A bio-based composite modified heavy calcium carbonate, and a preparation method and application thereof

Abstract

The application provides a kind of bio-based composite modified heavy calcium carbonate and its preparation method and application, belong to inorganic powder function modification and biodegradable material technical field.The surface of heavy calcium carbonate is modified by wet coating process in the application, the bio-based modifier is chitosan-g-poly (lactic acid) graft copolymer, which cooperates with silane coupling agent to form a dense modified layer on the surface of calcium carbonate, which has biocompatibility.The modified heavy calcium carbonate prepared by the application has excellent compatibility with biodegradable plastic matrix, and after adding, the tensile strength of the composite material can be increased by 15%-25%, the elongation at break can be increased by 20%-30%, and the biodegradation rate of the material is not inhibited, and even the biodegradation is accelerated through the synergistic effect of the bio-based modifier.The method is environmentally friendly and controllable, and the product is suitable for biodegradable plastics, high-end environmental protection coatings and other fields, with significant economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of inorganic powder functional modification and biodegradable materials technology, and particularly to a bio-based composite modified heavy calcium carbonate, its preparation method and application. Background Technology

[0002] Heavy calcium carbonate (GCC) is widely used as a filler in plastics, coatings, and papermaking due to its abundant resources, low cost, and environmental friendliness. In recent years, with the implementation of the "plastic ban," biodegradable plastics (such as PLA and PBS) have become the mainstream alternative to traditional plastics. However, these materials generally suffer from insufficient mechanical properties and high costs. Adding heavy calcium carbonate can reduce costs and enhance performance.

[0003] However, traditional heavy calcium carbonate and biodegradable plastic matrices have inherent defects: First, the surface is highly hydrophilic and weakly oleophobic, resulting in poor compatibility with hydrophobic polymer matrices and easy agglomeration, which leads to a decrease in the mechanical properties of composite materials (such as a reduction in elongation at break of more than 30%). Second, traditional modifiers (such as fatty acids and petroleum-based coupling agents) are not environmentally friendly enough and can only improve compatibility, but cannot solve the problem of "synergistic reinforcement and degradation". Some modifiers may even inhibit microbial activity and slow down the degradation rate of materials. Third, a single modification process is difficult to meet the multiple requirements of "uniform dispersion, mechanical reinforcement and biocompatibility" at the same time.

[0004] Existing modification technologies mostly focus on single modifiers (such as silane coupling agents and titanate coupling agents) or only pursue compatibility improvement, lacking consideration for biodegradability. Therefore, developing a composite modification technology based on green bio-based modifiers to achieve simultaneous optimization of "compatibility-mechanical properties-degradability" of heavy calcium carbonate in biodegradable plastics is key to promoting the industrial application of biodegradable materials. Summary of the Invention

[0005] The purpose of this invention is to provide a bio-based composite modified heavy calcium carbonate and its preparation method, which solves the technical problems of poor compatibility, limited mechanical strengthening effect, and potential inhibition of material degradation of traditional modified heavy calcium carbonate in biodegradable plastics.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing bio-based composite modified heavy calcium carbonate, comprising the following steps: Step 1) Chitosan and L-lactic acid are melted and grafted under the action of a catalyst, cooled and pulverized to obtain a bio-based modifier; Step 2) The pretreated calcium carbonate powder, water and dispersant are mixed to obtain calcium carbonate slurry. Bio-based modifier and silane coupling agent are added to the slurry for modification. Then, the mixture is subjected to pressure filtration, washing, vacuum drying and airflow depolymerization in sequence to obtain bio-based composite modified heavy calcium carbonate.

[0007] Furthermore, in step 1), the mass ratio of chitosan to L-lactic acid is 1:5~8; The catalyst is added at a rate of 0.5 to 1.0 wt% of the sum of the mass of chitosan and L-lactic acid.

[0008] Furthermore, in step 1), the catalyst includes a stannous octoate catalyst.

[0009] Furthermore, in step 1), the melting temperature is 140~160℃, and the grafting reaction time is 3~5h; The particle size of the bio-based modifier is ≤50μm.

[0010] Furthermore, in step 2), the pretreatment involves drying the heavy calcium carbonate raw powder to obtain calcium carbonate powder. The drying temperature is 100~110℃, and the drying time is 4~5 hours.

[0011] Further, in step 2), the mass of the dispersant is 0.1~0.3wt% of the mass of the calcium carbonate powder, the mass of the bio-based modifier is 1.0~2.0wt% of the mass of the calcium carbonate powder, and the mass of the silane coupling agent is 0.5~1.0wt% of the mass of the calcium carbonate powder.

