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Stiffness is one of the most relevant properties of composite materials. Although fiberglass has been traditionally used as reinforcement, natural fibers are seen as possible replacements due to concerns for environmental protection. In this work fibers from orange tree prunings were prepared and converted into mechanical, thermomechanical and chemi‐thermomechanical pulps, to be used as reinforcement for polypropylene. Polypropylene composite materials with 20–50% of reinforcing fibers were prepared and mechanically characterized. The intrinsic Young's modulus of the fibers was back calculated by means of the Hirsch model. The moduli were also obtained by Halpin‐Tsai equations with Tsai‐Pagano methods and then compared to establish the influence of the aspect ratio. Finally, a fiber tensile modulus factor was defined in order to characterize the contribution of the fibers to the Young's moduli of the composites. POLYM. COMPOS., 34:1840–1846, 2013. © 2013 Society of Plastics Engineers

Packaging consumes around 40% of the total plastic production. One of the most important fields with high requirements is food packaging. Food packaging products have been commonly produced with petrol polymers, but due to environmental concerns, the market is being moved to biopolymers. Poly (lactic acid) (PLA) is the most promising biopolymer, as it is bio-based and biodegradable, and it is well established in the market. Nonetheless, its barrier properties need to be enhanced to be competitive with other polymers such as polyethylene terephthalate (PET). Nanoclays improve the barrier properties of polymeric materials if correct dispersion and exfoliation are obtained. Thus, it marks a milestone to obtain an appropriate dispersion. A predispersed methodology is proposed as a compounding process to improve the dispersion of these composites instead of common melt procedures. Afterwards, the effect of the polarity of the matrix was analyzing using polar and surface modified nanoclays with contents ranging from 2 to 8% w/w. The results showed the suitability of the predispersed and concentrated compound, technically named masterbatch, to obtain intercalated structures and the higher dispersion of polar nanoclays. Finally, the mechanical performance and sustainability of the prepared materials were simulated in a food tray, showing the best assessment of these materials and their lower fingerprint.

aThough there has been a great deal of work concerning the development of natural fibers in reinforced starch-based composites, there is still more to be done. In general, cellulose fibers have lower strength than glass fibers; however, their specific strength is not far from that of fiberglass. In this work, alpha-fibers were obtained from alpha-grass through a mild cooking process. The fibers were used to reinforce a starch-based biopolymer. Composites including 5 to 35% (w/w) alpha-grass fibers in their formulation were prepared, tested, and subsequently compared with those of wood-and fiberglass-reinforced polypropylene (PP). The term "high-performance" refers to the tensile strength of the studied composites and is mainly due to a good interphase, a good dispersion of the fibers inside the matrix, and a good aspect ratio. The tensile strength of the composites showed a linear evolution for fiber contents up to 35% (w/w). The strain at break of the composites decreased with the fiber content and showed the stiffening effects of the reinforcement. The prepared composites showed high mechanical properties, even approaching those of glass fiber reinforced composites. Keywords INTRODUCTIONIt is commonly accepted that biopolymers and bio-fibers have the potential to replace or reduce the consumption of fossil fuel-derived plastics. In addition, to facilitate the recycling of these materials, such replacement should lead to reductions in energy consumption, pollution, and CO 2 emissions. Hence, fiber-reinforced composites are often described as eco-friendly materials. However, the mechanical properties and/or the price of such composites have rendered them inadequate for many applications to date. In general, cellulosic fibers have inferior strength compared to their synthetic counterparts, such as aramid, carbon, and glass fibers.Due to their lower density, some natural fibers have a specific strength not far from those of fiberglass. On the other hand, bio-based matrices (such as polylactic acid or polyhydroxybutyrate) remain more expensive than petroleum-derived polymers. Nevertheless, thanks to their price/performance balance, ongoing innovations are offering new commercial opportunities for bio-based polymers and their composites in several applications. PEER-REVIEWED ARTICLEbioresources.com Gironès et al. (2013). "Alpha/starch composites," BioResources 8(4), 6121-6135 6122Compared to lactones, butyrates, valerates, and other monomers used for the synthesis of biodegradable polymers, starch is an inexpensive product whose transformation into a thermoplastic polymer can be accomplished in a rather straight-forward manner (Coombs and Hall 1998;Teixeira et al. 2007;Averous and Halley 2009;Dogossy and Czigany 2011;Gandini 2011). As a result, thermoplastic starch (TPS) is considered one of the most promising biopolymers for large-scale applications. During the last few decades, TPS has received considerable attention among the scientific world (John and Thomas 2008;Belhassen et al. 2009;Cañigueral et al. 2009;Cha...

Alpha-grass was studied as the reinforcement in a starch-based polymer matrix. Mater-bi®-Y was chosen as a matrix due to its Young's modulus, in line with that of polypropylene. The test specimens were injection molded and tensile tested. The obtained results were compared to glass fiber reinforced polypropylene. The reinforcing fibers increased the Young's modulus significantly, obtaining values up to 7.2 GPa, comparable to those obtained with reinforced polypropylene. The contribution of the fibers to the final composite Young's modulus was also studied, and it was found that was in line with other natural fibers contribution to polypropylene-based composites. Finally, it was found that the value of the efficiency factor of the module remained similar to that of natural fiber reinforced polypropylene.

The inclusion of old newspaper as reinforcement in composites promotes the use of environmentally friendly materials, reduces landfilling, decreases chemical treatments to bleach the recycled paper, and provides alternatives to glass fiber. While there are studies on the tensile strength and stiffness of old newspaper reinforced materials, there is a lack of analysis of their flexural properties. Considering that bending loads are very common, the flexural stiffness of the materials must be examined prior to industrial use. In this study, the flexural moduli of composites made from old newspaper fibers and polypropylene were compared with other composites. The composites showed moduli ranging from 2.1 to 4.1 GPa, and a composite with 50% newspaper content had a flexural modulus comparable to 10% glass fiber composite. These values allow an industrial use of the composites for semi-structural purposes. A method to assess the intrinsic flexural modulus of the reinforcements was presented and evaluated against other micromechanics models. The value of the efficiency factors and a mean orientation angle were also obtained.