A biobased modified starch degradable EPS composite foaming material and a preparation method thereof

Abstract

The application relates to the technical field of high polymer composite materials, and discloses a biobased modified starch degradable EPS composite foaming material and a preparation method thereof, which is prepared from the following raw materials in parts by weight: starch 50-70 parts, PBS 30-50 parts, plasticizer 8-15 parts, polybasic carboxylic acid 2-4 parts, and reaction regulator 0.2-0.4 parts. The preparation method adopts a sequential feeding reaction extrusion process: firstly, starch, plasticizer, polybasic carboxylic acid and reaction regulator are premixed; then the premixed material is added into a double-screw extruder from a main port, PBS is added from a side port, and the pre-modification of the starch and the subsequent interface coupling reaction are realized in the extruder; finally, a foaming agent is introduced to perform extrusion foaming. In the application, chemical bonds are formed in situ at the interface between the starch and the PBS, the degradation of the polymer is effectively inhibited, the compatibility of the two phases is improved, and the composite foaming material has excellent mechanical strength, toughness, water resistance and dimensional stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer composite materials, and in particular to a biobased modified starch degradable EPS composite foaming material and a preparation method thereof. BACKGROUND

[0002] With the increasing emphasis on environmental protection and sustainable development worldwide, developing biodegradable materials to replace traditional petroleum-based plastics, especially disposable packaging materials such as expanded polystyrene (EPS), has become a key direction of material science research. Starch, as a widely available, low-cost and completely biodegradable natural polymer, is an ideal substrate for preparing such alternative materials. However, pure starch materials have inherent defects such as brittleness, strong moisture absorption and poor processing performance, making them difficult to be directly applied.

[0003] In order to improve the performance of starch, it is common to use a method of blending modification with degradable polyester having good toughness and hydrophobicity, and polybutylene succinate (PBS) is one of the commonly used blending components. However, since starch is a strongly polar and hydrophilic natural polymer, while PBS is a weakly polar and hydrophobic synthetic polyester, there is significant thermodynamic incompatibility between the two. This incompatibility results in very weak interfacial bonding between the two phases during melt blending, forming a coarse and unstable phase structure.

[0004] This defect in microstructure is directly reflected in the macroscopic properties of the composite material. When subjected to external force, stress concentration easily occurs at the interface between the two phases, which cannot effectively transfer stress, resulting in key mechanical indicators such as tensile strength and elongation at break of the material being far below the theoretical value, exhibiting obvious brittle characteristics. At the same time, the interfacial voids between the dispersed phase and the continuous phase also provide a channel for the invasion of water molecules, resulting in poor water resistance of the material, which is prone to dimensional change and performance degradation in humid environments. Therefore, how to effectively improve the interfacial compatibility between starch and PBS and achieve firm interfacial bonding is a core technical problem that must be solved in the preparation of high-performance starch / PBS composite materials. SUMMARY

[0005] The technical problem solved by the present application is that the physical blending of starch and polyester materials such as polybutylene succinate (PBS) in the prior art has poor interfacial compatibility, resulting in low mechanical strength, insufficient toughness and poor water resistance of the composite material, which limits its application as a packaging material.

[0006] To solve the above problems, the present application provides the following technical solutions:

[0007] In a first aspect, the present application provides a biobased modified starch degradable EPS composite foaming material.

[0008] The material is made of raw materials including starch 50-70 parts by weight, polybutylene succinate 30-50 parts by weight, plasticizer 8-15 parts by weight, polycarboxylic acid 2-4 parts by weight, and reaction regulator 0.2-0.4 parts by weight.

[0009] By adopting the technical scheme, the in-situ chemical reaction between specific components is utilized to fundamentally improve the interface bonding between starch and polybutylene succinate. The mechanism is that:

[0010] During the preparation, the polycarboxylic acid acts as a reactive compatibilizer. The multiple carboxyl functional groups contained in the molecular structure enable it to undergo esterification with the hydroxyl groups on the starch molecular chain and the hydroxyl groups at the end of the polybutylene succinate molecular chain. The reaction forms a "starch-polycarboxylic acid-polybutylene succinate" covalent bond structure centered on polycarboxylic acid at the interface of the two phases. This chemical bonding replaces the weak van der Waals force in traditional physical blending and forms a stable interface layer.

