A composite material based on thermoplastic modification of bamboo powder and a preparation method and application thereof

Abstract

The application relates to the field of bamboo-based composite materials, and discloses a composite material based on thermoplastic modification of bamboo powder and a preparation method and application thereof. The composite material comprises poly(3-hydroxybutyrate-co-3-hydroxyvalerate), a lubricant, C10-C18 fatty acid thermoplastic modified bamboo powder, and a coupling agent. The bamboo powder is thermoplastically modified through esterification of the fatty acid, and the coupling agent can be used to strengthen the two-phase interface bonding. After modification, the elongation at break of the material is increased by 1033% compared with the unmodified system, the tensile strength is increased by 61.4% at most after compounding the coupling agent, the thermal decomposition peak temperature is significantly improved, the strength and toughness are simultaneously improved, and the thermal stability is improved, so that the material is suitable for various biodegradable products such as packaging, agricultural use, and disposable products.

Description

Technical Field

[0001] This invention relates to the field of bamboo-based composite materials, and more specifically, to a composite material based on the thermoplastic modification of bamboo powder, its preparation method, and its application. Background Technology

[0002] Polyhydroxyalkanoates (PHAs) are fully bio-based polyesters synthesized by microbial fermentation, and PHBV is a commercially mature PHA. However, the inherent brittleness of PHBV severely restricts its practical application. When preparing PHBV-based wood-plastic composites, the brittleness of the composites is further increased due to poor interfacial compatibility, weak interfacial adhesion, and low strength.

[0003] Currently, research on toughening PHBV-based wood-plastic composites is relatively limited, with most studies focusing on the modification of PHBV itself. Toughening approaches mainly include: regulating its crystallization behavior to improve toughness; and combining it with other toughening polymers through physical or reactive blending. However, the external force-induced crystallization toughening method is only applicable to pure PHBV; the poor interphase bonding in the wood-plastic system makes precise crystallization control difficult, and the wood fibers introduce numerous heterogeneous nucleation sites, further disrupting crystallization behavior. Furthermore, toughening blends such as PBS and PBSA are petroleum-based raw materials, which are not only costly but also introduce multiple phase interfaces, significantly increasing the complexity of the composite system.

[0004] For composite materials, existing technologies commonly use bamboo powder as a filler. Natural bamboo powder is rich in hydroxyl groups, and its polarity and hydrophobicity (PHBV) differ significantly, resulting in weak interfacial adhesion between the two phases. Under stress, it is prone to fiber pull-out and interfacial cracking. Commonly used coupling agents in the industry, such as silanes and maleic anhydride, can only slightly improve the interfacial bonding strength and cannot alleviate the embrittlement problem caused by the filler. The material always faces the inherent contradiction of difficulty in synergistically optimizing strength and toughness (patent CN118347255A). Bamboo powder that has only undergone simple delignification treatment still has its cellulose hydroxyl groups masked by lignin, resulting in low reactivity of subsequent surface modification reactions, and the filler itself does not have plastic deformation capabilities.

[0005] In summary, current PHBV-based bamboo powder composite systems suffer from multiple limitations, including intrinsic matrix brittleness, weak interfacial bonding due to differences in the polarity of bamboo powder fillers, limited toughening improvement from conventional modification methods, increased cost and system complexity from petroleum-based toughening agents, and difficulty in balancing reactivity and thermoplastic processing performance in bamboo powder pretreatment and surface modification. Existing modification methods cannot simultaneously achieve uniform filler dispersion, interfacial strengthening, and synergistic improvement in material strength and toughness, making it difficult to meet the molding, processing, and performance requirements of fully biodegradable products. Summary of the Invention

[0006] To overcome the shortcomings of existing PHBV-based bamboo powder composite materials, such as high matrix brittleness, poor interfacial compatibility between bamboo powder and resin, inability to simultaneously and synergistically improve material strength and toughness, and low reactivity of bamboo powder filler modification without thermoplastic deformation capability, this invention provides a composite material based on bamboo powder thermoplastic modification. Another objective of this application is to provide a method for preparing a composite material based on bamboo powder thermoplastic modification; Another objective of this application is to provide an application of a bamboo powder thermoplasticized modified composite material.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A composite material based on thermoplastic modification of bamboo powder includes poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a lubricant, and thermoplastic modified bamboo powder; wherein the thermoplastic modified bamboo powder is modified by esterification of fatty acids with carbon chain lengths of C10 to C18.

