Changes in Physical Properties and Microstructure of Bamboo–Plastic Composites with Different Bamboo Powder/Polybutylene Succinate Ratios, Polypropylene, and Polyethylene

: As the most promising biomass material, bamboo has been widely used, but at the same time, it is subject to many problems, such as processing residues and the failure of high-value utilization of residues. In this paper, bamboo powder and polybutylene succinate (PBS) were used as the main raw materials, and by changing the ratio of bamboo powder to PBS and adding polypropylene (PP) or polyethylene (PE) in combination with PBS, the effects of the ratio, as well as the effects of the use of PP and PE, on the physical–mechanical, thermal, and degradation properties of bamboo–plastic composites were investigated, and the microscopic changes of the materials were studied by chemical component analysis. The optimal formulation of bamboo powder/PBS composite material has been identified through experimentation, yielding a flexural strength of 24.87 MPa and a compressive strength of 29.74 MPa. This material can be used for outdoor furniture, wall panels, flooring, road barriers, and other applications, providing a new environmentally friendly approach to the consumption of residual bamboo materials.


Introduction
Bamboo is one of the richest biomass resources in the world, with large reserves and excellent mechanical properties, and it has been used in various sectors such as construction and furniture [1][2][3].Looking at the bamboo processing enterprises around the world, the utilization rate of bamboo material is low, and there are many processing residues; therefore, how to utilize the processing residues is a problem that needs to be solved urgently [4][5][6][7][8][9].Bamboo-plastic composite material is a new type of composite with high strength, wear-resistance, and heat-insulating properties, made using a processing and molding technique with bamboo powder as a filler and reinforcing material, and thermoplastic as a matrix [10][11][12][13].It is an effective method of digesting bamboo processing residue.
Current research on bamboo-plastic composite materials mostly focuses on optimizing the process parameters, with the materials used being mainly bamboo powder combined with PE and other coupling agents.Zeng Chunxia conducted a study on bamboo-plastic composites made from low-density polyethylene (LDPE) and three different coupling agents, and the results indicated that the modification effect of maleic anhydride modified polyethylene (MAPE) was the most significant [14].The performance of bamboo-plastic composites is also significantly influenced by the different sources of plastic matrix and bamboo powder.The composite made with bamboo powder from moso bamboo and recycled PE exhibited the best water absorption performance, followed by the composite made with bamboo powder from moso bamboo and new PE [15].When using highdensity polyethylene (HDPE) as the plastic matrix for the bamboo-plastic composite, the Forests 2024, 15, 478 2 of 14 mechanical properties reached their optimal values at a bamboo powder content of 40%.Further improvement in the mechanical performance of the composite can be achieved by adding 5% maleic anhydride polypropylene (MAPP) at this bamboo powder content [16].Despite the application of bamboo-plastic composites in everyday areas such as packaging and the automotive industry, the poor degradability of the plastic matrix has always been a significant obstacle to the development of bamboo-plastic composites.
PBS is currently the most promising biodegradable polymer compound due to its easily hydrolyzed ester group in its structural unit, which can be easily decomposed by a variety of microorganisms in nature or enzymes in animals and plants [17,18].Cellulose nanocrystals extracted from bamboo fiber can be used as reinforcing materials in polylactic acid (PLA)/PBS polymer blends to improve the performance of the plastic matrix [19].In addition, PLA and PBS blended with 5% sweet bamboo sulfate pulp (SP) can be used to prepare biodegradable packaging with excellent thermal and mechanical properties [20].Pivsa-Art used bamboo fibers as the filling material and PBS as the plastic matrix to prepare high-strength bamboo fiber-reinforced biocomposite materials.Thus, using bamboo fiber as a filler material and PBS as a matrix to prepare bamboo fiber-reinforced biodegradable composite material is another environment-friendly idea for digesting bamboo processing residue [21].
Although PBS is biodegradable, its toughness is very poor; it is not as good as that of PE and PP, which have good stability and are low in price, and the composite materials prepared using them have good mechanical properties [22].Currently, bamboo-plastic composite materials generally contain a high proportion of plastic; therefore, this study is committed to safeguarding mechanical strength conditions, exploring the balance between the bamboo powder and the proportion of each plastic matrix, and preparing a kind of bamboo-plastic composite material with a high content of bamboo powder that is degradable and offers good performance.

Materials
The raw material bamboo powder was collected from moso bamboo processing enterprises in Anhui Province, China, and the residue of bamboo processing was collected without discrimination.After grinding and sieving, bamboo powder of about 60 mesh was selected to be used for the preparation of the bamboo/PBS composite material in this test.The rest of the raw materials (PBS, PP, and PE) were all procured with a purity exceeding 99.7% for use as experimental reagents.These materials were purchased from Showa Denko K.K., with their origin being Japan.The KBr used for FTIR testing was purchased from Shanghai Maclin Biochemical Technology Co., Ltd.(Shanghai, China), with its origin being Chengdu.

