Low-temperature thermoplastic composition, low-temperature thermoplastic material prepared therefrom, and use of same

Abstract

The present invention relates to the technical field of medical materials. Disclosed are a low-temperature thermoplastic composition, a low-temperature thermoplastic material prepared therefrom, and the use of same. The low-temperature thermoplastic composition consists of the following components, in parts by mass: 95-100 parts of a polyurethane with a melting point of 50-70℃ and 0.1-5 parts of a crosslinking aid, a polyol ingredient in the polyurethane coming from 70%-100% of poly(hexamethylene adipate) diol and 30%-0% of other aliphatic polyester polyols. The low-temperature thermoplastic composition provided by the present invention can form a low-temperature thermoplastic material with a relatively high gel content under irradiation treatment with a relatively low irradiation dose. The relatively low irradiation dose in the irradiation treatment enables the production cost of the product to be remarkably reduced, and avoids the problem of material degradation under high-intensity irradiation. In addition, the material has the characteristics of relatively small shrinkage force, relatively high gel content and high melt strength. Specifically, the low-temperature thermoplastic composition of the present invention can be used for obtaining a low-temperature thermoplastic material with the gel content of more than 20% and the shrinkage force of less than 37 N under an irradiation treatment with the irradiation dose of only 14-15 kGy.

Description

A low-temperature thermoplastic composition and low-temperature thermoplastic material made therefrom, and applications thereof Technical Field

[0001] The present invention relates to the technical field of medical materials, and more particularly to a low-temperature thermoplastic composition and a low-temperature thermoplastic material made therefrom, and applications thereof. Background Art

[0002] Common low-temperature thermoplastic materials are made primarily from polycaprolactone with additives. They soften when heated to around 65°C and can be molded into any shape. Once cooled to room temperature, they retain the rigidity of polyethylene. This characteristic allows them to be used for precise positioning of cancer patients during radiotherapy and for fixation of limbs or torsos during rehabilitation and orthopedic procedures. Currently, low-temperature thermoplastic materials are being used in the production of radiotherapy positioning membranes and in the rehabilitation and orthopedic fields.

[0003] When polycaprolactone is used in radiotherapy shaping and rehabilitation orthopedics, it must be cross-linked due to its very low melt strength, otherwise it will break with a slight pull. Polycaprolactone-based low-temperature thermoplastic materials are generally irradiation cross-linked. After irradiation cross-linking, chemical bonds occur between the molecular chains to form a three-dimensional network structure. The degree of formation of the three-dimensional network structure is usually expressed by the gel content. The gel content determines the melt strength of the low-temperature thermoplastic product after it is heated to the melting point. However, polycaprolactone-based low-temperature thermoplastic radiotherapy positioning products have a large shrinkage force after molding, which will exert strong pressure on the patient, resulting in greater discomfort.

[0004] Furthermore, a high-quality low-temperature thermoplastic material for radiotherapy positioning membranes should not only exhibit low shrinkage but also possess appropriate melt strength. As previously mentioned, the gel content of low-temperature thermoplastics determines the melt strength of the product after heating. The higher the gel content, the greater the melt strength. Gel content is also related to the product's tensile and memory properties. Generally, a higher gel content results in more uniform tensile strength and better memory properties. Products with higher gel content can be reshaped even after an initial shaping failure, while products with lower gel content lack this property. Clinical practice has demonstrated that a gel content of 20% or higher for low-temperature thermoplastics generally meets clinical application requirements. For even better performance, a gel content of 30% or higher is more desirable. Furthermore, gel content is positively correlated with the irradiation dose. Higher irradiation doses generally result in higher gel content. However, during irradiation, polymers undergo both crosslinking and degradation processes. Especially for materials prone to degradation, such as low-temperature thermoplastics, the irradiation crosslinking dose should be minimized. On the one hand, it can prevent degradation and ensure stable quality during the shelf life; on the other hand, it can reduce irradiation costs.