[0011] The presence of the reaction regulator controls the acidity and alkalinity of the reaction system. In an acidic environment without the regulator, the polycarboxylic acid at high temperature catalyzes the hydrolysis and cleavage of the glycosidic bond of starch and the ester bond of polybutylene succinate, leading to a decrease in polymer molecular weight and deterioration of material performance. The reaction regulator can neutralize excess acid in the system, providing a suitable weakly acidic environment for the interface esterification reaction, while effectively inhibiting the degradation side reaction of the polymer matrix.

[0012] Therefore, through the above synergistic effect, the composite material of the application has excellent interface compatibility, enabling stress to be effectively transmitted between the two phases, thereby significantly improving the tensile strength, elongation at break, and other macroscopic mechanical properties of the material. At the same time, the enhanced interface bonding enables the hydrophobic polybutylene succinate matrix to more closely coat the hydrophilic starch phase, greatly reducing the water absorption of the material and improving the dimensional stability.

[0013] Preferably, the parts by weight of the raw materials are: starch 60 parts by weight, polybutylene succinate 40 parts by weight, plasticizer 10 parts by weight, polycarboxylic acid 3 parts by weight, and reaction regulator 0.3 parts by weight.

[0014] By adopting the above technical scheme, the ratio is an optimized technical scheme of the application, which can achieve the best balance between mechanical properties and water resistance while ensuring the bio-based content of the material.

[0015] Preferably, the plasticizer is glycerol; the polycarboxylic acid is citric acid; and the reaction regulator is disodium hydrogen phosphate.

[0016] By adopting the technical scheme, glycerol is selected as the plasticizer, which can effectively plasticize the starch and reduce the melt processing temperature. Citric acid is selected as the polycarboxylic acid, which has three carboxyl groups and one hydroxyl group in the molecular structure, providing multiple reactive sites, which is conducive to the efficient formation of interfacial chemical bonding. Disodium hydrogen phosphate is selected as the reaction regulator, which can provide a stable pH buffer environment at the melting temperature and accurately control the reaction process.

[0017] Preferably, the raw material further comprises a foaming agent.

[0018] By adopting the technical scheme, the introduction of the foaming agent enables the material to form a porous cell structure, thereby greatly reducing the density of the material and endowing it with the properties of lightweight, cushioning and thermal insulation, so that it can meet the application requirements as a degradable EPS substitute material.

[0019] Further preferably, the foaming agent is supercritical carbon dioxide or azodicarbonamide.

[0020] By adopting the technical scheme, supercritical carbon dioxide is selected as the physical foaming agent, which has the advantages of non-toxicity, no residue and environmental friendliness. Azodicarbonamide is selected as the chemical foaming agent, which has a decomposition temperature matching the processing temperature window of the material, and the process control is simple and suitable for conventional extrusion foaming equipment. The selection of these two foaming agents provides a flexible technical path for the industrial production of the present application.

[0021] In a second aspect, the present application provides a method for preparing the biobased modified starch degradable EPS composite foaming material.

[0022] The method comprises the following steps:

[0023] a) pre-mixing starch, plasticizer, polycarboxylic acid and reaction regulator to obtain a reactive starch pre-mixture;

[0024] b) adding the reactive starch pre-mixture through the main feed port of a twin-screw extruder, and adding the polybutylene succinate through the side feed port of the extruder, and performing reaction extrusion;

[0025] c) introducing a foaming agent into the extruder to foam the melt, and extruding and forming through a die.

[0026] By adopting the technical scheme, the sequential feeding reaction extrusion process designed by the present application is the key to realizing the aforementioned high-performance composite material. The process ensures that the interfacial chemical bonding reaction can be efficiently and controllably performed. The innovative principle is reflected in the step-by-step and positioning reaction path:

[0027] The first stage: pre-modification of starch. In the front section of the twin-screw extruder, only the reactive starch premix is present. In this region, the starch is plasticized under the action of plasticizer and heat shear, and at the same time, the preliminary esterification reaction between the carboxyl functional groups of the polycarboxylic acid and the hydroxyl groups of the starch molecular chain occurs. This step successfully grafts the polycarboxylic acid molecules onto the starch macromolecular chain.

[0028] The second stage: interfacial coupling reaction. In the middle and rear sections of the extruder, polybutylene succinate is added from the side feeding port and melted. At this time, the melted polybutylene succinate meets the plasticized starch melt which has been modified by grafting with polycarboxylic acid. The remaining free carboxyl groups on the polycarboxylic acid molecules grafted on the starch then undergo a second esterification reaction with the hydroxyl groups at the end of the polybutylene succinate molecular chain.

