Cassava residue derived intrinsic flame-retardant polyol, flame-retardant polyurethane foam as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of biomass resource high-value utilization and high polymer materials, and relates to manioc waste derived intrinsic flame-retardant polyol, flame-retardant polyurethane foam and a preparation method and application thereof.The preparation method comprises the steps that wet manioc waste is pretreated through spiral extrusion dewatering, pulse airflow drying and superfine grinding, and manioc waste powder is obtained; converting starch and lignocellulose in the manioc waste into a starch-based phenolated liquefied product and a wood fiber-based phenolated liquefied product respectively by adopting a staged acid catalysis liquefaction technology; the intrinsic flame-retardant polyol is prepared through synergistic modification of oxypropylation and phosphorylation. The obtained polyol and isocyanate are subjected to one-step foaming to prepare the high-performance flame-retardant polyurethane foam, the limit oxygen index of the high-performance flame-retardant polyurethane foam reaches 26-32%, the UL-94 vertical combustion grade is V-0, the compression strength is 70-140 kPa, the density is 30-50 kg / m, all-component high-value utilization of the manioc waste is achieved, and the high-performance flame-retardant polyurethane foam is suitable for the fields of building heat preservation, cushion packaging and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of high-value utilization of biomass resources and polymer materials, and relates to a cassava residue-derived intrinsic flame-retardant polyol, a flame-retardant polyurethane foam, and a preparation method and application thereof. Background Art

[0002] With the global emphasis on the use of renewable resources and environmental protection, the high-value utilization of biomass resources has become an important research direction in the field of materials science and engineering. As the main by-product of cassava starch processing, cassava residue is considered to be a low-cost biomass resource with great potential because it is rich in convertible components such as starch and cellulose. However, the current utilization of cassava residue is still mainly low-value-added applications, such as feed granulation or packaging material adhesives. A large amount of untreated cassava residue faces severe environmental disposal pressure due to its high water content and easy corruption.

[0003] Over the years, domestic and foreign scholars have conducted extensive research on the resource utilization of cassava residue, mainly focusing on two major directions: bio-fermentation and composite materials. The bio-fermentation method aims to convert cassava residue into high-value-added products such as organic acids and fuel ethanol, but there are generally problems such as low enzymatic efficiency and high separation costs; the composite material field focuses on converting cassava residue into functional materials, such as extracting nanocellulose reinforced composite materials or degradable plastics, but these technologies still face challenges in practical applications such as poor compatibility between fiber and matrix interface and insufficient product performance.

[0004] In the field of polyurethane materials, polyols are core raw materials, and their traditional preparation methods are highly dependent on petrochemical resources. With the increasing depletion of fossil energy and increasingly stringent environmental regulations, the development of polyol synthesis technology based on renewable resources has become the focus of industry attention. In addition, traditional polyurethane foam materials generally have flammability problems, and their flame retardant properties are usually improved by adding flame retardants, but this method often leads to problems such as flame retardant migration and decreased mechanical properties of materials. Therefore, developing an intrinsic flame retardant polyol based on renewable resources and applying it to the preparation of polyurethane foam materials can not only achieve efficient utilization of biomass resources, but also provide an environmentally friendly and high-performance flame retardant solution for the polyurethane industry. Biomass liquefaction technology provides a feasible path to this goal. It converts the polysaccharide components in biomass into liquefied products with active hydroxyl groups through acid-catalyzed degradation and solvation, which are then used in polyurethane synthesis.

[0005] Chinese patent CN115044031A discloses a method for synthesizing biomass-based flame-retardant polyether polyols, wherein a typical biomass platform compound 5-hydroxymethylfurfural is molecularly grafted with melamine to form a new type of covalent compound intermediate, which is then subjected to a ring-opening polymerization reaction with ethylene oxide and / or propylene oxide to obtain a new type of flame-retardant polyether polyol product. This patent forms ethers by reacting the hydroxymethyl in hydroxymethylfurfural with the amine group of melamine, and then generates polyols by reacting the remaining amine group with propylene oxide, resulting in a small number of reactive sites and limited flame retardant ability of the prepared polyether polyols.

[0006] Chinese patent CN112778512A discloses a biomass-based polyether polyol using seaweed as raw material and a preparation method thereof, wherein seaweed powder is used as raw material, and reactive liquefied seaweed is prepared under the action of a liquefier and a catalyst; then the liquefied seaweed is used as an initiator and polymerized with olefin oxide under the action of a polymerization catalyst to obtain the polyether polyol. The seaweed in the patent contains fiber polysaccharides, and the fiber itself contains flame retardant elements, so the polyether polyol prepared therefrom has flame retardant properties; the olefin oxide here is used to react with liquefied seaweed (containing alcohol hydroxyl groups) to generate polyether polyol, and the flame retardancy is derived from the flame retardant element fiber polysaccharide contained in the seaweed fiber itself, and the flame retardancy is poor.

[0007] Based on the above-mentioned deficiencies in the preparation of intrinsic flame-retardant polyols, and the fact that existing research has mostly focused on raw materials such as vegetable oils, cellulose, and straw, research on the liquefaction of cassava residue and the preparation of polyols is still in its infancy, especially in the development of intrinsic flame-retardant polyols. Therefore, it is particularly important to develop a method for preparing cassava residue-derived intrinsic flame-retardant polyols with excellent flame retardant properties. Summary of the invention

[0008] The object of the present invention is to overcome the deficiencies of the prior art, and to provide a cassava residue-derived intrinsic flame-retardant polyol, a flame-retardant polyurethane foam, and a preparation method and application thereof, using cassava residue as a raw material, through solid acid-catalyzed phenolization, combined with oxypropyl ring-opening etherification and phosphatization reaction, and utilizing the high reactivity of phenolic hydroxyl, epoxy, amino and other groups to prepare NP efficient intrinsic synergistic flame-retardant polyol. The polyol is applied to polyurethane foam materials, has excellent flame retardant properties, and has significant environmental benefits and economic value. This technical route not only meets the strategic needs of sustainable development, but also opens up a new way for the high-value utilization of cassava residue, which is of great significance to promoting the green transformation of biomass resource conversion and polyurethane industry.

