Low water absorption MBPA material with in-situ grafted hydrophobic polymer and its preparation method

Abstract

This invention relates to the field of polymer materials technology, and discloses a low-water-absorption MBPA material with in-situ grafted hydrophobic polymers and its preparation method. The preparation method includes: cleaning and vacuum drying a molded multi-block microphase copolyamide substrate; fixing the pretreated substrate in a single-sided treatment fixture; performing short-term surface activation using 254nm ultraviolet light; contacting the activated surface to be modified with a grafting solution containing siloxane methacrylate monomers, long-chain alkyl methacrylate monomers, benzophenone, and a mixed organic solvent, and irradiating the surface to be modified with single-sided ultraviolet light from one side to initiate an in-situ grafting reaction; and obtaining the low-water-absorption MBPA material through extraction and vacuum drying. This invention reduces the water absorption rate of the material and minimizes the adverse effects of surface grafting treatment on the material's bulk mechanical properties by forming a covalently grafted hydrophobic modification layer with decreasing thickness from the outside to the inside within a 0.5-5μm effective grafting region.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a low water absorption MBPA material with surface in situ grafted hydrophobic polymers and its preparation method. Background Technology

[0002] Multi-block microphase copolyamide materials, or MBPA for short, are a class of block polymer materials composed of polyamide hard segments and flexible soft segments. In these materials, the polyamide hard segments typically form a hard segment-rich phase through hydrogen bonding and orderly stacking of chain segments, providing strength, heat resistance, and dimensional support as physical cross-linking regions. The flexible soft segments typically form a soft segment-rich phase, imparting flexibility, resilience, and processability to the material. Due to the microphase morphology between the hard and soft segment-rich phases, MBPA materials achieve a good balance between strength and flexibility, making them suitable for applications such as sealing, encapsulation, connection protection, flexible structural components, and impact-resistant functional components.

[0003] However, the polyamide hard segments in MBPA materials contain amide structures, which are polar and readily form hydrogen bonds with water molecules. This causes the material to absorb water in humid, submerged, or cycling environments. Water absorption leads to changes in size, surface condition, and dielectric properties. Furthermore, water molecules entering the hard segment-enriched phase or the interface between the hard and soft segments may weaken existing hydrogen bonds and physical cross-linking, affecting the material's tensile strength, flexibility retention, fatigue resistance, and long-term stability. Therefore, reducing the water absorption rate of MBPA materials while maintaining the microphase morphology formed by the hard and soft segment-enriched phases is a crucial problem that needs to be addressed in the application of this type of material.

[0004] Existing methods for reducing the water absorption rate of polyamide materials mainly include surface plasma treatment, surface coating with a hydrophobic layer, bulk grafting modification, and hydrophobic filler blending modification. Surface plasma treatment or surface coating methods can form a low surface energy structure on the material surface, but their modification effect is usually concentrated in a very shallow layer. Moreover, the hydrophobic layer formed by some treatments mainly relies on surface interaction or deposition to bond with the substrate. After friction, bending, immersion in water, or long-term aging, problems such as surface energy recovery, hydrophobic layer wear, or hydrophobic performance degradation are prone to occur, making it difficult to guarantee a long-term low water absorption effect.

[0005] Bulk grafting or bulk copolymerization can introduce hydrophobic segments throughout the material, but these methods alter the ratio, compatibility, and segmental motion of hard and soft segments within the MBPA material, potentially affecting the aggregation degree of the hard-segment-rich phase and the microphase morphology of both hard and soft segments. When the physical cross-linking structure of the hard segments is disrupted, the material's tensile strength, heat resistance, and dimensional stability may decrease; when the continuity of the soft segments is affected, the material's flexibility, resilience, and flexural strength may deteriorate. Therefore, while bulk modification can reduce water absorption, it carries the risk of sacrificing the material's original mechanical properties.

[0006] Blending with hydrophobic fillers is another common method. For example, adding silicon-containing, fluorine-containing, or long-chain alkyl hydrophobic fillers to polyamide materials can reduce the overall water absorption tendency of the material. However, the dispersion and interfacial compatibility of the filler in the polymer matrix are difficult to control stably. Filler agglomeration zones or interfacial defects between the filler and the matrix may actually form water molecule permeation channels. At the same time, the addition of fillers may also change the material's flowability, molding stability, and local stress distribution, which is detrimental to maintaining a uniform microphase morphology and stable mechanical properties in MBPA materials.

[0007] Therefore, it is necessary to provide a low water absorption modification method suitable for molded MBPA materials, so that the hydrophobic modification is mainly limited to the surface to subsurface region of the material to be modified, and a hydrophobic modification layer covalently connected with the substrate is formed in this region. At the same time, the modification reaction is avoided from penetrating into the interior of the material and destroying the microphase morphology formed by the original hard segment enriched phase and soft segment enriched phase, thereby taking into account low water absorption, hydrophobic durability and the material's bulk mechanical properties. Summary of the Invention

[0008] The purpose of this invention is to provide a low-water-absorption MBPA material with surface in-situ grafted hydrophobic polymers and its preparation method, so as to solve the above-mentioned technical problems.

