KR20240037528A - Ecofriendly polymer composite comprising microalgae and having improved mechanical properties and preparation method thereof - Google Patents

Abstract

The present invention relates to a polymer containing an ester group as a matrix; Microalgae forming a dispersed phase in the polymer matrix; and a reactive compatibilizer that forms cross-links between the microalgae and the polymer matrix, and a method for producing the same.
According to the present invention, when mixing polymer resin and microalgae, a reactive compatibilizer is added and melt mixing and compression molding are performed in a predetermined temperature range to induce an increase in reaction between the polymer resin and microalgae to improve interfacial adhesion. Through this, mechanical properties and processability can be improved.

Description

Microalgae-containing eco-friendly composite with improved mechanical properties and method for manufacturing the same {ECOFRIENDLY POLYMER COMPOSITE COMPRISING MICROALGAE AND HAVING IMPROVED MECHANICAL PROPERTIES AND PREPARATION METHOD THEREOF}

The present invention relates to an eco-friendly composite containing microalgae, which is biomass, and a method for manufacturing the same. More specifically, an eco-friendly composite with improved mechanical properties and processability by improving the dispersibility and interfacial adhesion of microalgae to polymer resin, and a method for manufacturing the same. It's about the manufacturing method.

To replace synthetic polymers based on fossil fuels, eco-friendly polymers or bioplastic materials using biomass are being developed. As the biomass, agricultural waste resources such as corn and rice straw or natural waste resources such as wood flour, sawdust, paper, and pulp are mainly used, and cellulose, the main component of these, has low compatibility with polymer materials, making it difficult to improve physical properties.

Meanwhile, the use of microalgae as another biomass is being studied. Microalgae are single-celled photosynthetic organisms that live in water and contain large amounts of proteins, lipids, vitamins and other nutritional supplements, so they have been used as raw materials for health foods. Recently, they have been used as raw materials for biodiesel, bio-hydrogen production and CO ₂ from fuel gas. It is attracting attention for its use in removing . More specifically, microalgae have a higher absorption rate of nutrients and CO ₂ compared to land plants, and have a high growth rate, so they can be mass-produced under stable conditions. In particular, their surface properties can be adjusted according to growth conditions, so they can be used in biomass and biomass mainly composed of cellulose. In contrast, it is being studied as an eco-friendly material that can secure compatibility with polymer materials.

Despite these advantages, microalgae exhibit a behavior that reduces mechanical properties and processability when mixed with some polymer materials, which limits their use. For example, there was an attempt to manufacture a composite by mixing microalgae with polylactic acid (PLA), but when the content of microalgae in the composite was increased to 40% by weight, the elongation of PLA dropped sharply to less than 3%, making it brittle. (Reference: Mindaugas Bulota, Tatiana Budtova, PLA/algae composites: Morphology and mechanical properties, Composites: Part A 73 (2015) 109-115). Another study limited the biomass content to 30% to maintain the ductility of the composite material (see Simonet Torres, et al., Green Composites from Residual Microalgae Biomass and Poly(butylene adipate-co-terephthalate): Processing and Plasticization, ACS Sustainable Chem. Eng. 2015, 3, 614624), there are still limitations that make specimen molding difficult due to low elongation and high brittleness.

Meanwhile, polypropylene-graft maleic anhydride (PP-g-MA) or polyethylene-graft maleic anhydride (PP-g-MA) is added to a composite material that is a mixture of HDPE resin and cornstarch-based biomass. An attempt was made to increase the tensile strength by adding 3 phr of anhydride (PE-g-MA) (Reference: Bo Chen et al, Corncob residual reinforced polyethylene composites considering the biorefinery process and the enhancement of performance, Journal of Cleaner Production 198 ( 2018) 452e462 453). However, since the ductility of the composite material was drastically reduced, it was limited to molding processing with very low deformation, such as autoclave processing.

As another example, a material was developed in which 10% or 70% by weight of cellulose fibers were mixed with PBS, but due to incompatibility between the fiber particles and the polymer, mechanical properties rapidly deteriorated (elongation rate <5%), and processability was impaired due to brittleness. fell sharply (Reference: Liang Zhao et al., A novel approach to fabricate fully biodegradable poly(butylene succinate) biocomposites using a paper-manufacturing and compression molding method, Composites Part A 139 (2020) 106117).

Therefore, the development of composite materials that can realize the synergistic effect of maintaining the advantages of microalgae and the mechanical properties of polymer materials is required.

The purpose of the present invention is to solve the problems of the prior art, by increasing the dispersibility of microalgae, increasing the contact area, and inducing a high reaction between microalgae and polymer resin to improve interfacial adhesion, thereby creating an eco-friendly product with improved mechanical properties and processability. To provide a composite and a method for manufacturing the same.

According to one aspect of the invention, a matrix comprising polyethylene vinyl acetate (EVA); And an eco-friendly composite comprising microalgae forming a dispersed phase in the matrix, wherein the content of the microalgae is more than 5% by weight and less than 70% by weight based on the total weight, is provided. Additionally, 0.6 to 2 phr of reactive compatibilizer is added based on the total weight of microalgae and polymer resin. Here, 'phr' is an abbreviation for 'parts per hundred resin' and means that 0.6 to 2 parts by weight of reactive compatibilizer is added when the total weight of microalgae and polymer resin is 100 parts by weight.