[0008] Preferably, the lubricant includes zinc stearate and dodecyl stearic acid.

[0009] Preferably, the lignin content of the bamboo powder is less than 3%.

[0010] Preferably, the bamboo is crushed, and the lignin is removed by circulating an aqueous solution of sodium chlorite and glacial acetic acid. After washing, neutralizing, filtration and drying, bamboo powder with a lignin content of less than 3% is obtained.

[0011] Preferably, the bamboo is pulverized and mixed with sodium chlorite and glacial acetic acid in water, and subjected to 1 to 4 cycles at 75 to 85°C. In each cycle, the mass ratio of sodium chlorite to natural bamboo fiber is 0.25 to 0.35:1, the volume mass ratio of glacial acetic acid to natural bamboo fiber is 0.2 to 0.3 mL / g, and the reaction time is 0.5 to 1 h. After each cycle, an equal amount of sodium chlorite and glacial acetic acid are added. After the cycle is completed, the mixture is washed until neutral, filtered, and dried to obtain bamboo powder with a lignin content of less than 3%.

[0012] Preferably, the molar content of 3-hydroxyvalerate monomer in PHBV is 0~12%.

[0013] Preferably, the fatty acids with a carbon chain length of C10 to C18 include decanoic acid, lauric acid, myristic acid, palmitic acid, and stearic acid.

[0014] Further, the components are in the following weight parts: 40-50 parts of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), 2-5 parts of lubricant, and 40-60 parts of thermoplasticized modified bamboo powder.

[0015] Furthermore, it also includes coupling agents.

[0016] Preferably, the coupling agent includes triglycidyl isocyanurate (TGIC), glycidyl methacrylate (GMA), and 4,4'-methylene diphenyl diisocyanate (MDI).

[0017] Preferably, the coupling agent is TGIC.

[0018] Further, by weight, the coupling agent is 1 to 8 parts.

[0019] Preferably, the coupling agent comprises 4 to 6 parts by weight.

[0020] A method for preparing the aforementioned bamboo powder thermoplasticized modified composite material includes the following steps: S1. Trifluoroacetic anhydride is used to activate fatty acids, which are then esterified with bamboo powder to obtain thermoplasticized modified bamboo powder. S2. Mix the raw materials for preparing the bamboo powder thermoplasticized modified composite material, melt blend and mold to obtain the bamboo powder thermoplasticized modified composite material.

[0021] Furthermore, the mass ratio of fatty acids to trifluoroacetic anhydride is 1:1~2; the mass ratio of trifluoroacetic anhydride to bamboo powder is 3~6:1.

[0022] Furthermore, the esterification reaction was carried out at 50~80℃ for 1~3 h.

[0023] Furthermore, the blending temperature is 170~190℃, and the blending time is 8~12 min.

[0024] Furthermore, the hot pressing temperature is 170~190℃, and the hot pressing pressure is 8~12 MPa.

[0025] An application of the aforementioned bamboo powder thermoplasticized modified composite material is characterized in that it is used to prepare biodegradable products.

[0026] Preferably, it is applied in fields including packaging, medical, agriculture, textiles, and disposable products.

[0027] This invention employs a synergistic modification system of bamboo powder modified with long-chain fatty acids and TGIC coupling agent: esterification of long-chain fatty acids imparts thermoplasticity to the bamboo powder, allowing it to be uniformly dispersed in a PHBV matrix. Under external force, the material induces extensive plastic deformation in the PHBV matrix, thereby consuming fracture energy and improving toughness. TGIC can covalently react with the terminal hydroxyl groups of both the modified bamboo powder and PHBV molecules, constructing a covalently linked structure of modified bamboo powder-TGIC-PHBV at the two-phase interface, fundamentally optimizing the interfacial bonding state. Simultaneously, fatty acid esterification blocks the active hydroxyl groups of the bamboo powder, enhancing its thermal stability.

