Hydrophobic porous starch with high oil absorbency as well as preparation method and application of hydrophobic porous starch

Abstract

The invention discloses hydrophobic porous starch with high oil absorbency as well as a preparation method and application thereof, which adopts a step-by-step synergistic modification strategy of'controllable enzymolysis-vapor deposition ': firstly, in a buffer system, performing controllable enzymolysis on native starch by using alpha-amylase to construct a porous starch matrix with uniform pore diameter and complete structure; and then performing surface grafting on the porous starch under vacuum and heating conditions by adopting a vapor deposition method and taking long-chain alkyl siloxane as a hydrophobic modifier to realize uniform hydrophobization of the inner and outer surfaces of starch particles. The BET specific surface area of the obtained modified starch is 1.8-2.5 m / g, the average pore size is 1.5-2.5 microns, the water contact angle is larger than 145 degrees, and the oil absorption rate of jojoba oil is not lower than 240%. The product still keeps a dry and loose powder state after absorbing oil, is fine and smooth in touch feeling, is free of greasy and sticky feeling, is suitable for cosmetics such as sunscreen cream, foundation make-up and oil control products and personal care products, and can remarkably reduce the greasy feeling, improve the spreadability and skin fitting performance and enhance the stability of the product at the same time.

Description

Technical Field

[0001] This invention relates to the field of starch modification technology, specifically to a hydrophobic porous starch with high oil absorption and excellent skin feel, its preparation method, and its applications. More specifically, this invention relates to a method for structurally reshaping and surface functionalizing starch particles through a synergistic modification strategy combining enzymatic hydrolysis and vapor-phase chemical deposition, thereby significantly improving their oil absorption performance and skin feel. The product is suitable for high-end cosmetics, personal care products (such as sunscreen, foundation, talcum powder, and oil-control products), and environmentally friendly absorbent materials. Background Technology

[0002] Starch is a widely available, biodegradable, and biocompatible natural polysaccharide, and its modified products have important applications in food, medicine, cosmetics, and industrial adsorption. However, natural starch, due to its rich hydroxyl groups in its molecular chain, exhibits strong hydrophilicity and has limited adsorption capacity for oils (usually with an oil absorption rate of less than 100%). Furthermore, after adsorbing oils, it is prone to gelatinization and clumping, resulting in a sticky texture and poor flowability, which severely limits its application in high-end cosmetics (such as foundation, sunscreen, and oil-control products).

[0003] Currently, technologies for improving the oil absorption performance of starch are mainly divided into two categories: physical modification and chemical modification. Physical modification typically involves preparing porous starch through methods such as hydrothermal treatment, mechanical ball milling, or partial enzymatic hydrolysis to increase the specific surface area and adsorption sites. For example, patent CN102533908A discloses a method for preparing porous starch using a hydrothermal-enzymatic hydrolysis composite method, achieving an oil absorption rate of 133.0%. However, the pores formed by this type of method are often unevenly distributed and structurally fragile. Furthermore, the starch surface remains hydrophilic, making it prone to forming oil-powder aggregates after oil absorption, resulting in limited improvement in skin feel and a tendency to cause structural collapse in high-oil systems.

[0004] Chemical modification mainly involves introducing hydrophobic groups onto starch molecules through esterification, etherification, and cross-linking to enhance their affinity for oils and fats. For example, existing technologies disclose a method for hydrophobic modification of starch using octenyl succinic anhydride (OSA) in an aqueous phase. While this method can improve the hydrophobicity of starch, the reaction takes place in a solution system, causing starch particles to swell or even gelatinize, damaging their morphology and porous structure, thus reducing their adsorption capacity. Furthermore, the hydrophobic chains introduced by OSA modification are relatively short (C8), resulting in little improvement in skin feel, and the product has limited acid and alkali resistance and storage stability.

[0005] Existing research has also attempted to combine porous preparation with hydrophobic modification in order to obtain both high adsorption capacity and good hydrophobicity. However, such methods usually face the following key technical bottlenecks: (1) The liquid chemical modification reagent in the second step is easy to penetrate and block the micropores formed in the first step, resulting in a decrease in porosity and a significant reduction in adsorption performance; (2) The liquid reaction system makes it difficult for the modifier to be evenly distributed on the surface and inside of starch particles, and it is easy to over-modify the particle surface while the internal modification is insufficient, affecting the consistency of product performance; (3) Most liquid hydrophobic modification reaction conditions are severe (such as strong alkali and high temperature), which can easily lead to starch degradation or structural damage.