Preparation of Bamboo Powder/PBS Composite Material
The objective of this experiment is to explore the impact of different raw material ratios on the performance of bamboo-plastic composite materials.A single-factor variable control method is employed, with group A adding only bamboo powder and PBS.Group B incorporates an appropriate amount of PP or PE as raw materials, with B3 serving as the control group for group B to facilitate the analysis of the role of PP and PE in the bamboo powder/PBS composite material.The specific design is detailed in Table 1.
Bamboo powder and PBS are prone to moisture absorption at room temperature in the air.If they are not dried before processing, it is easy for PBS to decompose, and this can also increase the bubble rate of the products.Therefore, before preparation, the bamboo powder and PBS are placed in a drying oven at 80 • C for 24 h to dry.Then, a high-speed mixer is used to blend the prepared bamboo powder, PBS, PP, and PE in proportion to obtain a bamboo-plastic blend.The extrusion granulation is carried out using a twin-screw extruder, with a feeding speed of 3 kg/h and an extrusion speed of 60 rpm.The extruded bamboo plastic composite material is in the form of strips and needs to be processed into Forests 2024, 15, 478 3 of 14 powder using a crusher.Finally, the powdered bamboo plastic composite material is placed in a mold, and a vacuum hot press is used for hot pressing.The vacuum is set to −80 kPa, the unit pressure to 4 MPa, the mold temperature to 150 • C, and the hot-pressing time to 4 min.After the hot pressing is completed, cooling down to 20 • C within 30 min takes place, followed by cold pressing for 6 min.Then, the mold is opened to take out the samples for future use.The preparation process is shown in Figure 1.Bamboo powder and PBS are prone to moisture absorption at room temperature in the air.If they are not dried before processing, it is easy for PBS to decompose, and this can also increase the bubble rate of the products.Therefore, before preparation, the bamboo powder and PBS are placed in a drying oven at 80 °C for 24 h to dry.Then, a highspeed mixer is used to blend the prepared bamboo powder, PBS, PP, and PE in proportion to obtain a bamboo-plastic blend.The extrusion granulation is carried out using a twinscrew extruder, with a feeding speed of 3 kg/h and an extrusion speed of 60 rpm.The extruded bamboo plastic composite material is in the form of strips and needs to be processed into powder using a crusher.Finally, the powdered bamboo plastic composite material is placed in a mold, and a vacuum hot press is used for hot pressing.The vacuum is set to −80 kPa, the unit pressure to 4 MPa, the mold temperature to 150 °C, and the hotpressing time to 4 min.After the hot pressing is completed, cooling down to 20 °C within 30 min takes place, followed by cold pressing for 6 min.Then, the mold is opened to take out the samples for future use.The preparation process is shown in Figure 1.

Physical Performance Test
Water absorption rate is an important physical property for testing the quality of bamboo-plastic composite material; the water absorption rate of bamboo-plastic composite material directly affects the mechanical properties of the material, so a water absorption rate test is very necessary.The water absorption rate test is conducted with reference to the relevant provisions of 4.6 in the standard GB/T 17657-2013.The sample size is 50 mm × 50 mm.Fifteen replicates are conducted for each group, and the average value is calculated after removing the extreme values.

Bamboo-Plastic Composite Material Performance Test 2.3.1. Physical Performance Test
Water absorption rate is an important physical property for testing the quality of bamboo-plastic composite material; the water absorption rate of bamboo-plastic composite material directly affects the mechanical properties of the material, so a water absorption rate test is very necessary.The water absorption rate test is conducted with reference to the relevant provisions of 4.6 in the standard GB/T 17657-2013.The sample size is 50 mm × 50 mm.Fifteen replicates are conducted for each group, and the average value is calculated after removing the extreme values.

Mechanical Properties Test
The mechanical performance tests in this experiment include a bending performance test, a compression performance test, and a dynamic mechanical analysis (DMA) test; each group undergoes 5 repeated tests to eliminate experimental randomness.Among them, in the bending performance test, in accordance with the provisions of GB/T 29418-2012 in 4.4, the sample size is 104 mm × 12 mm × 4 mm.In the compression performance test, in accordance with the provisions of GB/T 29418-2012 in 4.5 determination, the sample size is 4 mm × 12 mm × 12 mm.In dynamic mechanical analysis (DMA) testing, the dynamic thermal mechanical properties of the samples are tested using a dynamic mechanical analyzer.The sample size is 35 mm × 12 mm × 4 mm, and the testing method is the three-point bending method.In a nitrogen atmosphere, the temperature is lowered to −30 • C and held for 3 min to eliminate thermal history; then, it is heated to 130 • C at a heating rate of 4 • C/min.

Chemical Performance Test
The chemical indicators of bamboo-plastic composite materials are important analytical indices for explaining the influence of different raw material ratios on the mechanical properties of the materials.FTIR testing involves mixing the samples with KBr, pressing them into pellets, and then using a Fourier transform infrared spectrometer to analyze the differences in the chemical composition of each group of composite materials.The testing is conducted using the transmission method with a wavelength range of 4000-500 cm −1 and 40 scan cycles.DSC testing utilizes a differential scanning calorimeter to obtain the material's heat flow curve in order to analyze its crystalline properties.Thermal stability testing is performed using a thermogravimetric analyzer by taking 5-8 mg samples, placing them in crucibles, subjecting them to a nitrogen atmosphere at a flow rate of 60 mL/min, and heating them from 30 • C to 600 • C at a rate of 10 • C/min.

Microstructure Test
A scanning electron microscope (SEM) is necessary to analyze the material interface.The specimen is frozen by liquid nitrogen for brittle fracture purposes, and after the section is sprayed with gold, SEM is used to observe the section morphology.Photoshop 2023 software is used to enhance the SEM image to enable analysis of the binding interactions between bamboo powder and PBS in different groups of bamboo powder/PBS composite materials.

Degradation Performance Test
The degradation performance test is conducted with reference to the standard ASTM D5526-1994(2002); the sample size is 30 mm × 30 mm × 2 mm.Each sample is weighted and buried into natural soil with the same soil quality; the burial depth is 10-20 cm so that it can undergo microbial degradation in the natural environment.Every 30 days, for the purpose of measurement, the sample is taken out, cleaned with distilled water and ethanol, baked in the drying box at a temperature of 80 • C until a constant weight is achieved, and the rate of loss of weight of the sample is calculated.

