Enhanced PBAT and its preparation method and application

Abstract

The present invention discloses an enhanced PBAT, a preparation method thereof, and an application thereof. The method for preparing the enhanced PBAT comprises the following steps: S1: mixing PBAT with a composite chain extender to perform a chain extension reaction; S2: mixing the product after chain extension in S1 with a composite cross-linking agent to perform a cross-linking reaction to obtain the enhanced PBAT; the composite chain extender is a mixture of hexamethylene diisocyanate and 4-cyclohexene-1,2-dicarboxylic acid diglycidyl ester in a mass ratio of 0.5-1:1; and the composite cross-linking agent is a mixture of dicumyl peroxide, cyclohexanone peroxide, and di-tert-butyl peroxide in a mass ratio of 0.5-0.75:0.25-0.5:1. By first chain extending the PBAT and then cross-linking it, the present invention can increase the molecular chain length and cross-link between the molecular chains to form a network structure. The network structure is wider and the degree of cross-linking is deeper, which can further improve the melt strength and mechanical strength of the PBAT.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and in particular to enhanced PBAT and a preparation method and application thereof. Background Art

[0002] With the advancement of science and technology, polymer materials, especially synthetic polymers such as plastics and resins, have brought convenience to people's lives, but their waste has become a source of "white pollution", seriously affecting the environment and human sustainable development. In order to fundamentally solve the increasingly serious white pollution and other environmental pollution problems, the development of biodegradable polymer materials has become a research hotspot today. Polybutylene terephthalate-adipate (PBAT) is one of the biodegradable materials with mature technology and can be industrially produced. It can be processed in various forms such as injection molding, extrusion, and blow molding, and is widely used in the production of sheets, ground films, packaging and foaming materials. However, PBAT has problems such as poor crystallinity, low melt strength and low tensile strength, which limit its wider application. Therefore, it is necessary to modify PBAT to improve its comprehensive performance.

[0003] Currently, chain extension and cross-linking are common modification methods for enhancing PBAT. Epoxy and isocyanate chain extenders are commonly used in chain extension modification of PBAT. Patent CN115948033A describes using a substance containing multiple epoxy functional groups as an epoxy chain extender to improve the mechanical properties of PBAT. However, epoxy chain extenders react only with the carboxyl groups at the end of PBAT, resulting in limited chain extension effectiveness. Cross-linking modification primarily relies on chemical cross-linking, where the addition of a cross-linking agent creates cross-links between PBAT molecules, improving PBAT properties. Patent CN111849132A uses BPO as a cross-linking agent, significantly improving the tensile strength and thermal stability of the cross-linked PBAT. However, BPO decomposes at a relatively low temperature, making it unsuitable for the high-temperature reactions encountered during twin-screw extrusion. Furthermore, the varying temperature ranges during twin-screw extrusion significantly influence the cross-linker's activity, making it difficult for a single cross-linker to maintain high activity throughout the extrusion process. In addition, the mixing uniformity of solid chain extender and resin is poor, resulting in reduced product performance. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes an enhanced PBAT and its preparation method and application, which significantly improves the mechanical properties and processing performance of PBAT.

[0005] The preparation method of the enhanced PBAT proposed in the present invention comprises the following steps:

[0006] S1: Chain expansion of PBAT

[0007] Mixing PBAT with a composite chain extender to carry out a chain extension reaction;

[0008] S2: Cross-linking of PBAT

[0009] The product after chain extension of S1 is mixed with a composite cross-linking agent to carry out a cross-linking reaction to obtain an enhanced PBAT.

[0010] Preferably, the composite chain extender in S1 is a mixture of hexamethylene diisocyanate and 4-cyclohexene-1,2-dicarboxylic acid diglycidyl ester in a mass ratio of 0.5-1:1.

[0011] Preferably, the mass ratio of PBAT to the composite chain extender in S1 is 500:1-3.

