A gamma radiation resistant transparent polypropylene composition and method of making

Abstract

The application provides a kind of transparent polypropylene composition resistant to gamma ray irradiation and a preparation method.The polypropylene composition is composed of polypropylene, nucleating agent, antioxidant and acid absorbent, and has good transparency and significant radiation resistance.By optimizing the ratio of nucleating agent, antioxidant and acid absorbent and selecting specific types of antioxidant and acid absorbent, the radiation resistance of polypropylene material can be significantly improved, while maintaining good transparency after irradiation treatment.The composition of the application has stronger antioxidant capacity, longer service life and more stable performance, and is suitable for high-performance materials that require transparency and radiation resistance, such as medical, packaging and electronic fields.

Description

Technical Field

[0001] This invention relates to the field of radiation-resistant materials technology, and in particular to a transparent polypropylene composition resistant to gamma ray irradiation and its preparation method. Background Technology

[0002] Compared to traditional transparent materials, transparent polypropylene (PP) boasts advantages such as light weight, low cost, superior overall mechanical and optical properties, moisture resistance, and recyclability, leading to rapid consumption growth in recent years. It has wide applications in medical devices such as syringes and medicine bottles; transparent packaging such as cling film and candy wrappers; and household products such as microwaveable tableware, disposable lunch boxes, and transparent beverage cups. With the increasing emphasis on green and healthy products in sectors like baby products, food packaging, and medical devices, improving the hygiene, safety, and non-toxicity of transparent PP to adapt to market changes has become an inevitable trend and crucial factor.

[0003] Conventional disinfection and sterilization methods include high-temperature, high-pressure (HTHP) and gas fumigation. HTHP suffers from incomplete sterilization and is also limited by material selection, being unsuitable for heat-sensitive materials (such as plastics and some rubber products). Gas fumigation uses gases containing potent carcinogens like ethylene oxide; although there are strict limits on residual amounts, some residues still remain, posing a certain threat to human health. As a replacement, pollution-free cobalt-60 gamma-ray irradiation sterilization methods are employed.

[0004] Irradiation sterilization involves irradiating materials with a certain dose of radiation or high-energy electron beams at room temperature. This causes the chemical bonds of organic molecules such as DNA, proteins, and lipids in microorganisms to break, leading to microbial death and achieving sterilization. Compared with traditional autoclaving and chemical sterilization, irradiation sterilization has advantages such as thorough sterilization, safe operation, no environmental pollution, the ability to sterilize packaged products and heat-sensitive substances, and continuous operation. Radiation sterilization has significant advantages over the previous two sterilization methods and is very suitable for applications with high sterilization and disinfection requirements, such as medical supplies and food packaging. However, irradiation sterilization of polypropylene can cause the polymer molecular chains to break, resulting in yellowing of the product, decreased mechanical and optical properties, and increased susceptibility to breakage and damage during transportation, storage, and use. Therefore, there is a need to develop radiation-resistant polypropylene materials.

[0005] Existing technologies often improve the radiation resistance of polypropylene by reactive extrusion grafting and adding organic or inorganic radiation stabilizers. Below are some specific examples.

[0006] 1. Chinese Patent CN101602872B discloses a method for preparing radiation-resistant polypropylene. A reactive hindered amine stabilizer is prepared by using acid anhydride and piperidinol. The polypropylene is then pre-irradiated to obtain pre-irradiated polypropylene. Finally, the polypropylene, the reactive hindered amine stabilizer, and the pre-irradiated polypropylene are added to a twin-screw extruder. The reactive hindered amine stabilizer is grafted onto the polypropylene molecular chain via reactive extrusion to improve the anti-aging properties of the material after irradiation treatment. Compared with radiation-resistant polypropylene prepared by traditional physical blending methods, this method has advantages such as uniform stabilizer dispersion, less precipitation, and long-lasting anti-aging performance. This method for preparing radiation-resistant polypropylene is simple, environmentally friendly, and easy to implement for large-scale continuous production. The radiation-resistant polypropylene prepared by this invention can be used in medical infusion devices, food packaging, and pharmaceutical packaging. After sterilization by irradiation and within a one-year storage period, the product's elongation at break decreases by less than 50%, tensile strength decreases by less than 2 MPa, and yellowness index increases by less than 1.

[0007] 2. Chinese Patent CN101602877B discloses a method for preparing a radiation-resistant polypropylene alloy. A reactive hindered amine stabilizer is prepared using acid anhydride and piperidinol. Pre-irradiated polypropylene is then obtained by pre-irradiating polypropylene. Finally, polypropylene, the reactive hindered amine stabilizer, and the pre-irradiated polypropylene are added to a twin-screw extruder. The reactive hindered amine stabilizer is grafted onto the polypropylene molecular chain via reactive extrusion to improve the anti-aging properties of the alloy after radiation sterilization. The polypropylene resin grafted with the hindered amine stabilizer is mechanically mixed with a thermoplastic elastomer and then melt-blended in a twin-screw extruder to prepare the radiation-resistant polypropylene alloy. The reactive grafting method for preparing the radiation-resistant polypropylene alloy has advantages such as uniform stabilizer dispersion, low precipitation, and long-lasting anti-aging performance. This method for preparing radiation-resistant polypropylene alloys is simple, environmentally friendly, and easily achievable for large-scale continuous production. The radiation-resistant polypropylene alloy prepared by this invention can be used in medical infusion devices, food packaging, and pharmaceutical packaging. After sterilization by irradiation and within a one-year storage period, the product's elongation at break decreases by less than 50%, tensile strength decreases by less than 2 MPa, and yellowness index increases by less than 1. Therefore, this type of radiation-resistant polypropylene has strong resistance to radiation aging.

