Lactic gypsum / resin composite material as well as preparation method and application thereof

Abstract

The invention provides a lactic gypsum / resin composite material as well as a preparation method and application thereof, and belongs to the technical field of solid waste utilization and composite materials. The lactic acid gypsum / resin composite material provided by the invention comprises the following components in percentage by mass: 50-80% of modified lactic acid gypsum, 15-45% of thermoplastic resin, 2-3% of maleic anhydride and 1-2% of calcium stearate, the modified lactic acid gypsum is silane coupling agent modified lactic acid gypsum, and the grafting amount of a silane coupling agent in the modified lactic acid gypsum is 2-5% by mass. According to the lactic acid gypsum / resin composite material provided by the invention, the interfacial properties of the lactic acid gypsum and the thermoplastic resin are effectively improved through specific components, and the mechanical properties of the composite material are improved. The result of the embodiment shows that the bending strength of the composite material provided by the invention is 37-49 MPa, and the bending modulus of the composite material is 1357-1881 MPa.

Description

Technical Field

[0001] The present invention relates to the fields of solid waste utilization and composite materials, and particularly to a lactic acid gypsum / resin composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Lactic acid gypsum is a by-product generated during the production of lactic acid. At present, the utilization rate of lactic acid gypsum by-products is very low, and most of them are treated as waste, which not only wastes resources but also pollutes the environment. Currently, lactic acid gypsum is commonly used to prepare materials such as gypsum boards and gypsum statues to realize the utilization of lactic acid gypsum by-products. For example, a gypsum composite material prepared from lactic acid gypsum and polyolefins is provided in the prior art. However, the maximum compressive strength of this gypsum composite material is 5.3 MPa, and the mechanical properties of the composite material cannot meet the requirements of practical applications. Summary of the Invention

[0003] The purpose of the present invention is to provide a lactic acid gypsum / resin composite material, a preparation method thereof, and an application thereof. The lactic acid gypsum / resin composite material provided by the present invention has excellent mechanical properties.

[0004] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a lactic acid gypsum / resin composite material, comprising the following components in mass percentages: 50-80% of modified lactic acid gypsum, 15-45% of thermoplastic resin, 2-3% of maleic anhydride, and 1-2% of calcium stearate;

[0006] The modified lactic acid gypsum is lactic acid gypsum modified by a silane coupling agent. By mass percentage, the grafting amount of the silane coupling agent in the modified lactic acid gypsum is 2-5%.

[0007] Preferably, the lactic acid gypsum / resin composite material comprises the following components in mass percentages: 60-78% of modified lactic acid gypsum, 16-43% of thermoplastic resin, 2.1-2.9% of maleic anhydride, and 1.1-1.9% of calcium stearate.

[0008] Preferably, the composite material comprises the following components in mass percentages: 70-75% of modified lactic acid gypsum, 21-40% of thermoplastic resin, 2.2-2.8% of maleic anhydride, and 1.2-1.8% of calcium stearate.

[0009] Preferably, the water content of the lactic acid gypsum in the modified lactic acid gypsum is <1%, and the specific surface area is >450 m 2 / kg.

[0010] Preferably, the thermoplastic resin is one or more of polypropylene, polyethylene, and polyvinyl chloride.

[0011] The present invention also provides a method for preparing the lactic acid gypsum / resin composite material described in the above technical solution, comprising the following steps:

[0012] (1) First, stir and mix lactic acid gypsum and a silane coupling agent to obtain modified lactic acid gypsum;

[0013] (2) Then, second, stir and mix the modified lactic acid gypsum obtained in step (1) with a thermoplastic resin, maleic anhydride, and calcium stearate, and then granulate and extrude them in sequence to obtain the lactic acid gypsum / resin composite material.

[0014] Preferably, the time for the first stirring and mixing in step (1) is 8 - 10 min, and the rate of the first stirring and mixing is 800 - 1000 rpm / min.

