A Degradable Hot Melt Adhesive and Its Preparation Process

Abstract

The present invention belongs to the technical field of polymer materials. More specifically, it relates to a degradable hot melt adhesive and its preparation process. The product of the present invention comprises the following raw materials in parts by weight: 90 - 100 parts of ethylene-vinyl acetate copolymer, 18 - 20 parts of polylactic acid, 8 - 10 parts of nano filler, 1 - 3 parts of plasticizer, 1 - 3 parts of antioxidant, 2 - 4 parts of microcrystalline wax; wherein, the nano filler is composed of flaky nano boehmite and spherical nano alumina in a mass ratio of (0.9 - 1.0):1; the D50 of the flaky nano boehmite is 65 - 70nm; the D50 of the spherical nano alumina is 10 - 15nm; the particle size distribution range of the flaky nano boehmite is 30 - 90nm; and, the particle size distribution range of the spherical nano alumina is 1 - 30nm; the sphericity of the spherical nano alumina is 8.8 - 9.2.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials. More specifically, it relates to a degradable hot melt adhesive and its preparation process. Background Art

[0002] Hot melt adhesives are mainly used for wood or paper composite packaging or binding, and also for rapid bonding in industries such as vehicle, ship, and interior decoration of buildings.

[0003] Hot melt adhesives are thermoplastic materials melted from a thermoplastic resin as the matrix, supplemented with components such as tackifiers, plasticizers, and antioxidants. Due to their excellent performance and convenient sizing, they have become commonly used adhesives in various industries in modern society. Currently, most of the domestic and foreign hot melt adhesive markets are dominated by EVA-based hot melt adhesives, and also include different product types such as polyethylene, polypropylene, polyamide, polyimide, polyester, and polyurethane. Their matrix resins all belong to high molecular organic compounds and have special chemical structures and properties that are difficult to biodegradable. With the widespread application of hot melt adhesives, their long-term retention in the environment has become a hidden danger and harm to the ecological environment. Therefore, under the global ecological environmental protection and sustainable development situation, researching new green and environmentally friendly biodegradable hot melt adhesives has become an important development direction in the current adhesive industry.

[0004] When products bonded with hot melt adhesives are recycled, the hot melt adhesives therein must have the properties of biodegradation or chemical reaction degradation, otherwise it will bring great difficulties to recycling. Of course, while improving the environmental protection of hot melt adhesives, the bonding performance of hot melt adhesives also needs to be improved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: for EVA-based hot melt adhesives, their poor biodegradability, and when simply mixing in degradable hot melt resins, it is easy to lead to the problem that the bonding performance of the hot melt adhesive itself cannot be effectively taken into account. The present invention provides a degradable hot melt adhesive and its preparation process.

[0006] The purpose of the present invention is to provide a degradable hot melt adhesive.

[0007] Another purpose of the present invention is to provide a preparation process for a degradable hot melt adhesive.

[0008] The above purposes of the present invention are achieved through the following technical solutions:

[0009] A degradable hot melt adhesive, comprising the following raw materials in parts by weight:

[0010] 90 - 100 parts of ethylene-vinyl acetate copolymer, 18 - 20 parts of polylactic acid, 8 - 10 parts of nano filler, 1 - 3 parts of plasticizer, 1 - 3 parts of antioxidant, 2 - 4 parts of microcrystalline wax;

[0011] Among them, the nano filler is composed of flaky nano boehmite and spherical nano alumina in a mass ratio of (0.9 - 1.0):1;

[0012] The D50 of the flaky nano boehmite is 65 - 70 nm;

[0013] The D50 of the spherical nano alumina is 10 - 15 nm.

