A method for preparing an oxidized hydrogentated polyethylene wax emulsion

Abstract

The application discloses a preparation method of oxidized hydrogenated polyethylene wax emulsion and belongs to the field of high polymer material modification and fine chemical industry. The application aims at the core problems of the existing oxidized polyethylene wax emulsion, such as the contradiction between oxidation depth and crystallization performance, poor emulsion stability, high process cost and the like, and adopts a synergistic process route of "first catalytic hydrogenation of regular molecular chain, then oxidation of introduction of polar groups, and finally preparation of emulsion by normal pressure phase inversion emulsification", that is, first, the unsaturated bond of the polyethylene wax molecular chain is saturated and the branched structure is regularized by catalytic hydrogenation, so that the crystallinity and chemical stability are improved; then, the oxygen-containing polar groups are introduced by oxidation; finally, the emulsion is prepared by phase inversion emulsification. The application realizes the compatibility of high emulsifiability, high crystallinity and high stability, the obtained emulsion has small particle size, narrow distribution, excellent acid resistance and heat resistance stability, the amount of emulsifier is small, the process does not need high-pressure equipment, and the application can be widely applied in the fields of water-based paint, ink, textile and leather finishing and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer material modification and fine chemical technology, specifically relating to a method for preparing an oxidized hydrogenated polyethylene wax emulsion. The resulting emulsion can be widely used in water-based coatings, ink auxiliaries, textile and leather finishing agents, plastic processing auxiliaries, and other fields. Background Technology

[0002] Polyethylene wax (PEW) is a low molecular weight polyolefin synthetic wax that is solid at room temperature. It has advantages such as high melting point, high hardness, good gloss, and strong chemical stability. However, polyethylene wax molecules do not contain hydrophilic groups and have a high degree of non-polarity, making direct emulsification extremely difficult. The resulting emulsion has poor storage stability, which limits its widespread application in aqueous systems.

[0003] To improve the hydrophilicity and emulsifurability of polyethylene wax, oxidative modification is commonly used in this field. This involves introducing oxygen-containing polar groups such as carboxyl, hydroxyl, and carbonyl groups onto the PE wax molecular chain through air oxidation, resulting in oxidized polyethylene wax (OPEW). This OPEW is then prepared into a microemulsion via high-temperature, high-pressure emulsification. A typical process, such as the one disclosed in Chinese patent CN101942152B, uses a compound of nonionic surfactants and saponification with potassium hydroxide, followed by emulsification at 120–150°C and 2–5 atmospheres.

[0004] However, existing oxidized polyethylene wax emulsion technology still has the following core problems: 1. The polar groups introduced by oxidation will disrupt the regularity of the molecular chain arrangement. The deeper the oxidation, the more obvious the decrease in crystallinity, which directly leads to the deterioration of the hardness, melting point, wear resistance and gloss of the wax film. If the degree of oxidation is reduced to maintain crystallinity, there will be insufficient hydrophilic groups, which will greatly increase the difficulty of emulsification and require a higher amount of emulsifier.

[0005] 2. Traditional oxidized wax emulsions have poor acid resistance and stability. Small fluctuations in the pH of the system can cause flocculation or even coagulation. Furthermore, the unsaturated bonds and unstable oxygen-containing structures remaining in the oxidized wax molecules are prone to further oxidation under high temperature or light, leading to yellowing of the product. This makes it difficult to meet the application requirements of high-end fields such as light-colored coatings and bleached fabric finishing.

[0006] 3. Existing technologies generally require the compounding of two or more surfactants, and the emulsification process needs to be carried out under high temperature and high pressure conditions, which places high demands on equipment, consumes a lot of energy, and results in high production and operating costs. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing oxidized hydrogenated polyethylene wax emulsion, which solves the problems of difficulty in achieving both oxidation depth and crystallization performance, poor emulsion stability, and high process cost, thereby achieving a balance between high emulsification, high crystallinity, and high stability.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an oxidized hydrogenated polyethylene wax emulsion includes three steps: catalytic hydrogenation, oxidative modification, and emulsification molding. (1) Catalytic hydrogenation: The polyethylene wax raw material is hydrogenated with hydrogen under the action of a catalyst, so that the unsaturated bonds in the molecular chain are saturated and the branched structure is regularized to obtain hydrogenated polyethylene wax.