[0015] Preferably, the time for the second stirring and mixing in step (2) is 8 - 30 min, and the rate of the second stirring and mixing is 500 - 1500 rpm / min.

[0016] Preferably, the temperatures for granulation in step (2) are 190 - 220 °C, 180 - 200 °C, 180 - 190 °C, 170 - 190 °C, 170 - 180 °C, 170 - 180 °C, 165 - 175 °C, and 165 - 175 °C in sequence.

[0017] The present invention also provides the application of the lactic acid gypsum / resin composite material described in the above technical solution or the lactic acid gypsum / resin composite material prepared by the preparation method described in the above technical solution in packaging materials.

[0018] The present invention provides a composite material, comprising the following components in mass percentages: 50 - 80% of modified lactic acid gypsum, 15 - 45% of thermoplastic resin, 2 - 3% of maleic anhydride, and 1 - 2% of calcium stearate; the modified lactic acid gypsum is lactic acid gypsum modified by a silane coupling agent, and by mass percentage, the grafting amount of the silane coupling agent in the modified lactic acid gypsum is 2 - 5%. The present invention uses lactic acid gypsum and thermoplastic resin as the components of the composite material, and uses the inorganic component lactic acid gypsum as the skeleton material of the organic component thermoplastic resin, effectively improving the mechanical properties of the composite material; at the same time, using a silane coupling agent to perform surface modification on lactic acid gypsum, and under the combined action with maleic anhydride, effectively reducing the interfacial tension between lactic acid gypsum and thermoplastic resin, thereby improving their compatibility and further improving the mechanical properties of the composite material; using calcium stearate to achieve lubrication between lactic acid gypsum and thermoplastic resin, which is beneficial to their uniform dispersion and further improves the mechanical properties of the composite material. The results of the examples show that the flexural strength of the composite material provided by the present invention is 37 - 49 MPa, and the flexural modulus is 1357 - 1881 MPa. Detailed implementation manners

[0019] The present invention provides a lactic acid gypsum / resin composite material, comprising components in the following mass percentages: 50-80% of modified lactic acid gypsum, 15-45% of thermoplastic resin, 2-3% of maleic anhydride, and 1-2% of calcium stearate;

[0020] The modified lactic acid gypsum is lactic acid gypsum modified by a silane coupling agent. By mass percentage, the grafting amount of the silane coupling agent in the modified lactic acid gypsum is 2-5%.

[0021] By mass percentage, the lactic acid gypsum / resin composite material provided by the present invention comprises 50-80% of modified lactic acid gypsum; as an embodiment of the present invention, the mass content of the modified lactic acid gypsum can be 60-78%, or can be 70-75%; in the examples of the present invention, the mass content of the modified lactic acid gypsum can specifically be 50%, 51%, 52%, 55%, 60%, 65%, 70%, 72%, 75%, 76%, 78%, 79%, or 80%. In the present invention, the modified lactic acid gypsum serves as the main component of the composite material, playing a role of skeleton support and effectively improving the mechanical properties of the lactic acid gypsum / resin composite material.

[0022] As an embodiment of the present invention, the modified lactic acid gypsum is lactic acid gypsum modified by a silane coupling agent; the grafting amount of the silane coupling agent in the modified lactic acid gypsum is 2-5%, can be 3-4%, or can be 3.5-3.8%; the water content of the lactic acid gypsum in the modified lactic acid gypsum can be <1%, can also be <0.8%, or can also be <0.5%; the specific surface area of the lactic acid gypsum in the modified lactic acid gypsum can be >450 m 2 / kg, can also be >480 m 2 / kg, or can also be >500 m 2 / kg. In the present invention, by limiting the grafting amount of the silane coupling agent in the modified lactic acid gypsum, effective surface modification of the lactic acid gypsum is achieved, the interfacial tension between it and the resin component is reduced, and the binding force with the resin component is effectively improved; at the same time, the water content and specific surface area of the lactic acid gypsum in the modified lactic acid gypsum are limited, so as to achieve full contact modification of the lactic acid gypsum and the silane coupling agent, and further improve the mechanical properties of the composite material.

