|Title of Invention||
"A METHOD OF PRODUCING A REINFORCED EPOXY RESIN NANOCOMPOSITE"
|Abstract||A method of producing a reinforced epoxy resin nanocomposite comprising: mixing a layered silicate particles such as organophilically . modified montmorillonite with epoxy resin such as diglicidylether of bis phenol-A to form a treatable silicate-epoxy mixture; contacting the treatable mixture with a supercritical fluid being carbon dioxide for 1 hour followed by depressurizing the contacted mixture and treating at 90 ± 1°C with a curing agent such as tri ethylene at ambient pressure of 3000 psi to define a reinforced epoxy composite.|
|Full Text||FIELD OF INVENTION
The present invention relates to the application of supercritical solvents for preparing clay reinforced epoxy nanocomposite. More particularly, it relates to the preparation of a nanocomposite material in supercritical carbon dioxide suitable for use of automative, aircraft parts, house holds articles, packaging, printed circuit boards and biomedical applications.
BACKGROUND OF INVENTION
A variety of supercritical solvents, particularly supercritical carbon dioxide (scCO2) has recently gained considerable attention as environmentally benign, inexpensive, and nonflammable alternative" medium for the synthesis and processing of materials ranging from particles to nanocomposites. The low viscosity, near-zero surface tension, relative chemical inertness, and high diffusivity of scCO2 results in negligible competitive adsorption with guest molecules on the host substrate and therefore facilitates solute transfer relative to normal solvents (:Darlene K.etal. Annu. Rev. Energy Environ, 25: 2000, p 1 15, Y. Wang et al, J. of Supercritical Fluids, 28:2004, p 85, Nalawade et al, Progress in Polymer Sciences 1: 2006, p 19, Zaidi et al J Appl'. Polym Sci., 103:2007;pl303). Due to such unique combination of properties, scCO2 has extensively been studied as medium for the synthesis of polymer/clay nanocomposites comprising high degree of dispersed nanoscale fillers, particularly organoclay into a host polymer matrix (Q.Zhao and E.T. Samulski, Macromolecules, 36: 2003, p 6967Mielewski et al US patent 6,753,360 B2, 2004).
The major technical challenge is to synthesize the proposed class of nanocomposites comprising nanometer-size dispersions of clay with exfoliated morphology and markedly improved mechanical, thermal, barrier and flame retarding properties when compared with the pure or macroscopically filled polymers (Salahuddin et al, European Polymer Journal, 38 (7), 2002, 1477, Zeng et al, J. Nanosci. 85 Nanote'ch, 5, 2005, p 1574, US patent 4,889,885 issued in Dec. 26, 1989, US patent 5,554,670, 1996, US patent 5,760,106, 1998, US patent 6,548,159 B2, 2003, US patent 6,855,197 B2, 2005, European patent 1,656,411 I, 2005, European patent 0,782,593, 1996). To address this challenge, the
ability of scCOa to swell a polymer and facilitate its mixing with organoclay to synthesize such nanocomposites is disclosed in US patent 6,753, 360 B2, 2004. In this method, the polymer, in particular polypropylene and the organoclay are mixed thoroughly and processed in scCO2 at a temperature and pressure suitable for the given polymer/organoclay system followed by depressurization to remove CO2. During depressurization, CO2 expands and pushes the layers apart resulting in significant delaminated structures. The degree of filler dispersion is a function of the processing temperature, pressure, and depressurization rate. Such processing of materials may easily be accomplished through various extruders, blenders and mini mixers as earlier disclosed in US patent 6,753,360 B2 2004 and also described (Milan M. and Christopher W. M., Polymer Engineering and Science, 41(1): 2001, 118).
Currently, epoxy and other epoxy-based materials may particularly comprise at least percent of a given vehicle's weight. Realizing steadily increasing applications of epoxy resin in the aircraft, automative, packaging industry and biomedical applications due to their light weight, improved mechanical and thermal properties, and less toxic character. Conventionally layered silicates are reinforced into epoxy matrix through
either of curing with hardeners (US patent 5,554, 670, 1996, European patent 0782593, 1996, US patent 5,760,106, 1998, Tasi, et al US39835A1, 2003, European patent 1656411, 2005) and blending in organic solvents followed by curing with hardeners (US patent 6,548, 159 B2, 2003, US patent 039812A1, 2003, US patent 6,855,197,B2, 2005, US patent 7034, 089B2, 2006). Delaminating silicate layers therein assisted with supercritical fluids is therefore an attractive, cost effective and green friendly means of generating a well-exfoliated epoxy silicate material for any material system.
