Paul Kiekens

Biopolymers: overview of several properties and consequences on their applications

Abstract Recently, interest in composite manufacturing has shifted towards the use of natural fibres as reinforcement because of their environmental benefits. The use of a biodegradable matrix is worth considering since this would result in a completely biodegradable composite. In order to assess the most suitable matrix polymer, one must know the properties of the available polymers. Since data tend to be widely scattered over many sources and are very scarce compared to the conventional polymers, it is the purpose of this article to give an overview of the most relevant properties of a range of biodegradable polymers. An overview such as the one given here may provide a useful guide in establishing the best compromise between conflicting property demands. Data are presented mostly as ranges (in tables) as well as in graphs for quick comparison reasons. One specific application (thermoplastic pultrusion with flax as reinforcement) is also studied.

Thermoplastic pultrusion of natural fibre reinforced composites

Thanks to the good mechanical properties and the ecological and environmental advantages, the natural fibre flax offers good opportunities as a reinforcement material for composites, especially thermoplastic ones. One technique for the manufacture of composites on a continuous basis is pultrusion. This paper describes the possibility of the use of flax as reinforcement in thermoplastic pultruded composites.

Thermoplastic polymers: overview of several properties and their consequences in flax fibre reinforced composites

In order to assess the most suitable thermoplastic polymer for a certain application, one must know the properties of the available polymers. Since data tend to be widely scattered over many sources, it is the purpose of this article to give an overview of the most relevant properties of a range of thermoplastic polymers. The reported properties are divided into mechanical, physical, and thermal ones. It is clear that many of these properties are interrelated. By consequence some combinations of desired properties are not possible but an overview such as this may provide a useful guide in establishing the best compromise between conflicting property demands. Data are presented mostly as ranges (in tables) as well as in graphs for quick comparison reasons. One specific application (thermoplastic pultrusion with flax as reinforcement) is also studied. In this particular case, polypropylene is found to have the best combination of properties in order to be used as the composite matrix.

OPTIMIZING THE FIBER-TO-YARN PRODUCTION PROCESS WITH A COMBINED NEURAL NETWORK/GENETIC ALGORITHM APPROACH

An important aspect of the fiber-to-yam production process is the quality of the resulting yarn. The yarn should have optimal product characteristics (and minimal faults). In theory, this objective can be realized using an optimization algorithm. The complexity of a fiber-to-yarn process is very high, however, and no mathematical function is known to exist that represents the whole process. This paper presents a method to simulate and optimize the fiber-to-yam production process using a neural network combined with a genetic algorithm. The neural network is used to model the process, with the machine settings and fiber quality parameters as input and the yarn tenacity and elongation as output. The genetic algorithm is used afterward to optimize the input parameters for obtaining the best yarns. Since this is a multi-objective optimization, the genetic algorithm is enforced with a sharing function and a Pareto optimization. The paper shows that simultaneous optimization of yarn qualities is easily achieved as a function of the necessary (optimal) input parameters, and that the results are considerably better than current manual machine intervention. The last part of the paper is dedicated to finding an optimal mixture of available fiber qualities based on the predictions of the genetic algorithm.

Use of Neural Nets for Determining the Spinnability of Fibres

It is very important for a spinner to be able to predict the degree of spinnability of a given fibre quality. Certain process conditions must be taken into account here. This paper describes how the spinnability or a given fibre quality on a rotor and ring spinning machine can be predicted with a reliability of 95% by means of a neural network. The structure and the characteristics or the neural net used will be considered in greater depth, and a simple method of implementation of such a neural net will be described.

Influence of Fiber Surface Characteristics on the Flax/Polypropylene Interface

Dew retted hackled long flax was treated with propyltrimethoxysilane, phenylisocyanate, and maleic acid anhydride modified polypropylene (MAA-PP). The wetting parameters of the untreated and treated flax fibers were obtained with dynamic contact angle measurements. The results showed that the treated flax fibers are less polar than the untreated flax fiber. The interfacial adhesion between the flax fibers and poly-propylene, respectively, maleic acid anhydride modified polypropylene, was studied with fiber pull-out tests. The highest increase in apparent shear stress was obtained by treatment of the flax fiber with MAA-PP.

Wettability of natural fibres used as reinforcement for composites.

Wetting parameters e. g. contact angles, work of adhesion, fibre surface energy and interfacial energy of different flax and glass fibres in different liquids were determined. A polypropylene film was also studied by the Wilhelmy technique. The surface of the fibres was analysed with scanning electron microscopy. Results pointed out that the flax fibres are partially wetted out by polar solvents. A baseline shift hysteresis was observed, possibly due to hydratation of the surface. The wettability of the glass fibres with a finish for thermosets is higher in polar solvents, compared with glass fibres used as reinforcement for thermoplastics. It is observed that the wettability is independent of the fibre diameter for the glass fibres with the same cross-sectional shape. The difference in contact angle hysteresis between the fibres can be explained by the difference in presence of higher surface energy components. By comparing the wettability of the fibres and polypropylene, some fibres could be expected to have a better adhesion with polypropylene than the others.

The Use of Neural Nets to Simulate the Spinning Process

In a previous paper, a description was given of how the spinnability of a given fibre quality on a rotor- or a ring-spinning machine can be predicted with a reliability of 95% by means of a neural network. This paper goes further. It describes how yarn properties can be deduced from fibre properties and spinning-machine settings. In other words, a description is given of how to construct, train, and use a neural network in order to simulate the spinning process (predict yarn properties) on both rotor- and ring-spinning machines with an accuracy of over 95%.

Development of voltammetric sensors for the determination of sodium dithionite and indanthrene/indigo dyes in alkaline solutions

Abstract Linear sweep and cyclic voltammetric studies of indigo, indanthrene dyes and sodium dithionite in alkaline solutions are reported. The results were applied to develop amperometric determination methods for these vat dyes and reducing agent. On different electrode materials (Au, glassy carbon, Pd, Pt) the reduced dyes give an anodic voltammetric signal. This reaction referring to the oxidation of dyestuff is concentration, rotation and potential scan rate dependent. Adsorption of oxidized dyestuff on the electrode surface was found to impede the chronoamperometric determination. By introducing potential steps, in situ cleaning of the electrode surface leads to a repetitive renewal and activation of the electrode surface. The use of multi-pulse amperometry allowed to measure in a continuous way a voltammetric signal that is proportional to the dye concentration. The sodium dithionite concentration can also be monitored continuously using chronoamperometry but only in the absence of dyestuff due to the mentioned adsorption.

Kinetics of Ce(IV) reduction at gold, carbon and iridium electrodes

Abstract The characteristics of the cerium(IV) reduction have been examined at gold, glassy carbon and iridium rotating disk electrodes in 1 M sulphuric acid. Kinetic parameters have been evaluated from the reduction waves and are found to be independent of the electrode material. Cyclic voltammetric and radioactive measurements show that the adsorption of Ce(III) and Ce(IV) is extremely small or even nonexistent on all three electrode materials. The adsorption of oxygen at the electrode surface has only a small or negligible influence on the current—potential curves and the kinetic parameters.