A compound modified masterbatch for improving the heat-sealing strength of PLA tea bags and its preparation method

Abstract

This invention discloses a compound modified masterbatch for improving the heat-sealing strength of PLA tea bags and its preparation method, belonging to the field of polymer materials technology. By weight, it comprises the following components: 35-50 parts polylactic acid carrier; 18-28 parts toughening agent; 3-8 parts composite nucleating agent; 1-4 parts crystallization promoter; 2-5 parts interface compatibilizer; and 0.5-2 parts antioxidant. The toughening agent is a blend of polybutylene adipate-terephthalate and polybutylene succinate in a mass ratio of (1.5-2.5):1. The composite nucleating agent is composed of an organophosphate nucleating agent and an acylhydrazine compound in a mass ratio of 1:(0.8-1.5). This invention systematically improves the heat-sealing strength of PLA tea bags from three dimensions—toughening, nucleation, and promotion—from the perspectives of interfacial adhesion, crystal structure, and molecular motion, overcoming the limitations of single modification methods.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a compound modified masterbatch for improving the heat-sealing strength of PLA tea bags and its preparation method. Background Technology

[0002] Polylactic acid (PLA), as a bio-based biodegradable material, is widely used in tea filter bags due to its good biocompatibility and compostability. However, PLA tea bags face a key technical bottleneck in practical use—insufficient heat-sealing strength.

[0003] PLA is a semi-crystalline polymer with a slow crystallization rate. Under conventional heat-sealing conditions, it is difficult to form a complete crystal structure, resulting in insufficient diffusion of molecular chains at the heat-sealing interface, low entanglement, and poor sealing strength. Furthermore, PLA has a narrow heat-sealing window, is sensitive to heat-sealing temperature, pressure, and time, has poor process adaptability, and is prone to problems such as weak seals or overheating and melting through.

[0004] In the prior art, the main methods to improve the heat-sealing strength of PLA include: adding flexible polyester for toughening modification and using flexible segments to improve interfacial adhesion; adding nucleating agents to promote PLA crystallization and accelerate crystal formation during the heat-sealing process; and adding compatibilizers to improve the interfacial compatibility of PLA with other components.

[0005] However, the above methods have the following shortcomings: First, although single toughening modification can improve the toughness of the seal, it often comes at the cost of sacrificing the modulus of the material, affecting the spinning and processing performance; Second, although single nucleation modification can accelerate crystallization, uneven dispersion of the nucleating agent can easily lead to stress concentration points, which in turn reduces the seal strength; Third, the existing technology lacks a systematic modification scheme for the heat sealing process of PLA tea bags, making it difficult to simultaneously meet the comprehensive requirements of heat sealing strength, heat sealing window width, and processing performance.

[0006] Therefore, this invention proposes a compound modified masterbatch for improving the heat-sealing strength of PLA tea bags and its preparation method. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing a compound modified masterbatch for improving the heat-sealing strength of PLA tea bags and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] On the one hand, this invention proposes a compound modified masterbatch for improving the heat-sealing strength of PLA tea bags, comprising the following components by weight:

[0010] 35-50 parts of polylactic acid carrier;

[0011] 18-28 parts toughening agent;

[0012] 3-8 parts of composite nucleating agent;

[0013] 1-4 parts of crystallization accelerator;

[0014] 2-5 parts of interface compatibilizer;

[0015] Antioxidant 0.5-2 parts;

[0016] The toughening agent is a blend of polybutylene adipate terephthalate and polybutylene succinate, with a mass ratio of (1.5-2.5):1.

[0017] The composite nucleating agent is composed of an organophosphate nucleating agent and an acylhydrazine compound in a mass ratio of 1:(0.8-1.5);

[0018] The crystallization accelerator is polyethylene glycol, with a number average molecular weight of 4000-8000.

