WO2013139885A1

WO2013139885A1 - A process for template-assisted production of nanoporous amino resin foams

Info

Publication number: WO2013139885A1
Application number: PCT/EP2013/055882
Authority: WO
Inventors: Jan Kurt Walter Sandler; Sujandi Sujandi; Zhan BAO; Hermann Bergmann
Original assignee: Basf Se; Basf Schweiz Ag
Priority date: 2012-03-23
Filing date: 2013-03-21
Publication date: 2013-09-26

Abstract

A process for producing a nanoporous amino resin foams, comprising the steps of a) providing an aqueous micellar emulsion template, comprising a block copolymers based on ethylene oxide and propylene oxide, b) by adding an organic micelle expander, c)combining the expanded micelle from step b) with an amino resin, d) adding an curing catalyst, e) optionally adding an organosilane and/or an organoamine, f) optionally adding polyvinylformamide, g) curing the amino resin above 50°C to obtain a gel, h) optionally replacing water and micelle emulsion template by a solvent with a boiling point at atmospheric pressure below 100°C, and i)drying the gel at ambient temperature and atmospheric pressure.

Description

A process for template-assisted production of nanoporous amino resin foams Description The invention relates to nanoporous amino resin foams, obtainable by curing amino resins using expanded micellar emulsion templates. In a subsequent drying operation, the thus obtained wet gel is dried at ambient temperature and pressure. The invention further relates to nanoporous amino resin foam with a density below 200 kg/m³ and the porosity is above 80%, which are obtainable by this process.

Nanoporous polymer foams having a pore size of distinctly below 1 μηη and a total porosity of above 90% are particularly outstanding thermal insulators on the basis of theoretical considerations. Aerogels are a special class of highly porous solid materials with extremely low densities, ul- trafine pores with size less than 100 nm, open and continuous porosity, large surface area, and a microstructure composed of interconnected colloidal-like particle or polymeric chains with characteristic diameters of 10 nm. By definition this materials are prepared through the sol-gel process and can be either granular or monolithic. Supercritical drying condition is needed to remove the solvent that resides within the pores of the solid and to preserve the original gel structure. Aerogels have the lowest thermal conductivities of all solids due to the extreme low density (high porosity) and ultrafine pore size less than 100 nm. Thermal conductivity of 10 - 20 mW/m^*K is achievable with aerogels in contrast with the thermal conductivity of conventional polymeric foams which is 30 - 35 mW/m^*K.

Despite the potential applications as superior insulation materials, aerogels are not routinely found in daily application because their three-dimensional networks and pore structures collapse easily. The supercritical drying step is the most expensive and riskiest part for the preparation of aerogels that hinder their wide applications. Therefore for large scale commercial ap- plications cost competitive new drying method at ambient condition is needed to substitute the supercritical drying step.

US 2010/31 1852 A1 discloses the production of melamine-formaldehyde spheres containing nanopores on the surface with the aid of nonionic triblock copolymer surfactant. The obtained spheres may be carbonized at high temperatures to yield microporous carbon spheres. The obtained melamine-formaldehyd and carbon spheres are dense materials with low porosity and are therefore not suitable for thermal insulation application.

US 2007/0197744 A1 discloses a process for preparing melamine resin foams having a number average pore diameter not more than 1 μηη by gel formation in the presence of polymer particles having a mean diameter of from 20 - 500 nm and subsequent drying the water-containing gel at a pressure and a temperature below the critical pressure and critical temperature of the liquid phase. US 2007/0173552 disclose the synthesis of nanoporous polymer foams by using bicontinuous microemulsion as template. The drying method for the organic solvent given in the examples was by using freeze drying technique. This may lead to the formation of cracks during the drying step. No pore size, porosity and heat conductivity data were given in the examples. However, it was mentioned that the thermal conductivity was below 33 mW/m^*K.

US 2009/0005468 disclose a process for the production of nonporous polymer foams having a pore size below 1 μηη and a porosity of more than 90% by forming a gel of a melamine resin in an organic solvent and removing that solvent.