[0008] Technical shortcomings: Both patents 1 and 2 above involve preparing reactive hindered amine stabilizers using acid anhydrides and piperidinol, then pre-irradiating polypropylene to obtain pre-irradiated polypropylene. Finally, the polypropylene, reactive hindered amine stabilizers, and pre-irradiated polypropylene are added to a twin-screw extruder, and the reactive hindered amine stabilizers are grafted onto the polypropylene molecular chains via reactive extrusion to improve the anti-aging properties of the irradiated material. This patent's preparation process is lengthy and complex, and the reactive extrusion grafting process is difficult to control, easily resulting in reaction residues that introduce impurities and affect the material's mechanical and optical properties.

[0009] 3. Chinese Patent CN101955609B discloses a medical radiation-resistant polypropylene alloy material. This material is composed of polypropylene powder, polyolefin thermoplastic elastomer, hindered amine antioxidant, phosphite antioxidant, acid absorber, and nucleating agent. The content (mass percentage) of each component in the formula is as follows: polypropylene powder 85-95%, polyolefin thermoplastic elastomer 5-15%, hindered amine antioxidant 0.05-0.25%, phosphite antioxidant 0.05-0.25%, acid absorber 0.05-0.10%, and nucleating agent 0.10-0.20%. The polypropylene alloy material prepared by this invention, after irradiation with a high-energy electron accelerator, can prevent embrittlement, discoloration, and a decrease in elongation at break, while maintaining high toughness and good transparency, meeting the requirements for medical polypropylene materials. It can be used in the preparation of disposable medical devices.

[0010] Technical shortcomings: This invention improves the radiation aging resistance of materials by adding a compound of hindered amine antioxidants and phosphite antioxidants. However, the medical radiation-resistant polypropylene alloy material prepared by this invention has a high yellowing index after radiation testing, indicating insufficient radiation resistance and yellowing prevention, thus limiting its application areas.

[0011] 4. Chinese Patent CN111675856B discloses a gamma-ray irradiation-resistant, aging-resistant transparent polypropylene composite material and its preparation method. This polypropylene composite material includes polypropylene resin, a nucleating agent, an acid scavenger, and an irradiation stabilizer. The irradiation stabilizer includes methylphenyl vinyl silicone rubber, a coupling agent, montmorillonite, an antioxidant, and a light stabilizer. This invention improves the radiation resistance of polypropylene by optimizing the formulation of the irradiation stabilizer. The resulting polypropylene material exhibits good transparency after irradiation, excellent aging resistance, and can be used at high temperatures for extended periods without discoloration, while maintaining good mechanical properties.

[0012] Technical defects: The irradiation stabilizer used in this invention patent includes methylphenyl vinyl silicone rubber, coupling agent, montmorillonite material, antioxidant, and light stabilizer. The antioxidant used contains phenolic antioxidants such as 1010. Methylphenyl vinyl silicone rubber has poor compatibility with polypropylene. After irradiation with high cumulative dose rates of gamma rays, the phenolic antioxidants such as 1010 cause severe yellowing of the product. Furthermore, the material contains a high content of acid scavengers. These factors contribute to the poor optical properties of the polypropylene.

[0013] 5. Chinese Patent CN116926713A discloses a gamma-ray resistant medical protective clothing fabric and its preparation method. The fabric of this invention utilizes the synergistic effect of specific radiation stabilizers, light stabilizers, antioxidants, acid absorbers, etc., to achieve excellent radiation resistance. Further modification of polypropylene using an irradiation method also imparts good flexibility to the fabric. The radiation stabilizer is selected from at least one of barium salts, barium oxides, strontium salts, strontium oxides, bismuth salts, bismuth oxides, samarium salts, samarium oxides, neodymium salts, neodymium oxides, erbium salts, and erbium oxides.

[0014] Technical defects: The radiation stabilizer added in this invention patent is an inorganic salt or inorganic oxide, which has poor compatibility with polypropylene and affects the mechanical and optical properties of the material.

[0015] Existing technologies mainly improve the radiation resistance of polypropylene by reactive extrusion grafting of special functional components and adding organic or inorganic radiation-resistant stabilizers. However, this process is complex, involves long production lines, makes quality control difficult, and results in poor mechanical and optical properties of the finished product, as well as poor radiation resistance, thus limiting its application areas.