[0014] Beneficial effects of the above solution:

[0015] By using the ethylene - vinyl acetate copolymer and polylactic acid blend system as the main components of the hot melt adhesive, firstly, polylactic acid has good biodegradability. After adding polylactic acid, the biodegradability of the ethylene - vinyl acetate copolymer as the sole main component of the hot melt adhesive can be improved; secondly, a large number of ester groups are contained in the molecular structure of polylactic acid. The introduction of ester groups can increase the interfacial force of the hot melt adhesive system with the substrate, thereby enhancing the bonding strength of the product; in addition, polylactic acid itself is a semi - crystalline polymer. By controlling the added amount, the crystallization behavior of the ethylene - vinyl acetate copolymer can be affected. Specifically, the crystallinity of the hot melt adhesive system can be increased, further enhancing the reliability of product bonding and avoiding bonding failure caused by rapid erosion by oxygen and water in the air during normal use;

[0016] However, the inventor found that when the ethylene - vinyl acetate copolymer and polylactic acid are blended, due to their different chemical structures and polarities, there are problems with their compatibility, making it difficult to mix them evenly in a conventional manner. If the melting and mixing are carried out for too long during the preparation process, the hot melt adhesive is prone to oxidation; the inventor found that by adding a nano filler system composed of flaky nano boehmite and spherical nano alumina, this problem can be significantly improved; specifically, the cooperation of two nano fillers with different morphologies can synergistically act as a stress transfer medium during the resin blending process, overall improving the stress transfer efficiency and thus accelerating the mixing between the two different resins; in addition, both can act as nucleating agents to promote the crystallization of the resin, increasing the crystallization rate and crystallinity, thereby enhancing the bonding performance; moreover, due to the good water absorption performance of boehmite, it can play a role in improving the biodegradability performance in the later stage of product use.

[0017] Furthermore, the particle size distribution range of the flaky nano boehmite is 30 - 90 nm; and the particle size distribution range of the spherical nano alumina is 1 - 30 nm.

[0018] Furthermore, the sphericity of the spherical nano alumina is 8.8 - 9.2.

[0019] Furthermore, the surfaces of the flaky nano-boehmite and the spherical nano-aluminum oxide are coated with a silane coupling agent;

[0020] The silane coupling agent is selected from any one of silane coupling agent KH-550, silane coupling agent KH-560, and silane coupling agent KH-570.

[0021] Furthermore, the weight-average molecular weight Mw of the polylactic acid is 20,000 - 30,000 g / mol.

[0022] Furthermore, the plasticizer is selected from any one of tributyl citrate, acetyl tributyl citrate, epoxidized soybean oil, dicyclohexyl phthalate, glycerol tribenzoate, or trimethylolpropane tribenzoate.

[0023] Furthermore, the antioxidant is selected from any one of antioxidant 801, butylated hydroxytoluene, thiodi(3-methyl-6-tert-butyl)phenol, and 2,6-di-tert-butyl-p-cresol.

[0024] A preparation method of a degradable hot melt adhesive, the specific preparation steps include:

[0025] Weigh each component according to the raw material composition;

[0026] First, mix ethylene-vinyl acetate copolymer, polylactic acid, plasticizer, antioxidant, microcrystalline wax, and spherical nano-aluminum oxide, and then heat to 150 - 155 °C for stirring and premixing;

[0027] After the stirring and premixing is completed, add flaky nano-boehmite, heat to 160 - 165 °C, and then carry out stirring and final mixing;

[0028] Cool and solidify, discharge, and then the degradable hot melt adhesive is obtained.

[0029] The beneficial effects of the above solution:

[0030] During the melt blending process, first add spherical nano-aluminum oxide. At the initial stage of the stirring shear force, when the temperature is relatively low, the viscosity of the system is relatively large, so the shear force is relatively large. This can make the molecular chains of the two different resins fully stretch under its action at the initial stage of mixing shear, thus achieving sufficient preliminary dispersion. Then, at a higher temperature, add flaky nano-boehmite. Under this condition, the polylactic acid resin is fully melted and the viscosity of the system begins to decrease. At this time, it is beneficial to the rapid and uniform dispersion of flaky boehmite. Through the two-step mixing, the uniform mixing of each component can be achieved, and the oxidative decomposition of the resin caused by over-long mixing time can be avoided.

[0031] Furthermore,

[0032] The stirring premixing includes: stirring and mixing for 25 - 30 min under the condition of a rotation speed of 180 - 200 r / min;

[0033] The final stirring includes: stirring and mixing for 45 - 60 min under the condition of a rotation speed of 320 - 350 r / min.

