Cassava residue-derived intrinsically flame-retardant polyol, flame-retardant polyurethane foam, and preparation method and application thereof

Abstract

The present invention belongs to the technical field of high-value utilization of biomass resources and polymer materials, and relates to a cassava residue-derived intrinsically flame-retardant polyol, a flame-retardant polyurethane foam, and a preparation method and application thereof. The wet cassava residue is pretreated by screw extrusion dehydration, pulsed air drying and ultrafine pulverization to obtain cassava residue powder; a segmented acid-catalyzed liquefaction technology is adopted to separately convert the starch and lignocellulose in the cassava residue into starch-based and lignocellulose-based phenolic liquefaction products; an intrinsically flame-retardant polyol is prepared through the synergistic modification of oxypropylation and phosphoesterification. The obtained polyol is foamed in one step with isocyanate to prepare a high-performance flame-retardant polyurethane foam, which has a limiting oxygen index of 26-32%, a UL-94 vertical burning rating of V-0, a compressive strength of 70-140 kPa, and a density of 30-50 kg / m³, realizing the high-value utilization of all components of cassava residue and being applicable to fields such as building insulation and buffer packaging.

Description

Technical Field

[0001] The present invention belongs to the technical fields 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 utilization 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. Cassava residue, as the main by-product of cassava starch processing, is considered a highly potential low-cost biomass resource due to its rich starch and cellulose and other convertible components. However, the current utilization methods of cassava residue mainly focus on 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 spoilage.

[0003] Over the years, scholars at home and abroad have carried out extensive research on the resource utilization of cassava residue, mainly focusing on two directions: biological fermentation and composite materials. The biological fermentation method aims to convert cassava residue into high-value-added products such as organic acids and fuel ethanol, but generally suffers from problems such as low enzymatic hydrolysis efficiency and high separation costs; in the field of composite materials, efforts are focused on converting cassava residue into functional materials, such as extracting nanocellulose to enhance composite materials or biodegradable plastics, but these technologies still face challenges such as poor interfacial compatibility between fibers and matrices and insufficient product performance in practical applications.

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

[0005] Chinese Patent CN115044031A discloses a method for synthesizing a biomass-based flame-retardant polyether polyol. A typical biomass platform compound, 5-hydroxymethylfurfural, is molecularly grafted with melamine to form a novel covalent compound intermediate, which is then subjected to a ring-opening polymerization reaction with ethylene oxide and / or propylene oxide to obtain a novel flame-retardant polyether polyol product. In this patent, an ether is formed by the reaction of the hydroxymethyl group in hydroxymethylfurfural with the amino group of melamine, and then a polyol is generated through the reaction of the remaining amino group with propylene oxide. However, there are few reactive sites, resulting in limited flame-retardant ability of the prepared polyether polyol.

[0006] Chinese Patent CN112778512A discloses a biomass-based polyether polyol derived from seaweed and its preparation method. Using seaweed powder as the raw material, reactive liquefied seaweed is obtained under the action of a liquefying agent and a catalyst. Then, the liquefied seaweed is used as an initiator and polymerized with an alkylene oxide under the action of a polymerization catalyst. Since the seaweed contains fibrous polysaccharides and the fiber itself contains flame-retardant elements, the polyether polyol prepared therefrom has flame-retardant properties. Here, the alkylene oxide is used to undergo an etherification reaction with the liquefied seaweed (containing alcohol hydroxyl groups) to form a polyether polyol, and the flame retardancy stems from the fibrous polysaccharides containing flame-retardant elements in the seaweed fiber itself, but the flame-retardant ability is poor.