이하의 온도에서 용융 혼합하는 단계, 및 (S2) 상기 용융 혼합물을 압축 성형하고 냉각하는 단계를 포함하고, 상기 미세조류는 복합체 전체 중량의 5 중량% 초과 내지 70 중량% 이하의 함량으로 사용되는 제조방법을 제공한다.According to another aspect of the present invention, as a method of manufacturing the eco-friendly composite, (S1) polyethylene vinyl acetate (EVA) and microalgae are each dried and added to a mixer, and then the melting point of the EVA exceeds 100

Melt mixing at a temperature below, and (S2) compression molding and cooling the molten mixture, wherein the microalgae is used in an amount of more than 5% by weight and less than 70% by weight of the total weight of the composite. Provides a method.

According to the present invention, when mixing polymer resin and microalgae, a reactive compatibilizer is added and melt mixing and compression molding are performed in a predetermined temperature range to improve microalgae dispersion and increase the reaction between polymer resin and microalgae. Interfacial adhesion can be improved by induction, and through this, mechanical properties and processability can be improved.

Figure 1 shows FT-IR results chemically confirming the reactivity and structural change when dicumyl peroxide (DCP), used as a reactive compatibilizer in Example 1, is added to EVA resin and EVA/HS2 composite.
Figure 2 is an SEM image showing the change in morphology according to DCP content and molding temperature in the EVA/DCP/HS2 composite prepared in Example 1 [(a) HS2 10wt%, DCP 0phr, mold T=120°C; (b) HS2 10wt%, DCP 0phr, mold T=150℃; (c) HS2 10wt%, DCP 2phr, mold T=120℃; (d) HS2 10wt%, DCP 2phr, mold T=150℃].
Figure 3 is an SEM image showing the cross section of the EVA/DCP/HS2 composite prepared in Example 1 as the HS2 content and molding temperature increase [(a) HS2 10wt%, DCP 2phr, mold T=120°C; (b) HS2 30wt%, DCP 2phr, mold T=120℃; (c) HS2 10wt%, DCP 2phr, mold T=150℃; (d) HS2 30wt%, DCP 2phr, mold T=180℃].
Figure 4 shows the change in mechanical properties (tensile strength) of the EVA/DCP/HS2 composite prepared in Example 1 according to the DCP content, HS2 content, and molding temperature [(a) HS2 10wt%, mold T=150°C ; (b) HS2 30wt%, mold T=180℃].
Figure 5 shows the change in rheological properties according to the DCP content and molding temperature added to the EVA resin (a) and EVA/HS2 composite (b).
Figure 6 is an SEM image showing the fracture surface of the EVA/DCP/HS2 composite prepared in Example 1 after stretching (50 mm/min) as the HS2 content and molding temperature increased [(a) HS2 10wt%, DCP 2phr, mold T=150℃; (b) HS2 30wt%, DCP 2phr, mold T=180℃].
Figure 7 is an SEM image showing a cross-section of a specimen according to the DCP content and molding temperature of the EVA/DCP/HS2 (50wt%) composite prepared in Example 2 [(a) DCP 0phr, T=120°C, before stretching deformation; (a) DCP 0phr, T=180℃, after stretching deformation; (b) DCP 2phr, T=120℃, before stretching deformation; (b) DCP 2phr, T=180℃, after stretching deformation].
Figure 8 is an SEM image showing a cross-section of a specimen according to the DCP content and molding temperature of the EVA/DCP/HS2 (70wt%) composite prepared in Example 2 [(a) DCP 0phr, T=120°C, before stretching deformation; (a) DCP 0phr, T=180℃, after stretching deformation; (b) DCP 2phr, T=120℃, before stretching deformation; (b) DCP 2phr, T=180℃, after stretching deformation].
Figure 9 shows changes in mechanical properties according to DCP content, HS2 content, and molding temperature in the EVA/DCP/HS2 composite prepared in Example 2 [(a) HS2 50wt%, molding temperature (molding] T=180°C ; (b) HS2 70wt%, molding temperature T=180℃].
Figure 10 shows changes in stress-strain behavior according to DCP content, HS2 content, and molding temperature in the EVA/DCP/HS2 composite prepared in Example 2.
Figure 11 shows the molding processability of the DCP content and HS2 content in the EVA/DCP/HS2 composite prepared in Example 2.
Figure 12 is an SEM image showing the morphologies of control PBAT/HS2 (70 wt%), PBAT/ADR/HS2 (70 wt%) and PBAT/DCP/HS2 (70 wt%) composites prepared in Example 3.
Figure 13 shows the tensile strength (a) of the control PBAT/HS2 (70 wt%) (denoted neat), PBAT/ADR/HS2 (70 wt%) and PBAT/DCP/HS2 (70 wt%) composites prepared in Example 3. It represents the yield strength.