[0006] Therefore, developing a novel starch modification method that can simultaneously achieve high porosity, high hydrophobicity, uniform modification, and without damaging the pore structure is key to breaking through existing technological bottlenecks and meeting the application needs of high-end cosmetics. Summary of the Invention

[0007] To address the aforementioned problems in the existing technology, this invention provides a highly oil-absorbing hydrophobic porous starch, its preparation method, and its applications. The process conditions are mild, effectively protecting the porous structure of the starch and achieving uniform modification of the inner and outer surfaces, resulting in a hydrophobic porous starch with high oil absorption and a dry and delicate skin feel. The product is suitable for high-end cosmetics, personal care products (such as sunscreen, foundation, talcum powder, and oil-control products), and environmentally friendly adsorbent materials.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing highly oil-absorbing hydrophobic porous starch, comprising the following steps: S1. Controllable enzymatic hydrolysis for pore creation: Native starch was dispersed in a buffer solution to prepare a 30-40% (w / v) suspension. α-Amylase (enzyme activity ≥5000 U / g) was added at 0.5-1.5% of the dry weight of native starch. The mixture was reacted at 45-55℃ and 80-120 rpm for 4-8 hours. Under these conditions, the enzyme selectively hydrolyzes starch granules from weak points on the surface, forming a porous structure with interconnected internal structures and a relatively intact external surface. The mixture was then rapidly heated to 90℃ and held for 10 minutes to inactivate the enzyme. After cooling, the mixture was filtered, thoroughly washed with deionized water, and then freeze-dried to obtain pretreated porous starch.

[0009] The specific process conditions for freeze drying are as follows: pre-freeze at -40℃ for 2 hours, then gradually increase the temperature to -20℃ at a rate of 5℃ per hour below a vacuum of 10Pa and hold for 4 hours, then increase the temperature to 0℃ and hold for 2 hours, and finally increase the temperature to 25℃ and hold for 2 hours.

[0010] In step S1, controlling the amount of α-amylase at 0.5-1.5% is crucial. Too low a concentration (<0.5%) will result in insufficient enzymatic hydrolysis, inadequate starch pore structure formation, and decreased oil absorption. Too high a concentration (>1.5%) will cause excessive hydrolysis, damaging the integrity of starch granules and leading to pore collapse. The enzymatic hydrolysis temperature (45-55℃) and reaction time (4-8h) jointly regulate the hydrolysis rate. Too low a temperature or too short a time will result in incomplete hydrolysis and uneven pore size, while too high a temperature or too long a time will trigger non-specific hydrolysis, reducing pore uniformity. S2, vapor-phase hydrophobic modification: The pretreated porous starch obtained in step S1 was placed in a vacuum reactor. The long-chain alkylsiloxane hydrophobic modifier was diluted with anhydrous ethanol and uniformly applied to the starch surface by atomization spraying. The amount of long-chain alkylsiloxane was 3-8% of the dry weight of the pretreated porous starch. Subsequently, the vacuum reactor was sealed and the reaction was carried out at a vacuum of -0.08 MPa to -0.1 MPa and a temperature of 80-110℃ for 2-4 hours. Under vacuum and heating conditions, the long-chain alkylsiloxane vaporized and penetrated into the micropores of the starch particles, and underwent a condensation reaction with the hydroxyl groups on the starch molecules to form stable Si-OC bonds, thereby achieving uniform hydrophobic grafting from the inside out. After the reaction was completed, the mixture was cooled to room temperature and washed with an organic solvent (ethanol) to remove the physically adsorbed modifier. Finally, it was vacuum dried at 50℃ to obtain the final product - highly oil-absorbent hydrophobic porous starch.

[0011] Furthermore, the volume ratio of the long-chain alkylsiloxane to the anhydrous ethanol is 1:3 to 1:5.

[0012] In step S2, long-chain alkylsiloxanes are mixed with anhydrous ethanol at a volume ratio of 1:3 to 1:5 (this ratio ensures that the modifier is fully atomized and evenly covers the starch surface; too high a ratio (e.g., >1:3) will result in excessive modifier concentration, which can easily lead to local aggregation and blockage of pores; too low a ratio (e.g., <1:5) will result in excessive dilution and reduce grafting efficiency). The mixture is then evenly sprayed onto the starch surface using an atomizing spraying device. The modifier dosage is controlled at 3%-8% of the dry weight of the starch. The 3%-8% dosage of long-chain alkylsiloxanes is based on a balance between uniform grafting and cost: too low a dosage (<3%) will result in insufficient hydrophobicity and a low contact angle; too high a dosage (>8%) will cause intermolecular cross-linking, blocking pores and reducing oil absorption.