Effect of Ratio on Physical Properties of Composites
Figure 2 shows the average water absorption rate of bamboo powder/PBS composite material in group A. As can be seen from the figure, the water absorption rate of bamboo powder/PBS composite material increases with the increase in bamboo powder content.An increase in bamboo powder content makes the encapsulation by the PBS of the bamboo powder worse, increasing the amount of exposed bamboo powder on the surface of the material; an increase in bamboo powder content will also make the phenomenon of agglomeration of bamboo powder intensify, resulting in an increase in the water absorption rate of the material.An increase in the bamboo powder content will result in a decrease in the encapsulation of bamboo powder by PBS, increasing the amount of exposed bamboo powder on the material surface.At the same time, it will also intensify the phenomenon of bamboo powder agglomeration, leading to an increase in the material's water absorption rate.
rate of the material.An increase in the bamboo powder content will result in a decrease in the encapsulation of bamboo powder by PBS, increasing the amount of exposed bamboo powder on the material surface.At the same time, it will also intensify the phenomenon of bamboo powder agglomeration, leading to an increase in the material's water absorption rate.Figure 3 shows the histogram of water absorption of group B bamboo-plastic composite materials.Due to the hydrophobic nature of PBS, PP, and PE, as the amount of plastic matrix increases, the water absorption capabilities of the materials are all improved to some extent.The plastic matrix content in B1, B2, and B3 is higher than that in A, with B2 exhibiting the lowest water absorption rate and optimal water absorption performance.This indicates that the combination of PBS with a certain amount of PP can enhance the water absorption performance of bamboo powder/PBS composite materials.Meanwhile, among the bamboo powder/PBS composite materials with equal amounts of the three types of plastic matrix, B1 shows the highest water absorption rate, indicating that the addition of PE will increase the water absorption of the material and reduce the water absorption performance of bamboo powder/PBS composite materials.

Effect of Ratio on Mechanical Properties of Composites
Modulus of elasticity and flexural strength are the most convenient indicators to characterize the bending properties of materials.Figures 4 and 5 show the histograms of the bending properties of bamboo powder/PBS composites with different ratios.As can be seen from the figures, the bending strength of the material in group A increases and then decreases with the increase in PBS dosage.The bending strength of A3 is the largest, which is 24.87 Mpa, indicating that the ratio of A3 is optimal among the experimental Figure 3 shows the histogram of water absorption of group B bamboo-plastic composite materials.Due to the hydrophobic nature of PBS, PP, and PE, as the amount of plastic matrix increases, the water absorption capabilities of the materials are all improved to some extent.The plastic matrix content in B1, B2, and B3 is higher than that in A, with B2 exhibiting the lowest water absorption rate and optimal water absorption performance.This indicates that the combination of PBS with a certain amount of PP can enhance the water absorption performance of bamboo powder/PBS composite materials.Meanwhile, among the bamboo powder/PBS composite materials with equal amounts of the three types of plastic matrix, B1 shows the highest water absorption rate, indicating that the addition of PE will increase the water absorption of the material and reduce the water absorption performance of bamboo powder/PBS composite materials.
rate of the material.An increase in the bamboo powder content will result in a decrease in the encapsulation of bamboo powder by PBS, increasing the amount of exposed bamboo powder on the material surface.At the same time, it will also intensify the phenomenon of bamboo powder agglomeration, leading to an increase in the material's water absorption rate.Figure 3 shows the histogram of water absorption of group B bamboo-plastic composite materials.Due to the hydrophobic nature of PBS, PP, and PE, as the amount of plastic matrix increases, the water absorption capabilities of the materials are all improved to some extent.The plastic matrix content in B1, B2, and B3 is higher than that in A, with B2 exhibiting the lowest water absorption rate and optimal water absorption performance.This indicates that the combination of PBS with a certain amount of PP can enhance the water absorption performance of bamboo powder/PBS composite materials.Meanwhile, among the bamboo powder/PBS composite materials with equal amounts of the three types of plastic matrix, B1 shows the highest water absorption rate, indicating that the addition of PE will increase the water absorption of the material and reduce the water absorption performance of bamboo powder/PBS composite materials.

Effect of Ratio on Mechanical Properties of Composites
Modulus of elasticity and flexural strength are the most convenient indicators to characterize the bending properties of materials.Figures 4 and 5 show the histograms of the bending properties of bamboo powder/PBS composites with different ratios.As can be seen from the figures, the bending strength of the material in group A increases and then decreases with the increase in PBS dosage.The bending strength of A3 is the largest, which is 24.87 Mpa, indicating that the ratio of A3 is optimal among the experimental