[0023] By mass percentage, the lactic acid gypsum / resin composite material provided by the present invention comprises 15-45% of a thermoplastic resin; as an embodiment of the present invention, the mass content of the thermoplastic resin can be 16-43%, or can be 21-40%; in the embodiments of the present invention, the mass content of the thermoplastic resin can specifically be 15%, 16%, 20%, 21%, 25%, 30%, 35%, 40%, 42%, 43%, 44% or 45%. In the present invention, the thermoplastic resin, as the main component of the composite material, has excellent viscosity, can firmly connect the lactic acid gypsum, and enhance the cohesion of the material; at the same time, it has excellent flexibility, can effectively absorb and dissipate impact energy, and further improve the mechanical properties of the composite material.

[0024] As an embodiment of the present invention, the thermoplastic resin can be a polypropylene resin, a polyethylene resin or a polyvinyl chloride resin. In the present invention, by defining the type of the thermoplastic resin, the role of the thermoplastic resin is fully exerted, and the mechanical properties of the composite material are further improved.

[0025] By mass percentage, the lactic acid gypsum / resin composite material provided by the present invention comprises 2-3% of maleic anhydride; as an embodiment of the present invention, the mass content of the maleic anhydride can be 2.1-2.9%, or can be 2.2-2.8%; in the embodiments of the present invention, the mass content of the maleic anhydride can specifically be 2%, 2.1%, 2.2%, 2.5%, 2.6%, 2.8%, 2.9% or 3%. In the present invention, maleic anhydride can reduce the interfacial tension between the lactic acid gypsum and the thermoplastic resin, thereby improving the compatibility between the two, and further improving the mechanical properties of the composite material.

[0026] By mass percentage, the lactic acid gypsum / resin composite material provided by the present invention comprises 1-2% of calcium stearate; as an embodiment of the present invention, the mass content of the calcium stearate can be 1.1-1.9%, or can also be 1.2-1.8%. In the embodiments of the present invention, the mass content of the calcium stearate can specifically be 1%, 1.1%, 1.2%, 1.5%, 1.6%, 1.8%, 1.9% or 2%. In the present invention, calcium stearate can achieve lubrication between the lactic acid gypsum and the thermoplastic resin, is beneficial to the uniform dispersion of the two, and further improves the mechanical properties of the composite material.

[0027] As an embodiment of the present invention, the calcium stearate can be calcium stearate prepared by a melting method.

[0028] As an embodiment of the present invention, by mass percentage, the lactic acid gypsum / resin composite material provided by the present invention may include 0.3-0.6% of color powder. As an embodiment of the present invention, the mass content of the color powder may also be 0.35-0.5%, or may also be 0.4-0.45%. In the present invention, the color powder can make the composite material have different colors.

[0029] As an embodiment of the present invention, the color powder may be titanium dioxide and / or phthalocyanine blue series color powder.

[0030] The present invention uses lactic acid gypsum and thermoplastic resin plastic as the components of the composite material, and uses the inorganic component lactic acid gypsum as the skeleton material of the organic component thermoplastic resin to effectively improve the mechanical properties of the composite material; at the same time, the surface of lactic acid gypsum is modified by a silane coupling agent, and under the combined action of maleic anhydride, the interfacial tension between lactic acid gypsum and thermoplastic resin is effectively reduced, thereby improving the compatibility between the two and further improving the mechanical properties of the composite material; calcium stearate is used to achieve lubrication between lactic acid gypsum and thermoplastic resin, which is beneficial to their uniform dispersion and further improves the mechanical properties of the composite material.

