Mineral-based degradable plastic and preparation method thereof

Abstract

The invention discloses a mineral-based degradable plastic and a preparation method thereof.The plastic is prepared by taking PLA, PBAT and the like as matrixes, introducing modified mineral filler with nano calcium carbonate as a substrate and combining an extrusion technology, starch fragments are loaded inside and on the surface of nano calcium carbonate through physical adsorption and in-situ polymerization, and the mineral-based degradable plastic is obtained. The interface bonding energy between the nano calcium carbonate and the matrix is greatly improved, and the problems of plastic phase separation, mechanical property attenuation and starch thermal decomposition under high mineral filling are effectively solved. The plastic has high mechanical properties, excellent processing fluidity, controllable degradation rate and high recovery retention rate, and is suitable for the fields of degradable packaging, agricultural films and injection molding products with high performance and processing requirements.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly plastics technology, and specifically relates to a mineral-based biodegradable plastic and its preparation method. Background Technology

[0002] With the deepening of the "plastic restriction order," biodegradable plastics, represented by polybutylene terephthalate (PBAT), polylactic acid (PLA), and their blends, have been widely used in packaging, agriculture, and other fields. To reduce costs and impart more functions to materials (such as increasing specific gravity, rigidity, and degradation rate), natural or mineral fillers such as starch and calcium carbonate are often blended with biodegradable resins. However, existing physical blending technologies face significant bottlenecks:

[0003] 1. Poor interfacial compatibility: The hydrophilicity of starch and the high polarity of calcium carbonate result in weak interfacial bonding with hydrophobic resins (such as PBAT) matrices, easily leading to phase separation and severely impairing the mechanical properties (especially impact strength and elongation at break) and water resistance of the material. This usually requires the addition of silane coupling agents, dopamine, etc., to modify the filler surface, resulting in a complex process and increased costs.

[0004] 2. Uncontrollable degradation: The degradation rate of natural fillers such as starch is much faster than that of the resin matrix. This causes a large number of pores and defects to be generated in the early stage of use (such as storage or use) due to the rapid loss of fillers. Mechanical properties (such as tensile strength and elongation at break) will decline sharply in a short period of time (1-3 months), affecting the reliability and storage stability of the product.

[0005] 3. Deterioration of processing performance: At high filler content (usually >20 wt%), the filler is very prone to agglomeration, which leads to a sharp increase in melt viscosity (e.g., exceeding 800 Pa·s at 180℃), narrowing the processing window, increasing energy consumption, and starch is at risk of thermal decomposition during high-temperature (>180℃) extrusion processing, which limits its application in high-temperature processing scenarios (such as injection molding and blown film).

[0006] Therefore, developing a new type of composite material and process that can simultaneously solve the three major challenges of interface compatibility, degradation controllability, and processing stability has become a key breakthrough urgently needed in this field. Summary of the Invention

[0007] To address the aforementioned deficiencies of existing mineral-based plastics, this invention provides a mineral-based biodegradable plastic and its preparation method. By combining filler design with extrusion processes, a strong interfacial bonding and interpenetrating network structure is constructed at the molecular level, achieving a synergistic improvement in the mechanical properties, long-term stability, controllable degradation, and processing rheology of the mineral-based biodegradable plastic.

[0008] This invention is achieved through the following technical solution:

[0009] A mineral-based biodegradable plastic is made from the following components in parts by weight:

[0010] The composition includes 60-85 parts of bio-resin matrix, 15-40 parts of modified mineral filler, 0.5-3 parts of crosslinking agent, 0.05-0.5 parts of initiator, 0.2-1 parts of heat stabilizer, and 0.5-2 parts of lubricant.

[0011] The bioresin matrix is ​​one or a combination of two or more of polylactic acid, polybutylene adipate / terephthalate, and polybutylene succinate.

[0012] The modified mineral filler is a composite material with nano-calcium carbonate as the core, enzymatically hydrolyzed starch fragments loaded on the surface and within the pores, and coated with a polylactic acid shell; the nano-calcium carbonate has a pore size of 2-50 nm and a specific surface area ≥30 m². 2 / g;

[0013] The crosslinking agent is one of dicumyl peroxide and divinylbenzene, or a mixture of both.