[0016] Therefore, designing a novel polypropylene composition that simultaneously possesses good transparency, radiation resistance, and cost-effectiveness is one of the current research priorities.

[0017] Therefore, this invention is proposed. Summary of the Invention

[0018] To address the aforementioned technical problems, this invention provides a gamma-ray irradiation-resistant transparent polypropylene composition and its preparation method. The aim is to overcome the existing problems of polypropylene's susceptibility to oxidative degradation, embrittlement, or decreased transparency under irradiation conditions, thereby improving the oxidation resistance, radiation resistance, and processing adaptability of polypropylene materials. This meets the demand for high-performance transparent polypropylene materials in industries such as medical, packaging, and electronics, and provides simple and feasible industrial production conditions.

[0019] In order to achieve the objective of this invention, the following technical solution is adopted: This invention provides a gamma-ray irradiation-resistant transparent polypropylene composition, the composition comprising polypropylene, a nucleating agent, an antioxidant, and an acid absorber; Specifically, based on 100 parts by weight of polypropylene, the amount of nucleating agent is 0.12-0.42 parts by weight, the amount of antioxidant is 0.3-0.8 parts by weight, and the amount of acid absorbent is 0.06-0.15 parts by weight. The antioxidant is a composition of hydroxylamine antioxidants and pentaerythritol phosphite antioxidants; the acid absorber is magnesium aluminum hydrotalcite.

[0020] Furthermore, the MgO / Al2O3 molar ratio of the acid absorber magnesium aluminum hydrotalcite is <6:1, preferably (4.0-5.0):1; the particle size D50 of the acid absorber magnesium aluminum hydrotalcite is <1um, preferably 50-400nm.

[0021] Furthermore, the hydroxylamine antioxidant is selected from dialkyl hydroxylamine compounds, preferably at least one of diethyl hydroxylamine, bis(octadecyl) hydroxylamine and its derivatives.

[0022] Furthermore, the pentaerythritol phosphite antioxidant is selected from at least one of bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, pentaerythritol diphosphite dioctadecyl ester and its derivatives.

[0023] Furthermore, the weight ratio of the hydroxylamine antioxidant to the pentaerythritol phosphite antioxidant is (0.5-3):1.

[0024] Furthermore, the weight ratio of the pentaerythritol phosphite antioxidant to the acid absorber magnesium aluminum hydrotalcite is (1-10):1; preferably, the weight ratio of the pentaerythritol phosphite antioxidant to the acid absorber magnesium aluminum hydrotalcite is (1-5):1.

[0025] Furthermore, the nucleating agent is at least one of sorbitol and / or organophosphate compounds.

[0026] Further, wherein the polypropylene is selected from at least one homopolymer and / or random copolymer; preferably, the polypropylene has a melt index of 1-80 g / 10 min at 230°C and a load of 2.16 kg, and an ethylene comonomer content of 0-5 wt%; more preferably, the polypropylene has a melt index of 1-70 g / 10 min at 230°C and a load of 2.16 kg, and an ethylene comonomer content of 0-4 wt%.

[0027] The present invention also provides a method for preparing a gamma-ray irradiation-resistant transparent polypropylene composition as described above, wherein the preparation method includes the following steps: mixing polypropylene, a nucleating agent, an antioxidant, and an acid absorber, extruding, and granulating to obtain the gamma-ray irradiation-resistant transparent polypropylene composition.

[0028] Furthermore, the extrusion is carried out in a twin-screw extruder; preferably, the twin-screw extruder has a screw length-to-diameter ratio of (10-100):1 and an extrusion temperature of 140-220°C.

[0029] The present invention also provides a radiation-resistant polypropylene, wherein the polypropylene is prepared from the polypropylene composition provided above.

[0030] The present invention has the following technical effects: (1) The polypropylene composition of the present invention significantly enhances the stability of the material under high-energy irradiation by optimizing the type and ratio of antioxidants and acid scavengers through their synergistic effect. Antioxidants can effectively capture free radicals and slow down the oxidative degradation process, while acid scavengers neutralize possible acidic byproducts, thus extending the service life of polypropylene through their synergistic effect. Compared with traditional polypropylene materials, the composition of the present invention can still maintain mechanical strength and molecular structure integrity under long-term irradiation conditions, thereby achieving reliable gamma ray irradiation resistance and meeting the application requirements of high-requirement fields such as medical devices, packaging, and electronic products.