[0005] Although polycaprolactone has the disadvantages of strong shrinkage performance and high price, due to its incomparable advantage of easy radiation cross-linking, the material containing polycaprolactone is still the mainstream of low-temperature thermoplastic material. The inventor's previous study CN101698743A found that using polyurethane and polycaprolactone mixed as low-temperature thermoplastic material can improve its shrinkage performance, and the price of polyurethane is relatively cheaper than polycaprolactone, which helps to reduce costs. However, the inventor found that when polycaprolactone is lacking in the system, it is impossible to reach the ideal gel content under the same low cross-linking radiation dose. In order to achieve a better gel content when polycaprolactone is lacking, the demand for clinical stretching uniformity is often required to increase the gel content by increasing the radiation dose to more than 30KGy, which undoubtedly increases the cost. At the same time, high radiation dose can also cause low-temperature thermoplastic material to degrade and become brittle in a shorter time, affecting the long-term storage of products. The inventor analyzed and believed that this is because the molecular structure of polycaprolactone is different from that of polyurethane, causing their radiation cross-linking efficiency to also differ greatly.

[0006] In the existing technology, there is still a lack of a low-temperature thermoplastic material that can completely replace polycaprolactone and meet the requirements of clinical performance and long-term storage performance.

[0007] Summary of the Invention

[0008] The present invention aims to overcome the shortcomings of existing raw materials for preparing polyurethane-based low-temperature thermoplastic materials and to provide a novel low-temperature thermoplastic composition that can be used to form a low-temperature thermoplastic material with a desired gel content by radiation cross-linking at a relatively low radiation dose.

[0009] Another object of the present invention is to provide a low temperature thermoplastic material.

[0010] Another object of the present invention is to provide a method for preparing low-temperature thermoplastic material.

[0011] Another object of the present invention is to provide a low-temperature thermoplastic material for use in radiotherapy positioning diaphragms and rehabilitation orthopedic products.

[0012] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0013] The present invention protects a low-temperature thermoplastic composition, which is composed of the following components calculated by weight: 95 to 100 parts of polyurethane with a melting point of 50 to 70° C., and 0.1 to 5 parts of a radiation cross-linking auxiliary agent;

[0014] The polyol component in the polyurethane comes from 70% to 100% of polyhexamethylene adipate diol and 30% to 0% of other aliphatic polyester polyols.

[0015] The inventors discovered that, while most saturated polyurethanes exhibit difficulty crosslinking during radiation, likely due to a lack of carbon-carbon double bonds, polyurethanes made from poly(hexamethylene adipate glycol) unexpectedly exhibit different properties during radiation crosslinking. They can form low-temperature thermoplastic materials with a high gel content (over 20%) even at relatively low radiation doses (less than 15 kGy) without the addition of polycaprolactone. Because the radiation dose is relatively low, the production cost of the product is significantly reduced, material degradation under high-intensity radiation is avoided, product stability is improved, shelf life is guaranteed, and the material is more suitable for use in precision cancer radiotherapy. Furthermore, the resulting low-temperature thermoplastic material still has a significantly lower contractile force than polycaprolactone-based radiotherapy membranes, reducing pressure on patients and improving comfort. This advantage is consistent with the results obtained in our previous research using radiation crosslinking schemes for polyurethane and polycaprolactone.

[0016] The inventors also discovered that if the content of other aliphatic polyester polyols in the polyurethane does not exceed 30%, it will not significantly affect the properties of the polyurethane containing poly(hexamethylene adipate diol) as the main polyol component. However, if the content of other aliphatic polyester polyols is too high, it will be difficult to achieve the desired gel content at a lower irradiation dose.

[0017] Of course, if the proportion of poly(hexamethylene adipate glycol) in the polyurethane is higher, it is easier to obtain a low-temperature thermoplastic material with a higher gel content at a lower radiation dose. More preferably, the content of other aliphatic polyester polyols in the polyurethane does not exceed 10%.

[0018] More preferably, the content of other aliphatic polyester polyols in the polyurethane does not exceed 5%.

[0019] More preferably, the content of other aliphatic polyester polyols in the polyurethane does not exceed 3%.

[0020] As a further embodiment, the low-temperature thermoplastic composition is composed of the following components calculated in parts by mass: 95-100 parts of polyurethane with a melting point of 50-70° C. and 0.25-0.5 parts of a radiation crosslinking aid.

[0021] The function of the radiation cross-linking agent is to make the low-temperature polyurethane produce a better cross-linking effect during the radiation exchange process, thereby achieving the required gel content. In the present invention, the radiation cross-linking agent can be selected from radiation cross-linking agents commonly used in the art.

[0022] As a further embodiment, the radiation cross-linking auxiliary agent is one or more of triallyl isocyanurate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate or ethylene dimethacrylate.

