Biodegradable polyester foam material and preparation method thereof
阅读说明：本技术 可生物降解聚酯发泡材料及其制备方法 (Biodegradable polyester foam material and preparation method thereof ) 是由 郭宝华 于 2019-09-24 设计创作，主要内容包括：本发明提供一种能够制备泡孔均匀、发泡倍率高且可生物降解的聚酯发泡材料的制备方法、以及由该制备方法所制备的发泡材料。该制备方法包括：混合步骤,将可生物降解聚酯、成核剂、辐射敏化剂、微波敏化剂、发泡剂混合,得到混合物料；辐射处理步骤,在氮气或惰性气体气氛下对混合物料进行电子束辐射处理或γ-射线辐射处理,得到可生物降解聚酯组合物；以及对该组合物进行微波烘道发泡或微波炉发泡,得到可生物降解聚酯发泡材料,其中,辐射敏化剂为在单个分子中具有2个以上官能团的单体,相对于辐射处理步骤前的混合物料的熔体强度,该组合物的熔体强度提高了100％至500％,微波烘道或微波炉发泡的功率均为4kW至30kW,发泡时间均为20秒至1800秒。(The invention provides a preparation method capable of preparing a biodegradable polyester foam material with uniform foam holes and high foaming ratio, and the foam material prepared by the preparation method. The preparation method comprises the following steps: mixing, namely mixing biodegradable polyester, a nucleating agent, a radiation sensitizer, a microwave sensitizer and a foaming agent to obtain a mixed material; a radiation treatment step, in which the mixed material is subjected to electron beam radiation treatment or gamma-ray radiation treatment in the atmosphere of nitrogen or inert gas to obtain a biodegradable polyester composition; and performing microwave drying tunnel foaming or microwave oven foaming on the composition to obtain the biodegradable polyester foaming material, wherein the radiosensitizer is a monomer with more than 2 functional groups in a single molecule, the melt strength of the composition is improved by 100 to 500 percent compared with the melt strength of the mixed material before the radiation treatment step, the foaming power of the microwave drying tunnel or the microwave oven is 4 to 30kW, and the foaming time is 20 to 1800 seconds.)
1. A preparation method of biodegradable polyester foaming material is characterized by comprising the following steps:
a mixing step, wherein biodegradable polyester, a nucleating agent, a radiation sensitizer, a microwave sensitizer and a foaming agent are mixed to obtain a mixed material;
a radiation treatment step, wherein the mixed material is subjected to electron beam radiation treatment or gamma-ray radiation treatment in a nitrogen or inert gas atmosphere to obtain a biodegradable polyester composition; and
subjecting the biodegradable polyester composition to microwave oven foaming or microwave oven foaming to obtain a biodegradable polyester foam material, wherein,
the radiosensitizer is a monomer having 2 or more functional groups in a single molecule,
the melt strength of the biodegradable polyester composition is increased by 100 to 500% relative to the melt strength of the mixed material before the radiation treatment step, and
the foaming power of the microwave drying channel is 4kW to 30kW, the foaming time is 20 seconds to 1800 seconds,
the foaming power of the microwave oven is 4kW to 30kW, and the foaming time is 20 seconds to 1800 seconds.
2. The method of claim 1, wherein the functional group is an olefinic carbon-carbon double bond.
3. The production method according to claim 1 or 2, characterized in that the amount of the radiation sensitizer is 0.5 parts by weight to 15 parts by weight with respect to 100 parts by weight of the biodegradable polyester.
4. The production method according to claim 1 or 2, characterized in that the absorbed dose of the electron beam radiation treatment or the γ -ray radiation treatment is 2kGy to 50 kGy.
5. The production method according to claim 1 or 2, characterized in that the biodegradable polyester comprises at least one selected from the group consisting of polybutylene succinate and polybutylene terephthalate/adipate, and at least one selected from the group consisting of polylactic acid, polycaprolactone, polyhydroxyalkanoate,
preferably, the microwave sensitizer includes at least one selected from the group consisting of ferroferric oxide, manganese dioxide, zinc oxide, and calcium oxide.
