General approach to nanocomposite preparation

Details General approach to nanocomposite preparation General approach to nanocomposite preparation

1999-05-13

2001-08-07

Sanders, Kriellion (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S447000, C523S223000

Reexamination Certificate

active

06271297

ABSTRACT:

FIELD OF INVENTION
The field is the preparation of nanocomposite compositions from matrix polymers and platelike silicate or silicone fillers to form intercalates and/or exfoliated fillers. The general approach is applicable to a wide variety of polymers. They can typically form both intercalates and exfoliates of the fillers through the use of a small amount of a swelling agent which can enter into the spaces between the platelets of the filler and compatibilize the filler with most matrix polymers. Swelling agents are generally small mobile molecules, oligomer, and/or polymers with good compatibility toward the silicate filler or silicone filler with or without cation exchange.
BACKGROUND OF THE INVENTION
There is strong interest in nanocomposites due to the opportunity to prepare compositions with improved properties over those of the starting polymers through controlling the size and dispersion of fillers therein. Silicate fillers (many of which are mined and require only minimal processing before use) are available that include within each particle a multitude of platelike layers. During most conventional polymer processing steps the individual plates do not separate but rather the aggregates of many platelike layers are dispersed as a single particle. Some authors have found ways to pretreat silaceous fillers (often using the monomeric form of the matrix polymer) to cause intercalation and exfoliation with specific polymers.
Nanocomposites from nylon in the prior art exhibited substantial improvement in mechanical , thermal and Theological properties. Nanocomposites from epoxies exhibited improved tensile modulus and strength. Suspension of a sheet silicate in solvents such as water, acetonitrile, dimethyl acetamide (DMAC) has resulted in intercalated hybrids of poly(ethylene oxide). Melt methods have lead to the intercalation of polystyrene and exfoliated nanocomposites of epoxy via melt interlayer polymerization. Interlayer polymerization has also produced intercalated polystyrene, intercalated poly(&egr;-caprolactone), and poly-6-amide by intercalation of &egr;-caprolactam. Other approaches such as sol-gel process and monomer/polymer grafting to clay layers have also resulted in polymer clay hybrids.
Using an oligomeric form of the matrix polymer as an additive, allows the additive to swell the clay. For example Okada et al. have reported using a polyolefin oligomer with polar telechelic hydroxyl groups to prepare a polypropylene clay hybrid.
SUMMARY OF THE INVENTION
A process for preparing nanocomposites from fillers having platelike structure and a variety polymers is disclosed. The process often uses a surface modifying agent or surfactant exchanged for cations on the filler and uses a swelling agent that enters between the platelets of the inorganic filler facilitating both intercalation with a polymer and/or exfoliation of the platelets. The universality of the approach greatly expands the list of matrix polymers that can be used in nanocomposites with platelike fillers. Preferred swelling agents include caprolactam, epoxy monomers and/or oligomers and vinyl monomers. By varying the 1) amount of swelling agent, 2) the mixing sequence, 3) the swelling agent, and/or 4)other variables one can form various nanocomposites (e.g. intercalated clay and/or exfoliated clay) with predominantly intercalated or exfoliated platelets. A swelling agent can function either as an intercalation agent or as an exfoliating agent. Preferred inorganic fillers include clay. Preferred swelling agents include low molecular weight epoxy compounds. Preferred matrix polymers include polyolefins, polydiolefins, polycarbonates, polyesters, poly(alkyl)acrylates, poly(vinyl chloride), poly(vinyl acetate), nylons (polyamides), copolymers including repeating units from diolefins, and poly(styrene-acrylonitrile). The process does not require any complex equipment as intercalation and exfoliation can occur during simple mixing operations. The evidence of intercalation into the clay or exfoliation of the clay (both of which will be called nanocomposite formation) is a shift in or the absence of x-ray powder diffraction patterns from the clay.
Those skilled in the art have characterized fillers as either simple fillers or reinforcing fillers depending upon whether they were added to simply fill volume in a polymer composite (simple filler) or they increase one or more physical properties over that of the basic polymeric component (reinforcing fillers e.g. carbon black). Unfortunately sheet silicates have been typically considered as simple fillers since there is usually 1) little bonding between the sheet silicates and the polymer, 2) the amount of surface interaction between the silicate and the polymer is low because a macrocomposite is formed with large domain sizes, and 3) the sheet silicate is easily delaminated under high stress. The nanocomposite technology can make sheet silicates function as reinforcing fillers as it 1) increases the surface interaction and bonding between the silicate and the polymer especially when the polymer is intercalated into the silicate, 2) increases dramatically (by a factor of 10, 100, or 1000 or more) the surface contact between the sheet silicate and the polymer by intercalating polymer into the silicate or exfoliating the silicate, and 3) reduces the possibility of composite failure due to simple delamination of the sheet silicate. Nanocomposites are a combination of two or more phases, where at least one of the phases has at least one dimension in the nanoscale regime. The technology is different from the prior art in that the swelling agent is always different than the matrix polymer of the nanocomposite.
DETAILED DESCRIPTION OF THE INVENTION
The polymers useful in this invention include a variety of thermoset and thermoplastic polymers. Some polar polymers such as nylons may, with sufficient shear, tend to exfoliate silicate fillers without a swelling agent. The nonpolar polymers like the polymers from monoolefins, conjugated dienes, and vinyl aromatic monomers are generally incapable of intercalation into the clay interior in simple blends of clay and polymer. Preferred polymers include those typically processed above their glass transition temperature or above their melting point with traditional extruding, molding, and pressing equipment. These are rubbers and thermoplastics. Preferred polymers for some embodiments are those that are incapable of intercalating or exfoliating more than 5 or 10 weight percent of said fillers without the swelling agent. The polymers from monoolefins include those polymers from one or more olefin monomers having from 2 to 10 carbon atoms such as polypropylene, polyethylene, isobutylene polymers, EPDM rubber etc. The polymers from monoolefins can include repeating units from nonolefin monomers. The polymers from conjugated dienes include those from dienes having from 4 to 8 carbon atoms including halogenated monomers such as chloroprene and copolymers, terpolymers etc. which have at least 20, 30, or 50 wt. % repeating units from conjugated dienes such as styrene-butadiene copolymers. The polymers from vinyl aromatic monomers include those from styrene or various alkylated styrenes having from 8 to 12 carbon atoms and any copolymers, terpolymers, etc. having at least 20, 30, or 50 wt. % repeating units from said vinyl aromatic monomers such as styrene-acrylonitrile copolymers. Other polymers include polyesters generally from diacids having from 3 to 20 carbon atoms and diols having from 1 to 20 carbon atoms such as poly(ethylene-terephthalate); polyesters from the ring opening polymerization of cylic esters having from 2 to 5 or 6 carbon atoms; poly(vinyl alcohol); polyacetal; poly(vinyl acetate); poly(alkyl)acrylates from (alkyl) acrylates having from 3 to 30 carbon atoms; poly(vinyl chloride); poly(vinylidene chloride); polytetrafluoroethylene; copolymers of any of the monomers; polycarbonates from things such as phosgene and diols having from 1 to 20 carbon atoms; polyamides from diacids having from 3 to 20 carbon atoms and

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