Bifunctional graft modified polymer / biomass composite material as well as preparation method and application thereof

Abstract

The invention discloses a bifunctional graft modified polymer / biomass composite material as well as a preparation method and application thereof, and belongs to the technical field of polymer materials. The preparation method comprises the following steps: simultaneously grafting a grafting monomer and MAH to a polymer matrix through melt grafting to obtain a bifunctional graft modified polymer; the rigid hydrophobic structure of the graft monomer and the polar reaction activity of MAH have a synergistic effect, the interfacial compatibility of the polymer and the biomass is remarkably improved, the bifunctional graft modified polymer or the bifunctional graft modified mixture and the biomass are subjected to melt blending, and the composite material is prepared. The composite material shows synergistically enhanced mechanical properties, higher thermal stability, lower water absorption and controllable biodegradation rate, high-valued utilization of biomass such as the wine brewing waste residues is achieved, and the obtained composite material is balanced in performance and suitable for the fields of sustainable packaging and agriculture.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a bifunctional grafted modified polymer / biomass composite material, its preparation method, and its application. Background Technology

[0002] With increasing environmental awareness and the advancement of sustainable development strategies, the development of biodegradable and resource-recyclable polymer composites has become a research hotspot. Biodegradable polyesters such as polybutylene succinate (PBS) and polylactic acid (PLA), as well as traditional general-purpose plastics such as polypropylene (PP) and polyethylene (PE), are considered effective ways to prepare low-cost, environmentally friendly materials by combining them with agricultural processing byproducts such as distiller's grains and straw.

[0003] However, an inherent interfacial incompatibility exists between the polymer matrix (especially hydrophobic polymers) and the hydrophilic filler, often leading to a significant deterioration in the overall performance of the composite material, particularly its mechanical properties. Currently, the main technical means to improve compatibility include:

[0004] Filler pretreatment: Fillers are modified using methods such as alkali treatment and silane coupling agents. For example, treating distiller's grains (DG) with a silane coupling agent (such as KH560) can improve its interfacial binding with PBS to some extent. However, this method has significant drawbacks: the pretreatment process is lengthy (usually requiring tens of hours), complex, introduces a large amount of chemical reagents leading to increased costs, and is not suitable for large-scale continuous production. Furthermore, when the filler content is high (e.g., >10%), the modification effect drops sharply, interfacial defects remain prominent, and the problem cannot be fundamentally solved.

[0005] Polymer grafting of polar monomers: Introducing polar monomers such as maleic anhydride (MAH) into the polymer chain via melt grafting is another common strategy. The anhydride groups of MAH can undergo esterification or hydrogen bonding with the hydroxyl groups on the filler surface, thereby enhancing interfacial adhesion. However, this single-functional-group modification strategy has limitations: Single function: MAH mainly provides polar interactions, and its effect on suppressing agglomeration caused by filler-filler interactions is limited. At high filler concentrations, the filler is still prone to agglomeration, forming stress concentration points; Uneven performance improvement: Although MAH grafting can improve tensile strength to some extent, it has limited effect on improving the brittleness of the material, and the elongation at break is often still low. At the same time, it does not contribute much to the improvement of hydrophobicity and moisture resistance. The composite material has poor performance stability in high humidity environments. Single polar modification cannot simultaneously achieve the multi-objective synergistic improvement of "strong interfacial adhesion", "good dispersibility" and "excellent hydrophobicity".

[0006] Physical blending: The simplest and most direct method is to directly blend unmodified polymers with fillers. Numerous studies have shown that this method is the least effective. Due to extremely poor compatibility, weak interfacial bonding forces, and severe filler agglomeration, the mechanical properties (strength, toughness) of the composite material decrease sharply, and the water absorption rate increases significantly, making it difficult to meet the basic requirements of most practical applications.

[0007] CN105440716A discloses a compatibilizer for improving the properties of biomass composite materials and its preparation method. The compatibilizer has a polyolefin main chain and grafted side chains consisting of one or more of maleic anhydride, methacrylic acid, acrylic acid, or their derivatives, forming random copolymers or alternating copolymers with styrene or its derivatives. It exhibits excellent effects in improving the interfacial compatibility of highly filled biomass composite materials, thereby significantly improving the water resistance and mechanical properties of the biomass composite materials. CN119332539A discloses a rosin supplement / cationic rosin sizing agent and its preparation method. The rosin supplement is a graft-modified polyethylene wax, which is a copolymer of polyethylene wax, maleic anhydride, and styrene. The preparation method involves using an organic peroxide as an initiator, adding maleic anhydride and styrene as grafting monomers to the polyethylene wax, performing graft modification at a temperature of 130-180℃ for 3-6 hours, and then cooling to room temperature to obtain the graft-modified polyethylene wax. CN120056556A discloses a BOPP matte film suitable for direct coating process and its preparation method. One of the raw materials is maleic anhydride-styrene melt-grafted random copolymer polypropylene. It is prepared by melt grafting method. Styrene monomer and maleic anhydride monomer are added to xylene solvent. Azobisisobutyronitrile is used as an initiator to obtain styrene-maleic anhydride copolymer by free radical copolymerization. Then, using dicumyl peroxide as an initiator, styrene-maleic anhydride copolymer is grafted onto the random copolymer polypropylene molecular chain to form a branch chain, thus obtaining the film.

[0008] CN102746681A discloses a wood-plastic composite material using distiller's grains as a reinforcing phase. The distiller's grains are pre-treated and crushed into small-particle powder. The distiller's grains are used as the reinforcing phase, and plastic is used as the matrix phase. Various modifiers, lubricants, heat stabilizers, additives, and other raw materials are added and wood-plastic granules or products are obtained through different molding processes. The plastic used as the matrix phase can be a general thermoplastic such as polyethylene or polypropylene, or a biodegradable plastic such as polyvinyl alcohol or polylactic acid. The modifier can be maleic anhydride or its grafted PP, PE, ... styrene.

[0009] In summary, existing technologies either suffer from cumbersome processes, high costs, and low efficiency, or inherent defects such as poor synergistic effects, inability to simultaneously achieve reinforcement and toughening, and poor moisture resistance. Therefore, developing a novel modification technology that is efficient, universal, and can synergistically improve interfacial adhesion, filler dispersion, and material hydrophobicity is crucial for promoting the high-value application of biomass such as distiller's grains in polymer composites, and is also a pressing technical challenge to be solved in this field. Summary of the Invention

[0010] This invention aims to solve one or more of the following technical problems existing in the preparation technology of polymer biomass composite materials: poor interfacial compatibility: weak interfacial bonding between hydrophilic fillers and hydrophobic polymer matrix, leading to phase separation; poor filler dispersibility: fillers are prone to agglomeration, forming stress concentration points, which become the starting point of material failure; deterioration of mechanical properties: after the addition of fillers, the key mechanical properties of composite materials such as tensile strength and toughness decrease significantly; poor moisture resistance: composite materials have high water absorption due to interfacial defects and the hydrophilicity of fillers, resulting in low dimensional stability and wet-state retention of mechanical properties; difficulty in synergistic performance improvement: it is difficult to simultaneously achieve multiple properties such as reinforcement, toughening, heat resistance, and moisture resistance.

[0011] To address the aforementioned technical problems, this invention first provides a method for preparing a bifunctional grafted modified polymeric biomass composite material, comprising the following steps:

[0012] A. The polymer matrix, maleic anhydride, grafting monomer and free radical initiator are melt-blended and then melt-grafted to obtain a bifunctional grafted modified polymer.

[0013] B. Melt-blend the bifunctional grafted modified polymer obtained in step A with the biomass filler to obtain the bifunctional grafted modified polymer biomass composite material.

[0014] Alternatively, B‵, the bifunctional grafted modified polymer obtained in step A is mixed with the polymer matrix to obtain a bifunctional grafted modified mixture, and the bifunctional grafted modified mixture is melt-blended with biomass filler to obtain a bifunctional grafted modified polymer biomass composite material.

[0015] In steps A and B, the polymer matrix is ​​a biodegradable polyester;

[0016] In step A, the mass of maleic anhydride is 1.5% to 6% of the mass of the polymer matrix in step A, the mass of the grafted monomer is 1.5% to 12% of the mass of the polymer matrix in step A, and the mass ratio of maleic anhydride to grafted monomer is 1:1 to 3.