[0013] Subsequently, the reactor was sealed, and a vacuum was applied to -0.08 MPa to -0.1 MPa, followed by reaction at 80-110℃ for 2-4 hours. The coordinated control of vacuum (-0.08 MPa to -0.1 MPa), temperature (80-110℃), and time (2-4 hours) is crucial for the vapor deposition method: Too low a vacuum (e.g., >-0.08 MPa) reduces the diffusion kinetics of the modifier (long-chain alkylsiloxane), leading to uneven modification of internal pores; too high a vacuum (e.g., <-0.1 MPa), while enhancing diffusion, increases energy consumption. Too low a temperature (<80℃) results in insufficient vaporization of the modifier and a slow grafting reaction; too high a temperature (>110℃) causes thermal degradation of starch. Too short a time (<2 hours) results in insufficient grafting; too long a time (>4 hours) has no significant effect on performance improvement and wastes energy.

[0014] This invention, through the optimization of the above parameters, significantly differs from existing wet modification techniques, avoiding the pore blockage problem caused by solvent wetting. Under vacuum and heating conditions, the modifier (long-chain alkylsiloxane) vaporizes and penetrates deep into the micropores of starch particles, undergoing a condensation reaction with the hydroxyl groups on the starch molecules to form stable Si-OC bonds, thereby achieving uniform hydrophobic grafting from the inside out.

[0015] Furthermore, the long-chain alkylsiloxane is an alkyltrialkoxysilane with a carbon chain length of C12-C18.

[0016] Preferably, the long-chain alkylsiloxane is hexadecyltrimethoxysilane.

[0017] Furthermore, the original starch is corn starch, tapioca starch, or potato starch.

[0018] Furthermore, the buffer solution is a citrate-sodium citrate buffer solution with a pH of 5.8-6.2.

[0019] In a second aspect, the present invention provides a highly oil-absorbing hydrophobic porous starch, which is prepared by the above-described preparation method.

[0020] Furthermore, its BET specific surface area is 1.8-2.5 m² / g, its average pore size is 1.5-2.5 μm, and its water contact angle is greater than 145°.

[0021] Furthermore, its oil absorption rate for jojoba oil and caprylic / capric triglyceride light oils is no less than 240%.

[0022] A third aspect of the present invention provides an application of the above-mentioned highly oil-absorbing hydrophobic porous starch, wherein the highly oil-absorbing hydrophobic porous starch is used in cosmetics, personal care products (such as sunscreen, foundation, talcum powder, oil-control products) or oil-absorbing materials.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention first constructs an adsorption framework with high porosity through a precisely controlled enzymatic hydrolysis process, and then performs surface hydrophobic functionalization through vapor deposition. The two-step method has a clear objective and a significant synergistic effect, which not only ensures high oil absorption capacity, but also gives it an ultimate hydrophobic feel.

[0024] (2) This invention is the first to apply the vapor deposition technology of long-chain alkylsiloxanes to starch modification. This dry process completely avoids the wetting, swelling, and clogging of porous structures by liquid solvents, maximizing the preservation of the integrity and accessibility of the pores. The vacuum environment provides a strong diffusion driving force for hydrophobic agent molecules, ensuring that they can reach the deepest part of the pores and achieve uniform modification in three-dimensional space. The formed Si-OC bonds have high chemical stability, are resistant to hydrolysis, and are suitable for formulation systems with a wide pH range.

[0025] (3) The modified starch of this invention has a well-preserved pore structure and its internal surface is effectively hydrophobic. Its adsorption rate for common cosmetic oils such as jojoba oil and silicone oil can reach 240-260%, which is significantly better than existing products. The introduction of long-chain alkyl groups provides strong hydrophobicity, so that the starch particles after oil absorption remain in a discrete powder state, with a dry and smooth feel, without clumping or greasiness. The sensory evaluation score is significantly higher than that of the comparative example. The formed Si-OC bond has high chemical stability and is resistant to hydrolysis, making it suitable for cosmetic systems with a wide pH range. Moreover, its addition can improve the room temperature and high and low temperature stability of the formulation. Scanning electron microscopy (SEM) and nitrogen adsorption-desorption tests have confirmed that the product of this invention has a uniform microporous structure and a high specific surface area, and a water contact angle greater than 145°, exhibiting superhydrophobic properties. When applied to cosmetics, it can effectively adsorb excess oil, prevent high-temperature oil separation, improve the stability of the paste, and give it a matte and dry skin feel. Attached Figure Description

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] Figure 1 SEM images of the pretreated porous starch (A) and the final modified starch (B) prepared for Example 1.

