Degradable thermal polymerization resin and preparation method thereof

Abstract

The invention relates to the technical field of biodegradable polyester, in particular to degradable thermal polymerization resin and a preparation method thereof. The degradable thermal polymerization resin prepared by the invention overcomes the problems of poor environmental protection property and poor heat resistance of a mulching film. Carboxylated cross-linked starch and silanized nano cellulose whiskers are adopted as a nucleating system, and segmented temperature control polymerization, block copolymer induced crystallization and solid phase polycondensation post-treatment are combined, so that the heat resistance of the resin is improved; through interface covalent cross-linking, nanometer enhancement, flexible chain segment adjustment and cross-linked network construction, the mechanical property is optimized, a biodegradable chain segment and a flexible chain segment are introduced, the crystallinity is controlled, and the resin is endowed with good biodegradability; the degradable thermal polymerization resin has good heat resistance, mechanical properties and biodegradability.

Description

Technical Field

[0001] The invention relates to the technical field of biodegradable polyester, in particular to a degradable thermopolymer resin and a preparation method thereof. Background Art

[0002] With the rapid development of modern agriculture, mulching technology has become widely used in agricultural production worldwide due to its significant advantages, such as increasing warmth and moisture retention, resisting drought and suppressing weeds. It has become an important means of increasing crop yields. Polyester-based biodegradable mulches, such as polylactic acid and polycaprolactone, are green alternatives to traditional mulches. Made from bio-based raw materials or chemically synthesized, they theoretically degrade in the natural environment, reducing soil pollution. However, tens of millions of tons of traditional polyethylene mulches are still produced and used annually worldwide. These mulches are made from petroleum-based polymers with a stable chemical structure, making them difficult to degrade in soil. The large amount of discarded mulch left in farmland not only causes severe visual pollution but also triggers a series of ecological problems. Furthermore, the polyethylene used in mulch is difficult to degrade. Currently, mulch residue pollution has become a major environmental challenge hindering the sustainable development of agriculture.

[0003] To address this issue, researchers are committed to developing biodegradable polymer materials. While research progress has been made in recent years on biodegradable materials such as polylactic acid and polycaprolactone, their practical applications remain limited. Performance-wise, biodegradable materials have poor thermal stability and are prone to degradation during high-temperature processing, such as injection molding and extrusion. This leads to a decrease in the material's molecular weight and reduced mechanical properties, such as strength and toughness, making them unsuitable for demanding applications. Furthermore, the production of existing biodegradable materials often requires complex processes and expensive raw materials, making their production costs far higher than those of traditional plastics. This significantly limits their widespread application. Furthermore, some biodegradable materials exhibit demanding degradation conditions, requiring specific temperature, humidity, and microbial environments. Their slow degradation rate in natural environments makes it difficult to achieve environmental protection goals. Therefore, developing a biodegradable thermoplastic resin and its preparation method with excellent thermal stability, superior mechanical properties, outstanding degradation performance, and low production cost is of great significance for promoting the green and sustainable development of the plastics industry.

[0004] Therefore, a degradable thermopolymer resin and a preparation method thereof are proposed. Summary of the Invention

[0005] The present invention aims to provide a degradable thermopolymer resin and a method for preparing the same. By employing carboxylated cross-linked starch and silanized nanocellulose whiskers as a nucleation system, combined with segmented temperature-controlled polymerization, block copolymer-induced crystallization, and solid-phase polycondensation post-treatment, the resin's heat resistance is enhanced. Interfacial covalent cross-linking, nano-reinforcement, flexible segment regulation, and cross-linked network construction optimize mechanical properties. The introduction of biodegradable and flexible segments controls crystallinity, conferring excellent biodegradability. The degradable thermopolymer resin combines excellent heat resistance, mechanical properties, and biodegradability.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a degradable thermopolymer resin, and the preparation method is as follows:

[0008] After evacuating the reactor and introducing nitrogen for protection, L-lactide and stannous octoate were added, and the temperature was increased in one stage to carry out a lactide ring-opening polymerization reaction; after adding bio-based terephthalic acid, 2,5-furandicarboxylic acid, butanediol, and tetrabutyl titanate, the temperature was increased in two stages and the nitrogen flow rate was reduced to carry out an ester exchange coupling reaction; after adding itaconic acid, polycaprolactone polyol, and silanized nanocellulose whiskers, the temperature was increased in three stages to carry out condensation and cross-linking reactions, the temperature was lowered, the vacuum degree was reduced, and carboxylated cross-linked starch and triethyl citrate were added to obtain a degradable thermopolymer resin precursor after the reaction; the molecular weight of the polycaprolactone polyol was 530 g / mol, and the hydroxyl value was 215 KOH-mg / g.

[0009] The hydroxy-terminated polylactic acid obtained by the ring-opening polymerization of lactide has an Mn of 6000 and a viscosity of 0.2 Pa·s at 25°C. By reducing the nitrogen flow rate and rationally controlling the loss of raw materials such as butanediol, the ratios of the various components in the transesterification reaction, such as polylactic acid segments, terephthalic acid, furandicarboxylic acid, and butanediol, are ensured to meet the design requirements. This results in a more uniform oligomer intermediate, laying the foundation for the formation of high-molecular-weight polymers in the subsequent polycondensation stage, ultimately improving the resin's molecular weight and chain regularity, and ultimately ensuring the ultimate performance of the biodegradable thermoplastic resin.

[0010] After mixing a degradable thermopolymer resin precursor with a block copolymer, epoxy castor oil and carboxylated cross-linked starch are added, followed by melt extrusion in a twin-screw extruder, slicing, and solid-phase polycondensation post-treatment to obtain a degradable thermopolymer resin. By adding the block copolymer and performing subsequent solid-phase polycondensation post-treatment steps, GPC testing reduces the molecular weight distribution to 180,000-220,000 g / mol, and XRD detection shows a crystallinity of 58%.

[0011] More preferably, the amount of the block copolymer added does not exceed 5% of the total mixture mass, as exceeding this value results in a sharp increase in melt viscosity.

[0012] Preferably, the carboxylated cross-linked starch is obtained by reacting corn starch with sodium trimetaphosphate and citric acid; the degree of carboxyl substitution is 0.04 mmol / g; and the average particle size is 50-100 nm.

[0013] Preferably, the silanized nanocellulose whiskers are obtained by surface-treating nanocellulose whiskers with 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0014] A preferred method for preparing silanized nanocellulose whiskers is as follows: 3-(2,3-epoxypropoxy)propyltrimethoxysilane is added dropwise to an ethanol-water solution, stirred, the pH adjusted, and hydrolyzed to obtain a pre-hydrolyzed solution; nanocellulose whiskers are dispersed in deionized water, sonicated, heated, and the pre-hydrolyzed solution added dropwise. Dibutyltin dilaurate is added, and after reaction, centrifugation and freeze-drying are performed to obtain silanized nanocellulose whiskers. TGA analysis shows that the grafting rate of 3-(2,3-epoxypropoxy)propyltrimethoxysilane is 14.8%.

[0015] More preferably, the nanocellulose whiskers have an average diameter of 10-30 nm and an average length of 100-300 nm.

[0016] Preferably, the difference between the preparation method of the block copolymer and the degradable thermopolymer resin precursor is that the block copolymer does not contain silanized nanocellulose whiskers.

[0017] Preferably, the solid phase polycondensation post-treatment is performed using nitrogen gas under heating conditions.

[0018] The present invention also provides a degradable thermal polyester resin. The raw materials for preparing the degradable thermal polyester resin include L-lactide, terephthalic acid, 2,5-furandicarboxylic acid, butanediol, itaconic acid, polycaprolactone polyol and carboxylated cross-linked starch.

[0019] Preferably, the amount of L-lactide is 129.7-155.6 g, the amount of terephthalic acid is 425.5-558.5 g, the amount of 2,5-furandicarboxylic acid is 168.0-224.5 g, the amount of butanediol is 170.0-202.5 g, the amount of itaconic acid is 13.0-19.5 g, and the amount of polycaprolactone polyol is 56.5-75.0 g.