[0023] As a further embodiment, the type of the other aliphatic polyester polyol is not limited. Preferably, the other aliphatic polyester polyol is a linear aliphatic polyester polyol, such as polybutylene adipate diol, polyethylene adipate diol, etc.

[0024] Polyurethanes with a melting point of 50-70°C are also known as low-temperature polyurethanes, such as those described in CN101760165A. They are generally prepared from aliphatic polyester diols with a weight-average molecular weight of 2000-6000 and diisocyanates. The aliphatic polyester diols and diisocyanates used to prepare low-temperature polyurethanes are generally not limited. The diisocyanates include aliphatic diisocyanates, aromatic diisocyanates, or mixtures thereof. Specifically, the diisocyanates may be hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), cyclohexylmethane diisocyanate (HMDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and the like.

[0025] The polyurethane with a melting point of 50-70° C. used in the present invention can be a commercially available product, such as polyurethane hot melt adhesive particles, or can be prepared by a known method, such as the method described in CN101760165A.

[0026] When preparing polyurethane, a low molecular weight diol can be optionally added as a chain extender. The diol used as a chain extender typically contains 2 to 10 carbon atoms. Generally, the amount of chain extender used does not exceed 20% of the total mass of the aliphatic polyester polyol, preferably does not exceed 10%, and more preferably does not exceed 5%.

[0027] In addition, during the preparation of polyurethane, other additives such as catalysts, antioxidants, coupling agents, and anti-sticking agents may be optionally added.

[0028] Common anti-sticking agents include Fischer-Tropsch wax, talc, etc.

[0029] The present invention protects a low-temperature thermoplastic material, which is formed by irradiating the low-temperature thermoplastic composition. The gel content of the low-temperature thermoplastic material is not less than 20%.

[0030] More preferably, the gel content of the low-temperature thermoplastic material is not less than 30%.

[0031] More preferably, the gel content of the low temperature thermoplastic material is not higher than 50%.

[0032] More preferably, the gel content of the low temperature thermoplastic material is not higher than 35%.

[0033] In the art, "gel content" refers to the amount of gel material in a low-temperature thermoplastic material, reflecting the degree of radiation crosslinking. This can be done by referring to existing protocols, such as those described in CN112480616A.

[0034] Specifically, the gel content of the low-temperature thermoplastic material is tested as follows: a sample of mass m1 is weighed and placed in a ground-mouth bottle filled with 25 mL of toluene. The bottle is tightly capped and placed in a constant-temperature oven at 25°C to swell for 48 hours before removal. The sample is then extracted in toluene for 24 hours and finally dried in a vacuum drying oven at 50°C until the mass remains constant. The sample is then weighed to obtain a sample of mass m2. The gel content is calculated according to the formula: V c =m2 / m1×100%, the gel content Vc is calculated.

[0035] The present invention also protects a method for preparing a low-temperature thermoplastic material, comprising the following steps:

[0036] The low-temperature thermoplastic material is obtained by uniformly mixing polyurethane with a melting point of 50-70°C and a radiation cross-linking auxiliary agent, performing melt blending and extrusion molding, and then performing radiation treatment.

[0037] The melt blending and extrusion molding comprises: using an extruder to form a uniform material into a sheet of desired thickness.

[0038] The specific parameters for melt blending extrusion can be referred to as follows: the feeding section temperature is controlled at room temperature to 50°C, the compression section is controlled at 90-110°C, the homogenization section is controlled at 100-120°C, and the head and die sections are controlled at 85-90°C. The screw speed is preferably 0.3-0.4 m / min.

[0039] Other plastic molding machines can also be used to form sheets of desired thickness.

[0040] In the art, the radiation dose for radiation crosslinking generally does not exceed 30 kGy. This is because when polymer materials are irradiated with high-energy rays, crosslinking and degradation occur simultaneously, and higher radiation doses will lead to more severe degradation, resulting in a long-term decline in material performance.

[0041] More preferably, the irradiation dose does not exceed 20 kGy. In this application, the gel content increases with increasing irradiation dose. Excessively low irradiation doses fail to achieve the required gel content. However, as the irradiation dose increases, especially when the irradiation dose exceeds 20 kGy, the low-temperature thermoplastic material becomes more embrittled in a shorter period of time. In the present invention, when the irradiation dose exceeds 20 kGy, the low-temperature thermoplastic material is prone to embrittlement within 24 months, resulting in a shelf life that falls below the industry standard.