Effect of Ratio on Mechanical Properties of Composites
Modulus of elasticity and flexural strength are the most convenient indicators to characterize the bending properties of materials.Figures 4 and 5 show the histograms of the bending properties of bamboo powder/PBS composites with different ratios.As can be seen from the figures, the bending strength of the material in group A increases and then decreases with the increase in PBS dosage.The bending strength of A3 is the largest, which is 24.87 Mpa, indicating that the ratio of A3 is optimal among the experimental groups, and its interfacial bonding is also stronger than the other four groups.The bending strengths of A and A1 are similar; they are lower than those of other three groups.That is because, due to the high content of bamboo powder and the low content of PBS, it is difficult for bamboo powder to be dispersed in PBS matrix and there are interfacial defeats, which result in a decrease in structural strength.The modulus of elasticity of group A increases with the increase in bamboo powder content.In the phase where the bamboo powder content is <35%, the experimental results are consistent with the research findings Forests 2024, 15, 478 6 of 14 of Xin Zhikun and others [23].This is due to the fact that bamboo powder is more rigid than PBS [24].So, the higher the percentage of bamboo powder, the higher the modulus of elasticity.B2 in group B has the best mechanical properties among the four composites, which indicates the mixing of PBS and PP significantly improves the bending properties of bamboo powder/PBS composite materials.The bending properties of B1 are lower than those of B3, and also lower than those of bamboo-plastic composite using pure PBS under the same amount of plastic matrix, indicating that the adding of PE plays a negative role in the bending properties of the materials.
groups, and its interfacial bonding is also stronger than the other four groups.The bending strengths of A and A1 are similar; they are lower than those of other three groups.That is because, due to the high content of bamboo powder and the low content of PBS, it is difficult for bamboo powder to be dispersed in PBS matrix and there are interfacial defeats, which result in a decrease in structural strength.The modulus of elasticity of group A increases with the increase in bamboo powder content.In the phase where the bamboo powder content is <35%, the experimental results are consistent with the research findings of Xin Zhikun and others [23].This is due to the fact that bamboo powder is more rigid than PBS [24].So, the higher the percentage of bamboo powder, the higher the modulus of elasticity.B2 in group B has the best mechanical properties among the four composites, which indicates the mixing of PBS and PP significantly improves the bending properties of bamboo powder/PBS composite materials.The bending properties of B1 are lower than those of B3, and also lower than those of bamboo-plastic composite using pure PBS under the same amount of plastic matrix, indicating that the adding of PE plays a negative role in the bending properties of the materials.groups, and its interfacial bonding is also stronger than the other four groups.The bending strengths of A and A1 are similar; they are lower than those of other three groups.That is because, due to the high content of bamboo powder and the low content of PBS, it is difficult for bamboo powder to be dispersed in PBS matrix and there are interfacial defeats, which result in a decrease in structural strength.The modulus of elasticity of group A increases with the increase in bamboo powder content.In the phase where the bamboo powder content is <35%, the experimental results are consistent with the research findings of Xin Zhikun and others [23].This is due to the fact that bamboo powder is more rigid than PBS [24].So, the higher the percentage of bamboo powder, the higher the modulus of elasticity.B2 in group B has the best mechanical properties among the four composites, which indicates the mixing of PBS and PP significantly improves the bending properties of bamboo powder/PBS composite materials.The bending properties of B1 are lower than those of B3, and also lower than those of bamboo-plastic composite using pure PBS under the same amount of plastic matrix, indicating that the adding of PE plays a negative role in the bending properties of the materials.Figure 6 shows the compressive strength of bamboo-plastic composites with different ratios.As can been seen from the figure, the compressive strength of the materials in group A gradually decreases with the increase in the proportion of bamboo powder.This Figure 6 shows the compressive strength of bamboo-plastic composites with different ratios.As can been seen from the figure, the compressive strength of the materials in group A gradually decreases with the increase in the proportion of bamboo powder.This indicates that the addition of wood fiber material improves the rigidity of the material, which makes the material brittle.The change rule of group B is similar to its bending properties, in which the compression strength of B2 is highest and the strength of B1 is the lowest.That indicates that PE plays a negative role in the compression strength of bamboo-plastic as well.
indicates that the addition of wood fiber material improves the rigidity of the material, which makes the material brittle.The change rule of group B is similar to its bending properties, in which the compression strength of B2 is highest and the strength of B1 is the lowest.That indicates that PE plays a negative role in the compression strength of bamboo-plastic as well.The energy storage modulus is a very significant parameter in the assessment of interfacial properties of materials at the molecular level, which not only characterizes the stiffness of the material but also responds to the compatibility of the components in the material [25,26].Figure 7 shows the curves of energy storage modulus (E') versus temperature from bamboo powder-plastic composites with different ratios.From the figure, it can be seen that the energy storage modulus of all five specimens decreases with the increase in temperature, among which A4 with the highest PBS content has the largest energy storage modulus at low temperature; A, with the highest bamboo powder content, has the largest energy storage modulus at high temperature.This indicates that the material exhibits lower kinetic energy at low temperatures due to the higher crystallinity of the PBS matrix, which results in greater rigidity.However, at high temperatures, the PBS matrix softens, and the movement of some groups becomes more free.The large molecular matrix, which is difficult to move, and bamboo powder particles can store energy, with the stiffness of bamboo powder playing a dominant role.Therefore, as the temperature increases, the segmental motion within the material intensifies, ultimately leading to a decrease in the material's energy storage modulus.The energy storage modulus is a very significant parameter in the assessment of interfacial properties of materials at the molecular level, which not only characterizes the stiffness of the material but also responds to the compatibility of the components in the material [25,26].Figure 7 shows the curves of energy storage modulus (E') versus temperature from bamboo powder-plastic composites with different ratios.From the figure, it can be seen that the energy storage modulus of all five specimens decreases with the increase in temperature, among which A4 with the highest PBS content has the largest energy storage modulus at low temperature; A, with the highest bamboo powder content, has the largest energy storage modulus at high temperature.This indicates that the material exhibits lower kinetic energy at low temperatures due to the higher crystallinity of the PBS matrix, which results in greater rigidity.However, at high temperatures, the PBS matrix softens, and the movement of some groups becomes more free.The large molecular matrix, which is difficult to move, and bamboo powder particles can store energy, with the stiffness of bamboo powder playing a dominant role.Therefore, as the temperature increases, the segmental motion within the material intensifies, ultimately leading to a decrease in the material's energy storage modulus.