[0009] Furthermore, the catalyst is a supported noble metal catalyst or a Raney nickel catalyst; the supported noble metal catalyst is selected from at least one of Pd / C, Pd / Al2O3, and Pt / Al2O3.

[0010] Furthermore, the hydrogenation reaction is carried out at a temperature of 210–270°C and a pressure of 2.5–3.5 MPa.

[0011] Furthermore, the hydrogenation reaction is carried out in a tubular fixed-bed reactor; the polyethylene wax raw material is preheated and melted, then mixed with hydrogen gas and passed into a reaction tube filled with catalyst for reaction; the reaction product is separated by gas-liquid separation to obtain hydrogenated polyethylene wax; the hydrogenated polyethylene wax has an iodine value ≤0.1 gI2 / 100g and a crystallinity of 60%~80%.

[0012] (2) Oxidative modification: The hydrogenated polyethylene wax is subjected to an oxidative reaction to introduce oxygen-containing polar groups into the molecular chain to obtain oxidized hydrogenated polyethylene wax.

[0013] Furthermore, the oxidation reaction is oxygen oxidation or air oxidation, the reaction temperature is 130-150°C, and the reaction is carried out under normal pressure conditions.

[0014] Furthermore, the oxidation reaction is terminated when the acid value of the product reaches 15-50 mg KOH / g; the melting point of the resulting oxidized hydrogenated polyethylene wax is 90-130℃, and the molecular weight distribution index (PDI) is ≤4.5.

[0015] Preferably, the obtained oxidized hydrogenated polyethylene wax has an acid value of 20-35 mg KOH / g, a melting point of 100-110℃, and a crystallinity of 55%-70%.

[0016] (3) Emulsification molding: The hydrogenated polyethylene wax is mixed with emulsifier, pH adjuster and deionized water, and then emulsified to obtain hydrogenated polyethylene wax emulsion.

[0017] Further, by mass parts, the raw materials for emulsification include: 10-40 parts of oxidized hydrogenated polyethylene wax, 1-10 parts of emulsifier, 0.1-2 parts of pH adjuster, and 50-85 parts of deionized water; the emulsifier is a nonionic surfactant selected from at least one of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

[0018] Furthermore, in the emulsification process, the oxidized hydrogenated polyethylene wax, emulsifier and pH adjuster are first mixed, heated and melted for pre-dispersion, then added to hot water for phase inversion emulsification, and after cooling and stabilization and filtration, the finished emulsion is obtained.

[0019] Furthermore, the resulting emulsion has a solid content of 25%–40%, an average particle size of 20–70 nm, a pH of 7.0–8.5, and shows no stratification after centrifugation at 3000 rpm for 30 min.

[0020] Compared with the prior art, the beneficial effects of this invention are as follows: 1. By first hydrogenating to regulate the molecular chain and then oxidizing to introduce polar groups, the process ensures the number of polar groups required for emulsification while maintaining the crystallinity of the wax at 55% to 60%, which is significantly higher than that of traditional oxidized polyethylene wax. This fundamentally solves the contradiction between oxidation depth and crystallization performance, resulting in a wax film with superior hardness, wear resistance, and gloss.

[0021] 2. The well-ordered molecular chains form a dense and orderly interfacial film during emulsification, which simultaneously improves the acid resistance, thermal stability, centrifugal stability and storage stability of the emulsion; at the same time, hydrogenation removes unsaturated bonds and unstable structures, effectively inhibiting high-temperature yellowing and broadening the application scenarios.