[0019] Preferably, the organophosphate nucleating agent is sodium 2,2'-methylene-bis(4,6-di-tert-butylphenyl)phosphate or aluminum 2,2'-methylene-bis(4,6-di-tert-butylphenyl)phosphate; the acylhydrazine compound is diphenyl dihydrazide sebacate or diphenyl dihydrazide adipate.

[0020] Preferably, the interface compatibilizer is glycidyl methacrylate-grafted polylactic acid or maleic anhydride-grafted polylactic acid, with a grafting rate of 1.2-2.0%.

[0021] Preferably, it further includes 0.5-2 parts of a crosslinking aid, wherein the crosslinking aid is triallyl isocyanurate.

[0022] Preferably, it further includes 0.1-0.3 parts of an initiator, wherein the initiator is dicumyl peroxide.

[0023] On the other hand, this invention proposes a method for preparing a compound modified masterbatch for improving the heat-sealing strength of PLA tea bags, comprising the following steps:

[0024] (1) Premixing: Add polylactic acid carrier, toughening agent, composite nucleating agent, crystallization promoter, interface compatibilizer, antioxidant and other additives to a high-speed mixer according to the formula, and mix at 800-1200 rpm for 8-12 min to obtain premix;

[0025] (2) Melt blending: Add the premixed material into a twin-screw extruder, control the extrusion temperature at 165-185℃ and the screw speed at 250-350rpm, and carry out melt blending extrusion;

[0026] (3) Granulation and drying: After the extruded strip is cooled by water and granulated, it is vacuum dried at 55-65℃ for 5-7h to obtain the compound modified masterbatch.

[0027] Preferably, the twin-screw extruder in step (2) has nine temperature control zones, and the temperature of each zone is set as follows: Zone 1 165-168℃, Zone 2 168-172℃, Zone 3 172-175℃, Zone 4 175-178℃, Zone 5 178-182℃, Zone 6 182-185℃, Zone 7 178-182℃, Zone 8 175-178℃, Zone 9 170-175℃, and the die head temperature is 172-176℃.

[0028] Preferably, before the premixing in step (1), the composite nucleating agent and the crystallization accelerator are premixed at 60-80°C for 3-5 minutes to ensure that the nucleating agent is uniformly dispersed in the crystallization accelerator.

[0029] The present invention has the following technical effects:

[0030] This invention systematically enhances the heat-sealing strength of PLA tea bags by toughening, nucleation, and promoting interfacial adhesion, crystal structure, and molecular motion, overcoming the limitations of single modification methods.

[0031] This invention uses a PBAT / PBS compound toughening agent, and achieves a balance between rigidity and toughness by adjusting the ratio of the two, which ensures both sealing toughness and maintains the modulus required for spinning processing.

[0032] This invention employs a nucleating agent composed of organophosphates and hydrazides to synergistically promote PLA formation. Jinghe Crystal formation significantly improves the crystallization rate and crystallinity, and widens the heat-sealing window.

[0033] This invention improves the interfacial bonding between PLA and toughening agent through an interfacial compatibilizer, and the optional crosslinking aid further strengthens the sealing interface, ensuring the heat seal strength retention rate after hot water immersion.

[0034] This invention solves the problem of uneven dispersion of nucleating agents in PLA by pre-mixing nucleating agents and crystallization promoters, thereby improving the consistency of modification effects. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0036] Raw material source:

[0037] PLA: NatureWorks, USA, grade 4032D, weight-average molecular weight 2.0 × 10⁻⁶ 5;

[0038] PBAT: Xinjiang Lanshan Tunhe, brand name TH801;

[0039] PBS: Mitsubishi Chemical, Japan, brand name FZ91PM;

[0040] Organophosphate nucleating agent: Sodium 2,2'-methylene-bis(4,6-di-tert-butylphenyl)phosphate, Shanxi Chemical Research Institute, brand name TMP-6;

[0041] Acylhydrazide compounds: Diphenyl dihydrazide sebacate, Adik, Japan, brand name ADK STAB NA-11;