[0017] In step B, the mass ratio of the bifunctional grafted modified polymer to the biomass filler in step B is 90%~40%:10%~60%, totaling 100%.

[0018] In step B‵, the bifunctional grafted modified polymer accounts for 3~12% of the polymer matrix in step B‵; the mass ratio of the bifunctional grafted modified mixture to the biomass filler in step B‵ is 90%~40%:10%~60%, totaling 100%.

[0019] In the above preparation method, in step A, the polymer matrix is ​​selected from one of aliphatic polyester, aliphatic-aromatic copolyester, or polylactic acid and its copolymers.

[0020] Preferably, in the above preparation method, in step A, the polymer matrix is ​​selected from PBS, PES, PHA, PCL, PBAT, PEAT, PLA, or PLGA.

[0021] It should be noted that the polymer matrix used in step B‵ must be the same as the polymer matrix used in step A.

[0022] In the above preparation method, in step A, the grafting monomer is selected from at least one of styrene, divinylbenzene, trivinylbenzene, α-methylstyrene, or 4-methylstyrene.

[0023] Preferably, in the above preparation method, in step A, the grafting monomer is styrene, divinylbenzene, trivinylbenzene, or a mixture of styrene and divinylbenzene.

[0024] More preferably, in the above preparation method, in step A, the grafting monomer is divinylbenzene or a mixture of styrene and divinylbenzene in a mass ratio of 3 to 5:1.

[0025] Preferably, in the above preparation method, in step A, the mass of maleic anhydride is 3% to 5% of the mass of the polymer matrix in step A, and the mass of the grafted monomer is 3% to 5% of the mass of the polymer matrix in step A.

[0026] In the above preparation method, in step A, the total mass of maleic anhydride and grafted monomer is 6% to 10% of the mass of the polymer matrix in step A.

[0027] In the above preparation method, in step A, the free radical initiator is dicumyl peroxide, di-tert-butyl peroxide (DTBP), or 1,1-di(tert-butylperoxide)-3,3,5-trimethylcyclohexane (DBP).

[0028] In the above preparation method, in step A, the mass of the free radical initiator is 0.2% to 0.6% of the mass of the polymer matrix in step A.

[0029] In the above preparation method, in step A, the reaction temperature for melt blending is 110℃~180℃.

[0030] In the above preparation method, in step A, the melting and blending speed is 60 rpm to 200 rpm.

[0031] In the above preparation method, in step A, the reaction time for melt blending is 5 min to 10 min.

[0032] In the above preparation method, in step A, the reaction temperature of the melt grafting reaction is 110℃~180℃.

[0033] In the above preparation method, in step A, the rotation speed of the melt grafting reaction is 50 rpm to 200 rpm.

[0034] In the above preparation method, in step A, the reaction time of the melt grafting reaction is 3 min to 8 min.

[0035] In the above preparation method, step B, the biomass filler is at least one of distiller's grains, straw, bamboo, wood, or fruit peel. This invention demonstrates the broad applicability of this method to different biomass types using two biomass fillers with vastly different physicochemical properties: distiller's grains (DG) and corn straw (CS). Particularly with distiller's grains as a preferred filler, this method produced an unexpected synergistic effect, successfully solving the technical challenge of balancing strength and toughness at high filler volumes. In this invention, the biomass filler is pretreated using conventional methods in the art before melt blending with the bifunctional grafted modified polymer, such as drying and pulverizing.

[0036] Preferably, in the above preparation method, in step B, the biomass filler is distiller's grains or straw.

[0037] In the above preparation method, in step B, the particle size of the biomass filler is 100 mesh to 600 mesh.

[0038] In the above preparation method, in step B, the mass ratio of the bifunctional grafted modified polymer to the biomass filler in step B is 90%~45%:10%~55%, totaling 100%.

[0039] In some embodiments of the present invention, in step B of the above preparation method, when the polymer matrix is ​​PBS or PLA, the mass ratio of the bifunctional grafted modified polymer to the biomass filler is 75%~50%: 25%~50%, totaling 100%; when the polymer matrix is ​​PBAT, the mass ratio of the bifunctional grafted modified polymer to the biomass filler is 90%~75%: 10%~25%, totaling 100%.

[0040] In the above preparation method, in step B, the reaction temperature for melt blending is 110℃~200℃.

[0041] In the above preparation method, in step B, the reaction time for melt blending is 5 min to 10 min.

[0042] In the above preparation method, step B‵, the biomass filler is at least one of distiller's grains, straw, bamboo, wood, or fruit peel. This invention demonstrates the broad applicability of this method to different biomass types using two biomass fillers with vastly different physicochemical properties: distiller's grains (DG) and corn straw (CS). Particularly with distiller's grains as a preferred filler, this method produced an unexpected synergistic effect, successfully solving the technical challenge of balancing strength and toughness at high filler volumes. In this invention, the biomass filler is pretreated using conventional methods in the art before melt blending with the bifunctional grafted modified mixture, such as drying and pulverizing.

[0043] Preferably, in the above preparation method, in step B‵, the biomass filler is distiller's grains or straw.

[0044] In the above preparation method, in step B, the particle size of the biomass filler is 100 mesh to 600 mesh.

[0045] Preferably, in the above preparation method, in step B‵, the bifunctional grafted modified polymer accounts for 6~12% of the polymer matrix mass in step B‵.

[0046] In the above preparation method, in step B‵, the mass ratio of the bifunctional grafted modified mixture to the biomass filler in step B‵ is 90%~45%:10%~55%, totaling 100%.

[0047] In some embodiments of the present invention, in step B of the above preparation method, when the polymer matrix is ​​PBS or PLA, the mass ratio of the bifunctional grafted modified mixture to the biomass filler is 75%~50%:25%~50%, totaling 100%; when the polymer matrix is ​​PBAT, the mass ratio of the bifunctional grafted modified mixture to the biomass filler is 90%~75%:10%~25%, totaling 100%.

[0048] In the above preparation method, in step B, the reaction temperature for melt blending is 110℃~180℃.

[0049] In the above preparation method, in step B, the reaction time for melt blending is 5 min to 10 min.

[0050] The present invention also provides a bifunctional grafted modified polymer biomass composite material, which is prepared by the above-mentioned preparation method of the bifunctional grafted modified polymer biomass composite material.

[0051] This invention also provides the application of the above-mentioned bifunctional grafted modified polymer biomass composite material in the preparation of biodegradable packaging materials or agricultural mulch films.

[0052] The present invention also provides a bifunctional grafted modified polymer, which is prepared by step A in the above-mentioned preparation method of bifunctional grafted modified polymer biomass composite material.

[0053] This invention also provides the application of the above-mentioned bifunctional grafted modified polymer in the preparation of biodegradable packaging materials or agricultural mulch films.

[0054] This invention creatively introduces the St-MAH bifunctional grafting strategy, rather than simply applying known physicochemical principles. Instead, it aims to actively construct a multi-element synergistic interfacial interaction network. This network can produce unexpected synergistic effects in biodegradable polyester matrices (especially solving the strength-toughness contradiction), successfully addressing the problem of simultaneously achieving mechanical strength, toughness, heat resistance, and water resistance in high-performance biomass composites with high filler content.

[0055] While existing technologies disclose the use of the St-MAH system for grafting modification of polyolefins (such as PP and PE), traditional polyolefins (such as PP / PE) inherently possess excellent hydrophobicity and chemical stability. The main challenge in their application lies in how to make them compatible with hydrophilic biomass fillers. Therefore, the primary purpose of introducing St-MAH grafting in existing technologies is simply "compatibility enhancement," that is, to "accommodate" the filler through the polarity of MAH, without any urgent need to improve the inherent advantages of the matrix itself, such as water resistance and rigidity.

[0056] In contrast, the biodegradable polyesters of this invention (such as PBS / PBAT) contain a large number of hydrophilic ester bonds in their molecular chains to achieve biodegradability. This results in inherent limitations in their applications, such as hydrophilicity, moisture sensitivity, and insufficient strength and heat resistance. Therefore, when combined with more hydrophilic biomass such as distiller's grains, they face a worsening situation of "double hydrophilicity." Thus, the modification strategy of this invention cannot merely "increase compatibility" but must also "reinforce" the matrix, simultaneously improving the water resistance, rigidity, and dimensional stability of the composite material.