In Chem. Mater., 18, 5279 - 5288 (2006), F. Zhang et al. describe the production of nanoporous phenol-formaldehyde polymeric materials and its corresponding carbon materials by using Pluronic F127 (EO106PO70EO106) and P123 (EO20PO70EO20) triblock copolymer as a template. Hydrocarbon (hexadecane or decane) can be used in the Pluronic P123 template as swelling agent to tailor the pore size of obtained nanoporous PF polymer from 4.1 to 6.8 nm.

In Chem. Mater., 22, 428 - 434 (2010), K. Kailasam, et al. describe production of nanoporous melamine-formaldehyde polymeric materials by using hexamethoxymethyl melamine resin as monomer and Pluronic F127 (EO106PO70EO106) triblock copolymer surfactant as template. The pore size of the obtained nanoporous materials is ~ 8 nm. Evaporation induced self-assembly method was applied to produce the nanoporous polymeric materials with low porosity. Because of the very high density the mesopourous resins are not suitable for thermal insulation applications. It is therefore an object of the present invention to provide nanoporous polymer foams with superior thermal insulation properties having extremely small pores, high porosity and low density. In addition, the intention is to find a process which enables drying of the polymer gel without forming cracks and with low energy consumption and high space-time yields, preferably ambient temperature and pressure. The present application therefore provides materials which can be produced without supercritical fluids.

Accordingly, the above-described nanoporous amino resin foams have been found. Preferred nanoporous amino resin foams have an average pore diameter in the range from 10 to 200 nm, a density between 10 and 200 kg/m³ and porosity in the range from 85 to 99%. Most preferred nanoporous amino resin foams have an average pore diameter in the range from 50 to 150 nm, a density between 50 and 150 kg/m³ and porosity in the range from 90 to 95%.

The nanoporous amino resin foams can be obtained by a process, comprising the steps of a) providing an aqueous micellar emulsion template, comprising a block copolymers based on ethylene oxide and propylene oxide,

b) expanding the micelle prepared in step a) by adding an organic micelle expander, c) combining the expanded micelle from step b) with an amino resin,

d) adding a curing catalyst

e) optionally adding an organosilane and/or organoamine,

f) optionally adding linear polyvinylformamide,

g) curing the amino resin above 50 °C to obtain a gel

h) optionally replacing water and micellar emulsion template by a solvent with a boiling point at atmospheric pressure below 100°C, and

i) drying the gel at ambient temperature and atmospheric pressure. In a preferred process, the nanoporous amino resin foams may be prepared by the following stages:

a) providing an aqueous micellar emulsion template, comprising a block copolymers based on ethylene oxide and propylene oxide,

d) adding a curing catalyst

e) adding an organosilane and/or an organoamine,

f) adding polyvinylformamide,

g) curing the amino resin above 50°C to obtain a gel,

h) replacing water by a solvent with a boiling point at atmospheric pressure below 100°C, and

i) drying the gel at ambient temperature and atmospheric pressure.

Preferably the block copolymer used in step a) is a polyoxyethylene-polyoxypropylene- polyoxyethylene triblock copolymer. The block length can be varied in a wide range and many different types of these surfactants are commercially available, such as Pluronic® triblock copolymers from BASF SE. The number averaged molecular weight M_n of the block copolymer is preferably in the range from 2,500 to 10,000. The HLB-value of the block copolymer is preferably in the range of 7 - 12. Most preferably the block copolymer used in step a) is a polyoxyeth- ylene-polyoxypropylene-polyoxyethylene triblock copolymer having a number averaged molecular weight Mn in the range from 2,500 to 10,000.

In step b) the micelle is expanded by adding an organic micelle expander. Suitable micelle expanders are solvents such as hydrocarbon class, preferably pentane, hexane, cyclohexane, heptane, octane, cyclooctane, decane, isooctane, dodecane; aromatic class preferably toluene, xylene, ethylbenzene, isopropylbenzene. Most referably 1 ,3,5-trimethylbenzene is used as organic micelle expander.

The size of the pores of the nanoporous amino resin can be controlled by the ratio of organic micelle expander to ethylene oxide - propylene oxide block copolymer. Preferably the ratio by weight is in the range from 10 : 1 to 1 : 1 , most preferably in the range from 5 : 1 to 2 : 1 .