[0028] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: This invention utilizes only a thermoplasticized bamboo powder filler system, resulting in outstanding toughening effects. The elongation at break of C10-BP and C10-DP reached 12.9% and 13.6%, respectively, representing improvements of 975.0% and 1033% compared to the unmodified bamboo powder composite material. After introducing the TGIC coupling agent, the tensile strength of C10-TiBP reached 10.2 MPa, an increase of 61.4% compared to the uncoupled sample, and the elongation at break increased to 13.6%; the tensile strength of C10-TiDP reached 8.7 MPa, an increase of 27.6%, and the elongation at break increased significantly by 27.5%, an increase of 100.2%.

[0029] The thermal stability of bamboo powder after thermoplasticization modification is significantly improved, and the peak temperature of the maximum thermal degradation in the first stage of the composite material is reduced to T. max1 The temperature was increased from 270.2℃ for unmodified BP to 288.2℃ for C10-BP. max2 The temperature was increased from 348.4℃ to 369.7℃; after adding TGIC coupling agent, the T of C10-TiBP was increased. max2 Further increasing to 374.2℃, the T of C10-DP max1 The temperature of C10-TiDP increased from 271.3℃ to 285.5℃. max2 It reached 367.2℃. Attached Figure Description

[0030] Figure 1 (a~b) FTIR and (c~d) XRD spectra of BF, DBF and bamboo powder modified with fatty acids of different carbon chain lengths; Figure 2 SEM images of the microstructure of BF, DBF and their modified samples: (a) native bamboo powder BF; (bf) C10~C18 fatty acid modified BF; (g) delignified bamboo powder DBF; (hl) C10~C18 fatty acid modified DBF; Figure 3 The microstructure of the tensile cross section of the modified bamboo powder film is shown in (a) and (b) at different magnifications of C10-BM, and (c) and (d) at different magnifications of C10-DM. Figure 4 The microstructures of the tensile fracture surfaces of the coupling agent-free modified composite materials are shown in (a) BP, (b) DP, (ce) C10-BP, (fh) C12-BP, (ik) C14-BP, (ln) C10-DP, (oq) C12-DP, and (rt) C14-DP. Figure 5 Microstructure of the tensile fracture surface of coupling agent modified composite material; (ac) C10-TiBP at different magnifications, (df) C10-TiDP at different magnifications; Figure 6(a) Elongation at break and (b) Tensile strength of the composite material without coupling agent modification; Figure 7 (a) Elongation at break and (b) Tensile strength of the coupling agent modified composite material; Figure 8 (a) storage modulus; (b) loss modulus; (c) loss factor for the coupling agent-free modified composite material; Figure 9 (a) storage modulus; (b) loss modulus; (c) loss factor of the coupling agent modified composite material; Figure 10 (ab) FTIR spectrum; (cd) XRD spectrum of the composite material without coupling agent modification; Figure 11 (ab) FTIR spectrum; (cd) XRD spectrum of coupling agent modified composite material; Figure 12 DSC curves of composite materials without coupling agent modification; (ac) modified BF system, (df) modified DBF system; (a) (d) first heating curves, (b) (e) cooling curves, (c) (f) second heating curves; Figure 13 (a) Cooling curve and (b) Heating curve of the coupling agent modified composite material; Figure 14 (a) TG curve and (b) DTG curve of the coupling agent-free modified composite material; Figure 15 (a) TG curve and (b) DTG curve of the coupling agent modified composite material. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0032] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0033] Moso bamboo was purchased from Hengyang City, Hunan Province, China. After being pulverized, it was sieved through a 40-60 mesh screen. The resulting bamboo powder was dried in an oven at 103℃ for 24 hours before use. PHBV (model Y1000) was purchased from Ningbo Tianan Biomaterials Co., Ltd., Zhejiang Province. Long-chain fatty acids (decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid) and triglycidyl isocyanate (TGIC) were purchased from Shanghai Maclean Biochemical Co., Ltd. Trifluoroacetic anhydride was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Zinc stearate and dodecyl stearic acid can be used as lubricants; triglycidyl isocyanate (TGIC), glycidyl methacrylate (GMA), and 4,4'-methylene diphenyl diisocyanate (MDI) can be used as coupling agents.

