Low-temperature thermoplastic composition, low-temperature thermoplastic material prepared from low-temperature thermoplastic composition and application of low-temperature thermoplastic material

Abstract

The invention discloses a low-temperature thermoplastic composition, a low-temperature thermoplastic material prepared from the low-temperature thermoplastic composition and application of the low-temperature thermoplastic material, and relates to the technical field of medical materials. The low-temperature thermoplastic composition is prepared from the following components in parts by mass: 95 to 100 parts of polyurethane of which the melting point is 50 to 70 DEG C and 0.1 to 5 parts of cross-linking aid, the polyol component in the polyurethane is from 70%-100% of poly (hexanediol adipate) glycol and 30%-0% of other aliphatic polyester polyol. The low-temperature thermoplastic composition provided by the invention can form a low-temperature thermoplastic material with relatively high gel content under irradiation treatment with relatively low irradiation dose. Due to the fact that the irradiation dose of irradiation treatment is low, the production cost of the product is remarkably reduced, the problem that the material is degraded under high-strength irradiation is solved, and meanwhile the material has the advantages of being small in contractility, high in gel content and high in melt strength. Specifically, the low-temperature thermoplastic material with the gel content of more than 20% and the contractility of less than 37N can be obtained under the irradiation treatment of the low-temperature thermoplastic composition with the irradiation dose of only 14-15KGy.

Description

Technical Field

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

[0002] Common low-temperature thermoplastic materials are made with polycaprolactone as the main component and additives. Their characteristics are that they can be softened when heated to about 65°C and can be molded into any shape, and after cooling to room temperature, they have the rigidity of polyethylene. Based on this characteristic, this material can be used for precise positioning during radiotherapy for cancer patients and fixation of the limbs or trunk during rehabilitation orthopedics. Currently, low-temperature thermoplastic materials have been actually used in the preparation of radiotherapy positioning membrane products and the field of rehabilitation orthopedics.

[0003] When polycaprolactone is used in the fields of radiotherapy shaping and rehabilitation orthopedics, due to its very low melt strength, crosslinking must be carried out, otherwise it will break with a slight pull. Polycaprolactone-based low-temperature thermoplastic materials are generally radiation crosslinked. After radiation crosslinking, chemical bonds are formed between 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, and the gel content determines the melt strength of the low-temperature thermoplastic product after heating to the melting point. However, the polycaprolactone-based low-temperature thermoplastic radiotherapy positioning product has a relatively large shrinkage force after molding, which will generate a strong compressive force on the patient, so there will be a greater sense of discomfort.

[0004] In addition, a high-quality low-temperature thermoplastic material for radiotherapy positioning membranes should have a suitable melt strength in addition to a relatively small shrinkage force. As previously mentioned, for low-temperature thermoplastic materials, the gel content determines the melt strength of the low-temperature thermoplastic product after heating. For low-temperature thermoplastic materials, the greater the gel content, the greater the melt strength. The gel content is also related to the tensile properties and memory properties of the product. Generally, the higher the gel content, the more uniform the stretching and the better the memory properties. Products with a higher gel content can still be reshaped even if the first shaping fails, while products with a low gel content do not have this property. Clinical practice has proved that when the gel content of general low-temperature thermoplastic material products is above 20%, their performance basically meets the requirements of clinical applications. From the premise of hoping to have better performance, it is more desirable that the gel content is above 30%. In addition, the gel content is positively correlated with the radiation dose during the radiation process. The higher the radiation dose, generally the higher the gel content obtained. However, during the radiation process of high-molecular materials, the crosslinking and degradation processes exist simultaneously. Especially for low-temperature thermoplastic materials, which are easily degradable materials, the radiation crosslinking dose should be as small as possible. On the one hand, it is to prevent degradation and ensure stable quality within the shelf life; on the other hand, it is to reduce the radiation cost.