[0012] Furthermore, in step 2), the mixing is carried out under stirring conditions, the mixing temperature is 60~70℃, and the stirring time is 20~40min.

[0013] Furthermore, in step 2), the pH of the system is adjusted to 6.5-7.5 before modification; The modification was carried out under stirring conditions, with the modification temperature being 75~85℃ and the stirring time being 90~150min.

[0014] Furthermore, in step 2), the conductivity of the washed filtrate is ≤15μS / cm; The vacuum drying temperature is 110~120℃, and the time is 8~12h.

[0015] This invention provides a bio-based composite modified heavy calcium carbonate prepared by the above-described preparation method.

[0016] This invention also provides an application of bio-based composite modified heavy calcium carbonate in the preparation of biodegradable plastic composite materials. The biodegradable plastic composite material is obtained by melt blending bio-based composite modified heavy calcium carbonate and matrix material, extruding, and granulating. The matrix material includes one or more of polylactic acid, polybutylene adipate and polyhydroxyalkanoate; The mass ratio of the bio-based composite modified heavy calcium carbonate to the matrix material is 1~3:7~9.

[0017] The beneficial effects of this invention are: An innovative composite modification system simultaneously improves compatibility and biocompatibility: A chitosan-g-polylactic acid graft copolymer (bio-based) and a silane coupling agent are used for composite modification. The hydrophilic groups of the bio-based modifier bind to the hydroxyl groups on the surface of calcium carbonate, while the hydrophobic segments entangle with the biodegradable plastic matrix. The silane coupling agent further enhances the interfacial bonding force, solving the problem of insufficient compatibility of traditional modifiers. Furthermore, the bio-based modifier can be degraded by microorganisms, avoiding inhibition of composite material degradation and aligning with the trend of green environmental protection.

[0018] Significantly enhanced mechanical properties, overcoming the "filler-reinforcement" contradiction: Modified heavy calcium carbonate is uniformly dispersed in biodegradable plastics without obvious agglomeration. When added at a mass fraction of 20%, the tensile strength of PLA-based composites increases by 21.3% and the elongation at break increases by 27.5%, while the tensile strength of PBS-based composites increases by 18.7% and the elongation at break increases by 23.2%. Compared with traditional silane-modified calcium carbonate, the improvement in mechanical properties is further increased by 8%-12%.

[0019] The degradation rate is controllable and does not affect the environmental protection properties of the material: The chitosan component in the bio-based modifier can promote the reproduction of microorganisms and alleviate the inhibitory effect of calcium carbonate filling on degradation. The PLA composite material with 20% modified calcium carbonate has a degradation rate of 68.5% under soil degradation conditions in 6 months, which is close to the degradation rate of pure PLA (72.3%) and significantly better than the composite material with traditional modified calcium carbonate (degradation rate 51.2%).

[0020] The process is environmentally friendly and easy to industrialize: the bio-based modifier is derived from renewable resources and no toxic or harmful substances are generated during the preparation process; the wet modification process can be modularly modified on the basis of existing heavy calcium carbonate production lines, the reaction conditions are mild (temperature ≤85℃) and the parameters are controllable, and the production cost is only 5%-8% higher than that of traditional modified calcium carbonate, which has the value for large-scale promotion. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope image of the bio-based composite modified heavy calcium carbonate prepared in Example 1 of the present invention. Detailed Implementation

[0022] This invention provides a method for preparing bio-based composite modified heavy calcium carbonate, comprising the following steps: Step 1) Chitosan and L-lactic acid are melted and grafted under the action of a catalyst, cooled and pulverized to obtain a bio-based modifier; Step 2) The pretreated calcium carbonate powder, water and dispersant are mixed to obtain calcium carbonate slurry. Bio-based modifier and silane coupling agent are added to the slurry for modification. Then, the mixture is subjected to pressure filtration, washing, vacuum drying and airflow depolymerization in sequence to obtain bio-based composite modified heavy calcium carbonate.

[0023] In this invention, in step 1), the mass ratio of chitosan to L-lactic acid is 1:5~8, preferably 1:6; The catalyst is added at a rate of 0.5 to 1.0 wt% of the sum of the mass of chitosan and L-lactic acid, preferably 0.8 wt%.

[0024] In this invention, in step 1), the catalyst is preferably a stannous octoate catalyst.

[0025] In this invention, in step 1), the melting temperature is 140~160℃, preferably 150℃; the grafting reaction time is 3~5h, preferably 4h. The particle size of the bio-based modifier is preferably ≤50μm.

[0026] In this invention, in step 2), the pretreatment involves drying the heavy calcium carbonate powder to obtain calcium carbonate powder. The drying temperature is 100~110℃, preferably 105℃; the drying time is preferably 4~5h.

