Polymer/Clay. Nanocomposites for Paper Barrier Coating

Transcription

1 Polymer/Clay 2006 International Conference on Nanotechnology, April 26-28, 2006 Atlanta, GA Nanocomposites for Paper Barrier Coating Presented by: Qunhui Sun and Yulin Deng School of Chemical and Biomolecular Engineering GT, Georgia Institute of Technology

2 Background of Paper Barrier Coating Meat preservation, milk, juice, ice cream, meet, fish, fruit, microwave fast food, food plates and boxes, drink cups, photo papers, etc

3 Coating Materials Organic and polymeric coating layer, such as wax, PE (Polyethylene), PTFE (Polytetrafluoroethylene), PP (polypropylene), PET (Polyethylene teraphthalate), etc Metal layers, such as Al, Cu, etc Ceramic and metal oxide films

4 Coating Approaches Extrusion Coextrusion Coating: extruding several layers of polymers onto a substrate Impregnation coating Vacuum deposition

5 Some most common problems Primer layers are generally required for an effective coating Unrepulpability of the recycling paper or board Other problems of waxed food containers: limited to low temperature applications

6 Advantages of waterborne nanocomposites for barrier coating Environmental friendly Cost effective Nanocomposites should provide high barriers Gravure print Coating Impregnation Coating

7 Cationic Surfactant Additives Polymer Cation exchange by delaminating with polymer Additives intercalation Exfoliation Intercalation Mechanical shearing resulting in fully exfoliation Exfoliation

8 Our two approaches to make water-based nanocomposite suspension 1. In-situ emulsion or miniemulsion polymerization 2. Mechanical blending

9 Unexfoliated Clay particles Unexfoliated Saponite Exfoliated Saponite Challenges: 1. Nanoclay must be well dispersed in water-latex solution: hydrophilic surface is preferred 2. Nanoclay must have high affinity with polymer matrix after drying: hydrophobic surface is preferred Key question: Could bentonite and saponite clays be exfoliated by a simple mixing technique?

10 Why does the particle have to be a nanosized? One bentonite particle can split in to layers If 3% of nanoclay is needed, which equals 90% (= 3%x30) of large clay to keep the same total surface area. The thickness of nanoclay in the composite is about 1nm.

11 Raw Materials and method Polymers used: Two acrylics suspensions (763A, 763B) and a styrenebutadiene copolymer latex (226-NA) (commercially available barrier coating polymers from two different chemical suppliers) Clays used: 30B (Cationic exchanged Cloisite 30B, Southern Clay) H1 [cationic polymer and polystyrene modified KSF (a montmorrilonite from Southern Clay)] Sap-CTAB (Saponite modified with cationic surfactant, Sumecton SA, kunimine industries Co., Ltd. Japan) Modification methods: Cation exchange; in-situ solution polymerization.

12 PCNC (polymer-clay nanocomposite) preparation procedures Formulation: Aqueous solution mixing; Mechanical treatment: Ultrasonification and stirring; Coating method: Hand roller coating; Drying: Infrared light drying

13 Pristine clays PCNC preparation procedure Surface treatment of clay via cation exchange Mixing with suspension polymer latex and additives Homogeneous PCNC Ultrasonification

14 Characterization and test methods: Cobb test: TAPPI T441 om-98; WVTR (water vapor transmission rate): TAPPI T448 om-97; XRD: PW 1800 X-ray diffractometer; DSC, TEM

15 Table 1 Stability of 30B and H-1 in Aqueous Systems* No. Stability 1 Composition Notes B + Water Milky, swollen, and phase separated B + PAA + Water Milky, swollen, and phase separated B + TW85 + Water Milky, homogeneous B + TW85 + PAA + Water Milky, homogeneous B + TW85 + PAA + 763A + Water Milky, homogeneous H-1 + Water Yellow, precipitated out at bottom 7 -- H-1 + PAA + Water Yellow, swollen, and delaminated 8 - H-1 + TW85 + Water Yellow, swollen, and delaminated 9 + H-1 + TW85 + PAA + Water Homogeneous 10 - H-1 + TW85 + PAA + 763A + Water Swollen at bottom The clay loading was 30 wt.% of solid polymers. TW85: surfactant Tween-85; PAA: polyacrylic acid sodium salt 1 --, very poor; -: poor; +: good; ++: very good.

16 A B C D E Stability observation of 30B aqueous systems. A: 30B+water; B: 30B+PAA+water; C: 30B+TW85+Water; D: 30B+TW85+PAA+Water; and E: 30B+TW85+PAA+763A+Water. The preparation method was the same as described above. The clay loading was 30 wt.% of solid polymers.