[0005] Although polycaprolactone has the disadvantages of strong shrinkage performance and high price, due to its incomparable advantage of easy radiation cross-linking, the materials containing polycaprolactone are still the mainstream of low-temperature thermoplastic materials. In the inventor's prior research CN101698743A, it was found that using a mixture of polyurethane and polycaprolactone as a low-temperature thermoplastic material can improve its shrinkage performance, and the price of polyurethane is relatively lower than that of polycaprolactone, which helps to reduce costs. However, the inventor found that when polycaprolactone is missing in the system, the ideal gel content cannot be achieved under the same low cross-linking radiation dose. In order to achieve a better gel content and meet the requirements of clinical stretching uniformity when polycaprolactone is missing, it is often necessary to increase the gel content by increasing the radiation dose to more than 30 KGy, which undoubtedly increases the cost. At the same time, a high radiation dose will also cause the low-temperature thermoplastic material to degrade and embrittle in a shorter time, affecting the long-term storage of the product. The inventor analyzed that this is because the molecular structures of polycaprolactone and polyurethane are quite different, resulting in a large difference in their radiation cross-linking efficiency.

[0006] In the prior art, there is still a lack of a low-temperature thermoplastic material that can completely replace polycaprolactone and meet the needs of clinical performance and long-term storage performance. Summary of the Invention

[0007] The object of the present invention is to overcome the deficiencies of the raw materials for preparing polyurethane-based low-temperature thermoplastic materials in the prior art, and provide a new low-temperature thermoplastic composition. Using this composition, a low-temperature thermoplastic material with a gel content meeting the requirements can be formed under low-dose radiation cross-linking.

[0008] Another object of the present invention is to provide a low-temperature thermoplastic material.

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

[0010] Another object of the present invention is to provide an application of a low-temperature thermoplastic material in radiotherapy positioning diaphragms and rehabilitation orthopedic products.

[0011] The above objects of the present invention are achieved by the following technical solutions:

[0012] The present invention protects a low-temperature thermoplastic composition, which 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;

[0013] The polyol component in the polyurethane comes from 70%-100% of polyhexamethylene adipate diol and 30-0% of other aliphatic polyester polyols.

[0014] The inventors found that most saturated polyurethanes exhibit difficulties in radiation cross-linking, possibly due to the lack of carbon-carbon double bonds. Unexpectedly, polyurethanes made from poly(hexamethylene adipate) diol show different properties during radiation cross-linking. Without adding polycaprolactone, they can form low-temperature thermoplastic materials with a relatively high gel content (above 20%) under radiation treatment at a relatively low radiation dose (below 15 kGy). Since the radiation dose for radiation treatment is low, the production cost of the product is significantly reduced, and the problem of material degradation under high-intensity radiation is avoided, improving the stability of the product, ensuring the shelf life of the product, and being more conducive to use in precise radiotherapy for cancer. Moreover, the shrinkage force of the obtained low-temperature thermoplastic material still has the advantage of being significantly lower than that of the polycaprolactone-based radiotherapy film, which can reduce the compression force on patients and improve the comfort level. This advantage is consistent with the results obtained from the radiation cross-linking scheme of polyurethane and polycaprolactone in our previous research.

[0015] Meanwhile, the inventors found that if the content of other aliphatic polyester polyols in the polyurethane does not exceed 30%, it will not have too much impact on the properties of the polyurethane with 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 relatively low radiation dose.

[0016] Certainly, the higher the proportion of poly(hexamethylene adipate) diol in the polyurethane, the easier it is to obtain a low-temperature thermoplastic material with a relatively high gel content at a relatively low radiation dose. More preferably, the content of other aliphatic polyester polyols in the polyurethane does not exceed 10%.

[0017] More preferably, the content of other aliphatic polyester polyols in the polyurethane does not exceed 5%.

[0018] More preferably, the content of other aliphatic polyester polyols in the polyurethane does not exceed 3%.

[0019] As a further embodiment, the low-temperature thermoplastic composition 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.