Since the present invention can be modified in various ways and can have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all transformations, equivalents, and substitutes included in the spirit and technical scope of the present invention. In describing the present invention, if it is determined that a detailed description of related known technologies may obscure the gist of the present invention, the detailed description will be omitted.

An eco-friendly composite according to an embodiment of the present invention includes a polymer containing an ester group as a matrix; Microalgae forming a dispersed phase in the polymer matrix; and reactive compatibilizers.

The microalgae are single-celled photosynthetic organisms that live in water and contain proteins, lipids, vitamins, and other nutritional supplements. More specifically, the microalgae are hydrophilic, have a high cellulose content in the cell wall, and have protein components with C=O and N-H functional groups on the cell surface. The high content of cellulose contained in the microalgae can maintain the microalgae particles when mixed with other polymers, and the functional group of the protein component has partial affinity with the amine group or ester group contained in the polymer resin, resulting in good dispersibility.

Accordingly, in the present invention, the microalgae is used as a biomass filler, and the microalgae filler is distributed at the interface with the continuous phase of the polymer matrix to form a dispersive phase.

In one embodiment of the present invention, the microalgae include Chlorella genus, Botryococcus genus, Dunaliella genus, Nannochloropsis genus, Spirulina genus and Halo One or more selected from the genus Halochlorococcum may be used. Among these, the genus Chlorella can be advantageously used in terms of rapid growth and resistance to environmental changes.

In the present invention, the polymer matrix that forms a continuous phase surrounding the microalgae dispersed phase includes polyethylene vinyl acetate (EVA), thermoplastic polyurethane (TPU), and polybutylene adipate terephthalate (PBAT). , polylactic acid (PLA), polybutylene succinate (PBS), polybutylene succinate-co-adipate (PBSA), polybutylene succinate-co-butylene terephthalate (PBST), and polycaprolactone ( PCL) may be used, of which polyethylene vinyl acetate (EVA) and polybutylene adipate terephthalate are particularly preferred.

The polyethylene vinyl acetate (EVA) is a thermoplastic resin made of a copolymer of ethylene and vinyl acetate. It is an eco-friendly material that has excellent dimensional stability and chemical resistance, is harmless to the human body, and has a low melting point (T _m ) of 70 to 90°C. Due to the property of containing a carbonyl functional group in the molecular structure, it can secure thermodynamic compatibility with microalgae used as biomass filler, so higher compatibility can be expected compared to other polymers.

In addition, the polybutylene adipate terephthalate (PBAT) has a melting point (T _m ) of 115 to 125°C and has the advantage of being biodegradable and exhibiting high elongation and low glass transition temperature.

The microalgae and the matrix polymer have mutual affinity, but due to differences in interfacial properties, where the cellulose component on the surface of the microalgae is hydrophilic and the matrix polymer is hydrophobic, the mechanical properties of the composite may decrease as the content of microalgae increases. there is. To overcome this, in the present invention, a reactive compatibilizer is additionally added when mixing microalgae and a polymer matrix.

The reactive compatibilizer can act as a cross-linking agent that increases interfacial adhesion by causing a reaction between microalgae and the polymer matrix. In other words, the reactive compatibilizer forms radicals in the polymer and reacts with the proteins, amino acids, and cellulose radicals constituting the outer wall of the microalgae to form crosslinks, thereby reducing the agglomeration phenomenon of the microparticles and allowing the polymer to form on the particle surface of the microalgae. It surrounds the , and as a result, even if the content of microalgae increases, the dispersibility and interfacial adhesion of the microparticles to the polymer can be improved.

For example, the eco-friendly composite according to an embodiment of the present invention contains the microalgae in a high content of more than 5% by weight and less than 70% by weight, specifically 30 to 70% by weight or 50 to 70% by weight, based on the total weight. It may include, and the above content of microalgae may be uniformly dispersed in the polymer matrix and have an average size of less than 2 ㎛ to 30 ㎛. More specifically, it is possible to form a dispersed phase in which the average primary aggregate size of microalgae is 1 ㎛ to less than 10 ㎛, specifically 5 ㎛ to less than 10 ㎛. As the microalgae content increases to more than 30% by weight, primary particle agglomeration becomes secondary agglomeration, and the average size of particle agglomeration reaches the range of 10 to 30㎛, and they form percolation with each other. Therefore, as the content increases, particle agglomeration and polymer resin interfacial adhesion have a significant impact on mechanical properties. Uniform dispersion of microalgae in the polymer matrix and improvement of interfacial adhesion can improve mechanical properties such as tensile strength and rheological properties of the final composite.

In one embodiment of the present invention, the reactive compatibilizer may include a crosslinking agent, an epoxy group-containing chain extender, or a mixture thereof. Examples of the crosslinking agent include dicumyl peroxide (DCP), an acrylic anhydride-based additive, a maleic anhydride-based additive, or a mixture thereof, and the epoxy group-containing chain extender is poly(ethylene-co- Methyl acrylate-co-glycidyl methacrylate) (poly(ethylene-co-methyl acrylate-co-glycidyl methacrylate), JONCRYL ADR-4468 ^® , BASF), poly(ethylene-co-glycidyl methacrylate)(EGMA) Or a mixture thereof may be mentioned.

