AKL, 24.1% (12h), 56.9% (24h), and 69.5% (48h) for PKL, and 16.5% (12h), 31.8% (24h), and 55.5% (48h) for BKL. In other words, the conversion rate increased as the reaction time increased, and longer chain lengths exhibited lower conversion rates due to lower reactivity.

[0072] When the molecular weight of lignin before and after the esterification reaction was confirmed through GPG analysis, the weight-average molecular weight of lignin after the esterification reaction increased compared to the lignin before the esterification reaction. Additionally, referring to Figure 1, which shows the GPC curves of lignin and modified lignin, a single peak was observed after the reaction, confirming that the modification and purification process was successfully carried out.

[0073] As a result of analyzing the thermal stability of modified lignin through TGA analysis, the T of lignin before modification d,5% It showed 215℃, and exhibited an increasing trend to 259℃ at AcKL_12h, 259℃ at AKL_24h, and 264℃ at AcKL_48h. The maximum thermal decomposition temperature (T) showed a similar trend. max ) was observed to be 359.5°C for lignin, 418°C for AcKL_12h, 425°C for AcKL_24h, and 392°C for AcKL_48h. This is considered to be the result of improved thermal stability due to the substitution of hydroxyl groups by esterification hindering the formation of levoglucosan generated during the thermal decomposition of lignin.

[0074] The above analysis results confirm that the ester modification reaction of lignin proceeded effectively.

[0076] <Example 2> Preparation of ABS / BF / KL ​​Composite

[0077] All raw materials were dried in a vacuum oven at 70°C for 24 hours to completely remove moisture before processing, and ABS / BF and ABS / BF / KL ​​composites were prepared using a twin-screw kneader (Haake MiniLab-II, Germany). The ABS / BF composites were prepared with ABS / BF ratios of 100 / 0, 90 / 10, 85 / 15, 80 / 20, and 70 / 30, and the ABS / BF / KL ​​composites were prepared by adding AcKL and PrKL at 10, 15, 20, and 30 phr, respectively, to the ABS / BF composite with an ABS / BF ratio of 70 / 30.

[0079] Mechanical properties test

[0080] Specimens for evaluating the mechanical properties of composite materials were prepared using an injection molding machine (Haake Minijet Pro, Germany). At this time, the twin-screw extruder temperature was set to 220°C and the extrusion speed was set to 50 rpm to mix the samples. The specimen preparation conditions were set as follows: injection cylinder temperature to 220°C, mold temperature to 140°C, and injection pressure / injection time to 500 bar / 30 seconds.

[0081] Tensile specimens were prepared according to ASTM D638-5 and dried at room temperature for 24 hours at 30% relative humidity, and then tested using a universal testing machine (UTM, 5943U280, Instron, USA) at a speed of 50 mm / min. Impact strength specimens were prepared according to ISO 180 and dried at room temperature for 24 hours at 30% relative humidity, and then evaluated for impact. To derive the mean values ​​and standard deviations from the tensile and impact tests, five values ​​were averaged, and the results of the tensile test are shown in Fig. 2 and the impact test in Fig. 3.

[0082] Referring to Figures 2 and 3, the ABS / BF composite showed a tendency for tensile strength to increase and impact strength to decrease as the basalt fiber content increased. This is a phenomenon observed in general fiber-reinforced composites, and it can be confirmed that while the addition of basalt fibers strengthens the tensile strength of the resin, it reduces fluidity at the interface where the resin and basalt fibers interact, thereby reducing the ability to disperse impact.

[0083] To improve the above characteristics, based on the tensile strength test results, the present invention fixed the mixing ratio of the ABS / BF composite material at 70 / 30 (by weight) and added lignin and modified lignin to observe changes in mechanical properties. As a result, it was confirmed that the addition of lignin tends to increase impact strength. When lignin was added at less than 15 phr, the impact strength showed an increasing trend, and when it was added at 20 phr or more, the mechanical properties showed a decreasing trend again. A similar trend was observed when modified lignin was added. When AcKL and PrKL were added at 15 phr or less, the mechanical properties showed an increasing trend. After the addition of modified lignin, the impact strength value was higher than before lignin modification, which is judged to be because compatibility is imparted through lignin modification, thereby improving interfacial adhesion between ABS and BF.