[0020] The role of the radiation cross-linking aid is to enable better cross-linking effects during the radiation cross-linking of low-temperature polyurethane, so as to achieve the required gel content. In the present invention, the radiation cross-linking aid can be selected from the commonly used radiation cross-linking aids in the art.

[0021] As a further embodiment, the radiation cross-linking aid is one or more of triallyl isocyanurate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, or ethylene diisobutyrate.

[0022] As a further embodiment, the types of the other aliphatic polyester polyols are not limited. Preferably, the other aliphatic polyester polyols are linear aliphatic polyester polyols. For example, they are polybutylene adipate diol, polyethylene adipate diol, etc.

[0023] The polyurethane with a melting point of 50 - 70 °C is also called low-temperature polyurethane. For example, as introduced in CN101760165A, it is generally prepared from an aliphatic polyester diol with a weight-average molecular weight of 2000 - 6000 and a diisocyanate. The aliphatic polyester diol and diisocyanate used for preparing the low-temperature polyurethane are basically not limited. The diisocyanate includes an aliphatic diisocyanate, an aromatic diisocyanate or a mixture thereof. Specifically, the diisocyanate can be hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), cyclohexylmethane diisocyanate (HMDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), etc.

[0024] As the polyurethane with a melting point of 50 - 70 °C used in the present invention, it can be a commercially available product, such as polyurethane hot melt adhesive particles, or can be prepared by itself according to a known method, such as the method introduced in CN101760165A.

[0025] When preparing the polyurethane, a small-molecular-weight diol can be optionally added as a chain extender. The diol used as the chain extender usually contains 2 - 10 carbon atoms. Generally, the dosage of the chain extender 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%.

[0026] In addition, during the process of preparing the polyurethane, other additives such as a catalyst, an antioxidant, a coupling agent, an anti-sticking agent, etc. can be optionally added.

[0027] Common anti-sticking agents include Fischer-Tropsch wax, talcum powder, etc.

[0028] The present invention protects a low-temperature thermoplastic material formed by irradiating the low-temperature thermoplastic composition, and the gel content of the low-temperature thermoplastic material is not less than 20%.

[0029] More preferably, the gel content of the low-temperature thermoplastic material is not less than 30%.

[0030] More preferably, the gel content of the low-temperature thermoplastic material is not higher than 50%.

[0031] More preferably, the gel content of the low-temperature thermoplastic material is not higher than 35%.

[0032] In this field, the "gel content" refers to the content of gel substances in the low-temperature thermoplastic material, which reflects the degree of radiation cross-linking. It can be carried out with reference to existing solutions, as described in CN112480616A.

[0033] Specifically, the detection method for the gel content of the low-temperature thermoplastic material is as follows: Weigh a sample with a mass of m 1 . Place the sample in a ground-glass bottle containing 25 mL of toluene, tightly cap the bottle, and take 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 m 2 . According to the calculation formula for gel content: V c = m 2 / m 1 × 100%, calculate to obtain the gel content Vc.

[0034] The present invention also protects a preparation method of a low-temperature thermoplastic material, including the following steps:

[0035] Mix the polyurethane with a melting point of 50 - 70 °C and the radiation cross-linking aid evenly, then carry out melt blending and extrusion molding, and then carry out radiation treatment to obtain the described low-temperature thermoplastic material.

[0036] Among them, the melt blending and extrusion molding includes: making the uniform material into a sheet with the required thickness by an extruder.

[0037] The specific parameters of the melt blending and extrusion can be referred to as follows: The temperature of the feeding section is controlled at room temperature - 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 section is controlled at 85 - 90 °C. The screw speed is preferably 0.3 - 0.4 m / min.

[0038] It is also possible to use other plastic molding machines to make a sheet with the required thickness.

[0039] In this field, the radiation dose for radiation cross-linking generally does not exceed 30 kGy. Because when high-molecular materials are irradiated with high-energy rays, cross-linking and degradation exist simultaneously, and a higher radiation dose will cause more serious degradation, resulting in a decline in the long-term performance of the material.