OBJECTS OF INVENTION
It is an object of this invention to propose a method of producing reinforced epoxy nanocomposite, wherein providing cetyl pyridinium bromide exchanged particles or platelets of the layered silicate and a supercritical fluid and mixing the layered silicate particles with an epoxy resin to form a treatable silicate-epoxy mixture.
Another object of this invention include contacting the treatable mixture with the supercritical fluid and catastrophically or immediately depressurizing-the contacted mixture to exfoliate the layered silicate
particles so that the layered particles are to be substantially dispersed within the epoxy followed by treating with curing agent to define the reinforced epoxy nanocomposite.
DESCRIPTION OF ACCOMPANYING DRAWINGS;
Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings and wherein:
Fig. 1 is a flow chat depicting one method of preparing a layered silicate reinforced epoxy.
Fig .2 is a comparative view of the effect on Uv-vis absorbance of the
cured epoxy resin and the nanocomposite comprising dispersed silicate particles exfoliated throughout a epoxy with silicate particles.
Fig. 3 represents diffraction patterns from transmission electron micrographs of the epoxy composite  at 3500X.
Fig. 4 represents diffraction patterns from transmission electron micrographs of the nanocomposite at 2500X.
Fig. 5 represents diffraction patterns from transmission electron micrographs of the nanocomposite at 3500X.
Fig. 6 represents the comparative XRD spectra of organophilic layered silicate, epoxy.
DETAILD DESCRIPTION OF INVENTION
According to this invention there is provided A method of producing a reinforced epoxy resin nanocomposite comprising: mixing a layered silicate particles such as organophilically modified montmorillonite with epoxy resin such as diglicidylether of bis phenol-A to form a treatable silicate-epoxy mixture; contacting the treatable mixture with a supercritical fluid being carbon dioxide for 1 hour followed by depressurizing the contacted mixture and treating at 90 ± 1°C with a curing agent such as tri ethylene at ambient pressure of 3000 psi to define a reinforced epoxy composite.
Polymer nanocomposites represent a new class of material alternative to conventional filled polymers. In this class of material, nanosized inorganic filler are dispersed in polymer matrix offering tremendous improvement in performance properties of the polymer. In the present embodiment a supercritical fluid assisted method of preparation of clay/epoxy nanocomposites has been developed. A supercritical fluid is a substance above its critical temperature and critical pressure. Under these conditions the distinction between gases and liquids does not apply and the substance can only be described as a fluid. In this embodiment, the supercritical fluid is preferably carbon dioxide which can exist as a fluid having properties of both a liquid and gas at above its critical temperature and critical pressure. Carbon dioxide at its supercritical conditions has both a gaseous property of being able to penetrate through many materials and a liquid peroperty of being able to dissolve materials into their composnents.
In the present embodiment, the nanosized inorganic filter is a layered silicate called montmorillonite clay (K10). This is a hydrophobic material, comprising a platey structure with thickness of about one nanometer and diameters of about 50 to more than 2000 nanometers. In this embodiment, the clay used is modified through exchanging with cetyl pyridinium bromide in aqueous medium and is abbreviated as organophilic montmorillonite (Ommt). In this embodiment, the polymer is epoxy resin.
In the present embodiment a treatable Ommt/epoxy mixture is prepared in scCO2. This may be carried out with the use of a number of apparatus known in the art, such as a mixer, extruder, blender, injection molding machine, or any other suitable apparatus capable of loading material such as clay, into epoxy in supercritical fluid, and capable of maintaining a constant pressure onto the loaded material. Pressurizing and heating the silicate/epoxy mixture with the supercritical fluid may be accomplished by any conventional means. In this embodiment, the apparatus used is a high pressure reactor comprising stainless steel reaction vessel, connected to a temperature control system and mechanical stirrer. The source of supercritical fluid may be any conventional fluid source such as a gas cylinder containing the fluid of choice.