[0029] This sequential feeding process ensures that the polycarboxylic acid reacts with the starch first and then with the polybutylene succinate, thereby precisely building a covalent bond bridge at the interface between the two phases. Compared to mixing all components at once (one-step method), the method of the present application avoids random reactions of polycarboxylic acid in the system, such as self-condensation or preferential reaction with polybutylene succinate, thereby maximizing its efficiency as an interfacial compatibilizer and forming a well-defined and stable interfacial layer.

[0030] Preferably, before step a), there is also a step of drying the starch and polybutylene succinate.

[0031] By using the above technical solution, the raw materials are pre-dried, which can effectively remove the water therein. This prevents the hydrolysis of the ester bond of polybutylene succinate caused by water during high-temperature processing, avoids the degradation of the polymer matrix, and also prevents water from affecting the esterification reaction balance, thereby ensuring the stable progress of the interfacial chemical bonding reaction.

[0032] Preferably, the temperature for reaction extrusion in step b) is 140-170°C.

[0033] By using the above technical solution, this temperature range is optimized to meet multiple requirements in the process: a temperature of about 140°C is sufficient to achieve effective plasticization of starch and preliminary reaction with polycarboxylic acid; a temperature of about 170°C ensures the complete melting of polybutylene succinate and the smooth progress of the subsequent interfacial coupling reaction, while the upper limit of this temperature avoids significant thermal degradation of the system.

[0034] Preferably, the screw rotation speed of the extruder in step b) is 150-250 rpm.

[0035] By adopting the technical scheme, the residence time of the material in the extruder and the shearing mixing strength are well balanced in the screw rotation speed range. The material is ensured to have sufficient reaction time to complete the two-step esterification reaction, and sufficient mechanical energy is provided to promote the uniform dispersion and interface contact of the two phases.

[0036] Preferably, the specific implementation of step c) is that supercritical carbon dioxide is injected into the melt in the rear section of the extruder; or the chemical foaming agent is added into the melt together with the polybutylene succinate in step b) through the side feeding port, and is decomposed and foamed in the rear section of the extruder.

[0037] By adopting the technical scheme, two mature and efficient foaming technical paths are provided, and the flexibility of the process is enhanced. The supercritical carbon dioxide physical foaming technology helps to form a fine and uniform cell structure, and the chemical foaming agent method is compatible with the traditional extrusion process, and the equipment requirement is relatively simple, and the lightweight of the material can be effectively realized.

[0038] In summary, the present application has at least one of the following beneficial technical effects:

[0039] 1. The present application forms a stable chemical bond at the interface between starch and polybutylene succinate by introducing a polycarboxylic acid and a reaction regulator. The interface structure effectively improves the compatibility and promotes the transmission of stress between the two phases, thereby simultaneously improving the tensile strength and elongation at break of the material, and greatly reducing the water absorption and enhancing the dimensional stability due to the effective coating of the hydrophobic phase.

[0040] 2. The present application realizes efficient regulation of the interface reaction by designing a sequential feeding reaction extrusion process. The process modifies the pre-plasticization of starch and the subsequent interface coupling reaction in different sections of the extruder, ensuring the positioning of polycarboxylic acid as a chemical bridge, maximizing the reaction efficiency, avoiding ineffective side reactions, and obtaining a composite material with uniform structure and stable performance.

[0041] 3. The setting of the reaction regulator in the formula of the present application controls the pH environment of the reaction system, promotes the target esterification reaction, and successfully inhibits the hydrolytic degradation of starch and polybutylene succinate under acidic conditions, ensuring the obtainment of high mechanical properties of the material. The system is compatible with supercritical physical foaming or chemical foaming process, and has the potential for direct industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The Fourier transform infrared spectroscopy superimposed comparison chart of the raw material corn starch, the raw material PBS, example 1, and comparative example 1 of the present application. DETAILED DESCRIPTION

[0043] In order to further illustrate the present application, the present application is described in detail below in conjunction with examples, comparative examples and test examples, but the scope of protection of the present application is not limited by the following examples.

[0044] The sources and specifications of the main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically described are commercially available analytical pure or higher grade products.

[0045] Corn starch used in the present application is an industrial grade product, which is a natural high molecular polysaccharide polymerized from glucose units, containing amylose and amylopectin. It is treated by 80℃ air drying before use to reduce the moisture content to less than 1.0%.