[0020] In addition, during the preparation of the degradable thermal polyester resin, a degradable hindered phenol antioxidant may be added in an amount of 0.15 wt %. A degradable hindered amine light stabilizer may also be added in an amount of 0.20 wt %.

[0021] Degradable thermal polyester resin

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. By using carboxylated cross-linked starch as the cross-linking raw material and silanized nanocellulose whiskers as the nucleation system, combined with the segmented temperature control polymerization process and block copolymer induced crystallization technology, and after solid-phase polycondensation post-treatment, the heat resistance of the degradable thermopolymer resin is significantly improved; carboxylated cross-linked starch and silanized nanocellulose whiskers synergistically promote polyester crystallization, block copolymers induce the formation of a regular crystal structure, segmented temperature control avoids high-temperature degradation, solid-phase polycondensation increases molecular weight and crystallinity, restricts the movement of resin molecular chains, and significantly increases the glass transition temperature. It has good heat deformation resistance and is suitable for use in scenarios where ground films need to withstand a certain temperature.

[0024] 2. By means of the interfacial covalent cross-linking of carboxylated cross-linked starch, the nano-enhancement effect of silanized nanocellulose whiskers, the flexible segment adjustment of polycaprolactone polyol and the cross-linking network construction of itaconic acid, combined with the block copolymer grain refinement process, the present invention effectively optimizes the mechanical properties of the degradable thermopolymer resin; the carboxylated cross-linked starch forms a strong interfacial effect with the polyester matrix, the silanized nanocellulose whiskers are evenly dispersed to enhance the modulus, the polycaprolactone polyol improves the toughness, the itaconic acid cross-linking improves the strength, and the block copolymer refines the grains to reduce stress concentration, so that the resin has both high elongation at break and good puncture resistance, meeting the mechanical requirements of mulch film applications.

[0025] 3. By introducing biodegradable L-lactide chain segments, bio-based carboxylated cross-linked starch and polycaprolactone polyol flexible chain segments, combined with silanized nanocellulose whiskers to increase the specific surface area and control the crystallinity to avoid excessive cross-linking, the degradable thermopolymer resin is given good biodegradability; the L-lactide ester bond and starch glycosidic bond are easily enzymatically hydrolyzed by microorganisms, the polycaprolactone flexible chain segments increase the accessibility of the molecular chain, and the silanized nanocellulose whiskers provide more enzyme action sites, balancing the crystallinity mechanics and degradation rate, so that the resin can be gradually decomposed by microorganisms in the soil, meeting environmental protection requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a flow chart of the method for preparing the degradable thermopolymer resin. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] See also Figure 1 The present invention provides a degradable thermoplastic resin and a preparation method thereof, and the technical solution is as follows:

[0029] Example 1

[0030] Preparation of carboxylated cross-linked starch: 80 g corn starch was dissolved in 640 mL deionized water, stirred at 40° C. for 30 min until uniformly dispersed to form a uniform suspension, 5 g sodium trimetaphosphate was added, the pH was adjusted to 8.0 with 10% NaOH solution, and ultrasonic treatment was performed at 20° C. for 30 min with a treatment power of 150 W; 3 g citric acid was added, and the mixture was heated at 58° C. for 2 h; the mixture was washed three times with 70% ethanol, frozen at -20° C. for 1 h, and then freeze-dried and pulverized through a 200-mesh sieve to obtain the carboxylated cross-linked starch.

[0031] Preparation of silanized nanocellulose whiskers: 4 g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane was slowly added dropwise to 50 mL of ethanol / water solution (ethanol: water = 9:1 v / v), stirred for 10 min, adjusted to pH 4.5 with 0.1 M acetic acid solution, and stirred at room temperature for 60 min to ensure that the trimethoxysilyl group was completely hydrolyzed into silanol group; 15 g of nanocellulose whiskers was added to 100 mL of deionized water and ultrasonically dispersed at a power of 200 W for 30 min; adjusted to pH 9 with 0.1 M NaOH, slowly heated to 60 ° C, and added dropwise To the pre-hydrolyzed 3-(2,3-epoxypropoxy)propyltrimethoxysilane solution, 0.5 wt% dibutyltin dilaurate was added and the mixture was mechanically stirred at 200 rpm for 4 h. After the reaction was completed, the mixture was cooled to room temperature and the pH was adjusted to neutral with 0.1 M HCl. The precipitate was collected by centrifugation at 8000 rpm for 20 min, and the unreacted silane in the supernatant was discarded. The mixture was washed three times with an ethanol / water (1:1) mixed solvent to remove the physically adsorbed silane. The mixture was freeze-dried at -50 ° C and 10 Pa for 48 h to avoid CNC agglomeration, thereby preparing silanized nanocellulose whiskers.