The expanded micelle from step b) is combined in step c) with an amino resin, such as urea- formaldehyde, benzoguanamine-formaldehyde, melamine-formaldehyde resin or mixtures thereof. Preferably the amino resin is etherified with a Ci - C6 - alcohol, preferably with n- butanol, isobutanol, methanol or mixtures thereof. The amino resin is preferably added to the expanded micelle in form of a solution in water, methanol, ethanol, isobutanol, butyl glycol, xylene or mixtures thereof. Usually commercial available solutions with a nonvolatile content (2g/ 2h/125°C) in the range from 50 - 95% are employed.

The density of the nanoporous amino resin foam can be controlled by the amount of amino resin. Preferably the amino resin is used in an amount of 1 to 25 % by weight, most preferably in an amount of 5 to 15 % by weight, based on solids of all compounds used in step a) to d).

Particular preference is given to a melamine-formaldehyde resin modified by an alcohol and having a melamine/formaldehyde ratio in the range from 1 : 1 to 1 : 10, preferably from 1 : 2 to 1

: 6.

A curing catalyst is added in step d) .The type and amount of the catalyst depend upon the ami- no resin used. For amino resins, for example, organic or inorganic acids, e.g. phosphoric acid, hydrochloric acid or carboxylic acids such as acetic acid or formic acid, may be used. Combinations with salts are also helpful in the control of the reaction kinetics.

In addition, crosslinking components (curing agents) may be used, for example urea or 2,4- diamino-6-nonyl-1 ,3,5-triazine in the case of melamine-formaldehyde resins.

Nanopourous amino resin foams with higher porosity can be achieved by improve the network strength by adding an organosilane and/or organoamine in step e). Most advantageously alkoxysilanes are used, most preferably 3-aminoproyltriethoxysilane. Other amino group con- taining alkoxysilanes according to following structures of formula (I) to (IV) are also preferred:

(I) NH₂R¹SiY₃

(I I) R²NHR SiY₃

(Hi) NH₂R³NHR SiY₃

(iv) Y₃SiR⁴NHR SiY₃ wherein R¹, R², R³ and R⁴ represent an organic group with 1 to 20 carbon atoms, preferably 1 , 2, 3, 4, 5, 6, 7, or 8 carbon atoms, which does not undergo hydrolysis in the presence of water (non-hydrolysable group) and wherein each Y represents a hydrolysable alkoxy group. Preferably Y is methoxy, ethoxy, propoxy or isopropoxy.

Preferably R¹, R³ and R⁴ are an alkylene or arylene group, particularly preferred a linear al- kylene group. Preferred alkylene groups as R¹, R³ and R⁴ are methylene, ethylene, propylene, in particular n-propylene, hexylene, in particular n-hexylene, and octylene, in particular n-octylene according to formula -CnHbn-, where n = 1 , 2, 3, 6 or 8.

Preferably R² is an aliphatic group. Preferred aliphatic groups as R² are methyl, ethyl, propyl in particular n-propyl, butyl in particular n-butyl, hexyl in particular n-hexyl and octyl in particular n- octyl according to formula CnHbn+i-, where n = 1 , 2, 3, 4, 6, 8.

Preferred organoamines are primary and secondary organoamines according to following struc- ture formula (V) to (VI):

(V) R⁵NH₂

(VI) R⁵NHR⁶ wherein R⁵ and R⁶ represent an organic group with 1 to 20 carbon atoms, preferably 1 , 2, 3, 4, 5, 6, 7, or 8 carbon atoms.

Preferably R⁵ and R⁶ are an aliphatic group. Preferred aliphatic groups as R⁵ and R⁶ are methyl, ethyl, propyl in particular n-propyl, butyl in particular n-butyl, hexyl in particular n-hexyl and octyl in particular n-octyl according to formula CnHbn+i-, where n = 1 , 2, 3, 4, 6, 8. Dialkylamines, such as diethylamine (DEA) are most preferred.

