JOURNAL OF MATERIALS SCIENCE 34 (1 9 9 9 ) 385 – 394 Glass-fiber reinforcement of in situ compatibilized polypropylene/polyethylene blends CH. TSELIOS, D. BIKIARIS, P. SAVIDIS, C. PANAYIOTOU ∗ Department of Chemical Engineering, University of Thessaloniki, 54006 Thessaloniki, Greece A. LARENA Departamento de Ingenieria Quimica Industrial, Escuela Tecnica Superior de Ingenieros Industriales, Universidad Politecnica de Madrid, Jose Gutierrez Abascal 2, 28006 Madrid, Spain Polypropylene and low-density polyethylene (LDPE) were melt-blended at proportions 75/25, 50/50, and 25/75 w/w, respectively. These blends were reinforced with two types of glass fibers added at an amount of 20 wt %: the E-type fibers without any surface treatment and the M-type fibers, which were treated with y -methacryloxy propyltrimethoxy silane coupling agent. Poly(propylene-g-maleic anhydride) with 0.8 mol % maleic anhydride content and poly(ethylene-co-vinyl alcohol) with 7.5 mol % vinyl alcohol content were added at a 50/50 w/w proportion as in situ reactive compatibilizers at an amount of 10 wt %. The thermoplastic composite materials have higher tensile strength as well as impact strength compared to the unreinforced blends. The simultaneous process of the in situ blend compatibilization, along with the incorporation of glass fibers in the thermoplastic matrix, leads to a significant improvement of the mechanical properties as compared to the properties of the composite materials with the uncompatibilized matrix. Scanning electron microscopy and micro-Raman spectroscopy have been used to study the adhesion of the thermoplastic matrix onto the glass fibers. Significantly better adhesion characteristics were observed in the composites containing M-type glass fibers, with LDPE adhering the most on the fibers. This better adhesion was reflected in the improved mechanical properties of the composites. C  1999 Kluwer Academic Publishers 1. Introduction Glass-fiber reinforcement is often an attractive way to improve the mechanical properties of thermoplastic matrices, the improvement being attributed to the ex- cellent mechanical properties of the fibers [1–3]. Many studies have been published concerning the rheology, processing conditions, and the properties of thermo- plastics containing glass fibers [4–9]. The mechanical properties of these thermoplastic composites are sig- nificantly affected mainly by the interfacial adhesion between the glass fiber and the polymer matrix, the length and the diameter of the fiber, their concentra- tion in the thermoplastic, the fiber orientations, and their distribution in the polymer composite [10–14]. On the other hand, there is an ever-increasing interest in the development of new polymer alloys and blends. In the last few years, much interest has also been shown in the fiber reinforcement of polymer alloys and blends [15–19]. Blending and alloying of polymers are effective methods for tailor-making materials that possess spe- cific combinations of physical properties, processing characteristics, and cost. But because of the immiscibi- lity and incompatibility of most polymers, the resulting ∗ Author to whom correspondence should be addressed. material has inferior mechanical properties when com- pared to the pure-component polymers. These pro- perties could lie between the corresponding properties of the component polymers or even be inferior than either of the pure polymers. Polypropylene (PP) and low-density polyethylene (LDPE) are two of the most commonly used polymers, and their blends are of great interest. The possibility of preparing a blend of these polymers with acceptable mechanical properties would result in a valuable material and a useful recycling prac- tice, because in communal waste the main plastic com- ponents are usually the various types of the semicrys- talline PE and PP, which are used mainly in packaging applications [20]. Because PP and LDPE are incompatible, the use of a compatibilizer is always needed for the production of a blend with acceptable properties [21–24]. In a re- cent work, we studied the effect of polypropylene-g- maleic anhydride (PP-g-MA) and ethylene vinyl alco- hol copolymers, as compatibilizers in PP/LDPE blends [25]. It was found that the above mixture of copoly- mers can act as an effective compatibilizer, increasing all mechanical properties, with a maximum observed at a composition of 10 wt % of compatibilizer in the final 0022–2461 C  1999 Kluwer Academic Publishers 385