A method of making a gradient thermal conductive polyurethane foam

Abstract

The application discloses a preparation method of gradient heat-conducting polyurethane foam, and has the characteristics that: by virtue of the excellent heat conductivity of graphene, a polyurethane / graphene nanocomposite prepolymer is prepared in situ by adopting a prepolymer foaming process, is poured into a polytetrafluoroethylene mold, and is placed in an environment box with higher humidity and temperature; a concentration gradient is formed by diffusion of water vapor from the surface of the sample to the core layer, and CO2 is generated by reaction of the concentration gradient with a polyisocyanate, so that a concentration gradient of CO2 gas foaming agent is formed; meanwhile, by virtue of the heat insulation effect of the foam porous structure and the high heat conductivity of the graphene, the polyurethane foam with a gradient cell structure and a heat-conducting structure is obtained.

Description

Technical Field

[0001] This invention relates to a method for preparing gradient thermally conductive polyurethane foam, belonging to the field of polymer preparation. Background Technology

[0002] Polyurethane foam is one of the main types of polyurethane synthetic materials. Due to its porous structure and low thermal conductivity, it exhibits excellent properties such as wear resistance, tear resistance, chemical corrosion resistance, shock and pressure resistance, and thermal insulation, making it widely used. When polyurethane foam is applied in the electronics and electrical industry, in specific environments, in addition to its excellent thermal insulation function to protect electronic equipment and components from high-temperature impacts, the heat accumulated during use and the heat generated by electronic components must be dissipated in a timely manner to prevent the internal temperature of the equipment from becoming too high and causing failure. Therefore, it is necessary to construct a gradient thermal conductivity structure for the polyurethane foam, that is, the surface in contact with the high-temperature environment has excellent thermal insulation, while the surface in contact with the protected electronic components has good thermal conductivity and heat dissipation function, thereby achieving integrated heat dissipation / thermal insulation functions.

[0003] Liu Zhaoyang, Song Shuzheng, et al., Shandong Chemical Industry, 2023, 52(2): 18, studied the thermal conductivity of polyurethane elastomers, and investigated the effects of the type, amount and particle size ratio of thermal conductive agent on the elastomer properties. When the amount of thermal conductive agent Al2O3 added was 55% and the particle size was 40um / 10um, the composite material obtained had the best physicochemical properties and the thermal conductivity could reach 0.7W / mK, which can better meet the special product potting requirements in the field of new energy potting. He Zhiping, Li Min, Fiberglass / Composite Materials, 2013, 9: 26, prepared reduced graphene (RGO) from graphene oxide (GO) by thermal reduction method, and combined the two graphenes with thermoplastic polyurethane (TPU) to prepare nanocomposite films. Adding GO to TPU can obtain nanocomposite materials with high thermal conductivity and low electrical conductivity, while adding RGO can obtain nanocomposite materials with high thermal conductivity and high electrical conductivity. There are no reports on thermally conductive polyurethane foam and polyurethane foam with gradient thermal conductivity structure to date. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing gradient thermally conductive polyurethane foam to address the shortcomings of existing technologies. The method utilizes the excellent thermal conductivity of graphene. First, a polyurethane / graphene nanocomposite prepolymer is prepared in situ using a prepolymer foaming process. This prepolymer is poured into a polytetrafluoroethylene mold and placed in an environmental chamber with high humidity and temperature. Water vapor diffuses from the sample surface to the core layer, forming a concentration gradient, and reacts with polyisocyanate to generate CO2, thus creating a concentration gradient for the CO2 gas blowing agent. Simultaneously, the thermal insulation effect of the porous structure of the foam and the high thermal conductivity of graphene are utilized to obtain a polyurethane foam with a gradient pore structure and a thermally conductive structure.

[0005] The objective of this invention is achieved by the following technical measures, wherein the raw material fractions are all by weight unless otherwise specified.

[0006] A method for preparing a gradient thermally conductive polyurethane foam includes the following steps:

[0007] Coupling / reduction treatment of graphene oxide:

[0008] 0.5-20 parts of graphene oxide were dispersed in 400-3000 parts of a deionized water / ethanol composite solvent with a volume ratio of 1:9. 0.05-10 parts of a silane coupling agent were added and dissolved at room temperature and stirred until homogeneous. The mixture was then ultrasonically dispersed for 10-200 min at an ultrasonic power of 100-3000 W and an ultrasonic temperature of 40-65 °C. The product was filtered and washed with distilled water. The coupled graphene aqueous dispersion was then placed in a water bath at 70-95 °C, and 5-200 mL of 80% hydrazine hydrate was added dropwise. The reaction was carried out for 2-20 h. Finally, the reduced product was filtered and washed with deionized water and dried at 90 °C for 12 h to obtain reduced graphene oxide. The silane coupling agent was at least one of γ-ethylenediaminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ-phenylaminopropyltrimethoxysilane.