[0009] To achieve the above objectives, the present invention provides the following solution: On one hand, the method for preparing low-water-absorption MBPA materials with surface in-situ grafted hydrophobic polymers provided by the present invention includes: The molded multi-block microphase copolyamide substrate was cleaned and vacuum dried to obtain a pretreated substrate. The multi-block microphase morphology copolyamide substrate includes polyamide hard segments and flexible soft segments. The polyamide hard segments form a hard segment enriched phase, and the flexible soft segments form a soft segment enriched phase. The hard segment enriched phase and the soft segment enriched phase form a microphase morphology in the multi-block microphase morphology copolyamide substrate. The pretreated substrate is fixed in a single-sided treatment fixture, so that the surface of the pretreated substrate to be modified is exposed, and the unmodified surface of the pretreated substrate is covered. The surface to be modified is subjected to short-time surface activation treatment with ultraviolet light of wavelength 254nm to obtain a surface-activated substrate. The irradiation time of the short-time surface activation treatment is 15s to 60s, and the ultraviolet light intensity is 1mW / cm² to 8mW / cm². The surface to be modified of the surface-activated substrate is brought into contact with a grafting solution, the grafting solution comprising siloxane methacrylate monomer, long-chain alkyl methacrylate monomer, benzophenone and a mixed organic solvent; After the surface to be modified comes into contact with the grafting liquid, under oxygen-free conditions, one-sided ultraviolet light is applied to the surface to be modified to induce in-situ grafting reactions of the siloxane methacrylate monomer and the long-chain alkyl methacrylate monomer in the surface to subsurface region of the surface to be modified, forming a covalently grafted hydrophobic modified layer. The substrate after the in-situ grafting reaction was subjected to organic solvent extraction and vacuum drying to remove ungrafted monomers, homopolymers and residual initiators, thereby obtaining the low water absorption multi-block microphase copolyamide material. Wherein, the surface to subsurface region is an effective grafting region extending from the surface to be modified into the interior of the multi-block microphase copolyamide substrate at a depth of 0.5 μm to 5 μm; The content of hydrophobic polymer segments in the covalently grafted hydrophobic modified layer decreases from the surface to be modified towards the interior of the multi-block microphase copolyamide substrate.

[0010] Preferably, the polyamide hard segment is at least one of PA6 hard segment, PA66 hard segment, PA11 hard segment, and PA12 hard segment; the flexible soft segment is at least one of polyethylene glycol soft segment, polypropylene glycol soft segment, polytetrahydrofuran soft segment, and polycaprolactone soft segment, and the glass transition temperature of the flexible soft segment is below -20°C.

[0011] Preferably, the short-time surface activation treatment and the in-situ grafting reaction are confined within the effective grafting region, and the multi-block microphase morphology copolyamide substrate outside the effective grafting region does not come into direct contact with the grafting liquid.

[0012] Preferably, when cleaning and vacuum drying the molded multi-block microphase copolyamide substrate, anhydrous ethanol is used to ultrasonically clean the multi-block microphase copolyamide substrate for 10 to 20 minutes, and vacuum drying is performed at 50 to 70 degrees Celsius for 1 to 3 hours.

[0013] Preferably, during the short-time surface activation treatment, the distance between the ultraviolet lamp and the surface to be modified is controlled to be 5cm to 15cm, and the temperature of the surface to be modified is controlled to be no higher than 40°C.

[0014] Preferably, in the grafting solution, the mass percentage of the siloxane methacrylate monomer is 2% to 10%, the mass percentage of the long-chain alkyl methacrylate monomer is 5% to 20%, the mass percentage of the benzophenone is 0.2% to 1.5%, and the balance is the mixed organic solvent.

[0015] Preferably, the siloxane methacrylate monomer is methacryloyloxypropyl-terminated polydimethylsiloxane; the long-chain alkyl methacrylate monomer is a mixture of dodecyl methacrylate and octadecyl methacrylate, wherein the mass ratio of dodecyl methacrylate to octadecyl methacrylate is 1:3 to 3:1.

[0016] Preferably, the mixed organic solvent is composed of toluene and isopropanol, and the volume ratio of toluene to isopropanol is 70:30 to 90:10; when the surface to be modified of the surface-activated substrate is brought into contact with the grafting solution, the thickness of the liquid layer of the grafting solution on the surface to be modified is controlled to be 0.5 mm to 3 mm, and the surface to be modified is pre-wetted in the grafting solution for 1 min to 5 min.

[0017] Preferably, when performing the single-sided ultraviolet irradiation, ultraviolet light with a wavelength of 320nm to 380nm is used, the light intensity is 5mW / cm² to 15mW / cm², the irradiation time is 10min to 20min, and the grafting solution temperature is 20℃ to 30℃; the single-sided treatment fixture restricts the ultraviolet light from entering the multi-block microphase morphology copolyamide substrate from the unmodified surface.

