K. Friedrich

Structure–property relationships of irradiation grafted nano-inorganic particle filled polypropylene composites

An irradiation grafting method was applied for the modification of nanoparticles so that the latter can be added to polymeric materials for improving their mechanical performance, using existing compounding techniques. The following items are discussed in particular, in this paper: (a) chemical interaction between the grafting monomers and the nanoparticles during irradiation; (b) properties including modulus, yield strength, impact strength and fracture toughness of the resultant nanocomposites; and (c) possible morphological changes induced by the addition of nanoparticles. Through irradiation grafting polymerization, nanoparticle agglomerates turn into a nano-composite microstructure (comprising the nanoparticles and the grafted, homopolymerized secondary polymer), which in turn builds up a strong interfacial interaction with the surrounding, primary polymeric matrix during the subsequent mixing procedure. Due to the fact that different grafting polymers brought about different nanoparticle/matrix interfacial features, microstructures and properties of the ultimate nanocomposites could thus be tailored. It was found that the reinforcing and toughening effects of the nanoparticles on the polymer matrix could be fully brought into play at a rather low filler loading in comparison to conventional particulate filled composites. Unlike the approaches for manufacturing of the other types of nanocomposites, including intercalation polymerization, the current technique is characterized by many advantages, such as simple, low cost, easy to be controlled and broader applicability.

Tensile performance improvement of low nanoparticles filled-polypropylene composites

Abstract It was found beforehand that low nanoparticles loaded polymer composites with improved mechanical performance can be prepared by conventional compounding technique in which the nanoparticles are pre-grafted by some polymers using irradiation. To examine the applicability of the approach, a tougher polypropylene (PP) was compounded with nano-silica by industrial-scale twin screw extruder and injection molding machine in the present work. The results of tensile tests indicated that the nanoparticles can simultaneously provide PP with stiffening, strengthening and toughening effects at a rather low filler content (typically 0.5% by volume). The presence of grafting polymers on the nanoparticles improves the tailorability of the composites. Due to the viscoelastic nature of the matrix and the grafting polymers, the tensile performance of the composites filled with untreated and treated nanoparticles is highly dependent on loading rate. With increasing the crosshead speed for the tensile tests, the dominant failure mode changed from plastic yielding of the matrix to brittle cleavage.

Artificial neural networks applied to polymer composites: a review

Inspired by the biological nervous system, an artificial neural network (ANN) approach is a fascinating mathematical tool, which can be used to simulate a wide variety of complex scientific and engineering problems. A powerful ANN function is determined largely by the interconnections between artificial neurons, similar to those occurring in their natural counterparts of biological systems. Also in polymer composites, a certain amount of experimental results is required to train a well-designed neural network. After the network has learned to solve the material problems, new data from the similar domain can then be predicted without performing too many, long experiments. The objective of using ANNs is also to apply this tool for systematic parameter studies in the optimum design of composite materials for specific applications. In the present review, various principles of the neural network approach for predicting certain properties of polymer composite materials are discussed. These include fatigue life, wear performance, response under combined loading situations, and dynamic mechanical properties. Additionally, the ANN approach has been applied to composite processing optimizations. The goal of this review is to promote more consideration of using ANNs in the field of polymer composite property prediction and design.

Improvement of tensile properties of nano-SiO2/PP composites in relation to percolation mechanism

Abstract Low nano-silica loaded polypropylene composites are produced by conventional compounding technique in which the nanoparticles are grafted by polystyrene using irradiation beforehand. A high interfacial stress transfer efficiency is demonstrated by both strengthening and toughening effects perceived in tensile tests. The role of the modified nanoparticles in improvement of tensile properties of the nanocomposites is discussed in terms of percolation concept. A double percolation of yielded zones is presented to explain the specific influence generated by the nano-SiO 2 particles at low-filler loading regime.

Recent advances in polymer composites' tribology

An overview is given on the friction and wear properties of high temperature resistant polymers, in particular polyetheretherketone (PEEK), under various testing conditions against smooth steel counterparts. The effects of internal lubricants, especially polytetrafluoroethylene (PTFE), and short fibre reinforcements (glass vs. carbon) are outlined. In addition, results of sliding wear experiments with continuous glass, carbon or aramid fibre-polymer matrix composites against steel were used to develop a hypothetical model composite with optimum wear resistance.