[0009] Preparation of gradient thermally conductive polyurethane foam:

[0010] Graded thermally conductive polyurethane foam was prepared using a prepolymer foaming method: First, 100 parts of macromolecular polyol and 0.5-20 parts of reduced graphene oxide were weighed and stirred evenly. The mixture was then vacuum dehydrated at 100-130℃ for 2-4 hours, cooled to 50-80℃, and 10-50 parts of polyisocyanate were added. The mixture was stirred and reacted for 1-5 hours to generate a polyurethane / reduced graphene oxide composite prepolymer. Then, 0.2-5 parts of chain extender / crosslinker, 0.1-5 parts of catalyst, and 0.3-5 parts of foam stabilizer were added and stirred evenly. The mixture was then poured into a polytetrafluoroethylene mold and placed in an environmental chamber for 2-12 hours. The foam was then foamed and formed at a humidity ≥50%RH and a temperature ≥60℃. Subsequently, the foam was vacuum baked at 100-180℃ for 2-20 hours to crosslink and form the final product, thus obtaining the graded thermally conductive polyurethane foam.

[0011] Among them, the macromolecular polyol is at least one of hydroxyl-terminated polyethylene adipate (PEA), hydroxyl-terminated polycaprolactone (PCL), hydroxyl-terminated polyhexane adipate (PHA), hydroxyl-terminated polybutylene adipate (PBA), polytetramethylene ether glycol (PTHF), and polypropylene glycol, with an average molecular weight of 500-3000; the polyisocyanate is 4,4'-diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI), terephthalic diisocyanate (PPDI), and 1,4-cyclohexane diisocyanate (CH). At least one of DI); the chain extender / crosslinker is at least one of 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA), diethyltoluenediamine (DETDA), triethanolamine, trimethylolpropane, and pentaerythritol; the foam stabilizer is at least one of B8462 silicone oil type foam stabilizer, B8404 silicone oil type foam stabilizer, L-580 silicone oil type foam stabilizer, and AK-158 silicone oil type foam stabilizer; the catalyst is at least one of triethylenediamine, N-methylmorpholine, triethylamine, stannous octoate, and dioctyltin mercaptan.

[0012] The present invention has the following advantages

[0013] This invention innovates the construction and preparation method of polyurethane foam gradient structure. First, a polyurethane / graphene nanocomposite prepolymer is prepared in situ using a prepolymer foaming process. This prepolymer is poured into a polytetrafluoroethylene mold and placed in an environmental chamber with high humidity and temperature. Water vapor diffuses from the sample surface to the core layer, forming a water vapor concentration gradient from large to small. Water can react with polyisocyanate to generate CO2, thus forming a CO2 gas blowing agent concentration gradient, resulting in a polyurethane foam with a gradient cell structure. Simultaneously, the thermal insulation effect of the porous structure of the foam and the high thermal conductivity of graphene are utilized. That is, the surface layer with a larger cell density has a lower thermal conductivity and better thermal insulation, while from the surface layer to the core layer, the cell density gradually decreases and the thermal conductivity gradually increases, thus obtaining a polyurethane foam with a gradient thermal conductivity structure. Detailed Implementation

[0014] The present invention will be specifically described below through embodiments. It should be noted that these embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0015] Example 1

[0016] Five parts of graphene oxide were dispersed in 1000 parts of a deionized water / ethanol composite solvent with a volume ratio of 1:9. 0.1 parts of γ-ethylenediaminopropyltrimethoxysilane were added and dissolved at room temperature and stirred until homogeneous. The mixture was then ultrasonically dispersed for 20 min at a power of 1000 W and a temperature of 50 °C. The product was filtered and washed with distilled water. The coupled graphene aqueous dispersion was then placed in a 95 °C water bath, and 50 mL of 80% hydrazine hydrate was added dropwise. The reaction was carried out for 12 h. Finally, the reduced product was filtered and washed with deionized water and dried at 90 °C for 12 h to obtain reduced graphene oxide.

[0017] Weigh 100 parts of hydroxyl-terminated polyethylene adipate (PEA) with a molecular weight of 2000 and 5 parts of reduced graphene oxide, stir evenly, dehydrate under vacuum at 110℃ for 3 hours, cool to 60℃, add 30 parts of 4,4'-diphenylmethane diisocyanate (MDI), stir and react for 3 hours to generate a polyurethane / reduced graphene oxide composite prepolymer; then add 2 parts of trimethylolpropane, 0.2 parts of stannous octoate, and 0.5 parts of B8404 silicone oil-type foam stabilizer, stir evenly, pour into a polytetrafluoroethylene mold, and place in an environmental chamber for 8 hours. Foam at 80% RH and 70℃, and then crosslink and bake under vacuum at 120℃ for 18 hours to obtain a graded thermally conductive polyurethane foam. The core layer thermal conductivity can reach 0.69 W / mK. From the core layer to the surface layer, the cell density and cell size gradually increase, and the thermal conductivity gradually decreases.