Changes in Mechanical Composition of Bamboo-Plastic Composite after Adding PP and PE
Figure 8 and Table 2 show the infrared spectral fingerprint area spectra and the characteristic peaks attributed to the bamboo powder/PBS composites added to group B. From Figures 3-5, it can be seen that A, B1, B2, and B3 all have a relatively broad absorption peak at 3500-3200 cm −1 in their infrared spectra, which is mainly the absorption peak formed by the stretching vibrations of hydroxyl groups (-OH) in cellulose, hemicellulose, and lignin in bamboo powder.The absorption peaks of B1 and B2 at 1715 cm −1 , 1155 cm −1 ,   2 show the infrared spectral fingerprint area spectra and the characteristic peaks attributed to the bamboo powder/PBS composites added to group B. From Figures 3-5, it can be seen that A, B1, B2, and B3 all have a relatively broad absorption peak at 3500-3200 cm −1 in their infrared spectra, which is mainly the absorption peak formed by the stretching vibrations of hydroxyl groups (-OH) in cellulose, hemicellulose, and lignin in bamboo powder.The absorption peaks of B1 and B2 at 1715 cm −1 , 1155 cm −1 , and 1044 cm −1 show a significant decrease in the peak area compared with that of A, which indicates that the addition of PE and PP reduce the presence of C=O, C-O, and C-O-C in the composite.In addition, there are two strong absorption peaks at 2916 cm −1 and 2849 cm −1 for B1, corresponding to the -CH 2 -asymmetric and -CH 2 -symmetric stretching vibration peaks, respectively.There is also a small absorption peak at 2916 cm −1 for B2, which may be caused by the addition of stearate to PP and PE.Stearate is often used as a lubricant or acid-neutralizing agent in plastics.

Changes in Mechanical Composition of Bamboo-Plastic Composite after Adding PP and PE
Figure 8 and Table 2 show the infrared spectral fingerprint area spectra and the characteristic peaks attributed to the bamboo powder/PBS composites added to group B. From Figures 3-5, it can be seen that A, B1, B2, and B3 all have a relatively broad absorption peak at 3500-3200 cm −1 in their infrared spectra, which is mainly the absorption peak formed by the stretching vibrations of hydroxyl groups (-OH) in cellulose, hemicellulose, and lignin in bamboo powder.The absorption peaks of B1 and B2 at 1715 cm −1 , 1155 cm −1 , and 1044 cm −1 show a significant decrease in the peak area compared with that of A, which indicates that the addition of PE and PP reduce the presence of C=O, C-O, and C-O-C in the composite.In addition, there are two strong absorption peaks at 2916 cm −1 and 2849 cm −1 for B1, corresponding to the -CH2-asymmetric and -CH2-symmetric stretching vibration peaks, respectively.There is also a small absorption peak at 2916 cm −1 for B2, which may be caused by the addition of stearate to PP and PE.Stearate is often used as a lubricant or acid-neutralizing agent in plastics.Figure 9 shows the DSC curves of bamboo powder/PBS composites with the addition of PE and PP in the second temperature rise.As can be seen from the figure, the melting peaks of the four bamboo powder/PBS composites basically remain at the same temperature, which indicates that the addition of PP and PE does not change the melting temperature of the materials.The main melting peak is caused by the melting of the more stable wafer formed by the melt recrystallization of the original wafer, and there is a crystallization exothermic peak before the main peak of the four materials, which is due to the exothermic peak formed by the melt recrystallization of the material in the process of cooling, which is not fully crystallized.A and B1 have double melting peaks, which are located in the front and back of the main peak, respectively, and the A is a part of the non-isothermal crystallization process, while B1 is caused by the failure of PE to be fully compatible with PBS, indicating poor compatibility between the two.In addition, the melting peaks of B1 and B2 are broadened, indicating that the addition of PE and PP decreases the crystallization rate of PBS.ture, which indicates that the addition of PP and PE does not change the melting temperature of the materials.The main melting peak is caused by the melting of the more stable wafer formed by the melt recrystallization of the original wafer, and there is a crystallization exothermic peak before the main peak of the four materials, which is due to the exothermic peak formed by the melt recrystallization of the material in the process of cooling, which is not fully crystallized.A and B1 have double melting peaks, which are located in the front and back of the main peak, respectively, and the A is a part of the non-isothermal crystallization process, while B1 is caused by the failure of PE to be fully compatible with PBS, indicating poor compatibility between the two.In addition, the melting peaks of B1 and B2 are broadened, indicating that the addition of PE and PP decreases the crystallization rate of PBS.Table 3 lists the melting temperature (Tm), enthalpy of melting (ΔH), and crystallinity (Xc) of group B bamboo powder/PBS composites.From the table, it can be seen that the crystallinity of B1 is the largest, and that of B2 is the smallest, and the crystallinity of A and B3 is similar, which is due to the poor compatibility between PBS and PE and the existence of more stable components between the interfaces, which prompts the heterogeneous nucleation of PBS, resulting in the increase in the crystallinity of B1 [27,28].Combining this with Figure 9, it can be seen that the melting peak area of B2 decreases, indicating a reduction in crystallinity.This is due to the addition of PP, which enhances the interfacial interaction among bamboo powder, PP, and PBS, inhibiting the movement of PBS molecular chains and preventing them from forming an orderly arrangement.The melting peak area of B3, which increases the amount of PBS, increases significantly, but Table 3 lists the melting temperature (T m ), enthalpy of melting (∆H), and crystallinity (X c ) of group B bamboo powder/PBS composites.From the table, it can be seen that the crystallinity of B1 is the largest, and that of B2 is the smallest, and the crystallinity of A and B3 is similar, which is due to the poor compatibility between PBS and PE and the existence of more stable components between the interfaces, which prompts the heterogeneous nucleation of PBS, resulting in the increase in the crystallinity of B1 [27,28].Combining this with Figure 9, it can be seen that the melting peak area of B2 decreases, indicating a reduction in crystallinity.This is due to the addition of PP, which enhances the interfacial interaction among bamboo powder, PP, and PBS, inhibiting the movement of PBS molecular chains and preventing them from forming an orderly arrangement.The melting peak area of B3, which increases the amount of PBS, increases significantly, but its crystallinity does not increase compared with A. The reason is that the increase in the amount of PBS increases the melting peak area, but the proportion of PBS in the bamboo powder/PBS composite material also becomes larger, so the crystallinity of B3 is still close to that of A. Figures 10 and 11 display the TG and DTG curves of bamboo powder/PBS composites with varying ratios of raw materials, respectively.According to Figure 10, it is observed that the degradation onset temperatures of the four bamboo powder/PBS composites are lower than that of pure PBS.Above 400 • C, PBS has completely degraded, whereas the residual masses of the four bamboo powder/PBS composites are higher than that of PBS Forests 2024, 15, 478 10 of 14 alone, and these residual masses remain constant in the subsequent heating process.Under high-temperature conditions, B3 exhibits the best thermal stability with the highest residual mass.Although B1 and B2 also show high residual masses at 400 • C, their residual masses gradually decrease as the temperature continues to increase, eventually falling below that of A. This suggests that the addition of PP and PE effectively slows down the thermal degradation of the bamboo powder/PBS composites.