[0034] Example 1 Preparation of modified bamboo powder Delignification treatment: 40 g of bamboo powder (BF) was mixed with 1300 mL of deionized water, and 12 g of sodium chlorite and 10 mL of glacial acetic acid were added sequentially. The mixture was reacted in an oil bath at 80 °C for 1 h. The same amount of reagent was then added again, and this process was repeated four times. After the reaction was complete, the sample was vacuum filtered, washed repeatedly with deionized water until the filtrate was neutral, and dried in an oven at 105 °C for 24 h to obtain delignified bamboo powder (DBF). The lignin content was 2.7%, determined using the NREL standard method.

[0035] Long-chain fatty acid modification: Prepare the reactants according to the proportions in Table 1 and react at 80℃ for 2 hours. After the reaction, wash the product with ethanol and deionized water, and dry it in a 60℃ oven to obtain modified bamboo powder. The modified bamboo powder is numbered according to the type of bamboo powder used and the carbon chain length of the long-chain fatty acid (LCFA). For example, modifying BF with a long-chain fatty acid with a carbon chain length of 12 yields C12-BF.

[0036]

[0037] Table 1. Proportion of each component added in the thermoplasticization modification of bamboo powder

[0038] Example 2 Composite material preparation According to the component ratios in Table 2, the mixture was melt-blended at 180°C for 10 min using a small internal mixer. The mixture was then pulverized using a plastic pulverizer and hot-pressed at 180°C and 10 MPa. Zinc stearate was selected as the lubricant, and TGIC was selected as the coupling agent.

[0039] Composite materials are named according to the type of bamboo powder used. For example, the composite material corresponding to BF is BP, the composite material corresponding to C10-DBF is C10-DP, and the samples with added triglycidyl isocyanate (TGIC) as a coupling agent are C10-TiBP and C10-TiDP.

[0040] Table 2. Distribution ratio of each component in the composite material

[0041] Comparative Example 1 The technical solution of Comparative Example 1 is similar to that of Example 2, except that the hot pressing raw material is only C10-BF or C10-DBF, which are used to prepare materials C10-BM or C10-DM respectively.

[0042] Test methods 1. Characterization Test (1) X-ray diffraction analysis (XRD) Analysis was performed using an Ultima IV diffractometer (Rigaku, Japan) equipped with a Cu Kα radiation source (λ = 0.15406 nm). The test voltage and current were 40 kV and 30 mA, respectively, with a scan range of 10° to 40° and a scan rate of 10° / min.

[0043] (2) Fourier transform infrared spectroscopy (FTIR) FTIR spectra of bamboo powder were acquired using a Nicolet iS20 spectrometer (Thermo Fisher Scientific, USA) via the potassium bromide pelleting method, and FTIR spectra of the composite material were acquired using the ATR method. Each spectrum was plotted at 4 cm⁻¹. -1 The resolution was scanned a total of 32 times.

[0044] (3) Scanning electron microscopy (SEM) observation The microstructure of the tensile test sections of bamboo powder and composite materials was observed using a SU8020 field emission scanning electron microscope (Hitachi, Japan) at an accelerating voltage of 3 kV. All samples were dried and sputter-coated with gold before observation.

[0045] (4) Mechanical property testing The tensile properties of the composite material were tested using a UTM5504 electronic universal testing machine (Sansi, China) in accordance with ASTM D638 standard. The specimen was 50 mm × 10 mm × 0.3 mm, and the testing speed was 1 mm / min.

[0046] (5) Dynamic thermomechanical analysis (DMA) The dynamic thermomechanical properties of the materials were tested in tensile mode using a Q800 dynamic thermomechanical analyzer (TA, USA). The test employed strain-controlled mode with an amplitude of 10 μm, a frequency of 1 Hz, a test temperature range of 30℃ to 150℃, and a heating rate of 3℃ / min.

[0047] (6) Thermogravimetric analysis (TG) The thermal stability of the material was evaluated using an EXSTAR TG / DTA 6300 thermogravimetric analyzer (Seiko, Japan). 5–15 mg of sample was placed in an aluminum crucible and heated to 900 °C from room temperature at a rate of 10 °C / min under a nitrogen atmosphere.