[0007] Based on the deficiencies in the preparation of intrinsic flame-retardant polyols mentioned above, and the fact that existing research mainly focuses on raw materials such as vegetable oils, lignocellulose, and straw, the research on the liquefaction of cassava residues and the preparation of polyols is still in its infancy. In particular, there are no reports on the development of intrinsic flame-retardant polyols from cassava residues. Therefore, it is particularly important to develop a preparation method for cassava residue-derived intrinsic flame-retardant polyols with excellent flame-retardant performance. Summary of the Invention

[0008] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a cassava residue-derived intrinsic flame-retardant polyol, a flame-retardant polyurethane foam, and their preparation methods and applications. Using cassava residues as raw materials, through solid acid-catalyzed phenolation, combined with oxypropyl ring-opening etherification and phosphorylation reactions, an N-P highly efficient intrinsic synergistic flame-retardant polyol is prepared by utilizing the high reactivity of groups such as phenolic hydroxyl groups, epoxy groups, and amino groups. When this polyol is applied to polyurethane foam materials, it has excellent flame-retardant performance and significant environmental and economic value. This technical route not only meets the strategic requirements of sustainable development but also opens up a new way for the high-value utilization of cassava residues, which is of great significance for promoting the transformation of biomass resources and the green transformation of the polyurethane industry.

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

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

[0011] (1) Pretreatment of cassava residue: The wet cassava residue is successively subjected to screw extrusion, pneumatic drying, and ultrafine pulverization to obtain cassava residue powder;

[0012] (2) Stepwise acid-catalyzed liquefaction: In a closed reaction vessel, cassava residue powder and molten phenol with a mass ratio of 1:2.0 - 3.0 are stirred and mixed evenly at 60°C, and a solid acid catalyst accounting for 0.5 - 6.0% of the total mass of cassava residue powder and molten phenol is added for the first-stage reaction. The reaction is carried out at 110 - 150°C for 5 - 15 min, then ethanol is added for centrifugal separation. The upper mobile phase is the phenolated component A of cassava residue, and the lower solid matter 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 then ethanol is added for centrifugal separation to obtain the phenolated component B; The phenolated component A and the phenolated component B are combined, and ethanol is removed to obtain the phenolated liquefaction product of cassava residue for standby; The solid acid catalyst is one of solid superacids, molecular sieves, or composite oxides. The solid superacid is or , the molecular sieve is ZSM-5 or Y-type molecular sieve, and the composite oxide is ;

[0013] (3) Propoxylation and phosphation modification: The phenolated liquefaction product of cassava residue and potassium hydroxide are mixed in a high-pressure autoclave at a mass ratio of 100:2 - 5, and nitrogen is purged to remove air, and then water is removed by vacuum distillation. The temperature is raised to 120 - 130°C, and a propoxylation reagent with a mass 1.1 - 2.5 times that of the phenolated liquefaction product of cassava residue is slowly introduced. After the curing reaction for 2 - 5 h, phosphoric acid is added for neutralization to obtain the propoxylated product; The esterification reagent DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) is added to the high-pressure autoclave, and triethylamine is used as a catalyst. The reaction is carried out at 130 - 150°C for 2 - 4 h under nitrogen protection, and after phosphoric acid neutralization, it is cooled to room temperature to obtain the intrinsically flame-retardant polyol derived from cassava residue. The propoxylation reagent is propylene oxide, N-(2,3-epoxypropyl)amine, or N-methyl-2,3-epoxypropylamine. The mass ratio of DOPO to the propoxylated product is 1.5 - 2.5:10, and the dosage of triethylamine is 1 - 3% of the total mass of the reagents participating in the esterification reaction.