B3
94.67 15.74 61.83% Figures 10 and 11 display the TG and DTG curves of bamboo powder/PBS composites with varying ratios of raw materials, respectively.According to Figure 10, it is observed that the degradation onset temperatures of the four bamboo powder/PBS composites are lower than that of pure PBS.Above 400 °C, PBS has completely degraded, whereas the residual masses of the four bamboo powder/PBS composites are higher than that of PBS alone, and these residual masses remain constant in the subsequent heating process.Under high-temperature conditions, B3 exhibits the best thermal stability with the highest residual mass.Although B1 and B2 also show high residual masses at 400 °C, their residual masses gradually decrease as the temperature continues to increase, eventually falling below that of A. This suggests that the addition of PP and PE effectively slows down the thermal degradation of the bamboo powder/PBS composites.According to the DTG curves of bamboo powder/PBS composite shown in Figure 11, the maximum rate of thermal weight loss of the plastic matrix PBS is seen at around 400 °C.However, the maximum thermal weight loss rates of the four types of bamboo powder/PBS composite are lower than that of PBS, and the temperature at which the maximum rate of thermal weight loss occurs is also below the corresponding temperature for PBS, approximately 350 °C.Around 300 °C, all four types of bamboo powder/PBS composites exhibit a minor weight loss peak due to the degradation of cellulose and hemicellulose within the bamboo powder/PBS composites, with B3 showing the smallest weight loss peak and the lowest rate of thermal weight loss.At about 350 °C, all four types of bamboo powder/PBS composite exhibit a significant weight loss peak resulting from the

Analysis of Cross-Section Micromorphology of Bamboo-Plastic Composite Materials with Different Formulations
Figure 12 shows the cross-section microscopic morphology of bamboo powder/PBS composites in group A. The interfacial bonding between bamboo fibers and PBS matrix can be clearly observed in the figures.The interfacial combination of bamboo fiber and PBS matrix can be clearly observed in the figure, and the interfaces of materials with different ratios have obvious differences.The gaps between bamboo fiber and PBS in A and A1 are obviously larger than those in A3 and A4, which indicates that with the increase in the content of bamboo powder, it is difficult for the PBS to completely encapsulate the bamboo powder, so that the dispersion of bamboo powder in the material become poor, and agglomeration occurs, which affects the mechanical properties of the material; the results are consistent with those in the mechanical test.In addition, the bamboo fibers shown in the figure were pulled out from the PBS matrix without fracture, indicating that the strength of bamboo fibers is higher than that of the interface [29].This also confirms According to the DTG curves of bamboo powder/PBS composite shown in Figure 11, the maximum rate of thermal weight loss of the plastic matrix PBS is seen at around 400 • C.However, the maximum thermal weight loss rates of the four types of bamboo powder/PBS composite are lower than that of PBS, and the temperature at which the maximum rate of thermal weight loss occurs is also below the corresponding temperature for PBS, approximately 350 • C. Around 300 • C, all four types of bamboo powder/PBS composites exhibit a minor weight loss peak due to the degradation of cellulose and hemicellulose within the bamboo powder/PBS composites, with B3 showing the smallest weight loss peak and the lowest rate of thermal weight loss.At about 350 • C, all four types of bamboo powder/PBS composite exhibit a significant weight loss peak resulting from the degradation of both the plastic matrix PBS and lignin present in the bamboo powder.Around 470 • C, B1 and B2 exhibit a minor weight loss peak, which corresponds to the decomposition of PE and PP, respectively.In conclusion, B3 has the smallest peaks for both major and minor weight losses and the lowest rate of thermal weight loss when it is compared to A, B1, and B2.That indicates that B3 possesses better thermal stability than the other three types of bamboo powder/PBS composites.