[0022] 3. Only one nonionic surfactant is needed to achieve emulsification, without the need for co-emulsifiers; the emulsification process can be completed under normal pressure, without the need for high-pressure equipment, with low energy consumption, simple operation, and easy industrial scale-up production. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the preparation method of the oxidized hydrogenated polyethylene wax emulsion of the present invention; Figure 2 Comparison of infrared spectra of polyethylene wax before and after hydrogenation; Figure 3 DSC curve of hydrogenated polyethylene wax; Figure 4 DSC curve of oxidized polyethylene wax; Figure 5 Comparison of DSC curves for dried polyethylene wax emulsion products; Figure 6 The particle size distribution curve (a) and data statistics graph (b) of Embodiment 3 of the present invention are shown. Figure 7 The figures shown are the particle size distribution curve (a) and data statistics (b) of Comparative Example 1 of the present invention. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0025] Reference Figure 1 A method for preparing an oxidized hydrogenated polyethylene wax emulsion employs a process route of "hydrogenation to repair molecular chains—regular oxidation to introduce polar groups—synergistic emulsification to prepare a stable emulsion," and its mechanism of action is as follows: (1) Hydrogenation regularization mechanism: There are carbon-carbon double bonds and disordered branched structures on the polyethylene wax molecular chain. Through catalytic hydrogenation, the double bonds can be saturated and the branches can be rearranged appropriately, and the molecular chain can be transformed into a linear regular structure. At the same time, unstable oxygen-containing structures such as peroxide, aldehydes and ketones are reduced to inert groups. After the regularity of the molecular chain is improved, the crystallinity and chain packing density are significantly improved, which provides a structural basis for the formation of a stable interface film in subsequent emulsification.

[0026] The relevant reactions are as follows: ① Hydrogen saturation of carbon-carbon double bonds:

[0027] ②Regularization of branched structure:

[0028] ③ Reduction of unstable oxygen-containing structures:

[0029]

[0030] (2) Oxidation-hydrophilic mechanism: After hydrogenation, the linear polyethylene wax molecular chains are directionally introduced with oxygen-containing polar groups such as carboxyl, hydroxyl, and carbonyl groups through oxidation. These polar groups are partially saponified under alkaline conditions, imparting surface charge to the wax particles. Combined with nonionic surfactants, this reduces interfacial tension, allowing the high-melting-point wax to be stably dispersed in the aqueous phase. Due to the high background regularity of the molecular chains and the uniform distribution of polar groups, the problem of molecular chain disorder in traditional oxidized waxes is avoided.

[0031] The general formula for oxidation reactions is as follows: (3) Synergistic effect mechanism: Hydrogenation and oxidation produce synergistic effect: After hydrogenation, the flexibility of the molecular chain is improved, and it is easier to spread and form a dense interface film during emulsification, which reduces the requirements for emulsifier dosage and process conditions; the removal of unsaturated bonds simultaneously improves the chemical stability and anti-yellowing properties of the product, ultimately achieving a synergistic improvement in emulsification performance, crystallization performance and stability performance.

[0032] Example 1: Preparation of hydrogenated polyethylene wax (HPEW) This embodiment uses a fixed-bed catalytic hydrogenation process to prepare hydrogenated polyethylene wax. The specific steps are as follows: Catalyst loading and activation pretreatment A tubular fixed-bed reactor was selected, with an inner diameter of 50 mm and an effective packing section length of 300 mm. Inert ceramic balls with a diameter of 3–6 mm were packed at the bottom of the reactor tubes to a height of 50 mm as a support layer. A Pd / C catalyst (5% Pd loading, particle size 20–40 mesh) was packed in the middle to a height of 250 mm, forming a catalyst bed with a height-to-diameter ratio of 5:1. The top of the catalyst bed was then packed with inert ceramic balls with a diameter of 3–6 mm to a height of 50 mm as a feedstock distribution layer.

[0033] After loading, nitrogen is introduced to replace the air in the system three times, and then hydrogen is introduced continuously at a flow rate of 1L / min. The temperature is programmed to rise to 200℃, and the catalyst is reduced in situ for 3 hours in a hydrogen atmosphere to complete the catalyst activation. Then, the temperature is naturally cooled to the reaction temperature for later use.

[0034] Raw material melting and preheating Polyethylene wax raw material (melting point 105℃, crystallinity 44.42%, DSC curve shown) was used. Figure 4 Add iodine (0.3g I2 / 100g) to the raw material melting tank, turn on the stirrer (200rpm), heat to 165℃ to completely melt the wax and keep it at the temperature to obtain a uniform and transparent raw material liquid.