[0040] More preferably, the radiation dose does not exceed 20 kGy. In this application, the gel content increases with the increase of the radiation dose. If the radiation dose is too low, the required gel content cannot be achieved. However, with the increase of the radiation dose, especially when the radiation dose is higher than 20 kGy, the low-temperature thermoplastic material becomes brittle more significantly in a shorter time. In the present invention, after the radiation dose is higher than 20 kGy, the low-temperature thermoplastic material is prone to embrittlement within 24 months, resulting in the quality guarantee performance being lower than the industry general standard.

[0041] More preferably, the irradiation dose is 14 to 15 kGy. For the composition of the polyurethane with a melting point of 50 to 70°C and the irradiation crosslinking aid in the present application, when the irradiation dose is 14 to 15 kGy, the required gel content can already be achieved. If a low-temperature thermoplastic material with a higher gel content is desired, the irradiation dose can also be appropriately increased within the range where the long-term performance is acceptable.

[0042] As a further embodiment, the irradiation treatment uses high-energy rays from a linear accelerator or cobalt-60.

[0043] The present invention also protects the application of the low-temperature thermoplastic material in radiotherapy positioning diaphragms and rehabilitation orthopedic products.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] The present invention provides a low-temperature thermoplastic composition. The low-temperature thermoplastic composition can form a low-temperature thermoplastic material with a high gel content under irradiation treatment with a relatively low irradiation dose, and does not require adding polycaprolactone as a component, significantly reducing the production cost of the product. It has the characteristics of a small shrinkage force, a high gel content, and a high melt strength. It also avoids the problem of material degradation under high-intensity irradiation, improves the stability of the product, ensures the shelf life of the product, and is more conducive to use in the precise radiotherapy of cancer. More specifically, the present invention uses poly(hexamethylene adipate) glycol-based polyurethane as the main raw material component, and can achieve a gel content of more than 20% and a shrinkage force of less than 37 N for the product under irradiation treatment with an irradiation dose of only 14 to 15 kGy. The radiotherapy positioning diaphragms and rehabilitation orthopedic products made of the low-temperature thermoplastic material can reduce the compression force on patients and improve the comfort. Specific Embodiments

[0046] The following further illustrates the present invention in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventional purchased raw material reagents.

[0047] In the embodiments, the sources of the polyurethanes are as follows:

[0048] Polyurethane A: Poly(hexamethylene adipate) glycol-based polyurethane with a melting point of 60°C. Purchased from Taiwan Free Radical P.M.Co., Ltd, model number H6500N.

[0049] Polyurethane B: Poly(1,6 - butanediol adipate) diol - based polyurethane with a melting point of 60 °C. Purchased from Taiwan Free Radical P.M.Co.,Ltd, model number AH6010N

[0050] The following polyurethanes C, D, E, F, G, H, I, J, K are all self - prepared. The preparation processes of polyurethanes C, D, E, H, I, J, K are as follows: Weigh the aliphatic polyester polyol and add it to a flask, heat it to 120 °C, melt and stir, stir under vacuum and constant temperature to dehydrate for 0.5 - 1 hour, then add the weighed small - molecule diol chain extender and mix evenly, then cool down to about 90 °C, and finally add the diisocyanate and high - speed stir and mix with ultrafine talcum powder. The initial reaction viscosity is not high. As the reaction progresses, the temperature continuously rises. After mixing evenly, pour the material into a polytetrafluoroethylene tray and place it in an oven at 100 °C for curing for 3 hours. Finally, cool it, crush it and granulate it.

[0051] The preparation processes of polyurethanes F and G are as follows: Weigh poly(1,6 - hexanediol adipate) diol (PHA, molecular weight 3000) and poly(1,4 - butanediol adipate) diol (PBA, molecular weight 4000) and add them to a flask, heat it to 120 °C, melt and stir, and the subsequent processes are the same as those of the preparation of polyurethanes C, D, E, G.