[0031] (2) This invention, through the rational selection of nucleating agents, antioxidants, and acid scavengers, enables polypropylene compositions to maintain high transparency even under high-energy gamma ray irradiation. Nucleating agents promote uniform crystallization and improve the optical uniformity of the material, while antioxidants and acid scavengers work synergistically to inhibit irradiation-induced molecular chain degradation, preventing color changes and turbidity. This technology ensures that polypropylene maintains excellent visual properties in applications requiring high transparency, such as medical packaging and optical components, while also possessing durability, providing a reliable guarantee for practical industrial use. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0033] In a first aspect, the present invention provides a gamma-ray irradiation-resistant transparent polypropylene composition, the composition comprising polypropylene, a nucleating agent, an antioxidant, and an acid absorber; Specifically, based on 100 parts by weight of polypropylene, the amount of nucleating agent is 0.12-0.42 parts by weight, the amount of antioxidant is 0.3-0.8 parts by weight, and the amount of acid absorbent is 0.06-0.15 parts by weight. The antioxidant is a composition of hydroxylamine antioxidants and pentaerythritol phosphite antioxidants; the acid absorber is magnesium aluminum hydrotalcite.

[0034] This invention provides a transparent polypropylene composition resistant to gamma ray irradiation, the core components of which include polypropylene, nucleating agent, antioxidant and acid scavenger, and the performance is synergistically optimized through reasonable proportions of each component.

[0035] In this composition, the synergistic effect of antioxidants and acid scavengers is key to ensuring that polypropylene maintains excellent transparency and mechanical properties under high-energy irradiation. The inseparability of this effect is closely related to the specific antioxidants and acid scavengers selected. The antioxidants selected in this invention consist of hydroxylamine compounds and pentaerythritol phosphites. Hydroxylamine antioxidants, such as dialkyl hydroxylamine, can efficiently capture free radicals generated during irradiation, inhibiting the initial oxidation reaction of the polypropylene molecular chain. Pentaerythritol phosphite antioxidants, such as bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, have excellent molecular chain protection, effectively inhibiting the continuation of the oxidation chain reaction, thus achieving a combination of short-term rapid protection and long-term stable protection.

[0036] However, relying solely on antioxidants cannot completely guarantee the stability of polypropylene under irradiation conditions, because acidic byproducts are inevitably generated during irradiation and processing. These acidic substances can catalyze molecular chain breakage or accelerate localized oxidation, leading to decreased transparency and material embrittlement. Therefore, acid scavengers play an irreplaceable role in this composition, and their selection directly affects the effective functioning of antioxidants and the overall performance of the polypropylene material.

[0037] This invention explicitly uses magnesium aluminum hydrotalcite (MgA) as an acid absorber, a choice based on its unique chemical and physical properties. MgA has a layered structure and high specific surface area, allowing it to be uniformly dispersed in a polypropylene matrix, effectively adsorbing and neutralizing acidic products generated during processing and irradiation. Compared to other conventional acid absorbers, such as carbonates or magnesium oxide powder, MgA not only has higher neutralization efficiency but also exhibits better thermal and structural stability under high-energy gamma ray irradiation, enabling it to continuously perform its acid-absorbing function without introducing new degradation risks. More importantly, the molar ratio of MgO to Al2O3 in MgA is adjustable, optimized to a range of 4:1 to 5:1, ensuring both acid neutralization capacity and compatibility and dispersibility with antioxidants. This structural characteristic allows it to form a highly synergistic protective system with hydroxylamine and pentaerythritol phosphite antioxidants.

[0038] Furthermore, the addition of nucleating agents further enhances the synergistic effect between antioxidants and magnesium aluminum hydrotalcite acid scavengers. Nucleating agents improve the crystalline structure of polypropylene, making the material more microscopically uniform and dense, thereby reducing the impact of free radicals and acidic substances on the overall properties of polypropylene. Under this optimized crystalline structure, antioxidants and acid scavengers can function more uniformly and efficiently, ensuring the stability of polypropylene in macroscopic properties and optical transparency.

[0039] In processing and industrial production, this inseparable antioxidant-magnesium aluminum hydrotalcite acid scavenger system also demonstrates advantages. Under high-temperature conditions such as twin-screw extrusion, the antioxidant inhibits thermally initiated free radical reactions, while the magnesium aluminum hydrotalcite acid scavenger continuously neutralizes acidic byproducts, ensuring the stability and colorfastness of polypropylene in the molten state, thereby guaranteeing the consistency and reliability of extruded granules and film products. This irreplaceable property not only ensures the long-term performance of the material under irradiation conditions but also provides a stable technical guarantee for large-scale industrial production.

[0040] In some embodiments, the MgO / Al2O3 molar ratio of the acid absorber magnesium aluminum hydrotalcite is <6:1, preferably (4.0-5.0):1; the particle size D50 of the acid absorber magnesium aluminum hydrotalcite is <1µm, preferably 50-400nm.

[0041] In some embodiments, the hydroxylamine antioxidant is selected from dialkyl hydroxylamine compounds, preferably at least one of diethylhydroxylamine, bis(octadecyl)hydroxylamine and its derivatives.

[0042] In some embodiments, the pentaerythritol phosphite antioxidant is selected from at least one of bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, pentaerythritol diphosphite bisoctadecyl ester and its derivatives.

[0043] In some embodiments, the weight ratio of the hydroxylamine antioxidant to the pentaerythritol phosphite antioxidant is (0.5-3):1.

