Polyhydroxyalkanoate material as well as preparation process and application thereof

Abstract

The invention provides a polyhydroxyalkanoate material and a preparation process and application thereof.The preparation process includes the process that raw materials containing polyhydroxyalkanoate powder are extruded and granulated through a double-screw extruder, the specific torque of the double-screw extruder is 13-20 N.m, the main machine rotating speed of the double-screw extruder is 100-300 rpm, and the specific torque of the double-screw extruder is 13-20 N.m, the main machine rotating speed of the double-screw extruder is 100-300 rpm. The temperature interval of extrusion granulation is 60-140 DEG C or the softening point temperature of the raw materials is + / -5 DEG C. The PHA material is extruded and granulated under high pressure in a high-torque low-rotating-speed strong conveying mode, granules with the molecular weight reduced by 10% or below can be prepared, and the PHA material can be ideally applied to downstream product production. Besides, the high specific torque of the extruder is adopted, the rotating speed is reduced, shearing heat is reduced, meanwhile, the feeding amount is increased, the yield is not affected, and the provided production process is simple, low in cost and wide in application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of material processing, and particularly relates to a polyhydroxyalkanoate material, a preparation process thereof, and an application thereof. Background Art

[0002] Polyhydroxyalkanoate (hereinafter may be abbreviated as PHA), as a biosynthetic high molecular thermoplastic material, its products can be rapidly degraded into carbon dioxide and water in the natural environment, without bringing the white pollution problem of disposable products. In real life, many disposable items such as disposable shopping bags, disposable cutlery, disposable lunch boxes, milk tea cups, test tubes, etc. are likely to cause environmental pollution because traditional plastics are non-degradable. PHA can be used as a substitute for these traditional plastics, processed into products using the same process, and can be naturally degraded into carbon dioxide and water without polluting the environment. PHA is formed by biological fermentation, and the extracted and dried product is generally a powder with very small particle size, and the powder is not suitable for the production of downstream products. It is necessary to granulate the PHA powder first, and then perform injection molding, blow molding, thermoforming, 3D printing, fiber processing, etc. to prepare products. Therefore, from the powder to the product, PHA has to undergo at least 2 times of thermoforming processing. Due to the problems of PHA such as thermal sensitivity, shear sensitivity, and narrow processing window, it is necessary to fully protect it during the hot processing. During the process from powder to pellets, it is necessary to fully ensure that the reduction in molecular weight is very low, within 20% or even lower, preferably, in order to ensure that the downstream products have good performance.

[0003] At present, due to the thermal sensitivity and shear sensitivity of PHA, degradation is likely to occur during the granulation of PHA. After granulation using traditional parallel twin-screw extruder equipment, the molecular weight drops by up to about 60%, seriously affecting the performance of PHA and the performance of downstream products.

[0004] The existing granulation equipment in use is generally a parallel twin-screw extruder, with a high length-diameter ratio of the screw, high shear strength, high shear heat, and high processing temperature, which is likely to cause thermal degradation of PHA, resulting in a very high reduction in molecular weight, and thus affecting the performance and application of subsequent products.

[0005] In view of this, the present invention is particularly proposed. Summary of the Invention

[0006] The first object of the present invention is to provide a preparation process of a polyhydroxyalkanoate (PHA) material, so as to solve the problem that the existing equipment and process will significantly reduce the molecular weight, thereby affecting the performance and application of subsequent products.

[0007] The preparation process of the polyhydroxyalkanoate (PHA) material provided by the present invention includes the process of extrusion granulation of raw materials containing polyhydroxyalkanoate powder using a twin-screw extruder. The twin-screw extruder uses a torque of 13-20 N·m and a main machine speed of 100-300 rpm. The temperature range for the extrusion granulation is 60-140°C or the softening point temperature of the raw material ±5°C.

[0008] Preferably, the twin-screw extruder uses a specific torque of 13.5-16 N·m and a main machine speed of 100-300 RPM. The temperature for the extrusion granulation is the softening point temperature of the raw material ±1°C.

[0009] Those skilled in the art can understand that the softening point temperature ±5°C refers to the temperature range from 5°C lower than the softening point temperature to 5°C higher than the softening point temperature.