[0035] Fixed-bed hydrogenation reaction The metering pump is turned on to deliver the molten feed liquid to the reactor inlet at a flow rate of 200 g / h; at the same time, the hydrogen cylinder is turned on and the hydrogen flow rate is controlled by the mass flow meter to make the volume ratio of feed liquid to hydrogen 400:1 (under standard conditions). The two are fully mixed in the static mixer at the reactor inlet to form a gas-liquid two-phase flow, which passes through the catalyst bed from top to bottom for hydrogenation reaction.

[0036] During the reaction, the reaction temperature is stabilized at 240℃ by circulating heat transfer oil between pipes, and the system pressure is controlled at 3.0MPa by a back pressure valve. After the temperature, pressure and flow rate are stable, the reaction is continuously fed.

[0037] Product separation and characterization The reactants at the reactor outlet enter a high-pressure gas-liquid separator, where they undergo primary flash separation at a pressure of 3.0 MPa. The hydrogen gas released from the top is cooled and demisted by a condenser, then pressurized by a hydrogen compressor and recycled back to the reactor inlet for reuse. At the same time, fresh hydrogen is added to maintain stable system pressure.

[0038] The liquid product at the bottom of the gas-liquid separator is depressurized by a pressure reducing valve and then enters an atmospheric flash tank to remove a small amount of dissolved hydrogen. It is then released into a collection tank and naturally cooled to room temperature to obtain solid hydrogenated polyethylene wax (HPEW).

[0039] Product characterization: Infrared spectroscopy detection (see) Figure 2 (Blue line represents raw polyethylene wax, red line represents hydrogenated polyethylene wax): 908 cm⁻¹ in the hydrogenated product -1 The terminal vinyl characteristic peak at 2914 cm⁻¹ completely disappeared. -1 2847cm -1 The methylene characteristic peak at 1471 cm⁻¹ becomes narrower and its transmittance increases. -1 The weakening of the in-plane rocking vibration peak of the methyl group indicates that the carbon-carbon double bond has been fully hydrogenated and the regularity and uniformity of the molecular chain arrangement have been significantly improved.

[0040] DSC detection (see) Figure 3 The crystallinity of the hydrogenated polyethylene wax was 77.81%, which is significantly higher than that of the raw polyethylene wax (44.42%), proving that hydrogenation treatment effectively improves the crystallinity of the wax.

[0041] Iodine value test: The iodine value of the product was 0.08 g I2 / 100 g, and the degree of unsaturation was significantly reduced.

[0042] Example 2: Preparation of Oxidized Hydrogenated Polyethylene Wax (OHPEW) This embodiment uses the hydrogenated polyethylene wax prepared in Example 1 as a raw material for oxidative modification. The specific steps are as follows: Melt feed Weigh 1000g of the hydrogenated polyethylene wax prepared in Example 1 and add it to a 2L reactor equipped with a stirrer, a bottom vent distributor, and a temperature measuring device. Turn on the stirrer at 300rpm and turn on the heating system to raise the temperature. When the temperature inside the reactor reaches 135°C, the wax completely melts, forming a homogeneous molten system.

[0043] air oxidation reaction After heating to 140℃, the oxygen cylinder was connected, and the oxygen flow rate was controlled at 0.9L / min using a gas flow meter. The oxygen was dispersed into tiny bubbles from the bottom of the reactor through a distributor, ensuring full contact with the molten wax for oxidation. The reaction was carried out under normal pressure. During the reaction, the stirring speed was maintained at 400rpm, and the reaction temperature was kept stable at 140℃ using a temperature control system.

[0044] Acid value monitoring and endpoint control After the oxidation reaction begins, samples are taken every 30 minutes, and the acid value of the samples is determined according to GB / T264-1983 "Determination of Acid Value of Petroleum Products". When the measured acid value reaches 28 mg KOH / g, the oxygen inlet valve is immediately closed, heating is stopped, and the oxidation reaction is terminated. The total reaction time in this example is approximately 7 hours.