[0046] Polybutylene succinate (PBS) used in the present application is an extrusion grade linear aliphatic polyester, and its chemical structure repeating unit is [-O-(CH2)4-O-CO-(CH2)2-CO-]n. The specific grade selected has a melt index (MFI) of 3.0-8.0 g / 10 min at 190℃ under a load of 2.16 kg, and a density of about 1.26 g / cm 3 , with a melting point range of 112-116℃.

[0047] Azodicarbonamide (ADC), CAS No. 123-77-3. When used as a chemical foaming agent in the present application, it is an industrial grade product, and its initial decomposition temperature in air ranges from 195 to 215℃.

[0048] Maleic anhydride grafted polybutylene succinate (PBS-g-MAH) used in the comparative examples of the present application is a commercially available commercial compatibilizer product, and its structure is a random graft copolymer with polybutylene succinate as the main chain and maleic anhydride functional groups bonded to the side chains through grafting reaction. The specific grade selected has a maleic anhydride grafting rate of about 1.0%.

[0049] Example 1:

[0050] The present embodiment provides a preparation method of a biobased modified starch degradable EPS composite foaming material, comprising the following steps:

[0051] (1) Raw material pretreatment: 60 parts by weight of corn starch and 40 parts by weight of polybutylene succinate (PBS) were placed in a 80℃ air drying oven for drying for 6 hours. The dried corn starch was mixed with 10 parts by weight of glycerol, 3 parts by weight of anhydrous citric acid and 0.3 parts by weight of disodium hydrogen phosphate in a high-speed mixer to obtain a reactive starch premix A.

[0052] (2) Sequential feeding reaction extrusion: a co-rotating twin-screw extruder with a length-diameter ratio of 40:1 was used, and the screw rotation speed was set to 150 rpm. The barrel zone and die temperatures were set to 90°C, 140°C, 140°C, 140°C, 170°C, 170°C, 170°C, 185°C, 185°C, 185°C, and the die temperature was 180°C. The premix A prepared in step (1) was added to the extruder through the main feeding port, and the dried PBS particles were added through the side feeding port located in the fifth zone.

[0053] (3) Foaming and molding: in the eighth zone of the extruder, supercritical carbon dioxide was injected into the melt through a high-pressure metering pump, with an injection amount of 5% of the total mass flow rate of the polymer and an injection pressure of 15 MPa. The melt was extruded through the die and foamed, and then shaped by air cooling to obtain the final composite foamed material plate.

[0054] Example 2:

[0055] The present embodiment provides a preparation method of a biobased modified starch degradable EPS composite foamed material, comprising the following steps:

[0056] (1) Raw material pretreatment: 70 parts by weight of corn starch and 30 parts by weight of polybutylene succinate (PBS) were placed in a blast drying oven at 80°C and dried for 6 hours. The dried corn starch was mixed with 15 parts by weight of glycerol, 4 parts by weight of anhydrous citric acid, and 0.4 parts by weight of disodium hydrogen phosphate in a high-speed mixer to obtain a reactive starch premix A.

[0057] (2) Sequential feeding reaction extrusion and foaming molding: except for the raw material ratio, the remaining preparation process, equipment parameters and operation process are exactly the same as those of Example 1.

[0058] Example 3:

[0059] The present embodiment provides a preparation method of a biobased modified starch degradable EPS composite foamed material, comprising the following steps:

[0060] (1) Raw material pretreatment: 50 parts by weight of corn starch and 50 parts by weight of polybutylene succinate (PBS) were placed in a blast drying oven at 80°C and dried for 6 hours. The dried corn starch was mixed with 8 parts by weight of glycerol, 2 parts by weight of anhydrous citric acid, and 0.2 parts by weight of disodium hydrogen phosphate in a high-speed mixer to obtain a reactive starch premix A.

[0061] (2) Sequential feeding reaction extrusion and foaming molding: except for the raw material ratio, the remaining preparation process, equipment parameters and operation process are exactly the same as those of Example 1.

[0062] Example 4:

[0063] The embodiment provides a preparation method of a biobased modified starch degradable EPS composite foamed material, and comprises the following steps:

[0064] (1) raw material pretreatment: the types and the ratio of the raw materials are completely same as those in example 1.

[0065] (2) sequential feeding reaction extrusion and foaming molding: the preparation process, the equipment and the temperature parameter setting are basically same as those in example 1, and the difference lies in that the screw rotation speed of the double-screw extruder is increased to 250 rpm. The remaining operation processes are completely same as those in example 1.