[0010] In some embodiments provided by the present invention, when the polyhydroxyalkanoate powder is PHB powder, the suitable temperature for extrusion granulation is 100-140°C. When the polyhydroxyalkanoate powder is P34HB powder, the suitable temperature for extrusion granulation is 90-110°C. When the polyhydroxyalkanoate powder is PHBV powder, the suitable temperature for extrusion granulation is 110-130°C. When the polyhydroxyalkanoate powder is PHBHHx powder, the suitable temperature for extrusion granulation is 60-90°C.

[0011] More specifically, the inventors found that when different raw materials are selected for the polyhydroxyalkanoate powder, the adapted process conditions show significant differences. For example, when the heating temperature of PHB ≥180°C, even with a short heating time of 1 min, the molecular weight reduction amplitude is 20.8%, and the higher the temperature, the greater the degradation amplitude with the extension of the heating time. When the heating temperature is 200°C and the heating time is 30 min, the degradation amplitude reaches 70.4%. When the heating temperature of P34HB ≥180°C, even with a short heating time of 1 min, the molecular weight reduction amplitude is 24.2%, and the higher the temperature, the greater the degradation amplitude with the extension of the heating time. When the heating temperature is 200°C and the heating time is 30 min, the degradation amplitude reaches 59.3%.

[0012] In addition, when the heating temperature exceeds 160°C, the degradation rate of PHA during the hot processing is very rapid, while when the temperature is lower than 160°C, the degradation rate of PHA during the hot processing is relatively slow, having a sufficiently wide processing window. And it is found that when PHA is near the softening point, with a high die head pressure, good granulation can be achieved, and when the die head pressure is low near the softening point, granulation cannot be achieved. When the die head pressure is large, more power is required to rotate the screw to extrude the material from the die head, so a larger specific torque is needed, otherwise the equipment screw does not have enough power to rotate and cannot be extruded smoothly.

[0013] Thus, the present invention further controls the specific torque of the twin-screw extruder to be 13-20 N·m, while controlling the temperature of the extrusion granulation of the polyhydroxyalkanoate powder to be 60-140 °C, and maintaining the main machine speed at 100-300 rpm, so as to better ensure that the polyhydroxyalkanoate obtained by extrusion granulation has a smaller molecular weight reduction compared to the polyhydroxyalkanoate powder, that is, the molecular weight reduction of the polyhydroxyalkanoate compared to the polyhydroxyalkanoate powder is not greater than 10%, thereby obtaining a high-molecular-weight polyhydroxyalkanoate and ensuring better performance of downstream products.

[0014] In some embodiments provided by the present invention, the specific torque adopted by the twin-screw extruder may specifically be 13.5 N·m, 14 N·m, 14.5 N·m, 15 N·m, 15.5 N·m or 16 N·m.

[0015] In some embodiments provided by the present invention, the main machine speed adopted by the twin-screw extruder may be 100 rpm, 120 rpm, 150 rpm, 200 rpm, 240 rpm, 250 rpm, 260 rpm, 280 rpm or 300 rpm, preferably 200 rpm.

[0016] In some embodiments provided by the present invention, the temperature of the extrusion granulation is the softening point temperature of the raw material ±5 °C, preferably softening point temperature ±2 °C, more preferably softening point temperature ±1 °C. For different raw materials, the suitable extrusion granulation temperature is different. The present invention can effectively weaken the thermal degradation damage of temperature to PHA by controlling the extrusion temperature, and further protect the molecular weight of PHA.

[0017] For the preparation process provided by the present invention, the screw combination of the twin-screw extruder is mainly for conveying, and adopts weak shearing with 2-4 pieces of 45°-90° shearing blocks (that is, mainly for conveying and supplemented by weak shearing), such as 3 pieces of 45° shearing blocks, 3 pieces of 60° shearing blocks, and 3 pieces of 90° shearing blocks.

[0018] The present invention controls the shearing strength by controlling the shearing block combination, reduces the screw shearing strength of the twin-screw extruder, strengthens its conveying capacity, and further protects the molecular weight of PHA.

[0019] For the preparation process provided by the present invention, an extrusion pressure of 10-20 MPa is adopted, preferably 12-16 MPa. In some embodiments provided by the present invention, the extrusion pressure may be 10 MPa, 12 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, 20 MPa, etc. The present invention controls the die head pressure, and granulates by high-pressure extrusion near the softening point, which can effectively form dense particles, while protecting the small reduction of the molecular weight of PHA pellets and improving the molecular weight of the final product.

