JOURNAL OF COMPOSITE MATERIALS Article Mechanical, water absorption, and aging properties of polypropylene/flax/glass fiber hybrid composites Massoud Ghasemzadeh-Barvarz, Carl Duchesne and Denis Rodrigue Abstract This work investigates the mechanical and aging properties of flax/glass fibers reinforced polypropylene hybrid compos- ites. The mechanical properties as a function of reinforcement content show that adding glass fiber to polypropylene/flax composites improves tensile modulus and strength as well as impact resistance and hardness, but has negligible effect on strain at yield and elongation at break. Water uptake at 85  C and variations in mechanical behavior are determined after water, thermal, and accelerated UV aging tests. The results indicate that glass fibers enhance water resistance of poly- propylene/flax composites. Thermal aging at 85  C reveals that irrespective of filler type and content the composites are thermally resistant. According to accelerated UV aging tests, the presence of glass fiber accelerates the degradation of the polypropylene matrix, but flax fiber can protect the composites. Finally, a partial least-squares model is built to correlate the composite composition to the properties of aged and unaged specimens. Keywords Polypropylene, flax fiber, glass fiber, hybrid composite, projection to latent structures, formulation–property relationships, composite degradation Introduction In the past decades, considerable research activities have been carried out to develop polymer composites reinforced with natural fibers because of their low dens- ity, environmentally friendly nature, low cost, nontoxi- city, and ease of recyclability. 1–3 However, compared to synthetic fibers such as glass, natural fibers suf- fer from lower mechanical properties and higher mois- ture absorption. 4 To benefit from the advantages of different fibers (e.g. synthetic and natural fibers), two or more fiber types can be incorporated in a single matrix leading to hybrid composites with a great diver- sity of material attributes. 5 Various hybrid composites using different thermoset resins including epoxy, polyester, phenolic, and polyur- ethane are reported in the literature. 4,6–11 A review on the subject was presented by Jawaid and Khalil. 11 On the other hand, application of natural fibers as reinforcement in thermoplastic composites is relatively new compared to thermosets, dating back around 1995. 12 Due to thermal instability at elevated temperature (typically 200  C), a limited number of thermoplastics such as polyethylene, polystyrene (PS), and polypropylene (PP), which can be processed below 200  C, are commonly used in hybrid composites with the presence of natural fibers. 13 For instance, Kalaprasad et al. 14–16 investigated the effects of fiber orientation, composition and length, as well as chemical treatment for low density polyethylene/sisal/glass fiber hybrid composites pre- pared by a solution mixing technique. They observed that composites with longitudinally oriented fibers have better tensile properties than those with randomly ori- ented ones. It was also observed that with increasing glass fiber volume fraction all the properties, with the exception of elongation at break, increased. They also Department of Chemical Engineering and CERMA, Universite ´ Laval, Quebec City, Canada Corresponding author: Denis Rodrigue, Pavillon Adrien-Pouliot, 1065 avenue de la Me ´decine, Universite ´ Laval, Quebec City, Canada G1V 0A6. Email: denis.rodrigue@gch.ulaval.ca Journal of Composite Materials 0(0) 1–18 ! The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0021998314568576 jcm.sagepub.com at UNIVERSITE LAVAL on February 12, 2015 jcm.sagepub.com Downloaded from