[0018] On the other hand, the present invention provides a surface-grafted hydrophobic polymer MBPA material prepared by the above preparation method, wherein the low water absorption multi-block microphase morphology copolyamide material includes a multi-block microphase morphology copolyamide body and a covalently grafted hydrophobic modified layer formed on at least one side surface of the multi-block microphase morphology copolyamide body. The multi-block microphase morphology copolyamide body includes a hard segment enriched phase formed by polyamide hard segments and a soft segment enriched phase formed by flexible soft segments. The covalently grafted hydrophobic modified layer includes siloxane-long-chain alkyl hydrophobic polymer segments grafted onto the surface to subsurface region of the multi-block microphase morphology copolyamide bulk. The content of the siloxane-long-chain alkyl hydrophobic polymer segments decreases from the outer surface of the covalently grafted hydrophobic modified layer towards the interior of the multi-block microphase morphology copolyamide body. The effective distribution depth of the covalently grafted hydrophobic modified layer is 0.5 μm to 5 μm; The covalently grafted hydrophobic modified layer is formed on the surface to subsurface region of the multi-block microphase copolyamide body, and the body region inside the covalently grafted hydrophobic modified layer is not in direct contact with the grafting liquid.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention performs in-situ surface grafting modification on a molded multi-block microphase copolyamide substrate, rather than modifying the entire material. By confining the short-term surface activation treatment and in-situ grafting reaction to the surface to subsurface region of the surface to be modified, the covalently grafted hydrophobic modified layer is mainly formed in the effective grafting region extending inward from the surface to be modified by 0.5 μm to 5 μm, thereby reducing the material's water absorption.

[0020] A single-sided treatment fixture is used to fix the pretreated substrate, exposing the surface to be modified while shielding the unmodified surface. During the short-term surface activation stage and the single-sided UV irradiation stage, UV light acts on the substrate from the side of the surface to be modified, and the unmodified surface does not directly participate in the activation and grafting reaction. This avoids simultaneous reactions on both sides of the substrate or the grafting solution seeping in from the side, ensuring the directionality and regional controllability of the grafting reaction, which is beneficial for forming a single-sided hydrophobic modified structure.

[0021] This invention first employs 254nm ultraviolet light for short-term surface activation treatment of the surface to be modified, followed by single-sided photoinitiated grafting using a grafting solution containing siloxane methacrylate monomers, long-chain alkyl methacrylate monomers, benzophenone, and a mixed organic solvent. The short-term surface activation treatment enhances the grafting reactivity of the surface to be modified; subsequent single-sided ultraviolet irradiation induces in-situ grafting reactions of hydrophobic monomers in the surface to subsurface regions, allowing hydrophobic polymer segments to be covalently grafted onto the MBPA material surface. Compared to simple coating or physical deposition of hydrophobic layers, this results in better bonding stability and elution resistance.

[0022] The grafting solution of this invention contains both siloxane methacrylate monomers and long-chain alkyl methacrylate monomers. The siloxane segments help reduce the surface energy of the modified layer, while the long-chain alkyl segments increase the density of nonpolar hydrophobic segments. Together, they form siloxane-long-chain alkyl hydrophobic polymer segments in the area from the surface to the subsurface, thereby improving the material surface's ability to repel water molecules and reducing the possibility of water molecules diffusing into the material.

[0023] By controlling the composition of the mixed organic solvent, the thickness of the grafting solution layer on the surface to be modified, the pre-wetting time, the intensity of single-sided ultraviolet light irradiation, the irradiation time, and the temperature of the grafting solution, the content of hydrophobic polymer segments decreases from the surface to be modified towards the interior of the multi-block microphase copolyamide substrate. This decreasing distribution creates a water-blocking interface with a high content of hydrophobic segments on the outer surface of the material, forms a transitional water-blocking region on the subsurface, and reduces the extension of the grafting reaction into deeper regions of the material. This improves both surface hydrophobicity and subsurface water-blocking properties while minimizing adverse effects on the material's bulk mechanical properties.

[0024] The preparation method of the present invention does not require the addition of hydrophobic fillers to MBPA materials, thus avoiding problems such as filler agglomeration, interfacial porosity, and insufficient compatibility between fillers and the matrix, which lead to water molecule permeation channels. It is suitable for post-processing modification of already formed MBPA sheets, films, encapsulations, or structural components, and has good process adaptability.

[0025] In summary, this invention achieves a balance between low water absorption and hydrophobic modification and the preservation of the material's bulk properties through a continuous process involving post-molding cleaning and drying, single-sided fixture confinement, 254nm short-term surface activation, hydrophobic monomer confined contact, single-sided photo-initiated in-situ grafting, and extraction to remove free matter. This process forms a covalently grafted hydrophobic modification layer with decreasing thickness from the outside to the inside within the 0.5μm to 5μm effective grafting area on the surface of the MBPA material to be modified. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 An exploded view of the single-sided processing fixture provided in an embodiment of the present invention; Figure 2 This is a cross-sectional view of the single-sided processing fixture provided in an embodiment of the present invention.