[0066] Example 5:

[0067] The embodiment provides a preparation method of a biobased modified starch degradable EPS composite foamed material, and comprises the following steps:

[0068] (1) raw material pretreatment: the types and the ratio of the raw materials are basically same as those in example 1. After drying, the PBS particles are uniformly premixed with 1.0 parts by weight of azodicarbonamide (ADC) foaming agent to obtain PBS premix B containing the foaming agent.

[0069] (2) sequential feeding reaction extrusion: the same equipment as that in example 1 is used, and the screw rotation speed is set to 150 rpm. The barrel zone and the die temperature are set to 90 DEG C, 140 DEG C, 140 DEG C, 140 DEG C, 170 DEG C, 170 DEG C, 170 DEG C, 205 DEG C, 205 DEG C, 205 DEG C, and the die temperature is 195 DEG C. The premix A prepared in example 1 is added through the main feeding port, and the PBS premix B containing the foaming agent prepared in the step is added through the side feeding port.

[0070] (3) foaming and molding: the melt is in the high-temperature zone of the rear section of the extruder, and the ADC is decomposed to generate gas. After the melt is extruded through the die, it is foamed and shaped through air cooling to obtain the final composite foamed material plate.

[0071] Comparative example 1:

[0072] Compared with example 1, the difference lies in that the citric acid and the disodium hydrogen phosphate are not added, and the composition is only composed of 60 parts by weight of corn starch, 40 parts by weight of PBS and 10 parts by weight of glycerol, aiming at simulating a conventional physical blending method. The remaining preparation process and operation process are same.

[0073] Comparative example 2:

[0074] Compared with example 1, the difference lies in that the citric acid and the disodium hydrogen phosphate are not added, but 5 parts by weight of maleic anhydride grafted polybutylene succinate (PBS-g-MAH) is additionally added as a compatilizer, and the amount of PBS is reduced to 35 parts by weight. The remaining preparation process and operation process are same.

[0075] Comparative Example 3:

[0076] The difference compared with Example 1 is that no sodium phosphate dibasic is added in its composition, only containing citric acid as the reactive adjuvant. The rest of the component ratio, preparation process and operation process are the same.

[0077] Comparative Example 4:

[0078] The difference compared with Example 1 is that no citric acid is added in its composition, only containing sodium phosphate dibasic. The rest of the component ratio, preparation process and operation process are the same.

[0079] Comparative Example 5:

[0080] The difference compared with Example 1 is that the preparation process adopts one-step feeding method, that is, all components (corn starch, PBS, glycerol, citric acid, sodium phosphate dibasic) are added into the extruder from the main feeding port after pretreatment. The rest of the component ratio and process parameters are the same.

[0081] Test Example 1:

[0082] The experimental steps are as follows:

[0083] (1) Sample preparation: the composite foaming material samples prepared by Example 1 and Comparative Example 1 were respectively taken, and dried in a vacuum oven at 60°C for 12 hours to completely remove the water. The dried samples and raw materials corn starch, raw material polybutylene succinate (PBS), raw material anhydrous citric acid were respectively ground into fine powder in an agate mortar.

[0084] (2) Tabletting: about 1-2 mg of sample powder and 150-200 mg of spectrally pure potassium bromide (KBr) powder were weighed and placed in an agate mortar for further mixing and grinding. The mixed powder was transferred to a tabletting mold, and a pressure of 10-15 MPa was applied on an oil press for 2 minutes to prepare uniform and transparent tablets for testing.

[0085] (3) Spectrum acquisition: a Fourier transform infrared spectrometer was used, and a blank KBr tablet was used as a background for subtraction. The prepared sample tablet was placed in the light path and scanned in the wave number range of 4000-400 cm -1 . The spectral resolution was set to 4 cm -1 , and the signal accumulation scanning number was 32 times. The infrared transmission spectrum of each sample was collected.

[0086] As shown in Figure 1 , it is the superimposed Fourier transform infrared spectrum of raw material corn starch, raw material PBS, comparative example 1 sample and example 1 sample. The raw material PBS is at 1716 cm -1shows its characteristic ester carbonyl (C=0) stretching vibration strong absorption peak. The infrared spectrum of the sample of Comparative Example 1 is basically a physical superposition of the spectra of corn starch and PBS, and only a strong absorption peak consistent with the raw material PBS exists at 1717 cm -1 , and no new absorption peak appears, which indicates that no chemical bond is formed between the starch and PBS molecules during the preparation of Comparative Example 1.

