The research work is divided into three sections - (i) transparent barrier films, (ii) high expansion foams and (iii) transparent molded panels, all from polypropylene clay nanocomposites. Biaxially oriented polypropylene (BOPP) is used for transparent, flexible high-barrier packaging film. The biaxial orientation process improves the barrier to gases and the mechanical properties by rearrangement of the crystal structure. Polymer nanocomposites incorporating layered nanofiller have the potential to provide striking enhancements in barrier to water vapor and oxygen. However, there is a conflict between addition of nanoclay and stretchability in the BOPP process where rapid deformation and high stress are experienced. In this work, we demonstrated successful achievement of both stretchability and property improvements after incorporating an innovative masterbatch additive based on nanoclay into polypropylene. The maximum area stretch ratio of 7 x 7 achieved without film breakage during biaxial stretching of nanocomposite was as high as that obtained with the unfilled or neat polypropylene. Transmission electron micrographs and dynamic shear rheology revealed that the extent of dispersion of nanoclay in polypropylene was improved after the biaxial stretching. Small angle X-Ray scattering revealed that the crystalline lamellar thickness in the BOPP-NC was larger than in BOPP. Furthermore, the crystalline orientation was more evenly distributed in the plane of the BOPP-NC film as seen from 2D-SAXS images while the degree of crystallinity was seen to be very similar in BOPP and BOPP-NC from wide angle X-Ray diffraction (WAXD). As a result, BOPP nanocomposite film with significantly enhanced stiffness and barrier to both water vapor and oxygen was achieved without sacrificing transparency. In addition, the simultaneous and sequential biaxial stretching behavior of these nanocomposite under processing conditions relevant to industry practice were compared. It was found the characteristic deformation behavior differs significantly between two stretching modes. 2D SAXS revealed the morphology difference in terms of lamellar orientation where a more isotropic in-plane orientation was found in simultaneously stretched films and a preferential alignment along the two stretching directions especially TD was found in sequentially stretched films. In the second section, polypropylene nanocomposites were evaluated with batch foaming using supercritical CO2 in a pressure vessel. An ultra-high expansion ratio of 35.8 was achieved which can be ascribed to two factors: 1) The high melt strength and strain hardening behavior by addition of nanoclay helps the nanocomposite foam cell withstand the high expansion force allowing for a relatively larger cell size capability. 2) The nanoclay also increased the cell density significantly. It is found that biaxial expansion induced orientation and improved delamination of nanoclay. Consequently, the nanocomposite foam exhibited a well-defined cell structure compared to foamed PP. Finally, incorporation of the same nanolayers with selected proportions of compatibilizer in thermoplastic olefin blends or blends of polypropylene homopolymer with toughening copolymers of ethylene and propylene yielded significant improvements in the transmission of light and reduction of haze through molded panels of the multiphase composite compared to molded panels from the unfilled blends.
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