[0048] (7) Differential scanning calorimetry (DSC) The melting and crystallization behavior of the composite material was analyzed using a 3500 Sirius differential scanning calorimeter (NETZSCH, Germany). Approximately 8–10 mg of sample was weighed and placed in an aluminum crucible, and the test was conducted under a nitrogen atmosphere. The specific heating program was as follows: the temperature was increased to 200 °C at a rate of 10 °C / min and held for 2 minutes; then the temperature was decreased to -30 °C at a rate of 10 °C / min; finally, the temperature was increased to 200 °C at a rate of 10 °C / min.

[0049] Analysis and Explanation 1. Characteristics of modified bamboo powder Figure 2 As shown in a~b, the modified bamboo powder at 1740 cm⁻¹ -1 Characteristic peaks of ester carbonyl groups appear, 2800~3000 cm⁻¹ -1 The methylene double peak is visible at 720 cm⁻¹. -1 Characteristic absorption of long alkyl chains is observed, and the hydroxyl group has a 3400 cm⁻¹ absorption. -1 The peak weakens significantly, indicating that long-chain fatty acids are grafted onto the bamboo powder surface via esterification; DBF, due to delignification, exposes a large number of hydroxyl groups, resulting in a peak at 3400 cm⁻¹. -1 The peak intensity did not change significantly, but esterification characteristic peaks were still detected. Figure 2 In samples c-d, BF and DBF exhibit the characteristic Type I diffraction peaks of cellulose. After fatty acid modification, the diffraction peak at 16° disappears, while the 22° peak broadens and shifts to a lower angle, indicating that the alkyl chain disrupts the regular crystalline structure of cellulose. When the alkyl carbon chain is longer than 11, the side chains can spontaneously form an ordered structure. The longer the carbon chain, the more significant the effect of canceling cellulose lattice distortion, and the diffraction peak intensity increases synchronously. These results collectively confirm that long-chain fatty acids were successfully grafted onto BF via esterification, yielding esterified modified thermoplastic bamboo powder.

[0050] 2. Microstructure of bamboo powder and composite materials Figure 2It can be seen that both BF and DBF exhibit significant fibrous morphology, while after modification, all samples exhibit morphological characteristics similar to plastic powder, and the original fibrous morphology completely disappears.

[0051] Figure 3 The cross-section of the purely modified bamboo film exhibits a continuous coral reef-like structure with only a small number of spherical aggregates; this was used as a control for analyzing the cross-section of the composite material without coupling agent. Figure 4 It can be seen that the composite material without coupling agent has three distinct microstructures: a continuous network phase representing the PHBV matrix, and dispersed spherical particles and their surrounding sea urchin-like structures representing the modified bamboo powder filler. The clear and distinct boundaries between the two phases indicate weak interfacial adhesion between the matrix and filler without the addition of TGIC. When the material is subjected to tension and cracks extend to the modified bamboo powder, interface debonding easily occurs, stress concentrates around the filler, and ultimately forms a sea urchin-like morphology on the fracture surface. The interface debonding phenomenon is more pronounced in C10-BP, with a greater number of sea urchin-like structures. This structure gradually decreases with increasing carbon chain length of the long-chain fatty acids. Under the same carbon chain length conditions, the composite material with modified DBF has more and denser sea urchin-like structures in its cross-section than the composite material with modified BF.

[0052] like Figure 5 As shown, compared with C10-BP, the two-phase distinction inside C10-TiBP is significantly reduced, the cross-section is generally flat, and only minor delamination and cracks exist in some areas. TGIC effectively improves the interfacial compatibility between BF filler and PHBV. On the other hand, the cross-section of C10-TiDP has no sea urchin-like defects, the spherical filler is tightly integrated with the PHBV matrix, the interface is completely blurred, there are no obvious cracks, and the interfacial bonding strength is better than that of C10-TiDP. This indicates that TGIC has a better effect on the synergistic improvement of the interface between DBF modified bamboo powder and PHBV.