[0087] Compared with Comparative Example 1, the spectrum of Example 1 shows an essential change in the carbonyl region. In addition to the ester group absorption peak from the PBS matrix at 1718 cm -1 , a new shoulder peak appears at about 1738 cm -1 . This wave number position is higher than the absorption peak of the ester group of PBS itself, and is consistent with the characteristic of the newly generated ester carbonyl stretching vibration in a different chemical environment. The appearance of this new peak clearly indicates that a new ester bond structure is generated in the system during the preparation of Example 1. At the same time, the carboxyl O-H association broad peak (about 3000-2500 cm -1 ) from the citric acid raw material basically disappears in the spectrum of Example 1, which further proves that the carboxyl functional group of citric acid participates in the chemical reaction.

[0088] Comprehensive analysis, the new absorption peak at 1738 cm -1 is direct evidence of the in-situ chemical reaction in the method of the present application, and the formation of this new ester bond is attributed to the reaction path designed in the present application: the carboxyl group of citric acid first undergoes esterification with the hydroxyl group of starch, and then the remaining free carboxyl group of the citric acid unit grafted on the starch further undergoes esterification with the hydroxyl group at the end of the PBS chain. Finally, a covalent bond is formed between the starch and PBS two-phase interface with citric acid as the chemical bridge. Therefore, the analysis results of the Fourier transform infrared spectrum confirm that the in-situ esterification reaction between starch and PBS is successfully achieved by the sequential feeding reaction extrusion process in the method of the present application, a chemical bonded interface layer is formed, and the technical feasibility and chemical mechanism of the present application scheme are verified.

[0089] Test Example 2:

[0090] The experimental steps are as follows:

[0091] (1) Sample preparation: take the extrudate particles prepared in Example 1, Comparative Example 1 and Comparative Example 3, respectively, and place them in a vacuum oven at 80°C for 4 hours to dry the residual moisture inside the materials.

[0092] (2) Instrument and parameter setting: a standard melt flow rate instrument is used for testing according to the ASTM D1238 standard. The barrel temperature is set to 190°C and is kept constant. A standard load weight of 2.16 kg is selected.

[0093] (3) Test procedure: After the instrument temperature is stabilized, about 6-8 g of dry sample particles are added to the barrel, the piston is loaded and preheated for 5 minutes to ensure complete melting of the sample. After preheating, the weight is applied to the top of the piston, and the melt begins to be extruded from the standard die.

[0094] (4) Sampling and calculation: After the melt is extruded stably, the extruded strip is cut according to the fixed time interval (for example, 30 seconds), and the mass of each section is accurately weighed. Repeat sampling at least 3 times. The melt flow rate (MFI) is calculated in g / 10 min.

[0095] (5) Data processing: At least three independent complete tests are performed for each sample, and the average value and standard deviation of the MFI are calculated.

[0096] The experimental results are shown in Table 1:

[0097] Table 1 MFI test results of Example 1, Comparative Example 1 and Comparative Example 3:

[0098]

[0099] The melt flow rate is a key indicator of the melt viscosity of the polymer, and its value is inversely proportional to the melt viscosity.

[0100] Comparative Example 1 is a benchmark for pure physical blending, and its MFI value is 5.62 g / 10 min, which reflects the flow performance of the plasticized starch and PBS melt without chemical action, relying only on the van der Waals force and physical entanglement between molecular chains.

[0101] The MFI value of Example 1 is significantly reduced to 2.15 g / 10 min, which is only 38% of Comparative Example 1. The large decrease in melt flow rate directly corresponds to a significant increase in melt viscosity. The fundamental reason for this viscosity increase is that in the preparation process of Example 1, citric acid plays a chemical bridging role at the interface between starch and PBS, forming covalent bonds between the two phases through in-situ esterification reaction. The formation of these chemical bonding points is equivalent to slightly extending or cross-linking the system, effectively increasing the average molecular weight and entanglement network density of the polymer melt, thereby greatly hindering the relative slipping of molecular chains, which macroscopically manifests as a sharp increase in melt flow resistance.

[0102] The MFI value of Comparative Example 3 abnormally increased to 7.89 g / 10 min, which was much higher than that of physically blended Comparative Example 1. The result showed that, under the acidic condition lacking of pH adjustment of sodium phosphate dibasic, citric acid not only failed to effectively realize interface bonding during high-temperature extrusion, but also catalyzed the acidic hydrolytic degradation of PBS ester bond and starch glycosidic bond. The rupture of polymer chains led to a significant decrease in the average molecular weight of the system, and a sharp decrease in the melt viscosity and a sharp increase in the fluidity.