[0042] More preferably, the irradiation dose is 14-15 kGy. The composition of the polyurethane with a melting point of 50-70°C and the irradiation crosslinking aid of the present application can achieve the desired gel content at an irradiation dose of 14-15 kGy. To obtain a low-temperature thermoplastic material with a higher gel content, the irradiation dose can be appropriately increased within an acceptable range for long-term performance.

[0043] As a further embodiment, the irradiation treatment uses high-energy rays from a linear accelerator or cobalt 60.

[0044] The present invention also protects the application of the low-temperature thermoplastic material in radiotherapy positioning diaphragms and rehabilitation orthopedic products.

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

[0046] The present invention provides a low-temperature thermoplastic composition that can form a low-temperature thermoplastic material with a high gel content under irradiation at a relatively low radiation dose, without the need for the addition of polycaprolactone as a component. This significantly reduces product production costs, exhibits low shrinkage force, high gel content, and high melt strength. It also avoids degradation under high-intensity irradiation, improves product stability, ensures shelf life, and is more suitable for use in precision cancer radiotherapy. More specifically, the present invention uses poly(hexamethylene adipate glycol) diol-based polyurethane as the primary raw material component. Under irradiation doses of only 14-15 kGy, the product can achieve a gel content greater than 20% and a shrinkage force less than 37 N. Radiotherapy positioning diaphragms and rehabilitation orthopedic products made from this low-temperature thermoplastic material can reduce pressure on patients and improve comfort. DETAILED DESCRIPTION

[0047] The present invention will be further described below in conjunction with specific embodiments, but the examples do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the examples of the present invention are conventionally purchased raw materials and reagents.

[0048] In the embodiment, the polyurethane sources involved are as follows:

[0049] Polyurethane A: Poly(1,6-hexanediol adipate) diol polyurethane, melting point 60°C. Purchased from Taiwan Free Radical PM Co., Ltd., model H6500N.

[0050] Polyurethane B: Polybutylene adipate glycol polyurethane, melting point 60°C. Purchased from Taiwan Free Radical PM Co., Ltd., model AH6010N

[0051] The following polyurethanes C, D, E, F, G, H, I, J, and K were all prepared independently. The preparation process for polyurethanes C, D, E, H, I, J, and K is as follows: An aliphatic polyester polyol was weighed and added to a flask. The mixture was heated to 120°C, melt-stirred, and then dehydrated under vacuum with constant temperature stirring for 0.5 to 1 hour. A weighed amount of a small molecule diol chain extender was then added and mixed thoroughly. The mixture was then cooled to approximately 90°C. Finally, diisocyanate and ultrafine talc were added and mixed at high speed. The viscosity of the reaction was low at the beginning, but the temperature increased as the reaction proceeded. After uniform mixing, the mixture was poured into a tetrafluoroethylene tray and aged in a 100°C oven for 3 hours. Finally, the mixture was cooled, crushed, and granulated.

[0052] The preparation process of polyurethanes F and G is as follows: poly(1,6-hexanediol adipate) diol (PHA, molecular weight 3000) and poly(1,4-butylene adipate) diol (PBA, molecular weight 4000) are weighed and added to a flask, heated to 120°C, melt-stirred, and the subsequent process is the same as the preparation of polyurethanes C, D, E, and G.

[0053] The melting point tests of polyurethanes C, D, E, F, G, H, I, J, and K were consistent with those described in patent document CN101760165A, were conducted in accordance with GB / T19466.3-2004, and were determined by differential scanning calorimetry (DSC).

[0054] Raw Materials: Poly(1,6-hexanediol adipate) diol (PHA, molecular weight 3000) was purchased from Shandong Jiaying Chemical Technology Co., Ltd.; poly(1,4-butylene adipate) diol (PBA, molecular weight 4000) was purchased from Xuzhou Yihuiyang New Materials Co., Ltd.; polyethylene adipate (HY-4020, molecular weight 4000) was purchased from Shandong Baiqian Chemical Co., Ltd. Diisocyanates: 4,4-MDI and mixed MDI were produced by Bayer AG in Germany. HDI, IPDI, HMDI, and TDI were all produced by Yantai Wanhua Chemical Co., Ltd.

[0055] Chain extenders, 1,2-propylene glycol (1,2-PG, molecular weight 76) and 1,4-butanediol (1,4-BG, molecular weight 90.1), were purchased from a reagent company. Ultrafine talc powder (1000 mesh) was purchased commercially.

