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Greener composites, as alternatives to more common materials, should also achieve technical and economic feasibility to be commercially competitive. This study presents the results obtained from using a biodegradable starch-based matrix, and a natural fiber reinforcement coming from sugarcane bagasse, currently an agro-waste. The sugarcane bagasse biomass was treated to obtain four kinds of fibers with different morphological and chemical properties. The fibers were used to obtain composite materials, which were then tested for tensile properties. The results showed that some of the composites were suitable to replace high density polyethylene, from a technical and environmental point of view. The comparatively higher cost of the biobased matrices hinders the substitution, but the higher the fiber content, the lower the economic disadvantage. A micromechanical test and a sensitivity analysis showed that the fiber orientation had the highest impact on the tensile strength, followed by the fibers mean length and the quality of the interphase between the fibers and the matrix.

This paper explores the evolution in the tensile strength of orange pruning fiber-reinforced polypropylene composites. The exploitation of these pruning’s can effectively avoid incineration, with the consequence of CO2 emissions and fire risk, while extending the value chain of the agricultural industry. This biomass was subjected to three different treatments yielding mechanical, thermomechanical, and chemi-thermomechanical pulps. It was found that 20 to 50% of these pulps, together with a coupling agent, were used as polypropylene reinforcement. The evolution in the tensile strength and morphological properties of the fibers, and the effect of treatments on these properties were analyzed. A modified rule of mixtures (mROM) was used to analyze the micromechanical properties of the interface. In addition, the mechanical properties were weighted against the fiber treatment yields. Finally, factors to compute the net contribution of the fibers to the final strength of the composite materials were proposed.

A major drawback of natural-based composites is the incorporation of reinforcements that are less thermally stable than the matrix; therefore, the thermal properties of the resultant composite material needs to be studied. In this work, orange wood fibers were used to reinforce polypropylene. The effects on the thermal properties of the polymeric matrix were analyzed. To this end, differential scanning calorimetry (DSC), thermogravimetry (TGA), thermomechanical analysis (TMA), and dynamic-mechanical analysis (DMA) were performed. It was found that the degradation of the material took place in two distinct phases: the reinforcement, close to 250 °C, and the matrix, above 340 °C. DSC results showed that fiber reinforcement did not influence the transition temperatures of the materials, although it did affect the polymer crystallinity value, increasing by 7% when the composite is reinforced with 50% of the lignocellulosic reinforcement. The coefficient of expansion obtained by TMA indicated that thermal expansion decreased as the amount of reinforcement increased. DMA assays showed that the reinforcement did not modify the glass transition (20 to 25 °C) temperature and confirmed that the addition of reinforcement increased the crystallinity of the product.