In addition, the reactive compatibilizer may be included in an amount of 0.1 to 5 parts by weight, for example, 0.1 to 2 parts by weight, based on 100 parts by weight of matrix polymer/microalgae, and this content range is advantageous in terms of reaction control.

The eco-friendly composite of the present invention is melted by adding a reactive compatibilizer that forms a cross-link between the microalgae and the polymer matrix to a mixture obtained by drying (S1) a polymer resin containing an ester group and microalgae, respectively, and adding them to a mixer. It can be manufactured by a method including a mixing step, (S2) a reaction step of compression molding the molten mixture, and then cooling.

The microalgae are dried at 30 to 50°C (e.g., 40°C) for more than 8 hours, and then added in an amount of more than 5% by weight to 70% by weight or less, specifically 10 to 70% by weight, and 30 to 30% by weight, based on the total weight of the composite. It can be used in high amounts of 70% by weight or 50 to 70% by weight.

The polymer resin is a matrix that forms a continuous phase, and can be used by drying under the same conditions as microalgae.

In one embodiment of the present invention, polyethylene vinyl acetate (EVA) may be preferably used as the polymer matrix, as described above.

Additionally, the melt mixing may be performed at a temperature of 80 to 150° C., taking into account sufficient mixing of the components, ease of processing, and thermal deformation of the polymer resin. For example, if EVA is used, it has a low melting point (T _m ) of 70 to 90°C so that melt mixing can be carried out at milder conditions of 80 to 100°C, and if PBAT is used, at 120 to 150°C. Melt mixing may be performed.

The compression molding may be performed at 120 to 200° C. to activate the cross-linking action of the reactive compatibilizer.

The reactive compatibilizer acts to increase the interfacial adhesion by inducing a reaction between the microalgae and the polymer matrix. When the compression molding temperature is less than 120°C, the surface activity of the microalgae increased by the reactive compatibilizer and the crosslinking reaction is insufficient. can do. On the other hand, if the compression molding temperature exceeds 200°C, thermal denaturation of microalgae may occur.

As described above, in the present invention, when manufacturing an eco-friendly composite using microalgae, which is biomass, a reactive compatibilizer is added when mixing polymer resin and microalgae, and melt mixing and compression molding are performed in a predetermined temperature range. Interfacial adhesion can be improved by inducing an increase in the reaction between polymer resin and microalgae, which can improve mechanical properties and processability.

Hereinafter, the present invention will be described in detail through examples to aid understanding. However, the embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the following embodiments. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. Here, the content is based on weight unless otherwise specified.

Example 1: Preparation of EVA/DSP/HS2 composite

(Step 1) Melt mixing

Poly(ethylene-vinyl acetate, EVA) (melt index=2.5g/10min, T _m =71°C, vinyl acetate content=28wt%) as the polymer matrix, and dried microalgae ( Chlorella sp.) as the biomass filler. HS2, 51% protein, 28% carbohydrate, 18% lipid, 3% ash), and dicumyl peroxide (DCP), grade PERKADOX BC-FF, AkzoNobel) as a reactive compatibilizer. .

The EVA and HS2 were each dried in a convection oven at 40°C for 8 hours and then added to a sealed mixer (Rheocomp mixer 600, MKE, Korea). After adding DCP to the mixer, melt mixing was performed by operating at 85°C and 100rpm for 7 minutes. At this time, the content of HS2 was varied in the range of 10 to 30% of the total weight, and the content of DCP was varied in the range of 0 to 2 phr (per hundred resin).

(Step 2) Compression molding and cooling

The molten mixture was used to produce disk-shaped specimens (diameter 25 mm, thickness 1 mm) and dog bone-shaped specimens (total length 58 mm, thickness 1 mm) using a hot press (CH4386, Carver, USA).

The disk-shaped specimen was manufactured by placing the molten mixture on a plate at 120°C and compression molding it for a total of 6 minutes, then removing it from the plate and cooling it at room temperature for 4 minutes.

The dog bone-shaped specimen was manufactured by compression molding the molten mixture for a total of 6 minutes at each condition of 120°C, 150°C, and 180°C, and then cooling it at room temperature for 4 minutes.

Example 2: Preparation of HS2/LDPE composite

A composite specimen was prepared in the same manner as in Example 1, except that in Step 1, the content of HS2 was changed to a range of 50 to 70% of the total weight.

Example 3: Preparation of PBAT/ADR/HS2 and PBAT/DCP/HS2 complexes

(Step 1) Melt mixing

Polybutylene adipate terephthalate (PBAT), grade ecoflex C1200, ρ=1.25 g/cm ³ , BASF, Germany) as the polymer matrix, and dried microalgae ( Chlorella sp. HS2, protein 51) as the biomass filler. %, carbohydrate 28%, lipid 18%, ash 3%), and polymer chain extender (Joncryl, grade ADR-4468 (ADR-extender), BASF, Germany) and dicumyl peroxide as reactive compatibilizers. (Dicumyl peroxide (DCP), grade PERKADOX BC-FF, AkzoNobel) was prepared.