[0056] Preparation of polyurethane C:

[0057] This formulation was prepared according to the above-mentioned preparation process, and the melting point was measured to be 51° C. (DSC).

[0058] Preparation of polyurethane D:

[0059] This formulation was prepared according to the above-mentioned preparation process, and the melting point was measured to be 54° C. (DSC).

[0060] Preparation of polyurethane E:

[0061] This formula was prepared according to the above process and the melting point was measured to be 55°C (DSC)

[0062] Preparation of polyurethane F:

[0063] This formula was prepared according to the above process and the melting point was measured to be 56°C (DSC)

[0064] Preparation of polyurethane G:

[0065] This formula was prepared according to the above process and the melting point was measured to be 56°C (DSC)

[0066] Preparation of polyurethane H:

[0067] This formula was prepared according to the above process and the melting point was measured to be 57°C (DSC)

[0068] Preparation of Polyurethane I:

[0069] This formula was prepared according to the above process and the melting point was measured to be 51°C (DSC)

[0070] Preparation of polyurethane J:

[0071] This formula was prepared according to the above process and the melting point was measured to be 53°C (DSC)

[0072] Preparation of polyurethane K:

[0073] This formula was prepared according to the above process and the melting point was measured to be 52°C (DSC)

[0074] Polycaprolactone: purchased from Hunan Juren Chemical New Materials Technology Co., Ltd. in China, model PCL-6500.

[0075] The "gel content" mentioned in the present invention refers to the gel content data obtained by measuring the product.

[0076] Specifically, the gel content of the low-temperature thermoplastic materials prepared in the following examples and comparative examples is determined as follows: a sample of mass m1 is weighed and placed in a ground-mouth bottle filled with 25 mL of toluene. The bottle is tightly capped and placed in a 25°C constant-temperature oven to swell for 48 hours before removal. The sample is then extracted in toluene for 24 hours and finally dried in a 50°C vacuum drying oven until the mass remains constant. The sample is then weighed to obtain a sample of mass m2. The gel content is calculated according to the formula: V c =m2 / m1×100%, calculate the gel content.

[0077] "Irradiation treatment" as used herein refers to irradiating the sheet material with radiation from a radiation source such as cobalt-60, a linear accelerator, or other high-energy radiation-generating material. In the following examples and comparative examples, a linear accelerator is used as the radiation source.

[0078] The melt strength test is as follows: Cut a 100 x 10 mm strip from a 2.4 mm thick sheet. Use two clamps to hold the strip 2 mm from each end. Heat the strip in a 70°C water tank for 2 minutes until fully softened. Then, hang one end on a rack and a 65 g weight on the other. After 5 minutes, measure the strip's length in centimeters (cm). The room temperature during testing is 24°C.

[0079] Examples 1 to 7 and Comparative Examples 1 to 6

[0080] Examples 1-7 and Comparative Examples 1-6 provide a series of low-temperature thermoplastic compositions, wherein the polyurethane types are as listed in Table 1. 1000 g of the corresponding polyurethane listed in Table 1 was uniformly mixed with 3.5 g of triallyl isocyanurate, a radiation crosslinking aid. The mixture was extruded into pellets using a twin-screw extruder, and then extruded into sheets with a thickness of 2.4 mm. The sheets were irradiated and crosslinked using cobalt-60 according to the irradiation dose described in Table 1 to obtain the low-temperature thermoplastic materials.

[0081] In Comparative Example 4, 500 g of polyurethane B, 500 g of polycaprolactone, and 3.5 g of radiation crosslinking auxiliary agent triallyl isocyanurate were uniformly mixed and prepared according to the above method.

[0082] In Comparative Example 5, 1000 g of polycaprolactone and 3.5 g of irradiation crosslinking aid triallyl isocyanurate were mixed uniformly and prepared according to the above method.

[0083] Table 1 Relationship between irradiation dose and gel content

[0084] As can be seen from Table 1, for low-temperature thermoplastic materials, the higher the irradiation dose, the higher the gel content and the higher the melt strength.

[0085] As shown in Examples 1 and 3, for polyurethanes using poly(hexamethylene adipate glycol) as a main polyol component, the gel content of the product can reach over 20% at an irradiation dose of 14 to 15 KGy.