[0028] In the figure, 1. Support base; 2. Light-shielding back plate; 3. Substrate; 4. Circumferential seal; 5. Thickness limiting pressure frame; 6. Light-transmitting cover plate; 7. Clamping component; 8. Grafting fluid. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] The embodiments of this invention employ the following testing methods: (1) Water contact angle test: Under the conditions of 23℃ and 50% relative humidity, deionized water was added to the sample surface to be tested. The volume of a single drop of water was 5μL. Five different positions were tested for each sample, and the average value was taken.

[0032] (2) Water absorption test: Dry the sample under vacuum at 60℃ to constant weight and record the initial mass m0; then soak the sample in deionized water at 23℃ for 24h or 168h, take it out and wipe off the surface moisture, record the mass mt, and calculate the water absorption rate according to the following relationship: water absorption rate = (mt - m0) / m0 × 100%.

[0033] (3) Water contact angle test after wear: The surface of the sample to be modified was rubbed 100 times under a load of 500g using a lint-free cloth, and the water contact angle after rubbing was measured according to the water contact angle test method.

[0034] (4) Tensile strength retention rate test: Using untreated MBPA substrate as the reference sample, the tensile strength of each sample was tested, and the tensile strength retention rate was calculated. Tensile strength retention rate = tensile strength of treated sample / tensile strength of untreated MBPA substrate × 100%.

[0035] (5) Grafting layer depth test: X-ray photoelectron spectroscopy depth analysis, time-of-flight secondary ion mass spectrometry depth analysis or cross-sectional elemental energy spectrum analysis are used to detect the changes of siloxane characteristic signals and long-chain alkyl characteristic signals along the material thickness direction, so as to determine the effective grafting depth and the decreasing distribution of hydrophobic segment content.

[0036] See Figure 1 As shown, the single-sided processing fixture structure in this embodiment of the invention includes a bearing base 1, a light-shielding back plate 2, a sample positioning groove, a circumferential sealing element 4, a thickness limiting pressure frame 5, a light-transmitting cover plate 6, and a clamping element 7. The support base 1 is used to support the molded multi-block microphase copolyamide substrate 3; The light-shielding back plate 2 is set on the support base 1 to shield the unmodified surface of the substrate 3 and prevent ultraviolet light from entering the interior of the substrate 3 from the unmodified surface. The sample positioning groove is set on the support base 1 or the light-shielding back plate 2 to accommodate and position the substrate 3, so that the surface of the substrate 3 to be modified faces outward. The circumferential seal 4 is arranged around the edge of the surface to be modified to seal the substrate 3 and prevent the grafting liquid 8 from seeping into the unmodified surface along the side of the substrate 3. Thickness limiting frame 5 is pressed around the surface of the substrate 3 to be modified, and a grafting liquid 8 is formed between the thickness limiting frame 5 and the surface to be modified. The thickness of the liquid layer in the grafting liquid 8 is 0.5 mm to 3 mm. A light-transmitting cover plate 6 is positioned above the thickness-limiting pressure frame 5. The cover plate 6 allows ultraviolet light to pass through at least the area corresponding to the surface to be modified, enabling ultraviolet light to irradiate the grafting liquid 8 and the substrate 3 surface from one side of the surface to be modified. The cover plate 6 is a quartz glass plate or an ultraviolet-transmitting glass plate. The cover plate 6, together with the thickness-limiting pressure frame 5 and the circumferential seal 4, forms a sealed liquid layer space to contain the deoxidized grafting liquid 8. Under the action of the clamping member 7, the cover plate 6 presses against the circumferential seal 4, isolating the grafting liquid 8 from the outside air during unilateral ultraviolet irradiation, thereby reducing the quenching effect of oxygen on the excited state and growing chain free radicals of benzophenone.

[0037] The clamping component 7 is used to press and fix the bearing base 1, the light-shielding back plate 2, the substrate 3, the circumferential seal 4, the thickness limiting frame 5, and the light-transmitting cover plate 6.

[0038] More specifically, it can be understood in two processing stages: The first stage is a short-term surface activation stage at 254nm. At this stage, the grafting solution 8 can be omitted, and the fixture mainly serves the functions of positioning and light shielding. The substrate 3 is placed on the light-shielding back plate 2, and the unmodified surface is blocked by the light-shielding back plate 2. The surface to be modified is exposed through the opening in the middle of the thickness-limiting pressure frame 5, and the 254nm ultraviolet light only irradiates the exposed surface.

[0039] The second stage is the single-sided light-induced grafting stage. At this time, a shallow liquid pool is formed between the thickness-limiting pressure frame 5 and the surface to be modified, and the grafting liquid 8 is confined above the surface to be modified, with the liquid layer thickness controlled between 0.5 mm and 3 mm; the circumferential seal 4 prevents the grafting liquid 8 from seeping into the back side from the edge; the light-transmitting cover plate 6 allows 320 nm to 380 nm ultraviolet light to pass through and irradiate the grafting liquid 8, so that the grafting reaction only occurs in the area from the surface to the subsurface to be modified.