The HS2 was dried in a convection oven at 40°C for 8 hours, and the PBAT and ADR-extender were each dried in a convection oven at 80°C for 24 hours and then mixed. At this time, the content of the HS2 was fixed at 70% of the total weight, and the content of the ADR-extender was fixed at 1 phr. The dry mixture was put into a closed mixer (Rheocomp BIM-150, MKE, Korea) and operated at 130°C at 100 rpm for 7 minutes to perform melt mixing.

Additionally, dried HS2 and PBAT were put into a batch mixer, DCP was added thereto, and melt mixing was performed by operating at 130°C and 100rpm for 7 minutes.

(Step 2) Compression molding and cooling

For each molten mixture obtained in step 1, a dog bone-shaped specimen (total length 58 mm, thickness 1 mm) was compression molded at 130°C for a total of 6 minutes using a hot press (CH4386, Carver, USA), and then pressed at room temperature for 4 minutes. It was prepared by cooling for several minutes.

Experimental Example 1: Evaluation of morphology and physical properties of EVA/DSP/HS2 composite

Mechanical properties were analyzed with dog bone specimens of the EVA/DSP/HS2 composite prepared in Examples 1 and 2, and morphology, Fourier transform infrared spectrometry (FT-IR) analysis, and rheological property analysis were performed with disk-shaped specimens.

Specifically, the mechanical properties were measured more than 5 times for each sample by cutting the specimen to the ASTM D639 type V standard and applying a tensile speed of 50 mm/min using UTM (LF plus, Lloyd instruments Ltd), and then measuring the average value. was used. Morphological changes were analyzed by observing the cross-section of the specimen using a field emission scanning electron microscope (FE-SEM, SUPRA-55VP, Carl Zeiss, 2 kV). The cross section for SEM imaging was prepared by preparing a fractured surface of a coin-shaped specimen (thickness 1.0 mm, diameter 25 mm) produced through a hot press in a liquid nitrogen environment and then coating it with platinum.

The FT-IR analysis was performed using TENSOR 27 (Bruker, Germany) operating at a frequency of 400 to 4000 cm ^-1 , and the rheological properties were measured at 120°C, 150°C, and 180°C using RMS800 (Rheometrics, USA). Measurements were made in the linear viscoelastic region. The analysis results are shown in Figures 1 to 11.

Figure 1 shows FT-IR results chemically confirming the reactivity and structural change when dicumyl peroxide (DCP), used as a reactive compatibilizer in Example 1, is added to EVA resin and EVA/HS2 composite.

In Figure 1(a), EVA reacted with DCP and a peak appeared in the range of 1640 to 1540 cm ^-1 , which is an ether produced by the reaction between the -RO- functional group of DCP and the terminal ester (-COO-) functional group of EVA. It is a peak related to (-COC-). Microalgae have a high protein component content (> 40%), so functional groups related to amino bonds in the cell wall were identified in the range of 1740 to 1540 cm ^-1 , and ether functional groups due to cellulose components were identified in the range of 1300 to 1000 cm ^-1. It has been done.

In Figure 1(b), the intensity of the peak in the range of 1640 to 1540 cm ^-1 increased as a result of the reaction with DCP and HS2, and the position of the peak in the range of 1300 to 1000 cm ^-1 moved. This indicates that DCP reacts with EVA and microalgae at 180°C, and the reaction of protein and cellulose components of microalgae becomes more active.

Figure 2 is an SEM image showing the change in morphology according to DCP content and molding temperature in the EVA/DCP/HS2 composite prepared in Example 1 [(a) HS2 10wt%, DCP 0phr, mold T=120°C; (b) HS2 10wt%, DCP 0phr, mold T=150℃; (c) HS2 10wt%, DCP 2phr, mold T=120℃; (d) HS2 10wt%, DCP 2phr, mold T=150℃].

In Figures 2(a) and 2(c), as DCP was not added to the composite, voids were formed at the interface between EVA and HS2 regardless of the molding temperature. On the other hand, in Figures 2(b) and 2(d), when DCP was added, the number of observed HS2 particles decreased and the particle size decreased, and fibers were frequently observed between HS2-EVA. This is because DCP forms EVA radicals and at the same time reacts with the protein amino acids and cellulose radicals that make up the outer wall of HS2 to form bonds, thereby realizing strong interfacial adhesion. In other words, when DCP is added, EVA covers the surface of the microalgae particles and the particle interface is not exposed, which is the source of increasing mechanical properties. This effect was clearly seen in the case of a composite manufactured by increasing the content of microalgae (HS2) to 30%.

Figure 3 is an SEM image showing the cross section of the EVA/DCP/HS2 composite prepared in Example 1 as the HS2 content and molding temperature increase [(a) HS2 10wt%, DCP 2phr, mold T=120°C; (b) HS2 30wt%, DCP 2phr, mold T=120℃; (c) HS2 10wt%, DCP 2phr, mold T=150℃; (d) HS2 30wt%, DCP 2phr, mold T=180℃].