[0057] Based on the above contradictions, this invention repositions the St-MAH bifunctional strategy: (1) The core function of the MAH functional group remains "compressibility enhancement" by forming a chemical anchor with the distiller's grains filler. (2) The role of rigid hydrophobic units such as St is elevated to an unprecedented level of importance: it not only helps the filler disperse, but its core mission is to "impart" and "feed back" its hydrophobicity and rigidity to the biodegradable polyester matrix with inherent defects. The bifunctional strategy of this invention unexpectedly breaks this trade-off, achieving a synergistic effect of "both strong and tough".

[0058] Furthermore, through systematic experiments across different polymer matrices, this invention reveals that divinylbenzene (DVB) is key to achieving optimal overall performance in combinations of MAH and rigid aromatic ring monomers. In PBS and biodegradable polyester systems such as PBAT and PLA, the DVB-MAH combination significantly outperforms St-MAH and TVB-MAH in tensile strength, elongation at break, and thermal stability. A small amount of DVB introduced into the St-MAH combination can bring synergistic performance enhancement, but excessive amounts lead to performance degradation, highlighting the precision and complexity of formulation control. In the traditional polypropylene (PP) system, PP-g-(DVB-MAH) / DG was prepared using the method of this invention and compared with PP-g-(St-MAH) / DG. Experimental results show that DVB also exhibits the same performance advantages in the PP system, with a significantly better modification effect than styrene (St). This invention confirms the unique and excellent effect of DVB, a specific monomer, in constructing high-strength, high-toughness interfaces, providing a clear and efficient technical direction for the interface design of high-performance biomass composites.

[0059] The beneficial effects of the present invention: The technical solution provided by the present invention has the following significant advantages:

[0060] Synergistic interface compatibility enhancement: Through the synergistic effect of rigid hydrophobic units such as St (especially DVB and St-small amount of DVB) and polar reactive functional groups of MAH, the organic combination of "physical entanglement / hydrophobic shielding" and "chemical bonding / polar interaction" is achieved, fundamentally solving the interfacial compatibility problem between biomass and polymer matrix.

[0061] Synergistic Enhancement of Mechanical Properties: The described bifunctional grafting strategy not only significantly improves the tensile strength and elastic modulus of the composite material, but more importantly, it largely maintains the elongation at break, achieving a "strong and tough" effect and overcoming the problem of increased brittleness often seen in traditional modified materials. Furthermore, comparative studies on different rigid aromatic ring grafted monomers revealed that the technical effects of the described bifunctional grafting strategy vary under different monomer conditions. Specifically, divinylbenzene (DVB), containing a divinyl structure, can achieve a better strength-toughness balance and overall performance in different polymer matrices when used as a grafting monomer, which is a preferred embodiment of this invention. While monomers such as styrene, trivinylbenzene, and their substitutes can also improve interfacial compatibility and overall performance, the specific improvement varies depending on the monomer structure and dosage.

[0062] Overall performance is significantly improved: thermal stability is enhanced: the dense interface layer formed by grafting effectively delays thermal decomposition, and the thermal weight loss initiation temperature (T5%) of the composite material is significantly increased; crystallization behavior is optimized: the enhanced interface bonding reduces the hindering effect of fillers on crystallization, and the fillers can also serve as nucleation sites, resulting in higher crystallinity and more complete crystallization of the composite material; moisture resistance is significantly improved: the introduction of rigid hydrophobic units greatly enhances the hydrophobicity of the composite material, reducing its water absorption rate by more than 40% compared to the unmodified system, thus ensuring dimensional stability and durability.

[0063] Degradation controllability: By adjusting the degree of bifunctional grafting and biomass content, the biodegradation rate of composite materials can be effectively controlled to meet the product life requirements of different application scenarios.

[0064] Universality of the process and high value utilization of waste: The method is simple and applicable to a variety of polymer matrices and biomass, providing a high-value-added resource utilization pathway for large-scale accumulation of biomass such as distiller's grains, which meets the requirements of circular economy and sustainable development. Attached Figure Description

[0065] Figure 1 This is a flowchart of the composite material preparation process of the present invention.

[0066] Figure 2 Comparison of Fourier transform infrared spectra of PBS, PBS-g-MAH, and PBS-g-(St-MAH); where a is the full spectrum, and b and c are magnified views of the characteristic regions.

[0067] Figure 3 This is a schematic diagram of the interaction mechanism between PBS-g-(St-MAH) and distiller's grains; where a represents the chemical formulas of the four reactions and b represents the possible stereostructures after the reaction.

[0068] Figure 4A comparison of the mechanical properties of PBS / DG, PBS-g-MAH / DG and PBS-g-(St-MAH) / DG composites is shown; where a is tensile strength, b is elongation at break, c is yield strength, d is elastic modulus, and e is stress-strain curve.

[0069] Figure 5 X-ray diffraction patterns of PBS / DG and PBS-g-(St-MAH) / DG composites are shown; where a represents PBS / DG and b represents PBS-g-(St-MAH) / DG.

[0070] Figure 6 Scanning electron microscope images of tensile fracture surfaces of PBS, PBS / DG, and PBS-g-(St-MAH) / DG composites; where a is PBS, b is PBS / DG (10%), c is PBS / DG (20%), d is PBS / DG (30%), e is PBS / DG (40%), f is PBS / DG (50%), a' is PBS-g-(St-MAH), b' is PBS-g-(St-MAH) / DG (10%), c' is PBS-g-(St-MAH) / DG (20%), d' is PBS-g-(St-MAH) / DG (30%), e' is PBS-g-(St-MAH) / DG (40%), and f' is PBS-g-(St-MAH) / DG (50%).

[0071] Figure 7 High-magnification scanning electron microscope images of tensile fracture surfaces of PBS / DG (50%) and PBS-g-(St-MAH) / DG (50%) composites, where a is PBS / DG (50%) and b is PBS-g-(St-MAH) / DG (50%).

[0072] Figure 8 Differential scanning calorimetry (DSC) curves of PBS / DG and PBS-g-(St-MAH) / DG composites are shown; where a represents the first cooling of PBS / DG, b represents the first cooling of PBS-g-(St-MAH) / DG, c represents the second heating of PBS / DG, and d represents the second heating of PBS-g-(St-MAH) / DG.

[0073] Figure 9 Thermogravimetric analysis (TG) curves of PBS / DG and PBS-g-(St-MAH) / DG composites are shown; where a is the TG curve of PBS / DG, b is the TG curve of PBS-g-(St-MAH) / DG, c is the DTG curve of PBS / DG, and d is the DTG curve of PBS-g-(St-MAH) / DG.

[0074] Figure 10 The graph shows the water absorption rate curves of PBS / DG and PBS-g-(St-MAH) / DG composites.

[0075] Figure 11 The figures show the contact angle test results of PBS / DG and PBS-g-(St-MAH) / DG composite materials; where a is the contact angle, b is the water droplet image of PBS / DG, and c is the water droplet image of PBS-g-(St-MAH) / DG composite material.

[0076] Figure 12 Biodegradation rate curves of PBS / DG and PBS-g-(St-MAH) / DG composites buried in soil for 180 days are shown; where a represents PBS / DG, b represents PBS-g-(St-MAH) / DG, and c represents the comparison results of the degradation of samples after actual burial. Detailed Implementation

[0077] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described herein.

[0078] The main raw materials used in this invention are: polybutylene succinate (PBS), brand name TH803S, purchased from Sichuan Jiefeng Meian Chemical Co., Ltd.; distiller's grains (DG), Yibin Wuliangye Co., Ltd.; maleic anhydride (MAH), styrene (St), dicumyl peroxide (DCP), etc., purchased from Shanghai Titan Technology Co., Ltd.

[0079] Performance testing methods: Tensile properties were tested according to GB / T 1040-2006 standard; crystallinity was calculated by DSC test; thermal stability was tested by TGA test; water absorption was calculated by immersion weighing method.

[0080] Example 1: Preparation of PBS-g-(St-MAH) / DG composite material

[0081] 1. DG pretreatment: Rinse the distiller's grains (DG) with deionized water and dry it. Then, grind it to 400-600 mesh using a ball mill for later use.

[0082] 2. Preparation of PBS-g-(St-MAH):

[0083] Manually premix PBS, maleic anhydride (MAH), styrene (St), and initiator DCP in a beaker at a mass ratio of 100:4:4:0.4.

[0084] The mixture was added to a Hacker torque rheometer preheated to 125°C and mixed at 100 rpm for 5 minutes, followed by 180 rpm for 3 minutes to carry out the melt grafting reaction.

