Biodegradable polycarbonate resin as well as preparation method and preparation system thereof

Abstract

The invention provides biodegradable polycarbonate resin as well as a preparation method and a preparation system thereof, the preparation method comprises the following steps: mixing a catalyst and an epoxy monomer in a carbon dioxide atmosphere, introducing carbon dioxide to adjust the pressure in the system, and then heating to carry out polymerization reaction to obtain a polymer; heating the obtained polymer, mixing the heated polymer with a non-isocyanate chain extender, carrying out a chain extension reaction, and finally carrying out extrusion granulation. According to the preparation method, a polymer with relatively low molecular weight is subjected to chain extension by adopting a non-isocyanate chain extender, so that the molecular weight and the glass transition temperature of polycarbonate are rapidly increased, and the finally obtained polycarbonate resin has relatively high thermal stability and also has the characteristics of no toxicity and biodegradability.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer synthesis, and in particular relates to a biodegradable polycarbonate resin and a preparation method and a preparation system thereof. Background Art

[0002] Polycarbonate (PC) is a type of polymer compound containing carbonate groups in the polymer chain. As one of the five major engineering plastics, it is widely used in many fields. According to the type of polymer monomer, polycarbonate can be divided into aliphatic polycarbonate and aromatic polycarbonate. Among them, aromatic polycarbonate has a benzene ring structure in its polymer chain, which makes it more rigid and has good mechanical properties. It is currently the most widely used.

[0003] However, aromatic polycarbonates are difficult to biodegrade. At the same time, since the recycling of waste aromatic polycarbonates has certain technical barriers and the recycling process has great environmental pollution problems, the recycling cost of waste aromatic polycarbonates remains high. Currently, the main means of treating waste aromatic polycarbonates are still incineration or landfill. The large amount of carbon dioxide released during the incineration process will aggravate the "greenhouse effect", while landfills continue to consume precious land resources. Therefore, the environmental problems caused by waste aromatic polycarbonates are becoming increasingly serious. Polycarbonates prepared with carbon dioxide and epoxy monomers as raw materials can have both biodegradability and "carbon capture" characteristics. For example, polypropylene carbonate (PPC) has ester groups (-COOR) in its molecular chain, which has good biodegradability and can be degraded in air, water, soil and compost. However, due to the presence of ether bonds (-O-) in the PPC molecular chain, its main chain can easily rotate around the ether bonds, making the polymer chain highly flexible, and there is no strong interaction between the polymer molecular chains, resulting in poor mechanical properties of the molecular chains. In addition, the glass transition temperature (Tg) of PPC is low (30~41℃), and its thermal stability is poor at high temperatures. It is prone to softening and deformation, or even adhesion, which greatly limits the processing and application of PPC.

[0004] Tg is related to the molecular weight and molecular structure of the polymer. One of the effective ways to increase the Tg of the polymer is to add a chain extender to allow the end groups of the polymer to undergo a rapid and irreversible chain extension reaction with the chain extender to increase the molecular weight of the polymer. For example, CN116162222A discloses a method of using isocyanate as a chain extender to prepare a high molecular weight PPC through a two-step curing reaction; another example is CN118290696A discloses the use of a variety of diisocyanates as chain extenders to obtain a high molecular weight, high strength and high toughness carbon dioxide-based polyester. However, the above inventions all use isocyanate chain extenders to achieve the growth of PPC / carbon dioxide-based polyester polymers. However, isocyanate chain extenders have certain toxicity, which makes the PPC / carbon dioxide-based polyester polymers prepared with this as a chain extender unable to be used as food contact packaging materials, and thus cannot play its significant advantage of high water and oxygen barrier properties.

[0005] Therefore, it is necessary to develop a method for preparing a biodegradable polycarbonate resin with high molecular weight, excellent thermal stability and no toxicity to solve the above problems. Summary of the invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide a biodegradable polycarbonate resin and a preparation method and a preparation system thereof. The preparation method uses a non-isocyanate chain extender to undergo a coupling reaction with the end group of a polymer with a relatively low molecular weight to effectively extend the chain, thereby quickly increasing the molecular weight and glass transition temperature (Tg) of the polycarbonate resin, so that the final biodegradable polycarbonate resin has high thermal stability and is non-toxic.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a biodegradable polycarbonate resin, the preparation method comprising the following steps:

[0009] (1) mixing a catalyst and an epoxy monomer under a carbon dioxide atmosphere, introducing carbon dioxide to adjust the system pressure, and then raising the temperature to carry out a polymerization reaction to obtain a polymer;

[0010] (2) The polymer obtained in step (1) is heated, and then mixed with a non-isocyanate chain extender to undergo a chain extension reaction, and then extruded and granulated to obtain the biodegradable polycarbonate resin.

