Patent Application
20070299185
The present disclosure relates generally to nanocomposites, and more particularly to the formation of nanocomposite materials.
Nanotechnology can be defined as materials or devices engineered at the molecular level. Within this category are polymer nanocomposites, which are a class of materials that use molecular sized particles for reinforcing the polymer matrix, e.g. the reinforcing filler possesses one or more dimensions on a sub-micrometer scale. These materials blend a nanofiller with a polymer to produce a composite with equal or better physical and mechanical properties than their conventionally filled counterparts but at lower filler loadings.
Due to the surface area available with nanofillers, polymer nanocomposites offer the potential for enhanced mechanical properties, barrier properties, thermal properties, and flame retardant properties when compared to conventionally filled materials.
One class of polymer nanocomposites uses a filler material that is based on the smectite class of aluminum silicate clays, a common representative of which is montmorillonite.
Current processes for forming nanocomposites generally include individual steps for polymerizing each of the various monomers and for separately pelletizing each of the various formed polymers. After the individual polymers are pelletized, the formed pellets may be mixed with a nanofiller material in an extruder to form the nanocomposite material. While this process may, in some instances, be efficient for forming nanocomposites, it also may, at times, be time consuming and relatively expensive.
Embodiments of the method of forming a nanocomposite material substantially solve the drawbacks enumerated above. An embodiment of the method includes polymerizing a first monomer to form a first polymeric material. A second monomer is added to the first polymeric material, and the second monomer is also polymerized to form a polymeric mixture of the first and second polymers, or a polymeric reactor material. The polymeric mixture is compounded with a concentrate, thereby forming the nanocomposite material. The concentrate includes, but is not limited to, a nanofiller material mixed with a wetting material.
Objects, features, and advantages of embodiments of the present disclosure may become apparent upon reference to the following detailed description and drawing, in which
The present disclosure is predicated upon the unexpected and fortuitous discovery that by using an in-line processing method, a nanocomposite material having the required and/or desired properties may be formed substantially quickly and efficiently. An embodiment of the method includes polymerizing a first monomer in a gas phase to form a first polymeric material. A second monomer is added to the first polymeric material and the second monomer is also polymerized in a gas phase to form a polymeric reactor material. The polymeric reactor material may be compounded with a concentrate, thereby forming the nanocomposite material. The concentrate includes a nanofiller material mixed with a wetting material. An alternate embodiment of the method includes adding and polymerizing additional monomers (e.g. a third monomer) to the polymeric mixture of the first and second polymers to form a polymeric mixture (i.e. polymeric reactor material) of the first, second, and any additional polymers.
Referring now to
It is to be understood that the polymerization of the monomer(s) occurs using an in-line processing method. For example, box 12 represents a first monomer (e.g. propylene) being polymerized in the gas phase in the reactor 10 to form a first polymeric material (e.g. polypropylene). Box 14 represents the addition of a second monomer and an additional initiator into the still polymerizing first polymeric material. In an embodiment of the method, the second monomer is polymerized in the gas phase to form a polymeric mixture of the first and second polymers. Box 16 in
Non-limitative examples of the polymeric materials that are formed in the reactor 10 generally include polypropylenes, polyethylenes, elastomers, polyolefins, impact copolymers thereof, and/or mixtures thereof.
As shown in
Embodiment(s) of the method further include preparing a concentrate. It is to be understood that the concentrate may be prepared outside of the reactor 10 wherein the monomers are polymerized. Without being bound to any theory, it is also believed that the concentrate may be prepared inside the reactor 10. In such an embodiment, the nanofiller material may be used as a catalyst support and may be included in the final material.
In an embodiment, the concentrate includes a nanofiller material mixed in a wetting material, either with or without additional polymeric resins. The materials may be substantially homogeneously or non-homogeneously mixed and then extruded to form the concentrate.
Non-limitative examples of the wetting material include compatibilizers based on acrylic acid or maleic anhydride substitution on a polymer backbone, or any other polymer with attached groups that may lead to substantial polar interactions with the nanofiller material.
It is to be understood that the nanofiller material may be any suitable nanofiller material. In an embodiment, the nanofiller material is a clay material. Examples of suitable clay materials include, but are not limited to at least one of smectite, hectorite, montmorillonite, bentonite, beidelite, saponite, stevensite, sauconite, nontronite, illite, and/or mixtures thereof. It is to be understood that the clay material may be an organically modified clay material, e.g. an organoclay. In an embodiment, the nanofiller material is an aluminum silicate smectite clay. In a further embodiment, the nanofiller is organically modified montmorillonite.
In an embodiment, the concentrate has a ratio of nanofiller material to wetting material ranging between about 20:80 and about 80:20. In other embodiments, the concentrate has a ratio of nanofiller material to wetting material ranging from about 40:60 to about 70:30, or ranging from about 50:50 to about 70:30.
It is to be understood that the concentrate may be prepared before compounding the polymeric reactor material with the concentrate. It is also to be understood that the concentrate may further optionally include an antioxidant.