6. The production method according to claim 1 or 2, wherein the nucleating agent comprises at least one selected from the group consisting of calcium carbonate, talc, zinc oxide, nano-montmorillonite, silica,
preferably, the grain size of the nucleating agent is 1.6 μm or more and 23 μm or less.
7. The production method according to claim 1 or 2, wherein the blowing agent comprises at least one selected from the group consisting of an azo-based compound, a nitroso-based compound, and a urea-based compound,
preferably, the biodegradable polyester composition has a gel content of 5% to 20%.
8. The production method according to claim 1 or 2, characterized by further comprising: heating the biodegradable polyester at 40 ℃ to 80 ℃ for 1 hour to 24 hours prior to the mixing step.
9. A biodegradable polyester foam obtained by the production method according to any one of claims 1 to 8.
10. The biodegradable polyester foam according to claim 9, wherein the cells have a diameter of 200 to 500 μm, an expansion ratio of 2 to 15 times, and an apparent density of 10kg/m3To 200kg/m3。
Technical Field
The invention belongs to the field of polymer foam materials, and particularly relates to a biodegradable polyester foam material and a preparation method thereof.
Background
The polymer foaming material is a material which takes polymer as a base material and takes foaming gas as a disperse phase. The polymer foam material has the unique advantages of low density, good buffering performance, good vibration absorption performance and the like, so the polymer foam material is widely applied to daily life, and is particularly applied to the fields of vibration absorption packaging, heat preservation packaging, disposable tableware and the like in large quantities.
At present, most of the polymer foam materials on the market are foam materials using traditional plastics such as Polyethylene (PE), polypropylene (PP), Polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and the like as base materials. These foamed materials are stable in nature and are difficult to degrade, thereby creating serious environmental problems. The foam material made of biodegradable polymer material is one of the important ways to solve the above environmental problems.
Biodegradable polymer material refers to polymer material that can be degraded in natural aerobic and/or anaerobic environment, which is an important solution to solve environmental problems caused by conventional plastics as an alternative to conventional plastics. The biodegradable high molecular material is completely digested by taking microorganisms in the environment as food to obtain energy, and elements in the material are completely converted into humoid through biochemical reaction in microbial cells and are harmless to the environment.
Biodegradable polyesters are a very important class of biodegradable polymer materials and have recently become the most widely used branch of biodegradable polymer materials. The molecular chain of the conventional biodegradable polyester has a linear structure and a relatively narrow molecular weight distribution, which results in a low Melt Strength (MS) of the biodegradable polyester. As a result, in the extrusion foaming process, when the processing temperature is higher than the melting point of the biodegradable polyester, the melt strength and viscosity of the whole system are sharply reduced, cells are easily collapsed during extrusion foaming, and it is difficult to obtain a foamed material with a high foaming ratio.
Disclosure of Invention
Aiming at the current situation and the defects of the prior art, the invention aims to provide a preparation method capable of preparing a biodegradable polyester foam material with uniform cells, high foaming ratio and biodegradability, and the biodegradable polyester foam material prepared by the preparation method.
Therefore, the above problems are solved by the following means. That is to say that the first and second electrodes,
the invention relates to a preparation method of a biodegradable polyester foaming material, which is characterized by comprising the following steps:
a mixing step, wherein biodegradable polyester, a nucleating agent, a radiation sensitizer, a microwave sensitizer and a foaming agent are mixed to obtain a mixed material;
a radiation treatment step, wherein the mixed material is subjected to electron beam radiation treatment or gamma-ray radiation treatment in a nitrogen or inert gas atmosphere to obtain a biodegradable polyester composition; and
subjecting the biodegradable polyester composition to microwave oven foaming or microwave oven foaming to obtain a biodegradable polyester foam material, wherein,
the radiosensitizer is a monomer having 2 or more functional groups in a single molecule,
the melt strength of the biodegradable polyester composition is increased by 100 to 500% relative to the melt strength of the mixed material before the radiation treatment step, and
the foaming power of the microwave drying channel is 4kW to 30kW, the foaming time is 20 seconds to 1800 seconds,
the foaming power of the microwave oven is 4kW to 30kW, and the foaming time is 20 seconds to 1800 seconds.