[0011] In the preparation method provided by the present invention, first, the catalyst and the epoxy monomer are mixed under a carbon dioxide atmosphere, carbon dioxide is introduced to adjust the system pressure, and then the temperature is increased to perform a polymerization reaction to obtain a polycarbonate polymer with a relatively low molecular weight. The present invention has no special requirements for this step, and it can be performed in a conventional reactor. In actual operation, the air in the reactor can be replaced by a carbon dioxide atmosphere, and then the catalyst and the epoxy monomer are added and mixed, and then carbon dioxide is introduced to adjust the pressure in the reactor, and then the heating is turned on to increase the temperature, so that the raw materials in the reactor can undergo a polymerization reaction to obtain a polycarbonate polymer with a relatively low molecular weight; secondly, the above-obtained polymer is heated, and then mixed with a non-isocyanate chain extender to undergo a chain extension reaction, and extruded and granulated to obtain a biodegradable polycarbonate resin with a relatively high molecular weight and glass transition temperature (Tg). In this step, the polymer is first heated to reduce the viscosity of the polymer. It has better fluidity, and is easy to mix evenly with non-isocyanate chain extenders, which is beneficial to the uniform progress of subsequent chain extension reactions. On the one hand, if the polymer is mixed with the non-isocyanate chain extender without being heated, it is difficult to achieve effective mixing of the polymer and the non-isocyanate chain extender with the agitator in a conventional reactor due to the relatively low temperature of the polymer (the temperature of the polymerization reaction) and the high viscosity. The poor mixing effect will lead to uneven subsequent chain extension reactions, resulting in a wider molecular weight distribution of the biodegradable polycarbonate resin, a lower Tg, and limited improvement in thermal stability. On the other hand, if the mixing effect with the chain extender is improved by increasing the polymerization reaction temperature to reduce the viscosity of the obtained polymer, the polymer will undergo a long thermal shear process, which will in turn lead to partial degradation of the polymer, limiting the growth of the molecular weight, and also failing to obtain a high molecular weight, high Tg biodegradable polycarbonate resin.

[0012] In summary, the preparation method provided by the present invention achieves an increase in the molecular weight of the polymer by using a non-isocyanate chain extender to extend the polymer after the polymerization is completed, while ensuring that the obtained product is non-toxic and biodegradable, thereby improving the thermal stability of the obtained polycarbonate resin.

[0013] Preferably, the epoxy monomer in step (1) comprises any one of ethylene oxide, propylene oxide, cyclohexene oxide or epichlorohydrin, or a combination of at least two thereof.

[0014] Preferably, the catalyst in step (1) comprises an organic metal catalyst or a ternary rare earth metal catalyst.

[0015] Exemplarily, the organic metal catalyst can be selected from zinc glutarate, diethyl zinc, etc.; the ternary rare earth metal catalyst can be selected from Y(CF3CO2)3(I) / diethyl zinc(II) / glycerol system catalyst, Et2Zn-LnCl3-polyol system catalyst, etc.

[0016] Preferably, based on the usage of 1700 g of the epoxy monomer in step (1), the usage of the catalyst is 10-25 g, for example, 10 g, 12 g, 14 g, 16 g, 18 g, 20 g, 23 g or 25 g.

[0017] Preferably, in step (1), the carbon dioxide is introduced to adjust the system pressure so that the system pressure is maintained at 1-5.5 MPa, for example, 1 MPa, 1.5 MPa, 1.8 MPa, 2.1 MPa, 2.6 MPa, 3 MPa, 3.9 MPa, 4.3 MPa, 5.1 MPa or 5.5 MPa.

[0018] Preferably, the polymerization reaction temperature in step (1) is 50-70°C, for example, 50°C, 52°C, 55°C, 58°C, 60°C, 62°C, 64°C, 67°C, 69°C, or 70°C.