Analysis of Cross-Section Micromorphology of Bamboo-Plastic Composite Materials with Different Formulations
Figure 12 shows the cross-section microscopic morphology of bamboo powder/PBS composites in group A. The interfacial bonding between bamboo fibers and PBS matrix can be clearly observed in the figures.The interfacial combination of bamboo fiber and PBS matrix can be clearly observed in the figure, and the interfaces of materials with different ratios have obvious differences.The gaps between bamboo fiber and PBS in A and A1 are obviously larger than those in A3 and A4, which indicates that with the increase in the content of bamboo powder, it is difficult for the PBS to completely encapsulate the bamboo powder, so that the dispersion of bamboo powder in the material become poor, and agglomeration occurs, which affects the mechanical properties of the material; the results are consistent with those in the mechanical test.In addition, the bamboo fibers shown in the figure were pulled out from the PBS matrix without fracture, indicating that the strength of bamboo fibers is higher than that of the interface [29].This also confirms the phenomenon that the bending strength of A3 is greater than that of A4 in the mechanical test.

Effect of PE and PP on the Degradation Properties of Bamboo Powder/PBS Composite
The degradation performance of bamboo powder/PBS composite is an important index for its evaluation as a biodegradable material.PBS is a degradable plastic with better processing performance at present.Its degradation principle is the breakage of the chemical bond between the main chain and the branched chain in the macromolecule.Under natural conditions, the biological enzymes secreted by microorganisms can promote the alcoholysis of PBS polyester, and of the generated acyl enzymes and the remainder of the polyester; Under natural conditions, enzymes secreted by microorganisms can promote the hydrolysis of PBS polyester, with the resulting acyl enzyme continuing the hydrolysis reaction to produce regenerated enzymes and the remaining portion of the polyester.In this process, the enzymes can be reused, and the degradation of PBS is shown in Scheme 1. Bamboo powder itself has excellent degradability under natural conditions, and it can be inferred that bamboo powder/PBS composites should have good degradation properties.

Effect of PE and PP on the Degradation Properties of Bamboo Powder/PBS Composite
The degradation performance of bamboo powder/PBS composite is an important index for its evaluation as a biodegradable material.PBS is a degradable plastic with better processing performance at present.Its degradation principle is the breakage of the chemical bond between the main chain and the branched chain in the macromolecule.Under natural conditions, the biological enzymes secreted by microorganisms can promote the alcoholysis of PBS polyester, and of the generated acyl enzymes and the remainder of the polyester; Under natural conditions, enzymes secreted by microorganisms can promote the hydrolysis of PBS polyester, with the resulting acyl enzyme continuing the hydrolysis reaction to produce regenerated enzymes and the remaining portion of the polyester.In this process, the enzymes can be reused, and the degradation of PBS is shown in Scheme 1.
Bamboo powder itself has excellent degradability under natural conditions, and it can be inferred that bamboo powder/PBS composites should have good degradation properties.
natural conditions, the biological enzymes secreted by microorganisms can promote the alcoholysis of PBS polyester, and of the generated acyl enzymes and the remainder of the polyester; Under natural conditions, enzymes secreted by microorganisms can promote the hydrolysis of PBS polyester, with the resulting acyl enzyme continuing the hydrolysis reaction to produce regenerated enzymes and the remaining portion of the polyester.In this process, the enzymes can be reused, and the degradation of PBS is shown in Scheme 1. Bamboo powder itself has excellent degradability under natural conditions, and it can be inferred that bamboo powder/PBS composites should have good degradation properties.
Scheme 1.The biodegradation process of PBS.
According to Figures 13 and 14, the weight loss rate of bamboo powder/PBS composite materials increases with the prolongation of degradation time.The surface of the degraded bamboo powder/PBS composite material is no longer smooth and flat, and its structure also shows signs of loosening.Among the four bamboo powder/PBS composites, A's degradation performance is superior to that of B1, B2, and B3, with a final weight loss rate of 25.1%.This is because material A uses the least amount of plastic matrix and has a larger proportion of bamboo powder, resulting in better degradation performance, which is consistent with the research findings of Fu Yao et al. [30].The degradation performances of B1 and B3 materials are similar, with weight loss rates of 20.2% and 21.7%, respectively.This is due to the lower number of microbes that degrade PBS in the soil used for the Scheme 1.The biodegradation process of PBS.
According to Figures 13 and 14, the weight loss rate of bamboo powder/PBS composite materials increases with the prolongation of degradation time.The surface of the degraded bamboo powder/PBS composite material is no longer smooth and flat, and its structure also shows signs of loosening.Among the four bamboo powder/PBS composites, A's degradation performance is superior to that of B1, B2, and B3, with a final weight loss rate of 25.1%.This is because material A uses the least amount of plastic matrix and has a larger proportion of bamboo powder, resulting in better degradation performance, which is consistent with the research findings of Fu Yao et al. [30].The degradation performances of B1 and B3 materials are similar, with weight loss rates of 20.2% and 21.7%, respectively.This is due to the lower number of microbes that degrade PBS in the soil used for the experiment, hence the degradation rates do not vary significantly.Overall, all four bamboo powder/PBS composite materials demonstrate good degradability.experiment, hence the degradation rates do not vary significantly.Overall, all four bamboo powder/PBS composite materials demonstrate good degradability.

Conclusions
(1) The flexural strength of bamboo powder/PBS composite material showed a trend of increasing and decreasing with the increase in PBS content, and the material had the greatest flexural strength when the ratio was A3 and the modulus of elasticity was lower, which showed strong toughness.At the same time, A3 showed good compression resistance and high energy storage modulus; it was an excellent ratio of bamboo powder/PBS composite material.B2 with PP was significantly improved in water absorption and bending and compression properties, while B1 with PE was lower than B3 with pure PBS in bending and compression performance tests, and only reduced experiment, hence the degradation rates do not vary significantly.Overall, all four bamboo powder/PBS composite materials demonstrate good degradability.