[0034] Furthermore, the cooling and solidifying includes: cooling down to room temperature at a cooling rate of 2.0 - 2.5 °C / min.

[0035] By further controlling the cooling and solidifying rate, the crystallization rate of the resin under the action of the nano - seasoning is regulated. Specific Embodiments

[0036] The following specific embodiments are used to further illustrate the present invention, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0037] Unless otherwise specified, the reagents and materials used in the following embodiments are all commercially available.

[0038] Example 1

[0039] By weight, 90 parts of ethylene - vinyl acetate copolymer, 18 parts of polylactic acid, 8 parts of nano - filler, 1 part of plasticizer, 1 part of antioxidant, and 2 parts of microcrystalline wax are taken in sequence;

[0040] Among them, the nano - filler is composed of flaky nano - boehmite and spherical nano - alumina with a mass ratio of 0.9:1;

[0041] The D50 of the flaky nano - boehmite is 65 nm;

[0042] The D50 of the spherical nano - alumina is 10 nm;

[0043] The particle size distribution range of the flaky nano - boehmite is 30 - 90 nm; and the particle size distribution range of the spherical nano - alumina is 1 - 30 nm;

[0044] The sphericity of the spherical nano - alumina is 8.8;

[0045] The surfaces of the flaky nano - boehmite and the spherical nano - alumina are coated with a silane coupling agent;

[0046] The silane coupling agent is selected from silane coupling agent KH - 550;

[0047] The weight - average molecular weight Mw of the polylactic acid is 20000 g / mol;

[0048] The plasticizer is selected from tributyl citrate;

[0049] The antioxidant is selected from antioxidant 801;

[0050] First, ethylene-vinyl acetate copolymer, polylactic acid, plasticizer, antioxidant, microcrystalline wax and spherical nano-aluminum oxide are mixed, and then heated to 150 °C. Under the condition of a rotation speed of 180 r / min, the mixture is stirred and premixed for 25 min to obtain a premixed material;

[0051] Then, flaky nano-boehmite is added to the premixed material, and the mixture is heated to 160 °C. Under the condition of a rotation speed of 320 r / min, the mixture is stirred and finally mixed for 45 min to obtain a finally mixed material;

[0052] The obtained finally mixed material is cooled to room temperature at a cooling rate of 2.0 °C / min to solidify the finally mixed material, thereby obtaining the degradable hot melt adhesive.

[0053] Example 2

[0054] By weight, 95 parts of ethylene-vinyl acetate copolymer, 19 parts of polylactic acid, 9 parts of nano-filler, 2 parts of plasticizer, 2 parts of antioxidant, and 3 parts of microcrystalline wax are taken in sequence;

[0055] Among them, the nano-filler is composed of flaky nano-boehmite and spherical nano-aluminum oxide in a mass ratio of 0.96:1;

[0056] The D50 of the flaky nano-boehmite is 68 nm;

[0057] The D50 of the spherical nano-aluminum oxide is 12 nm;

[0058] The particle size distribution range of the flaky nano-boehmite is 30 - 90 nm; and the particle size distribution range of the spherical nano-aluminum oxide is 1 - 30 nm;

[0059] The sphericity of the spherical nano-aluminum oxide is 9;

[0060] The surfaces of the flaky nano-boehmite and the spherical nano-aluminum oxide are coated with a silane coupling agent;

[0061] The silane coupling agent is selected from silane coupling agent KH-560;

[0062] The weight-average molecular weight Mw of the polylactic acid is 25000 g / mol;

[0063] The plasticizer is selected from tributyl acetylcitrate;

[0064] The antioxidant is selected from butylated hydroxytoluene;

[0065] First, mix ethylene-vinyl acetate copolymer, polylactic acid, plasticizer, antioxidant, microcrystalline wax and spherical nano-aluminum oxide, then heat to 152 °C and stir and premix for 28 min at a rotation speed of 190 r / min to obtain a premix;

[0066] Then, add flaky nano-boehmite to the said premix, heat to 163 °C and stir and finally mix for 50 min at a rotation speed of 330 r / min to obtain a final mix;

[0067] Cool the obtained final mix to room temperature at a cooling rate of 2.2 °C / min to solidify the final mix, thus obtaining a degradable hot melt adhesive.