[0031] The lactic acid gypsum / resin composite material provided by the present invention uses a specific composition, which can make the composite material have a high whiteness, can be processed into different colors, and has high practicability; and under the combined action of each component, the tightness of the combination between components is effectively improved, the polarity of the material is reduced, and the water absorption rate of the composite material is effectively reduced; the inorganic lactic acid gypsum is surrounded by the organic thermoplastic resin, making it difficult to form an electron channel, effectively improving the resistivity of the composite material; and under the combined action of each component, the stability of the composite material is effectively improved and the combustion index is reduced.

[0032] The present invention also provides a preparation method of the lactic acid gypsum / resin composite material described in the above technical solution, including the following steps:

[0033] (1) First, stir and mix lactic acid gypsum and a silane coupling agent to obtain modified lactic acid gypsum;

[0034] (2) Second, stir and mix the modified lactic acid gypsum obtained in step (1) with thermoplastic resin, maleic anhydride and calcium stearate, and then granulate and extrude in sequence to obtain the lactic acid gypsum / resin composite material.

[0035] The present invention stirs and mixes lactic acid gypsum and a silane coupling agent to obtain modified lactic acid gypsum.

[0036] As an embodiment of the present invention, the source of the lactic acid gypsum is the original lactic acid gypsum, which is a by-product in the production process of lactic acid.

[0037] As an embodiment of the present invention, the preparation method of the lactic acid gypsum may be to sequentially dry and ball-mill the as-received lactic acid gypsum to obtain lactic acid gypsum.

[0038] The present invention has no special limitation on the drying operation, and the drying operations commonly used by those skilled in the art can be adopted.

[0039] As an embodiment of the present invention, the ball-to-material ratio of the ball milling may be (1-3):1, may also be (1.5-2.8):1, or may also be (2-2.5):1; the time of the ball milling may be 1-2 h, may also be 1.5-1.8 h; the rate of the ball milling may be 500-1500 rpm / min, may also be 800-1300 rpm / min, or may also be 1000-1200 rpm / min. By limiting the process parameters of the ball milling, the present invention can achieve sufficient ball milling of the as-received lactic acid gypsum, increase its surface area, improve the contact opportunity between the as-received lactic acid gypsum and the silane coupling agent, and further improve the bonding strength between the lactic acid gypsum and the thermoplastic resin.

[0040] As an embodiment of the present invention, the time of the first stirring and mixing may be 8-10 min, may also be 9-9.5 min; the rate of the first stirring and mixing may be 800-1000 rpm / min, may also be 850-980 rpm / min, or may also be 900-950 rpm / min. In the present invention, when the silane coupling agent contacts the lactic acid gypsum, the oxygen end of the silane coupling agent is compatible with the interface of the lactic acid gypsum, laying a foundation for the subsequent combination with the resin component; by limiting the process parameters of the stirring and mixing, the contact opportunity between the two is further improved, and the modification effect is effectively improved.

[0041] After obtaining the modified lactic acid gypsum, the present invention performs a second stirring and mixing of the modified lactic acid gypsum with a thermoplastic resin, maleic anhydride, and calcium stearate, and then granulates and extrudes them in sequence to obtain a lactic acid gypsum / resin composite material.

[0042] As an embodiment of the present invention, the source of the thermoplastic resin may be waste plastics. In the present invention, the thermoplastic resin can be recycled from waste plastics, and the flexibility of the thermoplastic resin can be used to achieve a tight combination between the thermoplastic resin and the modified lactic acid gypsum, further improving the mechanical properties of the composite material.

[0043] As an embodiment of the present invention, the time of the second stirring and mixing can be 8 to 30 min, can also be 10 to 25 min, and can also be 15 to 20 min; the rate of the second stirring and mixing can be 500 to 1500 rpm / min, can also be 600 to 1200 rpm / min, and can also be 800 to 1000 rpm / min. By defining the process parameters of the stirring and mixing, the reaction raw materials are fully mixed and contacted, further improving the mechanical properties of the composite material.