[0085] SEM test

[0086] SEM image analysis was performed to analyze the internal structure of the ABS / BF and ABS / BF / KL ​​composites. The samples were platinum coated with a turbo molecular pump coater (Q150T, Quorum, UK) and analyzed using FE-SEM (MIRA 3 LMH Inbeam detector, TESCAN Brno sro, Czech) and are shown in Figure 4.

[0087] The ABS / BF30 composite containing only basalt fibers exhibited a pattern where the basalt fibers were dispersed independently within the resin; this dispersion of basalt fibers is attributed to low interfacial interaction with ABS, and additionally, the fracture surface of the ABS resin appeared relatively smooth and uniform. On the other hand, the ABS / BF / KL ​​composite with added lignin exhibited a rough fracture surface. Notably, the ABS / BF / AcKL composite containing modified lignin (AcKL) displayed the roughest fracture surface among the samples, and this transition to a rough fracture surface indicates a change in fiber-matrix interaction. The rougher fracture surface in the composite with added modified lignin indicates reinforced fiber-matrix bonding, which is essential for improved load transfer and mechanical strength. Furthermore, a significant observation was that the addition of AcKL densely filled the fine gaps existing at the interface between the basalt fibers and the ABS resin. This suggests that the interfacial compatibility and miscibility between ABS and basalt fibers were improved by the introduction of modified lignin.

[0088] From the above results, it can be confirmed that the lignin modified by the esterification reaction of the present invention has minimized polarity and improved thermal stability, and that the tensile strength and impact strength are increased by increasing the compatibility of the ABS / BF / KL ​​composite formed by adding the modified lignin to an ABS resin containing basalt fibers, and preferably exhibits the best mechanical properties when 15 phr of AcKL is added. According to the present invention, a thermoplastic composite containing basalt fibers and modified lignin can be effectively applied to the commercialization of composite materials.

[0090] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not to limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments. The scope of protection of the present invention shall be interpreted by the claims, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

Claim 1 A thermoplastic fiber-reinforced composite comprising 100 parts by weight of a thermoplastic resin composite comprising a thermoplastic resin and basalt fibers in a weight ratio of 70:30 to 90:10, and further comprising 10 to 20 parts by weight of lignin modified with fatty acids relative to 100 parts by weight of the composite, wherein the thermoplastic resin is acrylonitrile butadiene styrene resin (ABS resin), and the modified lignin is dispersed within the thermoplastic resin composite to improve impact resistance by having compatibility with the thermoplastic resin and the basalt fibers. Claim 2 delete Claim 3 A thermoplastic fiber-reinforced composite comprising basalt fibers and modified lignin, wherein, in claim 1, the modified lignin is modified by an esterification reaction with an anhydrous fatty acid having 2 to 4 carbon atoms and is represented by the following chemical formula 1: [Chemical Formula 1] (However, in the above formula, R is a fatty acid among acetate, propionate, and butyrate, respectively.) Claim 4 A thermoplastic fiber-reinforced composite comprising basalt fibers and modified lignin, wherein the modified lignin is prepared by the following steps: preparing an anhydrous fatty acid solution by mixing an anhydrous fatty acid having 2 to 4 carbon atoms with an organic solvent; adding and mixing lignin to the anhydrous fatty acid solution to perform an esterification reaction; and precipitating and filtering the mixture in which the esterification reaction is completed in an alcohol solvent and drying to obtain fatty acid-modified lignin. Claim 5 In claim 1, the modified lignin is at a thermal decomposition temperature T d.5% A thermoplastic fiber-reinforced composite comprising basalt fibers and modified lignin, characterized in that the temperature is at least 250°C. Claim 6 delete

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