[0014] The initiator is one of benzoyl peroxide and dicumyl peroxide; the initiator is used to activate the crosslinking agent during extrusion to generate free radicals. Dicumyl peroxide is well matched with the processing temperature (170-185℃) of this invention, and the decomposition products have a low odor.

[0015] The heat stabilizer is one of triphenyl phosphite or triphenyl phosphate; the heat stabilizer is used to prevent PLA and other resins from undergoing thermal oxidative degradation and hydrolysis during high-temperature processing. The aforementioned heat stabilizer can effectively capture peroxide free radicals and inhibit the β-elimination degradation reaction of PLA.

[0016] The lubricant is one of polyethylene wax, oxidized polyethylene wax, glyceryl stearate, and pentaerythritol stearate.

[0017] Preferably, the composition of polylactic acid and poly(butylene adipate) / terephthalate is obtained by mixing them in a weight ratio of (4-8):(2-6).

[0018] Preferably, the modified mineral filler is prepared as follows:

[0019] A1: Prepare a suspension of corn starch with a mass concentration of 10%-30%, adjust the pH to 6.0-6.5, add 0.1%-0.5% of α-amylase by dry weight of corn starch, hydrolyze at 60-75℃ for 30-90 min, and then heat to 90-100℃ to inactivate the enzyme for 10-20 min to obtain a starch hydrolysate solution with a molecular weight of 1000-10000 Da;

[0020] A2: Disperse nano-calcium carbonate in starch hydrolysate solution at a dry weight ratio of (70-80):(20-30), stir and adsorb at 50-65℃ for 2-4 hours, and control the starch loading at 20-30 wt%; then centrifuge and vacuum dry at 60-80℃ to obtain supported calcium carbonate with starch fragments adsorbed on the surface;

[0021] A3: Supported calcium carbonate, L-lactic acid monomer, and stannous octoate catalyst are mixed at a weight ratio of 100:(50-150):(0.1-0.3) and prepolymerized and dehydrated at 120℃-140℃ for 2-3 hours under nitrogen protection; then the system temperature is raised to 150℃-170℃ and reacted at a vacuum degree <100Pa for 4-8 hours, with the shell thickness controlled at 5-20nm; after the reaction, the product is crushed and sieved to obtain the modified mineral filler.

[0022] By precisely controlling enzymatic hydrolysis conditions to obtain low-molecular-weight starch fragments of suitable size, it is beneficial for subsequent adsorption and as polymerization sites. Then, utilizing the high specific surface area and pore structure of porous calcium carbonate, high-capacity and robust adsorption of starch fragments is achieved, forming a stable intermediate transition layer. Under stannous octoate catalysis, lactic acid monomers not only undergo bulk polymerization, but more importantly, surface polymerization preferentially occurs using the hydroxyl groups on the adsorbed starch molecules as potential initiation sites and the active sites on the calcium carbonate surface as the core. This achieves chemical bonding or strong physical anchoring between the PLA shell and the calcium carbonate core, rather than simple physical encapsulation. This process ensures the uniformity and bonding strength of the shell, achieving an interfacial bonding target of 5.8 J / m².

[0023] The method for preparing the mineral-based biodegradable plastic includes the following steps:

[0024] B1: The premixed material is prepared by blending the bio-resin matrix, modified mineral filler, heat stabilizer and lubricant according to the weight ratio. The mixture is then put into a high-speed mixer and mixed at 800-1000 rpm for 8-10 minutes to obtain the premixed material.

[0025] B2: The premixed material is melt-mixed in a twin-screw extruder, while the crosslinking agent and initiator are dissolved in acetone and then injected into the extruder; the mixing temperature of the twin-screw extruder is 150-185℃, and the screw speed is 200-350rpm.

[0026] B3: The material strip extruded from the twin-screw extruder is immediately cooled and shaped in water at 25°C. After the surface moisture is dried, it is sent to a pelletizer to be cut into cylindrical particles with a diameter of 5-6 mm and a length of 8-10 mm. The particles are then placed in a vacuum dryer at 75-80°C for 6 hours to obtain mineral-based biodegradable plastic.

[0027] Preferably, the temperature of the twin-screw extruder is 105-155℃ in zone one, 156-168℃ in zone two, 169-173℃ in zone three, 174-178℃ in zone four, and 178-185℃ at the die head.