[0012] Preferably, the chain extension reaction in S1 is carried out by a twin-screw extruder for chain extension extrusion, the temperature zones of the twin-screw extruder are set to 175, 180, 185, 190, 195, 195, 190, 185°C, the speed is set to 40-80r / min, and the feeding rate is set to 1-3r / min.

[0013] Preferably, the composite cross-linking agent in S2 is a mixture of dicumyl peroxide, cyclohexanone peroxide and di-tert-butyl peroxide in a mass ratio of 0.5-0.75:0.25-0.5:1.

[0014] Preferably, the mass ratio of the chain-extended PBAT to the composite cross-linking agent in S2 is 100:0.9-1.5.

[0015] Preferably, the cross-linking reaction in S2 is carried out by a twin-screw extruder for cross-linking extrusion, the temperature zones of the twin-screw extruder are set to 160, 170, 180, 185, 190, 190, 185, 175°C, the speed is set to 60-100r / min, and the feeding rate is set to 1-3r / min.

[0016] The enhanced PBAT prepared by the above method proposed in the present invention.

[0017] The present invention proposes the application of the above-mentioned enhanced PBAT in degradable polyester.

[0018] Beneficial technical effects of the present invention:

[0019] (1) The present invention uses HDI and TPDE as raw materials to prepare a composite chain extender, wherein HDI reacts with the terminal hydroxyl group (-OH) of PBAT, and TPDE reacts with the terminal carboxyl group (-COOH) of PBAT, thereby overcoming the disadvantage that a single chain extender can only react with a single functional group, and synergistically increasing the length of the PBAT molecular chain; in addition, TPDE also has a C=C double bond, and after the chain extension reaction, the double bond functional group is still retained on the PBAT long chain. In the subsequent cross-linking reaction, the long-chain macromolecule after chain extension is grafted onto the PBAT molecular chain through the action of an initiator, thereby improving the branching degree of PBAT and making the cross-linked network structure wider.

[0020] (2) The present invention uses DCP, CP and DTBP as composite crosslinking agents to form hydrogen bonds in the system, so that hydrogen bond interactions exist between the composite crosslinking agents, which inhibits the decomposition of the crosslinking agent at high temperature when it just enters the screw, reduces the loss of the crosslinking agent, and improves the crosslinking efficiency; CP and DCP are highly active in the low temperature section, decompose to form free radicals in the early stage of extrusion, and play a crosslinking role on PBAT, while DTBP has a higher decomposition temperature and plays a major role in the crosslinking reaction in the high temperature section, forming a "low temperature-high temperature" continuous high-activity crosslinking reaction; in addition, CP can also serve as an auxiliary crosslinking agent to promote the crosslinking reaction.

[0021] (3) The present invention uses DCP, CP and DTBP as raw materials to prepare a composite crosslinking agent, wherein DTBP and CP are liquids. DCP can be evenly dispersed in DTBP and CP under a hydrogen bonding system. The three-component crosslinking agent interacts closely with each other, has higher uniformity, and has a better dispersion effect when mixed with the resin, thus avoiding the problem of poor uniformity of mixing traditional solid crosslinking agents with resins.

[0022] (4) The present invention utilizes a two-step process, namely, chain extension and cross-linking, to increase the molecular chain length and form a network structure between the molecular chains. This network structure is wider and the degree of cross-linking is deeper, which can further enhance the melt strength and mechanical strength of PBAT. The melt index of the prepared PBAT resin is reduced from 31.76 g / 10 min to 3.75 g / 10 min, the tensile strength is increased from 14.19 MPa to 26.86 MPa, the flexural strength is increased from 2.79 MPa to 4.08 MPa, and the elongation at break is increased from 477% to 644%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a diagram of the hydrogen bonding mechanism of DCP, CP and DTBP proposed in the present invention;

[0024] Figure 2 This is a diagram of the grafting mechanism of PBAT containing double bond functional groups in the presence of TPDE proposed in the present invention;

[0025] Figure 3 This is the "chain extension-crosslinking" mechanism proposed by the present invention, wherein (a) is the chain extension mechanism of the composite chain extender first, and (b) is the crosslinking mechanism of the composite crosslinker second. DETAILED DESCRIPTION

[0026] The present invention will be further explained below with reference to specific embodiments.

