The effect of alkaline lignin (AL) and sodium lignosulfonate (LSS) on the structure of thermoplastic zein (TPZ) was studied. Protein structural changes and the nature of the physical interaction between lignin and zein were investigated by means of X-ray diffraction and Fourier transform infrared (FT-IR) spectroscopy and correlated with physical properties. Most relevant protein structural changes were observed at low AL concentration, where strong H-bondings between the functional groups of AL and the amino acids in zein induced a destructuring of inter- and intramolecular interactions in α-helix, β-sheet, and β-turn secondary structures. This destructuring allowed for an extensive protein conformational modification which, in turn, resulted in a strong improvement of the physical properties of the bionanocomposite.
ABSTRACT:The aim of this work was to investigate the foaming process of high-performance thermoplastic polymers such as polyethersulfone (PES), polyphenylsulfone (PPSU), polyetherimide (PEI), and poly(ethylene-2,6-naphthalate) (PEN) expanded by using supercritical carbon dioxide as a blowing agent. All polymers were characterized by differential POLYMERIC FOAMS FROM HIGH-PERFORMANCE THERMOPLASTICSscanning calorimetry (DSC) and rheological analysis to roughly identify the foaming conditions. Batch and solid-state foaming methods were employed. In the first case, cell nucleation was promoted by inducing a fast pressure drop rate in a pressurized vessel. In the solid-state process, foaming was promoted by increasing the temperature of gas-saturated samples in an oil bath. The effects of foaming methods and process parameters on cellular morphology were analyzed. All polymers were successfully foamed by using the solid-state technique, showing relative densities ranging from 0.13 to 0.44 for PEN and from 0.27 to 0.57 for PES, PPSU, and PEI. The morphology was microcellular in all cases, and PES exhibited nanocellular cells after some processing conditions. The batch-foaming process was less effective to prepare foams than the solid-state one. In fact, higher relative densities and reduced temperature windows for foaming were evidenced for amorphous polymers, whereas PEN crystallized during the heating step and foams with poor morphology and high relative densities were obtained. C 2011 Wiley Periodicals, Inc. Adv Polym Techn 30: 234-243, 2011; View this article online at wileyonlinelibrary.com.
The foaming processes of nanocomposites based on high-performance thermoplastic polymers, namely, poly(ether sulfone) (PES; amorphous) and poly (ethylene-2,6-naphthalate) (PEN; semicrystalline), reinforced by two nanofiller types (expanded graphite and SiO 2 nanopowder), were investigated. Matrices were prepared by melt blending through extrusion, and a good dispersion of particles was achieved, as confirmed by microscopic and Xray diffraction analyses. A solid-state foaming technique was used to prepare the foams; the samples were solubilized with carbon dioxide and quickly heated in an oil bath to the selected foaming temperature. The effects of both the type and concentration of the filler and the polymer type (amorphous and semicrystalline) on the cellular morphology were analyzed. Foams prepared from PES-based nanocomposites showed microcellular morphologies and higher numbers of nucleated cells (up to 10 11 cells/cm 3 ), but low expansion ratios were achieved compared to PEN-based foams. Both SiO 2 and graphite nanoparticles acted as cell nucleating agents in the PES nanocomposites, but the latter gave better results, increasing the cell number by two orders of magnitude with respect to the neat polymer. This behavior was attributed to either the heterogeneous nucleation of cells or the improved barrier to gas diffusion of the graphite nanoplatelets with respect to SiO 2 nanoparticles. The PEN nanocomposite foams exhibited low foam densities, but fewer cells were nucleated with respect to the PES nanocomposites. The increase in the crystallization rate related to the presence of fillers, in particular when graphite was used, affected the expansion ratio at high foaming temperatures.
Poly(ethylene 2,6-naphthalate)- PEN is a thermoplastic polyester characterized by a high glass transition temperature (125°C), comparable to that of polyetheretherketone (143°C), but with a significantly lower melting temperature (265°C). Its physical and chemical properties are very promising for applications in transport industry and aeronautics. Nanocomposite matrices based on PEN and expanded graphite were developed to be used as matrix for foams. Expanded graphite was melt blended with the polymer by means of extrusion process and its effects on the foaming properties were investigated through solid state foaming process. Graphite nanoparticles increased the crystallization kinetics of the polymer, inducing the formation of small crystals but lowering the total amount of crystalline phase. Transmission electron microscopy analysis showed a good dispersion of the nanofiller but some aggregates were still present, as also confirmed by graphite peak in the X-ray diffraction patterns of all nanocomposites. The elastic modulus of nanocomposites with amorphous matrix increased with respect to the neat amorphous PEN, while the modulus of crystallized nanocomposites decreased. Nanocomposite foams were successfully prepared, and an higher cell density was obtained when compared to the neat PEN. In the latter case, a strong increase in both yield and strain at break was measured. Furthermore, the elastic modulus and compressive yield stress of foamed PEN nanocomposites increased with the expanded graphite.
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