Conclusions
(1) The flexural strength of bamboo powder/PBS composite material showed a trend of increasing and decreasing with the increase in PBS content, and the material had the greatest flexural strength when the ratio was A3 and the modulus of elasticity was lower, which showed strong toughness.At the same time, A3 showed good compression resistance and high energy storage modulus; it was an excellent ratio of bamboo powder/PBS composite material.B2 with PP was significantly improved in water absorption and bending and compression properties, while B1 with PE was lower than B3 with pure PBS in bending and compression performance tests, and only reduced

Conclusions
(1) The flexural strength of bamboo powder/PBS composite material showed a trend of increasing and decreasing with the increase in PBS content, and the material had the greatest flexural strength when the ratio was A3 and the modulus of elasticity was lower, which showed strong toughness.At the same time, A3 showed good compression resistance and high energy storage modulus; it was an excellent ratio of bamboo powder/PBS composite material.B2 with PP was significantly improved in water absorption and bending and compression properties, while B1 with PE was lower than B3 with pure PBS in bending and compression performance tests, and only reduced the material water absorption by 1.9%.The mixing of PP and PBS was the optimal choice when the amount of plastic matrix was the same.(2) The addition of PP and PE did not significantly change the melting temperature of the material; the addition of PE increased the crystallinity of material and made the material brittle, while PP decreased the crystallinity of the material and increased the toughness of the material, and the change in the amount of PBS did not have a significant effect on the crystallinity.Compared with PBS, the pyrolysis onset temperature of the bamboo powder/PBS composite was lower, and the maximum thermal degradation rate was smaller than that of PBS.(3) Bamboo powder/PBS composites all have good degradation performance and are environmentally friendly materials that are in line with the concept of industrial development put forward by the United Nations, and they have good commercial prospects.These products can be widely used in furniture manufacturing, for daily necessities, and in other areas, reducing the use of pure plastic products, which is conducive to the advancement of the international "Bamboo as a Substitute of Plastic" initiative.

Figure 2 .
Figure 2. Water absorption of bamboo powder/PBS composites with different ratios.

Figure 2 .
Figure 2. Water absorption of bamboo powder/PBS composites with different ratios.

Figure 4 .
Figure 4. Bending strength of bamboo powder/PBS composites with different ratios.

Figure 5 .
Figure 5. Modulus of elasticity of bamboo powder/PBS composites with different ratios.

Figure 6
Figure6shows the compressive strength of bamboo-plastic composites with different ratios.As can been seen from the figure, the compressive strength of the materials in group A gradually decreases with the increase in the proportion of bamboo powder.This

Figure 4 .
Figure 4. Bending strength of bamboo powder/PBS composites with different ratios.

Figure 4 .
Figure 4. Bending strength of bamboo powder/PBS composites with different ratios.

Figure 5 .
Figure 5. Modulus of elasticity of bamboo powder/PBS composites with different ratios.

Figure 5 .
Figure 5. Modulus of elasticity of bamboo powder/PBS composites with different ratios.

Figure 6 .
Figure 6.Compressive strength of bamboo powder/PBS composites with different ratios.

Figure 6 .
Figure 6.Compressive strength of bamboo powder/PBS composites with different ratios.

Figure 7 .
Figure 7. Storage modulus of bamboo powder/PBS composites with different ratios.

Forests 3 .
Figure 8 and Table2show the infrared spectral fingerprint area spectra and the characteristic peaks attributed to the bamboo powder/PBS composites added to group B. From Figures3-5, it can be seen that A, B1, B2, and B3 all have a relatively broad absorption peak at 3500-3200 cm −1 in their infrared spectra, which is mainly the absorption peak formed by the stretching vibrations of hydroxyl groups (-OH) in cellulose, hemicellulose, and lignin in bamboo powder.The absorption peaks of B1 and B2 at 1715 cm −1 , 1155 cm −1 , and 1044 cm −1 show a significant decrease in the peak area compared with that of A, which indicates that the addition of PE and PP reduce the presence of C=O, C-O, and C-O-C in the composite.In addition, there are two strong absorption peaks at 2916 cm −1 and 2849 cm −1 for B1, corresponding to the -CH 2 -asymmetric and -CH 2 -symmetric stretching vibration peaks, respectively.There is also a small absorption peak at 2916 cm −1 for B2, which may be caused by the addition of stearate to PP and PE.Stearate is often used as a lubricant or acid-neutralizing agent in plastics.

Figure 7 .
Figure 7. Storage modulus of bamboo powder/PBS composites with different ratios.

Figure 13 .
Figure 13.Weight loss rate of bamboo powder/PBS composites changed with degradation time.

Figure 13 .
Figure 13.Weight loss rate of bamboo powder/PBS composites changed with degradation time.

Figure 13 .
Figure 13.Weight loss rate of bamboo powder/PBS composites changed with degradation time.

Table 1 .
Preparation process design.
Note: phr (parts per hundred) represents the quantity added per hundred parts.It is a unit of measurement indicating "parts per hundred by weight".Note: phr (parts per hundred) represents the quantity added per hundred parts.It is a unit of measurement indicating "parts per hundred by weight".
Water absorption of bamboo powder/PBS composites with different ratios.

Table 3 .
DSC melting parameters of bamboo powder/PBS composites.