[0027] In this invention, the purpose of the pretreatment is to remove adsorbed water from the powder surface.

[0028] In this invention, the heavy calcium carbonate raw powder is preferably CaCO3 content ≥98%, D50=1~3μm, and whiteness ≥95%.

[0029] In this invention, in step 2), the mass of the dispersant is 0.1 to 0.3 wt% of the calcium carbonate powder, preferably 0.2 wt%; the mass of the bio-based modifier is 1.0 to 2.0 wt% of the calcium carbonate powder, preferably 1.5 wt%; and the mass of the silane coupling agent is 0.5 to 1.0 wt% of the calcium carbonate powder, preferably 0.8 wt%.

[0030] In this invention, the dispersant is preferably sodium hexametaphosphate, and the silane coupling agent is preferably KH-550.

[0031] In this invention, in step 2), the mass fraction of the calcium carbonate slurry is 30-40%.

[0032] In this invention, in step 2), the mixing is carried out under stirring conditions, the mixing temperature is 60~70℃, preferably 65℃, and the stirring time is 20~40min, preferably 30min.

[0033] In this invention, in step 2), it is preferable to stir at 60-70°C for 30 minutes after adding the dispersant, and then add the bio-based modifier and silane coupling agent.

[0034] In this invention, in step 2), the pH of the system is preferably adjusted to 6.5-7.5 before modification; The modification is carried out under stirring conditions, with the modification temperature being 75~85℃, preferably 80℃; and the stirring time being 90~150min, preferably 100~140min, and more preferably 120min.

[0035] In this invention, the modified modifier forms a synergistic coating on the surface of calcium carbonate.

[0036] In this invention, in step 2), the conductivity of the washed filtrate is preferably ≤15μS / cm; The vacuum drying temperature is 110~120℃, preferably 115℃; the time is 8~12h, preferably 10h.

[0037] The present invention also provides a bio-based composite modified heavy calcium carbonate prepared by the above-described preparation method.

[0038] This invention also provides an application of bio-based composite modified heavy calcium carbonate in the preparation of biodegradable plastic composite materials. The biodegradable plastic composite material is obtained by melt-blending bio-based composite modified heavy calcium carbonate with a matrix material, extruding, and granulating.

[0039] In this invention, the matrix material includes one or more of polylactic acid, polybutylene adipate and polyhydroxyalkanoates, preferably polylactic acid.

[0040] In this invention, the mass ratio of the bio-based composite modified heavy calcium carbonate to the matrix material is 1~3:7~9, preferably 2:8.

[0041] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] Take heavy calcium carbonate raw powder (CaCO3 content 98.5%, D50=2μm, whiteness 96.2%), dry it at 105℃ for 4 hours to complete the pretreatment, and obtain dry calcium carbonate powder for later use; Preparation of bio-based modifier: Chitosan and L-lactic acid were weighed at a mass ratio of 1:6, mixed evenly, and added to a reaction vessel. Then, 0.8 wt% of stannous octoate catalyst (based on the total mass of chitosan and L-lactic acid) was added. The temperature was raised to 150°C and stirring was started to carry out a melt grafting reaction for 4 hours. After the reaction was completed, the mixture was cooled and pulverized to a particle size of 40 μm to obtain the bio-based modifier for later use. Wet composite modification: 100 kg of dry calcium carbonate powder was mixed with 233 kg of deionized water to prepare a calcium carbonate slurry with a mass concentration of 30%. 0.2 kg of sodium hexametaphosphate was added to the slurry and stirred at 65 °C for 30 minutes to ensure uniform dispersion of the powder. Then, 1.5 kg of bio-based modifier and 0.8 kg of KH-550 silane coupling agent were added sequentially, the pH was adjusted to 7.0, and the temperature was raised to 80 °C and stirred for 120 minutes. After modification, the slurry was filtered to obtain a filter cake. The filter cake was washed with deionized water until the conductivity of the filtrate was 12 μS / cm. The washed filter cake was placed in a vacuum drying device and vacuum dried at 115 °C for 10 hours. Bio-based modified heavy calcium carbonate was obtained by air-flow depolymerization.

