Performance Of Polymeric Materials Research Articles

FSCT publishes book on quantifying weathering performance of polymeric materials

FSCT publishes book on quantifying weathering performance of polymeric materials

Thermal stability of frictional surface layer and wear debris of epoxy nanocomposites in relation to the mechanism of tribological performance improvement

To enhance service performance of polymeric materials for tribological applications, micrometer inorganic particulates are generally incorporated [1], which increases load-bearing capacity and thermal conductivity of the matrices, promotes adhesion of the transferred film to the counterface, etc. However, these micron particulate composites have some inherent disadvantages. The detached particles, for instance, tend to be entrapped within the rubbing interface, leading to severe abrasion of the composites [2]. Besides, the fraction of the particles needed to achieve sufficient improvement of the tribological properties of the composites is relatively high, which remarkably decreases the processability of the polymers. To solve the problems, employment of particles of reduced size, i.e., nanoparticles, proves to be an effective method. By either improving dispersion of nanoparticles in matrices [3] or enhancing their affinity to the surrounding polymers [4], the defects of the micro-sized particulate composites can be overcome. As shown by our previous works [4, 5], nano-silica filled epoxy has significantly low frictional coefficient and wear rate at rather low filler loading (∼2 vol%) in comparison with unfilled epoxy. Besides, the above positive effect can be further strengthened when the nanoparticles are pregrafted by some polymer chains that can take part in curing reaction of epoxy. Considering that friction and wear are involved mostly in the top layer of a rubbing surface when a bulk material serves in tribological environment, mechanophysically and mechanochemically induced changes in the surface layer would certainly in turn influence the tribological performance of the material [6, 7]. Therefore, post-mortem characterization of frictional surface is able to yield valuable information about the wear processes that cannot be obtained by other techniques.

RHEOLOGY AS A QUALITY CONTROL INSTRUMENT

Quality control in polymer production is a decisive success factor today, growing in importance with the steadily increasing demands regarding the performance of polymeric materials. Rhe-ological methods are ideal for application in quality control, as they allow to draw conclusions regarding both molecular structure and processability from their results. This is especially true for the linear viscoelastic parameters of a polymer melt. Using several examples from industrial practice, the capacity of rheological measurements to clarify quality problems like degradation effects or non-homogeneity is demonstrated. The question of precision and reliability is finally addressed, based on the results of two round-robin tests.

Service Performance of Polymeric Materials: Prediction from Short-term Tests

Service performance seems to be the ultimate test of successful synthesis, processing, characterization and testing of polymeric materials. Viscoelasticity and the time dependence of mechanical properties can be considered as a nuisance, but in fact they provide us with the capability of prediction of long-term performance in service on the basis of short-term tests. The material characteristics and their influence on long-term life prediction are evaluated using two concepts, the cooperative response of the material and the chain relaxation capability (CRC). We show quantitative predictions using the time-temperature correspondence, time-strain correspondence, frequency-temperature correspondence, stress-time correspondence and the slow crack propagation on the basis of these concepts. The predictions include the use of a generalized temperature shift factor aT formula. Our formula includes the W-L-F equation of 1955 as a special case and has a much larger range of applications. Our stress shift factor a [sgrave] equation provides a prediction tool for a phenomenon demonstrated experimentally already in 1948.

Flexible riser pipes: problems and unknowns

A personal viewpoint is presented of the problems and unknowns relating to the materials aspects of flexible riser pipes, and possible solutions/indications for future research given. Through a brief description of the functions, materials and construction of flexible risers, the pipe terminations are highlighted as the major problem. A discussion of safety, testing and inspection reveals the major unknowns to be the performance of polymeric materials under extreme service conditions, the effects of long-term erosion/corrosion and the performance of pipes under compression. Three types of termination are then considered in detail.

Predicting the Extrusion Performance of Epdms

Abstract A semiempirical model is described for predicting the extrusion performance of polymeric materials. The model relates polymer molecular weight and molecular weight distribution to rheological coefficients measured in a capillary rheometer and applies the onedimensional expressions of drag and pres sure flow for single-screw extruders to predict the extrusion performance of compounded EPDM stocks. The generalized model offers a mechanistic approach to designing improved extruding polymers from a knowledge of the molecular properties of the polymer.

The effect of the physiological environment on the mechanical properties of biomaterials in cardiovascular applications.

The long-term biocompatibility and physical performance of polymeric materials in the physiological environment depend both on adsorption and absorption processes. While the former has received significant attention in the literature, the latter has not been sufficiently appreciated. Accelerated testing of prosthetic devices in the wrong media and temperatures yield misleading information as exemplified by pumping bladders of heart assist devices and heart valves. Although glutaraldehyde-treated porcine heterograft heart valves performed better than expected in humans over a period of several years, physical degradations that have been observed may be associated with the breakdown of the cross-links. Appropriately selected smooth-surfaced biomaterials and hydrogels are far better suited for temporary blood contacting prosthetic applications such as left ventricular heart assist devices (LVADs) than polyester flocked fibril surfaces that result in the deposition of a thick layer of fibrin/cellular mesh with clot-like morphology with inherent dangers of loss of polyester fibrils, and the shedding of clots as the result of cyclic flexing of the pump bladders. With the proliferation of various medical devices, the possibility of increased litigations with secondary and tertiary liabilities involving not only physicians, surgeons, and device manufacturers, but also suppliers of materials and components, it is essential to select pertinent rather than complex test procedures.

Testing methods for predicting the life of polymeric materials

On the assumption that the performance of polymeric materials can be predicted only on the basis of long-time tests under conditions similar to those that obtain in practice, the authors consider creep, stress relaxation, and dynamic measurements at various temperatures and frequencies. Theoretical methods of estimating the life of polymeric materials are investigated with allowance for changes in the physical and chemical structure of the polymer and the nonconstancy of the activation energy of the relaxation processes over a broad temperature interval.