FTIR study of thermal cyclization processes in the synthesis of polyetherimidazopyrrolones

An FTIR method was used to investigate the thermal cyclization process in synthesis of polyetherimidazopyrrolones from dietherdianhydrides and 3,3′-diaminobenzidine. It was concluded that the highest degree of cyclization to imidazopyrrolone structure is observed in the case of polymer with bisphenol A group having electron-donating character after dynamic heating, though for the all polyether-imides investigated even at 320°C cyclization are not complete.     

Advances in calculating thermally induced stresses in nonlinear viscoelastic materials

Temperature change can build up tensile stresses into thermoplastic materials, if their thermal expansion is hindered. This paper describes how to calculate those stresses. Because thermoplastic materials are time dependent with respect to temperature and strain, a nonlinear viscoelastic material model is necessary for the prediction of thermal stresses. This paper presents a numerical model that is able to predict thermally induced stresses in dependency on the load history. The calibration as well as the numerical procedures are described. The model is evaluated with a semicrystalline high density polyethylene (HDPE). Finally, a simulation of a screwed joint reveals the importance of this modeling for a more effective use of thermoplastics in the future.     

Flow induced deformation of dual-phase continuity in polymer blends and alloys. Part I

A hypothesis for formation of bi-continuous phase structures in immiscible polymer blends is proposed. It is based on the observation that a critical volume fraction φ_cr for the dual continuity of phases may be calculated considering the geometry of the dispersed phase. The knowledge of the form of discrete domains at the volume fractions φ < φ_cr and the probability that two close neighbor domains will form a strongly fused connection are sufficient to calculate φ_cr. Furthermore, it can be predicted that φ_cr should increase with stabilization of the interface. A comparative study showed that an addition of block copolymer may narrow the volume fraction range where bi-continuous phase structures are formed. Both annealing in the molten state and shearing history influence the measured φ_cr for the formation of bi-continuous phase structure in amorphous immiscible polymer blends.     

Studying the mechanism of the interaction between silicon nitride, oxygen, and nitrogen in heating and the processes of defect formation in Si3N4 — gas systems

The method of precision thermal massometry is used to study the interaction between silicon nitride, oxygen, and nitrogen in nonisothermal heating at 300 -1300 K and a partial gas pressure of 19,998.3 Pa (150 Torr). The behavior of Si₃N₄ heated in forevacuum is studied. A special computer analysis of the experimentally obtained dependencies has provided kinetic equations for analyzing and determining the mechanisms of these processes and computing their activation energy. The experimental data are used for creating a hypothesis that the nitrogen sublattice of Si₃N₄ is dispersed before the beginning of its interaction with oxygen and nitrogen.     

High-strength ceramics from Zr02

Specimens of powder fabricated by codeposition of zirconium and yttrium nitrates with the using special dry ing techniques and regranulation by the method of hot isostatic pressing have been tested in air allowing for the laws of compaction of granulated powder at a final firing temperature of about 1500°C. The resulting ma terial had the following properties: a density p = 5.91 g/cm (98% of the theoretical value), an ultimate bend ing strength a = 1100 MPa, and a crack resistance K = 19.5 MPa . rn A set of the specimens was sub jected to hot isostatic pressing after natural sintering and exhibited the following properties: p = 6.08 g/cm = 1400 MPa, K = 17.5 MPa · m^1/2.     

New silicate-based powders for fire protection of thermoplastics

A new, intumescent powdered silicate additive for plastics (polyethylene and polyvinyl chloride) has been investigated that gives improved flame retardancy. Cone calorimeter evaluations of the compounds of polymer/powder show reduction in peak rate of heat release, total heat release, and rate of mass loss. The effects of various polymer/powder ratios and powder particle sizes on the fire protection performance are shown. The morphology of this powder and the polymer/powder compounds before and after combustion is observed. A fire-protection mechanism is discussed that suggests the importance of an interpenetrating char structure.     

Xylene Isomerization in the Liquid Phase Using Large‐Pore Zeolites

Three large‐pore zeolites, Beta with Si/Al ratios of 25 and 35 and Mordenite with an Si/Al ratio of 30, were studied in the conversion of o‐xylene at 493 K. Maximum conversion was achieved by the catalyst with the highest Si/Al ratio due to faster diffusion of the isomer inside the zeolite channels because of the lower acidity of the solid even with larger crystal size. A kinetic study was then carried out over this catalyst between 473 and 513 K in a batch reactor in the liquid phase. The activation energies obtained do not indicate the presence of diffusional constraints towards any isomer. Finally, the kinetic model obtained was simulated in a fixed‐bed reactor and compared to ZSM‐5 in the temperature range from 493 to 533 K. An increment in p‐xylene production of 20 % on average was obtained.