[0085] The reaction product was cooled, granulated, and purified by chloroform dissolution and methanol precipitation to remove unreacted monomers and homopolymers, resulting in purified bifunctional graft-modified polymer. The bifunctional graft-modified polymer and PBS were blended at a mass ratio of 10%:90% to obtain PBS-g-(St-MAH).

[0086] 3. Preparation of composite materials

[0087] The above-mentioned PBS-g-(St-MAH) and pretreated DG were melt-blended in an internal mixer at 125°C for 6 minutes at a mass ratio of 70:30 (i.e., DG content of 30 wt%) to obtain PBS-g-(St-MAH) / DG composite material, labeled as PBS-g-(St-MAH) / DG (30%).

[0088] 4. Repeat steps 1 to 3 above, except that the mass ratio of PBS-g-(St-MAH) to pretreated DG in step 3 is changed to 90:10, 80:20, 60:40, and 50:50, to obtain PBS-g-(St-MAH) / DG (10%), PBS-g-(St-MAH) / DG (20%), PBS-g-(St-MAH) / DG (40%), and PBS-g-(St-MAH) / DG (50%), respectively.

[0089] The blends were pressed into shape using a flat vulcanizing machine and cut into standard strips for performance testing.

[0090] Example 2: Preparation of PBS-g-(DVB-MAH) / DG composite material

[0091] The steps 1-3 of Example 1 are basically the same, except that styrene (St) is replaced with divinylbenzene (DVB) (chemical formula C). 10 H 10 ), labeled as PBS-g-(DVB-MAH) / DG (30%).

[0092] Example 3: Preparation of PBS-g-(TVB-MAH) / DG composite material

[0093] The steps 1-3 of Example 1 are basically the same, except that styrene (St) is replaced with trivinylbenzene (TVB) (chemical formula C). 12 H 12 ), labeled as PBS-g-(TVB-MAH) / DG (30%).

[0094] Comparative Example 1: Preparation of PBS-g-MAH / DG composite material with a single functional group modification

[0095] This comparative example is used to illustrate the effect of using maleic anhydride (MAH) modification alone.

[0096] 1. DG pretreatment is the same as in Example 1.

[0097] 2. Preparation of PBS-g-MAH:

[0098] The process is basically the same as step 2 in Example 1, but without the addition of styrene (St), i.e., the raw material ratio is PBS:MAH:DCP = 100:4:0.4.

[0099] 3. Preparation of composite material PBS-g-MAH / DG:

[0100] Similar to step 3 of Example 1, PBS-g-MAH was compounded with 30 wt% DG and labeled as PBS-g-MAH / DG (30%).

[0101] Comparative Example 2: Preparation of Unmodified Composite Material PBS / DG

[0102] This comparative example is used to illustrate the properties of the base composite material without any interface modification.

[0103] 1. DG pretreatment is the same as in Example 1.

[0104] 2. Pure PBS can be used directly without grafting modification.

[0105] 3. Preparation of composite material PBS / DG:

[0106] Similar to step 3 of Example 1, pure PBS was combined with 30 wt% DG and labeled as PBS / DG (30%).

[0107] Table 1 Comparison of key performance test results between Examples 1-3 and Comparative Examples 1-2

[0108]

[0109] As shown in Table 1, under the same filler content (30 wt%), the performance of Examples 1-3 and Comparative Examples 1-2 showed significant differences, fully verifying the universality and superiority of the bifunctional grafting strategy of the present invention. The specific analysis is as follows:

[0110] 1. The synergistic effect and universality of bifunctional grafting have been confirmed.

[0111] Compared to the unmodified Comparative Example 2 (PBS / DG), the performance of Comparative Example 1 (PBS-g-MAH / DG) was improved, but the improvement was limited. This demonstrates that the effect of single MAH grafting on improving interfacial compatibility has a bottleneck.

[0112] However, the performance of all the bifunctional grafted examples (Example 1: St-MAH, Example 2: DVB-MAH, Example 3: TVB-MAH) was significantly better than that of Comparative Examples 1-2. This result strongly demonstrates that the technical solution of "synergistic grafting maleic anhydride (MAH) with another monomer containing a rigid aromatic ring (such as St, DVB, TVB)" can produce a synergistic enhancement effect that surpasses that of single MAH modification. This indicates that the core innovation of this invention lies in the concept of bifunctional grafting itself, and its effect is universally applicable to a series of monomers with similar structural features.

[0113] 2. The correlation between performance improvement and monolithic structure reveals optimization directions.

[0114] In Examples 1-3, the overall performance trend was Example 2 (DVB-MAH) > Example 3 (TVB-MAH) > Example 1 (St-MAH) > Comparative Example 1 (MAH). Example 2 performed best, with the highest values ​​in tensile strength, elongation at break, yield strength, thermal stability, and crystallinity. This is presumably due to the presence of two vinyl groups in the divinylbenzene molecule, which allows for a higher degree of grafting or the formation of a slight cross-linked network during melt grafting, thereby more effectively enhancing matrix rigidity, inhibiting filler agglomeration, and forming a denser interfacial structure. The performance difference between Example 1 and Example 3 indicates that the functionality (number of vinyl groups) of the monomer is not necessarily better the more there are. Although trivinylbenzene has more active sites, its large steric hindrance may limit grafting efficiency or affect the regular arrangement of molecular chains, resulting in slightly lower performance than the DVB-MAH system, but still significantly better than the single MAH system. The above results indicate that, within the technical framework of synergistic grafting of MAH and rigid aromatic ring monomers proposed in this invention, different monomer structures have a significant impact on the final performance. Among them, DVB is more conducive to forming a stable interface enhancement effect due to its bifunctional structure. However, this difference does not affect the basic technical effect of the present invention in improving the compatibility of polymer / biomass interfaces under different grafting monomer conditions.

[0115] This discovery indicates that, based on the core structure of the "rigid aromatic ring," the functionality of the monomer is a key factor affecting the final performance, and DVB exhibits the optimal balance of performance. This provides a clear direction for the precise design and optimization of subsequent products.

[0116] 3. Comprehensive improvement in overall performance

[0117] (1) Mechanical properties: Examples 1 to 3 all achieved simultaneous improvement in strength and toughness, overcoming the contradiction of "strong but brittle" in traditional filler-reinforced materials; (2) Thermal stability: Examples 1 to 3 all had higher thermal decomposition temperatures, indicating that their thermal stability was significantly enhanced; (3) Crystallization behavior: Examples 1 to 3 all had higher crystallinity, proving that the modified interface was more conducive to the regular arrangement of PBS molecular chains, which directly contributed to the material's better mechanical strength and dimensional stability.

[0118] The above data fully demonstrates that the "bifunctional grafting strategy of MAH with rigid aromatic ring monomers (especially DVB)" provided by this invention is a highly efficient and universally applicable method. It can significantly improve the interfacial compatibility of biomass composites such as distiller's grains through synergistic effects, thereby simultaneously enhancing their mechanical, thermal, and crystallization properties. Example 2 (DVB-MAH), as the optimal implementation scheme, exhibits excellent comprehensive performance and has great application potential. Regardless of its specific microscopic mechanism, the above results clearly show that, under the same formulation and processing conditions, the technical solution of synergistic grafting of MAH with rigid aromatic ring monomers can stably achieve comprehensive performance improvements superior to single modification schemes in different polymer matrices. This technical effect is repeatable and has engineering stability.

[0119] Besides PBS, PBAT is a promising biodegradable material. Relevant embodiments of this invention are as follows:

[0120] Example 4: Preparation of PBAT-g-(St-MAH) / DG composite material

[0121] The procedure is basically the same as steps 1 to 3 of Example 1, except that the PBS matrix is ​​replaced with PBAT, the temperature is increased from 125°C to 160°C, and the DG content is changed from 30% to 10%, labeled as PBAT-g-(St-MAH) / DG (10%).

[0122] Example 5: Preparation of PBAT-g-(DVB-MAH) / DG composite material

[0123] It is basically the same as Example 4, except that styrene (St) is replaced with divinylbenzene (DVB), labeled as PBAT-g-(DVB-MAH) / DG (10%).

[0124] Comparative Example 3: Preparation of PBAT / DG composite material

[0125] The results were basically the same as those in Comparative Example 2, except that the PBS matrix was replaced with PBAT, the temperature was increased from 125°C to 160°C, and the DG content was changed from 30% to 10%, labeled as PBAT / DG (10%).