[0014] Preferably, the wet cassava residue in the above step (1) is a by-product after starch extraction in a cassava starch factory, with a water content of 80-85%, and its main components are lignocellulose, starch, protein and ash; the dehydration method preferably uses screw extrusion dehydration with continuous operation, low energy consumption and high automation. After treatment, the water content is not higher than 45%. The screen hole 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 air flow dryer with a intensifier for drying. Its characteristic is that the wet material enters the intensifier through screw feeding, and under the impact, crushing and propulsion of the rapidly rotating blades, it is fully mixed with the hot air flow. The material is broken into fine particles and suspended by the high-speed hot air flow. Through the alternating change of the pipe diameter, the relative speed and heat transfer area of the material and the air flow are greatly increased, greatly improving the heat transfer efficiency, and can efficiently dry the material in a short time. The inlet hot air temperature of the pulse air flow drying is 180-220 °C, the wind speed is 20-30 m / s, and the water content of the dried material is ≤12%; the ultrafine pulverization method is a jet mill, the pulverization pressure is 0.8-1.2 MPa, and the particle size of the pulverized material is controlled within 300-400 mesh. This process highly homogenizes starch and lignocellulose particles, significantly increases the specific surface area, improves the efficiency of phenolic liquefaction reaction, makes the physicochemical properties of the liquefied products prepared from cassava residue powder more stable, and promotes the fragmentation of starch particles, which is beneficial to the staged generation and separation of biomass components.

[0015] Preferably, the temperature of the centrifugal separation 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 phenolic reaction of starch and fiber in the cassava residue powder. The main product obtained from the first centrifugal separation is the liquefied product of the starch component, and the product obtained from the second centrifugation is the phenolic product of the lignocellulose component.

[0016] Preferably, when 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 the 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, which contains an oxypropylated and DOPO-phosphorylated modified structure of a cassava residue phenolation product, with a hydroxyl value of 280-650 mg KOH / g, a viscosity of 1000-6500 mPa·s, and a phosphorus element content of 1.2-2.8 wt%.

[0018] The third aspect of the present invention discloses a method for preparing a flame-retardant polyurethane foam, which mixes a mixed polyol containing a cassava residue-derived intrinsic flame-retardant polyol, a catalyst, an organosilicon foam stabilizer, and a physical foaming agent, adds isocyanate and stirs to foam, and obtains a flame-retardant polyurethane foam after curing.

[0019] Preferably, the above mixed polyol is composed of a cassava residue-derived intrinsic flame-retardant polyol and a bio-based polyol, a polyol synthesized from petrochemical raw materials, a polyether polyol or a polyester polyol in a certain proportion, and the proportion of the cassava residue-derived intrinsic flame-retardant polyol in the mixed polyol is 20-70 wt%.

[0020] Preferably, by weight fraction, the foaming formula is: 100 parts of mixed polyol, 0.5-3 parts of amine catalyst, 0.5-3 parts of organotin catalyst, 0.5-3 parts of organosilicon foam stabilizer, 10-30 parts of physical foaming agent, 1-10 parts of water, and 80-130 parts of isocyanate. 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-tetrafluoropropene), dichloroethane monofluoride or HFOs (hydrofluorocarbons). The isocyanate is one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) or polyisocyanate (polymeric MDI). The organosilicon 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, and the limiting oxygen index of the polyurethane foam is 26-32%, the UL-94 vertical burning grade is V-0, the compressive strength is 70-140 kPa, and the density is 30-50 kg / m³.

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

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

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

[0025] (2) The polyurethane foam prepared from 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 burning rating of V-0, a compressive strength of 70-140 kPa, and no obvious attenuation in compressive strength compared with petrochemical-based polyurethane, and a density of 30-50 kg / m³.

[0026] (3) Through screw extrusion-pulse air drying-ultrafine grinding pretreatment, efficient industrial dehydration of wet cassava residue is achieved, significantly increasing the specific surface area and enhancing the efficiency of phenol liquefaction reaction. Through methods such as particle size control, segmented liquefaction, and freeze centrifugal separation, the regulated phenolation of starch and lignocellulose is realized, and the hydroxyl value, viscosity, and intrinsic flame-retardant properties of the cassava residue phenolated product can be adjusted. Specific Embodiments

[0027] The present invention will be further described in detail below through specific embodiments. The following embodiments are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0028] Example 1

[0029] A preparation method of a cassava residue-derived intrinsic flame-retardant polyol, comprising:

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

[0031] 1) Dehydration: Take wet cassava residue with a moisture content of 83%, and perform dehydration treatment through a single-screw extrusion dehydrator, where the sieve hole diameter of the dehydrator is 0.2 mm, the compression ratio is 4.5, and the moisture content of the material after dehydration drops to 42%;