[0053] 3. Mechanical properties of composite materials (1) Mechanical properties like Figure 6 As shown, the elongation at break of all modified bamboo powder systems in the composite material without coupling agent was improved to varying degrees. Specifically, the elongation at break of C10-BP and C10-DP increased from 1.2% for BP and 3.4% for DP to 12.9% and 13.6%, respectively. However, the tensile strength of all groups decreased. This is because the modified bamboo powder possesses plasticity and is prone to debonding from the PHBV matrix interface during stretching. Although this can induce large-scale plastic deformation of the matrix and improve toughness, the weak interface will block stress transmission, resulting in strength reduction.

[0054] Under the premise of using the same carbon chain fatty acid modification, the toughening effect of the DBF-based composite material is superior to that of the BF system. In the TFAA catalytic system, cellulose, hemicellulose, and lignin in bamboo powder can all undergo esterification with long-chain fatty acids, but the lignin esterification product does not possess thermoplasticity. DBF pretreatment removes most of the lignin, reducing ineffective esterification reactions and allowing more fatty acids to graft onto cellulose and hemicellulose. The resulting modified bamboo powder has better inherent toughness and a more significant toughening effect on PHBV.

[0055] like Figure 7 As shown, the tensile strength of all samples with added TGIC coupling agent was improved; C10-TiBP increased from 6.3 MPa to 10.2 MPa, and C10-TiDP increased from 6.8 MPa to 8.7 MPa. TGIC improved the interfacial compatibility between plasticized bamboo powder and the PHBV matrix, resulting in a more stable interfacial bond and efficient stress transfer between the filler and the matrix, thus enhancing the overall load-bearing capacity of the material. The lignin esterification reaction products are non-thermoplastic and retain a rigid structure. Without TGIC, the interfacial bond between the two phases was weak, stress transfer was hindered, and the difference in tensile strength between the two systems was not significant. After introducing TGIC to optimize the interfacial bond, the stress transfer channels were opened, and a large number of rigid components in the BF system fully exerted their load-bearing role, ultimately demonstrating a greater increase in strength.

[0056] However, the elongation at break of C10-TiBP only increased from 12.9% to 13.6%, while the elongation at break of C10-TiDP increased from 13.6% to 27.5%. DBF itself has better toughness, and the TGIC-optimized interface can fully exert the toughening effect of plasticized bamboo powder. The microstructure of the cross section also supports this: the cross section structure of C10-TiBP is only beneficial to the strength improvement, and has a weak effect on the toughness improvement.

[0057] Dynamic thermomechanical properties of plasticized bamboo powder composites without coupling agents, such as Figure 8 As shown, the storage modulus of the composite material with plasticized bamboo powder is significantly lower than that of the unmodified BP and DP. This is because plasticization reduces the rigidity of the bamboo powder itself, leading to a decrease in the storage modulus of the composite material, which manifests as an increase in the toughness of the composite material in static mechanical tests.

[0058] (2) Interface interaction like Figure 9As shown, compared to C10-DP, the storage modulus of C10-TiDP is significantly reduced, indicating that the rigidity of the composite material is weakened, allowing for greater plastic deformation under stress and improved toughness. Meanwhile, the loss modulus of the coupling agent-modified systems is increased to varying degrees. This is because the coupling agent constructs a PHBV-TGIC-plasticized bamboo powder structure at the interface between plasticized bamboo powder and PHBV, improving interfacial compatibility, enhancing molecular chain entanglement, and thus increasing the loss modulus, consistent with the test results showing an increase in the tensile strength of the composite material.

[0059] from Figure 10 As can be seen from a and b, BP and DP are only at 1740 cm. -1 An ester carbonyl absorption peak was observed in the plasticized bamboo powder composite sample, and a peak was also observed at 1740 cm⁻¹. -1 (PHBV), 1700 cm -1 Two ester carbonyl peaks were observed in the (plasticized bamboo powder). No new characteristic peaks were found in the modified composite material, indicating that PHBV and plasticized bamboo powder did not chemically react during melt blending. The corresponding peak at 1700 cm⁻¹ for the plasticized bamboo powder is... -1 Carbonyl peak, relative to pure plasticized bamboo powder 1750 cm⁻¹ -1 The shift to lower wavenumbers indicates the presence of intermolecular interactions such as hydrogen bonds between the two molecules. Figure 10 In samples c and d, all samples exhibited characteristic diffraction peaks for each crystal plane of PHBV. The addition of plasticizing BF and DBF did not alter the main crystal structure of PHBV. The increased intensity of the diffraction peak corresponding to β-type crystals at 19° indicates that modified bamboo powder can induce the formation of more β-type crystals in PHBV, which is beneficial for improving material toughness. Combining SEM, IR, and XRD results, without TGIC, bamboo powder and PHBV have no covalent bonds and weak interfacial bonding; the toughening effect of bamboo powder inducing β-type crystals is limited, and the improvement in material toughness mainly relies on the bridging toughening effect of bamboo powder during crack propagation.