[0032] Preparation of biodegradable thermoplastic resin precursor: During the lactide ring-opening stage, the vacuum degree of the reactor was adjusted to <10Pa, dried at 120°C for 4 hours to remove moisture and impurities, and high-purity 99.999% nitrogen was introduced at a flow rate of 0.5L / min; 129.7g L-lactide and 0.019g stannous octoate were added to the reactor, and the temperature was raised to 140°C at a rate of 5°C / min. The reaction was stirred for 3 hours under nitrogen protection and 200rpm to obtain terminal hydroxyl polylactic acid; 498.4g bio-based terephthalic acid, 224.3g 2,5-furandicarboxylic acid, 184.0g butanediol and 0.75g tetrabutyl titanate were added during the ester exchange coupling stage, and the temperature was raised to 190°C at a rate of 5°C / min. , the nitrogen flow rate was reduced to 0.2 L / min, and the acid value dropped from the initial 400 mgKOH / g to below 20 mgKOH / g to stop the reaction; 14.5 g itaconic acid, 60.0 g polycaprolactone polyol and 15 g silanized nanocellulose whiskers were added in the polycondensation and cross-linking stage, and the temperature was maintained at 220 ° C for 1 hour to make the acid value <10 mgKOH / g, and the temperature was raised to 270 ° C, and the vacuum degree was gradually reduced to 40 Pa. The polycondensation time was 5 hours to an intrinsic viscosity of 1.2 dL / g (determined by Ubbelohde viscometer), and the temperature was lowered to 150 ° C, 60.0 g carboxylated cross-linked starch and 3 g triethyl citrate were added, and the vacuum reaction was carried out for 1 hour to cross-link the carboxylated cross-linked starch; finally, a degradable thermopolymer resin precursor was prepared;

[0033] Mix 50g of block copolymer with 961.5g of biodegradable thermoplastic resin precursor; add 10.5g of epoxy castor oil and 10g of carboxylated cross-linked starch; set the first block copolymer melting section at 180°C, where the block copolymer first melts to form nuclei; the second raw material blending section at 190°C, where the new material is mixed with the block copolymer melt; the third cross-linking section at 220°C, where epoxy castor oil promotes interfacial cross-linking, the screw speed is 200rpm, and the residence time in each zone is 3min; then slice the slices, with a sheet thickness of 0.02mm.

[0034] Solid phase polycondensation (SSP) post-treatment: the polyester masterbatch after melt extrusion is transferred to a single-screw film blowing machine via a conveyor belt, and blown into film after melting, with a blow-up ratio of 3.5:1, a traction ratio of 15:1, air ring cooling, and traction at a traction speed of 20 m / min, and then curled under a tension of 5 N; under the protection of nitrogen flow, it is heated at 190 ° C for 12 h, and the nitrogen flow rate is 100 mL / min·g polymer to prepare a biodegradable thermoplastic resin with a thickness of 0.02 mm.

[0035] Examples 2-5

[0036] Unlike Example 1, the following preparation conditions were changed, as shown in Table 1. The primary heating temperature in Table 1-1 refers to the temperature after the addition of the raw material L-lactide; the secondary heating temperature in Table 1-2 refers to the temperature after the addition of bio-based terephthalic acid, 2,5-furandicarboxylic acid, and butanediol.

