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CN-120775070-B - High-substitution-degree hydrophobic starch and preparation method and application thereof

CN120775070BCN 120775070 BCN120775070 BCN 120775070BCN-120775070-B

Abstract

The invention discloses hydrophobic starch with high substitution degree, and a preparation method and application thereof, and belongs to the field of high polymer materials. The hydrophobic starch is octenyl succinic acid modified starch, the substitution degree of the hydrophobic group is more than or equal to 1.8, the Fourier transform infrared spectrum (FTIR) of the hydrophobic starch does not have obvious characteristic peaks in the range of 3300-3400cm ‑1 , and the melting temperature is less than or equal to 150 ℃. The starch film packaging material obtained by hot pressing the hydrophobic starch is placed in an environment with relative humidity of 5% for at least 48 hours, and the elongation at break is more than or equal to 9%. The invention realizes normal-temperature homogeneous modification of starch through alkaline gelatinization, can effectively improve the grafting rate and uniformity of hydrophobic groups, and the obtained product has good thermoplasticity, can be used for preparing a film material through melt hot pressing, keeps excellent toughness in an ultralow humidity environment, and has wide application potential in the field of green drying packaging.

Inventors

  • YANG YIWEN
  • YU LONG
  • FU JUN
  • XU YUNLONG
  • YANG CHENGUANG
  • Duan Qingfei
  • XIE HUIFANG

Assignees

  • 河南省科学院
  • 河南省科学院化学研究所

Dates

Publication Date
20260512
Application Date
20250620

Claims (9)

  1. 1. A method for preparing hydrophobic starch, characterized in that the method comprises the following steps: (1) Adding starch into water to prepare suspension, slowly dripping the suspension into sodium hydroxide solution under the condition of stirring, gradually increasing the stirring speed to 1000-1500 rpm, and controlling the stirring time to be not less than 30 min to obtain gelatinized starch solution; (2) Dripping octenyl succinic anhydride into the gelatinized starch solution according to the mol ratio of (2-3) 1 to glucose units in the starch, stirring and reacting for 4-8h at 1500-2500 rpm, and controlling the pH of the solution in the reaction process to be 9-11; (3) After the reaction is finished, adding acid to neutralize and precipitate a product, and washing, dialyzing and drying to obtain the hydrophobically modified starch; the ratio of the sodium hydroxide to the starch in the step (1) is (1.5-2.0) g to 10g.
  2. 2. The process according to claim 1, wherein the amylose content of the starch in step (1) is not less than 50%.
  3. 3. The process according to claim 1 or 2, wherein the molar ratio of octenyl succinic anhydride to glucose units in starch in step (2) is 3:1.
  4. 4. The method according to claim 1 or 2, wherein in the step (2), the dropping speed is 0.01 to 0.05mL/s; And/or stirring and reacting for 4-6 hours under the condition of 1500-2000 rpm in the step (2).
  5. 5. The method according to claim 1 or 2, wherein the step of controlling the pH of the solution during the reaction in step (2) to 9-11 comprises monitoring the pH of the solution in real time using a pH meter, and adding sodium hydroxide solution when the pH of the solution approaches 9.
  6. 6. The method according to claim 1 or 2, wherein in the step (3), the acid used in the acid neutralization step comprises hydrochloric acid, and/or in the step (3), the washing step is to add 1-3 times the volume of absolute ethanol to the reaction solution containing the precipitated product for washing and then centrifuging, and/or the washing times are 1-3 times, and/or in the step (3), the dialysis is performed by using a dialysis bag having a molecular weight cut-off of 8,000-14,000 Da.
  7. 7. The hydrophobic starch obtained by the preparation method according to any one of claims 1 to 6, wherein the hydrophobic starch is octenyl succinic acid modified starch, the substitution degree of the octenyl succinic acid ester group of the hydrophobic group is not less than 1.8, the Fourier transform infrared spectrum of the hydrophobic starch does not have obvious characteristic peaks in the range of 3300 to 3400cm -1 , and the melting temperature of the hydrophobic starch is not more than 150 ℃.
  8. 8. Use of a hydrophobic starch according to claim 7 for the preparation of packaging materials.
  9. 9. A packaging material, characterized in that the packaging material is a starch film with the thickness of 0.25-0.3mm obtained by hot-pressing the hydrophobic starch of claim 7 for 9-12 minutes under the conditions of 150 ℃ and 6 MPa, and the elongation at break of the packaging material is more than or equal to 9% after the packaging material is stored for at least 48 hours under the environment with the relative humidity of 5%.