[0028] Setting a stepped extrusion temperature ensures both the complete melting of PLA / PBAT and the protection of the loaded starch by the PLA shell and pores from high-temperature decomposition. During this process, the premix is ​​melted and plasticized, and the injected crosslinking agent and initiator solution are rapidly dispersed under high temperature and high shear, initiating local crosslinking reactions of the unsaturated segments in the bioresin matrix. At the same time, the strong shear force breaks down and refines the generated crosslinked network, which interpenetrates and entangles with the uncrosslinked resin phase and the polylactic acid shell on the surface of the modified mineral filler, forming a microscopic "resin-filler" interpenetrating network structure.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. This invention utilizes a "core-shell" structure design to tightly bind the starch transition layer and the calcium carbonate core through hydrogen bonds and physical adsorption, significantly enhancing interfacial bonding. The starch fragments coated and loaded within the porous structure of calcium carbonate have their degradation pathways extended and blocked by microorganisms or water contact, thus transforming the degradation process from a rapid collapse mode "from the outside in" to a controlled, slow-release mode "from the inside out."

[0031] 2. The plastic prepared by this invention improves the dispersibility of the filler and reduces the melt viscosity through the polylactic acid shell. The interpenetrating network formed by extrusion enhances the melt strength. The starch inside the filler is protected by the polylactic acid shell and calcium carbonate core, and does not undergo significant thermal decomposition during processing below 200°C, thus expanding the application range of the material in high-temperature processing. After undergoing multiple melt reprocessing processes, the final product plastic retains more than 80% of its mechanical properties, which is significantly better than traditional blended materials. Detailed Implementation

[0032] The present invention will be further described below with reference to the embodiments. Unless otherwise specified, the technical means used in the embodiments are all conventional technical means in the art.

[0033] Example 1:

[0034] A mineral-based biodegradable plastic is made from the following components in parts by weight:

[0035] The composition includes 60 parts of bio-resin matrix, 15 parts of modified mineral filler, 0.5 parts of crosslinking agent, 0.05 parts of initiator, 0.2 parts of heat stabilizer, and 0.5 parts of lubricant.

[0036] The bioresin matrix is ​​a combination of polylactic acid and poly(butylene adipate) / poly(terephthalate); the composition is obtained by mixing the components in a weight ratio of 4:6.

[0037] The modified mineral filler is a composite material with nano-calcium carbonate as the core, enzymatically hydrolyzed starch fragments loaded on the surface and within the pores, and coated with a polylactic acid shell; the nano-calcium carbonate has a pore size of 2-50 nm and a specific surface area ≥30 m². 2 / g;

[0038] The crosslinking agent is dicumyl peroxide;

[0039] The initiator is benzoyl peroxide;

[0040] The heat stabilizer is triphenyl phosphite;

[0041] The lubricant is polyethylene wax.

[0042] The preparation method of the modified mineral filler is as follows:

[0043] A1: Prepare a 10% (w / w) suspension of corn starch, adjust the pH to 6.0, add 0.1% (w / w) of α-amylase from the dry weight of corn starch, hydrolyze at 60℃ for 30 min, then heat to 90℃ to inactivate the enzyme for 10 min, to obtain a starch hydrolysate solution with a molecular weight of 1000 Da.

[0044] A2: The nano-calcium carbonate was dispersed in the starch hydrolysate solution at a dry weight ratio of 70:30, and stirred and adsorbed at 50°C for 4 hours with the starch loading controlled at 20wt%. Then, it was centrifuged and vacuum dried at 60°C to obtain supported calcium carbonate with starch fragments adsorbed on the surface.

[0045] A3: Supported calcium carbonate, L-lactic acid monomer, and stannous octoate catalyst were mixed at a weight ratio of 100:50:0.1 and prepolymerized and dehydrated at 120°C for 3 hours under nitrogen protection. Then, the system temperature was raised to 150°C and reacted at a vacuum degree <100Pa for 8 hours, with the shell thickness controlled at 5nm. After the reaction, the product was crushed and sieved to obtain the modified mineral filler.