[0040] Example 1

[0041] A method for preparing low-water-absorption MBPA materials with in-situ grafted hydrophobic polymers includes the following steps: S1: Select the molded multi-block microphase copolyamide substrate with dimensions of 50mm × 50mm × 1mm. The multi-block microphase copolyamide substrate includes PA12 hard segments and polytetrahydrofuran soft segments. The PA12 hard segments form a hard segment enriched phase, and the polytetrahydrofuran soft segments form a soft segment enriched phase. The hard segment enriched phase and the soft segment enriched phase form a microphase morphology in the substrate.

[0042] S2: The multi-block microphase copolyamide substrate was ultrasonically cleaned with anhydrous ethanol for 15 min and then vacuum dried at 60°C for 2 h to obtain the pretreated substrate.

[0043] S3: Fix the pretreated substrate in a single-sided treatment fixture, exposing the surface of the pretreated substrate to be modified, and shielding the unmodified surface of the pretreated substrate with a light-shielding back plate, and sealing the sides of the substrate with a circumferential sealing ring.

[0044] S4: Use ultraviolet light with a wavelength of 254nm to perform short-term surface activation treatment on the surface to be modified. The irradiation time is 30s, the ultraviolet light intensity is 5mW / cm², the distance between the ultraviolet lamp and the surface to be modified is 10cm, and the temperature of the surface to be modified is controlled not to exceed 40℃ during the treatment to obtain the surface activated substrate.

[0045] S5: Preparation of grafting solution. The grafting solution comprises 6 wt% methacryloxypropyl-terminated polydimethylsiloxane, 6 wt% dodecyl methacrylate, 6 wt% octadecyl methacrylate, 0.8 wt% benzophenone, and the balance being a mixed organic solvent composed of toluene and isopropanol, with a volume ratio of toluene to isopropanol of 80:20.

[0046] S6: Before the in-situ grafting reaction, nitrogen gas is introduced into the grafting solution for 20 minutes to deoxygenate it. The deoxygenated grafting solution is then confined within a sealed liquid layer space formed by the circumferential seal 4, the thickness limiting frame 5, and the light-transmitting cover plate 6, and visible air bubbles in the sealed liquid layer space are removed. The light-transmitting cover plate 6 presses the circumferential seal to prevent outside air from entering the grafting solution during single-sided ultraviolet irradiation. The surface to be modified of the surface-activated substrate is brought into contact with the grafting solution, and the thickness of the grafting solution layer on the surface to be modified is controlled to be 1.5 mm. The surface to be modified is then pre-wetted in the grafting solution for 3 minutes.

[0047] S7: Single-sided ultraviolet irradiation is performed from one side of the surface to be modified. Ultraviolet light with a wavelength of 365nm is used, the light intensity is 10mW / cm², the irradiation time is 15min, and the grafting solution temperature is 25℃. This initiates an in-situ grafting reaction between siloxane methacrylate monomers and long-chain alkyl methacrylate monomers in the surface to subsurface region of the surface to be modified, forming a covalently grafted hydrophobic modified layer.

[0048] S8: Take out the substrate after the in-situ grafting reaction is completed, and perform Soxhlet extraction with toluene for 24 hours to remove ungrafted monomers, homopolymers and residual initiators. Then, vacuum dry at 80°C for 12 hours to obtain low water absorption MBPA material.

[0049] Example 2

[0050] This embodiment is basically the same as Embodiment 1, except that: The multi-block microphase copolyamide substrate includes PA6 hard segments and polyethylene glycol soft segments, with the glass transition temperature of the polyethylene glycol soft segments being below -20°C. The ultrasonic cleaning time is 10 minutes, the vacuum drying temperature is 50°C, and the vacuum drying time is 1 hour. The irradiation time for the 254nm ultraviolet light short-time surface activation treatment was 15s, the ultraviolet light intensity was 1mW / cm², and the distance between the ultraviolet lamp and the surface to be modified was 15cm. The grafting solution comprises 2 wt% methacryloxypropyl-terminated polydimethylsiloxane, 2.5 wt% dodecyl methacrylate, 2.5 wt% octadecyl methacrylate, 0.2 wt% benzophenone, and the balance being a mixed organic solvent composed of toluene and isopropanol, with a volume ratio of toluene to isopropanol of 70:30. The thickness of the grafting solution layer on the surface to be modified is 0.5 mm, and the pre-wetting time is 1 min. Single-sided ultraviolet irradiation uses ultraviolet light with a wavelength of 320nm, a light intensity of 5mW / cm², an irradiation time of 10min, and a grafting solution temperature of 20℃. After extraction, the sample was vacuum dried at 60°C for 6 hours.

