Background on clay polymer nanocomposites for improvements in barrier properties

Transcription

1 Abstract for AIMCAL Meeting October 16-19, 2005 Myrtle Beach, SC Nanocomposite Barrier Coatings H.A. Goldberg, C.A. Feeney, D.P. Karim, and M. Farrell; InMat Inc. Presented by Harris A. Goldberg, President and CEO, InMat Inc. 216 Route 206 Suite 7; Hillsborough, New Jersey InMat has developed an exciting new class of environmentally friendly aqueous based barrier coatings that combine exfoliated layered silicates with polymers. Its first product designed for the packaging industry, Nanolok PT, has an oxygen permeability of ~0.002 cc-mm/m2-day-atm. This means that thin coatings (<1 micron) can provide the same oxygen barrier as much thicker layers of EVOH or PVDC. InMat coatings can be applied using standard roll coating technology. In this paper we will describe InMat s technology platform, the performance of its first packaging product, and the potential for additional product improvements. Background on clay polymer nanocomposites for improvements in barrier properties The use of platelet fillers to reduce the permeability of polymers has been known for over 40 years. Early work concentrated on the use of mica and or other materials that are commonly obtained with an aspect ratio of The aspect ratio is commonly defined as the typical large dimension of a plate divided by its thickness. These early materials most often had a thickness in the range of several microns. Early models for the improvements in barrier properties due to platelet fillers were based on this work [1,2]. In the late 80 s and early 90 s, the concept of using exfoliated layered silicates as high aspect ratio fillers became very popular. Many silicates can be separated on a molecular level to form sheets 1 nm thick. Such materials can have much larger aspect ratio (100 10,000), and offered the potential for both barrier and mechanical improvements in polymers when used in much lower concentrations. Most of the effort has been focused on the development of organically functionalized clays that could be used as a filler for themoplastically processed polymers. These efforts have been described in several review articles [3-5]. InMat s approach to improved barrier coatings is quite different from the methods used to develop thermally processed nanocomposite polymers. The basic concept is described in

2 its early work on elastomeric nanocomposite coatings [6-8]. These coatings are all water based with both the clay and the polymer dispersed in the water phase. One product (Air D-Fense 2000) has been produced on a commercial scale for over four years and is used in Wilson s Double Core Tennis ball, the official ball of the Davis Cup. InMat s elastomeric nanocomposite coatings are unique in both the large reduction in permeability achieved by the addition of nanodispersed clay, and the degree of flexibility maintained in the dried coating enabling their use on rubber products. More recently, InMat has introduced nanocomposite coatings based on non-elastomeric polymers. Whereas the earlier elastomeric coatings provided oxygen permeability reductions of a factor of (as compared to the unfilled elastomer), these new materials have oxygen permeability reductions that typically exceed 1000 times. The subject of this paper is the properties, application, and commercialization status of these new products. Unique features of InMat s approach InMat s approach to reducing permeation through polymers differs from the nanoclay filled thermoplastic approach in several important ways: Exfoliated Clay: Not functionalized with cationic organic molecules High weight fraction (30-40%) Large aspect nanoclays are not broken during processing Nanoclay platelets self align in coating Formulations Good suspension stability Can be applied using standard coating techniques on standard packaging materials Dried Coating Very large reductions in permeability relative to the unfilled polymer Good dispersion and flexibility controlled by proprietary technology Very thin coating (<1-2 microns) can provide large reductions in oxygen permeations rates of flexible packaging film and other substrates Example: 1 micron Nanolok PT on 48 gauge PET film reduces the oxygen permeation rate of the PET by a factor of more than 100. Performance and Properties of InMat s Nanolok PT Figure 1 below shows the oxygen permeability of InMat s Nanolok PT compared with several other materials typically used in the food packaging industry. The permeability shown here is what has been achieved in preliminary gravure roll coating trials. Lab coatings have indicated with a more optimized coating (better uniformity) would lead to up to another 2x improvement. 2