[0068] Example 3

[0069] By weight, successively take 100 parts of ethylene-vinyl acetate copolymer, 20 parts of polylactic acid, 10 parts of nano-filler, 3 parts of plasticizer, 3 parts of antioxidant, and 4 parts of microcrystalline wax;

[0070] Among them, the said nano-filler is composed of flaky nano-boehmite and spherical nano-aluminum oxide in a mass ratio of 1:1;

[0071] The D50 of the said flaky nano-boehmite is 70 nm;

[0072] The D50 of the said spherical nano-aluminum oxide is 15 nm;

[0073] The particle size distribution range of the said flaky nano-boehmite is 30 - 90 nm; and the particle size distribution range of the said spherical nano-aluminum oxide is 1 - 30 nm;

[0074] The sphericity of the said spherical nano-aluminum oxide is 9.2;

[0075] The surfaces of the said flaky nano-boehmite and the said spherical nano-aluminum oxide are coated with a silane coupling agent;

[0076] The said silane coupling agent is selected from silane coupling agent KH-570;

[0077] The weight-average molecular weight Mw of the said polylactic acid is 30000 g / mol;

[0078] The said plasticizer is selected from epoxy soybean oil;

[0079] The said antioxidant is selected from thiodi(3-methyl-6-tert-butyl)phenol;

[0080] First, mix ethylene-vinyl acetate copolymer, polylactic acid, plasticizer, antioxidant, microcrystalline wax and spherical nano-aluminum oxide, then heat to 155 °C and stir and premix for 30 min at a rotation speed of 200 r / min to obtain a premix;

[0081] Then, flaky nano - boehmite is added to the premix, and the mixture is heated to 165 °C and stirred for 60 min at a rotation speed of 350 r / min for final mixing to obtain a final mixture.

[0082] The obtained final mixture is cooled to room temperature at a cooling rate of 2.5 °C / min to cure the final mixture, thereby obtaining a degradable hot - melt adhesive.

[0083] Example 4

[0084] The difference between this example and Example 1 is as follows:

[0085] The particle size distribution range of the flaky nano - boehmite is 10 - 120 nm; and the particle size distribution range of the spherical nano - alumina is 0.1 - 60 nm; other conditions remain unchanged.

[0086] Example 5

[0087] The difference between this example and Example 1 is as follows:

[0088] The sphericity of the spherical nano - alumina is 8.4, and other conditions remain unchanged.

[0089] Example 6

[0090] The difference between this example and Example 1 is as follows:

[0091] First, ethylene - vinyl acetate copolymer, polylactic acid, plasticizer, antioxidant, microcrystalline wax and flaky nano - boehmite are mixed and then heated to 150 °C and stirred for 25 min at a rotation speed of 180 r / min for premixing to obtain a premix.

[0092] Then, spherical nano - alumina is added to the premix, and the mixture is heated to 160 °C and stirred for 45 min at a rotation speed of 320 r / min for final mixing to obtain a final mixture.

[0093] Other conditions remain unchanged.

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 1 is as follows: Flaky nano - boehmite is not added, and other conditions remain unchanged.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is as follows: Spherical nano - alumina is not added, and other conditions remain unchanged.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 1 is that polylactic acid was not added, and the other conditions remained unchanged.

[0100] Performance tests were conducted on the products obtained from the above examples and comparative examples. The specific test methods and test results are as follows:

[0101] Tensile strength test:

[0102] According to the test standard of GB / T528-1998, the test conditions were as follows: an electronic tensile testing machine, temperature 25°C, humidity 50%, tensile rate 50 mm / min. Five samples were tested and the average value was taken. The detailed test results are shown in Table 1.

[0103] Biodegradability test:

[0104] The soil burial method was adopted. A square thin film with a specification of 10 cm × 10 cm was weighed as m1 and buried in moist soil. After one month, it was taken out, dried and weighed as m2. Its degradation performance was characterized by the mass change rate. The detailed test results are shown in Table 1.