[0009] The technical solution of the present invention is achieved through the following technical solutions:

[0010] The first aspect of the present invention discloses a method for preparing a cassava residue-derived intrinsic flame-retardant polyol, comprising the following steps:

[0011] (1) Cassava residue pretreatment: The wet cassava residue is subjected to spiral extrusion, airflow drying, and ultrafine grinding in sequence to obtain cassava residue powder;

[0012] (2) Segmented acid-catalyzed liquefaction: In a closed reaction vessel, cassava residue powder and molten phenol in a mass ratio of 1:2.0-3.0 are stirred and mixed uniformly at 60°C, a solid acid catalyst of 0.5-6.0% of the total mass of the cassava residue powder and the molten phenol is added to carry out a first-stage reaction, the reaction is carried out at 110-150°C for 5-15 min, ethanol is added for centrifugal separation, the upper mobile phase is the cassava residue phenolization component A, the lower solid and molten phenol are mixed in a mass ratio of 1:2.0-4.0, the second-stage reaction is carried out at 110-150°C for 10-30 min, ethanol is added for centrifugal separation to obtain the phenolization component B; the phenolization component A and the phenolization component B are combined, and the ethanol is removed to obtain the cassava residue phenolization liquefaction product, which is set aside; the solid acid catalyst is one of a solid superacid, a molecular sieve or a composite oxide, and the solid superacid is or The molecular sieve is ZSM-5 or Y-type molecular sieve, and the composite oxide is ;

[0013] (3) Oxypropylation and phosphating modification: The liquefied product of phenolization of cassava residue and potassium hydroxide are mixed in a mass ratio of 100:2-5 in an autoclave, the air is purged with nitrogen, and the water is removed by vacuum distillation. The temperature is raised to 120-130° C., and an oxypropylation agent of 1.1-2.5 times the mass of the phenolization liquefaction product of the cassava residue is slowly introduced. After aging reaction for 2-5 hours, phosphoric acid is added for neutralization to obtain an oxypropylation product. An esterification agent DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) is added into an autoclave, catalyzed by triethylamine, reacted at 130-150° C. for 2-4 hours under nitrogen protection, neutralized with phosphoric acid, and cooled to room temperature to obtain a cassava residue-derived intrinsic flame-retardant polyol. The oxypropylation agent is propylene oxide, N-(2,3-epoxypropyl)amine or N-methyl-2,3-epoxypropylamine, the mass ratio of DOPO to the oxypropylation product is 1.5-2.5:10, and the amount of triethylamine is 1-3% of the total mass of the reagents involved in the esterification reaction.

[0014] Preferably, the wet cassava residue in the above step (1) is a byproduct of starch extraction in a cassava starch factory, has a water content of 80-85%, and its main components are cellulose, starch, protein and ash; the dehydration method preferably has a continuous operation, low energy consumption, and high degree of automation screw extrusion dehydration, the moisture content after treatment is not higher than 45%, the mesh size of the screw extrusion dehydrator is 0.2-0.35 mm, and the compression ratio is not less than 4; the drying method uses a pulse airflow dryer with an intensifier for drying, which is characterized in that the wet material enters the intensifier through a spiral feeder, and is fully mixed with the hot air flow under the impact, crushing and propulsion of the rapidly rotating blade, and the material is crushed into fine particles and suspended by the high-speed hot air flow. By alternating the diameter of the tube, the relative speed and heat transfer area between the material and the airflow are greatly increased, the heat transfer efficiency is greatly improved, and the material can be dried efficiently in a short time. The inlet hot air temperature of the pulse airflow drying is 180-220°C, the wind speed is 20-30 m / s, and the moisture content of the dried material is ≤12%; the ultrafine grinding method is an airflow mill, the grinding pressure is 0.8-1.2 MPa, and the particle size of the material after grinding is controlled within 300-400 meshes. This process significantly increases the specific surface area and improves the efficiency of the phenolization liquefaction reaction by highly homogenizing starch and wood fiber particles, making the physical and chemical properties of the liquefied product prepared from cassava residue powder more stable, and promoting the fragmentation of starch particles, which is conducive to the staged generation and separation of biomass components.

[0015] Preferably, the centrifugal separation temperature is 5-10°C, the rotation speed is 10000-12000 r / min, and the time is 8-10 min. The centrifugal separation uses a refrigerated high-speed centrifuge to quickly cool down and control the degree of phenolization reaction of starch and fiber in the cassava residue powder. The first centrifugal separation mainly obtains the liquefied product of the starch component, and the second centrifugal separation obtains the phenolization product of the wood fiber component.

[0016] Preferably, the solid acid catalyst in step (2) is a solid superacid ( , ), the dosage is 0.5-1.0% of the total mass of the cassava residue powder and molten phenol in the first stage reaction; when the solid acid catalyst is a molecular sieve (ZSM-5, Y-type molecular sieve), the dosage is 2-4.0% of the total mass of the cassava residue powder and molten phenol in the first stage reaction; when the solid acid catalyst is a composite oxide ( ), the dosage is 3.0-6% of the total mass of cassava residue powder and molten phenol in the first stage reaction.

[0017] The second aspect of the present invention discloses a cassava residue-derived intrinsic flame-retardant polyol prepared by the above method, comprising an oxypropylated and DOPO phosphoesterified modified structure of a cassava residue phenolization product, a hydroxyl value of 280 to 650 mg KOH / g, a viscosity of 1000 to 6500 mPa·s, and a phosphorus content of 1.2 to 2.8 wt%.

[0018] The third aspect of the present invention discloses a method for preparing a flame retardant polyurethane foam, comprising mixing a mixed polyol containing cassava residue-derived intrinsic flame retardant polyol, a catalyst, an organosilicon foam stabilizer, and a physical foaming agent, adding isocyanate, stirring and foaming, and obtaining a flame retardant polyurethane foam after curing.