[0044] As an embodiment of the present invention, the temperatures for granulation can be successively 190 to 220 °C, 180 to 200 °C, 180 to 190 °C, 170 to 190 °C, 170 to 180 °C, 170 to 180 °C, 165 to 175 °C, and 165 to 175 °C; can also be successively 195 to 215 °C, 185 to 195 °C, 182 to 188 °C, 175 to 185 °C, 172 to 178 °C, 172 to 178 °C, 168 to 173 °C, and 168 to 173 °C, and can also be successively 200 to 210 °C, 188 to 190 °C, 185 to 186 °C, 180 to 182 °C, 175 to 176 °C, 175 to 176 °C, 170 to 172 °C, and 170 to 172 °C. The present invention has no special limitation on the time of granulation, and the time commonly used by those skilled in the art can be adopted. As an embodiment of the present invention, the particle size of the product after granulation can be 6 to 8 mm, or can also be 7 to 7.5 mm. During the granulation process of the present invention, the fluidity of the thermoplastic resin component is effectively improved, so that the thermoplastic resin and the calcium lactate gypsum are uniformly mixed to form a sea-island structure; by defining the process parameters of the extrusion granulation and the particle size of the product after granulation, the mixing process of the two is effectively controlled, further improving the mechanical properties of the composite material.

[0045] As an embodiment of the present invention, the temperatures for extrusion can be successively 180 to 200 °C, 180 to 200 °C, 170 to 190 °C, 170 to 180 °C, 160 to 180 °C, and 160 to 170 °C, can also be successively 185 to 195 °C, 182 to 190 °C, 175 to 185 °C, 172 to 178 °C, 165 to 175 °C, and 162 to 168 °C, and can also be successively 190 °C, 185 °C, 180 °C, 175 °C, 170 °C, and 165 °C. The present invention has no special limitation on the time of extrusion, and the extrusion time commonly used by those skilled in the art can be adopted. During the extrusion process of the present invention, the composite material obtained by granulation is secondary plasticized, so that the components are more uniformly mixed, and the bonding force between the calcium lactate gypsum and the thermoplastic resin is tighter, further improving the mechanical properties.

[0046] The preparation method provided by the present invention can effectively achieve the surface modification of lactic acid gypsum and the uniform mixing of raw materials, improve the bonding force between lactic acid gypsum and thermoplastic resin, and effectively improve the mechanical properties of the composite material.

[0047] The present invention also provides the application of the lactic acid gypsum / resin composite material described in the above technical solution or the lactic acid gypsum / resin composite material prepared by the preparation method described in the above technical solution in packaging materials.

[0048] In order to further illustrate the present invention, the lactic acid gypsum / resin composite material provided by the present invention, its preparation method and application will be described in detail below in conjunction with examples, but they cannot be understood as limiting the protection scope of the present invention.

[0049] Example 1

[0050] A lactic acid gypsum / resin composite material, the composition is by mass percentage: modified lactic acid gypsum 51.8%, polypropylene resin 44.5%, maleic anhydride (108-31-6) 2.2%, calcium stearate 1% and phthalocyanine blue powder 0.5%;

[0051] The modified lactic acid gypsum is lactic acid gypsum modified by a silane coupling agent. By mass percentage, the grafting amount of the silane coupling agent in the modified lactic acid gypsum is 4.5%;

[0052] The preparation method of the lactic acid gypsum / resin composite material is as follows:

[0053] (1) After drying the original lactic acid gypsum, ball milling it at 800 rpm / min (ball-to-material ratio is 2:1) for 1 h to obtain lactic acid gypsum with a moisture content of 0.2% and a specific surface area of 500 m 2 / kg; mixing the obtained lactic acid gypsum and silane coupling agent A151 under the condition of 1000 rpm / min for the first stirring for 8 min to obtain modified lactic acid gypsum;