[0086] Comparative Example 5 shows that polycaprolactone is more susceptible to radiation crosslinking than polyurethane, but its drawback is that its shrinkage is too high. Comparative Example 4 shows that when polycaprolactone and polybutylene adipate diol are mixed in a 1:1 ratio as the polyurethane polyol component, it is also easy to achieve the required gel content under lower irradiation conditions. However, when the polyol component is replaced with polybutylene adipate diol (commercially available in Comparative Example 1, independently synthesized in Comparative Example 2, and the diisocyanate is different from that in Comparative Example 1) or polyethylene adipate diol (Comparative Example 3), to achieve a gel content close to that of Example 1 that meets the application requirements, an irradiation dose of 29 to 30 kGy is required. The comparative example also shows that the presence of polycaprolactone helps the radiation crosslinking of polyurethane, but except for polyurethane with polybutylene adipate diol as the main polyol component, other polyurethanes are difficult to achieve a high gel content at a lower irradiation dose.

[0087] Comparative Example 6 shows that when the content of other aliphatic polyester polyols in the polyurethane is too high (accounting for 35% of the total polyol content), it is difficult to achieve the ideal gel content at a lower irradiation dose, such as 14-15 kGy. (Based on the inventors' experience and current research in this field, the gel content of low-temperature thermoplastic materials must be at least 20% to meet the performance requirements of the application.)

[0088] As can be seen from Examples 4, 5, and 7, the radiation crosslinking performance of the low-temperature thermoplastic composition is substantially unaffected by the type of diisocyanate. It can be seen from the examples that both commercially available polyurethanes and independently synthesized polyurethanes have similar effects.

[0089] 2. Contraction force test

[0090] From Table 2, examples and comparative examples with similar melt strength (about 50 cm) were selected to test their shrinkage force respectively. That is, the low-temperature thermoplastic materials of the above-mentioned Examples 1 to 7, Comparative Example 1, Comparative Example 4 and Comparative Example 5 were respectively made into facial mask sheet samples with a thickness of 2.4 mm and a mesh occupancy rate of 36%, and then the shrinkage force test was carried out. The test results are shown in Table 2.

[0091] The shrinkage force test method is:

[0092] A pressure sensor connected to a computer (installed with dedicated software) is placed beneath the head of a plaster model. A heated membrane sample is then placed on the model's face and stretched downward. After stretching, the membrane sample is secured to a base disconnected from the pressure sensor, and timing and recording are started. The computer then records the membrane sample's contraction force. The test is conducted at a room temperature of 24°C and a heating water temperature of 70°C. The contraction force measured over a 24-hour period is used as the standard.

[0093] Table 2 Contraction force measurement results

[0094] The low-temperature thermoplastic materials prepared by radiation crosslinking the low-temperature thermoplastic compositions of Examples 1 to 7 of the present invention have relatively low shrinkage forces. When used to mold radiotherapy positioning products, they are less likely to exert strong pressure on patients, providing improved comfort. Compared to the material of Comparative Example 4, their shrinkage forces are not significantly different, but the addition of polycaprolactone is not required, reducing raw material and production costs. The shrinkage forces of the polycaprolactone-based low-temperature thermoplastic material of Comparative Example 5 were significantly too high, while the products of Examples 1 to 7 of the present invention achieved shrinkage forces approximately 30.5% lower than this, significantly reducing shrinkage forces and significantly improving comfort.

[0095] The gel content of Example 3 is almost the same as that of Comparative Example 1, but the irradiation dose required to achieve the gel content in Comparative Example 1 is twice that of Example 3, which poses a hidden danger to the long-term shelf life of the product.

[0096] 3. Degradation embrittlement time determination method

[0097] The low-temperature thermoplastic compositions of Example 1, Example 3, Comparative Example 1, Comparative Example 4, Comparative Example 5, and Comparative Example 6 were uniformly mixed with 3.5 g of triallyl isocyanurate, a radiation crosslinking aid, in the ratios corresponding to the polyurethanes listed above. The mixtures were extruded and pelletized using a twin-screw extruder. The pellets were then formed into strips measuring 100 mm in length, 20 mm in width, and 0.24 mm in thickness. The strips were then irradiated and crosslinked at irradiation doses of 3-4 kg, 6-7 kg, 12-13 kg, 14-15 kg, 20-21 kg, and 29-30 kg, respectively. The crosslinked strips were then placed in a room at 23-25°C. After 16 months, the ends of each strip were folded together. If the strips broke, they were considered to have undergone degradation and embrittlement. The statistical time of onset of embrittlement was calculated as the month preceding the test breakage. For example, if the fracture is measured on November 28, 2023, the degradation embrittlement time is October 2023. The results are shown in Table 3.