[0028] Figure 2 These are photographs of the water contact angle test of Product (B) of Example 1 and Product (C) of Comparative Example 1. 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] Example 1 The preparation steps of a highly oil-absorbing, hydrophobic, porous starch are as follows: (1) Controllable enzymatic hydrolysis for pore creation: Weigh 100g of corn starch (dry basis) and add it to a citrate-sodium citrate buffer solution at pH 6.0 to prepare a suspension of approximately 36% (w / v). Then add 1.0g of α-amylase (1% of the dry starch weight) and place the mixture in a 50℃ constant temperature water bath shaker, shaking at 100 rpm for 6 hours. After the reaction, heat the mixture to 90℃ and hold for 10 minutes to inactivate the enzyme. After cooling to room temperature, filter the mixture and wash it three times with deionized water to remove residual buffer salts and soluble sugars. Finally, freeze-dry the filter cake under the following conditions: pre-freeze at -40℃ for 2 hours, then gradually increase the temperature to -20℃ at a rate of 5℃ per hour under a vacuum of less than 10 Pa and hold for 4 hours, then increase the temperature to 0℃ and hold for 2 hours, and finally increase the temperature to 25℃ and hold for 2 hours to obtain pretreated porous starch (A).

[0031] (2) Vapor-phase hydrophobic modification: Weigh 20g of the pretreated porous starch (A) and spread it evenly in a vacuum reactor lined with polytetrafluoroethylene. Mix 1.0g of hexadecyltrimethoxysilane (HDTMS) with 4.0g of anhydrous ethanol (volume ratio approximately 1:4) and spray the mixture evenly onto the starch surface through an atomizing nozzle, ensuring uniform coverage. The amount of HDTMS used is 5% of the dry weight of the starch. Seal the reactor, turn on the vacuum pump, and evacuate to -0.09MPa. Then, start the heating sequence and raise the temperature to 100℃ for 3 hours. After the reaction is complete, allow it to cool naturally to room temperature. Remove the product, wash it three times with anhydrous ethanol, and finally dry the filter cake in a vacuum drying oven at 50℃ for 4 hours to obtain the final modified starch (B).

[0032] Example 2 (1) Controllable enzymatic hydrolysis for pore creation: Weigh 100g of cassava starch (dry basis) and add it to a citrate-sodium citrate buffer solution at pH 5.8 to prepare a 30% (w / v) suspension. Add 0.5g of α-amylase (0.5% of the dry starch weight) and react at 45℃ and 80rpm for 8 hours. Subsequent enzyme inactivation, washing, and freeze-drying steps are the same as in Example 1 to obtain pretreated porous starch.

[0033] (2) Vapor-phase hydrophobic modification: Weigh 20g of pretreated porous starch, mix 0.6g of HDTMS (3% of dry starch) with 1.8g of anhydrous ethanol (volume ratio 1:3), and atomize and spray according to the method in Example 1. React at -0.08MPa and 80°C for 4h. After washing and drying according to the method in Example 1, the product is obtained.

[0034] Example 3 (1) Controllable enzymatic hydrolysis for pore creation: Weigh 100g of potato starch (dry basis) and add it to a citrate-sodium citrate buffer solution at pH 6.2 to prepare a 40% (w / v) suspension. Add 1.5g of α-amylase (1.5% of the dry starch weight) and react at 55℃ and 120rpm for 4 hours. Subsequent processing is the same as in Example 1 to obtain pretreated porous starch.

[0035] (2) Vapor-phase hydrophobic modification: Weigh 20g of pretreated porous starch, mix 1.6g of HDTMS (8% of the dry starch) with 8.0g of anhydrous ethanol (volume ratio 1:5), and atomize and spray according to the method in Example 1. React at -0.1MPa vacuum and 110℃ for 2h. After washing and drying according to the method in Example 1, the product is obtained.

[0036] Comparative Example 1 This comparative example discloses a conventional method for preparing porous starch, which only involves the first step of enzymatic hydrolysis in Example 1, and the resulting product is denoted as (C).