[0019] Preferably, the mixed polyol is prepared by mixing cassava residue-derived intrinsic flame retardant polyol with bio-based polyol, polyol extracted and synthesized from petrochemical raw materials, polyether polyol or polyester polyol in a certain proportion, wherein the cassava residue-derived intrinsic flame retardant polyol accounts for 20 to 70 wt% of the mixed polyol.

[0020] Preferably, the foaming formula is: 100 parts of mixed polyols, 0.5-3 parts of amine catalysts, 0.5-3 parts of organotin catalysts, 0.5-3 parts of organosilicon foam stabilizers, 10-30 parts of physical foaming agents, 1-10 parts of water, and 80-130 parts of isocyanates by weight. Further preferably, the amine catalyst is triethylenediamine, tetramethylethylenediamine or dimethylcyclohexylamine; the organotin catalyst is stannous octoate or dibutyltin dilaurate; the physical foaming agent is a low-boiling inert hydrocarbon compound, specifically HFO-1234ze (1,3,3,3-tetrafluoropropylene), monofluorinated dichloroethane or HFOs (hydrofluorocarbons). The isocyanate is one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) or polyisocyanate (polymeric MDI). The silicone foam stabilizer is one of polydimethylsiloxane (silicone oil), polyether-modified dimethylsiloxane, and polyether-modified polydimethylsiloxane.

[0021] The fourth aspect of the present invention discloses a flame retardant polyurethane foam prepared by the above preparation method, wherein the polyurethane foam has a limiting oxygen index of 26 to 32%, a UL-94 vertical combustion rating of V-0, a compressive strength of 70 to 140 kPa, and a density of 30 to 50 kg / m³.

[0022] The fifth aspect of the present invention discloses an application of the flame retardant polyurethane foam in thermal insulation of building exterior walls.

[0023] The beneficial effects of the present invention are:

[0024] (1) The present invention uses cassava residue as a raw material, and converts starch and lignocellulose in the cassava residue into starch and lignocellulose-based phenolic products respectively through segmented acid-catalyzed liquefaction (phenol-solid acid system), and adopts oxypropylation and phosphating esterification for synergistic modification to give the cassava residue-derived intrinsic flame-retardant polyol excellent flame retardancy, with a hydroxyl value of 280 to 650 mg KOH / g, a viscosity of 1000 to 6500 mPa·s (25°C), and a phosphorus content of 1.2 to 2.8 wt%.

[0025] (2) The polyurethane foam prepared by the cassava residue-derived intrinsic flame-retardant polyol of the present invention has a limiting oxygen index (LOI) of 26-32%, a UL-94 vertical combustion rating of V-0, a compressive strength of 70-140 kPa, and no obvious attenuation in the compressive strength compared with petrochemical-based polyurethane, and a density of 30-50 kg / m³.

[0026] (3) Through spiral extrusion-pulse airflow drying-ultrafine grinding pretreatment, efficient industrial dehydration of wet cassava residue was achieved, which significantly increased the specific surface area and improved the efficiency of phenolization liquefaction reaction. Through particle size control, segmented liquefaction, frozen centrifugal separation and other methods, the phenolization of starch and lignocellulose was achieved, and the hydroxyl value, viscosity and intrinsic flame retardant properties of the cassava residue phenolization product were adjustable. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0028] Example 1

[0029] A method for preparing cassava residue-derived intrinsic flame-retardant polyols, comprising:

[0030] (1) Pretreatment process of wet cassava residue:

[0031] 1) Dehydration: Wet cassava residue with a moisture content of 83% was dehydrated by a single screw extrusion dehydrator. The mesh diameter of the dehydrator was 0.2 mm and the compression ratio was 4.5. After dehydration, the moisture content of the material dropped to 42%;

[0032] 2) Drying: The dehydrated cassava residue is sent to the enhanced pulse airflow dryer, and the inlet hot air temperature is controlled to be 200°C and the wind speed is 25m / s. The moisture content of the cassava residue at the outlet after drying is 11.5%;

[0033] 3) Ultrafine grinding: The dried cassava residue is crushed by airflow ultrafine grinding machine, and the airflow pressure is controlled to be 1.0MPa, the airflow velocity is 200m / s, and the working temperature is 40℃ to obtain cassava residue powder with a particle size of 350 mesh and a dryness of 95%;

[0034] After the above treatment, the wood fiber tissue in the cassava residue is completely broken down and dispersed into irregular fragments of about 40μm, the coated starch particles are dispersed and released, and the specific surface area of ​​the dry powder is increased to 1.2m² / g.

[0035] (2) Segmented acid-catalyzed liquefaction: 10 g of cassava residue powder and 25 g of molten phenol were stirred at 60 °C for 10 min, heated to 110 °C under nitrogen protection, and 0.2 g of The solid acid catalyst was reacted for 10 min, 70 mL of ethanol was added to reduce the viscosity of the system, and the mixture was transferred to a centrifuge tube and centrifuged at 5°C and 12000 r / min for 8 min. The upper mobile phase was separated as the cassava residue phenolization component A for later use. 6.5 g of the lower solid was mixed with 13 g of molten phenol, and 30 mL of ethanol was added to reduce the viscosity after reacting at 120°C for 20 min. The phenolization component B was obtained by centrifugation under the same conditions for 10 min. The phenolization component A and the phenolization component B were combined, and the ethanol was removed by vacuum distillation to obtain the cassava residue phenolization liquefaction product. The comprehensive liquefaction rate of cassava residue reached 96.2%.