The invention according to a second aspect of the present invention is the production method according to the first aspect of the present invention, characterized in that the functional group is an olefinic carbon-carbon double bond.
The invention according to a third aspect of the present invention is the production method according to the first or second aspect of the present invention, characterized in that the amount of the radiation sensitizer is 0.5 parts by weight to 15 parts by weight with respect to 100 parts by weight of the biodegradable polyester.
An invention relating to a fourth aspect of the invention is the production method according to the first or second aspect of the invention, characterized in that the absorbed dose of the electron beam radiation treatment or the γ -ray radiation treatment is 2kGy to 50 kGy.
The invention relating to the fifth aspect is the production method according to the first or second aspect, characterized in that the biodegradable polyester comprises at least one selected from the group consisting of polybutylene succinate and polybutylene terephthalate/adipate, and at least one selected from the group consisting of polylactic acid, polycaprolactone, and polyhydroxyalkanoate,
preferably, the microwave sensitizer includes at least one selected from the group consisting of ferroferric oxide, manganese dioxide, zinc oxide, and calcium oxide.
The invention according to a sixth aspect of the present invention is the production method according to the first or second aspect of the present invention, characterized in that the nucleating agent comprises at least one selected from the group consisting of calcium carbonate, talc, zinc oxide, nano-montmorillonite, and silica,
preferably, the grain size of the nucleating agent is 1.6 μm or more and 23 μm or less.
The invention according to a seventh aspect of the present invention is the production method according to the first or second aspect of the present invention, characterized in that the blowing agent comprises at least one selected from the group consisting of azo-based compounds, nitroso-based compounds, urea-based compounds,
preferably, the biodegradable polyester composition has a gel content of 5% to 20%.
An eighth aspect of the present invention relates to the invention, which is the production method according to the first aspect or the second aspect, characterized by further comprising: heating the biodegradable polyester at 40 ℃ to 80 ℃ for 1 hour to 24 hours prior to the mixing step.
The invention according to a ninth aspect of the present invention is a biodegradable polyester foam material obtained by the production method according to any one of the first to eighth aspects of the present invention.
The invention according to a tenth aspect of the present invention is the biodegradable polyester foam material according to the ninth aspect of the present invention, characterized in that the diameter of the cells is 200 μm to 500 μm, the expansion ratio is 2 times to 15 times, and the apparent density is 10kg/m3To 200kg/m3。
Effects of the invention
According to the inventions of the first aspect to the eighth aspect of the present invention, by the microwave drying tunnel foaming or the microwave oven foaming, a biodegradable polyester foam material having a high foaming ratio, uniform cells and biodegradability can be prepared.
According to the invention of the ninth and tenth aspects of the invention, a biodegradable polyester foam material having a high foaming ratio, uniform cells and biodegradability can be provided.
Detailed Description
The method for preparing a biodegradable polyester composition according to one embodiment of the present invention is characterized by comprising: a mixing step, wherein biodegradable polyester, a nucleating agent, a radiation sensitizer, a microwave sensitizer and a foaming agent are mixed to obtain a mixed material; and a radiation treatment step in which the mixture is subjected to electron beam radiation treatment or gamma-ray radiation treatment under a nitrogen or inert gas atmosphere to obtain the biodegradable polyester composition, wherein the radiation sensitizer comprises a monomer having 2 or more functional groups in a single molecule, and the melt strength of the biodegradable polyester composition is increased by 100% to 500% with respect to the melt strength of the mixture before the radiation treatment step.