[0037] Comparative Example 2 This comparative example discloses the conventional OSA wet modification of starch, the specific process of which is as follows: 100g of raw corn starch was weighed and suspended in 150mL of deionized water. The pH was adjusted to 8.5 with 3wt% NaOH solution. While stirring vigorously, 3% (by weight of dry starch) of octenyl succinic anhydride (OSA) was slowly added dropwise, with alkali solution continuously added to maintain the pH between 8.5 and 9.0. After the reaction was complete, the pH was adjusted to 6.5 with dilute hydrochloric acid. The mixture was then filtered, washed with water, and dried to obtain OSA-modified starch, denoted as (D).

[0038] Comparative Example 3 Take 20g of the pretreated porous starch (A) obtained in Example 1 and perform hydrophobic treatment according to the OSA wet modification process in Comparative Example 2 to obtain the product, denoted as (E).

[0039] Comparative Example 4 Weigh 20g of the original corn starch obtained in Example 1, disperse it in 100mL of anhydrous ethanol, add 1.0g of HDTMS (5% of the dry starch), and stir the mixture at atmospheric pressure and 80℃ for 3h. After the reaction, wash and dry to obtain product (F).

[0040] Comparative Example 5 Comparative Example 5 is a comparative test case of Example 1. The difference between the two is: In this comparative example, 0.3g of α-amylase was added, accounting for 0.3% of the original starch dry weight.

[0041] Comparative Example 6 Comparative Example 6 is a comparative test case of Example 1. The difference between the two is: In this comparative example, 1.8g of α-amylase was added, accounting for 1.8% of the original starch dry weight.

[0042] Comparative Example 7 Comparative Example 7 is a comparative test case of Example 1. The difference between the two is: In this comparative example, 0.4 g of hexadecyltrimethoxysilane (HDTMS) was mixed with 4.0 g of anhydrous ethanol (volume ratio approximately 1:10). The amount of long-chain alkylsiloxane used was 2% of the dry weight of the pretreated porous starch.

[0043] Comparative Example 8 Comparative Example 8 is a comparative test case of Example 1. The difference between the two is: In this comparative example, 2.0 g of hexadecyltrimethoxysilane (HDTMS) was mixed with 4.0 g of anhydrous ethanol (volume ratio approximately 1:2). The amount of long-chain alkylsiloxane used was 10% of the dry weight of the pretreated porous starch.

[0044] Performance testing and data analysis: 1. Characterization of structure and physicochemical properties Scanning electron microscopy (SEM) was used to observe the original starch, pretreated porous starch (A), and final modified starch (B) in Example 1. The results are as follows: Figure 1 As shown, the original starch has a smooth surface; the pretreated porous starch (A) has a large number of uniform micropores on its surface, indicating that the starch surface forms a uniform and complete microporous structure after enzymatic hydrolysis; the final modified starch product (B) has a clear pore structure and no obvious blockage, indicating that the surface morphology of the starch granules remains intact after vapor deposition and no pore blockage is observed.

[0045] The specific surface area and pore size of the modified starch in each example and comparative example were tested using the BET nitrogen adsorption method. Nitrogen was used as the adsorbate, and the BET specific surface area was measured at 77 K. The pore size distribution was calculated using the BJH model. The test results are shown in Table 1.

[0046] The water contact angle of the modified starch in each embodiment and comparative example was measured using a static contact angle meter. The test results are shown in Table 1 and... Figure 2 , Figure 2 The illustration on the left shows that the water droplet is spherical on the sample surface with a contact angle of 152°, indicating that the product (B) prepared in Example 1 has superhydrophobicity; Figure 2 The diagram on the right shows that the water droplets are rapidly absorbed with a contact angle of less than 30°, indicating that the product (C) prepared in Comparative Example 1 is hydrophilic.