[0036] (3) Oxypropylation and phosphating modification: 20 g of the phenolized liquefied product of cassava residue and 0.5 g of potassium hydroxide were added to a high-pressure reactor, and the air was removed by nitrogen purging. After decompression and dehydration, 24 g of propylene oxide was introduced. The reaction was heated to 120 °C and the pressure in the reactor was controlled to be less than 0.2 MPa for oxypropylation reaction for 3 h until the pressure reached normal pressure. After phosphoric acid neutralization, 10 g of DOPO and 1.3 g of triethylamine were added. The reaction was carried out at 130 °C for 4 h under nitrogen protection. After phosphoric acid neutralization, the reaction was cooled to obtain cassava residue-derived intrinsic flame-retardant polyols.

[0037] The cassava residue-derived intrinsic flame-retardant polyol prepared in Example 1 was characterized. The polyol was a brown liquid with a dynamic viscosity of 5740 mPa·s (25° C.), a hydroxyl value of 490 mg KOH / g, and a phosphorus content of 2.2 wt %.

[0038] Process advantages: Based on the similar liquefaction paths and different liquefaction rates of starch and wood fiber in cassava residue in phenol, the process uses segmented low-temperature liquefaction combined with solid acid catalysis technology to achieve controllable liquefaction separation of starch and fiber components through freezing high-speed centrifugation. Oxypropyl modification effectively regulates the viscosity and hydroxyl value of the phenolization product, reduces the steric hindrance of the reaction between hydroxyl and DOPO, and thus improves the efficiency of the phosphoesterification reaction.

[0039] Preparation method of polyurethane foam:

[0040] Take 5.0 g of the above-mentioned cassava residue-derived intrinsic flame-retardant polyol, 5.0 g of polyether polyol 4110 (hydroxyl value 430 mg KOH / g), 0.12 g of triethylenediamine, 0.14 g of dibutyltin dilaurate, 0.15 g of dimethylsiloxane, 0.12 g of H2O, and 2.04 g of dichloroethane monofluoride and mix them evenly. After adding 10.30 g of diphenylmethane diisocyanate, stir rapidly at 2000 r / min for 15 to 20 seconds, the mixture becomes milky white and self-foaming, and is cured at 80°C for 12 hours.

[0041] The polyurethane foam prepared in Example 1 was characterized and was light brown hard foam with uniform and fine pores, a density of 38.6 kg / m³, a compressive strength of 108 kPa, a limiting oxygen index (LOI) of 29%, and a UL-94 vertical burning grade of V-1.

[0042] Example 2: Synergistic flame retardant modification of NPs from phenolization and liquefaction of cassava residues and their application in improving PUF performance

[0043] (1) A method for preparing a cassava residue-derived intrinsic flame-retardant polyol, comprising: taking 20 g of a cassava residue phenolization liquefaction product (the preparation method is the same as in Example 1) and 0.6 g of potassium hydroxide and adding them into a high-pressure reactor, purging with nitrogen to remove air, decompressing and dehydrating, adding 28 g of N-methyl-2,3-epoxypropylamine, heating to 130° C. for reaction for 3 h, and then adding phosphoric acid for neutralization; adding 7.3 g of DOPO and 1.5 g of triethylamine, reacting at 130° C. for 4 h under nitrogen protection, neutralizing with phosphoric acid, and cooling to obtain a liquefied product which is a cassava residue-derived intrinsic flame-retardant polyol.

[0044] The cassava residue-derived intrinsic flame retardant polyol prepared in Example 2 was characterized. The polyol was a brown liquid with a dynamic viscosity of 5340 mPa·s (25° C.), a hydroxyl value of 510 mg KOH / g, a phosphorus content of 1.5 wt %, and a nitrogen content of 4.8 wt %.

[0045] (2) Preparation method of polyurethane rigid foam

[0046] 6.0 g of the above-mentioned cassava residue-based liquefied product, 4.0 g of polyether polyol 4110 (430 mg KOH / g), 0.10 g of triethylenediamine, 0.12 g of dibutyltin dilaurate, 0.14 g of dimethylsiloxane, 0.15 g of H2O, and 2.20 g of dichloroethane monofluoride were mixed evenly, 10.30 g of diphenylmethane diisocyanate was added, and the mixture was rapidly stirred at a speed of 2000 r / min for 15 to 20 seconds to become milky white and self-foaming, and then cured at 80°C for 12 hours.

[0047] The flame retardant polyurethane foam prepared in Example 2 was characterized, and the foam performance was: brown hard foam, uniform and fine pores, density: 34.8 kg / m³, compression strength: 102 kPa, limiting oxygen index (LOI) 31%, UL-94 vertical burning grade V-0.

[0048] Example 3: Application of molecular sieve solid catalyst in liquefaction modification of cassava residue

[0049] (1) A method for preparing a cassava residue-derived intrinsic flame-retardant polyol, comprising:

[0050] 1) Preparation method of cassava residue phenolization liquefaction product:

[0051] 10 g of cassava residue powder (prepared in the same manner as in Example 1) and 30 g of molten phenol were premixed at 60°C for 15 min, heated to 130°C under nitrogen protection, and then 1.5 g of HZSM-5 molecular sieve catalyst was added. After liquefaction reaction for 20 min, 70 mL of ethanol was added for dilution, and the upper mobile phase, i.e., cassava residue phenolization component A, was collected by centrifugation at 5°C and 12000 r / min for 8 min for standby use. The lower solid (5.8 g) was mixed with 15 g of molten phenol for a second time, and liquefied at 140°C for 30 min. After adding 40 mL of ethanol, the mixture was centrifuged under the same conditions for 10 min to obtain phenolization component B. The phenolization component A and the phenolization component B were combined, and the ethanol was removed by vacuum distillation at 45°C to obtain a dark brown liquefied product, i.e., the cassava residue phenolization liquefied product, with a comprehensive liquefaction rate of 98.1%.