[0020] For the preparation process provided by the present invention, the feeding speed of the twin-screw extruder is 8 - 20 Hz, preferably 10 - 12 Hz. Under this condition, an appropriate feeding rate of raw materials can be ensured, the accuracy of the extrusion granulation temperature can be improved, and a relatively small reduction in the molecular weight of the product can be guaranteed.

[0021] The preparation process provided by the present invention can be realized by using various known devices disclosed in the prior art, as long as the above process conditions can be provided. In order to better ensure the die head pressure, a specially designed die orifice is used in the present invention.

[0022] Specifically, the twin-screw extruder of the present invention adopts a tapered die orifice with a gradually changing aperture. The inner end aperture of the tapered die orifice is 5 - 8 mm larger, the outer end aperture is 2.5 - 4 mm smaller, and the total length of the hole is 10 - 20 mm. Preferably, the inner end aperture of the tapered die orifice is 6 - 7 mm larger, the outer end aperture is 2.5 - 3 mm smaller, and the total length of the hole is 10 - 15 mm. By adopting this tapered die orifice, a relatively large pressure can be formed on the material at the die orifice, so that it is extruded and formed near the softening point and then flows out of the die orifice.

[0023] The polyhydroxyalkanoates mentioned in the present invention can be divided into homopolymers and copolymers according to the monomer composition. According to the number of carbon atoms of the monomer, it can be short-chain PHA (i.e., the monomer is a hydroxy fatty acid with C3 - C5) or medium-chain PHA (i.e., the monomer is a hydroxy fatty acid with C6 - C18), but not limited thereto.

[0024] In some embodiments of the present invention, PHA can be a homopolymer, including but not limited to polyhydroxypropionate (PHP), polyhydroxybutyrate (PHB), polyhydroxyoctanoate (PHO), polyhydroxyvalerate (PHV), etc. For example, poly-3-hydroxybutyrate (P3HB), poly-4-hydroxybutyrate (P4HB), poly-3-hydroxypropionate (P3HP), or poly-3-hydroxyvalerate (P3HV), etc.

[0025] In some embodiments of the present invention, PHA can be a copolymer. For example, a binary copolymer of 3-hydroxybutyric acid and 4-hydroxybutyric acid (P34HB), a binary copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid (PHBHHx), a binary copolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid (PHBV), a binary copolymer of 3-hydroxyoctanoic acid and 3-hydroxyhexanoic acid (P3HO3HHx), a terpolymer of 3-hydroxybutyric acid, 3-hydroxyvaleric acid, and 3-hydroxyhexanoic acid (PHBVHHx), a terpolymer of 3-hydroxybutyric acid, 4-hydroxybutyric acid, and 3-hydroxyvaleric acid (P3HB4HB3HV), etc.

[0026] The polyhydroxyalkanoate powder that can be used in the present invention includes, but is not limited to, at least one of PHB, P4HB, P3HB4HB3HV, PHBV, PHBHHX, P34HB, P3HO3HH, PHO, PHBVHHX; preferably one or more of PHB, P34HB, PHBHHX, PHBV.

[0027] Preferably, the weight-average molecular weight of the polyhydroxyalkanoate powder is 500,000 - 800,000, and the molecular weight distribution is 2.0 - 3.0. In the preparation process provided by the present invention, in addition to the aforementioned polyhydroxyalkanoate powder, the raw materials may further include inorganic materials, organic materials, etc. to meet different material application requirements.

[0028] In the preparation process provided by the present invention, in addition to the aforementioned extrusion granulation step, other steps may be included according to the processing needs of the material, such as one or several combinations of injection molding, blow molding, thermoforming, 3D printing.

[0029] The second object of the present invention is to provide a polyhydroxyalkanoate material prepared by the above preparation process. Depending on the different processes, the polyhydroxyalkanoate material can be polyhydroxyalkanoate pellets, or products further processed from the pellets, such as disposable knives, forks, spoons, straws, disposable film bags, milk tea cups, coffee cups, etc.

[0030] According to the polyhydroxyalkanoate material provided by the present invention, the decrease in the molecular weight of the polyhydroxyalkanoate in the polyhydroxyalkanoate material compared to the molecular weight of the polyhydroxyalkanoate powder is not more than 10%, preferably not more than 7%, for example, between 3% - 7%.

[0031] Furthermore, the weight-average molecular weight of the polyhydroxyalkanoate in the polyhydroxyalkanoate material is 450,000 - 750,000.