[0126] Comparative Example 4: Preparation of PBAT-g-MAH / DG composite material

[0127] The results were basically the same as those in Comparative Example 1, except that the PBS matrix was replaced with PBAT, the temperature was increased from 125°C to 160°C, and the DG content was changed from 30% to 10%, labeled as PBAT-g-MAH / DG (10%).

[0128] Comparative Example 5: Preparation of PBAT-g-st / DG composite material

[0129] The process is basically the same as steps 1 to 3 of Example 1, except that the PBS matrix is ​​replaced with PBAT and MAH is not added. The raw material ratio is PBAT:St:DCP = 100:4:0.4, the temperature is increased from 125°C to 160°C, and the DG content is changed from 30% to 10%, labeled as PBAT-g-St / DG (10%).

[0130] Comparative Example 6: Preparation of PBAT-g-DVB / DG composite material

[0131] It is basically the same as Comparative Example 5, except that styrene (St) is replaced with divinylbenzene (DVB), labeled as PBAT-g-DVB / DG (10%).

[0132] The tensile properties of the six types of lees composite materials obtained in Examples 4-5 and Comparative Examples 3-6 were tested, and the results are shown in Table 2.

[0133] Table 2 Comparison of key performance test results between Examples 4-5 and Comparative Examples 3-6

[0134]

[0135] The mechanical property data in Table 2, derived from another biodegradable polymer (PBAT) system, further validate and deepen the scientific validity and universality of the bifunctional grafting strategy of this invention. The specific analysis is as follows:

[0136] 1. The limitations of single functional group modification are highlighted.

[0137] Compared with the unmodified Comparative Example 3, Comparative Example 4 showed significant improvements in both tensile strength and elongation at break. This further demonstrates that the polar functional groups of MAH can effectively improve interfacial adhesion through reaction with the hydroxyl groups of DG, which is consistent with the conclusions in the PBS system.

[0138] However, a key and unexpected finding was that grafting St alone (Comparative Example 5) or DVB alone (Comparative Example 6) not only failed to improve performance, but its tensile strength was even lower than that of the unmodified system, and its elongation at break also showed no advantage. This proves that relying solely on the hydrophobicity and rigidity of rigid aromatic ring monomers, without the ability to form strong chemical bonds with fillers (such as the esterification reaction of MAH), not only fails to improve compatibility, but may also lead to performance degradation due to interfacial deterioration.

[0139] 2. The synergistic effect of bifunctional grafting is reproduced and enhanced in the PBAT system.

[0140] Although the effect of grafting St or DVB alone was not good, the tensile strength and elongation at break of the composite material were significantly better than the best effect of single MAH modification when MAH was combined with St (Example 4) or DVB (Example 5) for bifunctional grafting. (Comparative Example 4)

[0141] This result is significant because it demonstrates that the synergistic effect of this invention is not a coincidence unique to the PBS matrix, but also holds true in the PBAT polymer system, which has a different chemical structure. This strongly supports the universality of the technical solution of this invention. The synergistic mechanism lies in the fact that the MAH provides strong chemical bonding anchoring sites, while the rigid aromatic rings of St or DVB provide steric stabilization in the interfacial region, inhibiting filler aggregation and enhancing stress transfer efficiency. Both are indispensable and together constitute the foundation of a high-performance interface.

[0142] 3. The DVB-MAH combination exhibits optimal universality potential.

[0143] In the PBAT system, the performance of Example 5 was also superior to that of Example 4, consistent with the trend in the PBS system. This further confirms that DVB, due to its potentially higher grafting efficiency or slight crosslinking effect caused by its divinyl structure, can produce superior reinforcing effects in different polymer matrices, making it the preferred monomer with the greatest application potential.

[0144] 4. Significantly improved elongation at break

[0145] Examples 4-5 use PBAT, a polymer with extremely high elongation at break, as the matrix, which significantly improves the tensile properties of the composite material.

[0146] Conclusion: The experimental data of the PBAT system are crucial. Through "reverse verification" (i.e., proving the ineffectiveness of St / DVB alone) and "forward reproducibility" (i.e., proving the effectiveness of St-MAH / DVB-MAH), it eliminates the obviousness that those skilled in the art would readily think of "using hydrophobic monomers to improve compatibility," highlighting the non-obviousness and wide applicability of the technical solution of "combining MAH with specific rigid aromatic ring monomers." This invention is not merely a specific formulation, but a highly efficient interface engineering design strategy that can be widely applied to various biodegradable polymer / distillery waste and other biomass composite systems. Regardless of its specific microscopic mechanism of action, the above results clearly demonstrate that, under the same formulation and processing conditions, the technical solution of synergistic grafting of MAH with rigid aromatic ring monomers can stably achieve comprehensive performance improvements superior to single modification schemes in different polymer matrices. This technical effect is reproducible and engineering stable.

[0147] Example 6: Preparation of PLA-g-(St-MAH) / DG composite material

[0148] The steps 1-3 of Example 1 are basically the same, except that the PBS matrix is ​​replaced with PLA, the temperature is increased from 125°C to 180°C, and the bifunctional grafted modified polymer is 6% of the mass of PLA, labeled as PLA-g-(St-MAH) / DG (30%).

[0149] Example 7: Preparation of PLA-g-(DVB-MAH) / DG composite material

[0150] It is basically the same as Example 6, except that styrene (St) is replaced with divinylbenzene (DVB), labeled PLA-g-(DVB-MAH) / DG (30%).

[0151] Example 8: Preparation of PLA-g-(St-MAH-small amount of DVB) / DG (30%) composite material

[0152] The formulation is basically the same as that of Example 6, except that a small amount of divinylbenzene (DVB) is added to the formulation, that is, the raw material ratio is PLA:St:MAH:DVB:DCP = 100:4:4:1:0.4, labeled as PLA-g-(St-MAH-small amount of DVB) / DG (30%).

[0153] Example 9: Preparation of PLA-g-(St-MAH-equal DVB) / DG (30%) composite material

[0154] The formulation is basically the same as that of Example 6, except that an equal amount of divinylbenzene (DVB) is added to the formulation, that is, the raw material ratio is PLA:St:MAH:DVB:DCP = 100:4:4:4:0.4, labeled as PLA-g-(St-MAH-equal amount of DVB) / DG (30%).

[0155] Comparative Example 7: Preparation of PLA / DG composite material

[0156] The results were basically the same as those in Comparative Example 2, except that the PBS matrix was replaced with PLA and the temperature was increased from 125°C to 180°C. The results were labeled as PLA / DG (30%).

[0157] Comparative Example 8: Preparation of PLA-g-MAH / DG composite material

[0158] It is basically the same as Comparative Example 1, except that the PBS matrix is ​​replaced with PLA and the temperature is increased from 125°C to 180°C, and it is labeled as PLA-g-MAH / DG (30%).

[0159] Comparative Example 9: Preparation of PLA-g-St / DG composite material

[0160] The process is basically the same as steps 1 to 3 of Example 1, except that the PBS matrix is ​​replaced with PLA and MAH is not added. That is, the raw material ratio is PLA:St:DCP = 100:4:0.4, and the temperature is increased from 125°C to 180°C. It is labeled as PLA-g-St / DG (30%).

[0161] Comparative Example 10: Preparation of PBAT-g-DVB / DG composite material

[0162] It is basically the same as Comparative Example 9, except that styrene (St) is replaced with divinylbenzene (DVB), labeled as PLA-g-DVB / DG (30%).

[0163] The tensile properties of the seven types of lees composite materials obtained in Examples 6-9 and Comparative Examples 7-10 are shown in Table 3.

[0164] Table 3 Comparison of key performance test results between Examples 6-9 and Comparative Examples 7-10

[0165]

[0166] Table 3 contains data from composite materials based on polylactic acid (PLA). Although PLA is also a biodegradable material, its properties differ significantly from PBS and PBAT: it has higher tensile strength and modulus, but also greater brittleness, resulting in extremely poor toughness. Therefore, impact strength becomes a key indicator for evaluating its performance. Analysis of Table 3 reveals similarities between the PLA system and the PBAT system in Table 2, but also important differences, providing a new perspective for understanding the role of bifunctional grafting.