Embodiment(s) of the method further includes compounding the concentrate and the polymeric reactor material to form the nanocomposite material. It is to be understood that compounding occurs outside of the reactor 10 in which the polymeric materials are formed.
Compounding may be accomplished via any suitable process to incorporate the nanofiller material into the polymeric mixture. Such processes may include, but are not limited to, processes using co-rotating twin screw extruders, counter-rotating twin screw extruders, oscillating single screw extruders (non-limitative examples of which include those available under the tradename BUSS® kneaders), conical twin screw extruders, internal mixers (non-limitative examples of which include those that are available under the tradenames BANBURY® mixers and BRABENDER® mixers), or any suitable equipment by which polymers may be melt processed.
In an embodiment of the nanocomposite material, the concentrate material may be present in an amount ranging between about 2.5 wt. % and about 60 wt. %, and the polymeric mixture (one example of which is a reactor flake) may be present in an amount ranging between about 97.5 wt. % and about 40 wt. %. The final nanocomposite material also exhibits enhanced physical properties, including, but not limited to, improved tensile and flexural modulus, with the retention of ductile impact.
In an alternate embodiment, the method for forming a nanocomposite material includes compounding a polymeric mixture with the concentrate including a mixture of the nanofiller material and the wetting material, thereby forming the nanocomposite material.
To further illustrate embodiment(s) of the present disclosure, the following example is given. It is to be understood that this example is provided for illustrative purposes and is not to be construed as limiting the scope of embodiment(s) of the present disclosure.
In this example, commercially available polymers were mixed together to form the polymeric mixture. The nanofiller material was added to an amount of a wetting material to form a concentrate. The polymeric mixture was then compounded with the concentrate to form the nanocomposite materials. The nanocomposite materials were evaluated. The formulations of the various nanocomposites are shown in Table II.
Non-limitative examples of suitable polymeric materials are shown in Table I under the labels “Polypropylenes,” “Propylene Copolymers” and “Elastomers.” Non-limitative examples of suitable compatibilizing materials are shown in Table I under the label “Compatibilizing Resins.” Non-limitative examples of suitable optional additives are shown in Table I under the label “Antioxidants/Light Stabilizers.”
The formulations made and tested are shown in Table II under “Formulations 1-5.”
As shown in Table II, formulations 4 and 5 contain the concentrate (standard clay in maleated resin compatibilizer). One non-limitative example of a standard clay is CLOISITE 15A (a sodium montmorillonite clay treated with dimethyl, dihydrogenated tallow quaternary ammonium chloride). CLOISITE 15A is commercially available from Southern Clay Products, Inc. in Gonzales, Tex.
These formulations were compared with formulations having standard clay added (2 and 3) without a wetting material to wet the clay and a formulation with nothing added (1), the control. The operating parameters are also shown in Table II. The maximum melt temperature was kept for all formulations within a range of about 161° C. to about 167° C. The extruder was run at a constant of 300 RPM for all formulations. Lastly, the energy imparted to the extruder for all formulations was about 540 KJ/min. Depending on the torque, the energy input varied slightly for each formulation, but was within a range of about 1.71 KJ/g to about 1.87 KJ/g for all formulations.
The properties of the various formulations are given in Table III.
In the first formulation (1), the control (having no concentrate) had a flex modulus of 102 Kpsi at 2 mm/min. The second (2) and third (3) formulations containing the standard clay without a wetting material, yielded flex moduli of 110 and 144 Kpsi, respectively. For the second (2) formulation, this corresponded to a 7.8 percentage increase over the unfilled control formulation (1) and a 4.2 percentage increase per percentage of inorganic. In the third (3) formulation, the flex modulus corresponded to a 41.2 percentage increase over the unfilled control formulation (1) and a 16.4 percentage increase per percentage of inorganic. The fourth (4) and fifth (5) formulations, containing the concentrate including both standard clay and wetting material (compatibilizing resin), yielded flex moduli of 149 and 169 Kpsi, respectively. For the fourth (4) formulation, this corresponded to a 46.1 percentage increase over the unfilled control formulation (1) and a 44.8 percentage increase per percentage of inorganic. In the fifth (5) formulation, the flex modulus corresponded to a 65.7 percentage increase over the unfilled control formulation (1) and a 29.0 percentage increase per percentage of inorganic. Therefore, comparing formulation (2) with formulation (4), and comparing formulation (3) with formulation (5), it is demonstrated that when using embodiments of nanocomposites formed by embodiments of the present disclosure, a substantially higher flexural modulus is yielded when the concentrate of standard clay and wetting material is used.
The remaining properties, as shown in Table III, as observed and measured for formulations (4) and (5) (containing the concentrate) were consistent with the properties of a typical nanocomposite, as represented by the other formulations (1), (2), and (3). Therefore, it is demonstrated that the nanocomposite material yielded from using the in-line processing method according to embodiment(s) disclosed herein also has equal or better required and/or desired properties of typically formed nanocomposites.
While several embodiments of the disclosure have been described in detail, it will be apparent to those skilled in the art that the disclosed embodiments may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting.