[0051] Example 3

[0052] This embodiment is basically the same as Embodiment 1, except that: The multi-block microphase copolyamide substrate includes PA12 hard segments and polycaprolactone soft segments, with the glass transition temperature of the polycaprolactone soft segments being below -20°C. The ultrasonic cleaning time was 20 minutes, the vacuum drying temperature was 70°C, and the vacuum drying time was 3 hours. The irradiation time for the 254nm ultraviolet light short-time surface activation treatment was 60s, the ultraviolet light intensity was 8mW / cm², and the distance between the ultraviolet lamp and the surface to be modified was 5cm. The grafting solution comprises 10 wt% methacryloxypropyl-terminated polydimethylsiloxane, 10 wt% dodecyl methacrylate, 10 wt% octadecyl methacrylate, 1.5 wt% benzophenone, and the balance is a mixed organic solvent composed of toluene and isopropanol, with a volume ratio of toluene to isopropanol of 90:10. The thickness of the grafting solution layer on the surface to be modified is 3 mm, and the pre-wetting time is 5 min. Single-sided ultraviolet irradiation uses ultraviolet light with a wavelength of 380nm, an irradiation intensity of 15mW / cm², an irradiation time of 20min, and a grafting solution temperature of 30℃. After extraction, the sample was vacuum dried at 90℃ for 12 hours.

[0053] Example 4

[0054] This embodiment is basically the same as Embodiment 1, except that: The irradiation time for the 254nm ultraviolet light short-time surface activation treatment was 15s, the ultraviolet light intensity was 1mW / cm², and the distance between the ultraviolet lamp and the surface to be modified was 15cm.

[0055] The grafting solution comprises 2 wt% methacryloxypropyl-terminated polydimethylsiloxane, 2.5 wt% dodecyl methacrylate, 2.5 wt% octadecyl methacrylate, 0.2 wt% benzophenone, and the balance being a mixed organic solvent composed of toluene and isopropanol, with a volume ratio of toluene to isopropanol of 70:30.

[0056] The grafting solution was deoxygenated with nitrogen for 10 minutes and then added to a closed liquid layer space. The thickness of the grafting solution on the surface to be modified was 0.5 mm, and the pre-wetting time was 1 minute.

[0057] Single-sided ultraviolet irradiation uses ultraviolet light with a wavelength of 320nm, an irradiation intensity of 5mW / cm², an irradiation time of 10min, and a grafting solution temperature of 20℃.

[0058] The extraction and vacuum drying conditions were the same as in Example 1.

[0059] Example 5

[0060] This embodiment is basically the same as Embodiment 1, except that: The irradiation time for the 254nm ultraviolet light short-time surface activation treatment was 60s, the ultraviolet light intensity was 8mW / cm², and the distance between the ultraviolet lamp and the surface to be modified was 5cm.

[0061] The grafting solution comprises 10 wt% methacryloxypropyl-terminated polydimethylsiloxane, 10 wt% dodecyl methacrylate, 10 wt% octadecyl methacrylate, 1.5 wt% benzophenone, and the balance being a mixed organic solvent composed of toluene and isopropanol, with a volume ratio of toluene to isopropanol of 90:10.

[0062] The grafting solution was deoxygenated with nitrogen for 30 minutes and then added to a closed liquid layer space. The thickness of the grafting solution on the surface to be modified was 3 mm, and the pre-wetting time was 5 minutes.

[0063] Single-sided ultraviolet irradiation uses ultraviolet light with a wavelength of 380nm, an irradiation intensity of 15mW / cm², an irradiation time of 20min, and a grafting solution temperature of 30℃.

[0064] The extraction and vacuum drying conditions were the same as in Example 1.

[0065] Comparative Example 1

[0066] This comparative example uses the same multi-block microphase morphology copolyamide substrate as Example 1. It is only ultrasonically cleaned with anhydrous ethanol for 15 min and vacuum dried at 60°C for 2 h. It does not undergo short-term surface activation treatment with 254nm ultraviolet light, nor does it undergo grafting solution contact or single-sided ultraviolet light initiation grafting.

[0067] Comparative Example 2

[0068] This comparative example uses the same multi-block microphase morphology copolyamide substrate as in Example 1. After cleaning and drying, the surface to be modified is treated with hexamethyldisiloxane plasma for 3 minutes at a power of 100W. After treatment, no short-term surface activation treatment with 254nm ultraviolet light is performed, no grafting solution is used, and no single-sided ultraviolet light initiation grafting is performed.

[0069] Comparative Example 3

[0070] This comparative example is basically the same as Example 1, except that: the 254nm ultraviolet short-time surface activation treatment is omitted, the cleaned and dried substrate is directly contacted with the same grafting solution as in Example 1, and 365nm ultraviolet light is used for single-sided irradiation to initiate grafting.

[0071] Comparative Example 4

[0072] This comparative example is basically the same as Example 1, except that: instead of using a single-sided treatment fixture, the entire MBPA substrate is completely immersed in the grafting solution and simultaneously irradiated with ultraviolet light from both sides to induce an overall surface grafting reaction.

[0073] Comparative Example 5

[0074] This comparative example is basically the same as Example 1, except that the mixed organic solvent in the grafting solution is replaced with pure toluene, while the other monomer types, monomer concentrations, benzophenone content, light conditions and post-treatment conditions remain unchanged.