[0032] 2) Drying: Feed the dehydrated cassava residue into a strengthened pulse air dryer, control the inlet hot air temperature at 200 °C, the air velocity at 25 m / s, and the moisture content of the cassava residue at the outlet after drying is 11.5%;

[0033] 3) Ultrafine grinding: Use a pneumatic ultrafine grinder to grind the dried cassava residue, control the air pressure at 1.0 MPa, the air flow velocity at 200 m / s, and the working temperature at 40 °C to obtain cassava residue powder with a particle size of 350 mesh and a dryness of 95%;

[0034] After the above treatment, the lignocellulosic tissue in the cassava residue is completely disintegrated and dispersed into irregular fragments about 40 μm in size, and the coated starch granules are dispersed and removed, and the specific surface area of the dry powder is increased to 1.2 m² / g.

[0035] (2) Stepwise acid-catalyzed liquefaction: Mix 10 g of cassava residue powder with 25 g of molten phenol at 60 °C for 10 min, heat up to 110 °C under nitrogen protection, add 0.2 g of solid acid catalyst and react for 10 min, add 70 mL of ethanol to reduce the viscosity of the system, transfer to a centrifuge tube and centrifuge at 5 °C and 12,000 r / min for 8 min. The upper-layer mobile phase is the phenolated component A of the cassava residue and is reserved. Mix 6.5 g of the lower-layer solid matter with 13 g of molten phenol, react at 120 °C for 20 min, then add 30 mL of ethanol to reduce the viscosity, and centrifuge under the same conditions for 10 min to obtain the phenolated component B. Combine the phenolated component A and the phenolated component B, and remove ethanol by vacuum distillation to obtain the phenolated liquefaction product of the cassava residue. The comprehensive liquefaction rate of the cassava residue reaches 96.2%.

[0036] (3) Propoxylation and phosphation modification: Take 20 g of the above-mentioned phenolated liquefaction product of the cassava residue and 0.5 g of potassium hydroxide and add them to a high-pressure reaction kettle. Purge with nitrogen to remove air, dehydrate under reduced pressure, then introduce 24 g of propylene oxide, heat to 120 °C, and control the pressure in the kettle <0.2 MPa to carry out propoxylation reaction for 3 h until atmospheric pressure. After neutralization with phosphoric acid, add 10 g of DOPO and 1.3 g of triethylamine, react at 130 °C for 4 h under nitrogen protection, and cool after neutralization with phosphoric acid to obtain the intrinsically flame-retardant polyol derived from the cassava residue.

[0037] Characterize the intrinsically flame-retardant polyol derived from the cassava residue prepared in Example 1. The polyol is brownish liquid, the dynamic viscosity is 5740 mPa·s (25 °C), the hydroxyl value is 490 mg KOH / g, and the phosphorus element content is 2.2 wt%.

[0038] Process advantages: Based on the similar liquefaction paths and different liquefaction rates of starch and lignocellulose in the cassava residue in phenol, a stepwise low-temperature liquefaction combined with solid acid catalysis technology is adopted, and the controllable liquefaction separation of starch and fiber components is realized by freezing and high-speed centrifugation. Propoxylation modification effectively regulates the viscosity and hydroxyl value of the phenolated product, reduces the steric hindrance of the reaction between hydroxyl groups and DOPO, and thus improves the efficiency of the phosphation 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 dimethyl silicone, 0.12 g of H2O, and 2.04 g of dichloroethane monofluoride, mix them evenly, add 10.30 g of diphenylmethane diisocyanate, and then stir rapidly at a speed of 2000 r / min for 15 - 20 seconds until it turns milky white and foams spontaneously, and cure at 80 °C for 12 h.

[0041] Characterize the polyurethane foam prepared in Example 1. It is a light brown rigid foam with uniform and delicate pores. Density: 38.6 kg / m³, compressive strength: 108 kPa, limiting oxygen index (LOI): 29%, UL-94 vertical burning rating: V-1.