Description

High-substitution-degree hydrophobic starch and preparation method and application thereof Technical Field The invention relates to the field of high polymer materials, in particular to hydrophobic starch with high substitution degree, and a preparation method and application thereof. Background As a typical natural polysaccharide biological macromolecule, the starch has the advantages of easily available raw materials, low cost, environmental protection and the like, and the edible characteristic of the starch makes the starch an ideal substrate for food and medicine packaging. However, for ultra low humidity (relative humidity not exceeding 5%) packaging environments, starch based packaging materials have a critical commonality problem of toughness dip, even brittle shattering. This phenomenon makes it difficult to meet the packaging requirements of baked and fried foods and parts of medicines, and difficult to replace the predominance of non-degradable materials such as Polyethylene (PE), polypropylene (PP) and the like in the dry packaging market. The reason is that when starch and other polyhydroxy rigid polymers are subjected to tensile force, the polyhydroxy rigid polymers are difficult to flexibly deform, and the polyhydroxy rigid polymers mainly depend on the fracture recombination of a hydrogen bond network among molecular chains and the energy dissipation of the slippage of the molecular chains. However, the hydrogen bond is extremely sensitive to the moisture content, and the intensity and dynamic behavior of the hydrogen bond are regulated and controlled by water molecules through double functions, namely (1) the water molecules can prolong the length of the hydrogen bond between molecular chains and reduce the bond energy of the hydrogen bond, and (2) the migration capacity of the water molecules enables the hydrogen bond sites to have dynamic variability, so that the activity capacity of the molecular chains is effectively enhanced. Under the condition of ultralow humidity, the hydrogen bonding action among starch molecular chains becomes too strong, the free volume of the chains is drastically reduced, the molecular chain movement capability is limited, and the plasticity is lost. Energy can only be dissipated by crack propagation when tension is applied from the outside, and brittle fracture is shown. Grafting hydrophobic groups to starch backbones by chemical modification is a common strategy to increase starch hydrophobicity, reducing moisture sensitivity of starch packaging materials. The hydrophobic groups are grafted to the starch main chain through etherification, esterification and other modes in the chemical modification, so that the hydroxyl content is reduced, the hydrophilicity of the starch film is effectively reduced, and meanwhile, the toughness of the starch film under ultralow humidity is hopefully improved. In this process, the grafting rate and uniformity of the hydrophobic groups have a decisive influence on their mechanical properties at ultra-low humidity. However, in the current industrial hydrophobic modification process, heterogeneous modification is usually adopted, grafting reaction can only occur on the surface of starch particles, the starch crystal structure is not effectively destroyed, the activity improving effect of molecular chains is not great, and the subsequent melt hot pressing cannot be carried out, so that the hydrophobic starch is mostly used as a particle filler to be added into polyvinyl chloride (PVC), polyvinyl alcohol (PVA) and other materials, and non-biological base plastics are prepared through thermoplastic processing. As described in the Chinese patent application CN113041404A, CN107141364A, the pH of the solution is regulated after the hydrophobic substitution reagent octenyl succinic anhydride or benzoyl chloride is added into the starch suspension, so as to realize the esterification reaction of anhydride and hydroxyl or nucleophilic substitution of acyl chloride on the hydroxyl. However, the heterogeneous modification mode does not damage the crystal structure inside the starch, only can realize the surface modification of starch particles, and has low substitution degree. The Chinese patent application CN115466333A adopts ultrasonic treatment to destroy the chains of the polymer and the starch particles, so that the size of the starch particles is reduced, octenyl succinic anhydride is promoted to enter the starch particles, the accessibility of the octenyl succinic anhydride in the starch particles is improved, and the substitution degree of the product is improved. However, this method still has no means to completely destroy the crystal structure, and the degree of substitution can be only 0.0159. In contrast, a homogeneous modification strategy in which the hydrophobic group is grafted after the starch granule structure is broken by gelatinization or dissolution can achieve high and uniform substitution. For example, the Chinese pa