[0037] Table 1-1 Preparation method of degradable thermopolymer resin

[0038]

[0039] Table 1-2 Preparation parameters of degradable thermopolymer resin precursor

[0040]

[0041] Table 1-3 Degradable thermopolymer resin precursor and degradable thermopolymer resin preparation parameters

[0042]

[0043] Except for the following adjustments, the other conditions in the comparative example are the same as those in Example 2.

[0044] In Comparative Example 1, corn starch was used to replace the carboxylated cross-linked starch, and the amount used remained unchanged.

[0045] Comparative Example 2 uses nanocellulose whiskers to replace silanized nanocellulose whiskers.

[0046] In Comparative Example 3, the temperature during the lactide ring-opening stage was set to 160°C.

[0047] In Comparative Example 4, L-lactide was not used as a raw material for the lactide ring-opening process. Instead, L-lactide was directly replaced with polylactic acid (CAS 26023-30-3, 531162, Sigma-Aldrich, average Mw 75000-120000).

[0048] Comparative Example 5: No 2,5-furandicarboxylic acid was added during the preparation of the degradable thermopolymer resin precursor and the degradable thermopolymer resin.

[0049] In Comparative Example 6, no butanediol was added during the preparation of the degradable thermopolymer resin precursor and the degradable thermopolymer resin.

[0050] In Comparative Example 7, itaconic acid and polycaprolactone polyol were not added.

[0051] In Comparative Example 8, no silanized nanocellulose whiskers were added.

[0052] In Comparative Example 9, the temperature in the polycondensation and cross-linking stage was kept consistent with the temperature in the ester exchange coupling stage, and no heating process was performed. The reaction temperature was 190°C.

[0053] The reaction temperature after adding the carboxylated cross-linked starch in Comparative Example 10 remained consistent with the temperature in the polycondensation and cross-linking stages, which was still 270°C.

[0054] In Comparative Example 11, triethyl citrate was not added.

[0055] In Comparative Example 12, the added amount of the block copolymer was 100 g.

[0056] In Comparative Example 13, the added amount of the block copolymer was 30 g.

[0057] In Comparative Example 14, no block copolymer was added.

[0058] Comparative Example 15 did not undergo solid phase polycondensation (SSP) post-treatment.

[0059] Experimental Example 1

[0060] The degradable thermoplastic resins prepared in Examples 1-5 and Comparative Examples 2-3, Comparative Examples 5-9, and Comparative Examples 12-15 were tested for heat resistance by differential scanning calorimetry (DSC). The temperature was raised from -20°C to 250°C at a rate of 10°C / min, and then lowered to a low temperature of -20°C at a rate of 10°C / min to allow the sample to fully crystallize. A second temperature scan was then performed, and the final glass transition temperature Tg was determined based on the DSC curve of the test. The final test results are shown in Table 2.

[0061] Table 2 Heat resistance test

[0062]

[0063]

[0064] In Examples 1-5, the Tg value is high by adjusting the preparation methods of carboxylated cross-linked starch, silanized nanocellulose whiskers, degradable thermopolymer resin precursor and the final product. In Comparative Example 2, by using non-silanized nanocellulose whiskers as a crystal nucleating agent, the compatibility of the crystal nucleating agent with the system becomes poor, the crystallinity of the degradable thermopolymer resin is reduced, and the movement of the polymer chain segments cannot be effectively restricted, resulting in poor Tg enhancement effect; in Comparative Example 3, the temperature of the lactide ring-opening stage is higher than that of Example 2. The lactide ring-opening polymerization reaction rate is faster at higher temperatures, but too high a temperature also leads to side reactions or degradation of polylactic acid, affecting the molecular weight and structural integrity of the final polymer, and reducing heat resistance; in Comparative Example 5, 2,5-furandicarboxylic acid is not added, and the cross-linking of the rigid structure is missing, resulting in reduced heat resistance; in Comparative Example 6, butanediol is not added, and a complete polyester skeleton cannot be formed, resulting in reduced heat resistance of the degradable thermopolymer resin; in Comparative Example 7, polycaprolactone polyol introduces a flexible segment, which is used to improve toughness. Removing the flexible segment makes the overall flexibility of the polymer segment The reduced properties and the absence of itaconic acid-induced crosslinking loss ultimately led to a significant decrease in the glass transition temperature. The reduced Tg value of Comparative Example 8 indicates that the added silanized nanocellulose whisker nanofiller nucleating agent can enhance the mechanical properties of the polymer matrix and help increase the Tg by restricting segment motion. The copolymerization temperature of Comparative Example 9 is too low, and the molecular weight will not reach the expected high molecular weight, resulting in a decrease in heat resistance. In Comparative Examples 12-14, the addition amount of block copolymer is too high or too low, or no block copolymer is added, and the Tg values ​​do not change much compared with Example 2. The main function of the block copolymer is to accelerate crystallization and control the crystal form, and it has little effect on the Tg of the amorphous region of the polymer. In Comparative Example 15, the SSP post-treatment step is not performed, and the Tg value is significantly reduced. This is because this step is a key step to significantly increase the molecular weight and crystallinity. The absence of this step results in the Tg value remaining at a lower level after melt polycondensation. The segment motion of low-molecular-weight polymers is easier, so the Tg is significantly reduced.