[0045] Cooling and characterization After the reaction is terminated, continue stirring and allow it to cool naturally. When the temperature inside the vessel drops to 110°C, release the molten material while it is still hot, pour it into a mold, and allow it to cool naturally to room temperature to obtain oxidized hydrogenated polyethylene wax (OHPEW) solid.

[0046] Product characterization: The product was tested and found to have an acid value of 28 mg KOH / g, a saponification value of 75 mg KOH / g, and a melting point of 103℃; DSC results are shown below. Figure 5 The crystallinity of hydrogenated polyethylene wax was 66.99%, while the crystallinity of traditional oxidized polyethylene wax prepared under the same oxidation conditions was only 44.23%, indicating that the wax after hydrogenation and re-oxidation still maintained a much higher crystallinity than that of traditional oxidized wax.

[0047] Example 3: Preparation of oxidized hydrogenated polyethylene wax emulsion In this embodiment, the hydrogenated polyethylene wax prepared in Example 2 is used as a raw material to prepare an emulsion. The specific steps are as follows: Pre-dispersed melt mix Weigh the raw materials according to the following proportions by weight: 30 parts of hydrogenated polyethylene wax, 6 parts of fatty alcohol polyoxyethylene ether (HLB value 14), and 0.5 parts of potassium hydroxide. Add them to a mixing vessel equipped with a stirrer and a temperature control device. Turn on the stirrer at 300 rpm, heat to 100°C, and maintain the temperature while stirring for 15 minutes to completely melt the wax and thoroughly mix it with the emulsifier and pH adjuster to obtain a homogeneous oil phase mixture.

[0048] Phase inversion emulsification Add 63.5 parts of deionized water to the emulsification vessel, start stirring (400 rpm), heat to 95°C and maintain the temperature. Slowly add the oil phase mixture in the mixing vessel to the hot water in the emulsification vessel at a flow rate of 10 mL / min, keeping the system temperature above 90°C during the addition. After the addition is complete, maintain the temperature and stirring speed and continue stirring for 2 minutes to complete the phase inversion emulsification, obtaining a light blue, semi-transparent primary emulsion.

[0049] Cooling and stabilizing maturation After phase inversion, stop heating and turn on cooling water to slowly lower the temperature, while reducing the stirring speed to 200 rpm. When the system temperature drops to 55℃, stop cooling and continue stirring at the same speed for 15 minutes to further homogenize the emulsion particles and bring the system to a stable state.

[0050] Filter discharge The stabilized emulsion is filtered through a 150-mesh nylon filter to remove a small amount of undispersed large particles. The filtrate is then allowed to cool naturally to room temperature to obtain the finished oxidized hydrogenated polyethylene wax emulsion.

[0051] The emulsion was tested and found to have a solid content of 30%, an average particle size of 42.9 nm, a pH of 8.0, and showed no stratification or precipitation after centrifugation at 3000 rpm for 30 min.

[0052] Examples 4-6: Preparation of hydrogenated polyethylene wax emulsions with different process parameters The preparation steps of Examples 4, 5, and 6 are exactly the same as those of Example 3, except that the raw material ratio, type of emulsifier, type of pH adjuster, and emulsification temperature are adjusted. The specific parameters and product properties are shown in Table 1.

[0053] Table 1. Emulsion preparation formulations and properties under different process parameters.

[0054] Comparative Example Comparative Example 1: Preparation of Traditional Oxidized Polyethylene Wax Emulsion This comparative example uses unhydrogenated ordinary polyethylene wax as raw material and prepares a comparative sample according to the same oxidation and emulsification process as this invention. The specific steps are as follows: Oxidation of ordinary polyethylene wax 1000g of ordinary polyethylene wax raw material (melting point 105℃, crystallinity 45%, iodine value 0.3g I2 / 100g) was weighed and added to a 2L reactor. The reaction was carried out according to the same oxidation process as in Example 2: melting temperature 135℃, oxidation temperature 140℃, oxygen flow rate 0.9L / min, stirring speed 400rpm, and reaction under normal pressure. Acid value was measured every 30 minutes. The reaction was stopped when the acid value reached 28mg KOH / g, and the temperature was lowered to 110℃ before discharge. The product was then allowed to cool naturally to obtain conventional oxidized polyethylene wax (OPEW).