17 A B C D E Stability observation of H-1 aqueous systems. A: H-1+water; B: H- 1+PAA+water; C: H-1+TW85+Water; D: H-1+TW85+PAA+Water; and E: H- 1+TW85+PAA+763A+Water. The preparation method was the same as described above. The clay loading was 30 wt.% of solid polymers.

18 Cobb Value (g m h -1 ) Cobb Value (g m h -1 ) A H-1 Sap-CTAB Clay Varieties 30B B H-1 Clay Varieties Sap-CTAB 30B Water resistance (Cobb test) of barrier coatings comprised of 763A and 763B with various clays. The clay loading was 10 wt.% of solid polymer.

19 WVTR (g m h -1 ) WVTR (g m h -1 ) A H-1 Sap-CTAB Clay Varieties 30B B H-1 Clay Varieties Sap-CTAB 30B Water vapor resistance (WVTR) of barrier coatings comprised of 763A and 763B impregnating with various clays. The clay loading was 10 wt.% of solid polymer.

20 Influence of different polymer matrixes on water resistance (10% nanoclay 30B was used). Cobb Values (g m h -1 ) B 226-NA 763-A Polymer Matrixes The blank columns indicate the Cobb values of the pure polymer matrix, while the dense parts refer to the Cobb values of the composite systems. The preparation procedures were the same as described above.

21 Polymer/Clay Nanocomposites for Paper Barrier Coating 120 Cobb Values (g/m 2 30 m) in 763-B in 226NA in 763-A Clay content (wt. part to polymer) Influence of 30B content on the water resistance of PCNCs. The recipes are as the follows: Polymer latex solution or suspension dispersion: 10 g; D.I. water: 10g; clay: 3-30 wt.% of solid polymer; TW-85: 10 wt.% of clay; PAA: 50 wt.% of TW-85. The mixing conditions were the same as described above.

22 Polymer/Clay Nanocomposites for Paper Barrier Coating Cobb Value (g/m h) WVTR Cobb WVTR (g/m 2 24 h) Sap-CTAB Content (wt.%) Relationship between Cobb and WVTR values and modified Sap-CTAB content in the polymer matrix of 763-A. The recipes are as the follows: 763A dispersion: 10 g; D.I. water: 10g; clay: 2-16 wt.% of solid polymer; TW-85: 10 wt.% of clay; PAA: 50 wt.% of TW-85. The mixing conditions were the same as described above.

23 Polymer/Clay Nanocomposites for Paper Barrier Coating XRD patterns change of Saponite clay in the composites F E D C B A θ ( o ) A: pristine Saponite; B: Sap-HCl; C: Sap-CTAB; D: PCNC-763A (Sap-CTAB); E: PCNC-763B (Sap-CTAB); F: Sap-CTAB +TW85+PAA +763A+Water

24 XRD patterns change of nanoclay 30B in the composites A B θ ( o ) 1: pristine 30B; 2: 30B+Water; 3: 30B+TW-85+Water; 4: 30B+TW-85+PAA+Water; and 5: 30B +TW85+PAA +763A+Water

25 XRD patterns change of nanoclay H-1 in the composites F E D C B A θ ( o ) A: pristine H-1; B: H-1+Water; C: H-1+TW-85+Water; D: H-1+PAA+Water; E: H-1+TW-85+PAA+Water; and F: H-1+TW85+PAA +763A+Water

26 < endothermol (a.u.) C B A Temperature ( o C) DSC diagrams of polymer/modified montmorrilonite clay nanocomposites. A: pristine polymer latex 763A; B: 763A-H1-Water; and C: 763A-H1-TW85-PAA-Water.

27 Conclusions 1. Saponite clay and montmorrilonite clay nanocomposite could be prepared via an aqueous solution mixing approach; 2. The nanoclays could be fully exfoliated in the polymer matrix by a simple aqueous solution mixing process under ultrasonification 3. The agglomerates or macroparticles formation by clay particles in the polymer matrix result in pinholes or defects formation in the coating layer. 4. A simple economic estimation revealed that although the nanoclays are more expensive than the polymer latex, the overall costs of the PCNCs prepared are ca. 13 % lower than the pure polymer latex system, in terms of a thinner layer formation and ca. 300 % performance improvement at 10 wt.% nanoclay addition.

28 Acknowledgment NSF (CTS ), IPST financial support Dr. R. Popil; Mr. J. Cagle; Mrs. Y. Berta; Dr. M. Bucknan; Mr. Z. Zhou, Ms. Z. Tong; Ms. K. Nelson Thank You