[0075] Comparative Example 6

[0076] This comparative example is basically the same as Example 1, except that: dodecyl methacrylate and octadecyl methacrylate are not added to the grafting solution, and the grafting solution includes 18 wt% methacryloyloxypropyl-terminated polydimethylsiloxane, 0.8 wt% benzophenone and the balance mixed organic solvent, in which the volume ratio of toluene to isopropanol in the mixed organic solvent is 80:20.

[0077] Comparative Example 7

[0078] This comparative example is basically the same as Example 1, except that: no methacryloyloxypropyl-terminated polydimethylsiloxane is added to the grafting solution, and the grafting solution includes 9 wt% dodecyl methacrylate, 9 wt% octadecyl methacrylate, 0.8 wt% benzophenone and the balance mixed organic solvent, in which the volume ratio of toluene to isopropanol in the mixed organic solvent is 80:20.

[0079] The above embodiments and comparative examples were tested according to the aforementioned test methods, and the test results are shown in Table 1.

[0080] Table 1 Performance test results of the examples and comparative examples

[0081] Conclusion: As demonstrated in Examples 1 to 5, under the process conditions of this invention, using 254nm ultraviolet light for short-time surface activation, single-sided treatment with a clamping device, a grafting solution containing siloxane methacrylate monomers and long-chain alkyl methacrylate monomers, and single-sided ultraviolet light initiation grafting under oxygen-free conditions, a covalently grafted hydrophobic modified layer with an effective grafting depth of 0.5μm to 5μm can be formed on the surface of the MBPA material to be modified. The content of hydrophobic polymer segments in the covalently grafted hydrophobic modified layer decreases from the surface to be modified towards the interior of the substrate. The tensile strength retention rate in each example is 90% to 99%, indicating that this confined grafting treatment can reduce the water absorption rate while minimizing the adverse effects on the material's bulk mechanical properties.

[0082] As can be seen from the comparison between Example 1 and Comparative Example 1, the MBPA substrate without surface in-situ grafting treatment has a lower water contact angle and a higher water absorption rate after immersion in water; while Example 1, by forming a covalently grafted hydrophobic modified layer, significantly increases the initial water contact angle and significantly reduces the water absorption rate at 24h and 168h, indicating that the present invention can effectively reduce the water absorption of MBPA materials.

[0083] As can be seen from the comparison between Example 1 and Comparative Example 2, although plasma surface hydrophobic treatment can improve the initial water contact angle, the water contact angle decreases significantly after wear, and the water absorption rate rebounds significantly after long-term immersion in water. The water contact angle of Example 1 remains high after wear, indicating that the covalently grafted hydrophobic modified layer formed by the present invention has better friction resistance and elution resistance stability than ordinary surface-deposited hydrophobic layers.

[0084] A comparison of Example 1 and Comparative Example 3 shows that omitting the short-term surface activation treatment with 254nm ultraviolet light reduces the grafting reaction activity, results in insufficient effective grafting depth, and weakens the water contact angle and water absorption effect compared to Example 1. This indicates that short-term surface activation treatment is beneficial for forming grafting reaction sites on the surface to be modified and improves the stability of subsequent in-situ grafting reactions.

[0085] A comparison of Example 1 and Comparative Example 4 shows that when overall impregnation grafting is performed without using a single-sided treatment fixture, although a high water contact angle can be obtained on the material surface, the effective grafting depth is greater than 10 μm, and the tensile strength retention rate is significantly reduced. This indicates that the present invention, by limiting the direction of ultraviolet light and grafting liquid action through a single-sided treatment fixture, can prevent the grafting reaction from penetrating excessively into the material interior, thereby helping to maintain the bulk mechanical properties of the MBPA material.

[0086] A comparison of Example 1 and Comparative Example 5 shows that when pure toluene is used as the organic solvent, the grafting solution has a stronger swelling effect on the substrate surface, resulting in a grafting depth exceeding 5 μm and a decrease in tensile strength retention. This indicates that using a mixed organic solvent composed of toluene and isopropanol, and controlling their volume ratio to 70:30 to 90:10, is beneficial for regulating the wetting and diffusion of the grafting solution on the substrate surface and subsurface regions, thereby forming a controlled gradient grafting structure.

[0087] A comparison of Example 1 with Comparative Examples 6 and 7 shows that neither using only siloxane methacrylate monomers nor using only long-chain alkyl methacrylate monomers can simultaneously achieve the high initial water contact angle, good water contact angle retention after wear, and low water absorption rate shown in Example 1. This indicates that siloxane segments and long-chain alkyl segments have a synergistic effect in the covalently grafted hydrophobic modified layer. The former helps to reduce the surface energy of the modified layer, while the latter helps to increase the density of non-polar water-blocking segments. Together, they improve the low water absorption and hydrophobic durability of the MBPA material.

