Investigation of the influence of processing conditions on the thermal, rheological and mechanical behavior of polypropylene nanocomposites

Analysis of the Fire Behavior of Polymers (PP, PA 6 and PE-LD) and Their Improvement Using Various Flame Retardants

The fire behavior of polymers is examined primarily with the time-dependent heat release rate (HRR) measured with a cone calorimeter. The HRR is used to examine the fire behavior of materials with and without flame retardants, especially Polypropylene (PP-Copo) and Polyethylene (PE-LD). Polypropylene is stored for up to 99 days under normal conditions and the heat release rate shows especially changes about 100 s after irradiation with cone calorimeter, which may be caused by aging effects. The effect of crosslinking to the burning behavior of PP was examined too. Polyamides (PA 6) are irradiated with a radiation intensity of 25 kW/m² to 95 kW/m² and fire-related principles between radiation intensity and time to ignition can be derived from the measurement results. In order to comprehensively investigate the fire behavior of PP (also with flame retardant additives), the samples were also exposed to a flame, according to UL 94 with small power (50 W) and is inflamed with the power of a few 100 W. The irradiation causes different trigger mechanisms for the flame retardant additives in a plastic than the flame exposure. It is shown that the compound, which is favorable for irradiation, is not necessarily good for flame exposure. It can be seen that expandable graphite alone or with the addition of other additives is a very effective flame retardant for PP.

Influence of Processing Conditions on the Preparation of Clay-Based Nanocomposites by Twin-Screw Extrusion

This review paper is devoted to the preparation of clay-based thermoplastic nanocomposites by melt blending in a twin-screw extruder. The influence of the main processing parameters (screw speed, feed rate, barrel temperature, screw profile) on the state of the clay dispersion at the micro- and nanoscale is characterized. The change of dispersion state along the screws and the corresponding mechanisms are presented. The interest of process modelling to predict the state of dispersion is evaluated and, finally, the main modifications of the twin-screw extrusion process to improve the clay dispersion are reviewed.

Influence of Melt Compounding on Blast Furnace Slag Filled PP Compounds: A Comparative Study

In the current study, an assessment of the melt-compounding approach upon the behavior of blast furnace slag (BFS) filled polypropylene (PP) is reported. Two melt-compounding technologies are compared in terms of thermodynamic considerations as well as final behavior of the produced compounds. For this comparison, three PP-BFS formulations are introduced, where non-treated BFS is melt-mixed with PP via (1) internal lab mixer (IM) and (2) co-rotating twin-screw compounder (TSC). PP-BFS compounds from both processes are formed into plates via compression molding, characterized and tested for rheological, thermal and mechanical behavior. Processing parameters were evaluated for both processes such as specific shear work, residence time and shear rates. In addition, the rheological, thermal and mechanical behavior of comparable compounds are evaluated. The calculated specific shear work values for IM and TSC are 0.15 and 0.1 kW · h · kg−1. Calculated residence time for TSC is 55 s. Regarding the rheological behavior, it was found that melt mixing via both technologies did not show major differences in complex viscosity or storage- and loss moduli values. DSC findings show that crystallization and melting temperatures of IM- and TSC formulations are comparable. Decreased strain values are noticed for TSC compounds, while tensile modulus is found to be independent of process variation.

A Review of Multiscale Computational Methods in Polymeric Materials

Polymeric materials display distinguished characteristics which stem from the interplay of phenomena at various length and time scales. Further development of polymer systems critically relies on a comprehensive understanding of the fundamentals of their hierarchical structure and behaviors. As such, the inherent multiscale nature of polymer systems is only reflected by a multiscale analysis which accounts for all important mechanisms. Since multiscale modelling is a rapidly growing multidisciplinary field, the emerging possibilities and challenges can be of a truly diverse nature. The present review attempts to provide a rather comprehensive overview of the recent developments in the field of multiscale modelling and simulation of polymeric materials. In order to understand the characteristics of the building blocks of multiscale methods, first a brief review of some significant computational methods at individual length and time scales is provided. These methods cover quantum mechanical scale, atomistic domain (Monte Carlo and molecular dynamics), mesoscopic scale (Brownian dynamics, dissipative particle dynamics, and lattice Boltzmann method), and finally macroscopic realm (finite element and volume methods). Afterwards, different prescriptions to envelope these methods in a multiscale strategy are discussed in details. Sequential, concurrent, and adaptive resolution schemes are presented along with the latest updates and ongoing challenges in research. In sequential methods, various systematic coarse-graining and backmapping approaches are addressed. For the concurrent strategy, we aimed to introduce the fundamentals and significant methods including the handshaking concept, energy-based, and force-based coupling approaches. Although such methods are very popular in metals and carbon nanomaterials, their use in polymeric materials is still limited. We have illustrated their applications in polymer science by several examples hoping for raising attention towards the existing possibilities. The relatively new adaptive resolution schemes are then covered including their advantages and shortcomings. Finally, some novel ideas in order to extend the reaches of atomistic techniques are reviewed. We conclude the review by outlining the existing challenges and possibilities for future research.