In Figures 3(a) to 3(d), the DCP content is fixed at 2 phr and the change with increase in temperature can be confirmed. As the temperature increases (>130°C), the reaction activity of DCP increases, resulting in increased interaction between EVA and microalgae particles. It can be seen that a lot of crosslinking occurs, and as a result, the interface does not appear clearly.

In the case of 10 wt% of HS2, uniform dispersion of HS2 particles was observed at 120°C, and it was difficult to observe HS2 particles at 150°C. Similarly, in the case of HS2 30wt%, at 120°C, many particle interfaces are revealed and a rough surface is observed, but as the temperature increases, the interface becomes blurred and the particle shape disappears, making particle observation difficult. This is because the reaction between the particles and EVA is active at temperatures above 130°C, and the polymer completely surrounds the particles.

By this morphological change, the tensile strength of the composite specimen containing 30 wt% of HS2 and 2 phr of DCP increases without a significant decrease in elongation at break at 150°C and 180°C (see Figure 4). ). Therefore, when HS2 is mixed with EVA polymer, even if the content of HS2 increases, a reaction is induced between the particles and the polymer chain, thereby increasing interfacial adhesion and producing a microalgae-based polymer composite with improved mechanical properties.

Figure 4 shows the change in mechanical properties (tensile strength) of the EVA/DCP/HS2 composite prepared in Example 1 according to the DCP content, HS2 content, and molding temperature [(a) HS2 10wt%, mold T=150°C ; (b) HS2 30wt%, mold T=180℃]. For reference, tensile strength is the maximum strength shown by the polymer composite in a tensile test, and elongation at break refers to the elongation rate when the polymer composite breaks in a tensile test.

In Figure 4(a), the composite specimen containing 10wt% of HS2 maintained elongation at break and increased tensile strength under molding conditions at 150°C with the addition of 0.6phr of DCP, especially at DCP 2.0. When phr was added, the tensile strength further increased (elongation > 1000% maintained). In other words, in the case of pure EVA, if DCP is added and left at a high temperature of 150 degrees or higher, the mechanical properties decrease due to thermal denaturation of the cross-linked polymer, but if microalgae (HS2) is added, a reaction of HS2-DCP-EVA occurs and HS2 is dispersed. was further improved and at the same time showed improvement in physical properties.

In Figure 4(b), the composite specimen containing 30 wt% of HS2 showed an increase in physical properties under molding conditions at 180°C due to the addition of DCP. This requires high temperature conditions to activate the cross-linking effect with EVA when the content of HS2 increases, and at 180°C, the reactivity of DCP to microalgae further increased, so that mechanical properties increased even when a small amount of 0.6 phr of DCP was added. Therefore, if the DCP content is increased to 2 phr, the DCP molecules show sufficient reactivity to 30% microalgae and EVA, which can increase the mechanical properties under both 150 ℃ and 180 ℃ conditions.

Figure 5 shows the change in rheological properties according to the DCP content and molding temperature added to the EVA resin (a) and EVA/HS2 composite (b).

The rheological properties are a standard for checking the degree of cross-linking when DCP is added to EVA resin or EVA/HS2 composite, so the specimens are left for 1 hour at each temperature of 120°C, 150°C, and 180°C to determine structural changes. Rheological properties were confirmed. More specifically, a 'time sweep test' was performed on specimens at each temperature of 120℃, 150℃, and 180℃ for 1 hour under constant strain conditions, and a 'frequency sweep test' was performed before and after the test. The degree of DCP crosslinking progress was compared through linear viscoelasticity results obtained through a frequency sweep test after a time sweep test (1 hour heat treatment).

As a result, regardless of the presence or absence of microalgae, the storage modulus (G') at 0.1 rad/s decreased as the temperature increased when DCP was not contained, and when DCP was added, G' decreased depending on temperature and microalgae content. Each value changed differently. This means that DCP reacts not only with EVA polymer but also with microalgae particles to form a network structure, forming different structures depending on the temperature. This means that the reaction temperature of microalgae-DCP is different from that of EVA-DCP. .

In Figure 5(a), G' increased in the case of EVA-DCP at 120°C, but in Figure 5(b), G' of microalgae-EVA-DCP hardly increased. This is the result that the reaction of EVA-DCP mainly occurs at 120°C, and the reaction between microalgae and DCP cannot be expected, but when the temperature is increased to 150°C, the reaction activity of DCP and EVA polymer chains further increases. In addition, G' of EVA-DCP-HS2 varied depending on the DCP content and increased when 2 phr was added, which means that when the DCP concentration is sufficiently high, the microalgae-EVA-DCP reacts to form a network structure.

On the other hand, when the temperature increases to 180°C, G' of EVA-DCP decreases rapidly due to heat denaturation (Figure 5(a)), but in the case of EVA-DCP-H2P, the reaction activity of microalgae increases and reacts with DCP. This occurred actively and G' increased significantly (Figure 5(b)). When the DCP content was 2 phr, EVA showed maximum reactivity at 150 degrees, but the reactivity of EVA-DCP-HS2 (30%) increased linearly with increasing temperature.

