Placing the petri dish with the raw materials in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reactor pressure at 15 MPa, adjusting the reactor temperature to 48° C., reacting for 4 hours to obtain the graft product of silane and DOPO;

Mixing 7.5 g of TiO₂and 5 g of the obtained graft product of silane and DOPO in a petri dish, placing in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reaction system temperature at 55° C., and the reaction system pressure at 17 MPa, reacting for 5 hours, taking out the reaction product and placing it on a filter cake, washing with anhydrous ethanol 3 times; then air-drying in a fume hood, and transferring to a 90° C. vacuum oven for drying for 24 hours to obtain flame retardant B.

The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.8.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Example 2

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 0.8 of material A and material B; by mass parts, material A includes 100 parts of polyether polyol, 90 parts of polyester polyol, 10 parts of chain extender, 1 part of catalyst, 20 parts of flame retardant, 0.5 parts of water, and 3 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:0.8;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1.3;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is pentaerythritol; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.5;
- The catalyst is a mixture of triethanolamine and dibutyltin dilaurate in a mass ratio of 1:1;
- The flame retardant is composed of flame retardant A and flame retardant B in a mass ratio of 10:1;
- The preparation method of flame retardant B includes the following steps: placing 6.0 g of DOPO, 1.8 g of methacryloxypropyltrimethoxysilane, and 1.5 g of vinyltri(β-methoxyethoxy)silane in a petri dish, mixing, then adding 0.10 g of triethylamine to the petri dish as raw materials for standby;
- Placing the petri dish with the raw materials in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reactor pressure at 16.5 MPa, adjusting the reactor temperature to 40° C., reacting for 7 hours to obtain the graft product of silane and DOPO;
- Mixing 11 g of TiO₂and 5 g of the obtained graft product of silane and DOPO in a petri dish, placing in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reaction system temperature at 45° C., and the reaction system pressure at 19 MPa, reacting for 3 hours, taking out the reaction product and placing it on a filter cake, washing with anhydrous ethanol 3 times; then air-drying in a fume hood, and transferring to a 90° C. vacuum oven for drying for 24 hours to obtain flame retardant B.

The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.8.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Example 3

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 15 parts of flame retardant, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is a mixture of rhodium chloride and strontium chloride in a mass ratio of 1:1;
- The flame retardant is composed of flame retardant A and flame retardant B in a mass ratio of 10:1.5;

The preparation method of flame retardant B includes the following steps:

- Placing 5.8 g of DOPO, 2.1 g of methacryloxypropyltrimethoxysilane, and 1.6 g of vinyltri(β-methoxyethoxy)silane in a petri dish, mixing, then adding 0.12 g of triethylamine to the petri dish as raw materials for standby;
- Placing the petri dish with the raw materials in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reactor pressure at 16 MPa, adjusting the reactor temperature to 45° C., reacting for 6 hours to obtain the graft product of silane and DOPO;
- Mixing 10 g of TiO₂and 5 g of the obtained graft product of silane and DOPO in a petri dish, placing in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reaction system temperature at 50° C., and the reaction system pressure at 18 MPa, reacting for 4 hours, taking out the reaction product and placing it on a filter cake, washing with anhydrous ethanol 3 times; then air-drying in a fume hood, and transferring to a 90° C. vacuum oven for drying for 24 hours to obtain flame retardant B. The grafting rate of surface functional molecules of the obtained flame retardant B is 70%, as shown in FIG. 1, which is the thermogravimetric analysis diagram of flame retardant B;
- The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Example 4

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 15 parts of flame retardant, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is rhodium chloride;
- The flame retardant is composed of flame retardant A and flame retardant B in a mass ratio of 10:1.5;

The preparation method of flame retardant B includes the following steps:

- Placing 5.8 g of DOPO, 2.1 g of methacryloxypropyltrimethoxysilane, and 1.6 g of vinyltri(β-methoxyethoxy)silane in a petri dish, mixing, then adding 0.12 g of triethylamine to the petri dish as raw materials for standby;
- Placing the petri dish with the raw materials in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reactor pressure at 16 MPa, adjusting the reactor temperature to 45° C., reacting for 6 hours to obtain the graft product of silane and DOPO;
- Mixing 10 g of TiO₂and 5 g of the obtained graft product of silane and DOPO in a petri dish, placing in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reaction system temperature at 50° C., and the reaction system pressure at 18 MPa, reacting for 4 hours, taking out the reaction product and placing it on a filter cake, washing with anhydrous ethanol 3 times; then air-drying in a fume hood, and transferring to a 90° C. vacuum oven for drying for 24 hours to obtain flame retardant B. The grafting rate of surface functional molecules of the obtained flame retardant B is 70%;
- The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Example 5

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 15 parts of flame retardant, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is strontium chloride;
- The flame retardant is composed of flame retardant A and flame retardant B in a mass ratio of 10:1.5;

The preparation method of flame retardant B includes the following steps:

- Placing 5.8 g of DOPO, 2.1 g of methacryloxypropyltrimethoxysilane, and 1.6 g of vinyltri(β-methoxyethoxy)silane in a petri dish, mixing, then adding 0.12 g of triethylamine to the petri dish as raw materials for standby;
- Placing the petri dish with the raw materials in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reactor pressure at 16 MPa, adjusting the reactor temperature to 45° C., reacting for 6 hours to obtain the graft product of silane and DOPO;
- Mixing 10 g of TiO₂and 5 g of the obtained graft product of silane and DOPO in a petri dish, placing in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reaction system temperature at 50° C., and the reaction system pressure at 18 MPa, reacting for 4 hours, taking out the reaction product and placing it on a filter cake, washing with anhydrous ethanol 3 times; then air-drying in a fume hood, and transferring to a 90° C. vacuum oven for drying for 24 hours to obtain flame retardant B. The grafting rate of surface functional molecules of the obtained flame retardant B is 70%;
- The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Comparative Example 1

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 15 parts of flame retardant, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is a mixture of rhodium chloride and strontium chloride in a mass ratio of 1:1;
- The flame retardant is flame retardant A;
- The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Comparative Example 2

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 15 parts of flame retardant, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is a mixture of rhodium chloride and strontium chloride in a mass ratio of 1:1;
- The flame retardant is the same flame retardant B used in Example 3;
- The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Comparative Example 3

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is a mixture of rhodium chloride and strontium chloride in a mass ratio of 1:1;
- The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Comparative Example 4

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 15 parts of flame retardant, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is a mixture of rhodium chloride and strontium chloride in a mass ratio of 1:1;
- The flame retardant is composed of flame retardant A and flame retardant B in a mass ratio of 10:0.9; the flame retardant B is the same as used in Example 3;
- The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Comparative Example 5

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 15 parts of flame retardant, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is a mixture of rhodium chloride and strontium chloride in a mass ratio of 1:1;
- The flame retardant is composed of flame retardant A and flame retardant B in a mass ratio of 10:2.6; the flame retardant B is the same as used in Example 3;
- The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Comparative Example 6

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 15 parts of flame retardant, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is a mixture of rhodium chloride and strontium chloride in a mass ratio of 1:1;

The flame retardant is composed of flame retardant A and flame retardant B in a mass ratio of 10:1.5; the preparation method of flame retardant A is as follows:

- Adding 218 g (1 mol) of pyromellitic dianhydride, 212 g (2 mol) of diethylene glycol, and 0.43 g of potassium fluorotitanate sequentially into a four-neck flask, slowly heating to 120-140° C. Stopping the reaction when the acid value of the product is ≤1.5 mg KOH/g; cooling to below 90° C. and filtering to obtain pyromellitic polyester polyol.

2) Adding 120 g of the obtained pyromellitic polyester polyol and 120 g of phosphorus trichloride into a reaction flask, reacting at 70° C. for 3 hours, then heating to 100° C. and maintaining for 4 hours, cooling, filtering, washing, and drying to obtain pyromellitic flame retardant polyester polyol;

- Adding 400 g of pyromellitic polyester polyol and 0.04 g of dimethylamine into a polyether reactor, reducing pressure, gradually adding 400 g of propylene oxide into the reactor, slowly heating to 120° C. with an internal pressure of 0.2 MPa, reacting at this temperature and pressure for 3 hours, then vacuuming, cooling to below 90° C., and filtering to obtain flame retardant A.

The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Comparative Example 7

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 15 parts of flame retardant, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is a mixture of rhodium chloride and strontium chloride in a mass ratio of 1:1;
- The flame retardant is composed of flame retardant A and flame retardant B in a mass ratio of 10:1.5;

The preparation method of flame retardant B includes the following steps:

- Placing 5.8 g of DOPO, 3.7 g of vinyltri(β-methoxyethoxy)silane in a petri dish, mixing, then adding 0.12 g of triethylamine to the petri dish as raw materials for standby;
- Placing the petri dish with the raw materials in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reactor pressure at 16 MPa, adjusting the reactor temperature to 45° C., reacting for 6 hours to obtain the graft product of silane and DOPO;
- Mixing 10 g of TiO₂and 5 g of the obtained graft product of silane and DOPO in a petri dish, placing in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reaction system temperature at 50° C., and the reaction system pressure at 18 MPa, reacting for 4 hours, taking out the reaction product and placing it on a filter cake, washing with anhydrous ethanol 3 times; then air-drying in a fume hood, and transferring to a 90° C. vacuum oven for drying for 24 hours to obtain flame retardant B;
- The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Comparative Example 8

A spray-applied polyurethane insulation material for tunnels in cold regions, composed of raw materials with a mass ratio of 1:1 of material A and material B; by mass parts, material A includes 95 parts of polyether polyol, 95 parts of polyester polyol, 8 parts of chain extender, 3 parts of catalyst, 15 parts of flame retardant, 2 parts of water, and 2 parts of surfactant;