[0042] Polyethylene glycol: Number average molecular weight 6000, SK Chemicals, South Korea;

[0043] Glycidyl methacrylate grafted PLA: prepared in the laboratory, grafting rate 1.6%;

[0044] Maleic anhydride-grafted PLA: prepared in the laboratory, grafting rate 1.4%;

[0045] Triallyl isocyanurate: Shanghai Maclean, industrial grade;

[0046] Dicumyl peroxide: AkzoNobel, analytical grade;

[0047] Antioxidant 1010 / 168 compound: BASF, mass ratio 1:2.

[0048] Example 1

[0049] A compound modified masterbatch for improving the heat-sealing strength of PLA tea bags, by weight, comprises: 40 parts PLA carrier; 22 parts toughening agent; 5 parts composite nucleating agent; 3 parts polyethylene glycol; 4 parts glycidyl methacrylate grafted PLA; and 1 part antioxidant 1010 / 168 compound.

[0050] Preparation method:

[0051] (1) Pretreatment: The composite nucleating agent and polyethylene glycol are premixed at 70°C for 4 min to ensure that the nucleating agent is uniformly dispersed in polyethylene glycol;

[0052] (2) Premixing: The PLA carrier, toughening agent, pretreated composite nucleating agent, polyethylene glycol mixture, grafted PLA, and antioxidant are added to a high-speed mixer and mixed at 1000 rpm for 10 min to obtain a premix.

[0053] (3) Melt blending: The premixed material is added to a twin-screw extruder with a screw length-to-diameter ratio of L / D=40. The temperature of each zone is set as follows: Zone 1 166℃, Zone 2 170℃, Zone 3 174℃, Zone 4 177℃, Zone 5 180℃, Zone 6 184℃, Zone 7 180℃, Zone 8 176℃, Zone 9 172℃, Die head 174℃, and screw speed 300rpm.

[0054] (4) Granulation and drying: After the extruded strip is cooled by water and granulated, it is vacuum dried at 60°C for 6 hours to obtain the compound modified masterbatch.

[0055] (5) Spinning application: The modified masterbatch obtained is mixed with PLA base material at a mass ratio of 1:10, and then spun at 215℃ using a melt spinning machine at a spinning speed of 1000m / min to obtain PLA tea bag fiber.

[0056] Example 2

[0057] This embodiment is basically the same as Example 1, except that the mass ratio of PBAT to PBS in the toughening agent is adjusted to 1.5:1. Other components and preparation methods are the same.

[0058] Example 3

[0059] This embodiment is basically the same as Example 1, except that the mass ratio of organophosphate to acylhydrazine in the composite nucleating agent is adjusted to 1:1.2, while the other components and preparation methods are the same.

[0060] Example 4

[0061] This embodiment is basically the same as Example 1, except that 1.5 parts of crosslinking aid triallyl isocyanurate and 0.2 parts of initiator dicumyl peroxide are added. Other components and preparation methods are the same.

[0062] Example 5

[0063] This embodiment is basically the same as Example 1, except that the amount of composite nucleating agent is adjusted to 6 parts and the amount of polyethylene glycol is 2 parts, while the other components and preparation methods are the same.

[0064] Comparative Example 1

[0065] This comparative example is basically the same as Example 1, except that no composite nucleating agent and crystallization promoter are added, while the other components and preparation methods are the same.

[0066] Comparative Example 2

[0067] This comparative example is basically the same as Example 1, except that the composite nucleating agent is replaced with an equal amount of a single organophosphate nucleating agent, while the other components and preparation methods are the same.

[0068] Comparative Example 3

[0069] This comparative example is basically the same as Example 1, except that the composite nucleating agent is replaced with an equal amount of a single acylhydrazine compound, while the other components and preparation methods are the same.

[0070] Comparative Example 4

[0071] This comparative example is basically the same as Example 1, except that the toughening agent is replaced with an equal amount of single PBAT, while the other components and preparation methods are the same.