Effect of particle surface treatment on the tribological performance of epoxy based nanocomposites

To overcome the disadvantages generated by the loosened nanoparticle agglomerates dispersed in polymer composites, an irradiation grafting method was applied to modify nanosilica by covalently bonding polyacrylamide (PAAM) onto the particles. When the grafted nanosilica was added to epoxy, the curing kinetics of the matrix was accelerated. Moreover, the grafting PAAM can take part in the curing of epoxy so that chemical bonding was established between the nanometer fillers and the matrix. Sliding wear tests of the materials demonstrated that the frictional coefficient and the specific wear rate of nanosilica/epoxy composites are lower than those of the unfilled epoxy. With a rise in nominal load, both frictional coefficient and wear rate of the composites decrease, suggesting a wear mechanism different from that involved in wearing of epoxy. Grafted nanosilica reinforced composites have the lowest frictional property and the highest wear resistance of the examined composites. Compared with the cases of microsized silica and untreated nanosilica, the employment of grafted nanosilica provided the composites with much higher tribological performance enhancement efficiency.

Mechanical properties and failure behaviour of carbon fibre-reinforced polymer composites under the influence of moisture

The effect of moisture on the mechanical properties and the failure behaviour of fibre-reinforced polymer composites was investigated. Moisture was introduced into the specimens by immersion in distilled water. Three materials were investigated, which were all reinforced with continuous carbon fibres. Two thermosetting matrices (unmodified and toughness-modified epoxy) and one thermoplastic matrix (polyetheretherketone) were used. The results showed that the absorbed moisture decreases those properties of both epoxy-based composites which were dominated by the matrix or the interface. The influence of water on the fibre-dominated values, as well as on the properties of the thermoplastic material, was not detectable. The distinct fall of the matrix- and interface-based values due to moisture can be ascribed to the weakening of bonding between fibre and matrix and softening of the matrix material.

On sliding friction and wear of PEEK and its composites

Abstract The friction and wear behaviour of different molecular weight virgin poly(ether ether)ketones (PEEK) and of PEEK blends with polytetrafluoroethylene (PTFE), as well as of PEEK composites with short carbon fibres was studied under dry sliding conditions against hard steel on a pin-on-disc apparatus. As characterised by the melt viscosity, and similar crystallinities after heat treatment, the high molecular weight PEEK had a better wear resistance than low molecular weight PEEK. The effects were greatest when the pv -level was high. Opposite to the wear rate, the coefficient of friction was not clearly affected by the pv combination term. The spherulite size and hardness of the PEEK play an important role in both friction and wear performance. Concerning the friction and wear properties of PEEK-PTFE blends, the inclusion of PTFE reduced the friction of PEEK. The lowest friction coefficient was measured for the blend with a PTFE volume fraction of 15%. The wear rates of the blends with PTFE volume fraction varying from 5–85% were lower than that of virgin PEEK. A minimum value in wear rate existed at a PTFE volume fraction of 5%. Wear of the PEEK-composites was always lower than for the neat PEEK matrix, but was increased with increasing temperature. For minimum friction coefficient there was an optimum content of fibres at about 10 vol.%.

Microstructure and tribological behavior of polymeric nanocomposites

Nanocomposites represent a new prospective branch in the huge field of polymer materials science and technology. It has been shown that an overall enhancement of properties of polymers can be achieved under certain conditions by the addition of nanoparticles. To examine the influence of microstructure on the tribological performance of nanocomposites, different ways of compounding were used in this study. It was found that the friction and wear behavior of polymeric nanocomposites under sliding environment was rather sensitive to the dispersion states of the nanoparticles. When the microstructural homogeneity of the nanocomposites was improved, their wear resistance could be increased significantly. The present work demonstrates the importance of TiO2‐nanoparticles dispersion in an epoxy resin matrix, on the materials’ tribological properties, when sliding against a smooth steel counterpart.

The electrical conductivity of carbon-fibre-reinforced polypropylene/polyaniline complex-blends: experimental characterisation and modelling

The aim of this study is to characterise and model the electrical conductivity of carbon-fibre-reinforced polypropylene/polyaniline-complex blends. A correlation between the electrical conductivity and the microstructure of both the blends and the composites was found; the fibre concentration, orientation and average length affected the electrical conductivity. In addition, a synergy effect between PANI-complex and carbon fibres in the polypropylene matrix regarding the electrical conductivity occurred. In particular, the percolation threshold of carbon-fibre composites was moved towards a reduced fibre content when the blend consisted of both PANI-complex and carbon fibre. A fibre-contact model was used to describe the electrical conductivity of carbon-fibre-composites and PANI-complex-blends. It was expanded to predict also the synergy effect between LCF and PANI-complex. The predictions were in good agreement with the experimental data.