[0042] Example 2: Application of N-P Synergistic Flame Retardant Modification of Cassava Residue Phenolic Liquefaction Product and Improvement of Its PUF Performance

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

[0044] Characterize the cassava residue-derived intrinsic flame-retardant polyol prepared in Example 2. The polyol is a brownish 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 rigid polyurethane foam

[0046] Mix 6.0 g of the above-mentioned cassava residue-based liquefaction 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 dimethyl silicone, 0.15 g of H2O, and 2.20 g of dichloroethane monofluoride evenly, add 10.30 g of diphenylmethane diisocyanate, and then stir rapidly at a speed of 2000 r / min for 15 - 20 seconds until it turns milky white and foams spontaneously, and cure at 80 °C for 12 h.

[0047] The flame-retardant polyurethane foam prepared in Example 2 was characterized. The foam properties are as follows: it is a brown rigid foam with uniform and delicate pores, the density is 34.8 kg / m³, the compressive strength is 102 kPa, the limiting oxygen index (LOI) is 31%, and the UL-94 vertical burning rating is V-0 grade.

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

[0049] (1) A preparation method of cassava residue-derived intrinsically flame-retardant polyol, comprising:

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

[0051] Mix 10 g of cassava residue powder (prepared in the same way as in Example 1) with 30 g of molten phenol at 60°C for 15 min. After heating to 130°C under nitrogen protection, add 1.5 g of HZSM-5 molecular sieve catalyst. After liquefaction reaction for 20 min, add 70 mL of ethanol for dilution, and centrifuge at 5°C and 12,000 r / min for 8 min to collect the upper mobile phase, which is the phenolic component A of cassava residue and is reserved. The lower solid (5.8 g) is mixed with 15 g of molten phenol for the second time and liquefied at 140°C for 30 min. After adding 40 mL of ethanol, centrifuge under the same conditions for 10 min to obtain phenolic component B. Combine phenolic component A and phenolic component B, and remove ethanol by vacuum distillation at 45°C to obtain a dark brown liquefaction product, which is the phenolic liquefaction product of cassava residue, and the comprehensive liquefaction rate reaches 98.1%.

[0052] 2) Synthesis of cassava residue-derived intrinsically flame-retardant polyol:

[0053] Take 20 g of the phenolic liquefaction product of cassava residue and 0.6 g of potassium hydroxide and add them to a high-pressure reaction kettle. Purge air with nitrogen. After vacuum dehydration at 105°C for 1 h, add 35 g of N-(2,3-epoxypropyl)amine in three portions. Control the reaction temperature at 130°C and carry out ring-opening grafting reaction for 3 h. After neutralization with phosphoric acid, add 12 g of DOPO and 1.5 g of triethylamine, and react at 135°C for 6 h under nitrogen protection. The final product is neutralized to obtain a brown viscous cassava residue-derived intrinsically flame-retardant polyol.

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

[0055] Preparation method of polyurethane foam:

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

[0057] Characterize the polyurethane foam prepared in Example 3. It is a yellowish-brown rigid foam with uniform cell structure, density: 40 kg / m³, compressive strength of 120 kPa, limiting oxygen index (LOI) of 31%, and UL-94 vertical burning rating of V-0.

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

[0059] (1) A preparation method of a cassava residue-derived intrinsic flame-retardant polyol, including:

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

[0061] Premix 10 g of cassava residue powder (the preparation method is the same as that in Example 1) with 25 g of molten phenol at 60 °C for 15 min, heat up to 120 °C under nitrogen protection, add 1.2 g of HZSM-5 (molecular sieve catalyst), react for 10 min, add 70 mL of ethanol for dilution, centrifuge at 5 °C and 12000 r / min for 10 min, and collect the upper layer of wine-red mobile phase, namely cassava residue phenolic component A, for standby. Mix the lower-layer solid (6.9 g) with 15 g of molten phenol, continue to liquefy at 120 °C for 35 min, add 40 mL of ethanol and centrifuge under the same conditions for 10 min to obtain phenolic component B. Combine phenolic component A and phenolic component B, and remove ethanol by vacuum distillation at 45 °C to obtain a dark red liquefaction product, namely cassava residue phenolic liquefaction product (comprehensive liquefaction rate 97.2%).

