Response of Polypropylene Composites Reinforced with Natural Fibers: Impact Strength and Water-Uptake Behaviors.

Composites from polypropylene (PP) reinforced with hemp strands (HS) are prepared in the current work with the aim of deepening on the influence of this reinforcement on the impact performance of these specific composites. Despite all the research conducted in this field, the effect of this natural reinforcement on the absorbed energy during crack formation and propagation is not fully tackled in previous research works. From the methodology and samples' geometry, the results concluded that the quality of the interface has a noticeable role in the impact resistance of these materials. The interface strength, fiber dispersion and fiber pullout are the main contributors to crack formation, whereas fiber pullout is the main one responsible for crack propagation. Maximum values of absorbed energy were found for PP composites comprising 20-30 wt% of HS and 8 wt% of the coupling agent for the un-notched samples, whereas maximum absorbed energy values corresponded to PP composites with 40 wt% of HS and 4 wt% of coupling agent for the notched samples. The water-absorption behavior in different humid environments is also examined. From the kinetic study, the water diffusion followed a Fickean behavior showing low-diffusion coefficients, increasing with fiber content. This systematic investigation represents a contribution to the analysis of the potential of reinforcing conventional polymers with natural materials, as a strategy towards more sustainable development.

Process Design for Value-Added Products in a Biorefinery Platform from Agro and Forest Industrial Byproducts.

Agroforestry wastes are industrial byproducts available locally such as eucalyptus sawdust (EUC) and sugarcane bagasse (SCB). These byproducts can be used as lignocellulosic raw materials to produce high-value products. This study is a techno-economic analysis of four potential scenarios to produce polyhydroxybutyrate (PHB) and levulinic acid (LA) from hemicellulosic sugars by a fermentative pathway in a biomass waste biorefinery. Mass and energy balances were developed, and technical and economic assessments were carried out to obtain gas, char, and tar from residual solids from autohydrolysis treatment. It was determined that microbial culture could be an attractive option for added-value product production. More than 1500 t/year of PHB and 2600 t/year of LA could be obtained by the proposed pathways. Microbial and enzymatic conversion of LA from sugars could significantly improve energy consumption on the conversion strategy. The products from solid residual valorization (char and tar) are the most important for economic performance. Finally, a variation in specific variables could mean substantial improvements in the final indicators of the processes, reaching a higher NPV than USD 17 million.

Behavior of the Flexural Strength of Hemp/Polypropylene Composites: Evaluation of the Intrinsic Flexural Strength of Untreated Hemp Strands.

The growing demand for plant fiber-reinforced composites offers new opportunities to compete against glass fiber (GF)-reinforced composites, but their performance must be assessed, revised, and improved as much as possible. This work reports on the production and the flexural strength of composites from polypropylene (PP) and hemp strands (20-50 wt.%), using maleic anhydride-grafted PP (MAPP) as a compatibilizer. A computational assessment of the reaction between cellulose and MAPP suggested the formation of only one ester bond per maleic anhydride unit as the most stable product. We determined the most favorable MAPP dosage to be 0.06 g per gram of fiber. The maximum enhancement in flexural strength that was attained with this proportion of MAPP was 148%, corresponding to the maximum fiber load. The modified rule of mixtures and the assumption of similar coupling factors for tensile and flexural strength allowed us to estimate the intrinsic flexural strength of hemp strands as 953 ± 116 MPa. While falling short of the values for sized GF (2415 MPa), the reinforcement efficiency parameter of the natural fibers (0.209) was found to be higher than that of GF (0.045).

3D Printing High-Consistency Enzymatic Nanocellulose Obtained from a Soda-Ethanol-O2 Pine Sawdust Pulp.

Soda-ethanol pulps, prepared from a forestry residue pine sawdust, were treated according to high-consistency enzymatic fibrillation technology to manufacture nanocellulose. The obtained nanocellulose was characterized and used as ink for three-dimensional (3D) printing of various structures. It was also tested for its moisture sorption capacity and cytotoxicity, as preliminary tests for evaluating its suitability for wound dressing and similar applications. During the high-consistency enzymatic treatment it was found that only the treatment of the O2-delignified pine pulp resulted in fibrillation into nano-scale. For 3D printing trials, the material needed to be fluidized further. By 3D printing, it was possible to fabricate various structures from the high-consistency enzymatic nanocellulose. However, the water sorption capacity of the structures was lower than previously seen with porous nanocellulose structures, indicating that further optimization of the material is needed. The material was found not to be cytotoxic, thus showing potential as material, e.g., for wound dressings and for printing tissue models.