Mechanical Properties and Viscoelastic Behavior of Basalt Fiber-Reinforced Polypropylene M. BOTEV, 1 H. BETCHEV, 1 D. BIKIARIS, 2 C. PANAYIOTOU 2 1 Department of Physics, University of Chemical Technology and Metallurgy, 8, Kliment Ohridsky Boulevard, 1756 Sofia, Bulgaria 2 Department of Chemical Engineering, Aristotle University of Thessaloniki, 540 06 Thessaloniki, Greece Received 9 September 1998; accepted 2 November 1998 ABSTRACT: In the present article, a series of commercial-grade polypropylenes (PP) filled with different contents of short basalt fibers were studied. This composite mate- rial presented deterioration of both mechanical characteristics, for example, stress and strain at yield with increasing of the fiber content. On the other hand, the impact strength was fourfold higher than that of unfilled PP. A poor adhesion between the PP matrix and the basalt fibers was detected. This is why interfacial interactions were promoted by the adding of poly(propylene-g-maleic anhydride) (PP-g-MA). It was ob- served that the tensile properties of the obtained materials and their impact strengths increased significantly with increasing of the amount of PP-g-MA in the blend. The adhesion improvement was confirmed by scanning electron microscopy as well. Fourier transform infrared spectroscopy was applied to assess if any chemical interactions in the system PP/PP-g-MA/basalt fibers exist. Dynamic mechanical thermal analysis data showed an increase of the storage modulus with increasing fiber content. The conclu- sion was made that the modification of the PP matrix led to a higher stiffness but its value remained constant, irrespective of the PP-g-MA content. With increasing fiber content, damping in the -region decreased, but increase of the coupling agent content restored its value back to that of PP. The loss modulus spectra presented a strong influence of fiber content on the -relaxation process of PP. The position of the peaks of the above-mentioned relaxation processes are discussed as well. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 523–531, 1999 Key words: polypropylene composites; mechanical properties; dynamic mechanical analysis INTRODUCTION The expanding use of polypropylene (PP) resins in different production areas is an indisputable fact nowadays. The favorable price–performance ratio encourages new developments, making PP the second most produced thermoplastic in the world. The need to meet growing sophisticated demands has lead to extensive studies in order to find new ways to improve the resin properties. Thus, a great number of studies have appeared in the literature. For some interesting examples, one could refer to articles discussing PP resins filled with smectite, 1 Mg(OH) 2 , 2 wheat and flax straw fibers, 3,4 and bamboo fibers, 5 etc. It is evident that there are no obstacles in the way of searching for new fillers and for the im- provement of the PP properties. Most of the at- Correspondence to: H. Betchev. Journal of Applied Polymer Science, Vol. 74, 523–531 (1999) © 1999 John Wiley & Sons, Inc. CCC 0021-8995/99/030523-09 523