[0065] The invention prepares carboxylated cross-linked starch, performs silanization treatment on nanocellulose whiskers, and then uses L-lactide, terephthalic acid, 2,5-furandicarboxylic acid, butanediol, itaconic acid and polycaprolactone polyol as raw materials to prepare a degradable thermopolymer resin precursor. The crystals and the precursor are mixed and reacted to prepare the degradable thermopolymer resin. By adjusting the preparation process conditions, the degradable thermopolymer resin has a higher glass transition temperature and improved heat resistance.

[0066] Experimental Example 2

[0067] The mechanical properties of the degradable thermoplastic resins prepared in Examples 1-5 and Comparative Examples 1-15 were tested. The specific test methods are as follows: the elongation at break was measured with reference to ASTM D882, Standard Test Method for Tensile Properties of Plastic Films. A dumbbell-shaped specimen was prepared and tested at a constant tensile rate of 50 mm / min until the sample broke, and the elongation at break was recorded. The tear strength was measured with reference to ASTM D1004, Standard Test Method for Tear Strength of Plastic Film and Sheet. A right-angle tear specimen was prepared and the sample was torn at a constant speed of 50 mm / min. The force required for tearing was recorded and the tear strength was calculated. The final test results are shown in Table 3.

[0068] Table 3 Mechanical properties test results

[0069]