[0062] 2) Synthesis of cassava residue-derived intrinsic flame-retardant polyol flexible foam polyol:

[0063] Take 20 g of the phenolic liquefaction product of cassava residue and 0.6 g of potassium hydroxide and add them to an autoclave. Purge the air with nitrogen and dehydrate under reduced pressure at 105°C for 1 hour. Add 15 ml of acetone to adjust the viscosity (since the liquefaction conditions become milder and the viscosity of the liquefaction product is too high, which is not conducive to the subsequent reaction, the purpose of adding acetone is to reduce the viscosity of the flame retardant modification system), and then add 35 g of N-methyl-2,3-epoxypropylamine in three portions. Control the temperature at 130°C and react for 4.5 h. After neutralization with phosphoric acid, add 8 g of DOPO and 1.5 g of triethylamine, and react at 135°C for 4 hours under nitrogen protection. After neutralization with phosphoric acid and cooling, a brownish-red cassava residue-derived intrinsic flame-retardant polyol is obtained.

[0064] Characterize the cassava residue-derived intrinsic flame-retardant polyol prepared in Example 4. It is a brownish-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 above-mentioned 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 surfactant, 0.1 g of water, 2.5 g of physical blowing 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 to stir for 15 seconds after adding MDI for spontaneous foaming, and cure at 80°C for 2 h.

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

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

[0069] (1)A preparation method of a cassava residue-derived intrinsic flame-retardant polyol, including:

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

[0071] Premix 10 g of cassava residue powder (the preparation method is the same as in Example 1) with 30 g of molten phenol at 60°C for 15 min, and raise the temperature to 150°C under nitrogen protection. Add 1.2 g React for 30 min, add 70 mL of ethanol for dilution, centrifuge at 5 °C and 12,000 r / min for 10 min, collect the upper black-brown mobile phase, which is the phenolic component A of cassava residue, and reserve it. Mix the lower solid (5.6 g) with 15 g of molten phenol, continue to liquefy at 150 °C for 45 min, add 40 mL of ethanol and centrifuge under the same conditions for 10 min to obtain the phenolic component B. Combine the phenolic component A and the phenolic component B, combine the two centrifugates, and remove ethanol by vacuum distillation at 45 °C to obtain a black-brown phenolic liquefied product of cassava residue (the comprehensive liquefaction rate is 99.1%).

[0072] 2) Synthesis of cassava residue-derived intrinsic flame-retardant polyol:

[0073] Take 20 g of the phenolic liquefied product of cassava residue and 0.6 g of potassium hydroxide and add them to a high-pressure reactor. Purge with nitrogen to remove air, and dehydrate under reduced pressure at 105 °C for 1 h. After dehydration under reduced pressure, introduce 24 g of propylene oxide, heat to 120 °C, control the pressure in the reactor <0.2 MPa, and carry out the oxypropylation reaction for 3 h until normal pressure. After neutralization with phosphoric acid, add 8 g of DOPO and 1.3 g of triethylamine, and react at 130 °C for 4.5 h under nitrogen protection. After neutralization with phosphoric acid, cool to obtain the cassava residue-derived intrinsic flame-retardant polyol.

[0074] Characterize the cassava residue-derived intrinsic flame-retardant polyol prepared in Example 5. It is 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 thermal insulation rigid polyurethane foam

[0076] Take 4.5 g of the above-mentioned 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 blowing 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 to stir for 20 seconds for spontaneous foaming, and cure at 80 °C for 8 h.

[0077] The polyurethane foam prepared in Example 5 was characterized. It was a grayish-brown rigid foam with uniform and delicate pores. Density: 42 kg / m³, thermal conductivity 0.021 w / (m•K), compressive strength 130 kPa, limiting oxygen index (LOI) 29%, reaching Class B-1 of GB 8624 - 2017 "Classification of the Burning Performance of Building Materials and Products".