[0055] The product was tested and found to have an acid value of 28 mg KOH / g, a melting point of 98℃, and a crystallinity of 44.23% (DSC determination, see [reference]). Figure 5 It is a pale yellow solid.

[0056] Preparation of traditional oxidized polyethylene wax emulsion Using the conventional oxidized polyethylene wax prepared above as raw material, an emulsion was prepared according to the same emulsification process as in Example 3: the oil phase consisted of 30 parts of oxidized polyethylene wax, 6 parts of fatty alcohol polyoxyethylene ether (HLB=14), and 0.5 parts of potassium hydroxide, with a pre-dispersion temperature of 100°C; the emulsification water temperature was 95°C, and the phase inversion was stirred for 2 min; the temperature was lowered to 55°C and stirred for 15 min; the material was then filtered through a 150-mesh filter.

[0057] The obtained emulsion was found to have a solid content of 30%, an average particle size of 502.24 nm, and a pH of 8.0. It showed obvious stratification after centrifugation at 3000 rpm for 30 min.

[0058] Performance Testing and Result Analysis To verify the performance advantages of the product of the present invention, a series of comparative tests were conducted on the samples of Example 3 and Comparative Example 1. The test methods and results are as follows: (1) Centrifugal acceleration stability test Instrument: Benchtop high-speed centrifuge Test conditions: 3000 rpm, centrifugation time 30 min, test temperature 25℃ Operating steps: Add 10 mL of the emulsion to be tested to a graduated centrifuge tube, and balance the centrifuge tubes at symmetrical positions using the differential weight method; Place the centrifuge tubes into the centrifuge rotor, set the speed to 3000 rpm and the time to 30 minutes, then start the centrifuge; After centrifugation, remove the centrifuge tube and let it stand to observe whether stratification, sedimentation, or floating oil occurs. Take 1 mL of the emulsion from the upper and lower layers of the centrifuge tube using a pipette, and determine the solid content using the drying method (105℃, 3 h). Calculate the stability coefficient R using the following formula: Test results: Example 3 (OHPEW emulsion): No stratification, no sedimentation, no floating oil, stability coefficient R=0.98, close to 1.0; Comparative Example 1 (OPEW emulsion): Obvious stratification was observed, with the upper layer becoming thinner and the lower layer showing thick precipitation, with a stability coefficient R=0.72.

[0059] Results analysis: The OHPEW emulsion prepared by this invention has higher interfacial film strength and can effectively resist droplet compression and aggregation caused by centrifugal force. The emulsion uniformity and stability are significantly better than those of traditional oxidized polyethylene wax emulsion.

[0060] (2) Particle size and particle size distribution test Instrument: 90 nm particle size analyzer Test conditions: test temperature 25℃, scattering angle 90°, medium refractive index 1.33, equilibrium time 60s, dynamic light scattering (DLS) method was used for detection.

[0061] Sample preparation: Since high concentrations of sample viscosity can affect Brownian motion detection results, the sample needs to be diluted to a stable concentration range. Traditional OPEW emulsions have high turbidity and viscosity, so they are diluted 1000 times before testing; the OHPEW emulsion of this invention has low turbidity, so it is diluted 100 times before testing. After dilution, the particle size results do not change with concentration, reflecting the true particle size of the system.

[0062] Operating procedure: Dilute the emulsion to be tested with deionized water to a solid content of about 0.1%, shake well, add it to the sample cell, place it in the instrument for testing, and record the average particle size (Z-mean) and particle size distribution index (PDI).

[0063] Test results: Example 3 (OHPEW Emulsion 1): The particle size distribution curve of Example 3 is shown in the figure below. Figure 6 As shown in (a), the average particle size is 42.9 nm, and PDI = 0.288 (as shown in the image). Figure 6 (b) shows that the particle size is small and the distribution is narrow.

