Some observations by scanning electron microscopy on a new craze phenomenon in bisphenol-A polycarbonate

Summary A dense pattern of very fine crazes may be observed in unoriented and pre-oriented PC samples drawn to high stresses and strains. Scanning electron microscopy clearly revealed the microstructure of these crazes which are composed of fibrils of considerably larger diameters than those normally observed.Dedicated to C. C. Hsiao and J. A. Sauer on the occasion of the 30th anniversary of the publication of their paper: On Crazing of Linear High Polymers     

Effect of nanoparticle size and size‐distribution on mechanical behavior of filled amorphous thermoplastic polymers

Different types of polymer nanocomposites on the base of polystyrene, polymethylmethacrylate, and polycarbonate with alumina and SiO₂ nanoparticles and carbon nanotubes have been studied. Miniaturized, microdimensional samples were used, enabling a good control of morphology and distribution of particles by means of transmission and scanning electron microscopy. Special preparation techniques had been applied, which resulted in a very good dispersion of the nanoparticles. Using these materials with really nanosized particles of a few 10nm in size the effect on toughness enhancement could be studied without agglomerates as they often appear in the generally used large samples. Micromechanical mechanisms were studied in detail by TEM and SEM investigations of deformed samples. A “nanoparticle modulated crazing” could be detected as a toughness enhancing effect. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Current transport in conducting particle filled epoxies

The electrical contact resistance between isolated pairs of micron-sized gold particles has been measured as a function of their separation using apparatus constructed in house. When incorporated into a percolation model for current transport in a conducting particle filled insulator, the results of such measurements have been shown to be consistent with the observed variation of conductivity with filler content beyond the percolation threshold in gold filled epoxies. This has been tested further by using adsorbed alkanethiol monolayers to control the interparticle spacing in the composites, demonstrating the importance of the contact resistance for the macroscopic current transport properties. Received: 22 September 1997/Revised version: 30 October 1997/Accepted: 31 October 1997     

Creep failure mechanisms in a particulate-filled epoxy resin

The deformation-induced volume damage in a series of creep specimens is examined in this investigation in order to improve the basic understanding of creep failure in particulate-reinforced epoxy resins. The results are correlated with the fracture surface morphology reported elsewhere. Volume damage was found to consist of matrix shear yielding, silica-particle debonding and matrix cracking. Fracture is shown to be initiated by shear yielding and debonding which is followed by sub-critical crack growth, demonstrating the importance of volume damage in fracture. Sub-critical crack growth occurs by debonding or by void coalescence depending on the temperature and loading conditions. The temperature and loading dependence of volume damage and the above crack propagation mechanisms are examined and presented graphically in a damage mechanism map.     

Parameters determining the strength and toughness of particulate filled epoxide resins

The effects of such parameters as the filler volume fraction, particle size, aspect ratio, modulus and strength of filler, resin-filler adhesion and toughness of the matrix on the stiffness, strength and toughness of particulate filled epoxide resins have been evaluated. The mechanisms of deformation and rupture in these multiphase materials are discussed, illustrated byin situ mechanical tests in the scanning electron microscope.     

The graphite gauge and its application to the measurement of crack velocity

Existing methods for the measurement of crack position (and hence crack velocity) are briefly reviewed. Those methods are principally based on the optical, mechanical, electrical or acoustic behaviour of a cracking sample, or on an inspection of the fracture surfaces. None of the above techniques fulfills all conditions required to measure continually slow and fast crack growth in polymers up to 250°C, the only method capable of doing this is a potentiometric gauge without support. The development and application of such a graphite gauge to crack propagation in polymers is described in this paper. The experimental arrangement in general and the results obtained from “instrumented samples” in Charpy impact tests and from crack propagation across an interface between dissimilar materials are discussed and the advantages (large sensitivity, range of crack speeds from 10^?7 to 10³ m sec^?1) and disadvantages (gauge is also sensitive to plastic deformations) are indicated.     

Tensile behaviour and fracture toughness of poly(ether ether ketone)/poly(ether imide) blends

Summary The bulk tensile behaviour of poly(ether ether ketone) and poly(ether imide) homopolymers and their blends has been investigated, and the temperature and strain rate dependence of the yield stress discussed in terms of simple Eyring rate theory. In fracture mechanics tests, the K_IC of PEEK was found to decrease significantly with increasing test speed, whereas the K_IC of PEI showed little rate sensitivity. Therefore, although a gradual increase in K_IC with increasing PEEK content was observed in the blends at low loading rates, this effect was anticipated to be less pronounced at higher loading rates.     

Treatment of recurrent penile condylomata acuminata with external application and intraurethral instillation of bacillus Calmette-Guerin

PURPOSE: Condylomata acuminata are caused by human papillomavirus infection. Despite numerous treatment modalities these patients often demonstrate recurrent disease. We report initial experience with bacillus Calmette-Guerin (BCG) therapy in patients not responding to standard treatment. MATERIALS AND METHODS: Between October 1994 and March 1997, 6 men with rapidly recurrent external and intraurethral condylomata acuminata underwent BCG therapy after initial laser treatment. External application and intraurethral instillation of BCG were performed 6 times in weekly intervals. Followup studies included examination and endoscopic inspection of the urethra and bladder. RESULTS: Of the patients 3 completed 1 course of BCG and had no relapse of condylomata acuminata, 2 underwent a second course of BCG and 1 had relapse, and 1 had relapse after discontinuing therapy due to penile edema. The annual recurrence rate decreased from 3.2 before to 0.75 after BCG therapy (p < 0.05, test of equality of 2 percentages). CONCLUSIONS: Immunotherapy with BCG is accepted treatment for superficial transitional cell carcinoma. The BCG induced immune response appears to reduce the recurrence rate in patients with condylomata acuminata.     

Brown coal opencast mining and landscaping in the rhineland

The brown coal deposits in the world form an important reserve of energy and raw material, which can also be widely used economically in the present state of opencast mining techniques. Rhenish brown coal mining with its high values of production and productivity proves also that brown coal deposits, though low in energy, are economically exploitable if, for the mining of this coal, necessary preconditions are fulfilled. These are large-scale mining fields and the use of an appropriate opencast mining technique which includes reclamation and landscaping after mining. the measures necessary for this and the technical development have been carried out by mining Rhenish brown coal on an economical basis. Thanks to the rich deposit reserves, to the high level of development of the opencast mining technique as well as to new or further development of refining processes, Rhenish brown coal mining will also be able in the future, to contribute considerably to securing the supply of energy and raw material.