[0078] Comparative Example 1

[0079] The difference from Example 1 was only that the pretreatment process of wet cassava residue was a conventional process. The specific steps were as follows: After air-drying the wet cassava residue, it was dried to a constant weight using a blast dryer; 100 g of dry cassava residue was taken and pulverized with a traditional Chinese medicine powder grinder for standby. According to the method of Example 1, the cassava residue powder was subjected to phenolic liquefaction and flame retardant modification, and 5 groups of 10 g of cassava residue powder were taken for parallel experiments.

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

[0081] The method for preparing the polyurethane foam was the same as that in Example 1. The prepared polyurethane foam was in colors such as beige, brownish-yellow, and dark brown, with uneven colors, semi-rigid foam or rigid foam, uneven pores or burned pores. Density: 35 - 40 kg / m³, compressive strength 70 - 110 kPa, limiting oxygen index (LOI) 25 - 26%.

[0082] Comparative Example 2

[0083] The difference from Example 1 was only that the step (2) did not adopt the segmented catalytic liquefaction reaction. The specific steps were as follows:

[0084] (1) Catalytic liquefaction of cassava residue powder: 10 g of cassava residue powder was stirred and mixed with 40 g of molten phenol at 60°C for 10 min, heated to 110°C under nitrogen protection, 0.2 g of solid acid catalyst was added and reacted for 10 min, then heated to 120°C and reacted for 20 min. 100 mL of ethanol was added to reduce the viscosity, transferred to a centrifuge tube, centrifuged at 5°C and 12,000 r / min for 10 min, and ethanol was removed by vacuum distillation to obtain the phenolic liquefaction product of cassava residue. The comprehensive liquefaction rate of cassava residue reached 91.5%.

[0085] (3)Oxidation propylation and phosphorylation modification: Take 20 g of the phenolic liquefaction product of the above-mentioned cassava residue and 0.5 g of potassium hydroxide and add them to a high-pressure reactor. Purge with nitrogen to remove air. After dehydration under reduced pressure, introduce 24 g of propylene oxide, heat to 120 °C, control the pressure in the reactor <0.2 MPa, and carry out the oxidation propylation reaction for 3 h until normal pressure. After neutralization with phosphoric acid, add 10 g of DOPO and 1.3 g of triethylamine, and react at 130 °C for 4 h under nitrogen protection. After neutralization with phosphoric acid and cooling, the cassava residue-derived intrinsic flame-retardant polyol is obtained.

[0086] Characterize the cassava residue-derived intrinsic flame-retardant polyol prepared in Comparative Example 2. The polyol is 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 element content of 1.2 wt%.

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

[0088] Comparative Example 3

[0089] The difference from Example 1 is only that in step (3), only phosphorylation modification is carried out without oxidation propylation. The specific steps are as follows: Take 20 g of the phenolic liquefaction product of the cassava residue described in Example 1 and 0.5 g of potassium hydroxide and add them to a high-pressure reactor. Purge with nitrogen to remove air. After dehydration under reduced pressure, add 10 g of DOPO and 1.3 g of triethylamine, and react at 130 °C for 4 h under nitrogen protection. After neutralization with phosphoric acid and cooling, the cassava residue-derived intrinsic flame-retardant polyol is obtained.

[0090] Characterize the cassava residue-derived intrinsic flame-retardant polyol prepared in Comparative Example 3. The polyol is 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 element content of 0.7 wt%.

[0091] The method for preparing the polyurethane foam is the same as that in Example 1. The prepared polyurethane foam is brown, with surface cracks and internal collapse of the foam.