[0046] The method for preparing the mineral-based biodegradable plastic includes the following steps:

[0047] B1: The premixed material is prepared by blending the bio-resin matrix, modified mineral filler, heat stabilizer and lubricant according to the weight ratio. The mixture is then put into a high-speed mixer and mixed at 800 rpm for 8 minutes to obtain the premixed material.

[0048] B2: The premixed material is melt-mixed in a twin-screw extruder, while the crosslinking agent and initiator are dissolved in acetone and then injected into the extruder; the temperature of the twin-screw extruder is 105℃ in zone 1, 156℃ in zone 2, 169℃ in zone 3, 174℃ in zone 4, and 178℃ at the die head; the screw speed is 200 rpm.

[0049] B3: The material strip extruded from the twin-screw extruder is immediately cooled and shaped in water at 25°C. After the surface moisture is dried, it is sent to a pelletizer to be cut into cylindrical particles with a diameter of 5mm and a length of 8mm. The particles are then placed in a vacuum dryer at 75°C for 6 hours to obtain mineral-based biodegradable plastic.

[0050] Example 2:

[0051] A mineral-based biodegradable plastic is made from the following components in parts by weight:

[0052] The composition includes 85 parts of bio-resin matrix, 40 parts of modified mineral filler, 3 parts of crosslinking agent, 0.5 parts of initiator, 1 part of heat stabilizer, and 2 parts of lubricant.

[0053] The bioresin matrix is ​​a combination of polylactic acid and polybutylene succinate; the composition is obtained by mixing the components in a weight ratio of 1:1.

[0054] The modified mineral filler is a composite material with nano-calcium carbonate as the core, enzymatically hydrolyzed starch fragments loaded on the surface and within the pores, and coated with a polylactic acid shell; the nano-calcium carbonate has a pore size of 2-50 nm and a specific surface area ≥30 m². 2 / g;

[0055] The crosslinking agent is divinylbenzene;

[0056] The initiator is dicumyl peroxide;

[0057] The heat stabilizer mentioned is triphenyl phosphate;

[0058] The lubricant is oxidized polyethylene wax.

[0059] The preparation method of the modified mineral filler is as follows:

[0060] A1: Prepare a 30% (w / w) suspension of corn starch, adjust the pH to 6.5, add 0.5% (w / w) of α-amylase from the dry weight of corn starch, hydrolyze at 75℃ for 90 min, then heat to 100℃ to inactivate the enzyme for 20 min, and obtain a starch hydrolysate solution with a molecular weight of 10000 Da.

[0061] A2: The nano-calcium carbonate was dispersed in the starch hydrolysate solution at a dry weight ratio of 80:20, and stirred and adsorbed at 65°C for 2 hours, with the starch loading controlled at 30 wt%. Then, it was centrifuged and vacuum dried at 80°C to obtain supported calcium carbonate with starch fragments adsorbed on its surface.

[0062] A3: Supported calcium carbonate, L-lactic acid monomer, and stannous octoate catalyst were mixed at a weight ratio of 100:150:0.3 and prepolymerized and dehydrated at 140°C for 2 hours under nitrogen protection. Subsequently, the system temperature was raised to 170°C and reacted at a vacuum degree <100Pa for 4 hours, with the shell thickness controlled at 20nm. After the reaction, the product was crushed and sieved to obtain the modified mineral filler.

[0063] The method for preparing the mineral-based biodegradable plastic includes the following steps:

[0064] B1: The premixed material is prepared by mixing the bio-resin matrix, modified mineral filler, heat stabilizer and lubricant according to the weight ratio. The mixture is then put into a high-speed mixer and mixed at 1000 rpm for 8 minutes to obtain the premixed material.

[0065] B2: The premixed material is melt-blended in a twin-screw extruder, while the crosslinking agent and initiator are dissolved in acetone and then injected into the extruder; the twin-screw extruder has the following temperatures: Zone 1: 155°C; Zone 2: 168°C; Zone 3: 173°C; Zone 4: 178°C; and Die head: 185°C. The screw speed is 350 rpm.

[0066] B3: The material strip extruded from the twin-screw extruder is immediately cooled and shaped in water at 25°C. After the surface moisture is dried, it is sent to a pelletizer to be cut into cylindrical particles with a diameter of 6mm and a length of 10mm. The particles are then placed in a vacuum dryer at 80°C for 6 hours to obtain mineral-based biodegradable plastic.