According to the preparation method of the embodiment, the biodegradable polyester is subjected to radiation treatment through electron beams or gamma-rays, so that the biodegradable polyester macromolecules are excited and ionized under the action of high-energy rays to generate macromolecular free radicals, the free radicals are subjected to molecular collision or the free radicals are reacted with a polyfunctional radiation sensitizer to initiate further crosslinking reaction, and the obtained crosslinking structure can remarkably improve the melt strength of the biodegradable polyester, so that the biodegradable polyester subjected to radiation treatment generates strain hardening behavior in the heating process. Thus, a biodegradable polyester composition can be prepared, which has stably increased cells and can suppress the breakage of cell walls when subjected to microwave oven foaming or microwave oven foaming, thereby enabling to obtain a biodegradable polyester foam material having a high foaming ratio, uniform cells and biodegradability.
Biodegradable polyesters mainly include: biosynthetic polyesters such as polyhydroxyalkanoates (PHA, PHB, PHBV), and the like; polyesters derived from biologically produced monomers and synthesized, such as polylactic acid (PLA) and the like; petroleum-based synthetic aliphatic polyesters such as polybutylene succinate (PBS), polybutylene succinate/adipate copolymer (PBSA), Polycaprolactone (PCL), and the like; petroleum-based synthetic aromatic polyesters or copolymers, such as polybutylene terephthalate/adipate copolymer (PBAT), polybutylene terephthalate/succinate copolymer (PBST), and the like.
In the common biodegradable polyester in the current market, polybutylene succinate and polybutylene terephthalate/adipate copolymer have good processing performance and mechanical property, and the melting points of the two materials are both higher than 100 ℃, so that the biodegradable polyester can be used for preparing food boxes for containing hot food. In addition, polylactic acid and polyhydroxyalkanoates (PHA, PHB, PHBV) have good biodegradability, and have higher hardness than polybutylene succinate and polybutylene terephthalate/adipate copolymers, so that the polylactic acid and the polyhydroxyalkanoates can be used as a combined material to adjust the degradation speed of the blended material and improve the hardness of the blended material. In addition, the glass transition temperature and the melting point of the polycaprolactone are both very low, and the polycaprolactone has better low-temperature performance, so that the low-temperature toughness of the blended material can be increased by using the polycaprolactone in the biodegradable polyester composition, and the material used under the freezing or refrigerating condition can be prepared.
The biodegradable polyester in the above embodiment preferably includes at least one selected from the group consisting of polybutylene succinate and polybutylene terephthalate/adipate copolymer, and at least one selected from the group consisting of polylactic acid, polycaprolactone, and polyhydroxyalkanoate (PHA, PHB, PHBV), according to properties of different biodegradable polyester materials.
However, when a biodegradable polyester such as polybutylene succinate is directly subjected to radiation treatment, the mechanical properties (such as tensile strength, elongation at break, etc.) and melt strength of the biodegradable polyester subjected to radiation treatment are reduced. Therefore, it is necessary to add a radiation sensitizer to the biodegradable polyester and then perform a radiation treatment to form a crosslinked structure, so that the mechanical properties of the biodegradable polyester after the radiation treatment can be maintained or slightly improved, and the melt strength can be significantly improved.
In order to form a crosslinked structure well in the molecular chain of the biodegradable polyester under the irradiation treatment, the radiosensitizer in the above embodiment includes a monomer having 2 or more functional groups in a single molecule. Compared with a carbon-carbon single bond and a carbon-hydrogen bond in a biodegradable polyester molecule, a functional group contained in a molecule of the radiation sensitizer has higher reactivity. The functional groups are more likely to generate free radicals under radiation treatment, and then form a graft structure on the biodegradable polyester molecular chain to perform crosslinking. Since there are more than 2 functional groups that can participate in the reaction in the radiosensitizer molecule, a cross-linked structure can be formed when all the functional groups in the molecule are reacted. In order to enhance the radiation effect of the biodegradable polyester, the functional group in the above radiation sensitizer is preferably an olefinic carbon-carbon double bond, more preferably an allyl group and/or a (meth) acryloyl group.