[0072] Comparative Example 5

[0073] This comparative example is basically the same as Example 1, except that no crystallization promoter is added, while the other components and preparation methods are the same.

[0074] Performance testing methods:

[0075] (1) Heat seal strength test: Refer to QB / T 2358-1998 "Test method for heat seal strength of plastic film packaging bags", mix the compound modified masterbatch and PLA base material at a mass ratio of 1:10 to make tea bag fiber, and then make tea bag bag body. Heat seal at a heat sealing temperature of 140℃, heat sealing pressure of 0.2MPa and heat sealing time of 1s. Cut 15mm wide samples and use a universal testing machine at a speed of 200mm / min to determine the heat seal strength. Each sample is tested 5 times and the average value is taken.

[0076] (2) Heat sealing window test: Heat sealing was carried out at different heat sealing temperatures (120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃) and the heat sealing strength was measured. The temperature range with heat sealing strength ≥ 5.0N / 15mm was used as the heat sealing window width.

[0077] (3) Heat seal strength retention rate test: Immerse the heat-sealed tea bag in 95℃ hot water for 30 minutes, take it out and dry it, and then measure the heat seal strength according to method (1) and calculate the retention rate.

[0078] (4) Crystallization performance test: Differential scanning calorimeter (TA Q2000) was used in a nitrogen atmosphere with a heating rate of 10℃ / min to determine the crystallization half-life (t1 / 2) and crystallinity (Xc) of the sample during isothermal crystallization at 130℃.

[0079] (5) Evaluation of spinning performance: Observe the breakage of fibers and fiber uniformity during the spinning process, and comprehensively evaluate the spinnability. Excellent: No breakage of fibers during continuous spinning for 8 hours; Good: Occasional breakage of fibers; Poor: Frequent breakage of fibers.

[0080] Performance test results:

[0081] The modified masterbatches obtained in Examples 1-5 and Comparative Examples 1-5 were respectively made into PLA tea bag fibers according to the method of step (5) in Example 1. The performance was evaluated according to the aforementioned test method, and the results are shown in Table 1.

[0082] Table 1 Performance test results of each embodiment and comparative example

[0083]

[0084] As can be seen from the data in Table 1:

[0085] (1) The heat-sealing strength of Examples 1-5 was between 8.0 and 9.0 N / 15 mm, which was better than that of Comparative Examples 1-5, indicating that the ternary synergistic mechanism of the present invention effectively improved the heat-sealing strength. Example 4 achieved the best effect with 9.0 N / 15 mm due to the introduction of the crosslinking aid.

[0086] (2) Regarding the heat sealing window width, Examples 1-5 are all ≥31℃, Example 4 reaches 38℃, while Comparative Example 1 is only 12℃, and Comparative Examples 2-5 are 18-24℃, proving that the compound system of the present invention significantly widens the heat sealing process window.

[0087] (3) In terms of crystallization performance, the crystallization half-life of Examples 1-5 was significantly shorter than that of the comparative example, and the crystallinity was significantly higher than that of the comparative example, indicating that the composite nucleating agent and the crystallization promoter synergistically promoted the rapid crystallization of PLA.

[0088] (4) In terms of spinnability, Examples 1-5 all showed good or excellent spinnability, while Comparative Example 4 had poor spinnability, proving that the PBAT / PBS compound toughening not only ensured the sealing toughness, but also maintained the modulus required for spinning.

[0089] (5) Regarding the strength retention rate after hot water immersion, all of Examples 1-5 were ≥85%, Example 4 reached 90%, while Comparative Example 1 was only 62%, indicating that the modified masterbatch of the present invention imparts good hot water resistance to tea bags.