[0027] PBAT, hexamethylene diisocyanate (HDI), 4-cyclohexene-1,2-dicarboxylic acid diglycidyl ester (TPDE), dicumyl peroxide (DCP), cyclohexanone peroxide (CP) and di-tert-butyl peroxide (DTBP) in the embodiments of the present invention are all commercially available.

[0028] Example 1

[0029] The preparation method of the enhanced PBAT proposed in the present invention comprises the following steps:

[0030] S1: Preparation of composite chain extender

[0031] Weigh 3g of HDI and 3g of TPDE and mix them evenly.

[0032] S2: Preparation of E-PBAT

[0033] First, 1 kg of PBAT and the composite chain extender prepared by S1 were weighed and mixed evenly in a mixer; then, the evenly mixed raw materials were melt-extruded through a twin-screw extruder, and the temperature zones of the twin-screw extruder were set to 175, 180, 185, 190, 195, 195, 190, and 185°C, the speed was set to 60 r / min, and the feeding rate was set to 2 r / min.

[0034] S3: Preparation of composite crosslinking agent

[0035] Weigh 3g DCP, 1.5g CP and 6g DTBP and mix them evenly.

[0036] S4: Preparation of CE-PBAT

[0037] First, 1 kg of E-PBAT prepared by S2 and the composite cross-linking agent prepared by S3 were weighed and mixed evenly in a mixer; then the evenly mixed raw materials were melt-extruded through a twin-screw extruder, and the temperature zones of the twin-screw extruder were set to 160, 170, 180, 185, 190, 190, 185, and 175°C, the speed was set to 80 r / min, and the feeding rate was set to 2 r / min.

[0038] Example 2

[0039] The preparation method of the enhanced PBAT proposed in the present invention comprises the following steps:

[0040] S1: Preparation of composite chain extender

[0041] Weigh 2g of HDI and 2g of TPDE and mix them evenly.

[0042] S2: Preparation of E-PBAT

[0043] First, 1 kg of PBAT and the composite chain extender prepared by S1 were weighed and mixed evenly in a mixer; then, the evenly mixed raw materials were melt-extruded through a twin-screw extruder, and the temperature zones of the twin-screw extruder were set to 175, 180, 185, 190, 195, 195, 190, and 185°C, the speed was set to 60 r / min, and the feeding rate was set to 2 r / min.

[0044] S3: Preparation of composite crosslinking agent

[0045] Weigh 3g DCP, 1.5g CP and 6g DTBP and mix them evenly.

[0046] S4: Preparation of CE-PBAT

[0047] First, 1 kg of E-PBAT prepared by S2 and the composite cross-linking agent prepared by S3 were weighed and mixed evenly in a mixer; then, the evenly mixed raw materials were melt-extruded through a twin-screw extruder, and the temperature zones of the twin-screw extruder were set to 160, 170, 180, 185, 190, 190, 185, and 175°C, the speed was set to 80 r / min, and the feeding rate was set to 2 r / min.

[0048] Example 3

[0049] The preparation method of the enhanced PBAT proposed in the present invention comprises the following steps:

[0050] S1: Preparation of composite chain extender

[0051] Weigh 1g of HDI and 1g of TPDE and mix them evenly.

[0052] S2: Preparation of E-PBAT

[0053] First, 1 kg of PBAT and the composite chain extender prepared by S1 were weighed and mixed evenly in a mixer; then, the evenly mixed raw materials were melt-extruded through a twin-screw extruder, and the temperature zones of the twin-screw extruder were set to 175, 180, 185, 190, 195, 195, 190, and 185°C, the speed was set to 60 r / min, and the feeding rate was set to 2 r / min.