[0092] Comparative Example 4

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

[0094] 20 g of the phenolic liquefaction product of cassava residue described in Example 1 and 0.5 g of potassium hydroxide were added to an autoclave. The air was purged with nitrogen, and after dehydration under reduced pressure, 24 g of propylene oxide was introduced. It was heated to 120 °C, and the oxypropylation reaction was carried out at a pressure in the autoclave <0.2 MPa for 3 h until normal pressure. After neutralization with phosphoric acid, 10 g of DPP (diphenyl phosphate) and 1.3 g of triethylamine were added, and the reaction was carried out at 130 °C for 4 h under nitrogen protection. After neutralization with phosphoric acid and cooling, cassava residue-derived polyol was obtained.

[0095] The characteristics of the cassava residue-derived polyol prepared in Comparative Example 4 were 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 element content of 0.2 wt%.

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

[0097] The characteristic parameters of the cassava residue-derived intrinsically 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 intrinsically 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, it can be seen that the viscosities and hydroxyl values of the cassava residue-derived intrinsically flame-retardant polyols prepared by the method of the present application in Examples 1-5 are controllable, the phosphorus content and / or nitrogen content are relatively high, and the limiting oxygen indices of the prepared polyurethane foams are all higher than those of the comparative examples, with uniform cell sizes and excellent flame-retardant properties.

[0103] In the cassava residue powder prepared in Comparative Example 1, the lignin fibers were not sufficiently pulverized, and the obtained particles were irregular in shape, with a size distribution of dozens to hundreds of micrometers, and short coarse fiber fragments could be seen in the residue powder. During the pulverization process, the starch and fiber components showed a separation and concentration phenomenon. The small particles (mainly starch) were distributed in the upper layer, and the large particles (mainly fiber) were deposited at the bottom. Due to the uneven distribution of starch and fiber, the ratios of starch and fiber in the 5 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 and hydroxyl value of the liquefaction product in the first stage are high, and the lignocellulose degradation in the second stage is more complete; when the lignocellulose content is high, although the starch can be rapidly degraded and deeply phenolated in the first stage, the liquefaction of lignocellulose in the second stage is insufficient. In addition, due to the large fluctuations in the ratio of starch to lignocellulose in cassava residue powder, it is difficult to concentrate the molecular structure of the phenolated liquefaction product and it shows diverse complexity, resulting in a low comprehensive liquefaction rate, unstable subsequent flame retardant modification effect, and obvious fluctuations in the physical properties of the foam.

[0105] In Comparative Example 2, starch was rapidly degraded and underwent a phenolation reaction under liquefaction conditions, first generating initial pyranose glucosyl phenol, and then further cracking into carbohydrate fragments, and finally reacting with phenol to form structural units similar to traditional phenolic resins. During this process, the hydroxyl value and viscosity of the system showed a trend of first increasing and then decreasing, but the rate of chain scission and phenolation of lignocellulose under the action of solid acid was slow.

[0106] In the present invention, by controlling appropriate reaction conditions and reaction time, the phenolated liquefaction products of starch and lignocellulose are timely separated from the reaction system to ensure that their molecular structures and viscosities are suitable for subsequent flame retardant modification. However, in Comparative Example 2, the degradation degree of the starch phenolation product is relatively deep, the content of phenolic hydroxyl groups in the molecular structure is high, and the content of alcoholic hydroxyl groups is low, resulting in poor molecular chain stretchability and being unfavorable for subsequent modification.

[0107] In Comparative Example 3, since the phenolated liquefaction product of cassava residue was prepared under relatively mild conditions, the molecular weight of the degraded biomass components is relatively large, and both the viscosity and hydroxyl value are high. Directly performing phosphorylation modification, the phosphorus content in the prepared flame retardant polyol is low and the flame retardancy is poor. Through the ring-opening reaction with propylene oxide or glycidylamine in this application, the molecular configuration and the hydroxyl value of the system are appropriately adjusted, which is beneficial to the introduction of subsequent 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 reaction activity 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 cannot endow it with intrinsic flame retardant properties. 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-mentioned embodiments are only some embodiments with better effects of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments. Any equivalent replacement, deformation, and modification of some technical features within the creative concept and principles of the present invention shall be included within 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.

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