[0064] Comparative Example 1 (OPEW emulsion): The particle size distribution curve of Comparative Example 1 is shown in the figure below. Figure 7 As shown in (a), the average particle size is 502.24 nm, and PDI = 0.327 (as shown in the image). Figure 7 (b) shows that the particle size is large and the distribution is wide.

[0065] Example 6 (OHPEW emulsion 2): average particle size 25.25 nm, PDI=0.120, smaller particle size and narrower distribution.

[0066] Results analysis: The interfacial film formed by the regular molecular chains after hydrogenation during emulsification can effectively inhibit the aggregation between droplets, so that the particles are uniformly dispersed, resulting in smaller particle size and narrower particle size distribution.

[0067] (3) Differential scanning calorimetry (DSC) crystallinity test Instrument: METTLERTOLEDODSC3+ Differential Scanning Calorimeter Test conditions: nitrogen atmosphere, heating rate 10℃ / min, temperature range 20℃~170℃ Operating steps: The emulsion to be tested was placed in an oven and dried at 105°C for 3 hours to completely remove moisture and obtain a solid wax sample. Weigh approximately 8 mg of solid wax sample, seal it in an aluminum crucible, and place it on the sample stage of the instrument. The temperature was increased from 20℃ to 170℃ at a rate of 10℃ / min, and the melting heat flow curve was recorded. The enthalpy of fusion is calculated based on the melting peak area. The crystallinity of the sample is calculated using the enthalpy of fusion of 293 J / g for 100% crystalline polyethylene as a benchmark.

[0068] Test results (see) Figure 5 ): Example 3 corresponds to the dried product of OHPEW emulsion: the wax component has a crystallinity of 59.64% and a sharp melting peak; Comparative Example 1 corresponds to the dried product of OPEW emulsion: the crystallinity of the wax component is 29.49%, and the melting peak is broadened.

[0069] Results analysis: Hydrogenation treatment effectively improves the molecular chain regularity of polyethylene wax. Even after oxidation and emulsification processes, it can still maintain a crystallinity significantly higher than that of traditional oxidized wax, providing a rigid structural basis for the interfacial film.

[0070] (4) Acid resistance stability test Procedure: Take 20 mL of the emulsion to be tested into a stoppered test tube, gradually adjust the pH to 5.0 with 1 mol / L hydrochloric acid solution, shake well and seal, place in a 25℃ constant temperature incubator and let stand for 7 days, observing the state of the emulsion every day.

[0071] Test results: Example 3: After 7 days, the emulsion was uniform, with no flocculation, no stratification, and no sedimentation; Comparative Example 1: Flocculation began to appear on day 3, and obvious sedimentation and stratification appeared on day 7.

[0072] Results analysis: The wax component in the emulsion of this invention has high molecular chain regularity and high crystallinity, forming a dense and orderly interfacial film at the emulsion particle interface. Combined with the stabilizing effect of nonionic emulsifier, the tolerance to pH changes is significantly improved, and the acid resistance is excellent, thus broadening the application scenarios.

[0073] (5) Thermal stability and resistance to yellowing test Operating procedure: Take 30 mL of the emulsion to be tested into a sealed sample bottle, place it in a 60℃ constant temperature water bath for 10 days, observe the appearance of the emulsion regularly, use a colorimeter to measure the yellowness index b* of the sample, and calculate the yellowness change rate.

[0074] Test results: Example 3: After 10 days, the emulsion showed no demulsification or stratification, and the yellowness index changed by less than 5%, with almost no yellowing. Comparative Example 1: Slight demulsification and stratification occurred after 10 days, with a yellowing index change rate of >20%, resulting in a noticeable yellowing.

[0075] Results analysis: The hydrogenation reaction removes unsaturated bonds and unstable oxygen-containing structures from the molecular chain, significantly improving the chemical stability of the wax and effectively inhibiting oxidative yellowing at high temperatures. The product can meet the application needs of high-end fields such as light-colored coatings and bleached fabric finishing.