[0052] 2) Synthesis of intrinsic flame retardant polyols derived from cassava residue:

[0053] 20 g of phenolization liquefaction product of cassava residue and 0.6 g of potassium hydroxide were added to a high-pressure reactor, and the air was removed by nitrogen purging. After dehydration at 105 °C for 1 h, 35 g of N-(2,3-epoxypropyl)amine was added in three times. The reaction temperature was controlled at 130 °C, and the ring-opening grafting reaction was carried out for 3 h. After neutralization with phosphoric acid, 12 g DOPO and 1.5 g triethylamine were added, and the reaction was carried out at 135 °C for 6 h under nitrogen protection. The final product was neutralized to obtain a brown and viscous cassava residue-derived intrinsic flame-retardant polyol.

[0054] The cassava residue-derived intrinsic flame retardant polyol prepared in Example 3 was characterized. The obtained polyol was a brown liquid with a viscosity of 4820 mPa•s (25°C), a hydroxyl value reduced to 410 mg KOH / g, a phosphorus content of 2.3 wt%, and a nitrogen content of 5.7 wt%.

[0055] Preparation method of polyurethane foam:

[0056] Take 5.0 g of the cassava residue-derived intrinsic flame retardant polyol and 5.0 g of polyester polyol (WANOL @ R2380, hydroxyl value 380 mgKOH / g) 5.0 g, stannous octoate 0.15 g, silicone oil surfactant 0.2 g, water 0.2 g, physical foaming agent (HFO-1234ze) 2.5 g, isocyanate (MDI, NCO index 1.1) 12.0 g, mix the components except isocyanate evenly, stir at high speed (2500 r / min) for 30 seconds, continue stirring for 20 seconds after adding MDI for self-foaming, and cure at 80°C for 5 hours.

[0057] The polyurethane foam prepared in Example 3 was characterized and was found to be a yellow-brown rigid foam with uniform pores, a density of 40 kg / m³, a compressive strength of 120 kPa, a limiting oxygen index (LOI) of 31%, and a UL-94 vertical burning grade of V-0.

[0058] Example 4: Preparation of low-color soft foam polyol and its application in polyurethane foam

[0059] (1) A method for preparing a cassava residue-derived intrinsic flame-retardant polyol, comprising:

[0060] 1) Preparation method of cassava residue phenolization liquefaction product:

[0061] 10 g of cassava residue powder (prepared in the same manner as in Example 1) and 25 g of molten phenol were premixed at 60°C for 15 min, heated to 120°C under nitrogen protection, 1.2 g of HZSM-5 (molecular sieve catalyst) was added, reacted for 10 min, diluted with 70 mL of ethanol, centrifuged at 5°C and 12000 r / min for 10 min, and the upper wine-red mobile phase, i.e., cassava residue phenolization component A, was collected for later use. The lower solid (6.9 g) was mixed with 15 g of molten phenol, and liquefied at 120°C for 35 min. After adding 40 mL of ethanol, the phenolization component B was obtained by centrifugation under the same conditions for 10 min. The phenolization component A and the phenolization component B were combined, and the ethanol was removed by vacuum distillation at 45°C to obtain a sauce-red liquefied product, i.e., the cassava residue phenolization liquefied product (comprehensive liquefaction rate 97.2%).

[0062] 2) Synthesis of cassava residue derived intrinsic flame retardant polyols and soft foam flame retardant polyols:

[0063] Take 20 g of phenolized liquefied product of cassava residue and 0.6 g of potassium hydroxide and add them to the autoclave. Expel air with nitrogen purge and dehydrate at 105°C for 1 hour. Add 15 ml of acetone to adjust the viscosity (because the liquefaction conditions become milder, the viscosity of the liquefied product is too large, which is not conducive to the subsequent reaction. The purpose of adding acetone is to reduce the viscosity of the flame retardant modified system). Then add 35 g of N-methyl-2,3-epoxypropylamine three times and control the temperature at 130°C for 4.5 hours. After phosphoric acid neutralization, add 8 g of DOPO and 1.5 g of triethylamine and react at 135°C for 4 hours under nitrogen protection. After phosphoric acid neutralization, cool and obtain brown-red cassava residue-derived intrinsic flame retardant polyol.

[0064] The cassava residue-derived intrinsic flame retardant polyol prepared in Example 4 was characterized and found to be a brown-red viscous liquid with a dynamic viscosity of 5850 mPa·s (25° C.), a hydroxyl value of 560 mg KOH / g, a phosphorus content of 1.4 wt %, and a nitrogen content of 5.6 wt %.

[0065] (2) Preparation method of light-colored high-resilience semi-rigid polyurethane foam

[0066] Take 6.0 g of the cassava residue-derived intrinsic flame-retardant polyol, 4.0 g of high-activity polyether polyol (EO content 20%, hydroxyl value 450 mg KOH / g), 0.5 g of 1,4-butanediol, 0.15 g of stannous octoate, 0.2 g of silicone oil surfactant, 0.1 g of water, 2.5 g of physical foaming agent (HFO-1234ze), and 11.0 g of isocyanate (MDI, NCO index 1.05), mix the components except isocyanate evenly, stir at high speed (2500 r / min) for 20 seconds, continue stirring for 15 seconds after adding MDI for self-foaming, and cure at 80°C for 2 hours.

[0067] The polyurethane foam prepared in Example 4 was characterized and was a light beige semi-rigid foam with uniform and fine pores, a density of 45 kg / m³, a rebound rate of 75%, a compression strength of 95 kPa, a limiting oxygen index (LOI) of 30%, and a UL-94 vertical burning grade of V-0.