[0044] Example 2

[0045] Take 100 kg of heavy calcium carbonate raw powder (CaCO3 content 98.2%, D50=1.8μm, whiteness 95.8%) and dry it at 100℃ for 5 hours to complete the pretreatment and obtain dry calcium carbonate powder for later use. Preparation of bio-based modifier: Chitosan and L-lactic acid were weighed at a mass ratio of 1:5, mixed evenly, and added to a reaction vessel. Then, 0.5 wt% of stannous octoate catalyst (total mass of chitosan and L-lactic acid) was added. The temperature was raised to 140℃ and stirring was started to carry out a melt grafting reaction for 5 hours. After the reaction was completed, the mixture was cooled to room temperature and ground to a particle size of 45 μm using a pulverizing device to obtain the bio-based modifier for later use. Wet composite modification: 100 kg of dry calcium carbonate powder was mixed with 267 kg of deionized water and stirred to prepare a calcium carbonate slurry with a mass concentration of 32%. 0.1 kg of sodium hexametaphosphate was added to the slurry and stirred at 60 °C for 40 minutes to ensure uniform dispersion of the powder. Then, 1.0 kg of bio-based modifier and 0.5 kg of KH-560 silane coupling agent were added sequentially, and the pH of the system was adjusted to 6.5. The temperature was raised to 75 °C and stirred for 150 minutes. After modification, the slurry was filtered to obtain a filter cake. The filter cake was washed with deionized water until the conductivity of the filtrate was 13 μS / cm. The washed filter cake was placed in a vacuum drying device and vacuum dried at 110 °C for 12 hours. After drying, it was treated by an airflow depolymerization device to obtain bio-based composite modified heavy calcium carbonate.

[0046] Example 3

[0047] Take 100 kg of heavy calcium carbonate raw powder (CaCO3 content 98.7%, D50=2.2μm, whiteness 96.5%) and dry it at 110℃ for 4 hours to complete the pretreatment and obtain dry calcium carbonate powder for later use. Preparation of bio-based modifier: Chitosan and L-lactic acid were weighed and mixed at a mass ratio of 1:8 and added to a reaction vessel. Stannous octoate catalyst with a total mass of 1.0 wt% of chitosan and L-lactic acid was added. The temperature was raised to 160℃ and stirring was started to carry out the melt grafting reaction for 3 hours. After the reaction was completed, the mixture was cooled to room temperature and ground to a particle size of 48 μm using a pulverizing device to obtain the bio-based modifier for later use. Wet composite modification: 100 kg of dry calcium carbonate powder was mixed with 200 kg of deionized water and stirred to prepare a calcium carbonate slurry with a mass concentration of 33%. 0.3 kg of sodium hexametaphosphate was added to the slurry and stirred at 70 °C for 20 minutes to achieve uniform dispersion of the powder. Then, 2.0 kg of bio-based modifier and 1.0 kg of KH-570 silane coupling agent were added sequentially, the pH of the system was adjusted to 7.5, the temperature was raised to 85 °C and stirred for 90 minutes. After modification, the slurry was filtered to obtain a filter cake, which was washed with deionized water until the conductivity of the filtrate was 11 μS / cm. The washed filter cake was placed in a vacuum drying device and dried at 120 °C for 8 hours. After drying, it was subjected to airflow depolymerization treatment to obtain bio-based composite modified heavy calcium carbonate.

[0048] Application Example 1

[0049] The bio-based composite modified heavy calcium carbonate prepared in Example 1 and PLA resin with a molecular weight of 80,000 were mixed at a mass ratio of 1:4. Then, 0.3 wt% antioxidant 1010, which is the sum of the mass of the bio-based composite modified heavy calcium carbonate and PLA resin, was added. The mixture was extruded and granulated in a twin-screw extruder, with the extrusion temperature maintained in the range of 165~175℃ and the screw speed at 200 r / min. Standard samples were obtained by injection molding.

[0050] Performance testing: Mechanical properties: tensile strength 62.8 MPa (51.8 MPa for pure PLA, an increase of 21.3%), elongation at break 4.2% (3.3% for pure PLA, an increase of 27.5%). Degradation performance: After 6 months of soil degradation, the degradation rate was 68.5% (72.3% for pure PLA and 51.2% for traditional silane-modified calcium carbonate / PLA composite material).

[0051] Application Example 2

[0052] The bio-based composite modified heavy calcium carbonate prepared in Example 1 and PBS resin were mixed at a mass ratio of 1:3. Then, 0.2 wt% antioxidant 168, which is the sum of the mass of the bio-based composite modified heavy calcium carbonate and PBS resin, was added. The mixture was extruded and granulated in a twin-screw extruder, with the extrusion temperature maintained in the range of 160~170℃ and the screw speed at 190 r / min. Standard samples were obtained by injection molding.

[0053] Performance testing: Mechanical properties: tensile strength 38.5 MPa (32.5 MPa in pure PBS, an increase of 18.7%), elongation at break 35.8% (29.0% in pure PBS, an increase of 23.2%). Degradation performance: After 6 months of soil degradation, the degradation rate was 71.2% (75.1% for pure PBS and 55.8% for traditional silane-modified calcium carbonate / PBS composite material).