[0076] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an oxidized hydrogenated polyethylene wax emulsion, comprising the steps of oxidizing and modifying polyethylene wax and emulsifying it to prepare the emulsion, characterized in that, Prior to oxidative modification, a catalytic hydrogenation process is included to regulate the molecular chain, specifically comprising the following steps: (1) Catalytic hydrogenation: The polyethylene wax raw material is hydrogenated with hydrogen under the action of a catalyst, so that the unsaturated bonds in the molecular chain are saturated and the branched structure is regularized to obtain hydrogenated polyethylene wax. (2) Oxidative modification: The hydrogenated polyethylene wax is subjected to an oxidative reaction to introduce oxygen-containing polar groups into the molecular chain to obtain oxidized hydrogenated polyethylene wax; (3) Emulsification molding: The hydrogenated polyethylene wax is mixed with emulsifier, pH adjuster and deionized water, and then emulsified to obtain hydrogenated polyethylene wax emulsion.

2. The method for preparing an oxidized hydrogenated polyethylene wax emulsion according to claim 1, characterized in that, The catalyst mentioned in step (1) is a supported noble metal catalyst or a Raney nickel catalyst; the supported noble metal catalyst is selected from at least one of Pd / C, Pd / Al2O3, and Pt / Al2O3.

3. The method for preparing an oxidized hydrogenated polyethylene wax emulsion according to claim 2, characterized in that, The reaction temperature of the hydrogenation reaction in step (1) is 210-270℃ and the reaction pressure is 2.5-3.5MPa.

4. The method for preparing an oxidized hydrogenated polyethylene wax emulsion according to claim 3, characterized in that, The hydrogenation reaction described in step (1) is carried out in a tubular fixed-bed reactor; the polyethylene wax raw material is preheated and melted and mixed with hydrogen gas, and then introduced into a reaction tube filled with catalyst for reaction. The reaction product is separated by gas-liquid separation to obtain hydrogenated polyethylene wax; the hydrogenated polyethylene wax has an iodine value ≤0.1g I2 / 100g and a crystallinity of 60%~80%.

5. The method for preparing an oxidized hydrogenated polyethylene wax emulsion according to claim 1, characterized in that, The oxidation reaction described in step (2) is oxygen oxidation or air oxidation, the reaction temperature is 130-150℃, and the reaction is carried out under normal pressure.

6. The method for preparing an oxidized hydrogenated polyethylene wax emulsion according to claim 5, characterized in that, In step (2), the oxidation reaction is terminated when the acid value of the product reaches 15-50 mg KOH / g; the melting point of the resulting oxidized hydrogenated polyethylene wax is 90-130℃ and the molecular weight distribution index PDI≤4.

5.

7. The method for preparing an oxidized hydrogenated polyethylene wax emulsion according to claim 6, characterized in that, The resulting oxidized hydrogenated polyethylene wax has an acid value of 20–35 mg KOH / g, a melting point of 100–110 °C, and a crystallinity of 55%–70%.

8. The method for preparing an oxidized hydrogenated polyethylene wax emulsion according to claim 1, characterized in that, In step (3), the raw materials for emulsification include, by mass parts: 10-40 parts of oxidized hydrogenated polyethylene wax, 1-10 parts of emulsifier, 0.1-2 parts of pH adjuster, and 50-85 parts of deionized water; the emulsifier is a nonionic surfactant selected from at least one of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

9. The method for preparing an oxidized hydrogenated polyethylene wax emulsion according to claim 8, characterized in that, Step (3) specifically includes: Mix the oxidized hydrogenated polyethylene wax, emulsifier and pH adjuster, heat to 80-110℃, stir until completely melted and mixed evenly to complete the pre-dispersion; The pre-dispersed mixture was added to deionized water at a temperature above 90°C and stirred to carry out phase inversion emulsification. After emulsification is complete, cool the mixture to 50-60°C and continue stirring until the emulsion system is stable. Undispersed particles were removed by filtration to obtain an oxidized hydrogenated polyethylene wax emulsion.

10. The oxidized hydrogenated polyethylene wax emulsion prepared by the method for preparing an oxidized hydrogenated polyethylene wax emulsion according to any one of claims 1-9, characterized in that, The emulsion has a solid content of 25%–40%, an average particle size of 20–70 nm, a pH of 7.0–8.5, and shows no stratification after centrifugation at 3000 rpm for 30 min.

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