[0068] Example 5: Rigid foam flame retardant polyol and its application in building exterior wall insulation polyurethane foam

[0069] (1) A method for preparing a cassava residue-derived intrinsic flame-retardant polyol, comprising:

[0070] 1) Preparation method of cassava residue phenolization liquefaction product:

[0071] 10 g of cassava residue powder (prepared in the same manner as in Example 1) was premixed with 30 g of molten phenol at 60°C for 15 min, and the mixture was heated to 150°C under nitrogen protection. 1.2 g , react for 30 minutes, add 70 mL of ethanol to dilute, centrifuge at 5°C and 12000r / min for 10 minutes, collect the upper dark brown mobile phase, i.e. cassava residue phenolization component A, and set aside. The lower solid (5.6 g) was mixed with 15 g of molten phenol, and continued to liquefy at 150°C for 45 minutes. After adding 40 mL of ethanol, centrifuge under the same conditions for 10 minutes to obtain phenolization component B, combine phenolization component A and phenolization component B, combine the two centrifuges, and remove ethanol by vacuum distillation at 45°C to obtain a dark brown cassava residue phenolization liquefaction product (comprehensive liquefaction rate 99.1%).

[0072] 2) Synthesis of intrinsic flame retardant polyols derived from cassava residue:

[0073] 20 g of phenolic liquefied product of cassava residue and 0.6 g of potassium hydroxide were added to a high-pressure reactor, and the air was removed by nitrogen purging. The reactor was dehydrated under reduced pressure for 1 h at 105 ° C. After dehydration under reduced pressure, 24 g of propylene oxide was introduced, and the reactor was heated to 120 ° C. The pressure in the reactor was controlled to be less than 0.2 MPa for oxypropylation reaction for 3 h until the pressure reached normal pressure. After phosphoric acid neutralization, 8 g of DOPO and 1.3 g of triethylamine were added, and the reaction was carried out at 130 ° C for 4.5 h under nitrogen protection. After phosphoric acid neutralization, the reactor was cooled to obtain cassava residue intrinsic flame retardant polyol.

[0074] The cassava residue-derived intrinsic flame retardant polyol prepared in Example 5 was characterized and was a black liquid with a dynamic viscosity of 2360 mPa•s (25° C.), a hydroxyl value of 280 mg KOH / g, and a phosphorus content of 1.5 wt %.

[0075] (2) Preparation of flame retardant and heat-insulating rigid polyurethane foam

[0076] Take 4.5 g of the cassava residue-derived intrinsic flame-retardant polyol, 5.5 g of high-activity polyether polyol (polyether 4110, hydroxyl value 440 mg KOH / g), 0.15 g of triethylenediamine, 0.1 g of dibutyltin dilaurate (T-12), 0.2 g of silicone foam stabilizer (polyether modified polydimethylsiloxane), 0.15 g of water, 4.0 g of physical foaming agent (HFOs), and 12.0 g of polymeric MDI (PM-200, NCO content 30%), mix the components except isocyanate evenly, stir at high speed (2500 r / min) for 20 seconds, add polymeric MDI and continue stirring for 20 seconds for self-foaming, and cure at 80°C for 8 h.

[0077] The polyurethane foam prepared in Example 5 was characterized and found to be a gray-brown rigid foam with uniform and fine pores, a density of 42 kg / m³, a thermal conductivity of 0.021 w / (m•K), a compressive strength of 130 kPa, and a limiting oxygen index (LOI) of 29%, reaching the B-1 grade of GB 8624-2017 "Classification of Combustion Performance of Building Materials and Products".

[0078] Comparative Example 1

[0079] The only difference from Example 1 is that the pretreatment process of wet cassava residue is a conventional process, and the specific steps are: after the wet cassava residue is air-dried, it is dried to constant weight using a blast dryer; 100g of dry cassava residue is taken and crushed with a traditional Chinese medicine powder machine for later use. Phenolization liquefaction and flame retardant modification of cassava residue powder are carried out according to the method of Example 1, and 5 groups of 10g cassava residue powder are taken for parallel experiments.

[0080] The comprehensive liquefaction rate of the phenolization liquefaction product of cassava residue is 75-90%. The color of the liquefied product ranges from brown to dark brown, the viscosity is 3850-7280 mPa·s (25°C), the hydroxyl value is 320-690 mg KOH / g, and the phosphorus content is 1.1-1.3 wt%.

[0081] The method for preparing polyurethane foam is the same as that in Example 1. The prepared polyurethane foam is beige, brown, dark brown, etc., with uneven color, semi-rigid foam or rigid foam, uneven pores or burnt foam. Density: 35-40 kg / m³, compression strength: 70-110 kPa, limiting oxygen index (LOI) 25-26%,

[0082] Comparative Example 2

[0083] The only difference from Example 1 is that step (2) does not use a staged catalytic liquefaction reaction. The specific steps are:

[0084] (1) Catalytic liquefaction of cassava residue powder: 10 g of cassava residue powder and 40 g of molten phenol were stirred and mixed at 60 °C for 10 min, and then heated to 110 °C under nitrogen protection. 0.2 g The solid acid catalyst was reacted for 10 min, then the temperature was raised to 120°C for 20 min, 100 mL of ethanol was added to reduce the viscosity, the mixture was transferred to a centrifuge tube and centrifuged at 5°C and 12000 r / min for 10 min, and the ethanol was removed by vacuum distillation to obtain the phenolization liquefaction product of cassava residue. The comprehensive liquefaction rate of cassava residue reached 91.5%.

[0085] (3) Oxypropylation and phosphating modification: 20 g of the phenolized liquefied product of cassava residue and 0.5 g of potassium hydroxide were added to a high-pressure reactor, and the air was removed by nitrogen purging. After decompression and dehydration, 24 g of propylene oxide was introduced. The reaction was heated to 120 °C and the pressure in the reactor was controlled to be less than 0.2 MPa for oxypropylation reaction for 3 h until the pressure reached normal pressure. After phosphoric acid neutralization, 10 g of DOPO and 1.3 g of triethylamine were added. The reaction was carried out at 130 °C for 4 h under nitrogen protection. After phosphoric acid neutralization, the reaction was cooled to obtain cassava residue-derived intrinsic flame-retardant polyols.

[0086] The cassava residue-derived intrinsic flame-retardant polyol prepared in Comparative Example 2 was characterized. The polyol was a dark brown liquid with a dynamic viscosity of 4960 mPa·s (25° C.), a hydroxyl value of 430 mg KOH / g, and a phosphorus content of 1.2 wt %.