[0054] S3: Preparation of composite crosslinking agent

[0055] Weigh 3g DCP, 1.5g CP and 6g DTBP and mix them evenly.

[0056] S4: Preparation of CE-PBAT

[0057] First, 1 kg of E-PBAT prepared by S2 and the composite cross-linking agent prepared by S3 were weighed and mixed evenly in a mixer; then, the evenly mixed raw materials were melt-extruded through a twin-screw extruder, and the temperature zones of the twin-screw extruder were set to 160, 170, 180, 185, 190, 190, 185, and 175°C, the speed was set to 80 r / min, and the feeding rate was set to 2 r / min.

[0058] Comparative Example 1

[0059] First, 3g HDI and 3g TPDE were weighed and mixed uniformly. Next, 1kg PBAT and the compound chain extender were weighed and mixed uniformly in a mixer. Finally, the mixed raw materials were melt-extruded through a twin-screw extruder with the temperature zones set to 175, 180, 185, 190, 195, 195, 190, and 185°C, the speed set to 60r / min, and the feed rate set to 2r / min.

[0060] Comparative Example 2

[0061] First, 3g DCP, 1.5g CP, and 6g DTBP were weighed and uniformly mixed. Next, 1kg PBAT and the composite crosslinking agent were weighed and uniformly mixed in a mixer. The uniformly mixed raw materials were then melt-extruded through a twin-screw extruder with the temperature zones set to 160, 170, 180, 185, 190, 190, 185, and 175°C, the speed set to 80r / min, and the feed rate set to 2r / min.

[0062] Comparative Example 3

[0063] S1: Preparation of single-chain extended PBAT

[0064] First, 6g of HDI and 1kg of PBAT were weighed and mixed in a mixer. The mixed materials were then melt-extruded through a twin-screw extruder with the temperature zones set to 175, 180, 185, 190, 195, 195, 190, and 185°C, the speed set to 60 rpm, and the feed rate set to 2 rpm.

[0065] S2: Preparation of single “chain extension-crosslinking” PBAT

[0066] Weigh 10.5g of DCP and 1kg of single-chain-extended PBAT prepared with S1 and mix them evenly in a blender. Then, melt extrude the mixed materials through a twin-screw extruder with the temperature zones set to 160, 170, 180, 185, 190, 190, 185, and 175°C, a speed of 80 rpm, and a feed rate of 2 rpm.

[0067] The present invention uses CP, DCP, and DTBP as composite crosslinking agents. The half-lives of CP, DCP, and DTBP at different temperatures are shown in Table 1. As can be seen from Table 1, CP has the lowest decomposition temperature, DCP has a higher decomposition temperature than CP, and DTBP has the highest decomposition temperature. Therefore, CP and DCP decompose to form free radicals at a relatively low temperature in the early stage of extrusion and maintain high activity, playing an early crosslinking role for PBAT. DTBP, on the other hand, has a relatively high decomposition temperature and still maintains high activity in the high-temperature section, playing a major crosslinking role during the high-temperature extrusion process. Therefore, the composite crosslinking agent prepared using CP, DCP, and DTBP as raw materials can form a "low-temperature-high-temperature" continuous high-activity crosslinking reaction throughout the entire twin-screw extrusion process.

[0068] Table 1 Half-lives of cross-linking agents CP, DCP and DTBP at different temperatures

[0069]