Adding polyvinylformamide in step f) prevents the nanopourous amino resin foam from cracking during drying. Preferably the polyvinylformamide used in step f) is a linear high molecular weight polyvinylformamide produced by polymerization of vinylformamide such as Lupamin® from

BASF SE. The polymer chain length can be varied in a wide range and many different types of these polymers are commercially available. The number averaged molecular weight M_n of the linear polyvinylformamide is preferably in the range from 10,000 - 340,000. The formamide group can be hydrolyzed to form amine group with hydrolysis degree in the range from 10 - 95%. The term of hydrolysis degree mean the percentage of formamide group that are hydrolyzed to amino group.

The combination of the amino resin, the ethylene oxide - propylene oxide block copolymer, the catalyst components, the organic expander component, the organosilane, the organoamine, the polyvinylformamide and the amount of water required to set the desired structure thus provides a curable microemulsion whose microstructure is substantially preserved during the polycon- densation of the reactive components. The microemusion of the combined components are preferably homogenized with a high pressure homogenizer at a pressure in the range of 10 - 90 MPa to yield an emulsion with micellar droplets, preferably in the range of 10 - 200 nm.

The weight ratio of the overall aqueous phase to the overall oil phase (W/O ratio) is generally 95 : 5 - 5 : 95, preferably 80 : 20 - 20 : 80.

The solvent in step h) for replacing the water and the micelle template in the wet gel is preferably a hydrocarbon, alcohol, ketone, ether, alkyl ester, or mixture thereof having a boiling point at atmospheric pressure between 25 and 75°C.

The gel can be dried in step i) at ambient temperature and atmospheric pressure. Ambient temperature is usually a temperature from 1 to 40°C, preferably from 15 to 25°C. Atmospheric pressure is usually between 95 and 105 kPa. The gel volume during the drying process can be preserved in case of larger pore sizes in the range of 50 - 200 nm due to the lower capillary force.

The process according to the invention applies simple sol-gel chemistry and allows control of density and tailorable pore size even below 100 nm. The generation of nanosized pores may be achieved by removal of the template by simple solvent extraction and drying at ambient conditions. Expensive and tedious drying with supercritical CO2 is not necessary.

The nanoporous polymer foams obtainable after drying the cured microemulsions feature high overall porosity and associated low bulk density and small pore size. The bulk density is preferably in the range from 5 to 200 kg/m³ and the average pore diameter in the range from 10 to 200 nm, preferably in the range from 50 to 150 nm. The inventive nanoporous polymer foams have low thermal conductivity in the range from 24 to 33 mW/mK and are therefore particularly suitable for thermal insulation applications such as insulation panels in the construction sector, cooling units, vehicles or industrial plants.

Examples:

Raw materials

P123 Pluronic® P123, difunctional polyoxyethylene-polyoxypropylene- polyoxyethylene triblock copolymer surfactant terminated in primary hydroxyl groups, number averaged molecular weight M_n = 5.750.

TMB 1 ,3,5-Trimethylbenzene

Luwipal® 063 Methanol-etherified melamine-formaldehyde resin, 70 wt.-% in water

Luwipal® 073 Methanol-etherified melamine-formaldehyde resin, 80 wt.-% in water Lupamin® 9000 Polyvinylformamide , 13 wt.-% in water, number average molecular weight M_n = 340,000.

APTES 3-aminoproyltriethoxysilane

DEA diethylamine

Pore volume, porosity and density were measured by mercury intrusion porosimetry according to DIN 66133.

Mercury is non-wetting liquid to most solids and consequently pressure is required to force mer- cury to enter pores of the solids. It is the non-wetting property of mercury combined with its high surface tension that almost uniquely qualifies it for use in probing pore space. Surface tension, then, can be defined as the force per unit length acting along the surface of a liquid at right angles to a line that separates the two phases. If mercury is placed in contact with a pore opening, the surface tension of the mercury acts along the line of contact with the opening equal in length to the perimeter of the opening and creating a force-resisting entry.