Note that the above-mentioned monomer having 2 or more functional groups in a single molecule includes a monomer having 2 functional groups in a single molecule and a monomer having 3 or more functional groups in a single molecule. Examples of the monomer having 2 functional groups in a single molecule include dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, 1, 4-butanediol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and neopentyl glycol di (meth) acrylate. Examples of the monomer having 3 or more functional groups in a single molecule include triallyl isocyanurate, triallyl trimellitate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and the like. The sensitizer may be used alone or in combination of two or more.
In the above embodiment, the lower limit of the amount of the radiation sensitizer used may be 0.5 parts by weight, preferably 1 part by weight, and more preferably 2 parts by weight, relative to 100 parts by weight of the biodegradable polyester. In addition, the upper limit value of the amount of the radiation sensitizer used may be 15 parts by weight, preferably 12 parts by weight, more preferably 10 parts by weight, relative to 100 parts by weight of the biodegradable polyester. In the radiation treatment of biodegradable polyesters, the radiation degradation and crosslinking reactions are two competing reactions that occur simultaneously. If the dosage of the radiation sensitizer is lower than the lower limit value, the crosslinking reaction cannot account for the dominant reaction due to the low content of the radiation sensitizer, the radiation degradation reaction is the main reaction, and the overall radiation effect of the biodegradable polyester is represented by radiation degradation rather than the formation of a crosslinking structure. On the contrary, if the amount of the radiosensitizer is higher than the above upper limit, an excessive crosslinked structure is formed due to an excessive amount of the radiosensitizer contained in the reaction system, resulting in a large amount of gel contained in the biodegradable polyester, and the processability and biodegradability of the biodegradable polyester are reduced.
In the above embodiments, the main function of the nucleating agent is to rely on the interface between the nucleating agent and the biodegradable polyester melt as nucleation sites, thereby increasing the cell density of the foamed material obtained from the above biodegradable polyester composition. The nucleating agent can be conventional nucleating agent, and calcium carbonate, talcum powder, zinc oxide, nano montmorillonite, silicon dioxide and the like are preferably used. The nucleating agents may be used alone or in combination of two or more.
In the above embodiment, the lower limit of the amount of the nucleating agent may be 0 part by weight with respect to 100 parts by weight of the biodegradable polyester, that is, the nucleating agent may not be included in the above biodegradable polyester composition, but the lower limit of the amount of the nucleating agent is preferably 0.1 part by weight, more preferably 0.5 part by weight, from the viewpoint of increasing the cell density of the foamed material. In addition, the nucleating agent may be used in an amount of 10 parts by weight, preferably 5 parts by weight, and more preferably 2 parts by weight, based on 100 parts by weight of the biodegradable polyester, as an upper limit value. When no nucleating agent is added, the biodegradable polyester is relatively easy to generate homogeneous nucleation due to the existence of a crosslinking structure, so that a satisfactory foaming material can be obtained without adding the nucleating agent. After the nucleating agent is added, the biodegradable polyester foaming material can carry out heterogeneous nucleation, and the nucleation is easier, so that the density of foam cells is improved, and the size of the foam cells is reduced; along with the increase of the using amount of the nucleating agent, the number of bubble nuclei is gradually increased, the effect of the nucleating agent is fully exerted, and the nucleation number is rapidly increased; when the amount of the nucleating agent is excessively large (higher than the upper limit value), the particles of the nucleating agent are agglomerated to form large and non-uniform particles, so that the distribution of the nucleating points becomes non-uniform, resulting in non-uniformity in cell size.