[0070] The degradable thermoplastic resin prepared by the present invention is directly used in ground films and has good mechanical properties. The degradable thermoplastic resins of Examples 1-5 have good elongation at break and tear strength. Comparative Example 1 uses corn starch that has not been carboxylated and cross-linked. This unmodified starch has extremely poor compatibility with the polyester matrix, is difficult to disperse evenly, and cannot form an effective cross-linked network or serve as an effective reinforcement. As a larger particle defect, thereby reducing the toughness and strength of the material; Comparative Example 2 uses an unmodified nucleating agent, the crystallization performance decreases, and the mechanical strength decreases; Comparative Example 3 The temperature in the lactide ring-opening stage is too high, resulting in side reactions or degradation of polylactic acid, affecting the molecular weight and structural integrity of the final polymer, thereby reducing heat resistance, and the reduction in molecular weight has a direct negative impact on elongation at break and tear strength; Comparative Example 4 Direct substitution results in a huge difference in molecular weight and terminal groups from the in-situ ring-opening polymerized polylactic acid, and cannot effectively participate in subsequent ester exchange and polycondensation, making it difficult to form an effective degradable thermoplastic resin, unable to form a film or shape, and having reduced mechanical properties; Comparative Example 5 lacks 2,5-furandicarboxylic acid, the rigid structure The structure leads to increased molecular chain mobility, thereby reducing the strength and tear strength of the material; the lack of butanediol in comparative example 6 will lead to the loss of the main skeleton of the polyester, and low molecular weight oligomers cannot be formed, and the mechanical properties are reduced; in comparative example 7, itaconic acid is a cross-linking agent, and its absence causes the material to lose the cross-linking network, and the strength and solvent resistance are reduced. The polycaprolactone polyol is a flexible chain segment, and its absence causes the material to have serious insufficient toughness. Therefore, the material is very brittle, and the elongation at break and tear strength are significantly reduced; the lack of nucleating agent in comparative example 8 leads to reduced mechanical properties of the material; in comparative example 9, the condensation temperature is reduced. High-temperature condensation is the key to increasing the molecular weight and forming a three-dimensional network. Too low a temperature causes the molecular weight to fail to increase effectively, and the cross-linking is also insufficient. The chain segments of low molecular weight polymers move more easily, their heat resistance decreases, and their mechanical properties decrease significantly; in Comparative Example 10, the reaction temperature after adding carboxylated cross-linked starch is consistent with the temperature of the polycondensation and cross-linking stages, both of which are 270°C, resulting in excessive cross-linking or degradation of the starch in the polymer melt, forming a more brittle area and initiating degradation of the polymer itself, seriously affecting the toughness of the material, and significantly reducing the elongation at break and tear strength; Comparative Example 11 does not add triethyl citrate, which acts as a thermal stabilizer to protect the starch hydroxyl groups through hydrogen bonding and inhibit the decarboxylation reaction. The absence of triethyl citrate causes the performance of the final degradable thermopolymer resin to decrease; in Comparative Examples 12 and 13, the amount of block copolymer added is too high or too low, resulting in decreased mechanical properties of the material. Too high an amount causes uneven dispersion of the block copolymer in the polymer, forming agglomerates, thereby introducing defects, while too low an amount causes decreased crystallization effect; in Comparative Example 14, no block copolymer is added, and the mechanical properties of the degradable thermopolymer resin decrease; Comparative Example 15 lacks SSP post-treatment, the crystallization effect is significantly reduced, and the mechanical properties are reduced to the lowest.

[0071] Experimental Example 3

[0072] Examples 1-5 and Comparative Examples 1, 4, 7, 10-11 and 15 were tested for degradation performance, and positive and negative control group test materials were set up, wherein the negative control group was a traditional polyethylene (PE) mulch film, and the positive control group was a polyhydroxybutyrate (PHB) mulch film; the specific test method was as follows: the degradable thermoplastic resin was cut into 5 cm × 5 cm, with a thickness of 0.02 mm, and evenly buried in the soil to a depth of 8 cm, ensuring that there was sufficient spacing between the samples to avoid mutual influence, the processing temperature was 30 ° C, and deionized water was sprayed regularly to keep the soil moist but not waterlogged, and at the same time, the soil had a certain degree of air permeability. The samples were taken out after 6 months of testing, and the degradation rate was calculated, degradation rate (%) = (W0-W1) / W0×100%, wherein W0 is the initial mass of the mulch film, and W1 is the mass after the test; the final test results are shown in Table 4.

[0073] Table 4 Degradation performance test results

[0074] Degradation rate (%) Example 1 72.3 Example 2 68.5 Example 3 70.0 Example 4 75.1 Example 5 73.6 Comparative Example 1 82.0 Comparative Example 4 64.9 Comparative Example 7 60.4 Comparative Example 10 88.6 Comparative Example 11 78.5 Comparative Example 15 90.2 Positive control group 95.3 Negative control group 3.0

[0075] The degradable thermoplastic resin prepared by the present invention is used in ground film. It not only has excellent mechanical properties and heat resistance, but also has good biodegradability, meeting environmental requirements. A positive control group using PHB, a naturally degradable polyester, achieved nearly complete degradation; a negative control group showed virtually no degradation. In Comparative Example 1, ordinary corn starch has poor compatibility with the resin, is easily swollen by water and is directly decomposed by microorganisms, has a faster degradation rate but a loose structure, and an increased degradation rate; in Comparative Example 4, the degradation rate is lower than that of the embodiment, and polylactic acid is directly used to replace the lactide ring opening, the copolymer structure is uneven, the molecular weight distribution is wide, the degradation rate is inconsistent and the overall degradation rate is slow; in Comparative Example 7, the itaconic acid easily degradable flexible chain segment and itaconic acid cross-linking point are missing, the resin structure is more stable, mainly composed of rigid segments, and the degradation rate is significantly reduced; the carboxylated cross-linked starch in Comparative Example 10 is partially decomposed at a high temperature of 270°C, producing small molecular fragments, accelerating microbial erosion, the degradation rate is the fastest, but the material becomes brittle and disintegrates prematurely, and the degradation rate is significantly increased; in Comparative Example 11, the triethyl citrate starch stabilizer is missing, the starch hydroxyl group is easily decarboxylated, hydrolysis and enzymatic hydrolysis are accelerated, and the degradation rate is higher than that of the embodiment; in Comparative Example 15, no SSP post-treatment is performed, the molecular weight is low and it is more easily decomposed by microorganisms, the degradation rate is the fastest, but the mechanical properties are poor, and premature breakage occurs.