[0087] The method for preparing polyurethane foam is the same as that in Example 1. The prepared polyurethane foam is brown, hard foam, with pores of different sizes, a density of 45 kg / m³, a compression strength of 128 kPa, and a limiting oxygen index (LOI) of 27%.

[0088] Comparative Example 3

[0089] The only difference from Example 1 is that step (3) only performs phosphoesterification modification without oxypropylation. The specific steps are as follows: 20 g of the phenolized liquefied product of cassava residue described in Example 1 and 0.5 g of potassium hydroxide are added to a high-pressure reactor, nitrogen is purged to remove air, and dehydration is performed under reduced pressure. 10 g of DOPO and 1.3 g of triethylamine are added, and the reaction is carried out at 130° C. for 4 h under nitrogen protection. After neutralization with phosphoric acid, the mixture is cooled to obtain a cassava residue-derived intrinsic flame retardant polyol.

[0090] The cassava residue-derived intrinsic flame-retardant polyol prepared in Comparative Example 3 was characterized. The polyol was a dark brown liquid with a dynamic viscosity of 9480 mPa•s (25° C.), a hydroxyl value of 880 mg KOH / g, and a phosphorus content of 0.7 wt %.

[0091] The method for preparing polyurethane foam is the same as that in Example 1. The prepared polyurethane foam is brown, has cracks on the surface, and has collapsed bubbles inside.

[0092] Comparative Example 4

[0093] The only difference from Example 1 is that the phosphoesterification reagent in step (3) is different. The specific steps are:

[0094] Take 20 g of the phenolized liquefied product of cassava residue described in Example 1 and 0.5 g of potassium hydroxide, add them into a high-pressure reactor, purge with nitrogen to remove air, introduce 24 g of propylene oxide after reduced pressure dehydration, heat to 120°C, control the pressure in the reactor to be less than 0.2 MPa, and carry out oxypropylation reaction for 3 hours to normal pressure. After neutralization with phosphoric acid, add 10 g DPP (diphenyl phosphate) and 1.3 g triethylamine, react at 130°C for 4 hours under nitrogen protection, neutralize with phosphoric acid, and cool to obtain cassava residue-derived polyol.

[0095] The cassava residue-derived polyol prepared in Comparative Example 4 was characterized. The polyol was a brown liquid with a dynamic viscosity of 5450 mPa•s (25° C.), a hydroxyl value of 530 mg KOH / g, and a phosphorus content of 0.2 wt %.

[0096] The method for preparing polyurethane foam is the same as that in Example 1. The prepared polyurethane foam is light brown hard foam with different cell sizes, a density of 42 kg / m³, a compression strength of 94 kPa, and a limiting oxygen index (LOI) of 27%.

[0097] The characteristic parameters of the cassava residue-derived intrinsic flame-retardant polyols prepared in the examples and comparative examples are shown in Table 1, and the main performance parameters of the polyurethane foams are shown in Table 2.

[0098] Table 1 Characteristic parameters of cassava residue-derived intrinsic flame retardant polyols prepared in Examples and Comparative Examples

[0099]

[0100] Table 2 Main performance parameters of polyurethane foams prepared in Examples and Comparative Examples

[0101]

[0102] According to Table 1 and Table 2, the cassava residue-derived intrinsic flame-retardant polyols prepared by the method of the present application in Examples 1 to 5 have controllable viscosity and hydroxyl value, high phosphorus content and / or nitrogen content, and the limited oxygen index of the prepared polyurethane foams is higher than that of the control example, the foam cells are uniform, and the flame retardant properties are excellent.

[0103] The wood fiber in the cassava residue powder prepared in Comparative Example 1 was not fully crushed, and the obtained particles were irregular in shape, with a size distribution of tens to hundreds of microns, and short coarse fiber fragments were visible in the residue powder. During the crushing process, the starch and fiber components were separated and concentrated, with small particles (mainly starch) distributed in the upper layer and large particles (mainly fiber) deposited at the bottom. Due to the uneven distribution of starch and fiber, the proportion of starch and fiber in the five parallel samples showed random differences.

[0104] The randomness of this component distribution leads to significant fluctuations in liquefaction efficiency: when the starch content is high, the viscosity of the liquefied product in the first stage is large, the hydroxyl value is high, and the wood fiber degradation in the second stage is more complete; when the wood fiber content is high, although the starch can be quickly degraded and deeply phenolized in the first stage, the wood fiber liquefaction in the second stage is not complete. In addition, due to the large fluctuations in the ratio of starch to wood fiber in cassava residue powder, the molecular structure of the phenolized liquefied product is difficult to concentrate and shows diverse complexity, and the comprehensive liquefaction rate is low, resulting in unstable subsequent flame retardant modification effects and obvious fluctuations in the physical properties of the foam.

[0105] In Comparative Example 2, starch rapidly degrades and undergoes phenolization under liquefaction conditions, first generating initial pyranose glucopyranose phenol, which is then further cleaved into carbohydrate fragments, and finally reacts with phenol to generate structural units similar to traditional phenolic resins. During this process, the hydroxyl value and viscosity of the system show a trend of first increasing and then decreasing, but the chain scission and phenolization rate of wood fiber under the action of solid acid is relatively slow.

[0106] The present invention controls the appropriate reaction conditions and reaction time to timely separate the phenolic liquefied product of starch and wood fiber from the reaction system to ensure that its molecular structure and viscosity are suitable for subsequent flame retardant modification. However, in Comparative Example 2, the starch phenolic product has a deep degree of degradation, a high content of phenolic hydroxyl groups in the molecular structure, and a low content of alcoholic hydroxyl groups, resulting in poor molecular chain stretchability, which is not conducive to subsequent modification.