[0052] The melting point tests of polyurethanes C, D, E, F, G, H, I, J, K are consistent with those recorded in the patent document CN101760165A, carried out in accordance with GB / T19466.3 - 2004, and determined by differential scanning calorimetry DSC.

[0053] Sources of raw materials: The poly(1,6 - hexanediol adipate) diol (PHA, molecular weight 3000) used was purchased from Shandong Jiaying Chemical Technology Co., Ltd; the poly(1,4 - butanediol adipate) diol (PBA, molecular weight 4000) was purchased from Xuzhou Yihuiyang New Materials Co., Ltd. Poly(ethylene glycol adipate) (HY - 4020 with a molecular weight of 4000) was purchased from Shandong Baiqian Chemical Co., Ltd. Diisocyanates: 4,4 - MDI and mixed MDI are produced by Bayer AG of Germany. HDI, IPDI, HMDI, TDI are all produced by Yantai Wanhua Chemical Group Co., Ltd.

[0054] Chain extenders, 1,2 - propanediol (1,2 - PG, molecular weight 76) and 1,4 - butanediol (1,4 - BG molecular weight 90.1) were purchased from a reagent company. Ultrafine talcum powder (1000 mesh) was purchased on the market.

[0055] Preparation of polyurethane C:

[0056]

[0057] Prepare this formulation according to the above manufacturing process, and the measured melting point is 51 °C (DSC). Prepare polyurethane D:

[0058]

[0059] Prepare this formulation according to the above manufacturing process, and the measured melting point is 54 °C (DSC). Prepare polyurethane E:

[0060]

[0061] Prepare this formulation according to the above manufacturing process, and the measured melting point is 55 °C (DSC). Prepare polyurethane F:

[0062]

[0063] Prepare this formulation according to the above manufacturing process, and the measured melting point is 56 °C (DSC). Prepare polyurethane G:

[0064]

[0065] Prepare this formulation according to the above manufacturing process, and the measured melting point is 56 °C (DSC). Prepare polyurethane H:

[0066]

[0067] Prepare this formulation according to the above manufacturing process, and the measured melting point is 57 °C (DSC). Prepare polyurethane I:

[0068]

[0069] Prepare this formulation according to the above manufacturing process, and the measured melting point is 51 °C (DSC). Prepare polyurethane J:

[0070]

[0071] Prepare this formulation according to the above manufacturing process, and the measured melting point is 53 °C (DSC)

[0072] Prepare polyurethane K:

[0073]

[0074] Prepare this formulation according to the above manufacturing process, and the measured melting point is 52 °C (DSC)

[0075] Polycaprolactone: Purchased from Hunan Juli New Chemical Materials Technology Co., Ltd. in China, model PCL-6500.

[0076] The "gel content" described in the present invention refers to the gel content data obtained by measuring the product.

[0077] Specifically, the method for measuring the gel content of the low-temperature thermoplastic materials prepared in the following examples and comparative examples is as follows: Weigh a sample with a mass of m 1 and place the sample in a ground-glass bottle containing 25 mL of toluene. Tighten the bottle cap and place it in a constant-temperature oven at 25 °C for 48 hours for swelling, and then take it out. Then, extract the sample in toluene for 24 hours. 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 m 2 . According to the calculation formula for the gel content: V c = m 2 / m 1 ×100%, calculate to obtain the gel content.

[0078] The "irradiation treatment" described in the present invention refers to using cobalt-60, a linear accelerator or other substances that generate high-energy rays as a radiation source, and irradiating the sheet material with the radiation of the radiation source. In the following examples and comparative examples, a linear accelerator is used as the radiation source for irradiation.

[0079] The test of the melt strength is as follows: Cut a small strip of 100×10 mm from a sheet with a thickness of 2.4 mm, clamp the two ends of the small strip at 2 mm with two clips respectively, place it in a constant-temperature water tank with a water temperature of 70 °C for heating for 2 minutes until the small strip is fully softened, then hang one end on a shelf and hang a 65-gram weight on the other end. After 5 minutes, measure the length of the small strip in centimeters (cm). The room temperature during the test is 24 °C.