[0054] (2) Mix the modified lactic acid gypsum obtained in step (1) with recycled polypropylene resin for white water dispensers, maleic anhydride (108-31-6), calcium stearate and phthalocyanine blue powder under the condition of 1000 rpm / min for the second stirring for 10 min, and then granulate under the conditions of temperatures of 220 °C, 200 °C, 190 °C, 180 °C, 175 °C, 175 °C, 170 °C and 170 °C in sequence to obtain composite particles with a particle size of 6 - 8 mm, and extrude the obtained composite particles under the conditions of temperatures of 200 °C, 195 °C, 190 °C, 180 °C, 175 °C and 165 °C in sequence to obtain the lactic acid gypsum / resin composite material.

[0055] Example 2

[0056] Example 2 is only different from Example 1 in that the mass content of the modified gypsum lactate in the composition of the gypsum lactate / resin composite material is 56.8%, and the mass content of the polypropylene resin is 39.5%;

[0057] The modified gypsum lactate is the gypsum lactate modified by a silane coupling agent. By mass percentage, the grafting amount of the silane coupling agent in the modified gypsum lactate is 3.2%;

[0058] In the preparation method of the gypsum lactate / resin composite material, the raw material of the polypropylene resin is the recycled polypropylene resin of a white vacuum cleaner base, and the rest is the same as in Example 1.

[0059] Example 3

[0060] Example 3 is only different from Example 1 in that the mass content of the modified gypsum lactate in the composition of the gypsum lactate / resin composite material is 61.8%, and the mass content of the polypropylene resin is 34.5%;

[0061] The modified gypsum lactate is the gypsum lactate modified by a silane coupling agent. By mass percentage, the grafting amount of the silane coupling agent in the modified gypsum lactate is 3.9%;

[0062] In the preparation method of the gypsum lactate / resin composite material, the raw material of the polypropylene resin is the recycled polypropylene resin of a natural color plastic bag, and the rest is the same as in Example 1.

[0063] Example 4

[0064] Example 4 is only different from Example 1 in that the mass content of the modified gypsum lactate in the composition of the gypsum lactate / resin composite material is 66.8%, and the mass content of the polypropylene resin is 29.5%;

[0065] The modified gypsum lactate is the gypsum lactate modified by a silane coupling agent. By mass percentage, the grafting amount of the silane coupling agent in the modified gypsum lactate is 2.7%;

[0066] In the preparation method of the gypsum lactate / resin composite material, the raw material of the polypropylene resin is the recycled polypropylene resin of white air conditioner interior parts, and the rest is the same as in Example 1.

[0067] Example 5

[0068] Example 5 is only different from Example 1 in that the mass content of the modified gypsum lactate in the composition of the gypsum lactate / resin composite material is 71.8%, and the mass content of the polypropylene resin is 24.5%;

[0069] The modified gypsum lactate is the gypsum lactate modified by a silane coupling agent. By mass percentage, the grafting amount of the silane coupling agent in the modified gypsum lactate is 2.9%;

[0070] In the preparation method of the lactic acid gypsum / resin composite material, the raw material of the polypropylene resin is the recycled polypropylene resin for white automotive interiors, and the rest is the same as in Example 1.

[0071] Example 6

[0072] The difference between Example 6 and Example 1 is only that in the composition of the lactic acid gypsum / resin composite material, the mass content of the modified lactic acid gypsum is 76.8%, and the mass content of the polypropylene resin is 19.5%;

[0073] The modified lactic acid gypsum is the lactic acid gypsum modified by a silane coupling agent. By mass percentage, the grafting amount of the silane coupling agent in the modified lactic acid gypsum is 2.3%;

[0074] In the preparation method of the lactic acid gypsum / resin composite material, the raw material of the polypropylene resin is the recycled polypropylene resin for white lubricating oil drums, and the rest is the same as in Example 1.