[0044] In some embodiments, the weight ratio of the pentaerythritol phosphite antioxidant to the acid absorber magnesium aluminum hydrotalcite is (1-10):1; preferably, the weight ratio of the pentaerythritol phosphite antioxidant to the acid absorber magnesium aluminum hydrotalcite is (1-5):1.

[0045] Firstly, pentaerythritol phosphite antioxidants, as commonly used antioxidants in polyolefins, significantly inhibit free radical reactions and delay the oxidative degradation of polypropylene. During irradiation, polypropylene molecular chains are prone to generating free radicals due to high-energy radiation, which can trigger chain breakage or cross-linking reactions, leading to a decrease in the material's mechanical properties and impaired transparency. Introducing pentaerythritol phosphite antioxidants can effectively capture these free radicals, maintaining the structural stability of the polypropylene molecular chains at a high level. Simultaneously, these antioxidants are typically nonpolar or weakly polar, exhibiting good compatibility with the polypropylene matrix and enabling uniform dispersion in the polymer melt, thus providing uniform protection during extrusion or granulation processing.

[0046] However, simply using antioxidants is insufficient to comprehensively protect materials from performance degradation under high radiation conditions. Acid absorbers, especially the magnesium aluminum hydrotalcite used in this invention, can better absorb acidic substances that may be generated during the processing and use of polypropylene. Accumulation of these acidic substances can accelerate the degradation of polypropylene chains, reduce transparency, and cause yellowing. The layered structure and small particle size of magnesium aluminum hydrotalcite give it a high specific surface area, enabling it to react effectively with acidic byproducts at the microscopic level, thereby further inhibiting oxidation chain reactions. Furthermore, the molar ratio of MgO to Al2O3 in the magnesium aluminum hydrotalcite is designed to be in the range of (4-5):1, which also helps to balance acid absorption efficiency and material dispersibility, preventing the formation of excessively large particles in the polypropylene matrix that could affect transparency.

[0047] In this context, if the ratio of the two is too low (i.e., the antioxidant content is too low relative to the acid scavenger), it may lead to insufficient free radical capture, making the material still prone to yellowing or embrittlement after irradiation; if the ratio is too high (i.e., excessive antioxidant), although the free radical capture ability is strong, the antioxidant itself is easily degraded by heat or irradiation, and excessive amount may introduce additional by-products, which is detrimental to the long-term transparency and stability of the material.

[0048] In some embodiments, the nucleating agent is at least one of sorbitol and / or organophosphate compounds.

[0049] In some embodiments, the nucleating agent is one or more of sorbitol compounds and organophosphate compounds.

[0050] In some embodiments, the polypropylene is selected from at least one homopolymer and / or random copolymer; preferably, the polypropylene has a melt index of 1-80 g / 10 min at 230°C and a load of 2.16 kg, and an ethylene comonomer content of 0-5 wt%; more preferably, the polypropylene has a melt index of 1-70 g / 10 min at 230°C and a load of 2.16 kg, and an ethylene comonomer content of 0-4 wt%.

[0051] Secondly, the present invention also provides a method for preparing the above-mentioned gamma-ray irradiation-resistant transparent polypropylene composition, wherein the preparation method includes the following steps: mixing polypropylene, nucleating agent, antioxidant and acid absorber, extruding and granulating to obtain the gamma-ray irradiation-resistant transparent polypropylene composition.

[0052] In some embodiments, the extrusion is carried out in a twin-screw extruder; preferably, the twin-screw extruder has a screw length-to-diameter ratio of (10-100):1 and an extrusion temperature of 140-220°C.

[0053] The following is a detailed explanation using specific embodiments: Example 1 1. Raw material ratio

[0054] 2. Preparation steps Step 2.1: Mixing raw materials Polypropylene powder, nucleating agent, antioxidant 1, antioxidant 2 and acid absorber 1 are weighed according to the above ratio and added to the mixing device for premixing to make the components evenly dispersed and obtain a mixture.

[0055] Premixing can be done using a high-speed mixer or a twin-screw mixer to ensure uniform dispersion of the additives.

[0056] Step 2.2: Melt extrusion The uniformly mixed raw materials are fed into a twin-screw extruder for melt blending and extrusion.

[0057] Screw temperature range: 140℃→150℃→175℃→180℃→195℃→205℃→210℃→220℃→210℃→205℃ Feeding speed: 8 Screw speed: 100 rpm Screw length-to-diameter ratio: 40:1 The purpose of melt extrusion is to fully mix polypropylene and additives to form a homogeneous compound system.

[0058] Step 2.3: Granulation The extruded melt is passed through a water-cooled pelletizing system to form uniform particles, resulting in a transparent polypropylene composition resistant to gamma irradiation.

[0059] Example 2 1. Raw material ratio

[0060] 2. Preparation steps Step 2.1: Mixing raw materials Polypropylene powder, nucleating agent, antioxidant 1, antioxidant 2 and acid absorber 1 are weighed according to the above ratio and added to the mixing device for premixing to make the components evenly dispersed and obtain a mixture.