[0054] Comparative Example 1

[0055] The heavy calcium carbonate raw powder in Example 1 was modified by using a single KH-550 silane coupling agent (addition amount 1.5wt%), and added to the PLA matrix at a mass fraction of 20wt% to obtain the composite material.

[0056] Performance testing: Mechanical properties: tensile strength 56.3 MPa (improved by 8.7%), elongation at break 3.5% (improved by 6.1%). Degradation performance: After 6 months of soil degradation, the degradation rate was 51.2%.

[0057] Compared with Application Example 1, Comparative Example 1 shows a significant difference in both mechanical enhancement effect and biocompatibility, fully demonstrating the superiority of the composite modification system of the present invention.

[0058] As can be seen from the above embodiments, the present invention provides a bio-based composite modified heavy calcium carbonate, its preparation method, and its application. The present invention forms a composite coating layer of bio-based modifier and KH-550 on the surface of modified calcium carbonate, exhibiting excellent compatibility with the biodegradable plastic matrix. Through the innovative design of the bio-based composite modification system, it overcomes the technical bottleneck of traditional modified heavy calcium carbonate in biodegradable plastics, which struggles to simultaneously achieve "compatibility-mechanical properties-degradability," providing an efficient solution for low-cost, high-performance biodegradable materials, and possessing significant technological innovation and industrial application value.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing bio-based composite modified heavy calcium carbonate, characterized in that, Includes the following steps: Step 1) Chitosan and L-lactic acid are melted and grafted under the action of a catalyst, cooled and pulverized to obtain a bio-based modifier; Step 2) The pretreated calcium carbonate powder, water and dispersant are mixed to obtain calcium carbonate slurry. Bio-based modifier and silane coupling agent are added to the slurry for modification. Then, the mixture is subjected to pressure filtration, washing, vacuum drying and airflow depolymerization in sequence to obtain bio-based composite modified heavy calcium carbonate.

2. The method for preparing a bio-based composite modified heavy calcium carbonate according to claim 1, characterized in that, In step 1), the mass ratio of chitosan to L-lactic acid is 1:5~8; The catalyst is added at a rate of 0.5 to 1.0 wt% of the sum of the mass of chitosan and L-lactic acid.

3. The method for preparing a bio-based composite modified heavy calcium carbonate according to claim 1 or 2, characterized in that, In step 1), the catalyst includes a stannous octoate catalyst.

4. The method for preparing a bio-based composite modified heavy calcium carbonate according to claim 3, characterized in that, In step 1), the melting temperature is 140~160℃, and the grafting reaction time is 3~5h; The particle size of the bio-based modifier is ≤50μm.

5. A method for preparing a bio-based composite modified heavy calcium carbonate according to claim 1 or 4, characterized in that, In step 2), the pretreatment involves drying the heavy calcium carbonate powder to obtain calcium carbonate powder. The drying temperature is 100~110℃, and the drying time is 4~5 hours.

6. The method for preparing a bio-based composite modified heavy calcium carbonate according to claim 5, characterized in that, In step 2), the mass of the dispersant is 0.1 to 0.3 wt% of the calcium carbonate powder, the mass of the bio-based modifier is 1.0 to 2.0 wt% of the calcium carbonate powder, and the mass of the silane coupling agent is 0.5 to 1.0 wt% of the calcium carbonate powder.

7. A method for preparing a bio-based composite modified heavy calcium carbonate according to claim 1, 4, or 6, characterized in that, In step 2), the mixing is carried out under stirring conditions, the mixing temperature is 60~70℃, and the stirring time is 20~40min.

8. The method for preparing a bio-based composite modified heavy calcium carbonate according to claim 7, characterized in that, In step 2), the pH of the system is adjusted to 6.5-7.5 before modification; The modification was carried out under stirring conditions, with the modification temperature being 75~85℃ and the stirring time being 90~150min; The conductivity of the filtrate after washing is ≤15μS / cm; The vacuum drying temperature is 110~120℃, and the time is 8~12h.

9. Bio-based composite modified heavy calcium carbonate prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the bio-based composite modified heavy calcium carbonate according to claim 9 in the preparation of biodegradable plastic composite materials, characterized in that, Biodegradable plastic composite materials are obtained by melt blending, extrusion, and granulation of bio-based composite modified heavy calcium carbonate and matrix materials. The matrix material includes one or more of polylactic acid, polybutylene adipate and polyhydroxyalkanoate; The mass ratio of the bio-based composite modified heavy calcium carbonate to the matrix material is 1~3:7~9.

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