[0019] Preferably, the polymerization reaction time in step (1) is 18 to 42 h, for example, 18 h, 20 h, 24 h, 28 h, 31 h, 35 h, 40 h or 42 h.

[0020] Preferably, the mixing and polymerization reaction in step (1) are both carried out in a reactor.

[0021] Preferably, after the polymerization reaction in step (1) is completed, the process further includes depressurizing the reactor and discharging high-pressure tail gas.

[0022] Preferably, the polymer is heated in step (2) so that the temperature of the heated polymer rises by 30-60°C, which means that the difference between the temperature of the polymer after heating and the temperature of the polymer before heating is 30-60°C, such as 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C, that is, the total temperature rise of the polymer after heating is 30-60°C; if the temperature difference before and after heating is too large, excessive heating will cause thermal degradation of the polymer, thereby limiting the growth of polymer chain segments; and if the temperature difference before and after heating is too small, the viscosity of the heated polymer is still high, the molecular chain fluidity is poor, which is not conducive to mixing with the chain extender and the chain extension reaction, resulting in the final polymer molecular chain growth being less than expected.

[0023] Preferably, the heating in step (2) is carried out in at least one heater, the heat medium in the heater flows in the coil, and the polymer melt flows in the shell, and the melt is heated when passing through the shell. The equipment has a large heat transfer coefficient and a good heat transfer effect. At the same time, there is no local dead corner in the melt flow, and there is no local overheating of the melt during the heating process.

[0024] Preferably, based on the mass of the polymer in step (2) as 100%, the mass of the non-isocyanate chain extender is 0.4-1.5%, for example, 0.4%, 0.5%, 0.6%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%.

[0025] Preferably, the non-isocyanate chain extender in step (2) includes a glycidyl ether chain extender and / or an epoxy chain extender, and more preferably an epoxy chain extender.

[0026] For example, the glycidyl ether chain extender may be any one of ethylene glycol diglycidyl ether, butanediol diglycidyl ether or neopentyl glycol diglycidyl ether, or a combination of at least two thereof.

[0027] For example, the epoxy chain extender may be a multifunctional epoxide styrene-acrylic chain extender, such as BASF ADR-4468 and / or BASF ADR-4368C.

[0028] Preferably, the mixing in step (2) is carried out in at least one dynamic mixer. In actual operation, the polymer can be allowed to enter the dynamic mixer through an inlet, and the non-isocyanate chain extender can be added to the dynamic mixer through at least one addition port to mix the two.

[0029] A dynamic mixer refers to a device that relies on mechanical power elements to force a fluid system to flow in order to achieve uniform mixing of materials. Compared with a static mixer, a dynamic mixer has the following advantages: more deflections, changeable gaps and rotation speeds, so that the mixing effect and shear intensity can be adjusted, powered transmission, short pipe lengths, low pressure drop, and sufficient mixing within a short material residence time. Using a dynamic mixer for mixing can quickly update the surface of the polymer, and with a lower addition ratio of the chain extender, the chain extender can be evenly mixed in the polymer melt within a shorter residence time. In addition, it should be noted that the dynamic mixer described in the present invention does not include an extruder, but specifically refers to a mixing device relative to a static mixer.

[0030] Preferably, the rotation speed of the dynamic mixer in step (2) is 100-1000 rpm, for example, 100 rpm, 200 rpm, 400 rpm, 600 rpm, 800 rpm or 1000 rpm.

[0031] Preferably, the mixing time in step (2) is 1 to 10 s, for example, 1 s, 2 s, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s or 10 s, etc., that is, the residence time of the mixture in the dynamic mixer is 1 to 10 s.

[0032] In the present invention, the mixing time of the obtained polymer and the non-isocyanate chain extender, that is, the residence time in the dynamic mixer is also very important for the subsequent chain extension reaction. The residence mixing time determines the mixing degree of the non-isocyanate chain extender in the polymer molecules. Too short a residence time will lead to poor mixing degree of the chain extender, thereby making the subsequent chain extension reaction uneven and the molecular weight distribution of the obtained polycarbonate wider; if the residence time is too long, the polymer will experience a longer thermal shear process in the dynamic mixer, which will increase the degree of side reactions such as degradation, thereby limiting the molecular weight growth of the polymer after the chain extension reaction.