- The B component is diphenylmethane diisocyanate;
- The polyether polyol includes polyether polyol a, polyether polyol b, and polyether polyol c in a mass ratio of 1:1:1;
- The polyester polyol includes polyester polyol a and b in a mass ratio of 1:1;
- Polyester polyol a is a polycondensation product obtained by reacting polyol and dicarboxylic acid at 140-200° C., with a functionality of 2, viscosity of 9000-15000 mPa·s, and hydroxyl value of 500-600 mgKOH/g; the polyol is a mixture of diethylene glycol and trimethylolpropane in a mass ratio of 1:1; the dicarboxylic acid is phthalic anhydride;
- The chain extender is 1,4-butanediol and pentaerythritol in a mass ratio of 1:0.3-0.5;
- The catalyst is a mixture of rhodium chloride and strontium chloride in a mass ratio of 1:1;
- The flame retardant is composed of flame retardant A and flame retardant B in a mass ratio of 10:1.5;

The preparation method of flame retardant B includes the following steps:

- Placing 5.8 g of DOPO, 3.7 g of methacryloxypropyltrimethoxysilane in a petri dish, mixing, then adding 0.12 g of triethylamine to the petri dish as raw materials for standby;
- Placing the petri dish with the raw materials in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reactor pressure at 16 MPa, adjusting the reactor temperature to 45° C., reacting for 6 hours to obtain the graft product of silane and DOPO;
- Mixing 10 g of TiO₂and 5 g of the obtained graft product of silane and DOPO in a petri dish, placing in a supercritical CO₂reactor and sealing, then introducing CO₂gas, with the reaction system temperature at 50° C., and the reaction system pressure at 18 MPa, reacting for 4 hours, taking out the reaction product and placing it on a filter cake, washing with anhydrous ethanol 3 times; then air-drying in a fume hood, and transferring to a 90° C. vacuum oven for drying for 24 hours to obtain flame retardant B;
- The surfactant is AK 8806 and AK 8810 organosilicon surfactants in a mass ratio of 1:0.6.

Using a two-component high-pressure spray foaming machine for foaming, controlling the temperature of material A and material B at 25±5° C., setting the pipeline temperature of the high-pressure foaming machine to 40° C., and atomizing and reacting material A and material B from the high-pressure gun head to form spray-applied polyurethane foam.

Performance Testing

Performance tests were conducted on the spray-applied polyurethane insulation materials for tunnels in cold regions from Examples 1-5 and Comparative Examples 1-8. The performance tests were based on the following standards:

- Testing density according to GB/T6343-2009;
- Testing compressive strength according to GB/T8813-2008;
- Testing oxygen index according to GB/T2406.2-2009;
- Testing closed-cell rate according to GB/T 10799-1989;
- Testing dimensional stability according to GB/T8811-2008;
- Testing thermal conductivity according to GB/T10294-2008;
- Testing cell diameter, flame retardant grade, smoke production grade, and smoke toxicity grade according to GB 8624-2012.

The results are shown in Tables 1-2:

TABLE 1

Sample
Example1
Example2
Example3
Example 4
Example 5

Closed-cell rate %
98.9
99.1
99.9
99.0
98.6

Cell diameter um
50
30
10
23
24

Density kg/m³
45
48
46
48
47

Dimensional stability (−30° C.,
−0.3
−0.3
−0.2
−0.2
−0.2

48 h) %

Thermal conductivity
0.022
0.022
0.020
0.021
0.022

W/(m · K)

Compressive strength kPa
157
156
160
152
154

Flame retardant grade
B1
B1
B1
B1
B1

Smoke production grade
S1
S1
S1
S1
S1

Smoke toxicity grade
t0
t0
t0
t0
t0

TABLE 2

Comparative
Comparative
Comparative
Comparative
Comparative
Comparative
Comparative
Comparative

Sample
Example 1
Example 2
Example 3
Example 4
Example 5
Example 6
Example 7
Example 8

Closed-cell
94.1
93.4
90.5
97.6
97.2
96.8
97.8
98.1

rate %

Cell diameter
90
97
100
84
85
92
74
72

um

Density
46
45
48
47
48
46
47
46

kg/m³

Dimensional
−0.5
−0.5
−0.6
−0.5
−0.6
−0.5
−0.4
−0.3

stability

(−30° C.,

48 h) %

Thermal
0.25
0.024
0.030
0.026
0.028
0.025
0.025
0.026

conductivity

W/(m · K)

Compressive
146
144
140
147
145
147
150
150

strength

kPa

Flame
B2
B2
B2
B2
B2
B1
B1
B1

retardant

grade

Smoke
S2
S2
S2
S2
S2
S2
S2
S2

production

grade

Smoke
t1
t1
t1
t1
t1
t1
t1
t1

toxicity

grade

Application Example 1

As shown in FIG. 2, a tunnel structure with spray-applied polyurethane as the insulation layer for cold regions is composed of, from outside to inside, tunnel rock wall, primary shotcrete layer, geotextile layer, self-adhesive waterproof board layer, spray-applied polyurethane foam layer, and secondary lining concrete layer; the spray-applied polyurethane insulation material for tunnels in cold regions is sprayed on the surface of the self-adhesive waterproof board to form the spray-applied polyurethane foam layer; the thickness of the primary shotcrete layer is 100-280 mm; the thickness of the self-adhesive waterproof board layer is 1-1.5 mm; the thickness of the spray-applied polyurethane foam layer is 50-70 mm; the thickness of the secondary lining concrete layer is 400-600 mm.