[0105] Mass change rate = (m1 - m2) / m1 × 100%;

[0106] Table 1: Product performance test results:

[0107] Tensile strength / MPa Mass change rate / % Example 1 5.28 27.6 Example 2 5.35 28.2 Example 3 5.44 28.3 Example 4 5.11 26.6 Example 5 5.14 26.8 Example 6 5.08 26.3 Comparative Example 1 4.55 23.5 Comparative Example 2 4.63 24.1 Comparative Example 3 4.44 18.5

[0108] It can be seen from the test results in Table 1 that the products obtained by the present invention can effectively guarantee the basic bonding performance of the products, and at the same time, they can also have higher biodegradability.

[0109] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A degradable hot melt adhesive, characterized in that: The invention comprises the following raw materials in parts by weight: 90-100 parts of ethylene-vinyl acetate copolymer, 18-20 parts of polylactic acid, 8-10 parts of nanofiller, 1-3 parts of plasticizer, 1-3 parts of antioxidant, 2-4 parts of microcrystalline wax; Wherein, the nano filler is composed of flaky nano boehmite and spherical nano alumina in a mass ratio of (0.9-1.0): 1; The D50 of the flaky nano-boehmite is 65-70 nm; The D50 of the spherical nano-alumina is 10-15nm; When preparing the degradable hot melt adhesive, First, ethylene-vinyl acetate copolymer, polylactic acid, plasticizer, antioxidant, microcrystalline wax and spherical nano-alumina are mixed, heated to 150-155° C., and stirred for premixing; After the stirring and premixing is completed, add the flaky nano-boehmite, heat to 160-165°C, and then stir and final mix.

2. A degradable hot melt adhesive according to claim 1, characterized in that: The particle size distribution range of the flaky nano-boehmite is 30-90 nm; and the particle size distribution range of the spherical nano-alumina is 1-30 nm.

3. A degradable hot melt adhesive according to any one of claims 1-2, characterized in that: The sphericity of the spherical nano-alumina is 8.8-9.

2.

4. The degradable hot melt adhesive according to claim 1, characterized in that: The surfaces of the flaky nano-boehmite and the spherical nano-alumina are coated with a silane coupling agent; The silane coupling agent is selected from any one of silane coupling agent KH-550, silane coupling agent KH-560 and silane coupling agent KH-570.

5. The degradable hot melt adhesive according to claim 1, characterized in that: The weight average molecular weight Mw of the polylactic acid is 20000-30000 g / mol.

6. The degradable hot melt adhesive according to claim 1, characterized in that: The plasticizer is selected from any one of tributyl citrate, acetyl tributyl citrate, epoxy soybean oil, dicyclohexyl phthalate, glycerol tribenzoate or trimethylolpropane tribenzoate.

7. The degradable hot melt adhesive according to claim 1, characterized in that: The antioxidant is selected from any one of antioxidant 801, butylated hydroxytoluene, thiobis(3-methyl-6-tert-butyl)phenol, and 2,6-di-tert-butyl-p-cresol.

8. A method for preparing the degradable hot melt adhesive according to any one of claims 1 to 7, characterized in that: The specific preparation steps include: Weigh each component according to the raw material composition; First, ethylene-vinyl acetate copolymer, polylactic acid, plasticizer, antioxidant, microcrystalline wax and spherical nano-alumina are mixed, heated to 150-155° C., and stirred for premixing; After the stirring and premixing is completed, add the flaky nano-boehmite, heat to 160-165°C, and then stir and final mix; Cooling and solidification, discharging, and obtaining the degradable hot melt adhesive.

9. The method for preparing a degradable hot melt adhesive according to claim 8, characterized in that: The stirring premixing comprises: stirring and mixing for 25-30 minutes at a rotation speed of 180-200 r / min; The stirring and final mixing comprises: stirring and mixing for 45-60 minutes at a rotation speed of 320-350 r / min.

10. The method for preparing a degradable hot melt adhesive according to claim 8, characterized in that: The cooling and solidification comprises: cooling down to room temperature at a cooling rate of 2.0-2.5°C / min.