[0060] Figure 11 As can be seen, the modified sample is 1750 cm⁻¹ -1 The PHBV carbonyl peak disappears at 1700 cm⁻¹. -1 The carbonyl peak intensity of bamboo powder decreased to 1720 cm⁻¹. -1 New absorption peaks appear. The epoxy groups in TGIC can react with the terminal hydroxyl groups of bamboo powder and PHBV to form new ester carbonyl groups, causing the original carbonyl peaks to overlap and shift. Figure 11Results showed that the diffraction peak intensities at approximately 13.3°, 16.8°, and 22.4°, belonging to the α-type crystal structure of PHBV, decreased significantly in C10-TiBP, and these peaks even disappeared in C10-TiDP. The β-type crystal diffraction peak at 19° showed no significant change. Infrared and XRD analyses confirmed that TGIC reacted with both phases to construct a PHBV-TGIC-plasticized bamboo powder covalent structure at the interface, optimizing interfacial compatibility and bonding strength. Simultaneously, it suppressed the formation of PHBV α-type crystals, mitigating the toughness degradation caused by α-type crystals.

[0061] 4. Thermal properties of composite materials (1) Crystallization melting behavior according to Figure 12 The results showed that the crystallization temperature of the composite material increased significantly from 58.4℃ for BP, reaching 92.31℃, 98.12℃, and 98.43℃ for C10-BP, C12-BP, and C14-BP, respectively. This indicates that plasticized BF lowers the crystallization energy barrier of PHBV and promotes crystallization. The secondary heating curves showed an exothermic peak for PHBV cold crystallization between 40 and 70℃: although plasticized BF facilitates crystallization, it slows down the crystallization rate. After cooling, a large number of molecular chains remain in an amorphous metastable state, and during heating, chain segment rearrangement forms the cold crystallization peak. The cold crystallization temperature gradually decreased with increasing alkyl chain length, reaching 64.81℃, 47.63℃, and 40.22℃ for C10-BP, C12-BP, and C14-BP, respectively; the DP series samples also showed the same trend. Figure 12 ef).

[0062] As shown in Table 3, the melting temperature T of the plasticized bamboo powder composite material in the coupling agent-free system is... m2 The melting temperature was lower than BP and DP. Insufficient crystallization during the cooling stage resulted in crystals with low crystal integrity and thin lamellar layers, leading to a decrease in melting temperature. Additionally, all plasticized bamboo powder samples exhibited small melting peaks between 100 and 120°C, which originated from the melting of the plasticized bamboo powder itself.

[0063] Table 3 Melting temperature T of unmodified composite materials m1 and T m2

[0064] like Figure 13 The melting and crystallization temperature Tc and melting temperature T of the composite material after adding TGIC mCompared to the system without coupling agent, all peaks shift towards lower temperatures. C10-TiBP still exhibits a cold crystallization peak, but its position shifts towards higher temperatures compared to C10-BP; the cold crystallization peak of C10-TiDP completely disappears. Combined with XRD results, this cold crystallization behavior is directly related to PHBV α-type crystals. TGIC weakens the intensity of the α-type crystal diffraction peaks, and the attenuation of the α-type crystal peaks is more pronounced in C10-TiDP.

[0065] (2) Thermal stability performance like Figure 14 As shown, the thermal degradation of the unmodified composite material is divided into three stages: BP and DP degrade hemicellulose and PHBV in the first stage, degrade cellulose and continue to decompose PHBV in the second stage, and slowly carbonize lignin in the third stage; plasticized bamboo powder system decomposes plasticized hemicellulose and PHBV in the first stage, degrades plasticized cellulose in the second stage, and plasticized BF system degrades modified lignin in the third stage, while plasticized DBF system only continues to decompose cellulose.