[0103] In summary, the method of the present application (Example 1) significantly improves the melt viscosity of the composite material through chemical reaction, which proves the success of interface bonding; secondly, simple physical blending (Comparative Example 1) cannot achieve this effect; finally, the pH regulating component (sodium phosphate dibasic) in the system is crucial for inhibiting polymer degradation and ensuring the realization of constructive interface modification (Comparative Example 3).

[0104] Test Example 3:

[0105] In this test example, the comprehensive performance of the materials of Examples 1-5 and Comparative Examples 1-5 was tested.

[0106] The experimental steps are as follows:

[0107] 1) Mechanical property test:

[0108] (1) Sample preparation: The foamed material plates prepared in each example and comparative example were heat pressed to prepare uniform-thickness bubble-free solid sheets. The sheets were conditioned in an environment of 23±2℃ and 50±5% relative humidity for 48 hours.

[0109] (2) Tensile property test: According to ASTM D638 standard, the conditioned sheets were cut into standard dumbbell-shaped sample bars. A universal material testing machine was used to test at a tensile rate of 50 mm / min. The tensile strength and elongation at break of the material were recorded and calculated.

[0110] (3) Flexural property test: According to ASTM D790 standard, the conditioned sheets were cut into standard rectangular sample bars. Three-point bending test was performed on a universal material testing machine with a span of 16 times the thickness and a loading rate of 2 mm / min. The flexural strength and flexural modulus of the material were recorded and calculated.

[0111] The mechanical property test of each formula took the average value of 5 effective samples.

[0112] 2) Foamed material physical property test:

[0113] (1) Apparent density test: According to ASTM D1622 standard, cut regular cubic samples (at least 3) from the foamed board, measure the length, width and height accurately with vernier caliper to calculate the volume, and weigh the mass with electronic balance. The apparent density is calculated by the ratio of mass and volume.

[0114] (2) Water absorption test: According to ASTM D570 standard, cut samples of about 50 mm x 50 mm x 10 mm, dry in a 60℃ oven to constant weight, and weigh the initial mass (m1). Immers the dried sample in distilled water at 23±2℃ for 24 hours. After taking out, quickly wipe the water on the surface of the sample with filter paper, and immediately weigh the final mass (m2). The water absorption is calculated by [(m2-m1) / m1]x100%.

[0115] (3) Dimensional stability test: Cut samples of about 100 mm x 20 mm x 10 mm, and adjust the state in 23±2℃, 50±5% RH environment for 24 hours. Then measure the length (L1) accurately with vernier caliper. Subsequently, place the sample in a constant temperature and humidity chamber at 40℃, 95% RH for 24 hours. Take out the sample and restore in standard environment for 4 hours, and then measure the length again (L2). The dimensional change rate is calculated by [(L2-L1) / L1]x100%.

[0116] Each physical property test takes the average value of 3 samples.

[0117] The experimental results are shown in Table 2:

[0118] Table 2 Comprehensive performance test results of each example and comparative example:

[0119]

[0120] The comprehensive performance data of this test example systematically verifies the superiority of the present technology and reveals the internal mechanism.

[0121] (1) Decisive role of interface modification:

[0122] The comparison between Example 1 and Comparative Example 1 demonstrates the effectiveness of the core technology of the present application. Comparative Example 1 is a physical blend of starch and PBS, which has poor interfacial compatibility between the two phases, resulting in ineffective stress transmission, which is manifested as very low tensile strength (5.1 MPa) and elongation at break (16%), and the material exhibits brittle fracture. At the same time, the exposed hydrophilic starch phase results in a water absorption rate as high as 12.34% and poor dimensional stability. Example 1, by in-situ reactive extrusion, forms chemical bonding at the interface, improving the compatibility. This results in a jump in tensile strength and elongation at break to 11.3 MPa and 87%, respectively, achieving a synergistic improvement in strength and toughness. The enhancement of interfacial bonding also effectively encapsulates the starch phase, resulting in a dramatic reduction in water absorption rate and dimensional change rate to 4.52% and 0.41%, respectively, significantly improving the water resistance and use reliability of the material.