The magnitude of resisting force is proportional to the length of the line of contact, the surface tension (γ) of mercury, and the cosine of the contact angle (Θ). For a pore with a circular opening at the surface, the resisting force is expressed as

f_R = nD cosO

An externally applied pressure tending to force mercury into the opening acts over the surface of the interface bridging the opening. The externally applied force, therefore, is the product of the pressure (P) and area (A) over which the pressure is applied. For a pore of circular cross- section, f_Ext = PA = PnD² /4

At equilibrium, just before the resistive force is overcome, the equation is,

- DY COS0 = 7ZD²P/4 Therefore, at any pressure, the pores into which mercury has intruded have diameters greater than D = -4y cose /P

For irregular shaped pores the ratio between the pore cross-section (related to the pressure exerted) and the pore circumference (related to the surface tension) is not proportional to the diameter. The wetting angle taken as 141.3° should be considered as an average value only. Surface tension value taken as 480 dynes/cm² should also be considered as an average value. By measuring the volume of mercury that intrudes into the sample material with each pressure change, the volume of pores in the corresponding size class is known. The volume of mercury that enters pores is measured by a mercury penetrometer.

Nanofoam sample specimens prepared for testing are dried to remove all moisture from the pore structure. They are then placed into sealed 'penetrometers' which are weighed both before and after being loaded with the specimen. The penetrometers are placed into the machine where they are evacuated and then filled with mercury. The pressurized testing then commences stepwise to a maximum pressure of 60,000 psia and the machine calculates and records how much mercury is being forced into the pore structure based on the above equations. Following data are possible to be obtained from the measurement: pore size distribution, hysteresis curve, specific surface area, and total pore volume. Total pore volume is the most direct deter- mination of a physical property by mercury intrusion, involving only the volume of mercury entering the sample pores. At the lowest filling pressure, intrusion is considered nil and no pore volume of interest has been filled. At maximum pressure mercury has been forced into all pore voids of the sample accessible to the mercury. The volume of mercury required to fill all accessible pores is considered the total pore volume.

The porosity of the nanofoam sample was derived from the total pore volume as followed: φ = (1 ^l- ) x 100%

V_t * P_MF + i The nanofoam density value was calculated by using following equation

P nanofoam ⁼ P MF ^X (1 ^~~ Φ)

Where φ is porosity, V_t is total pore volume, P^MF is density of dense MF resin and P^nan°f°^am is density of MF nanofoam. Heat conductivity measurment

Sixteen nanofoam samples were synthesized at 100 grams scale and powderised by mechani- cal grinding. The nanofoam powders are evaluated as a powder packing inside a foam container (Styrodur®) with known properties, this set-up is measured and the properties of the powder are calculated. Here the obtained Tc of the nanofoam powder represents a bi-modal pore size distribution (nanopores + interparticle volumes) and no further analysis regarding individual contributions is possible.

Preparation of micellar emulsion template (P123 : TMB : H20 = 1 : 3.5 : 5.67)

Into 200 g of 20 w% P123 aqueous solution, 66.67 g of water was added to obtain 15 w% P123 aqueous solution. The solution was poured into 1 L beaker and put in a water bath to maintain the temperature. Trimethylbenzene (mesitylene), 140 g, was introduced slowly into the middle of solution through syringe with long needle. The mixture was blend continuously by using ultra- turrax during the course of trimethylbenzene introduction to yield a white milky emulsion. The emulsion was blend for another 2 min after complete introduction of trimethylbenzene. The obtained emulsion was cooled down to 5 °C and passed through high pressure homogenizer with pressure of 100 - 900 bars to yield emulsion with nanosize micellar droplets.

Example 1 - 8 and Comparative Example

In a typical experiment to produce nanofoam, 31.86 g of Luwipal 063 is added into 183.0 g of the obtained emulsion. The mixture was stirred at room temperature until the Luwipal completely dissolved in the emulsion. Then 1.27 ml. of 37% HCI was added and the mixture was stirred for 5 minutes. Followed by addition of 2.24 ml. 3-aminopropyltriethoxysilane. The final mixture was transferred to 1 L glass reactor. The reactor is heated in water bath at 95 °C for 15 min and then 80 °C for 5 hours to yield white wet gel. The obtained wet gel was soaked with acetone for 24 hours and followed by soaking in n-hexane for another 24 hours. White nanofoam was obtained by drying the soaked wet gel under ambient temperature and pressure.