[0033] Preferably, the temperature of the chain extension reaction in step (2) is 100-150°C, for example, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C.

[0034] Preferably, the chain extension reaction time in step (2) is 1 to 9 min, for example, 1 min, 1.7 min, 2.5 min, 3.2 min, 4.2 min, 5 min, 5.8 min, 6.7 min or 9 min.

[0035] Preferably, the chain extension reaction in step (2) is carried out in a tubular reactor.

[0036] Preferably, the length of the tubular reactor is 1 to 10 m, for example, 1 m, 2 m, 3 m, 4 m, 5 m, 6 m, 7 m, 8 m or 10 m, etc.

[0037] At a fixed melt flow rate, the length of the tubular reactor determines the time of the chain extension reaction. If the length is insufficient, the reaction time is short, resulting in a low degree of chain extension reaction; if the length is too long, the pressure loss increases, the outlet pressure of the upstream pump is increased, and the equipment cost is increased.

[0038] As a preferred technical solution of the present invention, the preparation method specifically comprises the following steps:

[0039] (1) After drying and dehydration and replacing the air in the reactor with carbon dioxide, a catalyst and an epoxy monomer are added to the reactor and mixed, and then carbon dioxide is introduced into the reactor to maintain the pressure in the reactor at 1-5.5 MPa, and then the heating is turned on to maintain the temperature in the reactor at 50-70°C for polymerization for 18-42 hours. After the reaction is completed, the reactor is depressurized and the high-pressure tail gas is discharged to obtain a polymer;

[0040] (2) The polymer obtained in step (1) is heated by at least one heater so that the temperature difference between the polymer before and after heating is 30-60° C., and then the heated polymer is introduced into a dynamic reactor and mixed with a non-isocyanate chain extender at a rotation speed of 100-1000 rpm for 1-10 s. After the mixing is completed, the polymer is introduced into a tubular reactor with a length of 1-10 m and a chain extension reaction is carried out at 100-150° C. for 1-9 min. Finally, the obtained product is introduced into a downstream link through a delivery pump for extrusion granulation to obtain the biodegradable polycarbonate resin.

[0041] In a second aspect, the present invention provides a biodegradable polycarbonate resin, which is prepared by the preparation method described in the first aspect.

[0042] Preferably, the number average molecular weight of the biodegradable polycarbonate resin is not less than 50,000, for example, 50,000, 60,000, 80,000, 100,000, 120,000, 140,000, 150,000 or 200,000.

[0043] In a third aspect, the present invention provides a system for preparing a biodegradable polycarbonate resin, wherein the system is used to prepare the biodegradable polycarbonate resin as described in the second aspect;

[0044] The preparation system comprises a reaction kettle, a first delivery pump, a heater, a dynamic mixer, a tubular reactor and a second delivery pump which are connected in sequence.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The method for preparing a biodegradable polycarbonate resin provided by the present invention uses a non-isocyanate chain extender to carry out a chain extension reaction on a polycarbonate polymer with a relatively low molecular weight, thereby rapidly increasing the molecular weight and Tg of the polymer, so that the resulting biodegradable polycarbonate resin has a higher thermal stability.

[0047] (2) The non-isocyanate chain extender selected in the preparation method of the biodegradable polycarbonate resin provided by the present invention is non-toxic, thereby ensuring that the biodegradable polycarbonate resin obtained by chain extension can reach food grade and can be in direct contact with food. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic diagram of the structure of a preparation system for a biodegradable polycarbonate resin provided by the present invention;

[0049] Among them, 1 is a reaction kettle, 2 is a first delivery pump, 3 is a heater, 4 is a dynamic mixer, 5 is a tubular reactor and 6 is a second delivery pump. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0051] Example 1

[0052] A method for preparing a biodegradable polycarbonate resin, the structural schematic diagram of the preparation system is as follows Figure 1 As shown, the preparation method specifically comprises the following steps:

[0053] (1) Dry and remove water from the reactor 1, introduce CO2 atmosphere to replace the air in the reactor, add 20 g of zinc glutarate and 1700 g of propylene oxide into the reactor and mix them, then introduce CO2 atmosphere to adjust the pressure in the reactor to 5 MPa, then turn on the stirrer in the reactor and turn on the heating, maintain the temperature in the reactor at 65°C for polymerization reaction for 20 h, then stop heating, depressurize the reactor 1 and discharge the high-pressure tail gas to obtain a polymer;

[0054] (2) The polymer obtained in step (1) is conveyed to a heater 3 by a first conveying pump 2 for heating, so that the temperature of the heated polymer is 105° C. (the difference between the temperature of the polymer after heating and the temperature of the polymer before heating is 40° C.), and then the polymer is fed into a dynamic mixer 4 while maintaining the temperature, and a BASF ADR-4368C chain extender (the addition ratio is 0.6% of the polymer mass) is added from an addition port of the dynamic mixer 4, the rotation speed of the dynamic mixer is 540 rpm, the polymer and the BASF ADR-4368C chain extender are mixed in the dynamic mixer for 5 s, and then the two are passed through a tubular reactor 5 with a length of 3 m for a chain extension reaction for 2.5 min, and finally the product is conveyed to a devolatilization extruder and granulation system by a second conveying pump 6 for extrusion and granulation to obtain the biodegradable polycarbonate resin.

[0055] Example 2

[0056] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the temperature of the polymer after heating in step (2) is 115° C., that is, the temperature difference between the polymer after heating and before heating is 50° C., and the rotation speed of the dynamic mixer is adjusted to 480 rpm. Other substances, amounts and steps are the same as those in Example 1.

[0057] Example 3

[0058] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the temperature of the polymer after heating in step (2) is 85°C, that is, the temperature difference between the polymer after heating and before heating is 20°C, and the rotation speed of the dynamic mixer is adjusted to 680 rpm, and other substances, amounts and steps are the same as those in Example 1.

[0059] Example 4

[0060] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the temperature of the polymer after heating in step (2) is 145°C, that is, the temperature difference between the polymer after heating and before heating is 80°C, and the speed of the dynamic mixer is adjusted to 280 rpm. Other substances, amounts and steps are the same as those in Example 1.

[0061] Example 5

[0062] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the addition ratio of BASF ADR-4368C chain extender is 0.4% of the polymer mass, and other substances, amounts and steps are the same as those in Example 1.

[0063] Example 6

[0064] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the addition ratio of BASF ADR-4368C chain extender is 1% of the polymer mass, and other substances, amounts and steps are the same as those in Example 1.

[0065] Example 7

[0066] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the addition ratio of BASF ADR-4368C chain extender is 0.2% of the polymer mass, and other substances, amounts and steps are the same as those in Example 1.

[0067] Example 8

[0068] A method for preparing a biodegradable polycarbonate resin is disclosed. The method differs from Example 1 in that butanediol diglycidyl ether is used to replace the BASF ADR-4368C chain extender, and other substances, amounts and steps are the same as those in Example 1.

[0069] Example 9

[0070] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the residence mixing time of the polymer and BASF ADR-4368C chain extender in the dynamic mixer is 8 s, and other substances, amounts and steps are the same as those in Example 1.

[0071] Example 10

[0072] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the residence mixing time of the polymer and BASF ADR-4368C chain extender in the dynamic mixer is 2 s, and other substances, amounts and steps are the same as those in Example 1.

[0073] Embodiment 11

[0074] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the residence mixing time of the polymer and BASF ADR-4368C chain extender in the dynamic mixer is 12 s, and other substances, amounts and steps are the same as those in Example 1.

[0075] Example 12

[0076] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the residence mixing time of the polymer and BASF ADR-4368C chain extender in the dynamic mixer is 0.5 s, and other substances, amounts and steps are the same as those in Example 1.

[0077] Embodiment 13

[0078] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the length of the tubular reactor is 1.2 m, the time of the chain extension reaction is 1 min, and other substances, amounts and steps are the same as those in Example 1.

[0079] Embodiment 14

[0080] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the length of the tubular reactor is 6 m, the time of the chain extension reaction is 5 min, and other substances, amounts and steps are the same as those in Example 1.

[0081] Embodiment 15

[0082] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the length of the tubular reactor is 12 m, the time of the chain extension reaction is 10 min, and other substances, amounts and steps are the same as those in Example 1.