[0070] The present invention conducted melt index tests on pure PBAT samples, one-step chain extension samples (E-PBAT), one-step cross-linked samples (C-PBAT), single "chain extension-cross-linking" samples (PBAT-1) and "chain extension-cross-linking" two-step samples (CE-PBAT). The results are shown in Table 2. As shown in Table 2, the melt index of CE-PBAT is significantly lower than that of PBAT, E-PBAT, C-PBAT and PBAT-1. This is because the single chain extender only reacts with a single PBAT end group, the molecular chain growth is limited, and the single cross-linker cannot maintain high reactivity in different temperature ranges; however, the composite chain extender reacts with both the PBAT terminal hydroxyl group and the PBAT terminal carboxyl group, synergistically increasing the PBAT molecular chain length while retaining the carbon-carbon double bond on the molecular chain. During the cross-linking process, the degree of molecular chain branching is increased through grafting reaction; the composite cross-linker plays a major cross-linking role in the low temperature range and the high temperature range respectively, and the "chain extension-cross-linking" two-step process increases the molecular chain length and then cross-links between the molecular chains to form a network structure with a higher degree of cross-linking. The melt index of PBAT is significantly reduced, and the melt strength and processing performance of the material are improved.

[0071] Table 2 Melt index of samples

[0072]

[0073]

[0074] The present invention conducted mechanical testing on pure PBAT samples, a one-step chain extension sample (E-PBAT), a one-step crosslinking sample (C-PBAT), a single "chain extension + crosslinking" sample (PBAT-1), and a two-step "chain extension + crosslinking" sample (CE-PBAT). The results are shown in Table 3. Table 3 shows that CE-PBAT exhibits significant improvements in both tensile and flexural strength compared to PBAT, E-PBAT, C-PBAT, and PBAT-1. This is because PBAT is chain extended with a composite chain extender and then crosslinked with a composite crosslinker, forming a long-chain network structure. Furthermore, the double-bond functional groups remaining on the PBAT long chains after the chain extension reaction are then grafted onto other PBAT chains by the initiator in the subsequent crosslinking reaction, increasing the degree of PBAT crosslinking and forming a more extensive network structure. The long-chain network structure of PBAT products obtained through the two-step "chain extension + crosslinking" process can further enhance the tensile and flexural strengths of PBAT, as well as significantly improve elongation at break.

[0075] Table 3 Mechanical properties of samples

[0076]

Claims

1. A method for preparing enhanced PBAT, characterized in that: The steps are as follows: S1: Chain expansion of PBAT Mixing PBAT with a composite chain extender to carry out a chain extension reaction; S2: Cross-linking of PBAT The product after chain extension of S1 is mixed with a composite cross-linking agent to carry out a cross-linking reaction to obtain an enhanced PBAT; The composite chain extender in S1 is a mixture of hexamethylene diisocyanate and 4-cyclohexene-1,2-dicarboxylic acid diglycidyl ester in a mass ratio of 0.5-1:1; The composite cross-linking agent in S2 is a mixture of dicumyl peroxide, cyclohexanone peroxide and di-tert-butyl peroxide in a mass ratio of 0.5-0.75:0.25-0.5:

1.

2. The method for preparing the enhanced PBAT according to claim 1, wherein: The mass ratio of PBAT to composite chain extender in S1 is 500:1-3.

3. The method for preparing the enhanced PBAT according to claim 1, wherein: The chain extension reaction in S1 is carried out by a twin-screw extruder, and the temperature zones of the twin-screw extruder are set to 175, 180, 185, 190, 195, 195, 190, 185°C, the speed is set to 40-80r / min, and the feeding rate is set to 1-3r / min.

4. The method for preparing the enhanced PBAT according to claim 1, wherein: The mass ratio of the chain-extended PBAT to the composite cross-linking agent in S2 is 100:0.9-1.

5.

5. The method for preparing the enhanced PBAT according to claim 1, wherein: The cross-linking reaction in S2 is carried out by a twin-screw extruder for cross-linking extrusion. The temperature zones of the twin-screw extruder are set to 160, 170, 180, 185, 190, 190, 185, and 175°C, the rotation speed is set to 60-100 r / min, and the feeding rate is set to 1-3 r / min.

6. An enhanced PBAT prepared by the method according to any one of claims 1 to 5.

7. Use of the enhanced PBAT as claimed in claim 6 in degradable polyester.

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