[0018] Example 2

[0019] Eight parts of graphene oxide were dispersed in 1500 parts of a deionized water / ethanol composite solvent with a volume ratio of 1:9. 0.5 parts of γ-aminopropyltriethoxysilane were added and dissolved at room temperature and stirred until homogeneous. The mixture was then ultrasonically dispersed for 40 min at a power of 1500 W and a temperature of 60 °C. The product was filtered and washed with distilled water. The coupled graphene aqueous dispersion was then placed in a 90 °C water bath, and 80 mL of 80% hydrazine hydrate was added dropwise. The reaction was carried out for 8 h. Finally, the reduced product was filtered and washed with deionized water and dried at 90 °C for 12 h to obtain reduced graphene oxide.

[0020] Weigh 100 parts of hydroxyl-terminated polycaprolactone (PCL) with a molecular weight of 1000 and 8 parts of reduced graphene oxide, stir evenly, dehydrate under vacuum at 120℃ for 2 hours, cool to 80℃, add 35 parts of terephthalic diisocyanate (PPDI), stir and react for 2.5 hours to generate a polyurethane / reduced graphene oxide composite prepolymer; then add 3 parts of trimethylolpropane, 0.1 parts of stannous octoate, and 1 part of B8404 silicone oil-type foam stabilizer, stir evenly, pour into a polytetrafluoroethylene mold, and place in an environmental chamber for 10 hours. Foam at 90% RH and 90℃, and then crosslink and bake under vacuum at 150℃ for 12 hours to obtain a graded thermally conductive polyurethane foam. Its core thermal conductivity can reach 1.08 W / mK. From the core layer to the surface layer, its cell density and cell size gradually increase, and its thermal conductivity gradually decreases.

Claims

1. A gradient thermally conductive polyurethane foam, characterized in that... The method for preparing and molding this polyurethane foam includes the following steps: Coupling / reduction treatment of graphene oxide: 0.5-20 parts of graphene oxide were dispersed in 400-3000 parts of a deionized water / ethanol composite solvent with a volume ratio of 1:

9. 0.05-10 parts of a silane coupling agent were added and dissolved at room temperature. The mixture was stirred until homogeneous and then ultrasonically dispersed for 10-200 min at a power of 100-3000 W and a temperature of 40-65℃. The product was filtered and washed with distilled water. The coupled graphene aqueous dispersion was then placed in a 70-95℃ water bath, and 5-200 mL of 80% hydrazine hydrate was added dropwise. The reaction was carried out for 2-20 h. Finally, the reduced product was filtered and washed with deionized water and dried at 90℃ for 12 h to obtain reduced graphene oxide. The silane coupling agent was at least one of γ-ethylenediaminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ-phenylaminopropyltrimethoxysilane. Preparation of gradient thermally conductive polyurethane foam: Graded thermally conductive polyurethane foam was prepared using a prepolymer foaming method: First, 100 parts of macromolecular polyol and 0.5-20 parts of reduced graphene oxide were weighed and stirred evenly. The mixture was then vacuum dehydrated at 100-130℃ for 2-4 hours, cooled to 50-80℃, and 10-50 parts of polyisocyanate were added. The mixture was stirred and reacted for 1-5 hours to generate a polyurethane / reduced graphene oxide composite prepolymer. Then, 0.2-5 parts of chain extender / crosslinker, 0.1-5 parts of catalyst, and 0.3-5 parts of foam stabilizer were added and stirred evenly. The mixture was then poured into a polytetrafluoroethylene mold and placed in an environmental chamber for 2-12 hours. The foam was then foamed and formed at a humidity ≥50%RH and a temperature ≥60℃. Subsequently, the foam was vacuum baked at 100-180℃ for 2-20 hours to crosslink and form the final product, thus obtaining the graded thermally conductive polyurethane foam. Among them, the macromolecular polyol is at least one of hydroxyl-terminated polyethylene adipate (PEA), hydroxyl-terminated polycaprolactone (PCL), hydroxyl-terminated polyhexane adipate (PHA), hydroxyl-terminated polybutylene adipate (PBA), polytetramethylene ether glycol (PTHF), and polypropylene glycol, with an average molecular weight of 500-3000; the polyisocyanate is 4,4'-diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI), terephthalic diisocyanate (PPDI), and 1,4-cyclohexane diisocyanate (CH). At least one of DI); the chain extender / crosslinker is at least one of 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA), diethyltoluenediamine (DETDA), triethanolamine, trimethylolpropane, and pentaerythritol; the foam stabilizer is at least one of B8462 silicone oil type foam stabilizer, B8404 silicone oil type foam stabilizer, L-580 silicone oil type foam stabilizer, and AK-158 silicone oil type foam stabilizer; the catalyst is at least one of triethylenediamine, N-methylmorpholine, triethylamine, stannous octoate, and dioctyltin mercaptan.