[0107] In Comparative Example 3, since the phenolization liquefaction product of cassava residue is prepared under relatively mild conditions, the molecular weight of the degraded biomass component is relatively large, and the viscosity and hydroxyl value are both high, and the phosphating modification is directly performed. The phosphorus content in the prepared flame-retardant polyol is low and the flame retardancy is poor. The present application appropriately adjusts the molecular configuration and the hydroxyl value of the system through a ring-opening reaction with propylene oxide or glycidylamine, which is beneficial to the subsequent introduction of phosphorus-containing flame retardants.

[0108] The phosphorus content in the cassava residue-derived intrinsic flame-retardant polyol prepared in Comparative Example 4 is low. Although diphenyl phosphate has a high phosphorus content, its reactivity is low. Under the same esterification modification conditions as in Example 1, diphenyl phosphate is difficult to react with the phenolic hydroxyl or alcoholic hydroxyl groups of the cassava residue liquefaction product, so it is impossible to impart intrinsic flame retardant properties to it. However, in the subsequent foaming process, diphenyl phosphate can be used as an additive flame retardant to effectively inhibit the combustion reaction by promoting the formation of a carbon layer and capturing free radicals.

[0109] The above embodiments are only some better implementation methods of the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any equivalent replacement, deformation and modification of some technical features within the creative concept and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing cassava residue-derived intrinsic flame-retardant polyols, characterized in that: The following steps are involved: (1) Cassava residue pretreatment: The wet cassava residue is subjected to spiral extrusion dehydration, pulse airflow drying and ultrafine grinding in sequence to obtain cassava residue powder; (2) Segmented acid-catalyzed liquefaction: In a closed reaction vessel, cassava residue powder and molten phenol are uniformly mixed at a mass ratio of 1:2.0-3.0, and a solid acid catalyst of 0.5-6.0% of the total mass of the cassava residue powder and the molten phenol is added to carry out a first-stage reaction, and the reaction is carried out at 110-150° C. for 5-15 min, and ethanol is added for centrifugal separation, the upper mobile phase is the cassava residue phenolization component A, and the lower solid is mixed with molten phenol at a mass ratio of 1:2.0-4.0, and the second-stage reaction is carried out at 110-150° C. for 10-30 min, and ethanol is added for centrifugal separation to obtain the phenolization component B; the phenolization component A and the phenolization component B are combined, and the ethanol is removed to obtain the cassava residue phenolization liquefaction product, which is set aside; the solid acid catalyst is one of a solid superacid, a molecular sieve or a composite oxide, and the solid superacid is or The molecular sieve is ZSM-5 or Y-type molecular sieve, and the composite oxide is ; (3) Oxypropylation and phosphating modification: The phenolization liquefaction product of cassava residue is mixed with potassium hydroxide in a mass ratio of 100:2-5. An oxypropylation agent in an amount of 1.1-2.5 times the mass of the phenolization liquefaction product of cassava residue is added at 120-130°C for reaction for 2-5 hours. After neutralization with phosphoric acid, an oxypropylation product is obtained. Subsequently, an esterification agent DOPO is added. Under the catalysis of triethylamine, the mixture is reacted at 130-150°C for 2-4 hours. After neutralization with phosphoric acid, the mixture is cooled to room temperature to obtain a cassava residue-derived intrinsic flame retardant polyol. The oxypropylation agent is propylene oxide, N-(2,3-epoxypropyl)amine or N-methyl-2,3-epoxypropylamine. The mass ratio of DOPO to the oxypropylation product is 1.5-2.5:

10. The amount of triethylamine used is 1-3% of the total mass of the reagents involved in the esterification reaction.

2. The preparation method according to claim 1, characterized in that: In step (1), the mesh size of the spiral extrusion dehydration is 0.2-0.35 mm, the compression ratio is ≥4, and the moisture content of the material after dehydration is ≤45%; the inlet hot air temperature of the pulse airflow drying is 180-220°C, the wind speed is 20-30 m / s, and the moisture content of the material after drying is ≤12%; the ultrafine grinding adopts an airflow grinder, the grinding pressure is 0.8-1.2 MPa, and a powder with a particle size of 300-400 mesh is obtained.

3. The preparation method according to claim 1, characterized in that: The centrifugal separation in step (2) is performed at a temperature of 5 to 10°C, a rotation speed of 10,000 to 12,000 r / min, and a time of 8 to 10 min.

4. A cassava residue-derived intrinsic flame retardant polyol prepared according to any one of claims 1 to 3, characterized in that: The invention comprises an oxypropylated and DOPO phosphoesterified modified structure of a cassava residue phenolization product, a hydroxyl value of 280-650 mg KOH / g, a viscosity of 1000-6500 mPa·s at 25°C, and a phosphorus content of 1.2-2.8 wt%.

5. A method for preparing a flame retardant polyurethane foam, characterized in that: The mixed polyol containing the cassava residue-derived intrinsic flame-retardant polyol according to claim 4, a catalyst, an organosilicon foam stabilizer, and a physical foaming agent are mixed, isocyanate is added, stirred and foamed, and flame-retardant polyurethane foam is obtained after curing.

6. The preparation method according to claim 5, characterized in that: Calculated by weight, the foaming formula includes: 100 parts of mixed polyols, of which cassava residue-derived intrinsic flame retardant polyols account for 20-70% of the mixed polyols; 0.5-3 parts of amine catalysts; 0.5-3 parts of organotin catalysts; 0.5-3 parts of organosilicon foam stabilizers; 10-30 parts of physical foaming agents; 1-10 parts of water; and 80-130 parts of isocyanates.

7. The preparation method according to claim 6, characterized in that: The isocyanate is selected from one of TDI, MDI and polymeric MDI.

8. A flame retardant polyurethane foam prepared according to any one of claims 5 to 7, characterized in that: The limiting oxygen index of polyurethane foam is 26-32%, the UL-94 vertical combustion grade is V-0, the compression strength is 70-140 kPa, and the density is 30-50 kg / m³.

9. Use of the flame retardant polyurethane foam according to claim 8 in thermal insulation of building exterior walls.

Images