[0067] Example 3:

[0068] A mineral-based biodegradable plastic is made from the following components in parts by weight:

[0069] 70 parts of bio-resin matrix, 25 parts of modified mineral filler, 2 parts of crosslinking agent, 0.2 parts of initiator, 0.5 parts of heat stabilizer, and 1 part of lubricant;

[0070] The bioresin matrix is ​​poly(butylene adipate / terephthalate);

[0071] The modified mineral filler is a composite material with nano-calcium carbonate as the core, enzymatically hydrolyzed starch fragments loaded on the surface and within the pores, and coated with a polylactic acid shell; the nano-calcium carbonate has a pore size of 30 nm and a specific surface area ≥ 30 m². 2 / g;

[0072] The crosslinking agent is dicumyl peroxide;

[0073] The initiator is dicumyl peroxide;

[0074] The heat stabilizer is triphenyl phosphite;

[0075] The lubricant is pentaerythritol stearate.

[0076] The preparation method of the modified mineral filler is as follows:

[0077] A1: Prepare a 20% (w / w) suspension of corn starch, adjust the pH to 6.2, add 0.4% (w / w) of α-amylase from the dry weight of corn starch, hydrolyze at 65℃ for 60 min, then heat to 95℃ to inactivate the enzyme for 15 min, to obtain a starch hydrolysate solution with a molecular weight of 8000 Da.

[0078] A2: The nano-calcium carbonate was dispersed in the starch hydrolysate solution at a dry weight ratio of 75:25, and stirred and adsorbed at 60°C for 3 hours with the starch loading controlled at 25wt%. Then, it was centrifuged and vacuum dried at 70°C to obtain supported calcium carbonate with starch fragments adsorbed on its surface.

[0079] A3: Supported calcium carbonate, L-lactic acid monomer, and stannous octoate catalyst were mixed at a weight ratio of 100:100:0.2 and prepolymerized and dehydrated at 130°C for 2 hours under nitrogen protection. Subsequently, the system temperature was raised to 160°C and reacted at a vacuum degree <100Pa for 6 hours, with the shell thickness controlled at 10nm. After the reaction, the product was crushed and sieved to obtain the modified mineral filler.

[0080] The method for preparing the mineral-based biodegradable plastic includes the following steps:

[0081] B1: The premixed material is prepared by blending the bio-resin matrix, modified mineral filler, heat stabilizer and lubricant according to the weight ratio. The mixture is then put into a high-speed mixer and mixed at 900 rpm for 10 min to obtain the premixed material.

[0082] B2: The premixed material is melt-blended in a twin-screw extruder, while the crosslinking agent and initiator are dissolved in acetone and then injected into the extruder; the twin-screw extruder has the following temperatures: Zone 1: 120°C; Zone 2: 160°C; Zone 3: 172°C; Zone 4: 176°C; and Die Head: 180°C. The screw speed is 300 rpm.

[0083] B3: The material strip extruded from the twin-screw extruder is immediately cooled and shaped in water at 25°C. After the surface moisture is dried, it is sent to a pelletizer to be cut into cylindrical particles with a diameter of 6mm and a length of 9mm. The particles are then placed in a vacuum dryer at 76°C for 6 hours to obtain mineral-based biodegradable plastic.

[0084] Comparative Example 1:

[0085] Following the method described in Example 3, the modified mineral filler was replaced with ordinary calcium carbonate, and the remaining steps were the same to prepare the plastic.

[0086] Mechanical properties and decomposition capability were tested on the products produced in Examples 1-3 and the comparative examples. The specific results are shown in Table 1.

[0087] Table 1:

[0088] Product testing projects Example 1 Example 2 Example 3 Comparative Example Tensile strength (MPa) 29.6 32.5 30.8 16.2 Elongation at break (%) 492 536 468 134 Notched impact strength (kJ / m²) 15.8 16.5 14.2 6.0 Melt viscosity at 180℃ (Pa·s) 395 418 366 842 60-day tensile strength retention rate of compost (%) 86 90 80 42 Impact strength retention rate (%) after 5 recycling cycles 82 88 82 46

[0089] The data in Table 1 show that the plastics prepared in Examples 1-3 of this invention are significantly superior to plastics prepared by traditional blending in terms of mechanical properties, processing rheology, degradability controllability, and recyclability.