Example 9 - 14 In a typical experiment to produce nanofoam, 38.2 g of Luwipal 063 (or Luwipal 073) is added into 183.0 g of the obtained emulsion. In some case, Lupamin 9000 (10 w% with regard to Luwipal) was also added into the emulsion. The mixture was stirred in an ice bath to keep the temperature below 10 °C. Then 1.27 mL of 37% HCI was added and the mixture was stirred for 5 minutes. Followed by addition of 2.648 mL 3-aminopropyltriethoxysilane. The final mixture was ultrasonicated for 2.5 min and then transferred to a metal reactor. The reactor is heated in water bath at 95 °C for 15 min and then 80 °C for 5 hours to yield white wet gel. The obtained wet gel was soaked with acetone for 24 hours and followed by soaking in n-hexane for another 24 hours. White nanofoam was obtained by drying the soaked wet gel under ambient temperature and pressure. Example 15

In a typical experiment to produce nanofoam, 27.9 g of Luwipal 073 is added into 183.0 g of the obtained emulsion. The mixture was stirred in an ice bath to keep the temperature below 10 °C. Then 1.07 mL of 37% HCI was added and the mixture was stirred for 5 minutes. Followed by addition of 0.49 mL diethylamine. The final mixture was ultrasonicated for 2.5 min and then transferred to a metal reactor. The reactor is heated in water bath at 95 °C for 15 min and then 80 °C for 5 hours to yield white wet gel. The obtained wet gel was soaked with acetone for 24 hours and followed by soaking in n-hexane for another 24 hours. White nanofoam was obtained by drying the soaked wet gel under ambient temperature and pressure.

Table 1 : Chemical composition (w/w) and porosity data of Examples 1 - 15 and Comparative Experiment

Claims

Claims:

A process for producing nanoporous amino resin foams, comprising the steps of

b) by adding an organic micelle expander,

c) combining the expanded micelle from step b) with an amino resin,

d) adding an curing catalyst,

e) optionally adding an organosilane and/or an organoamine,

f) optionally adding polyvinylformamide,

g) curing the amino resin above 50°C to obtain a gel,

h) optionally replacing water and micelle emulsion template by a solvent with a boiling point at atmospheric pressure below 100°C, and

i) drying the gel at ambient temperature and atmospheric pressure.

The process according to claim 1 , wherein the block copolymer is a polyoxyethylene- polyoxypropylene-polyoxyethylene triblock copolymer having a number averaged molecular weight Mn in the range from 2,500 to 10,000.

The process according to claim 1 or 2, wherein 1 ,3,5-trimethylbenzene is used as organic micelle expander.

The process according to any of claims 1 to 3, wherein the amino resin is a urea- formaldehyde, benzoguanamine-formaldehyde, melamine-formaldehyde resin or mixtures thereof.

The process according to any of claims 1 to 4, wherein the curing catalyst is an organic or inorganic acid.

The process according to any of claims 1 to 5, wherein the organosilane is selected from at least one compound according to following formula (I) to (IV)

NH₂R¹SiY₃

R²NHR SiY₃

NH₂R³NHR SiY₃ (IV) Y₃SiR⁴NHR SiY₃ wherein R¹, R², R⁴ and R⁴ represent a non-hydrolysable organic group and wherein each Y represents a hydrolysable alkoxy group.

7. The process according to any of claims 1 to 6, wherein the organosilane is 3- aminoproyltrietoxysilane.

8. The process according to any of claims 1 to 7, wherein organoamine is selected from at least one compound according to following formula (V) to (VI) (V) R⁵NH₂

(VI) R⁵NHR⁶ wherein R⁵ and R⁶ are aliphatic groups. 9. The process according to any of claims 1 to 8, wherein the organoamine is diethylamine.

10. The process according to claim 1 to 9, wherein the polyvinylformamide is linear polyvinylformamide having a number averaged molecular weight M_n in the range from 10,000 to 340,000 with hydrolysis degree of the formamide group to amine group in the range from 10 - 95%. 1 1 . The process according to any of claims 1 to 10, wherein the solvent in step h) is a hydrocarbon, alcohol, ketone, ether, alkyl ester, or mixture thereof having a boiling point at atmospheric pressure between 25 and 75°C.

12. A nanoporous amino resin foam, obtainable by the process of claim 1 to 1 1 .

13. The nanoporous amino resin foam according to claim 12, wherein the density is 200 kg/m³ or lower and the porosity is 85% or more.