Pultrusion of a flax/polypropylene yarn

doi:10.1016/j.compositesa.2006.01.024

Composites Part A: Applied Science and Manufacturing

Volume 38, Issue 5, May 2007, Pages 1431-1438

https://doi.org/10.1016/j.compositesa.2006.01.024 Get rights and content

Abstract

The present work reports the pultrusion of a flax reinforced polypropylene commingled yarn containing discontinuous flax and polypropylene fibers. This was the first attempt to pultrude this material. Rectangular cross-sectional profiles have been successfully produced using a self-designed pultrusion line. In a series of experiments carried out with yarns of two different flax fiber contents, the pultrusion parameters were varied. In particular, the preheating and die temperatures and also the pulling speed, which are the most relevant parameters regarding the potential future pultrusion of natural fiber composite profiles at industrial scale. A complete characterization of each profile was conducted in order to examine the influence of processing parameters on the profile quality. The mechanical properties were evaluated by performing three point bending as well as Charpy impact tests.

Introduction

Natural fibers reinforced composites have shown a growth of interest in the last decade. This is principally due to their high environmental friendliness and recyclability as well as to their high specific properties. Gensewich [1] reported about the pultrusion of natural fibers and different matrices. Depending on the natural fiber used, the profiles exhibited specific properties equivalent to the properties of glass fiber reinforced composites. This makes natural fibers reinforced composites appropriate candidates for potential applications in the automotive and construction industries [2], [3]. In fact, they are already used for many car components, as it has been demonstrated by various automotive manufacturers, e.g., Daimler Chrysler, BMW and others. The different kinds of fibers available are flax, kenaf, ramine hemp, jute, as well as hard fibers such as caroá or sisal.

Pultrusion processing is one sector of the composites industry, which is steadily growing. Compared with the common composite production processes, it offers the advantage of continuous production of profiles with a constant cross-section. Until now the process has been quite exclusively developed for thermosetting matrices, however, thermoplastic pultrusion shows a growth of interest, and considerable efforts have been made over the last decade. This can be explained by certain advantages associated with thermoplastics, e.g., good mechanical performance, high-temperature resistance, good chemical resistance, good recyclability, and their ability to be post-shaped [4], [5], [6].

The main problem with using thermoplastic matrices lies in the full impregnation of the fiber reinforcement due to the high matrix melt viscosities. In order to overcome this problem, the distance of the polymer melt flow should be reduced. A great number of semi-finished products has been developed where the matrices and the reinforcement fibers are closely mingled, for instance in pre-impregnated tapes, hybrid yarns or powder impregnated bundles. Nevertheless there still remain some difficulties to achieve a good mingling of the matrix with the reinforcing fibers [7].

The process parameters having an important effect on the properties of the pultruded composites were found to be the pulling speed, the preheating conditions, the heating temperature in the die, and the cooling rate [8], [9], [10].

This study concentrates on the pultrusion of polypropylene/flax (PP/Fl) hybrid yarn, consisting of discontinuous PP and flax fibers. A series of experiments has been conducted to produce rectangular profiles, using two types of yarn with two different fiber volume contents. The influence of various processing parameters, such as temperature and pulling speed, on the final properties of the profile, was determined. Additional experiments were also performed on compression molded plates made from pultruded profiles with poor quality.

Section snippets

Materials

The pultrusion experiments have been conducted on two different types of polypropylene/flax yarn. Table 1 gives an overview of the yarn properties. The matrix and flax fibers are spun together. The yarns have been produced by the Thüringisches Institut für Textil-und Kunststoff-Forschung, Rudolstadt, Germany. The flax weight fraction in the yarns amounted to 30% and 50% respectively, and the two yarn types were designed as PP/FL 30% and PP/FL 50%.

Pultrusion experiment

Rectangular profiles have been manufactured

Results and discussion

Initially two sets of experiments were conducted using PP/FL 30%. In the first set, the pultrusion parameters, heating die temperature and pulling speed, were varied to determine the best processing window for this material. The preheating temperature was fixed at 160 °C. The pultrusion parameters used for these five samples are summarized in Table 2.

Fig. 2, Fig. 3 represent the flexural strength and the flexural modulus of the pultruded profiles, as well as of the compression molded samples.

Conclusion

In this study, the first attempt to pultrude profiles using a flax fiber reinforced polypropylene yarn was successfully conducted. The flax fibers are high moisture sensitive and should be necessarily dried before manufacturing in order to achieve better mechanical properties.

The impact test results have shown to be specially sensitive to the quality of the impregnation obtained in the pultruded profiles.

Under certain conditions of speed and temperature, the profiles manufactured exhibit

Acknowledgements

This work was financially supported by the German Research Foundation (DFG ME 563/38-1). Many thanks are due to Dr.–Ing. Thomas Reußmann of the Thüringisches Institut für Textil- und Kunststoff-Forschung, Germany, supplying us with the various flax/PP yarns.

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Pultrusion of a flax/polypropylene yarn

Abstract

Introduction

Section snippets

Materials

Pultrusion experiment

Results and discussion

Conclusion

Acknowledgements

Composites

Natural fibres in the european automotive industry

J Ind Hemp

Activities in biocomposites

Mater Today