[0061] Step 2.2: Melt extrusion The uniformly mixed raw materials are fed into a twin-screw extruder for melt blending and extrusion.

[0062] Screw temperature range: 140℃→150℃→175℃→180℃→195℃→205℃→210℃→220℃→210℃→205℃ Feeding speed: 8 Screw speed: 100 rpm Screw length-to-diameter ratio: 40:1 The purpose of melt extrusion is to fully mix polypropylene and additives to form a homogeneous compound system.

[0063] Step 2.3: Granulation The extruded melt is passed through a water-cooled pelletizing system to form uniform particles, resulting in a transparent polypropylene composition resistant to gamma irradiation.

[0064] Example 3 1. Raw material ratio

[0065] 2. Preparation steps Step 2.1: Mixing raw materials Polypropylene powder, nucleating agent, antioxidant 1, antioxidant 3 and acid absorber 1 are weighed according to the above ratio and added to the mixing device for premixing to make the components evenly dispersed and obtain a mixture.

[0066] Step 2.2: Melt extrusion The uniformly mixed raw materials are fed into a twin-screw extruder for melt blending and extrusion.

[0067] Screw temperature range: 140℃→150℃→175℃→180℃→195℃→205℃→210℃→220℃→210℃→205℃ Feeding speed: 8 Screw speed: 100 rpm Screw length-to-diameter ratio: 40:1 The purpose of melt extrusion is to fully mix polypropylene and additives to form a homogeneous compound system.

[0068] Step 2.3: Granulation The extruded melt is passed through a water-cooled pelletizing system to form uniform particles, resulting in a transparent polypropylene composition resistant to gamma irradiation.

[0069] Comparative Example The proportions of raw materials for comparison are shown in Table 4 below, by mass parts.

[0070] Table 4 Comparative Example Raw Material Proportioning Data

[0071] The polypropylene powder has a melt index of 28 g / 10 min and a ethylene content of 3.3 wt%; the nucleating agent is 1,3:2,4-di(3,4-dimethylbenzyl)-D-sorbitol; antioxidant 1 is bis(octadecyl)hydroxylamine; antioxidant 2 is bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite; antioxidant 3 is bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite; antioxidant 4 is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; acid scavenger 1 is magnesium aluminum hydrotalcite with a MgO / Al2O3 molar ratio of 4.71 and a particle size D50 of 220 nm; acid scavenger 2 is magnesium aluminum hydrotalcite with a MgO / Al2O3 molar ratio of 3.75 and a particle size D50 of 3.7 μm. Comparative Examples 1 through 8 were prepared according to the raw material ratios of each comparative example in Table 4 and the preparation steps in Example 3.

[0072] Example 1: Performance Evaluation of Gamma-Ray Irradiation-Resistant Transparent Polypropylene Composition 1. Experimental Objective The changes in optical properties (haze, yellowness index) and mechanical properties (tensile strength, elongation at break) of the polypropylene compositions prepared in Examples 1-3 and Comparative Examples 1-8 before and after γ-ray irradiation were evaluated to verify the stability advantages of the compositions in the irradiation environment.

[0073] 2. Preparation of experimental samples 2.1 Sample Grouping A total of 11 groups of samples were collected: Example 1, Example 2, Example 3, and Comparative Examples 1-8.

[0074] 2.2 Injection Molding After drying each group of granules at 80℃ for 4 hours, the following two types of test samples were prepared using an injection molding machine: Optical performance test samples: Circular samples with a diameter of 50 mm and a thickness of 1.0 mm were prepared. During injection molding, the mold temperature was maintained at 40℃, and the injection pressure was moderate to ensure that the sample surface was smooth, free of bubbles and flow marks. Ten samples were prepared for each formulation, with 5 samples used for pre-irradiation testing and 5 samples used for post-irradiation testing.

[0075] Mechanical property test samples: Prepare type I dumbbell-shaped specimens with a total length of not less than 150 mm, a parallel section length of 60 mm, a parallel section width of 10 mm, and a thickness of 4.0 mm. Injection molding conditions are the same as for optical specimens, ensuring the specimens are free of flash, shrinkage marks, and internal pores. Prepare 10 specimens for each formulation, with 5 used for pre-irradiation testing and 5 for post-irradiation testing.

[0076] 3. Irradiation treatment The samples from each group used for post-irradiation testing were neatly arranged in a tray and placed... 60 The irradiation process is carried out in a Co γ-ray irradiation device.

[0077] Cumulative irradiation dose: 50 kGy Irradiation dose rate: 5 kGy / h Irradiation environment: room temperature, air atmosphere After irradiation, all irradiated samples and strips were removed and placed in a standard laboratory environment (temperature 23±2℃, relative humidity 50±5%) for 7 days to allow the free radicals generated during irradiation to fully decay and the sample performance to stabilize before subsequent testing.

[0078] 4. Performance Testing Methods and Detailed Procedures 4.1 Haze test: The haze of the samples before and after irradiation was tested according to the national standard GB2410-80.