Known that, the critical temperature of carbon dioxide is about 31 degree Celsius at 1050 pounds per square inch. Thus, in this embodiment, the step of contacting includes heating the silicate-polymer mixture to above critical temperature of carbon dioxide, which is 90 degree Celsius. The
predetermined amounts of Ommt (5% w/v) into epoxy, and carbon dioxide are loaded into reactor and pressurized above critical temperature and critical pressure of carbon dioxide to achieve supercritical conditions therein. In the present embodiment, processing pressure and temperature are 3000 psi and 90±1°C. Contacting the mixture with the supercritical fluid further includes maintaining contact between the mixture and the fluid and shearing during the residence time which may be 1.0 hr. This is to be noted that these conditions may vary with different supercritical fluids and polymers used. The source of scCO2 may be any conventional source such as gas cylinder. The method further includes catastrophically or immediately depressurizing the contacted mixture to exfoliate silicate particles such that the particles are substantially dispersed, to define a treated silicate-epoxy mixture. The step of depressurizing includes immediately depressurizing the reactor down to ambient pressure and 40±1°C temperature. As immediate depressurizing occurs, the silicate/epoxy mixture includes silicate particles which are substantially singly dispersed apart from each other within the epoxy to define the treated epoxy/clay mixture. In the present embodiment, it is believed that the epoxy swells due to contact with the supercritical fluid that lowers its viscosity. The decreased viscosity allows the silicate particles to become intercalated by supercritical fluid, resulting in exfoliation and dispersion of single particles. Further exfoliation occurs during depressurization. Thus, a substantially uniformly dispersed amount of treated silicate particles result within the treatable mixture. Reaction of treatable mixture with a suitable curing
agent result, the layered silicate reinforced epoxy having dispersed silicate particles within the epoxy. It has been found that the reinforced epoxy with the above-mentioned montmorillonite clay weight to surface area ratio and weight percent provides substantially increased mechanical and thermal properties at a lower manufacturing time and cost.
This is a method of preparing epoxy composite  in supercritical fluid. In this example, the method provides diglicidylether of bis phenol-A as the epoxy resin, carbon dioxide as the supercritical fluid and triethylene as curing agent. The method then includes substantially loading the
diglicidylether of Bisphenol-A in a high pressure reactor system followed by carbon dioxide from a line connected to a high pressure carbon dioxide cylinder at about 3000 psi. The epoxy is treated at a temperature of about 90+1 degree Celsius. The content remains at these conditions for 1 hr and is the catastrophically depressurized at 40±1 degree Celsius, thereafter cured with triethylene tetramine at 40±1 degrees.Celsius and ambient pressure to define the epoxy composite. As depressurization occurs, heating is stopped.
This is a method of preparing a nanoclay reinforced epoxy [I] in supercritical fluid. In this example, the method provides for montmorillonite clay as the layered silicate, diglicidylether of bis phenol-A as the epoxy resin, carbon dioxide as the supercritical fluid and triethylene tetramine as curing agent. The method then includes substantially simultaneously loading the clay and the diglicidylether of Bisphenol-A in a high pressure reactor system to define a treatable silicate-epoxy mixture. The weight ratio of the clay to loaded digilicidyletehr of bis phenol-A is 1:05 (% w/v). During the mixing process, carbon dioxide is applied to the mixture from a line connected to a high pressure carbon dioxide cylinder at about 3000 psi. The mixture is treated at a, temperature of about 90±1 degree Celsius. The mixture remains at these conditions for 1 hrs and is the catastrophically depressurized at 40±1 degree Celsius, thereafter cured with triethylene tetramine at ambient pressure to define the nanocomposite structure. As depressurization occurs, heating is stopped.