[0167] First, the universality of bifunctional grafting was once again verified in the PLA system, but the focus of DVB's role changed. Compared with the unmodified Comparative Example 7, both Example 6 (St-MAH) and Example 7 (DVB-MAH) showed significant improvements in tensile, elongation, and impact properties. However, Comparative Examples 8 to 10, modified with only a single functional group (MAH, St, or DVB), showed very limited performance improvements. This strongly demonstrates once again that the core concept of "synergistic effect between maleic anhydride and rigid aromatic ring monomers" is universally effective in improving the interface between polymer matrices and biomass fillers with different properties. Notably, in the brittle PLA matrix, the DVB-MAH combination (Example 7) exhibited exceptionally high impact strength (15.4 KJ / m²), far superior to the St-MAH combination (Example 6, 9.3 KJ / m²). 2 This indicates that DVB, through its bifunctional properties, may more effectively induce plastic deformation or form microcrack termination points in the brittle PLA matrix, thereby significantly improving the material's impact resistance, which is a unique advantage of it in the PLA system.

[0168] Secondly, the introduction of a small amount of DVB can bring synergistic performance enhancement, but excessive amounts will lead to performance degradation, highlighting the precision and complexity of formulation control. Based on Example 6 (St-MAH), a small amount of DVB was introduced (Example 8). The experimental results were encouraging: the tensile strength of the composite material was further increased to 55.9 MPa, while its high impact toughness (14.8 KJ / m²) was maintained. This indicates that St and MAH constitute a good basic compatible system, and the addition of a small amount of DVB acts as a "toughening and reinforcing agent," further improving strength without sacrificing toughness, achieving a better strength-toughness balance.

[0169] However, when the amount of DVB added was increased to the same level as MAH and St (Example 9), all mechanical properties showed a significant decrease. This dramatic turn of events clearly demonstrates that the use of multifunctional monomers is not a case of "the more the better." Excessive DVB is likely to lead to over-crosslinking during grafting, severely restricting the mobility of polymer chain segments, making the material brittle, and hindering effective stress transfer. This reveals that in complex grafting systems involving multifunctional monomers, the ratio of each monomer is an extremely sensitive and critical factor determining the final performance. The performance of the system is not a simple sum of the effects of each component, but rather there exists an "optimal window" that needs to be carefully sought.

[0170] In summary, the experiments on the PLA system not only reaffirmed the broad applicability of the bifunctional group strategy of this invention, but more importantly, they revealed that the emphasis of the influence of different rigid monomers (such as St and DVB) on material properties may vary depending on the nature of the matrix. Simultaneously, the experiments also clarified that precise dosage control is necessary for highly reactive monomers like DVB. By finely adjusting the ratio of MAH, St, and DVB, it is entirely possible to customize high-performance biomass composite materials with excellent strength, modulus, and outstanding impact toughness for high-strength and brittle materials like PLA. This provides important practical evidence and a clear direction for optimizing this technology. Regardless of the specific microscopic mechanism, the above results clearly demonstrate that, under the same formulation and processing conditions, the technical solution of synergistic grafting of MAH and rigid aromatic ring monomers can stably achieve comprehensive performance improvements superior to single modification schemes in different polymer matrices. This technical effect exhibits repeatability and engineering stability.

[0171] Besides biodegradable polymers such as PBS, PBAT, and PLA, PP is a promising traditional plastic, and corn stalks are another promising bio-based filler. Relevant implementation examples of this invention are as follows (it should be noted that comparative examples 11-15 are not intended to compare with existing disclosed solutions, but rather are used by this invention to verify the applicability and operational rules of the bifunctional grafting strategy under different polymer matrix conditions, thereby further illustrating the universality and technical effects of the present invention):

[0172] Comparative Example 11: Preparation of PBAT-g-(St-MAH) / CS (30%) composite material

[0173] The process is basically the same as steps 1-3 in Example 1, except that the PBS matrix is ​​replaced with PP, the filler is changed to 30% stalk cypress (CS), the temperature is increased from 125°C to 180°C, and the bifunctional grafted modified polymer is 4.5% of the mass of PP, labeled as PP-g-(St-MAH) / CS (30%).

[0174] Comparative Example 12: Preparation of PP-g-(DVB-MAH) / CS (30%) composite material

[0175] It is basically the same as Comparative Example 11, except that PP-g-(St-MAH) is changed to PP-g-(DVB-MAH) and labeled as PP-g-(DVB-MAH) / CS (30%).

[0176] Comparative Example 13: Preparation of PP-g-(TVB-MAH) / CS (30%) composite material

[0177] It is basically the same as Comparative Example 11, except that PP-g-(St-MAH) is changed to PP-g-(TVB-MAH) and labeled as PP-g-(TVB-MAH) / CS (30%).

[0178] Comparative Example 14: Preparation of PP / CS (30%) Composite Material

[0179] It is basically the same as failure example 11, except that PP-g-(St-MAH) is changed to PP and marked as PP / CS (30%).

[0180] Comparative Example 15: Preparation of PP-g-MAH / CS (30%) composite material

[0181] It is basically the same as Comparative Example 11, except that PP-g-(St-MAH) is changed to PP-g-MAH / CS and labeled as PP-g-MAH / CS (30%).

[0182] The tensile properties of the seven types of lees composite materials obtained in Comparative Examples 11-15 are shown in Table 4.

[0183] Table 4 Comparison of key performance test results for Comparative Examples 11-15

[0184]

[0185] The following results analysis aims to reveal the differences in the effects of the bifunctional grafting strategy of this invention on different matrices by comparing the performance of different modification methods in the PP / CS system, and is not intended to define the level of existing technology. The results show that in the polypropylene (PP) and corn straw (CS) composite system, the bifunctional grafting strategy of this invention also exhibits significant modification effects, but its mechanism of action differs profoundly from that of the biodegradable polyester system. This further confirms the universality and uniqueness of the technical solution of this invention. Specifically:

[0186] 1. In terms of stiffness / strength enhancement, bifunctional grafting, especially DVB, exhibits clear and superior advantages: the tensile strength of all grafted modified materials (Comparative Examples 11-13 and 15) is significantly higher than the unmodified baseline (Comparative Example 14). Among them, PP-g-(DVB-MAH) / CS (Comparative Example 12) achieves the highest tensile strength (21.8 MPa), which is significantly better than the single MAH modified Comparative Example 15 (17.1 MPa). This demonstrates the universality of DVB as the optimal stiffness-enhancing monomer across different polymer matrices (PP and PBS / PBAT), representing an important technological discovery.

[0187] 2. Regarding toughness performance, the PP system reveals the inherent trade-offs of the bifunctional strategy: Notably, Comparative Example 15, modified with a single MAH, achieved the highest elongation at break (7.3%), while the toughness of the bifunctional modified organisms decreased. This phenomenon contrasts sharply with the "synergistic improvement in strength and toughness" achieved in the PBS / PBAT system of this invention.

[0188] The aforementioned differences indicate that the final effect of applying the St-MAH bifunctional strategy to different matrices is highly dependent on the inherent properties of the matrix itself. For flexible PP, introducing a rigid aromatic ring increases strength but sacrifices some toughness, a "trade-off" effect consistent with conventional understanding in the field. However, for biodegradable polyesters (such as PBS / PBAT) that inherently possess a "soft" defect, the bifunctional strategy of this invention differs significantly from single-modification systems, achieving a synergistic effect of "both strong and tough."

[0189] Figure 1 This is a flowchart of the composite material preparation process of the present invention, which shows the complete process from raw material pretreatment, melt grafting to composite material molding.

[0190] Figure 2 Comparison of Fourier transform infrared (FTIR) spectra of PBS, PBS-g-MAH, and PBS-g-(St-MAH); where a is the full spectrum, and b and c are magnified views of the characteristic regions, used to confirm that the MAH and St functional groups were successfully grafted onto the PBS molecular chain.