3 Superior O 2 barrier Relative Oxygen Barrier Effectiveness Least Most O2 permeability (cc-mil/100in 2 -day) 1000 LDPE LDPE 100 PP PP 10 Nylon PET Nylon PVDC LCP 0.01 PET EVOH EVOH Nanolok TM LCP PT InMat 0.01 Nanolok TM PT Water Vapor Transmission (gm-mil/100in 2 -day, 70 o F) InMat 2005 Figure 1 The moisture barrier value shown in figure 1 was tested at room temperature and 70% RH. At higher relative humidity, the water vapor transmission rate of this coating decreases significantly. The humidity dependence of the coating relative to a few other available barrier materials is shown in Figure 2. Although we do not have quantitative data above 75% RH, there is a significant increase in oxygen permeability above 85% RH. The changes observed above 85% RH are similar to those typically seen in EVOH barrier films. Nanolok TM barrier vs. EVOH, Bairocade & PVDC 1 O2 Permeability (cc-mil/100in 2 /day/atm) PVDC EVOH Bairocade Nanolok PT TM % Relative Humidity Source: PPG, Nippon-Gohsei, Solvin and InMat, 25 o C Figure 2 InMat

4 Commercialization status and processing Nanolok PT has been designed for use on standard gravure coating equipment. It is water based with a relatively neutral PH and contains no solvents or hazardous materials. It therefore provides customers with coating equipment the opportunity to put down their own barrier coating and get EVOH levels of performance in a much thinner structure. It does not have the corrosion problems of the very acidic PVDC aqueous dispersions, and does not contain any halogens. It is thus environmentally friendly, and is not expected to interfere with any recycling process or waste recovery. Initial coating trials have already been successfully run at several hundred feet per minute. Typically, coatings of microns can be deposited in a single pass, and multiple passes can be used to build additional thickness. Adhesion lamination to a heat sealable polyethylene has also been successfully demonstrated. It is expected that the coating will be used in a laminated structure in flexible packaging applications. Because there are extractable components in this coating, it is not recommended for extended direct contact with liquids. On the other hand, it is expected to achieve direct food contact notification status with the FDA. This is based on the fact that all components are either already listed as GRAS materials, or are themselves already listed on the food contact notification list. Potential improvements lab results Nanolok PT offers an exciting new and cost effective alternative to both EVOH and PVDC oxygen barriers. As already discussed, it offers the advantage over EVOH in that it can be gravure coated, while it offers significant processing and environmental advantages over PVDC dispersions. On the other hand, it still has the same disadvantage as EVOH in that its performance degrades at high humidity. We do not believe this is intrinsic to our aqueous nanocomposite coating approach, but rather depends upon both the details of the formulation and the intrinsic moisture sensitivity of the matrix polymer. Nanolok PT is based on an aqueous dispersed polyester which is itself moisture sensitive. In order to develop coatings that have better performance at higher humidity, we have begun developing acrylic based nanocomposite barrier materials. At this time, we can only present data which shows that this class of materials look very promising for transparent high barrier coatings. 4

5 Aqueous Oxygen Dispersed Polymer Permeability+ unfilled Oxygen Permeability+ (30-40% filled) Times reduction Nanolok PT Nanolok Ac 1* ,000 Nanolok Ac 2* ,000 + Units of cc-mm/m 2 0% RH This table shows that although the acrylics used in the development grade Nanolok AC formulations start with much higher oxygen permeability than the unfilled polyester used in Nanolok PT, the clay filler has a much larger effect and thus leads to coatings with much lower oxygen transmission rate. Summary and conclusions InMat has developed aqueous nanocomposite coatings that are more cost effective than currently used barrier materials. Lab demonstrations clearly show the potential for even larger performance improvements. InMat is seeking partnerships with raw material suppliers and customers in order to rapidly commercialize this technology in the packaging industry, and to take full advantage of the broad potential of InMat s approach to high barrier materials. 5

6 References: 1. Nielsen LE. J Macromol Sci (Chem) 1967; A1: Perry D, Ward WJ, Cussler EL. J Membr Sci 1989; 44: Sinha Ray S, Okamoto M. Prog Polym Sci 2003; 28: Giannelis EP. Appl Organometal Chem 1998; 12: Giannelis EP. Adv Mater 1996; 8: Goldberg HA, Feeney CA, Karim DP, Farrell M. Rubber World 2002; 226(5): 15-17, 20, Feeney CA, Farrell M, Tannert K, Goldberg HA, Lu M, Grah MD, Steiner WG, Winston PB. United States Patent No. 6,087,016, 2000 (assigned to InMat LLC and Michelin Recherche et technique S.A.). 8. Feeney CA, Farrell M, Tannert K, Goldberg HA, Lu M, Grah MD, Steiner WG, Winston PB. United States Patent No. 6,232,389, 2001 (assigned to InMat LLC and Michelin Recherche et technique S.A.). 6

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