[0079] Preparation before testing: Check that all optical sample surfaces are clean and free of contamination. If there is dust or fingerprints, gently wipe them with anhydrous ethanol and dry them with a non-woven cloth.

[0080] Place the sample in the test environment (23±2℃) for at least 2 hours to allow the sample temperature to equilibrate with the environment.

[0081] Testing process: Turn on the haze meter and preheat it for 30 minutes to stabilize the instrument's light source.

[0082] Use a standard calibration board to perform zero-point and full-scale calibration on the instrument to ensure that the instrument is in normal working order.

[0083] Place the optical sample before irradiation on the sample holder, ensuring that the sample is flat and free of bending, and the test beam is incident perpendicularly on the sample surface.

[0084] Press the test button, and the instrument will automatically record the transmittance and haze values. Each sample is tested three times, and the sample is reset after each test. The average of the three measurements is taken as the final haze value of the sample.

[0085] Repeat the above steps to complete the testing of all pre-irradiation samples.

[0086] Following the same steps, the haze value of each group of irradiated samples was tested sequentially.

[0087] Record all data and calculate the rate of change in haze before and after irradiation for each group of samples.

[0088] 4.2 Yellowness Index Test Preparation before testing: Ensure that the surface of the optical sample is clean, free of scratches and contaminants.

[0089] The spectrophotometer must be calibrated using a standard white board before testing can begin.

[0090] Testing process: Turn on the spectrophotometer, select the D65 light source, 10° observation angle, set the measurement mode to reflection mode, and calculate the yellowness index according to the standard ASTM E313 method (instrument built-in algorithm).

[0091] Place the optical sample before irradiation at the test port, ensuring a tight fit to prevent light leakage.

[0092] Press the measurement button, and the instrument will automatically read the color parameters of the sample and record the yellowness index (YI).

[0093] For each sample, measurements were taken at three different locations (the center and the edge), and the average value was taken as the yellowness index of that sample.

[0094] Repeat the above steps to complete the testing of all pre-irradiation samples.

[0095] Following the same steps, the yellowness index of each group of irradiated samples was tested sequentially.

[0096] Record all data and calculate the change in yellowness index before and after irradiation for each group of samples.

[0097] 4.3 Tensile strength and elongation at break test: Samples were prepared and tensile properties were tested in accordance with the national standard GB / T 1040.1-2018.

[0098] Preparation before testing: Use vernier calipers to measure the width and thickness of the parallel section of each dumbbell-shaped spline, accurate to 0.01 mm, and record the original dimensions.

[0099] Lightly draw gauge lines at both ends of the parallel section of the spline with a marker pen. The gauge length is 50 mm and is used for calibration of elongation at break.

[0100] Place the sample in the test environment for at least 4 hours to allow the material temperature to become uniform.

[0101] Testing process: Turn on the electronic universal testing machine, preheat for 15 minutes, and check the equipment's operating status.

[0102] Adjust the tension fixture to an initial spacing of 50mm, consistent with the gauge length of the spline.

[0103] Take a dumbbell-shaped specimen before irradiation, and clamp both ends flat in the upper and lower fixtures, ensuring that the axis of the specimen coincides with the center line of the fixture. After clamping, the specimen should remain vertical and without twisting.

[0104] Set the stretching rate to 50 mm / min and start the test.

[0105] During the tensile testing process, the testing machine automatically records the changes in tensile force and displacement. When the specimen breaks, the instrument automatically stops and records the maximum tensile force and the displacement at the point of breakage.

[0106] Remove the fractured specimen and check if the fracture location is within the parallel section. If the fracture is outside the gauge length, discard the data and retest the spare specimen in the same group.

[0107] Calculate the tensile strength and elongation at break.

[0108] Five valid specimens were tested before each formulation was irradiated, and the average value was taken as the tensile strength and elongation at break of the formulation before irradiation.

[0109] Following the same steps, the tensile strength and elongation at break of each group of irradiated specimens were tested sequentially.

[0110] Record all data and calculate the rate of change of tensile strength and the rate of change of elongation at break for each group of samples after irradiation.

[0111] The relevant calculation formulas are as follows: Haze change = post-irradiation haze - pre-irradiation haze; Tensile strength change rate = (Tensile strength after irradiation - Tensile strength before irradiation) / Tensile strength before irradiation × 100%; Change in elongation at break = (Elongation at break after irradiation - Elongation at break before irradiation) / Elongation at break before irradiation × 100%; Change in yellowness index = Yellowness index after irradiation - Yellowness index before irradiation; Record all data; the final data is shown in Tables 5 and 6 below.