Further, in the above embodiment, the upper limit value of the particle diameter of the nucleating agent may be 23 μm, preferably 18 μm, and more preferably 15 μm. The lower limit of the grain size of the nucleating agent may be 1.6. mu.m, preferably 2 μm, and more preferably 3 μm. When the grain size of the nucleating agent exceeds the above upper limit, coalescence of cell nuclei is easily caused, cell coalescence occurs, the cell size is large, and the cell size distribution is not uniform. On the other hand, when the particle diameter of the nucleating agent is less than the above lower limit, the surface energy of the particles increases, and the particles are easily agglomerated to form large and non-uniform particles, so that the distribution of nucleation points becomes non-uniform, resulting in non-uniformity of cell size.
In the above embodiment, the microwave sensitizer mainly functions to generate polarization inside the dielectric under the action of the microwave field, and the polarization intensity vector thereof lags behind the electric field by an angle, so as to generate current in phase with the electric field, and thus, the power dissipation inside the dielectric material is converted into heat energy. Due to the ultra-high frequency fluctuations, the temperature of the material rises rapidly in a short time. The microwave sensitizer may be a conventional microwave sensitizer, and preferably ferroferric oxide, manganese dioxide, zinc oxide, calcium oxide, or the like is used. The microwave sensitizer may be used alone or in combination of two or more.
In the above embodiment, the lower limit value of the amount of the microwave sensitizer used may be 0.1 parts by weight, preferably 0.3 parts by weight, and more preferably 0.5 parts by weight, relative to 100 parts by weight of the biodegradable polyester. In addition, the upper limit value of the amount of the microwave sensitizer used may be 5 parts by weight, preferably 4 parts by weight, and more preferably 3 parts by weight, relative to 100 parts by weight of the biodegradable polyester. The microwave sensitizer has the function of rapidly heating the biodegradable polyester composition under the action of microwaves, so that the foaming agent is decomposed to generate gas, and the biodegradable polyester composition is foamed. If the amount of the microwave sensitizer is less than the above lower limit, the degree of polarization of the biodegradable polyester composition itself is not high due to low heat generation, so that the temperature-raising rate of the material is slow, and a satisfactory foamed material cannot be obtained due to heat loss caused by heat dissipation. On the contrary, if the amount of the microwave sensitizer is higher than the above upper limit, the microwave sensitizer is likely to aggregate in the material, resulting in a local temperature rise too fast, thereby affecting the uniformity of the overall foaming of the material.
In the above embodiment, the main function of the foaming agent is to decompose after heating, and release gases such as carbon dioxide and nitrogen, so as to foam the biodegradable polyester composition. As the blowing agent, a blowing agent having a thermal decomposition temperature of 180 ℃ or higher can be used, and azo compounds, nitroso compounds, urea compounds and the like are preferably used, and azodicarbonamide, diisopropyl azodicarboxylate, N '-dinitrosopentamethylenetetramine, N-dinitrosopentamethylenetetramine, p-toluenesulfonylurea, 4' -oxybis (benzenesulfonamidourea) and the like are more preferably used. The blowing agents may be used alone or in combination of two or more.
In the above embodiment, the foaming agent undergoes decomposition reaction under heating to release gases such as carbon dioxide and nitrogen, thereby foaming the biodegradable polyester composition. The lower limit of the amount of the foaming agent may be 0.1 part by weight, preferably 1 part by weight, and more preferably 2 parts by weight, relative to 100 parts by weight of the biodegradable polyester. In addition, the upper limit of the amount of the foaming agent may be 20 parts by weight, preferably 15 parts by weight, and more preferably 10 parts by weight, relative to 100 parts by weight of the biodegradable polyester. If the amount of the blowing agent is less than the above lower limit, the blowing agent generates too little gas, the biodegradable polyester composition has a poor foaming effect, and the cells are not uniform. On the contrary, if the amount of the blowing agent is more than the above upper limit, the blowing agent is likely to agglomerate in the biodegradable polyester composition to cause uneven dispersion, and the agglomerated blowing agent generates a large amount of gas during foaming, which may cause cell coalescence, cell wall breakage, and adversely affect the foaming properties of the biodegradable polyester composition.