[0191] Figure 3This is a schematic diagram of the interaction mechanism between PBS-g-(St-MAH) and distiller's grains (DG); where a represents the chemical formulas after four reactions, and b represents the possible stereostructures after the reactions, showing four interfacial binding modes including esterification, hydrogen bonding, and π-π stacking. While esterification, hydrogen bonding, and π-π stacking are known bonding mechanisms when viewed individually, this invention introduces a synergistic effect between the nonpolar and rigid bulk structure of St and the polar monomer MAH by grafting St and MAH onto the PBS chain. Unexpectedly (it is generally believed that nonpolar St would disrupt the polar compatibility provided by MAH, or that its rigid structure would hinder processing, but the experimental results of this invention show the opposite; St brings unexpected benefits), this systematically and simultaneously introduces these multiple strong interactions at the PBS / DG interface. When esterification, hydrogen bonding, and π-π stacking occur simultaneously and densely in the interfacial region, a three-dimensional bonding network-like interfacial structure is formed. This structural effect is directly reflected in the macroscopic properties of the composite material: under high-filling conditions with a content of 30-50 wt% distillers' grains filler, the tensile strength and elongation at break of the composite material are still significantly higher than those of the unmodified system and the single MAH modified system, avoiding the brittle failure problem common under high-filling conditions. This results in a significant improvement in mechanical properties (tensile strength and toughness). Simultaneously, it overcomes the contradiction of "increased strength leading to decreased toughness," utilizing MAH to ensure strength while maintaining toughness with St, achieving "both strong and tough." Furthermore, the multi-layered, multi-dimensional interface combination forms a denser and more complete interface layer at the microscopic level. This layer not only more effectively transfers stress but also hinders the penetration and diffusion of water molecules, oxygen, and heat, explaining the simultaneous improvement in the composite material's thermal stability (increased T5%) and moisture resistance (reduced water absorption). This unexpected simultaneous optimization of multiple properties is impossible to achieve with a single modification method. These multiple interface effects are not isolated but indirectly verified through experimental data: compared to the unmodified composite material, the composite material of this invention exhibits a more continuous and dense cross-sectional morphology under a scanning electron microscope (Figures 6-7). Simultaneously, its macroscopic performance indicators, such as tensile strength, elongation at break, thermal decomposition initiation temperature, and water absorption, all show simultaneous improvement, indicating that this multi-dimensional interface effect makes a substantial contribution to the overall material performance.

[0192] Figure 4 A comparative graph showing the mechanical properties of PBS / DG, PBS-g-MAH / DG, and PBS-g-(St-MAH) / DG composites is presented; where a represents tensile strength, b represents elongation at break, c represents yield strength, d represents elastic modulus, and e represents stress-strain curves. Figure 4It is evident that the composite material of this invention possesses two main advantages: structural stability: even with high distiller's grains content, it maintains both high rigidity (elastic modulus) and excellent structural integrity, avoiding drastic performance degradation; and excellent toughness: exhibiting significantly enhanced toughness, it absorbs more energy before failure, achieving a synergistic improvement in strength and toughness. This unique combination of mechanical properties fully demonstrates that the bifunctional grafting strategy produces a non-simple linear superposition, making the composite material particularly suitable for applications such as biodegradable packaging and agricultural mulch films that require withstanding certain impacts or complex stress environments.

[0193] Figure 5 X-ray diffraction (XRD) patterns of PBS / DG and PBS-g-(St-MAH) / DG composites are shown; where a represents PBS / DG and b represents PBS-g-(St-MAH) / DG, used to illustrate the effects of DG addition and bifunctional grafting on the crystalline structure and crystallinity of PBS.

[0194] Figure 6 Scanning electron microscope (SEM) images of tensile fracture surfaces of PBS, PBS / DG, and PBS-g-(St-MAH) / DG composites are shown. Among them, a is PBS, b is PBS / DG (10%), c is PBS / DG (20%), d is PBS / DG (30%), e is PBS / DG (40%), f is PBS / DG (50%), a' is PBS-g-(St-MAH), b' is PBS-g-(St-MAH) / DG (10%), c' is PBS-g-(St-MAH) / DG (20%), d' is PBS-g-(St-MAH) / DG (30%), e' is PBS-g-(St-MAH) / DG (40%), and f' is PBS-g-(St-MAH) / DG (50%). These images visually demonstrate the dispersion state, agglomeration phenomenon, and interfacial bonding between the matrix and the filler in the different composite materials.

[0195] Figure 6 The microstructure revealed the dispersion state of the filler and its interfacial compatibility with the matrix. Pure PBS exhibited a uniform, smooth, and dense cross-section with a fish-scale-like arrangement, indicating tightly packed molecular chains and excellent mechanical properties. PBS-g-(St-MAH) showed a partially striped pattern and a smoother overall cross-section. However, for the PBS / DG composite, the cross-section became significantly rougher, with irregularly shaped DG particles clearly visible within the fracture surface. As the DG content increased, particle agglomeration became increasingly apparent, especially when the DG content exceeded 30%. This agglomeration disrupted the continuity of the PBS matrix, significantly reduced the interfacial compatibility between the matrix and the filler, and led to a substantial decrease in mechanical properties (including tensile strength and elongation at break).

[0196] In contrast, the PBS-g-(St-MAH) / DG composite exhibits a relatively smooth fracture surface. At low DG contents (≤10%), the DG particles are uniformly dispersed throughout the matrix without significant gaps, indicating strong interfacial adhesion and effective filler dispersion. Notably, at a DG content of 10%, the fracture surface displays a dense morphology with only a limited network structure, which contributes to a more uniform stress distribution and explains the significant improvement in elongation at break.

[0197] When the DG content exceeds 30%, although some agglomeration occurs, the PBS-g-(St-MAH) / DG composite still exhibits more uniform filler dispersion and tighter interfacial bonding compared to the unmodified PBS / DG composite. Even at a DG addition of 50%, the PBS-g-(St-MAH) matrix can effectively encapsulate DG particles, maintaining a dense cross-section without visible pores, indicating that the dual grafting of styrene and maleic anhydride imparts excellent compatibility.

[0198] Figure 7 High-magnification SEM images of cross sections of PBS / DG (50%) and PBS-g-(St-MAH) / DG (50%); where a is PBS / DG (50%) and b is PBS-g-(St-MAH) / DG (50%). Figure 7 Further evaluation of interfacial interactions revealed that the PBS / DG sample exhibited significant gaps and exposed DG particles, reflecting poor filler-matrix adhesion. In contrast, the PBS-g-(St-MAH) / DG sample presented a compact and continuous interface with DG particles tightly embedded in the matrix, demonstrating improved compatibility.

[0199] This difference is particularly pronounced at high filler contents. The PBS / DG (50%) composite exhibited numerous interfacial defects and severe filler agglomeration, resulting in a significant reduction in mechanical properties, including the lowest tensile strength and elongation at break among all samples. In contrast, PBS-g-(St-MAH) / DG (50%) maintained excellent structural integrity, with the matrix effectively encapsulating the DG particles and no visible cracks at the interface. This enhanced interfacial adhesion significantly improved the mechanical properties.

[0200] The excellent morphology and mechanical properties of the PBS-g-(St-MAH) / DG composite are attributed to the synergistic grafting effect of St and MAH. The rigid aromatic structure of styrene helps to suppress filler agglomeration, while the polar functional groups of MAH (such as COOH or anhydride groups) interact with the hydroxyl groups in DG through hydrogen bonding or esterification, strengthening the matrix-filler interface. These effects together enable the composite to maintain ideal structure and mechanical properties even under high filler loads, demonstrating its potential in high-performance and sustainable composite applications.

[0201] Figure 8 Differential scanning calorimetry (DSC) curves of PBS / DG and PBS-g-(St-MAH) / DG composites are shown. Among them, a represents the first cooling of PBS / DG, b represents the first cooling of PBS-g-(St-MAH) / DG, c represents the second heating of PBS / DG, and d represents the second heating of PBS-g-(St-MAH) / DG. These curves are used to analyze the crystallization temperature, melting temperature, and crystallinity of the composites. Figure 8 DSC analysis showed that the PBS-g-(St-MAH) / DG composite material of the present invention exhibits significant advantages in crystallization behavior: stronger crystallization ability: 1. Under the same cooling rate, the crystallization temperature (Tc) of the composite material of the present invention (Figures b and d) is higher, indicating that the DG filler has a better nucleation effect in the modified matrix, and the crystallization process is faster and easier to occur; 2. higher crystallinity: Under the same DG content, the melting enthalpy (ΔHm) and crystallinity (Xc) of the composite material of the present invention (Figure d) are always higher than those of the unmodified PBS / DG composite material (Figure c), which proves that the St-MAH bifunctional grafting improves the interfacial compatibility and reduces the obstruction of the filler to the regular arrangement of PBS molecular chains, thereby enabling the PBS matrix to form more complete and richer crystals; 3. key to performance improvement: higher crystallinity directly contributes to the better mechanical strength, heat distortion temperature and dimensional stability of the composite material, indicating that the modification strategy of the present invention not only improves the interface, but also fundamentally optimizes the aggregated state structure of the PBS matrix, which is one of the fundamental reasons for its excellent comprehensive performance. In summary, the composite material of the present invention has more and better "crystals", thus it is stronger and more heat-resistant.