[0047] Table 1 sample BET specific surface area (m² / g) Average pore size (μm) Water contact angle (°) Remark Original starch 0.5±0.1 - 25±3 Hydrophilic, water droplets quickly soak in Comparative Example 1(C) 1.6±0.2 1.8±0.3 30±4 Hydrophilic, pores not modified Comparative Example 2(D) 0.8±0.1 - 105±5 It has moderate hydrophobicity and a dense structure. Comparative Example 3(E) 1.2±0.2 1.5±0.4 98±6 The pores are partially blocked, reducing hydrophobicity. Comparative Example 4(F) 1.0±0.2 1.2±0.3 110±5 Wet modification method, pore blockage Comparative Example 5 1.2±0.2 1.3±0.2 125±5 Insufficient enzymatic hydrolysis and inadequate pore development Comparative Example 6 1.4±0.3 1.6±0.4 118±6 Excessive enzymatic hydrolysis leads to partial structural damage. Comparative Example 7 1.8±0.2 1.9±0.3 132±4 The modifier was over-diluted and lacked sufficient hydrophobicity. Comparative Example 8 1.5±0.3 1.4±0.2 140±5 Excessive modifier concentration leads to blockage of pores. Example 1(B) 2.2±0.3 2.0±0.2 152±3 Superhydrophobic, with well-preserved pores Example 2 1.9±0.2 1.8±0.3 148±3 Good hydrophobicity, and well-preserved pores. Example 3 2.1±0.3 2.2±0.2 150±3 Superhydrophobic, with excellent performance The oil absorption performance of the products in each embodiment and comparative example was tested, and the test results are shown in Table 2. The test methods are as follows: Accurately weigh 1.0 g (W1) of sample into a centrifuge tube, slowly add jojoba oil dropwise, and gently stir with a glass rod until the sample is completely soaked in oil and there is no dry powder. Let stand for 30 min to allow the oil to be fully adsorbed, then centrifuge at 4000 rpm for 20 min, discard the free oil, and weigh the total weight of the centrifuge tube (W2). Oil absorption rate (%) = [(W2 - W1 - centrifuge tube weight) / W1] × 100%. Each sample was tested in triplicate, and the average value was taken.

[0048] Table 2 sample Oil absorption rate (%) Relative starch enhancement rate (%) Original starch 88±5 - Comparative Example 1(C) 145±7 64.80% Comparative Example 2(D) 112±6 27.30% Comparative Example 3(E) 165±8 87.50% Comparative Example 4(F) 130±6 47.7% Comparative Example 5 158±8 79.50% Comparative Example 6 172±9 95.50% Comparative Example 7 195±10 121.60% Comparative Example 8 180±8 104.50% Example 1(B) 248±10 181.8% Example 2 235±9 167.00% Example 3 255±11 189.80% Sensory evaluation tests were conducted on the products in each embodiment and comparative example. The test results are shown in Table 3. The test methods are as follows: Fifteen trained sensory evaluators conducted blind tests on the oil-absorbing samples. Evaluation criteria included: oiliness (1 = very oily, 5 = not oily at all), smoothness (1 = very sticky, 5 = very dry), and powder texture (1 = clumpy and rough, 5 = smooth and fine). Average scores for each criterion and an overall skin feel score (average of the three criteria) were calculated.

[0049] The methods for oil absorption treatment and oil absorption volume control are as follows: 1. Standardized procedure for sample oil absorption: Accurately weigh 2.0g of each sample (accurate to 0.0001g) and place it in a 50mL beaker.

[0050] Using a microburette, add standard jojoba oil slowly at a constant rate (approximately 0.1 mL / min).

[0051] During the dropwise addition, use a glass rod to gently and continuously stir at a constant rate (60 rpm) to ensure that the oil and sample are in full and uniform contact.

[0052] Stop adding the powder when it changes from a loose state to a completely moist state with no dry powder particles and initially shows a slight tendency to agglomerate. This endpoint determination should be performed by the same experienced laboratory technician to ensure consistency in the determination criteria for all samples.

[0053] Record the volume (V, mL) of jojoba oil consumed and allow it to stand for 30 minutes to allow the oil to be fully absorbed.

[0054] 2. Precise control and calculation of oil absorption: The amount of oil absorbed was determined by the mass difference of jojoba oil before and after the addition. Since a microburette was used and the density of jojoba oil was known (approximately 0.865 g / mL, measured before the experiment), the amount of oil adsorbed could be accurately calculated.

[0055] The actual oil absorption rate (%) is calculated using the following formula and serves as objective data on the sample's actual adsorption capacity during sensory evaluation: Oil absorption rate (%) = [(volume of oil consumed V × oil density) / sample mass] × 100%.

[0056] The target oil absorption rate of the samples used for sensory evaluation is uniformly controlled at 90% of their maximum oil absorption rate (for example, if a sample's maximum oil absorption rate is 250%, then the oil absorption rate is controlled at around 225% during sensory evaluation). This is to simulate the near-saturated absorption state of the product in actual use, more realistically reflecting its skin feel in high-oil environments, while avoiding potential oil seepage due to complete saturation.