In the above embodiment, the biodegradable polyester, the nucleating agent, the radiation sensitizer, the microwave sensitizer, and the foaming agent are mixed to obtain a mixed material. Specifically, the biodegradable polyester, the nucleating agent, the radiation sensitizer, the microwave sensitizer and the foaming agent can be added into a twin-screw extruder (for example) according to the specific proportion, and then the mixture is extruded and granulated to obtain the mixed material.
It should be noted that, in addition to the biodegradable polyester, the nucleating agent, the radiation sensitizer, the microwave sensitizer, and the foaming agent, other additives and auxiliaries, such as a lubricant, a leveling agent, a plasticizer, an antioxidant, a UV inhibitor, and a filler, may be further mixed in the mixture.
Further, in the above embodiment, the mixed material is subjected to electron beam irradiation treatment or γ -ray irradiation treatment under a nitrogen or inert gas atmosphere. Specifically, the mixture may be placed in a radiation reaction apparatus filled with nitrogen or an inert gas, and subjected to electron beam radiation treatment or γ -ray radiation treatment at a specific absorption dose. The volume fraction of nitrogen or inert gas in the radiation reaction apparatus may be 90% or more, and more preferably 95% or more. When the biodegradable polyester is subjected to radiation treatment, oxygen prevents the crosslinking reaction and can generate peroxide radicals. The peroxide radicals are slowly decomposed during the subsequent storage of the material, thereby affecting the storage stability of the material. When the volume fraction of the nitrogen or other inert gas concentration in the ambient atmosphere is above 90%, the influence of oxygen is substantially negligible.
Further, the lower limit value of the absorbed dose may be 2kGy, preferably 5kGy, and more preferably 10 kGy. In addition, the upper limit value of the absorbed dose may be 50kGy, preferably 40kGy, and more preferably 30 kGy. The absorbed dose is the energy absorbed by the unit mass (1 kg). When the biodegradable polyester absorbs energy, the molecules are activated to form free radicals that initiate a series of reactions, such as crosslinking reactions. Thus, the extent of reaction (such as the degree of crosslinking, etc.) of the biodegradable polyester can be controlled by the absorbed dose. If the absorbed dose is less than the lower limit value, the crosslinking reaction hardly occurs or only a small amount of branched structure is formed, and the influence on the melt strength of the material is insignificant. On the contrary, if the absorbent content is higher than the above upper limit, the biodegradable polyester forms a large amount of gel structure, which reduces the biodegradability of the biodegradable polyester, and is not beneficial to the foaming of the subsequent material, and the foaming ratio of the biodegradable polyester is reduced, even the biodegradable polyester cannot be foamed.
In the above embodiment, the melt strength of the biodegradable polyester composition is increased by 100% to 500% relative to the melt strength of the mixed material before the radiation treatment step. Wherein the melt strength is determined by a melt strength testing device. Specifically, the melt strength test apparatus consists of a capillary rheometer and a melt strength tester, in which the melt is uniaxially stretched. The melt is first extruded down from a capillary rheometer die while being drawn by two counter-moving rollers mounted on a balance beam. The force experienced by the melt beam as it is stretched is a function of the speed and time of the rollers. The rollers are uniformly accelerated until the melt strand breaks, and the force to break the melt strand is the "melt strength" of the material.
In general, the melt strength of the mixed material before the radiation treatment step is 14mN to 17mN, and the melt strength of the resulting biodegradable polyester composition after the radiation treatment step may be 30mN to 110 mN. The melt strength of the biodegradable polyester composition can be increased by 100% to 500%, and preferably by 150% to 500%, and more preferably by 200% to 500%, relative to the melt strength of the mixed material before the radiation treatment step.