[0098] Table 3 Relationship between irradiation dose and embrittlement time

[0099] It can be seen from Table 3 that compared with polyurethane cross-linked products, polycaprolactone cross-linked products have better long-term stability.

[0100] For polyurethane, embrittlement performance decreases significantly with increasing radiation dose. When the radiation dose exceeds 20 kGy, the cross-linked product will show brittle degradation within 23 months, and the shelf life cannot meet the two-year shelf life required by the domestic and international low-temperature thermoplastic materials industry. Low-temperature thermoplastic polyurethane compositions using poly(hexamethylene adipate glycol) as the primary polyol component can achieve a gel content that meets application requirements at lower radiation doses, ensuring performance that meets clinical needs. The lower radiation dose also ensures better long-term stability of the resulting material.

[0101] The above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications may be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the claims of the present invention.

Claims

1. A low-temperature thermoplastic composition, characterized in that, it is composed of the following components calculated by mass: 95-100 parts of polyurethane with a melting point of 50-70°C, and 0.1-5 parts of radiation cross-linking aid; in the polyurethane, the polyol component comes from 70%-100% of polyhexamethylene adipate diol and 30-0% of other aliphatic polyester polyols.

2. The low-temperature thermoplastic composition according to claim 1, characterized in that, it is composed of the following components calculated by mass: 95-100 parts of polyurethane with a melting point of 50-70°C, and 0.25-0.5 parts of radiation cross-linking aid.

3. The low-temperature thermoplastic composition according to claim 1, characterized in that, the radiation cross-linking aid is one or more of triallyl isocyanurate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate or ethylene diisobutyrate.

4. The low-temperature thermoplastic composition according to claim 1, characterized in that, the other aliphatic polyester polyol is a linear aliphatic polyester polyol.

5. The low-temperature thermoplastic composition according to claim 4, characterized in that, the other aliphatic polyester polyol is polybutylene adipate diol and / or polyethylene adipate diol.

6. The low-temperature thermoplastic composition according to claim 1, characterized in that, in the polyurethane, the diisocyanate component comes from aliphatic diisocyanate and / or aromatic diisocyanate.

7. The low-temperature thermoplastic composition according to claim 6, characterized in that, the diisocyanate is hexamethylene diisocyanate, isophorone diisocyanate, cyclohexylmethane diisocyanate, toluene diisocyanate and / or diphenylmethane diisocyanate.

8. A low-temperature thermoplastic material, characterized in that, it is formed by irradiating the low-temperature thermoplastic composition according to any one of claims 1-7, and the gel content of the low-temperature thermoplastic material is not less than 20%.

9. The low-temperature thermoplastic material according to claim 8, characterized in that, the gel content of the low-temperature thermoplastic material is not less than 30%.

10. The low-temperature thermoplastic material according to claim 8, characterized in that, the gel content of the low-temperature thermoplastic material is not higher than 50%.

11. The low-temperature thermoplastic material according to any one of claims 8-10, characterized in that, the detection method of the gel content of the low-temperature thermoplastic material is: weighing a sample with a mass of m1, placing the sample in a ground-mouth bottle containing 25 mL of toluene, tightening the bottle cap, and taking it out after swelling in a constant-temperature oven at 25°C for 48 hours. Then extract the sample in toluene for 24 hours, and finally dry the sample in a vacuum drying oven at 50°C until the mass is constant, and then weigh its mass to obtain a sample with a mass of m2. According to the calculation formula of the gel content: Vc = m2 / m1×100%, the gel content Vc is calculated.

12. The preparation method of the low-temperature thermoplastic material according to any one of claims 8-10, characterized in that, it includes the following steps: After mixing the polyurethane with a melting point of 50-70°C and the radiation crosslinking aid evenly, it is melt-blended and extruded into a shape, and then irradiated to obtain the low-temperature thermoplastic material described above.

13. The preparation method of the low-temperature thermoplastic material according to claim 12, characterized in that, the radiation dose is 14-15 kGy.

14. The preparation method of the low-temperature thermoplastic material according to claim 12, characterized in that, the irradiation treatment uses high-energy rays of a linear accelerator or cobalt-60.

15. The application of the low-temperature thermoplastic material according to any one of claims 8-11 in radiotherapy positioning diaphragms and rehabilitation orthopedic products.

Images