[0088] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing low-water-absorption MBPA materials with in-situ grafted hydrophobic polymers, characterized in that, include: The molded multi-block microphase copolyamide substrate was cleaned and vacuum dried to obtain a pretreated substrate. The multi-block microphase morphology copolyamide substrate includes polyamide hard segments and flexible soft segments. The polyamide hard segments form a hard segment enriched phase, and the flexible soft segments form a soft segment enriched phase. The hard segment enriched phase and the soft segment enriched phase form a microphase morphology in the multi-block microphase morphology copolyamide substrate. The pretreated substrate is fixed in a single-sided treatment fixture, so that the surface of the pretreated substrate to be modified is exposed, and the unmodified surface of the pretreated substrate is covered. The surface to be modified is subjected to short-time surface activation treatment with ultraviolet light of wavelength 254nm to obtain a surface-activated substrate. The irradiation time of the short-time surface activation treatment is 15s to 60s, and the ultraviolet light intensity is 1mW / cm² to 8mW / cm². The surface to be modified of the surface-activated substrate is brought into contact with a grafting solution, the grafting solution comprising siloxane methacrylate monomer, long-chain alkyl methacrylate monomer, benzophenone and a mixed organic solvent; After the surface to be modified comes into contact with the grafting liquid, under oxygen-free conditions, one-sided ultraviolet light is applied to the surface to be modified to induce in-situ grafting reactions of the siloxane methacrylate monomer and the long-chain alkyl methacrylate monomer in the surface to subsurface region of the surface to be modified, forming a covalently grafted hydrophobic modified layer. The substrate after the in-situ grafting reaction was subjected to organic solvent extraction and vacuum drying to remove ungrafted monomers, homopolymers and residual initiators, thereby obtaining the low water absorption multi-block microphase copolyamide material. Wherein, the surface to subsurface region is an effective grafting region extending from the surface to be modified into the interior of the multi-block microphase copolyamide substrate at a depth of 0.5 μm to 5 μm; The content of hydrophobic polymer segments in the covalently grafted hydrophobic modified layer decreases from the surface to be modified towards the interior of the multi-block microphase copolyamide substrate.

2. The preparation method according to claim 1, characterized in that, The polyamide hard segment is at least one of PA6 hard segment, PA66 hard segment, PA11 hard segment and PA12 hard segment; the flexible soft segment is at least one of polyethylene glycol soft segment, polypropylene glycol soft segment, polytetrahydrofuran soft segment and polycaprolactone soft segment, and the glass transition temperature of the flexible soft segment is below -20°C.

3. The preparation method according to claim 1, characterized in that, The short-time surface activation treatment and the in-situ grafting reaction are confined within the effective grafting area, and the multi-block microphase morphology copolyamide substrate outside the effective grafting area does not come into direct contact with the grafting liquid.

4. The preparation method according to claim 1, characterized in that, When cleaning and vacuum drying the molded multi-block microphase copolyamide substrate, anhydrous ethanol is used to ultrasonically clean the multi-block microphase copolyamide substrate for 10 to 20 minutes, and vacuum drying is carried out at 50 to 70 degrees Celsius for 1 to 3 hours.

5. The preparation method according to claim 1, characterized in that, During the short-term surface activation treatment, the distance between the ultraviolet lamp and the surface to be modified is controlled to be 5cm to 15cm, and the temperature of the surface to be modified is controlled to be no higher than 40℃.

6. The preparation method according to claim 1, characterized in that, In the grafting solution, the mass percentage of the siloxane methacrylate monomer is 2% to 10%, the mass percentage of the long-chain alkyl methacrylate monomer is 5% to 20%, the mass percentage of the benzophenone is 0.2% to 1.5%, and the balance is the mixed organic solvent.

7. The preparation method according to claim 6, characterized in that, The siloxane methacrylate monomer is methacryloyloxypropyl-terminated polydimethylsiloxane; the long-chain alkyl methacrylate monomer is a mixture of dodecyl methacrylate and octadecyl methacrylate, wherein the mass ratio of dodecyl methacrylate to octadecyl methacrylate is 1:3 to 3:

1.

8. The preparation method according to claim 1, characterized in that, The mixed organic solvent is composed of toluene and isopropanol, wherein the volume ratio of toluene to isopropanol is 70:30 to 90:

10. When the surface to be modified of the surface-activated substrate is brought into contact with the grafting solution, the thickness of the liquid layer of the grafting solution on the surface to be modified is controlled to be 0.5 mm to 3 mm, and the surface to be modified is pre-immersed in the grafting solution for 1 min to 5 min.

9. The preparation method according to claim 1, characterized in that, When performing the single-sided ultraviolet irradiation, ultraviolet light with a wavelength of 320nm to 380nm is used, the light intensity is 5mW / cm² to 15mW / cm², the irradiation time is 10min to 20min, and the grafting solution temperature is 20℃ to 30℃. The single-sided processing fixture restricts ultraviolet light from entering the multi-block microphase copolyamide substrate from the unmodified surface.

10. A low-water-absorption MBPA material with surface in-situ grafted hydrophobic polymer, characterized in that, The low water absorption MBPA material was prepared by the method described in any one of claims 1-9 for in-situ grafting hydrophobic polymers.

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