[0057] 3. Parallel Samples and Data Recording: Each sample was processed in triplicate for sensory evaluation. Evaluators evaluated the three parallel samples of the same product, and the average score was used as their final score to minimize operational error.

[0058] Table 3. Sensory evaluation results of the samples after oil absorption (mean score ± standard deviation) sample Greasiness (the higher the better) Smoothness (the higher the better) Powder feel (the higher the better) Overall skin feel score Comparative Example 1 (C) 2.3 ± 0.4 2.5 ± 0.5 2.7 ± 0.4 2.5 ± 0.3 Comparative Example 2 (D) 3.2 ± 0.5 2.8 ± 0.4 2.9 ± 0.5 3.0 ± 0.3 Comparative Example 3 (E) 2.9 ± 0.4 2.6 ± 0.5 2.8 ± 0.4 2.8 ± 0.3 Comparative Example 4 (F) 3.0±0.4 2.9±0.5 3.1±0.4 3.0±0.3 Comparative Example 5 2.8±0.5 2.7±0.4 2.9±0.5 2.8±0.3 Comparative Example 6 2.6±0.4 2.5±0.6 2.7±0.4 2.6±0.4 Comparative Example 7 3.5±0.5 3.3±0.4 3.4±0.5 3.4±0.3 Comparative Example 8 3.2±0.6 3.1±0.5 3.3±0.4 3.2±0.4 Example 1 (B) 4.7 ± 0.3 4.6 ± 0.3 4.5 ± 0.4 4.6 ± 0.2 Example 2 4.5±0.4 4.4±0.3 4.3±0.4 4.4±0.2 Example 3 4.6±0.3 4.5±0.4 4.4±0.3 4.5±0.2 Cosmetic application testing (taking sunscreen as an example) Basic formula: organic sunscreen (10%), titanium dioxide (15%), jojoba oil (10%), caprylic / capric triglycerides (10%), emulsifier, thickener, deionized water, etc.

[0059] Experimental group: 5% of the modified starch (B) prepared in Example 1 of this invention was added to the basic formula.

[0060] Control group 1: No oil absorbent was added to the basic formula (blank).

[0061] Control group 2: Sample (C) prepared by adding 5% of Comparative Example 1 to the basic formulation.

[0062] Control group 3: Sample (D) prepared by adding 5% of Comparative Example 2 to the basic formulation.

[0063] Control group 4: Sample (E) prepared by adding 5% of Comparative Example 3 to the basic formulation.

[0064] Control group 5: Sample (F) prepared by adding 5% of Comparative Example 4 to the basic formulation.

[0065] Control group 6: The sample prepared by adding 5% of the comparative example 5 to the basic formula.

[0066] Control group 7: The sample prepared by adding 5% of the comparative example 6 to the basic formula.

[0067] Control group 8: The sample prepared by adding 5% of the comparative example 7 to the basic formula.

[0068] Control group 9: The sample prepared by adding 5% of the comparative example 8 to the basic formula.

[0069] Test results: Sunscreen efficacy: In vitro SPF value tests showed no significant differences among the three groups (experimental group, control group 1, and control group 2) (P>0.05), indicating that the addition of the starch of this invention does not affect the sunscreen efficacy.

[0070] Sensory evaluation: The results of a blind test with 10 participants showed that the experimental group product had a significantly lower greasiness than the two control groups (control group 1 and control group 2), better spreadability, and left the skin with a matte and dry feel after application.

[0071] Stability testing: The product was subjected to accelerated stability cycling tests for 3 months at 40℃ / 75%RH and -15℃ (one cycle per month). The results are shown in Table 4 below.