[0090] Example 1: Effect of the ratio of composite nucleating agent on crystallization performance

[0091] To further investigate the effect of the proportion of each component in the composite nucleating agent on the crystallization performance, based on Example 1, the total amount of composite nucleating agent was kept at 5 parts, the mass ratio of organophosphate to hydrazide was adjusted, a series of samples were prepared and tested, and the results are shown in Table 2.

[0092] Table 2 Effect of composite nucleating agent ratio on crystallization properties

[0093]

[0094] As shown in Table 2, when the mass ratio of organophosphates to hydrazides is within the range of 1:(0.8-1.5), both crystallization properties and heat-sealing strength are at their optimal levels; outside this range, the properties decrease. This indicates a synergistic effect between the two, with the optimal ratio range being 1:(0.8-1.5).

[0095] Example 2: Effect of toughening agent compound on spinning properties

[0096] To verify the necessity of toughening with PBAT / PBS compound, spinning experiments were conducted using toughening agent systems with different proportions, and the results are shown in Table 3.

[0097] Table 3 Effect of toughening agent combination on spinning properties

[0098]

[0099] As shown in Table 3, although PBAT alone has high heat-sealing strength, it has poor spinnability; PBS alone has good spinnability but insufficient heat-sealing strength. When the mass ratio of PBAT / PBS is in the range of (1.5-2.5):1, a balance between stiffness and toughness can be achieved, ensuring good spinnability while maintaining heat-sealing strength.

[0100] Example 3: Effect of nucleating agent pretreatment on dispersibility

[0101] To verify the effect of premixing nucleating agent and crystallization promoter, samples of Example 1 were prepared with and without pretreatment processes, and the dispersibility of nucleating agent in masterbatch was tested. The results are shown in Table 4.

[0102] Table 4. Effect of pretreatment process on nucleating agent dispersibility

[0103]

[0104] As shown in Table 4, after premixing, the particle size of the nucleating agent in the masterbatch was significantly reduced, and the batch-to-batch fluctuation of the heat sealing strength was significantly reduced, indicating that the pretreatment process improved the stability of the product.

[0105] Example 4: Effect of heat sealing temperature on heat sealing strength

[0106] Using the masterbatches obtained in Examples 1 and 4 as examples, the effect of different heat sealing temperatures on heat sealing strength was investigated, and the results are shown in Table 5.

[0107] Table 5. Effect of heat sealing temperature on heat sealing strength (N / 15mm)

[0108]

[0109] As shown in Table 5, Example 1 exhibits a heat-sealing strength ≥6.2 N / 15 mm within the temperature range of 130-155°C, with a window width exceeding 30°C; Example 4 demonstrates a heat-sealing strength ≥6.8 N / 15 mm within the temperature range of 130-160°C, with a window width exceeding 35°C; while Comparative Example 1 barely achieves 5.0 N / 15 mm within a narrow window of 135-145°C. The introduction of the crosslinking aid further widens the heat-sealing window and improves the strength.

[0110] discuss

[0111] Based on the above experimental results, this invention successfully improves the heat-sealing strength of PLA tea bags through three aspects: toughening, nucleation, and promotion. The PBAT / PBS compound toughening agent imparts good flexibility to the seal while ensuring spinnability; the organophosphate and hydrazide compound nucleating agent synergistically promotes rapid PLA crystallization, significantly shortening the crystallization half-life and increasing crystallinity; the polyethylene glycol crystallization promoter improves molecular chain mobility and accelerates diffusion entanglement during the heat-sealing process. The synergistic effect of these three agents constructs a heat-sealing strength enhancement system from three dimensions: interfacial adhesion, crystal structure, and molecular motion.

[0112] Compared with existing technologies, the heat-sealing strength of this invention is increased by more than 30%, and the heat-sealing window width is widened to 30-38°C, while maintaining good spinning processing performance and hot water resistance. In particular, after introducing the crosslinking system in Example 4, the heat-sealing strength reaches 9.0 N / 15 mm, and the strength retention rate after hot water immersion is as high as 90%, demonstrating excellent comprehensive performance.