[0083] Example 16

[0084] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that the length of the tubular reactor is 0.5 m, the time of the chain extension reaction is 0.5 min, and other substances, amounts and steps are the same as those in Example 1.

[0085] Embodiment 17

[0086] A method for preparing a biodegradable polycarbonate resin specifically comprises: drying and removing water from a reactor, introducing a CO2 atmosphere to replace air in the reactor, adding 20 g of zinc glutarate and 1700 g of propylene oxide to mix, introducing a CO2 atmosphere to adjust the pressure in the reactor to 5 MPa, then starting a stirrer in the reactor and starting heating, maintaining the temperature in the reactor at 65°C for polymerization reaction for 20 h, then stopping heating, depressurizing the reactor to obtain a polymer, then increasing the temperature in the reactor to 105°C and keeping the temperature, injecting a BASF ADR-4368C chain extender into the reactor using an injection pump (the addition ratio is 0.6% of the polymer mass), using a stirrer in the reactor to evenly mix the polymer and the BASF ADR-4368C chain extender, and performing a chain extension reaction for 2.5 min, then stopping stirring the reactor, and conveying the reactor material to a devolatilization extruder and granulation system by a melt conveying pump for extrusion and granulation to obtain the biodegradable polycarbonate resin.

[0087] Comparative Example 1

[0088] A method for preparing a biodegradable polycarbonate resin specifically comprises: drying and removing water from a reaction kettle, introducing a CO2 atmosphere to replace the air in the kettle, adding 20 g of zinc glutarate and 1700 g of propylene oxide to mix, introducing a CO2 atmosphere to adjust the pressure in the kettle to 5 MPa, then turning on the stirrer in the kettle and turning on the heating, maintaining the temperature in the kettle at 65°C for polymerization reaction for 20 hours, then stopping the heating, depressurizing the reaction kettle and discharging the high-pressure tail gas, and conveying the materials in the reaction kettle to a devolatilization extruder and granulation system by a melt conveying pump for extrusion and granulation operations to obtain the biodegradable polycarbonate resin.

[0089] Comparative Example 2

[0090] A type of polypropylene carbonate, produced by Zhejiang Huafeng, with the brand name HF901.

[0091] Comparative Example 3

[0092] A method for preparing a biodegradable polycarbonate resin, which differs from Example 1 in that in step (2), the polymer is not heated, but directly transported to a dynamic mixer; other substances, amounts and steps are the same as those in Example 1.

[0093] Performance Test:

[0094] (1) Number average molecular weight (Mn) and molecular weight distribution (PDI): The test was performed using HLC-8320GPC gel permeation chromatograph; mobile phase: THF, detection temperature: 30°C, flow rate: 1.00 mL, injection volume: 100.0 μL, standard sample: standard polystyrene (PS).

[0095] (2) Glass transition temperature (Tg): The glass transition temperature was measured by differential scanning calorimetry (DSC) on a Q100 TA analyzer. The sample was heated from -25°C to 200°C at a heating rate of 10°C / min in a nitrogen atmosphere, and the Tg was recorded.

[0096] (3) Thermal weight loss temperature: The test was carried out using a PerkinElmer STA600 thermogravimetric analyzer. The sample was heated from 25°C to 400°C at a heating rate of 20°C / min in 40 mL / min nitrogen, and the temperatures corresponding to the weight loss rates of 5% and 50% were recorded respectively.

[0097] The biodegradable polycarbonate resins provided in Examples 1 to 17 and Comparative Examples 1 to 3 were tested according to the above test method. The test results are shown in Table 1:

[0098] Table 1

[0099]

[0100] From the data in Table 1, we can see that:

[0101] (1) Compared with the biodegradable polycarbonate resins provided in Comparative Examples 1 to 3, the biodegradable polycarbonate resin obtained by the preparation method provided in the embodiment has a significantly higher number average molecular weight, a significantly narrower molecular weight distribution, a higher Tg, and a higher thermal weight loss temperature, indicating that the thermal stability has been significantly improved.

[0102] (2) Further comparison of the data of Examples 1 to 4 shows that the temperature rise of the polymer after heating is better when it is controlled within the range of 30 to 60°C. If the temperature rise is too low, the molecular weight increase is limited and the molecular weight distribution becomes wider. If the temperature rise is too high, the degree of polymer degradation side reactions increases, thereby inhibiting the growth of molecular weight.