In the above embodiment, the biodegradable polyester is preferably heated at 40 to 80 ℃ for 1 to 24 hours before the mixing step. By the above heating, a slight amount of water on the surface of the biodegradable polyester can be removed, thereby suppressing the thermal degradation reaction of the biodegradable polyester due to the presence of the slight amount of water. Further, from the viewpoint of water removal effect and production efficiency in practical use, the heating temperature is more preferably 60 ℃ to 80 ℃, and the heating time is more preferably 4 hours to 12 hours.
The biodegradable polyester composition according to another embodiment of the present invention, which is obtained by the above-mentioned production method. The upper limit value of the gel content of the biodegradable polyester composition may be 20%. On the other hand, the lower limit of the gel content may be 5%, preferably 10%. If the gel content is higher than the above upper limit, the biodegradable polyester composition will have a reduced biodegradability and a prolonged complete degradation time. If the gel content is less than the lower limit, the melt strength of the biodegradable polyester composition is too low, and the phenomena of cell wall breakage, cell coalescence, and the like may occur during the foaming process, or even the biodegradable composition may not be foamed.
The gel content can be measured by the following method.
About 0.5g (m) is accurately weighed on an analytical balances) The sample to be measured after radiation treatment is put into a stainless steel wire mesh bag with 100 meshes, and the weight of the wire mesh is (m)N). Then it was soaked in 100ml of chloroform at room temperature for 48 hours. Finally, taking out the sample and the steel wire mesh and blastingThe sample and wire mesh were weighed again (m) after 12 hours of drying in an ovent). The above operation was repeated for samples not subjected to radiation treatment, and the residue content of the material was measured:
rs＝(mt1–mN1)/ms1×100
after deducting the residue content in the biodegradable polyester, the gel content (gel%) was:
gel％＝(mt–mN–ms×rs)/(ms–ms×rs)×100
the method for preparing a biodegradable polyester foam according to another embodiment of the present invention is characterized by comprising: carrying out microwave drying tunnel foaming or microwave oven foaming on the biodegradable polyester composition to obtain a biodegradable polyester foaming material, wherein the microwave drying tunnel foaming power is 4kW to 30kW, and the foaming time is 20 seconds to 1800 seconds; the power of the microwave oven foaming is 4kW to 30kW, and the foaming time is 20 seconds to 1800 seconds.
Microwave foaming is generally carried out in two ways, one being tunnel (i.e., microwave tunnel foaming) and the other being oven (i.e., microwave oven foaming). The microwave drying tunnel foaming can be continuously produced, and the microwave oven foaming is used for batch production and is discontinuous. In microwave tunnel foaming, the foamed material continuously enters the tunnel at an inlet, travels at a speed during which foaming occurs, and then exits the tunnel at an outlet. In the microwave oven foaming, the material is put into a foaming oven to be foamed under certain conditions, and the material is taken out after the foaming is finished.
From the viewpoint of practical use, the power of the microwave drying tunnel is preferably 6kW to 25kW, and more preferably 10kW to 20 kW; and the foaming time is preferably 60 seconds to 1200 seconds, more preferably 120 seconds to 900 seconds. The power of the microwave oven is preferably 4kW to 20kW, more preferably 4kW to 15 kW; and the foaming time is preferably 300 to 1500 seconds, more preferably 600 to 1200 seconds.
According to the preparation method of the above embodiment, a biodegradable polyester foam material having a high foaming ratio, uniform cells and biodegradability can be prepared. In addition, the production process of the preparation method is highly continuous and stable, safe and free of environmental pollution, and is suitable for industrial mass production.
The biodegradable polyester foam according to another embodiment of the present invention, which is obtained by the above-described manufacturing method. The diameter of the cells of the biodegradable polyester foaming material can be 200 to 500 mu m, the foaming ratio can be 2 to 15 times, and the apparent density can be 10kg/m3To 200kg/m3. When the diameter and the foaming ratio of the cells are within the above ranges, the size and the distribution of the cells in the biodegradable polyester foaming material are uniform, and the foamed biodegradable polyester material has good comprehensive performance.