Fig. 1 depicts in 110 one method of preparing a layered silicate reinforced epoxy according to present invention. In this embodiment, the layered silicate is the layered silicate clay called montmorillonite, a hydrophilic material having layered platy structure. The silicate has layered individual particles with thickness of nanometer order. The method in 112 includes modifying the layered silicate having layered particles or platelets to be organophilic through cation exchange with cetyl pyridinium bromide. In this embodiment, a mixture of organophilically modified clay (Ommt) and epoxy resin is allowed contact with
supercritical fluid as depicted in box 114 and mixed thoroughly therein through mechanical stirrer at 1500 rpm as depicted in box 116 to form a treatable silicate epoxy mixture. The epoxy may be diglycidyl ether of bis phenol A. The vessel is heated to achieve the required supercritical condition therein as shown in box 116. This step of containing includes pressurizing the silicate-epoxy mixture with the supercritical fluid to above about 3000 pounds per square inch gauge and heating the silicate-polymer mixture and the supercritical fluid to above the critical temperature of the supercritical fluid. In this embodiment, the required temperature is '90±l degree Celsius. As depicted in box 118, the method further includes catastrophically or immediately depressurizing the contacted mixture to exfoliate silicate particles such that the particles are substantially dispersed, to define a treated silicate-polymer mixture. In this embodiment, as depressurizing occurs, heating is stopped, thus lowering temperature of the mixture. As depicted in box 120, the final step of the embodiment involves curing of treated mixture with suitable hardener to define the layered silicate epoxy nanocomposite. In this embodiment the curing agent is triethylene tetramine.
Fig. 2 represents the Uv/vis absorption spectra of individual
components, triethylene tetramine cured epoxy  and corresponding nanocomposite with Ommt (5%) [I]. The spectra shows that the visible region (400-700 nm) was significantly affected at all by the presence of the silicate and induced loss in transparency of epoxy. For the ultraviolet wavelength, there is weak scattering and or absorption resulting in a very high absorption of the UV light. This is not surprising as a typical Ommt lateral sizes are 50-1000 nm.
Fig. 3 shows the comparative X-ray diffraction curves of Ommt, epoxy composite  and corresponding layered silicate reinforced epoxy nanocomposite [I] in the region 20=5 to 80°. The curves shows common peak at 20=20° corresponding to MMT and [I]. This fact revels the hat MMT in polymer matrix has no specific inter layer spacing and Ommt disperses into the epoxy matrix homogeneously. Each of the two curves has one peak which is assigned to the 001 lattice spacing of organoclay.
Fig. 4 represents diffraction patterns of the epoxy composite  at 3500X, whereas Fig. 5 represents the distribution of layered silicate into  at the 2500X magnification corresponding to nanocomposite [I]. With further increase in magnification to 3500X, TEM pattern indicate a clear distribution of layered silicate into epoxy matrix as depicted in Fig. 6. These TEM reveled hybrid structure of nanocomposite with uniform distribution of exfoliated layered silicate into epoxy matrix.
It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims:-
1. A method of producing a reinforced epoxy resin nanocomposite comprising: mixing a layered silicate particles such as organophilically modified montmorillonite with epoxy resin such as diglicidylcther of bis phenol-A to form a treatable silicatc-epoxy mixture; contacting the treatable mixture with a supercritical fluid being carbon dioxide for 1 hour followed by depressurizing the contacted mixture and treating at 90 ± 1°C with a curing agent such as tri ethylene at ambient pressure of 3000 psi to define a reinforced epoxy composite.
2. The method as claimed in claim 1, wherein the supercritical fluid is used to exfoliate the silicate so that the silicate particles disperse within the epoxy resin.
3. The method as claimed in claim 1, wherein contacting the mixture includes pressurizing the mixture with the supercritical fluid.
4. The method as claimed in claim 1, wherein contacting the mixture includes heating the mixture with the supcrctitical fluid to above the critical temperature and pressure of the supercritical fluid.
5. The method as claimed in claim 1, wherein the silicate particles are substantially dispersed upon depressurization.
6. The method as claimed in claim 1, wherein the reinforced epoxy includes 5.0 percent weight of the silicate particles.
7. The method as claimed in claim 1 wherein mixing includes shearing the silicatc-cpoxy mixture.
|Indian Patent Application Number||1784/DEL/2007|
|PG Journal Number||19/2013|
|Date of Filing||21-Aug-2007|
|Name of Patentee||G.B.PANT UNIVERSITY OF AGRICULTURE & TECHNOLOGY|
|Applicant Address||PANTNAGAR, UTTARAKHAND, 263 145 INDIA|
|PCT International Classification Number||C08L63/00|
|PCT International Application Number||N/A|
|PCT International Filing date|