[0113] Furthermore, by premixing the nucleating agent and the crystallization promoter, this invention effectively solves the problem of uneven dispersion of the nucleating agent in the PLA matrix, improves the consistency of the modification effect, and is beneficial to quality control in industrial production.

[0114] The compound modified masterbatch provided by this invention can be used in the production of various PLA tea bags, especially suitable for triangular bags, flat bags, and other packaging forms that require high heat-sealing strength. The preparation process of this invention is compatible with existing PLA spinning production lines, requires no equipment modification, and has high industrialization potential.

[0115] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A compound modified masterbatch for improving the heat-sealing strength of PLA tea bags, characterized in that, By weight, it includes the following components: 35-50 parts of polylactic acid carrier; 18-28 parts toughening agent; 3-8 parts of composite nucleating agent; 1-4 parts of crystallization accelerator; 2-5 parts of interface compatibilizer; Antioxidant 0.5-2 parts; The toughening agent is a blend of polybutylene adipate terephthalate and polybutylene succinate, with a mass ratio of (1.5-2.5):

1. The composite nucleating agent is composed of an organophosphate nucleating agent and an acylhydrazine compound in a mass ratio of 1:(0.8-1.5); The crystallization accelerator is polyethylene glycol, with a number average molecular weight of 4000-8000.

2. The compound modified masterbatch for improving the heat-sealing strength of PLA tea bags according to claim 1, characterized in that, The organophosphate nucleating agent is sodium 2,2'-methylene-bis(4,6-di-tert-butylphenyl)phosphate or aluminum 2,2'-methylene-bis(4,6-di-tert-butylphenyl)phosphate; the acylhydrazine compound is diphenyl dihydrazide sebacate or diphenyl dihydrazide adipate.

3. The compound modified masterbatch for improving the heat-sealing strength of PLA tea bags according to claim 1, characterized in that, The interface compatibilizer is glycidyl methacrylate-grafted polylactic acid or maleic anhydride-grafted polylactic acid, with a grafting rate of 1.2-2.0%.

4. The compound modified masterbatch for improving the heat-sealing strength of PLA tea bags according to claim 1, characterized in that, It also includes 0.5-2 parts of a crosslinking aid, wherein the crosslinking aid is triallyl isocyanurate.

5. The compound modified masterbatch for improving the heat-sealing strength of PLA tea bags according to claim 4, characterized in that, It also includes 0.1-0.3 parts of an initiator, wherein the initiator is dicumyl peroxide.

6. A method for preparing a compound modified masterbatch for improving the heat-sealing strength of PLA tea bags as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Premixing: Add polylactic acid carrier, toughening agent, composite nucleating agent, crystallization promoter, interface compatibilizer, antioxidant and other additives to a high-speed mixer according to the formula, and mix at 800-1200 rpm for 8-12 min to obtain premix; (2) Melt blending: Add the premixed material into a twin-screw extruder, control the extrusion temperature at 165-185℃ and the screw speed at 250-350rpm, and carry out melt blending extrusion; (3) Granulation and drying: After the extruded strip is cooled by water and granulated, it is vacuum dried at 55-65℃ for 5-7h to obtain the compound modified masterbatch.

7. The preparation method according to claim 6, characterized in that, The twin-screw extruder described in step (2) has nine temperature control zones, with the following temperature settings: Zone 1 165-168℃, Zone 2 168-172℃, Zone 3 172-175℃, Zone 4 175-178℃, Zone 5 178-182℃, Zone 6 182-185℃, Zone 7 178-182℃, Zone 8 175-178℃, Zone 9 170-175℃, and the die head temperature 172-176℃.

8. The preparation method according to claim 6, characterized in that, Before the premixing in step (1), the composite nucleating agent and the crystallization accelerator are premixed at 60-80℃ for 3-5 minutes to ensure that the nucleating agent is uniformly dispersed in the crystallization accelerator.

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