[0123] (1) Comparison between the method of the present application and prior art:

[0124] Comparative Example 2 uses a traditional maleic anhydride grafting product as a compatibilizer, and its performance is better than that of physically blended Comparative Example 1, but it still lags behind Example 1. This shows that the interfacial layer formed in-situ by the present application is more effective in improving compatibility and overall performance than the approach of adding a general-purpose compatibilizer. Comparative Example 5 uses a one-step feeding method, and its performance is inferior to that of Example 1, demonstrating the necessity of the sequential feeding process designed by the present application. This process ensures the pre-plasticization of starch and the preliminary reaction with citric acid, creating optimal conditions for subsequent interfacial bonding with PBS, while the one-step method results in insufficient reaction.

[0125] (3) Necessity of each component of the formulation:

[0126] The results of Comparative Example 3 (without disodium hydrogen phosphate) and Comparative Example 4 (without citric acid) confirm the scientificity of the formulation design. The performance of Comparative Example 4 is basically the same as that of Comparative Example 1, indicating that the absence of citric acid, a key reactant, prevents the formation of interfacial bonding in the system. The performance of Comparative Example 3 is even worse than that of physical blending, because of the absence of a pH regulator, and the acidic environment catalyzes the degradation of the polymer at high temperatures, which is fully consistent with the MFI data conclusion of Test Example 2.

[0127] (4) Adaptability of the formulation and process:

[0128] The results of Examples 2 and 3 show that the method of the present application is suitable for systems with different starch / PBS ratios, and by adjusting the ratio, the stiffness and toughness properties (flexural modulus and elongation at break) and water resistance of the material can be effectively controlled. The performance of Example 4 (increasing the screw speed) and Example 5 (using a chemical blowing agent) is at the same level as Example 1, which confirms that the process of the present application has good stability and wide applicability, and whether the process parameters are adjusted or the blowing system is changed, the core interfacial modification mechanism can still play a stable role.

[0129] In summary, the macroscopic mechanical properties of the material and the test results of the foaming physical properties prove that the chemical bonding interface formed by the in-situ reactive extrusion of the present application is the key to realizing high-performance bio-based composites, and the formulation and process design of the present application is complete, scientific, and has good industrial application potential.

[0130] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A bio-based modified starch-degradable EPS composite foaming material, characterized in that, Made from the following ingredients in parts by weight: Starch: 50-70 parts by weight; Polybutylene succinate: 30-50 parts by weight; Plasticizer: 8-15 parts by weight; Polycarboxylic acids: 2-4 parts by weight; Reaction regulator: 0.2–0.4 parts by weight; and foaming agent; The plasticizer is glycerol; the polycarboxylic acid is citric acid; the reaction regulator is disodium hydrogen phosphate; The preparation method of the bio-based modified starch-degradable EPS composite foaming material includes the following steps: a) Starch, plasticizer, polycarboxylic acid and reaction regulator are premixed to obtain reactive starch premix; b) The reactive starch premix is ​​added through the main feed port of a twin-screw extruder, and polybutylene succinate is added through the side feed port of the extruder for reactive extrusion; c) Introduce a foaming agent into the extruder to foam the melt, and then extrude it through a die to form the final product.

2. The bio-based modified starch-degradable EPS composite foaming material according to claim 1, characterized in that, Made from the following ingredients in parts by weight: Starch: 60 parts by weight; Polybutylene succinate: 40 parts by weight; Plasticizer: 10 parts by weight; Polycarboxylic acids: 3 parts by weight; Reaction regulator: 0.3 parts by weight.

3. The bio-based modified starch-degradable EPS composite foaming material according to claim 1, characterized in that, The foaming agent is supercritical carbon dioxide or azodicarbonamide.

4. The bio-based modified starch-degradable EPS composite foaming material according to claim 1, characterized in that, Prior to step a), the process further includes a step of drying the starch and polybutylene succinate.

5. The bio-based modified starch-degradable EPS composite foaming material according to claim 1, characterized in that, The temperature of the reaction extrusion described in step b) is 140–170 °C.

6. The bio-based modified starch-degradable EPS composite foaming material according to claim 1, characterized in that, The screw speed of the extruder described in step b) is 150-250 rpm.

7. The bio-based modified starch-degradable EPS composite foaming material according to claim 1, characterized in that, The specific implementation of step c) is as follows: supercritical carbon dioxide is injected into the melt in the rear section of the extruder; or, in step b), the chemical foaming agent is added together with the polybutylene succinate through the side feed port and decomposed and foamed by heating in the rear section of the extruder.

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