[0112] Table 5 Experimental results before irradiation

[0113] Table 6. Experimental results after irradiation

[0114] As can be seen from Tables 5-6, Examples 1-3 and Comparative Examples 1-5 show that Example 1 demonstrates that adding a specific compound additive system to polypropylene powder can produce a transparent polypropylene sample resistant to gamma irradiation with excellent radiation resistance and anti-yellowing properties, as well as superior mechanical and optical properties. Comparative Example 1 shows that the material prepared by adding a nucleating agent to polypropylene powder has good optical and mechanical properties, but the mechanical properties of the sample are poor after irradiation, with a sharp drop in elongation at break. Comparative Example 2 shows that adding only bis(octadecyl)hydroxylamine results in good anti-yellowing properties, but the haze and mechanical properties of the material are poor after irradiation. Simultaneously, the comparative examples show that adding only bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite results in high haze, poor transparency, low tensile strength, poor mechanical properties after irradiation, and high yellowing. Comparative Example 4 shows that the simultaneous addition of bis(octadecyl)hydroxylamine and bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite resulted in high haze and poor transparency in the material, leading to poor mechanical properties after irradiation. Comparative Example 5 shows that the addition of ordinary magnesium aluminum hydrotalcite resulted in high haze, low elongation at break, and poor resistance to yellowing after irradiation in the polypropylene material. Considering Examples 1-3 and Comparative Examples 1-5, the combination of the specially structured magnesium aluminum hydrotalcite with hydroxylamine antioxidant and pentaerythritol diphosphite has a certain synergistic effect, which can effectively improve the gamma ray irradiation resistance of transparent polypropylene materials.

[0115] Examples 1 and 6 show that replacing bis(octadecyl)hydroxylamine with pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (hindered phenolic antioxidant 1010) results in poorer anti-yellowing properties of the material.

[0116] Comparative Examples 1-2 and 7-8 show that various additives need to be added within the appropriate ratio range; adding too much or too little will result in poor overall performance of the product.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A transparent polypropylene composition resistant to gamma ray irradiation, characterized in that, The composition includes polypropylene, a nucleating agent, an antioxidant, and an acid absorber; Specifically, based on 100 parts by weight of polypropylene, the amount of nucleating agent is 0.12-0.42 parts by weight, the amount of antioxidant is 0.3-0.8 parts by weight, and the amount of acid absorbent is 0.06-0.15 parts by weight. The antioxidant is a composition of hydroxylamine antioxidants and pentaerythritol phosphite antioxidants; the acid absorber is magnesium aluminum hydrotalcite.

2. The gamma-ray irradiation resistant transparent polypropylene composition according to claim 1, wherein the MgO / Al2O3 molar ratio of the acid absorber magnesium aluminum hydrotalcite is <6:1, preferably (4.0-5.0):1; and the particle size D50 of the acid absorber magnesium aluminum hydrotalcite is <1μm, preferably 50-400nm.

3. The gamma-ray resistant transparent polypropylene composition according to claim 1, wherein the hydroxylamine antioxidant is selected from dialkyl hydroxylamine compounds, preferably at least one of diethylhydroxylamine, bis(octadecyl)hydroxylamine and its derivatives.

4. The gamma-ray irradiation-resistant transparent polypropylene composition according to claim 1, wherein the pentaerythritol phosphite antioxidant is selected from at least one of bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, pentaerythritol diphosphite bisoctadecyl ester and its derivatives.

5. The gamma-ray irradiation-resistant transparent polypropylene composition according to claims 1-4, wherein the weight ratio of the hydroxylamine antioxidant to the pentaerythritol phosphite antioxidant is (0.5-3):

1.

6. The gamma-ray irradiation-resistant transparent polypropylene composition according to claims 1-4, wherein the weight ratio of the pentaerythritol phosphite antioxidant to the acid absorber magnesium aluminum hydrotalcite is (1-10):1; preferably, the weight ratio of the pentaerythritol phosphite antioxidant to the acid absorber magnesium aluminum hydrotalcite is (1-5):

1.

7. A gamma-ray irradiation-resistant transparent polypropylene composition according to any one of claims 1-6, wherein the nucleating agent is at least one of sorbitol and / or organophosphate compounds.

8. A gamma-ray irradiation-resistant transparent polypropylene composition according to any one of claims 1-7, wherein, The polypropylene is selected from at least one homopolymer and / or random copolymer; preferably, the polypropylene has a melt index of 1-80 g / 10 min at 230°C and a load of 2.16 kg, and an ethylene comonomer content of 0-5 wt%; more preferably, the polypropylene has a melt index of 1-70 g / 10 min at 230°C and a load of 2.16 kg, and an ethylene comonomer content of 0-4 wt%.

9. A method for preparing a gamma-ray irradiation-resistant transparent polypropylene composition according to any one of claims 1-8, wherein, The preparation method includes the following steps: mixing polypropylene, nucleating agent, antioxidant and acid absorber, extruding and granulating to obtain the gamma-ray irradiation resistant transparent polypropylene composition.

10. The preparation method according to claim 9, wherein, The extrusion is carried out in a twin-screw extruder; preferably, the screw length-to-diameter ratio of the twin-screw extruder is (10-100):1, and the extrusion temperature is 140-220℃.

11. A radiation-resistant polypropylene, wherein, The polypropylene is prepared from the polypropylene composition according to any one of claims 1-8.

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