[0032] The third object of the present invention is to provide the application of the above preparation process and the polyhydroxyalkanoate material prepared thereby in raw material granulation. Due to the advantages of the process, the polyhydroxyalkanoate material of the present invention has a very small decrease in molecular weight, and thus can be secondary processed and formed. When applied to disposable knives, forks, spoons, straws, disposable film bags, milk tea cups, coffee cups, etc., it shows ideal practical application value.

[0033] The present invention optimizes the extrusion granulation process by reforming the technology of weakening the screw shear combination of a twin-screw extruder through a high-torque, low-speed, and strong-conveying method. Meanwhile, the present invention extrudes near the softening point temperature (i.e., controlling the extrusion processing temperature at 60 - 140°C, close to the softening temperature of PHA), and increases the pressure resistance of the die, so that the PHA material is extruded under high pressure for granulation, to weaken the thermal degradation damage of PHA by temperature. Dense particles are formed by high-pressure extrusion for granulation. By taking multiple measures simultaneously, pellets with a molecular weight reduction of less than 10% can be produced, and then can be ideally applied to the production of downstream products. In addition, the present invention adopts a high specific torque of the extruder, reduces the speed, reduces the shear heat while increasing the feeding amount, and thus does not affect the output. The provided production process is simple and has low costs, and has broad application prospects. Detailed Embodiments

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention are described clearly and completely. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0035] The raw materials used in the following examples and comparative examples are all known commercially available products, and can be purchased from Beijing Microstruct Biotech Co., Ltd.

[0036] Example 1 This example provides a polyhydroxyalkanoate (PHB) and its preparation method, which are as follows: Using PHB powder as the raw material (molecular weight 723778), it is put into a twin-screw extruder for extrusion granulation. Among them, the extrusion processing temperature is 100 - 140°C, the specific torque of the extruder is 13.5 N·m, the screw combination is mainly for conveying, with weak shear of 3 pieces of 60° shear blocks, the total length of the screw shear blocks is 10 cm, the screw speed is 200 rpm, the feeding speed is 10 Hz, and the die head pressure is 12 MPa.

[0037] Using the above process provided in this example, the molecular weight of the prepared PHB pellets is 698426, and the molecular weight reduction is 3.5%.

[0038] Example 2 This example provides a polyhydroxyalkanoate (P34HB) and its preparation method, which are as follows: Using P34HB powder as the raw material (the proportion of 4HB is 15%, and the molecular weight of the powder raw material is 498773), it is put into a twin-screw extruder for extrusion granulation. Among them, the extrusion processing temperature is 90 - 110 °C, the specific torque of the extruder is 14 N·m, the screw combination is mainly for conveying, with weak shearing of 3 pieces of 45° shearing blocks, the total length of the screw shearing blocks is 10 cm, the screw speed is 200 rpm, the feeding speed is 10 Hz, and the die head pressure is 15 MPa.

[0039] Using the above process provided in this example, the molecular weight of the prepared P34HB pellets is 465592, and the reduction rate of the molecular weight is 6.7%.

[0040] Example 3 This example provides a polyhydroxyalkanoate (PHBV) and its preparation method, which are as follows: Using PHBV powder as the raw material (the proportion of HV is 10%, and the molecular weight of the powder raw material is 688556), it is put into a twin-screw extruder for extrusion granulation. Among them, the extrusion processing temperature is 110 - 130 °C, the specific torque of the extruder is 16 N·m, the screw combination is mainly for conveying, with weak shearing of 3 pieces of 90° shearing blocks, the total length of the screw shearing blocks is 10 cm, the screw speed is 200 rpm, the feeding speed is 10 Hz, and the die head pressure is 16 MPa.

[0041] Using the above process provided in this example, the molecular weight of the prepared PHBV pellets is 657571, and the reduction rate of the molecular weight is 4.5%.

[0042] Example 4 This example provides a polyhydroxyalkanoate (PHBHHx) and its preparation method, which are as follows: Using PHBHHx powder as the raw material (the proportion of HHx is 12%, and the molecular weight of the powder raw material is 603321), it is put into a twin-screw extruder for extrusion granulation. Among them, the extrusion processing temperature is 60 - 90 °C, the specific torque of the extruder is 14 N·m, the screw combination is mainly for conveying, with weak shearing of 3 pieces of 45° shearing blocks, the total length of the screw shearing blocks is 10 cm, the screw speed is 200 rpm, the feeding speed is 10 Hz, and the die head pressure is 20 MPa.