[0080] Examples 1 to 7 and Comparative Examples 1 to 6

[0081] Examples 1 to 7 and Comparative Examples 1 to 6 provide a series of low-temperature thermoplastic compositions. The types of polyurethanes are listed in Table 1. Mix 1000 g of the corresponding polyurethane in Table 1 with 3.5 g of the irradiation crosslinking aid triallyl isocyanurate evenly, extrude and granulate with a twin-screw extruder, and then extrude to form a sheet with a thickness of 2.4 mm; according to the irradiation dose described in Table 1, irradiate and crosslink the sheet with cobalt-60 to obtain the low-temperature thermoplastic material.

[0082] In Comparative Example 4, 500 g of polyurethane B and 500 g of polycaprolactone are mixed evenly with 3.5 g of the irradiation crosslinking aid triallyl isocyanurate and prepared by referring to the above method.

[0083] In Comparative Example 5, 1000 g of polycaprolactone is mixed evenly with 3.5 g of the irradiation crosslinking aid triallyl isocyanurate and prepared by referring to the above method.

[0084] Table 1 Relationship between irradiation dose and gel content

[0085]

[0086]

[0087] As can be seen from Table 1, for low-temperature thermoplastic materials, the higher the irradiation dose, the higher the gel content, and the melt strength also increases accordingly.

[0088] As shown in Example 1 and Example 3, for polyurethanes with poly(hexamethylene adipate) diol as the main polyol component, at an irradiation dose of 14 - 15 kGy, the gel content of the product can reach more than 20%.

[0089] Comparative Example 5 shows that polycaprolactone is more prone to irradiation cross-linking than polyurethane, but its defect is that the shrinkage rate is too high. Comparative Example 4 shows that when a 1:1 mixture of polyurethane with polycaprolactone and poly(butylene adipate) diol as polyol components is used, it is also easy to reach the required gel content under lower irradiation conditions. However, when the polyol component is replaced with poly(butylene adipate) diol (commercially available in Comparative Example 1, self-synthesized in Comparative Example 2, and the diisocyanate is different from that in Comparative Example 1) or poly(ethylene adipate) diol (Comparative Example 3), an irradiation dose of 29 - 30 kGy is required to reach a gel content close to that in Example 1 for application. The comparative examples also show that the presence of polycaprolactone helps the irradiation cross-linking of polyurethane, but except for polyurethanes with poly(hexamethylene adipate) diol as the main polyol component, other polyurethanes are difficult to reach a higher gel content at a lower irradiation dose.

[0090] From Comparative Example 6, it can be seen that when the content of other aliphatic polyester polyols in the polyurethane is too high (accounting for 35% of the total polyol), it is difficult to reach the ideal gel content at a lower irradiation dose, such as 14 - 15 kGy (according to the inventor's experience and the results of current research in this field, the gel content in low-temperature thermoplastic materials should be at least 20% or more to meet the application performance requirements).

[0091] From Examples 4, 5, and 7, it can be seen that the irradiation cross-linking performance of the low-temperature thermoplastic composition is basically not affected by the change in the type of diisocyanate. As can be seen from the examples, whether it is commercially available polyurethane or self-synthesized polyurethane, similar effects are obtained.

[0092] 2. Shrinkage force test

[0093] Select examples and comparative examples with similar melt strengths (about 50 cm) from Table 2 to test their shrinkage forces respectively, that is, the low-temperature thermoplastic materials of the above Examples 1 - 7, Comparative Example 1, Comparative Example 4, and Comparative Example 5 are respectively made into mask sheet samples with a thickness of 2.4 mm and a mesh void ratio of 36%, and then the shrinkage force test is carried out. The test results are shown in Table 2.