[0202] Figure 9 Thermogravimetric analysis (TG) curves of PBS / DG and PBS-g-(St-MAH) / DG composites are shown; where a is the TG curve of PBS / DG, b is the TG curve of PBS-g-(St-MAH) / DG, c is the DTG curve of PBS / DG, and d is the DTG curve of PBS-g-(St-MAH) / DG, used to compare their thermal stability and degradation behavior.

[0203] Figure 10 The water absorption curves of PBS / DG and PBS-g-(St-MAH) / DG composites show the effect of bifunctional grafting on improving the water resistance of the composites under different DG contents.

[0204] Figure 11The figures show the contact angle test results of PBS / DG and PBS-g-(St-MAH) / DG composites; where a is the contact angle, b is the water droplet image of PBS / DG, and c is the water droplet image of PBS-g-(St-MAH) / DG composite, used to illustrate the changes in the hydrophilicity and hydrophobicity of the composite surface.

[0205] Figure 12 Biodegradation rate curves of PBS / DG and PBS-g-(St-MAH) / DG composites buried in soil for 180 days are shown. Among them, a represents PBS / DG, b represents PBS-g-(St-MAH) / DG, and c represents the comparison results of the degradation of samples after actual burial, showing the changes in degradation behavior with time and filler content. Figure 12 The degradation curves clearly demonstrate one of the core advantages of the composite material of this invention: controllable biodegradability. 1. Controllable degradation rate: The degradation rate of the composite material of this invention (curve b) is consistently slower than that of the unmodified material (curve a). This indicates that the interface bonding is strengthened by St-MAH bifunctional grafting, effectively delaying the erosion by moisture and microorganisms, thus achieving a "slowdown" in the degradation process. 2. Balance between performance and lifespan: This "controllable degradation" characteristic is significant. It means that while maintaining good mechanical properties and moisture resistance, the lifespan of the material of this invention is predictable and designable. Users can "customize" the degradation cycle by adjusting the DG content and grafting ratio according to application needs (such as short-term packaging or long-term agricultural film). 3. Meeting diverse application needs: Unmodified PBS / DG degrades too quickly and has poor mechanical properties, while pure PBS degrades too slowly. This invention successfully achieves an excellent balance between "performance during use" and "post-disposal degradability," broadening its application scope in sustainable packaging and agriculture. It is evident that the material of this invention does not simply degrade quickly or slowly, but rather "is strong when it should be strong and degrades when it should be degraded," achieving predictable and designable degradation regulation characteristics.

[0206] The comparisons between the above embodiments and comparative examples fully demonstrate that the St-MAH bifunctional grafting strategy provided by this invention is far superior to traditional blending methods that rely solely on MAH grafting modification or no modification in solving the interfacial compatibility problem between biomass such as distiller's grains and polymer matrices. This invention not only significantly improves the mechanical strength and toughness of the composite material but also simultaneously achieves a significant improvement in thermal stability and moisture resistance. This synergistic enhancement of multiple performance indicators is unattainable by existing single modification techniques, fully demonstrating the outstanding substantive features and significant progress of this invention.

Claims

1. A method for preparing bifunctional grafted modified polymeric biomass composite materials, characterized in that: Includes the following steps: A. The polymer matrix, maleic anhydride, grafting monomer and free radical initiator are melt-blended and then melt-grafted to obtain a bifunctional grafted modified polymer. B. Melt-blend the bifunctional grafted modified polymer obtained in step A with the biomass filler to obtain the bifunctional grafted modified polymer biomass composite material. Alternatively, B‵, the bifunctional grafted modified polymer obtained in step A is mixed with the polymer matrix to obtain a bifunctional grafted modified mixture, and the bifunctional grafted modified mixture is melt-blended with biomass filler to obtain a bifunctional grafted modified polymer biomass composite material. In steps A and B, the polymer matrix is ​​a biodegradable polyester; In step A, the mass of maleic anhydride is 1.5% to 6% of the mass of the polymer matrix in step A, the mass of the grafted monomer is 1.5% to 12% of the mass of the polymer matrix in step A, and the mass ratio of maleic anhydride to grafted monomer is 1:1 to 3. In step B, the mass ratio of the bifunctional grafted modified polymer to the biomass filler in step B is 90%~40%:10%~60%, totaling 100%. In step B‵, the bifunctional grafted modified polymer accounts for 3~12% of the polymer matrix in step B‵; the mass ratio of the bifunctional grafted modified mixture to the biomass filler in step B‵ is 90%~40%:10%~60%, totaling 100%.

2. The preparation method according to claim 1, characterized in that: In step A, the polymer matrix is ​​selected from one of aliphatic polyester, aliphatic-aromatic copolyester, or polylactic acid and its copolymers; preferably, the polymer matrix is ​​selected from PBS, PES, PHA, PCL, PBAT, PEAT, PLA, or PLGA.

3. The preparation method according to claim 1, characterized in that: In step A, the grafting monomer is selected from at least one of styrene, divinylbenzene, trivinylbenzene, α-methylstyrene, or 4-methylstyrene; preferably, the grafting monomer is styrene, divinylbenzene, trivinylbenzene, or a mixture of styrene and divinylbenzene; more preferably, the grafting monomer is divinylbenzene or a mixture of styrene and divinylbenzene in a mass ratio of 3 to 5:

1.

4. The preparation method according to claim 1, characterized in that: At least one of the following must be met: In step A, the mass of maleic anhydride is 3% to 5% of the mass of the polymer matrix in step A, and the mass of the grafted monomer is 3% to 5% of the mass of the polymer matrix in step A. In step A, the total mass of the maleic anhydride and the grafted monomer is 6% to 10% of the mass of the polymer matrix in step A; In step A, the free radical initiator is dicumyl peroxide, di-tert-butyl peroxide, or 1,1-di(tert-butylperoxide)-3,3,5-trimethylcyclohexane (bis(diphenylpentane)). In step A, the mass of the free radical initiator is 0.2% to 0.6% of the mass of the polymer matrix in step A.

5. The preparation method according to claim 1, characterized in that: At least one of the following must be met: In step A, the reaction temperature for melt blending is 110℃~180℃; In step A, the rotation speed of the melt blending is 60 rpm to 200 rpm; In step A, the reaction time for melt blending is 5 min to 10 min; In step A, the reaction temperature of the melt grafting reaction is 110℃~180℃; In step A, the rotation speed of the melt grafting reaction is 50 rpm to 200 rpm; In step A, the reaction time of the melt grafting reaction is 3 min to 8 min.

6. The preparation method according to claim 1, characterized in that: At least one of the following must be met: In step B, the biomass filler is at least one of distiller's grains, straw, bamboo, wood, or fruit peel; preferably distiller's grains or straw. In step B, the particle size of the biomass filler is 100 mesh to 600 mesh; In step B, the mass ratio of the bifunctional grafted modified polymer to the biomass filler in step B is 90%~45%:10%~55%, totaling 100%. In step B, the reaction temperature for melt blending is 110℃~200℃; In step B, the reaction time for melt blending is 5 min to 10 min.

7. The preparation method according to claim 1, characterized in that: At least one of the following must be met: In step B‵, the biomass filler is at least one of distiller's grains, straw, bamboo, wood, or fruit peel; preferably distiller's grains or straw. In step B‵, the particle size of the biomass filler is 100 mesh to 600 mesh; In step B‵, the bifunctional grafted modified polymer accounts for 6-12% of the polymer matrix mass in step B‵; In step B‵, the mass ratio of the bifunctional grafted modified mixture to the biomass filler in step B‵ is 90%~45%:10%~55%, totaling 100%; In step B‵, the reaction temperature for melt blending is 110℃~200℃; In step B‵, the reaction time for melt blending is 5 min to 10 min.

8. The bifunctional grafted modified polymer biomass composite material prepared by the preparation method according to any one of claims 1 to 7.

9. The bifunctional grafted modified polymer prepared by step A of the preparation method according to any one of claims 1 to 5.

10. The application of the bifunctional grafted modified polymer biomass composite material of claim 8 or the bifunctional grafted modified polymer of claim 9 in the preparation of biodegradable packaging materials or agricultural mulch films.

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