[0066] As shown in Table 4, the maximum degradation rate in the first stage decreased and the corresponding temperature increased after plasticization modification, indicating stronger thermal stability of the modified hemicellulose. In the second stage, the degradation rate and peak temperature increased synchronously, improving the heat resistance of the material. The original thermal protection effect of lignin in BF was destroyed after esterification, while DBF contained almost no lignin. Therefore, the degradation rate in the second stage of all modified samples increased, and the residual amount decreased significantly.

[0067] Table 4. Maximum weight loss rates L1 and L2 of composite materials in the first and second stages and their corresponding temperatures T max1 and T max2

[0068] Figure 15 The results showed that the coupling agent had no significant effect on the residual rate, and the degradation still proceeded in three stages. Table 5 shows that the maximum weight loss rates L1 and L2 in the first and second stages of C10-TiBP and C10-TiDP decreased, corresponding to peak temperatures T. max1 T max2 The increase in thermal stability is due to the interaction of interfacial chemical bonding and molecular chain entanglement.

[0069] Table 5. Maximum weight loss rates L1 and L2 and corresponding temperatures T in the first and second stages of the modified composite material. max1 and T max2

[0070] In summary, C10–C18 long-chain fatty acids can all plasticize bamboo powder, with the C10 carbon chain corresponding to the composite material exhibiting the best overall performance. This application incorporates TGIC into the C10 carbon chain system, which directly demonstrates the material performance improvement brought about by the covalent interface structure. TGIC relies on its epoxy groups to covalently bond with the hydroxyl groups of the plasticized bamboo powder and PHBV. This interfacial bonding process is not constrained by the carbon chain length of the fatty acids, and this mechanism is applicable to all C10–C18 plasticized modified bamboo powder composite systems. Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A composite material based on thermoplastic modification of bamboo powder, characterized in that, It includes poly(3-hydroxybutyrate-co-3-hydroxyvalerate), lubricant, and thermoplasticized modified bamboo powder; the thermoplasticized modified bamboo powder is modified by esterification of fatty acids with carbon chain length of C10~C18.

2. The composite material based on bamboo powder thermoplasticization modification according to claim 1, characterized in that, The components are in the following parts by weight: 40-50 parts of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), 2-5 parts of lubricant, and 40-60 parts of thermoplasticized modified bamboo powder.

3. The composite material based on bamboo powder thermoplastic modification according to claim 1, characterized in that, It also includes coupling agents.

4. The composite material based on bamboo powder thermoplasticization modification according to claim 3, characterized in that, The coupling agent is 1 to 8 parts by weight.

5. A method for preparing a bamboo powder thermoplasticized modified composite material according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Trifluoroacetic anhydride is used to activate fatty acids, which are then esterified with bamboo powder to obtain thermoplasticized modified bamboo powder. S2. Mix the raw materials for preparing the bamboo powder thermoplasticized modified composite material, melt blend, and hot press to obtain the bamboo powder thermoplasticized modified composite material.

6. The preparation method of the bamboo powder thermoplasticized modified composite material according to claim 5, characterized in that, The mass ratio of fatty acids to trifluoroacetic anhydride is 1:1~2; the mass ratio of trifluoroacetic anhydride to bamboo powder is 3~6:

1.

7. The preparation method of the bamboo powder thermoplasticized modified composite material according to claim 5, characterized in that, Esterification reaction at 50~80℃ for 1~3 h.

8. The preparation method of the bamboo powder thermoplasticized modified composite material according to claim 5, characterized in that, The blending temperature is 170~190℃ and the blending time is 8~12 min.

9. The preparation method of the bamboo powder thermoplasticized modified composite material according to claim 5, characterized in that, Hot pressing temperature: 170~190℃, hot pressing pressure: 8~12 MPa.

10. An application of the bamboo powder thermoplasticized modified composite material according to any one of claims 1 to 4, characterized in that, Used to prepare biodegradable products.

Images