[0094] The method for the shrinkage force test is as follows:

[0095] Place the pressure sensor connected to a computer (equipped with dedicated software) under the head of a plaster model. Then, place the heated diaphragm sample on the face of the plaster model and stretch it downward. After stretching, fix the diaphragm sample on a base that is not connected to the pressure sensor, and start timing and recording. In this way, the computer can record the contraction force of the diaphragm sample. During the test, the room temperature is 24°C and the heating water temperature is 70°C. Use the contraction force measured in 24 hours as the standard.

[0096] Table 2 Results of Contraction Force Measurement

[0097]

[0098]

[0099] The contraction force of the low-temperature thermoplastic material prepared by irradiating and crosslinking the low-temperature thermoplastic compositions of Examples 1 to 7 of the present invention is relatively low. When used for the molding of radiotherapy positioning products, it is not easy to generate a strong compressive force on patients, and the comfort is good; compared with the material of Comparative Example 4, its contraction force has no obvious change, but there is no need to add polycaprolactone, reducing raw material and production costs; the contraction force of the polycaprolactone-based low-temperature thermoplastic material in Comparative Example 5 is significantly too high, and the products of Examples 1 to 7 of the present invention have a contraction force about 30.5% lower than that of Comparative Example 5, and the contraction force is significantly reduced, which can greatly improve the comfort.

[0100] The gel content of Example 3 is almost the same as that of Comparative Example 1, but the irradiation dose required for Comparative Example 1 to reach this gel content is twice that of Example 3, and it poses a hidden danger to the long-term quality preservation of the product.

[0101] 3. Method for Measuring Degradation and Brittleness Time

[0102] Mix the low-temperature thermoplastic compositions of Example 1, Example 3, Comparative Example 1, Comparative Example 4, Comparative Example 5, and Comparative Example 6 uniformly according to the ratio of 1000 g of the listed polyurethane and 3.5 g of the irradiation crosslinking aid triallyl isocyanurate. Extrude and granulate with a twin-screw extruder, and then make multiple splines with a length × width × thickness of 100 × 20 × 0.24 mm respectively. Irradiate and crosslink the splines with irradiation doses of 3 - 4 KGy, 6 - 7 KGy, 12 - 13 KGy, 14 - 15 KGy, 20 - 21 KGy, and 29 - 30 KGy respectively. Then place the irradiated and crosslinked splines in a room at a temperature of 23 - 25°C. After 16 months, fold the two ends of each spline together. If the spline breaks, it is judged to be degraded and brittle. The statistical time for the start of brittleness is counted according to the previous month of the test fracture. For example, if the fracture is measured on November 28, 2023, the degradation and brittleness time is October 2023. The results are shown in Table 3.

[0103] Table 3 Relationship between Irradiation Dose and Brittleness Time

[0104]

[0105] As can be seen from Table 3, compared with the polyurethane cross-linked products, the polycaprolactone cross-linked products have better long-term stability.

[0106] For polyurethane, the embrittlement performance decreases significantly with the increase of irradiation dose. When the irradiation dose is greater than 20 KGy, the cross-linked products will show embrittlement degradation within 23 months, and the shelf life cannot meet the generally accepted two-year requirement of the domestic and foreign cryogenic thermoplastic materials industry. The cryogenic thermoplastic composition of polyurethane using poly(hexamethylene adipate)diol as the main component of the polyol component can obtain a gel content that meets the application requirements at a lower irradiation dose, so that the performance meets the clinical needs, and the lower irradiation dose ensures that the materials made from it have better long-term stability.

[0107] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope 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 poly(hexamethylene 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 poly(butylene adipate) diol and / or poly(ethylene 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, putting the sample in a ground-glass 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%, calculate the gel content Vc.

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 uniformly mixing a polyurethane with a melting point of 50 to 70 °C and an irradiation crosslinking aid, melt blending and extrusion molding are carried out, and then irradiation treatment is performed to obtain the described low-temperature thermoplastic material.

13. The preparation method of the low-temperature thermoplastic material according to claim 12, characterized in that, the irradiation dose is 14 to 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 to 11 in radiotherapy positioning diaphragms and rehabilitation orthopedic products.

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