[0072] Table 4. Results of sunscreen formulation stability test sample Appearance changes Centrifugal stability Heat and cold resistance Skin feel retention experimental group No oil separation, no water separation, uniform texture 4000rpm, 30min, no stratification Cycled at 40℃ / -15℃ 3 times, and the properties return to normal after returning to room temperature. Even after storage, the skin still feels dry when applied. Control group 1 There was no obvious oil separation, but the paste was slightly soft. 4000rpm, 30min, no stratification Cycle at 40℃ / -15℃ 3 times; after recovery, a slight oil seepage will occur. After storing and applying, it feels noticeably oily. Control group 2 Slight oil separation, surface has an oily sheen 4000 rpm, 30 min, slight stratification Significant oil-water separation occurred after two cycles at 40℃ / -15℃. Applying it after storage increases the greasiness. Control group 3 Slight oil separation, the paste is slightly soft. 4000 rpm, 30 min, slight stratification Oil separation occurred after two cycles at 40℃ / -15℃. The oiliness increases after storage. Control group 4 Obvious oil separation, oily surface 4000 rpm, 30 min, obvious stratification Oil and water separate after one cycle at 40℃ / -15℃. Extremely greasy after storage Control group 5 Oil separation was obvious, and the paste softened. 4000 rpm, 30 min, severe stratification Unable to complete loop test Poor skin feel Control group 6 Oil-water separation is obvious 3000rpm is the point at which the layers separate. Poor stability Unable to be used normally Control group 7 Slight oil separation is acceptable. 4000 rpm, 30 min, slight stratification Stability decreases after 2 cycles Skin feel is average control group 8 Oil separation is obvious 4000 rpm, 30 min, obvious stratification Problem occurred after one loop. Poor skin feel Control group 9 Severe oil separation 2000rpm is the point at which the layers separate. Extremely poor stability not available This invention successfully prepared a hydrophobic porous starch with ultra-high oil absorption, superhydrophobic properties, and excellent skin feel through a synergistic modification process of "controlled enzymatic hydrolysis-vapor deposition". This method effectively solves key problems in traditional modification techniques such as pore blockage, uneven modification, and sticky skin feel. The prepared product significantly outperforms existing technologies in terms of structure, adsorption performance, and cosmetic application, demonstrating promising industrialization prospects and market application value.

[0073] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a highly oil-absorbing, hydrophobic, porous starch, characterized in that, Includes the following steps: S1. Controllable enzymatic hydrolysis for pore creation: The original starch was dispersed in a buffer solution to prepare a suspension. 0.5-1.5% of α-amylase based on the dry weight of the original starch was added. The mixture was reacted at 45-55℃ and 80-120 rpm for 4-8 hours. The enzyme was then inactivated by heating. After washing and freeze-drying, pretreated porous starch was obtained. S2, vapor-phase hydrophobic modification: The pretreated porous starch obtained in step S1 was placed in a vacuum reactor. The long-chain alkylsiloxane hydrophobic modifier was diluted with anhydrous ethanol and then uniformly applied to the starch surface by atomization spraying. The amount of long-chain alkylsiloxane was 3-8% of the dry weight of the pretreated porous starch. The reaction was then carried out for 2-4 hours under the conditions of vacuum degree of -0.08 MPa to -0.1 MPa and temperature of 80-110℃. After the reaction was completed, the starch was washed with organic solvent and dried to obtain highly oil-absorbing hydrophobic porous starch.

2. The method for preparing highly oil-absorbing, hydrophobic, porous starch according to claim 1, characterized in that, The long-chain alkylsiloxane is an alkyltrialkoxysilane with a carbon chain length of C12-C18.

3. The method for preparing highly oil-absorbing, hydrophobic, porous starch according to claim 2, characterized in that, The long-chain alkylsiloxane is hexadecyltrimethoxysilane.

4. The method for preparing highly oil-absorbing, hydrophobic, porous starch according to claim 1, characterized in that, The volume ratio of the long-chain alkylsiloxane to the anhydrous ethanol is 1:3 to 1:

5.

5. The method for preparing highly oil-absorbing, hydrophobic, porous starch according to claim 1, characterized in that, The original starch is corn starch, cassava starch, or potato starch.

6. The method for preparing highly oil-absorbing, hydrophobic, porous starch according to claim 1, characterized in that, The buffer solution is a citrate-sodium citrate buffer solution with a pH of 5.8-6.

2.

7. A highly oil-absorbing, hydrophobic, porous starch, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The highly oil-absorbing, hydrophobic, porous starch according to claim 7, characterized in that, Its BET specific surface area is 1.8-2.5 m² / g, its average pore size is 1.5-2.5 μm, and its water contact angle is greater than 145°.

9. The highly oil-absorbing, hydrophobic, porous starch according to claim 7 or 8, characterized in that, Its oil absorption rate for jojoba oil and caprylic / capric triglyceride light oils is no less than 240%.

10. An application of a highly oil-absorbing, hydrophobic, porous starch as described in any one of claims 7-9, characterized in that, The highly oil-absorbing hydrophobic porous starch is used in cosmetics, personal care products, or oil-absorbing materials.

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