[0043] Using the above process provided in this example, the molecular weight of the prepared PHBHHx pellets is 577378, and the reduction rate of the molecular weight is 4.3%.

[0044] Comparative Example 1 This comparative example provides a polyhydroxyalkanoate (PHB) and its preparation method, which are as follows: Using PHB powder as raw material (the molecular weight of the powder raw material is 853778), it is put into a twin-screw extruder for extrusion granulation. Among them, the extrusion processing temperature is 140 - 170 °C, the specific torque of the extruder is 8.5 N·m, the screw combination has strong shear, 2 pieces of 45° shear blocks, 2 pieces of 60° shear blocks, 2 pieces of 90° shear blocks, the total length of the screw shear blocks is 10 cm, the screw speed is 200 rpm, the feeding speed is 10 Hz, and the die head pressure is 1.4 MPa.

[0045] Using the above process provided by this comparative example, the molecular weight of the prepared PHB pellets is 210883, and the reduction amplitude of the molecular weight is 75.3%.

[0046] Comparative Example 2 This comparative example provides a polyhydroxyalkanoate (PHB) and its preparation method, which are as follows: Using PHB powder as raw material (the molecular weight of the powder raw material is 723778), it is put into a twin-screw extruder for extrusion granulation. Among them, the extrusion processing temperature is 100 - 120 °C, the specific torque of the extruder is 8.5 N·m, the screw combination is mainly for conveying, with weak shear of 3 pieces of 45° shear blocks, the total length of the screw shear blocks is 10 cm, the screw speed is 200 rpm, the feeding speed is 10 Hz, and the die head pressure is 1.8 MPa.

[0047] Using the above process provided by this comparative example, the powder is not plasticized, the pressure is too small to be extruded, and granulation cannot be carried out.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for preparing a polyhydroxyalkanoate material, comprising extruding and granulating a raw material containing polyhydroxyalkanoate powder by a twin-screw extruder, characterized in that: The twin-screw extruder adopts a specific torque of 13-20 N·m and a main engine speed of 100-300 rpm. The temperature range of the extrusion granulation is 60-140° C. or the softening point temperature of the raw material ±5° C.

2. The preparation process according to claim 1, characterized in that: The screw combination of the twin-screw extruder is mainly used for conveying, and adopts weak shearing of 2-4 45°-90° shearing blocks.

3. The preparation process according to claim 1 or 2, characterized in that: An extrusion pressure of 10-20 MPa is used, preferably 12-16 MPa.

4. The preparation process according to any one of claims 1 to 3, characterized in that: The feeding speed of the twin-screw extruder is 8-20 Hz, preferably 10-12 Hz.

5. The preparation process according to any one of claims 1 to 4, characterized in that: The twin-screw extruder adopts a tapered die with a gradually changing aperture, wherein the aperture at the inner end of the tapered die is 5-8 mm larger, the aperture at the outer end is 2.5-4 mm smaller, and the total length of the aperture is 10-20 mm.

6. The preparation process according to any one of claims 1 to 5, characterized in that: The polyhydroxyalkanoate powder includes at least one of PHB, P4HB, P3HB4HB3HV, PHBV, PHBHHX, P34HB, P3HO3HH, PHO, and PHBVHHX; preferably one or more of PHB, P34HB, PHBHHx, and PHBV; more preferably, the weight average molecular weight of the polyhydroxyalkanoate powder is 500,000-800,000, and the molecular weight dispersion is 2.0-3.

0.

7. The preparation process according to any one of claims 1 to 6, characterized in that: The raw materials also include one or more of inorganic materials and organic materials; And / or, the preparation process also includes one or a combination of injection molding, blow molding, vacuum forming, and 3D printing.

8. A polyhydroxyalkanoate material, characterized in that: The polyhydroxyalkanoate material is prepared by the preparation method according to any one of claims 1 to 7.

9. The polyhydroxyalkanoate material according to claim 8, characterized in that: The molecular weight of the polyhydroxyalkanoate in the polyhydroxyalkanoate material decreases by no more than 10% compared with the molecular weight of the polyhydroxyalkanoate powder.

10. Use of the preparation process according to any one of claims 1 to 7 and the polyhydroxyalkanoate material according to claim 8 or 9 in injection molding of cutlery, fork and spoon, blown film and blister cup.