[0075] Test Example 1

[0076] The water absorption rate of the lactic acid gypsum / resin composite materials of Examples 1 to 6 was tested using a moisture tester, and the test parameters refer to GB / T 1482-2010; the resistivity of the lactic acid gypsum / resin composite materials of Examples 1 to 6 was tested using a plastic resistivity meter, and the test parameters refer to GB / T 1410; the flexural strength and flexural modulus of the lactic acid gypsum / resin composite materials of Examples 1 to 6 were tested using a universal testing machine, and the test parameters refer to GB / T 9341-2008; the limiting oxygen index of the lactic acid gypsum / resin composite materials of Examples 1 to 6 was tested using a plastic oxygen index tester, and the test parameters refer to GB / T 2406.2-2009. The test data obtained are shown in Table 1.

[0077] Table 1 Test data of the lactic acid gypsum / resin composite materials of Examples 1 to 6

[0078]

[0079]

[0080] It can be seen from Table 1 that as the amount of the modified lactic acid gypsum in the composite material increases, the mechanical properties of the composite material increase accordingly; the flexural strength of the composite material provided by the present invention is 37-49 MPa, and the flexural modulus is 1357-1881 MPa, having excellent mechanical properties, and at the same time having low water absorption rate, relatively high limiting oxygen index and high resistivity.

[0081] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A lactic acid gypsum / resin composite material, comprising the following components in percentage by mass: 50-80% of modified lactic acid gypsum, 15-45% of thermoplastic resin, 2-3% of maleic anhydride and 1-2% of calcium stearate; The modified lactic acid gypsum is silane coupling agent modified lactic acid gypsum, and the grafting amount of the silane coupling agent in the modified lactic acid gypsum is 2-5% by mass percentage.

2. The lactic acid gypsum / resin composite material according to claim 1, characterized in that: The invention comprises the following components in percentage by mass: 60-78% of modified lactic acid gypsum, 16-43% of thermoplastic resin, 2.1-2.9% of maleic anhydride and 1.1-1.9% of calcium stearate.

3. The lactic acid gypsum / resin composite material according to claim 1, characterized in that: The invention comprises the following components in percentage by mass: 70-75% of modified lactic acid gypsum, 21-40% of thermoplastic resin, 2.2-2.8% of maleic anhydride and 1.2-1.8% of calcium stearate.

4. The lactic acid gypsum / resin composite material according to any one of claims 1 to 3, characterized in that: The water content of the lactic acid gypsum in the modified lactic acid gypsum is less than 1%, and the specific surface area is greater than 450m 2 / kg.

5. The lactic acid gypsum / resin composite material according to any one of claims 1 to 3, characterized in that: The thermoplastic resin is one or more of polypropylene, polyethylene and polyvinyl chloride.

6. The method for preparing the lactic acid gypsum / resin composite material according to any one of claims 1 to 5, comprising the following steps: (1) mixing lactic acid gypsum and a silane coupling agent and performing a first stirring and mixing to obtain modified lactic acid gypsum; (2) The modified lactic acid gypsum obtained in step (1) is mixed with a thermoplastic resin, maleic anhydride, and calcium stearate for a second time, and then granulated and extruded in sequence to obtain a lactic acid gypsum / resin composite material.

7. The preparation method according to claim 6, characterized in that: The first stirring and mixing time in step (1) is 8 to 10 minutes, and the first stirring and mixing speed is 800 to 1000 rpm / min.

8. The preparation method according to claim 6, characterized in that: The second stirring and mixing time in step (2) is 8 to 30 minutes, and the second stirring and mixing speed is 500 to 1500 rpm / min.

9. The preparation method according to claim 6, characterized in that: The granulation temperatures in the step (2) are 190-220°C, 180-200°C, 180-190°C, 170-190°C, 170-180°C, 170-180°C, 165-175°C and 165-175°C, respectively.

10. Use of the lactic acid gypsum / resin composite material according to any one of claims 1 to 5 or the lactic acid gypsum / resin composite material prepared by the preparation method according to claims 6 to 9 in packaging materials.

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