[0076] In summary, the present invention optimizes the preparation method of the degradable thermopolymer resin and uses it in ground film to make the ground film have good heat resistance, mechanical properties and good biodegradability.

[0077] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a degradable thermoplastic resin, characterized in that: The preparation method is as follows: After evacuating the reactor and introducing nitrogen for protection, L-lactide and stannous octoate are added, and the temperature is increased in one stage to carry out a lactide ring-opening polymerization reaction; after adding bio-based terephthalic acid, 2,5-furandicarboxylic acid, butanediol, and tetrabutyl titanate, the temperature is increased in two stages and the nitrogen flow rate is reduced to carry out an ester exchange coupling reaction; after adding itaconic acid, polycaprolactone polyol, and silanized nanocellulose whiskers, the temperature is increased in three stages to carry out a condensation polymerization and cross-linking reaction, the temperature is lowered, the vacuum degree is reduced, and carboxylated cross-linked starch and triethyl citrate are added to obtain a degradable thermopolymer resin precursor after the reaction; The degradable thermopolymer resin precursor is mixed with the block copolymer, and epoxy castor oil and the carboxylated cross-linked starch are added thereto, followed by melt extrusion in a twin-screw extruder, slicing, and solid phase polycondensation post-treatment to obtain the degradable thermopolymer resin.

2. The method for preparing a degradable thermoplastic resin according to claim 1, wherein: The carboxylated cross-linked starch is obtained by reacting corn starch with sodium trimetaphosphate and citric acid.

3. The method for preparing a degradable thermopolymer resin according to claim 1, wherein: The silanized nanocellulose whiskers are obtained by surface-treating nanocellulose whiskers with 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

4. The method for preparing a degradable thermopolymer resin according to claim 3, wherein: The preparation method of the silanized nanocellulose whiskers is as follows: the 3-(2,3-epoxypropoxy)propyltrimethoxysilane is added dropwise to an ethanol aqueous solution, the pH is adjusted after stirring, and a pre-hydrolysis solution is obtained after hydrolysis; the nanocellulose whiskers are dispersed in deionized water, the water is ultrasonically heated, the pre-hydrolysis solution is added dropwise, dibutyltin dilaurate is added, and after reaction, the silanized nanocellulose whiskers are centrifuged and freeze-dried to obtain the silanized nanocellulose whiskers.

5. The method for preparing a degradable thermopolymer resin according to claim 1, wherein: The difference between the block copolymer and the preparation method of the degradable thermopolymer resin precursor is that the block copolymer does not contain the silanized nanocellulose whiskers.

6. The method for preparing a degradable thermopolymer resin according to claim 1, wherein: The solid phase polycondensation post-treatment is performed using nitrogen gas under heating conditions.

7. The method for preparing a degradable thermopolymer resin according to claim 1, wherein: The twin-screw extruder is provided with a three-zone extrusion process, wherein the first zone is a block copolymer melting zone, the second zone is a raw material blending zone, and the third zone is a cross-linking zone.

8. A degradable thermal polyester resin prepared by the method according to any one of claims 1 to 7, characterized in that: The raw materials for preparing the degradable thermal polyester resin include L-lactide, terephthalic acid, 2,5-furandicarboxylic acid, butanediol, itaconic acid, polycaprolactone polyol and carboxylated cross-linked starch.

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