Figure 6 is an SEM image showing the fracture surface of the EVA/DCP/HS2 composite prepared in Example 1 after stretching (50 mm/min) as the HS2 content and molding temperature increased [(a) HS2 10wt%, DCP 2phr, mold T=150℃; (b) HS2 30wt%, DCP 2phr, mold T=180℃].

From Figure 6, it can be seen that the addition of 2 phr of DCP induced a reaction at the interface between microalgae particles and EVA and increased the interfacial contact force, so that the EVA bond was maintained at the interface even after deformation under 50 mm/min stretching conditions.

Figure 7 is an SEM image showing a cross-section of a specimen according to the DCP content and molding temperature of the EVA/DCP/HS2 (50wt%) composite prepared in Example 2 [(a) DCP 0phr, T=120°C, before stretching deformation ; (a) DCP 0phr, T=180℃, after stretching deformation; (b) DCP 2phr, T=120℃, before stretching deformation; (b) DCP 2phr, T=180℃, after stretching deformation]. More specifically, electron micrographs of cross-sections parallel to the stretching axis direction of the specimen before and after measuring the mechanical properties of the composite were observed.

In the EVA/HS2 (50 wt%) composite of Figure 7(a), HS2 particle aggregates with a size of 10 μm or more are in close contact, and EVA polymer is distributed between the aggregates. In other words, when stretching strain was applied to the specimen, it was observed that EVA was located between microalgae aggregates, stretched according to strain, and connected to each other in the form of fibrils. It can be seen that EVA acts like a plasticizer between microalgae particle aggregates to maintain the ductility of the material.

In the EVA/DSP (2phr)/HS2 (50wt%) composite of Figure 7(b), the size of the HS2 particle aggregates was rapidly reduced, and the aggregate interface was not revealed in the cross section compared to Figure 7(a). This shows that the addition of DCP not only increases the interfacial adhesion between particle aggregates and EVA polymer, but also further activates particle dispersion, enabling uniform dispersion.

Figure 8 is an SEM image showing a cross-section of a specimen according to the DCP content and forming molding temperature of the EVA/DCP/HS2 (70wt%) composite prepared in Example 2 [(a) DCP 0phr, T=120°C, before stretching deformation ; (a) DCP 0phr, T=180℃, after stretching deformation; (b) DCP 2phr, T=120℃, before stretching deformation; (b) DCP 2phr, T=180℃, after stretching deformation].

In the EVA/HS2 (70wt%) composite of Figure 8(a), even when the content of HS2 increased, most particle aggregates were observed and it was difficult to distinguish the EVA polymer, and the EVA polymer was rarely observed in the void where the particles escaped. . In particular, in the image after stretching deformation (Figure 8(a')), the particle aggregate size was distributed around 20 μm, and aggregates smaller than 10 μm were hardly found. EVA is located between particle aggregates to provide ductility upon deformation, but due to the uneven distribution of EVA, thin fibrils were formed unevenly between HS2 particles.

In the EVA/DSP (2phr)/HS2 (70wt%) complex shown in Figure 8(b), the size of the HS2 aggregates was clearly reduced by the addition of DCP, and the aggregate interface was not revealed because EVA surrounded the HS2 aggregates. This means that DCP not only causes a reaction between the aggregates and EVA, but is also effective in reducing the size of HS2 particle aggregates. In addition, in the cross-sectional image (FIG. 8(b')) of the same composite after stretching and deformation, the size of the HS2 aggregates decreased, most of them were distributed in sizes of 10 μm or more, and EVA fibrils were uniformly distributed.

Figure 9 shows changes in mechanical properties according to DCP content, HS2 content, and molding temperature in the EVA/DCP/HS2 composite prepared in Example 2 [(a) HS2 50wt%, mold T=180°C; (b) HS2 70wt%, mold T=180℃].

More specifically, to confirm the reactivity between DCP, HS2, and EVA polymers in a composite containing a high content of HS2, specimens were prepared at 180°C for composites with different DCP contents added, and stretched at a stretching speed of 50 mm/min. Mechanical properties were measured.

In Figure 9, as the DCP content increased, the tensile strength of the composite increased. Because the microalgae HS2 content was high, it showed a strong dependence on the DCP content, showing an increase in tensile strength at 2 phr conditions.

Normally, when high content of microalgae HS2 particles are mixed with polymer resin, it is difficult to observe improvement in tensile strength because the interfacial adhesion between HS2 particles and polymer resin rapidly decreases, especially at high temperature conditions of 180℃ due to thermal denaturation of polymer resin. As it gets worse, the tensile strength further decreases. However, when DCP was added, the adhesion between the microalgae particles and EVA increased as DCP induced a reaction between the microalgae containing protein and cellulose and the EVA polymer chain in the composite containing a high content of HS2, and the tensile strength of the composite increased. increased.

Figure 10 shows changes in stress-strain behavior according to DCP content, HS2 content, and molding temperature in the EVA/DCP/HS2 composite prepared in Example 2.