[0103] (3) Further comparison of the data of Example 1 and Examples 5 to 7 shows that the amount of chain extender added will also affect the molecular weight and Tg of the final polycarbonate. When the amount added is in the range of 0.4 to 1.5% of the polymer mass, as the addition ratio increases, the polymer molecular weight increases, the Tg rises, and the thermal stability increases.

[0104] (4) Further comparison of the data of Example 1 and Example 8 shows that the glycerol ether chain extender represented by butanediol diglycidyl ether can also achieve good chain extension effect, but the degree of increase in molecular weight and Tg is not as good as that of the multifunctional epoxide styrene-acrylic chain extender.

[0105] (5) Further comparison of the data of Example 1 and Examples 9 to 12 also shows that the residence time of the polymer and the chain extender in the dynamic mixer will also affect the molecular weight of the final polycarbonate resin. If the residence time is too short, the mixing degree is insufficient, resulting in a broadening of the molecular weight distribution of the polymer and a limited increase in the molecular weight. If the mixing time is too long, the thermal degradation process of the polymer is prolonged, the molecular weight growth degree is inhibited, and the thermal stability also increases to a limited extent.

[0106] (6) Further comparison of the data of Example 1 and Examples 13 to 16 also shows that, since the length of the tubular reactor affects the extent of the chain extension reaction, a tubular reactor that is too short will result in insufficient chain extension reaction time, a limited increase in the Tg of the polymer obtained after chain extension, and insufficient improvement in the thermal stability of the polymer; while a tubular reactor that is too long will increase the residence time of the chain extension reaction, but will not result in a greater improvement in the molecular weight, Tg, and thermal stability of the polymer.

[0107] (7) Finally, by comparing the data of Example 1 and Comparative Example 3, it can be seen that when the chain extension reaction is carried out directly in the reactor, the molecular weight Tg of the polymer obtained after chain extension also increases to a limited extent.

[0108] The applicant declares that the present invention illustrates a biodegradable polycarbonate and its preparation method and preparation system through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a biodegradable polycarbonate resin, characterized in that: The preparation method comprises the following steps: (1) mixing a catalyst and an epoxy monomer under a carbon dioxide atmosphere, introducing carbon dioxide to adjust the system pressure, and then raising the temperature to carry out a polymerization reaction to obtain a polymer; (2) The polymer obtained in step (1) is heated, and then mixed with a non-isocyanate chain extender to undergo a chain extension reaction, and then extruded and granulated to obtain the biodegradable polycarbonate resin.

2. The preparation method according to claim 1, characterized in that: The epoxy monomer in step (1) includes any one of ethylene oxide, propylene oxide, cyclohexene oxide or epichlorohydrin, or a combination of at least two thereof.

3. The preparation method according to claim 1, characterized in that: The polymerization reaction temperature in step (1) is 50-70°C and the reaction time is 18-42 h.

4. The preparation method according to claim 1, characterized in that: In step (2), the polymer is heated so that the temperature of the heated polymer increases by 30-60°C.

5. The preparation method according to claim 1, characterized in that: Taking the mass of the polymer in step (2) as 100%, the mass of the non-isocyanate chain extender is 0.4-1.5%.

6. The preparation method according to claim 1, characterized in that: The non-isocyanate chain extender in step (2) includes a glycidyl ether chain extender and / or an epoxy chain extender.

7. The preparation method according to claim 1, characterized in that: The mixing in step (2) is carried out in at least one dynamic mixer, and the mixing time is 1 to 10 s.

8. The preparation method according to claim 1, characterized in that: The chain extension reaction in step (2) is carried out in a tubular reactor, and the chain extension reaction time is 1 to 9 minutes.

9. A biodegradable polycarbonate resin, characterized in that: The biodegradable polycarbonate resin is prepared by the preparation method according to any one of claims 1 to 8.

10. A system for preparing a biodegradable polycarbonate resin, characterized in that: The preparation system is used to prepare the biodegradable polycarbonate resin as claimed in claim 9; The preparation system comprises a reaction kettle, a first delivery pump, a heater, a dynamic mixer, a tubular reactor and a second delivery pump which are connected in sequence.

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