[0090] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A mineral-based biodegradable plastic, characterized in that, It is made from the following components in the following weight ratio: The composition includes 60-85 parts of bio-resin matrix, 15-40 parts of modified mineral filler, 0.5-3 parts of crosslinking agent, 0.05-0.5 parts of initiator, 0.2-1 parts of heat stabilizer, and 0.5-2 parts of lubricant. The bioresin matrix is ​​one or a combination of two or more of polylactic acid, polybutylene adipate / terephthalate, and polybutylene succinate. The modified mineral filler is a composite material with nano-calcium carbonate as the core, enzymatically hydrolyzed starch fragments loaded on the surface and within the pores, and coated with a polylactic acid shell; the nano-calcium carbonate has a pore size of 2-50 nm and a specific surface area ≥30 m². 2 / g; The crosslinking agent is one of dicumyl peroxide and divinylbenzene, or a mixture of both. The initiator is one of benzoyl peroxide and dicumyl peroxide; The heat stabilizer is one of triphenyl phosphite and triphenyl phosphate; The lubricant is one of polyethylene wax, oxidized polyethylene wax, glyceryl stearate, and pentaerythritol stearate.

2. The mineral-based biodegradable plastic according to claim 1, characterized in that: The composition of polylactic acid and poly(butylene adipate) / terephthalate is obtained by mixing them in a weight ratio of (4-8):(2-6).

3. The mineral-based biodegradable plastic according to claim 1, characterized in that: The preparation method of the modified mineral filler is as follows: A1: Prepare a suspension of corn starch with a mass concentration of 10%-30%, adjust the pH to 6.0-6.5, add 0.1%-0.5% of α-amylase by dry weight of corn starch, hydrolyze at 60-75℃ for 30-90 min, and then heat to 90-100℃ to inactivate the enzyme for 10-20 min to obtain a starch hydrolysate solution with a molecular weight of 1000-10000 Da; A2: Disperse nano-calcium carbonate in starch hydrolysate solution at a dry weight ratio of (70-80):(20-30), stir and adsorb at 50-65℃ for 2-4 hours, and control the starch loading at 20-30 wt%; then centrifuge and vacuum dry at 60-80℃ to obtain supported calcium carbonate with starch fragments adsorbed on the surface; A3: Supported calcium carbonate, L-lactic acid monomer, and stannous octoate catalyst are mixed at a weight ratio of 100:(50-150):(0.1-0.3) and prepolymerized and dehydrated at 120℃-140℃ for 2-3 hours under nitrogen protection; then the system temperature is raised to 150℃-170℃ and reacted at a vacuum degree <100Pa for 4-8 hours, with the shell thickness controlled at 5-20nm; after the reaction, the product is crushed and sieved to obtain the modified mineral filler.

4. The method for preparing mineral-based biodegradable plastics as described in any one of claims 1-3, characterized in that, Includes the following steps: B1: The premixed material is prepared by blending the bio-resin matrix, modified mineral filler, heat stabilizer and lubricant according to the weight ratio. The mixture is then put into a high-speed mixer and mixed at 800-1000 rpm for 8-10 minutes to obtain the premixed material. B2: The premixed material is melt-mixed in a twin-screw extruder, while the crosslinking agent and initiator are dissolved in acetone and then injected into the extruder; the mixing temperature of the twin-screw extruder is 150-185℃, and the screw speed is 200-350rpm; B3: The material strip extruded from the twin-screw extruder is immediately cooled and shaped in water at 25°C. After the surface moisture is dried, it is sent to a pelletizer to be cut into cylindrical particles with a diameter of 5-6 mm and a length of 8-10 mm. The particles are then placed in a vacuum dryer at 75-80°C for 6 hours to obtain mineral-based biodegradable plastic.

5. The method for preparing mineral-based biodegradable plastics according to claim 4, characterized in that: The twin-screw extruder has a zone temperature of 105-155℃, a zone temperature of 156-168℃, a zone temperature of 169-173℃, a zone temperature of 174-178℃, and a die head temperature of 178-185℃.