In Figure 10, the composite containing HS2 at a high content of 50 wt% induced a reaction at 180°C upon addition of DCP, doubling the tensile strength and increasing the elongation from 850% to 930%. Even when the HS2 content was increased to 70%, the tensile strength increased from 1 MPa to 2.5 MPa at 180°C, and the elongation increased from 570% to 670% at 120°C. This shows the processability and industrial applicability of a composite plastic material containing a high content of HS2.

Figure 11 shows the molding processability and deformability of the DCP content and HS2 content in the EVA/DCP/HS2 composite prepared in Example 2. Polymer molding processing was possible in a dog-bone mold without additional processing of the composite, and the processed Plastic deformation of the specimen was possible at a stretching speed of 50 mm/min.

Experimental Example 2: Evaluation of morphology and physical properties of PBAT/ADR/HS2 and PBAT/DCP/HS2 composites

The analysis as described in Experimental Example 1 was performed on PBAT/ADR/HS2 and PBAT/DCP/HS2 prepared in Example 1.

Figure 12 is an SEM image showing the morphologies of control PBAT/HS2 (70 wt%), PBAT/ADR/HS2 (70 wt%) and PBAT/DCP/HS2 (70 wt%) composites prepared in Example 3.

In the control HS2/PBAT complex of Figure 12(a), HS2 particle aggregates were distributed in sizes of 10 to 20 ㎛, and the interface was clearly observed. In the PBAT/ADR/HS2 composite of Figure 12(b) and the PBAT/DCP/HS2 composite of Figure 12(c), the size of the HS2 particle aggregates became smaller and the particle interface became compatibilized, so it was not clear.

Figure 13 shows the tensile strength (a) of the control PBAT/HS2 (70 wt%) (denoted neat), PBAT/ADR/HS2 (70 wt%) and PBAT/DCP/HS2 (70 wt%) composites prepared in Example 3. It represents the yield strength.

In Figure 13(a), the control HS2/PBAT composite using a high content of 70wt HS2 had low tensile strength and yield strength, but the tensile strength increased when ADR or DCP was added. In other words, although PBAT has the disadvantage of having high ductility but low strength, when mixed with a high content of HS2, the use of ADR or DCP induces a reaction of PBAT-HS2, resulting in an increase in tensile strength. Meanwhile, in the case of the DCP additive, the interfacial adhesion effect of HS2 and PBAT was lower than that of the ADR-extender, but it still had an effect of increasing tensile strength.

As the specific parts of the present invention have been described in detail above, it is clear to those skilled in the art that these specific techniques are merely preferred embodiments and do not limit the scope of the present invention. something to do. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (15)

A polymer containing an ester group as a matrix; Microalgae forming a dispersed phase in the polymer matrix; And an eco-friendly composite comprising a reactive compatibilizer that forms cross-links between the microalgae and the polymer matrix. The method of claim 1, wherein the polymer matrix is polyethylene vinyl acetate (EVA), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), and polybutylene succinate-co-adipate (PBSA). , an eco-friendly composite comprising one or more selected from polylactic acid (PLA), thermoplastic polyurethane (TPU), and polycaprolactone (PCL). The eco-friendly composite according to claim 1, wherein the microalgae content is greater than 5% by weight and less than 70% by weight based on the total weight. The eco-friendly composite according to claim 3, wherein the microalgae content is 30 to 70% by weight based on the total weight. The method of claim 1, wherein the microalgae are Chlorella genus, Botryococcus genus, Dunaliella genus, Nannochloropsis genus, Spirulina genus and Halochlorococcus. ( Halochlorococcum ) An eco-friendly complex selected from one or more of the genus. The eco-friendly composite according to claim 1, wherein the dispersed phase formed by the microalgae has an average size of less than 2㎛ to 30㎛. The eco-friendly composite of claim 1, wherein the reactive compatibilizer includes a vulcanizing agent, an epoxy group-containing chain extender, or a mixture thereof. The eco-friendly composite according to claim 7, wherein the vulcanizing agent includes dicumyl peroxide (DCP), an acrylic anhydride-based additive, a maleic anhydride-based additive, or a mixture thereof. The method of claim 7, wherein the epoxy group-containing chain extender is poly(ethylene-co-methyl acrylate-co-glycidyl methacrylate), Eco-friendly composite containing poly(ethylene-co-glycidyl methacrylate) (EGMA) or mixtures thereof. The eco-friendly composite according to claim 1, wherein the reactive compatibilizer is included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the polymer matrix. As a method of manufacturing the eco-friendly composite according to claim 1,
(S1) Adding a reactive compatibilizer that forms a cross-link between the microalgae and the polymer matrix to the mixture obtained by drying the polymer resin and microalgae containing an ester group and adding them to a mixer, melting and mixing, and
(S2) A manufacturing method including the step of compression molding the molten mixture and then cooling it. The method of claim 11, wherein the microalgae is used in an amount of more than 5% by weight and less than 70% by weight based on the total weight of the composite. The manufacturing method of claim 11, wherein the reactive compatibilizer is used in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the polymer matrix. The manufacturing method according to claim 11, wherein the melt mixing in step (S1) is performed at 80 to 150°C. The manufacturing method according to claim 11, wherein the compression molding in step (S2) is performed at 120 to 180°C.