Analysis of the nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone) (PEEKK) was performed by using differential scanning calorimetry (DSC). The Avrami equation modified by Jeziorny could describe only the primary stage of nonisothermal crystallization of PEEKK. And, the Ozawa analysis, when applied to this polymer system, failed to describe its nonisothermal crystallization behavior. A new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation. By evaluating the kinetic parameters in this approach, the crystallization behavior of PEEKK was analyzed. According to the Kissinger method, the activation energies were determined to be 189 and 328 kJ/mol for nonisothermal melt and cold crystallization, respectively.

Nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone)

Reversible crystallization and the rigid-amorphous phase in semicrystalline macromolecules

Six polylactides, polymerized with Salen−Al−OCH3 initiator and having optical purities between 43% and 100%, were analyzed by differential scanning calorimetry, X-ray diffraction, and optical microscopy, following various crystallization conditions. It was found that each of those polylactides can crystallize, even those with low optical purities; their crystallization rate is, however, slower than those for high optical purity polyesters. Moreover, the low optical purity polymers tend to form stereocomplexes between the l and d sequences of the same polylactide, which behavior is ascribed to their multiblock microstructure. A correlation was found between the measured melting temperature of optically active polylactides and their average sequence length.

Crystallization and Melting Behavior of Polylactides

All-Polyolefin Composites Markus Stürzel,† Shahram Mihan,‡ and Rolf Mülhaupt*,†,§ †Freiburg Materials Research Center (FMF) and Institute for Macromolecular Chemistry, Albert-Ludwigs-University Freiburg, Stefan-Meier-Strasse 31, D-79104 Freiburg, Germany ‡Basell Polyolefine GmbH, Catalyst Systems, Industriepark Hoechst, D-65926 Frankfurt am Main, Germany Sustainability Center Freiburg, Ecker-Strasse 4, D-79104 Freiburg, Germany

From Multisite Polymerization Catalysis to Sustainable Materials and All-Polyolefin Composites

Joining composite materials is an issue because traditional joining technologies are not directly transferable to composite structures. Fusion bonding and the use of thermoplastic films as hot melt adhesives offer an alternative to mechanical fastening and thermosetting adhesive bonding. Fusion bonding technology which originated from the thermoplastic polymer industry has gain a new interest with the introduction of thermoplastic matrix composites (TPC) which are currently regarded as candidates for primary structures. The improvement of thermoplastic polymer matrices, with the introduction of recent chemistries such as PEEK, PEI and PEKEKK. exhibiting increased mechanical performance, service temperature and solvent resistance (for the semi-crystalline systems) also supported the growth of interest for fusion bonding. This review looks at the state of the art of fusion bonding technology and focuses particularly on the three most promising fusion bonding techniques: ultrasonic welding, induction welding and resistance welding. Physical mechanisms involved in the fusion bonding process for modelling purposes are discussed including heat transfer, consolidation and crystallinity aspects. Finally, the application of fusion bonding to joining dissimilar materials, namely thermosetting composites (TSC)/TPC and metal/TPC joints, is reviewed.

Advances in fusion bonding techniques for joining thermoplastic matrix composites: a review

: The melting behavior of semicrystalline poly(ether-ether-ketone) (PEEK) has been studied using differential scanning calorimetry (DSC). When cold-crystallized from the amorphous glassy state at high supercooling or when melt-crystallized at low supercooling, PEEK usually shows two melting peaks. This double melting behavior can be explained by the sum of four contributions: melting of most original crystals, their recrystallization, remelting of recrystallized PEEK and finally the melting of residual crystalline regions.

Double-melting behavior of poly(ether ether ketone)

: The tendency of carbon fiber to nucleate the crystallization of PEEK has been evaluated by DSC and other techniques. As the carbon fiber content was increased, the supercooling necessary for PEEK crystallization decreased. The repeated melting (at 396 C) of thhe same PEEK sample results in a decrease of the number of nuclei for crystallization. At equivalent thermal histories, PEEK with carbon fiber was found to have a higher nucleation density than PEEK itself. The surface growth of carbon fiber and nuclei in the PEEK matrix compete for crystallization growth. As the holding time in melt was increased, the number of matrix spherulites formed on cooling decreased, hence a more pronounced transcrystalline region was developed. Correspondingly, the composites preheated in the melt for 100 min. showed about two times the transverse tensile strength and strain-to-failure of those preheated for only 30 min. Corresponding fracture surface produced in tension showed that the former samples had a greater matrix adhesion to the carbon fiber than the latter. A strong interfacial bond is thus developed by crystallization on carbon fiber surface. Destroying nuclei in the PEEK matrix by long preheating enhances crystallization on the carbon fiber.

Crystallization of poly(etheretherketone) (PEEK) in carbon fiber composites

Etude par calorimetrie differentielle et diffusion RX aux petits et aux grands angles. La chaleur de fusion (39,5 cal/g) est mesuree a partir d'une relation lineaire entre la chaleur de fusion et la densite

On the double-melting behavior of poly(ether ether ketone)

Effects of thermal history on crystallization of poly(ether ether ketone) (PEEK)

A Ziegler-Natta catalyst was modified with a metallocene catalyst and its polymerization behavior was examined. In the modification of the TiCl 4 catalyst supported on MgCl 2 (MgCl 2 -Ti) with a rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind) 2 ZrCl 2 , EIZ) catalyst, the obtained catalyst showed relatively low activity but produced high isotactic polypropylene. These results suggest that the EIZ catalyst might block a non-isospecific site and modify a Ti-active site to form highly isospecific sites. To combine two catalysts in olefin polymerization by catalyst transitioning methods, the sequential addition of catalysts and a co-catalyst was tried. It was found that an alkylaluminum like triethylaluminum (TEA) can act as a deactivation agent for a metallocene catalyst. In ethylene polymerization, catalyst transitioning was accomplished with the sequential addition of bis(cyclopentadienyl)zirconium dichloride (Cp 2 ZrCl 2 )/methylaluminoxane (MAO), TEA, and a titanium tetrachloride/vanadium oxytrichloride (TiCl 4 /VOCl 3 , Ti-V) catalyst. Using this method, it was possible to control the molecular weight distribution (MWD) of polyethylene in a bimodal pattern. In the presence of hydrogen, polyethylene with a very broad MWD was obtained due to a different hydrogen effect on the Cp 2 -ZrCl 2 and Ti-V catalyst. The obtained polyethylene with a broader MWD exhibited more apparent shear thinning.

Youngchul Lee

Papers

Double-melting behavior of poly(ether ether ketone)

Crystallization of poly(etheretherketone) (PEEK) in carbon fiber composites

On the double-melting behavior of poly(ether ether ketone)

Effects of thermal history on crystallization of poly(ether ether ketone) (PEEK)

Modification of a Ziegler-Natta catalyst with a metallocene catalyst and its olefin polymerization behavior