F.X. Espinach

Effect of Sodium Hydroxide Treatments on the Tensile Strength and the Interphase Quality of Hemp Core Fiber-Reinforced Polypropylene Composites

The formulation of greener composite materials by substituting glass fibers with natural fibers is a current field of research. If such natural fiber reinforcements come from industrial side streams, as hemp core fibers (HCFs) come from the extraction of hemp strands for the textile industry, an additional advantage can be identified. Nonetheless, such by-product fibers show some drawbacks, such as high lignin contents, which can make it difficult to obtain a good interphase between the fibers and the matrix and to obtain a good fiber individualization. A digestion treatment at different NaOH contents is proposed to eliminate soluble lignin and extractives from the surface of the fibers. At the same time, the use of a coupling agent solves incompatibilities between the fibers and the matrix. The composites were tensile tested and the impact of the proposed treatments is evaluated and discussed. Later, the Kelly-Tyson modified equation and a modified rule of mixtures—the micro-mechanic models—is used to study the impact of such treatments on the quality of the interphase between the polymer and the reinforcement. Both treatments showed a high impact on the tensile strength and the quality of the interphase, obtaining competitive composite materials reinforced with HCFs derived from a by-product.

Evaluation of Thermal and Thermomechanical Behaviour of Bio-Based Polyamide 11 Based Composites Reinforced with Lignocellulosic Fibres

In this work, polyamide 11 (PA11) and stone ground wood fibres (SGW) were used, as an alternative to non-bio-based polymer matrices and reinforcements, to obtain short fibre reinforced composites. The impact of the reinforcement on the thermal degradation, thermal transitions and microstructure of PA11-based composites were studied. Natural fibres have lower degradation temperatures than PA11, thus, composites showed lower onset degradation temperatures than PA11, as well. The thermal transition and the semi-crystalline structure of the composites were similar to PA11. On the other hand, when SGW was submitted to an annealing treatment, the composites prepared with these fibres increased its crystallinity, with increasing fibre contents, compared to PA11. The differences between the glass transition temperatures of annealed and untreated composites decreased with the fibre contents. Thus, the fibres had a higher impact in the composites mechanical behaviour than on the mobility of the amorphous phase. The crystalline structure of PA11 and PA11-SGW composites, after annealing, was transformed to α’ more stable phase, without any negative impact on the properties of the fibres.

Bleached kraft softwood fibers reinforced polylactic acid composites, tensile and flexural strengths

An increasing ecological consciousness in society has led to the development of materials with a lower environmental impact. PLA is a biodegradable polymer with higher mechanical properties than polypropylene. There are a few important works published about PLA-reinforced biocomposites in which satisfactory results were obtained. A good interphase generation when around 30% reinforcement percentages are extruded is, nowadays, an unsolved fact. The main objective of this study is obtaining PLA biocomposite with a good interphase that allows a satisfactory improvement on tensile and flexural strength. Pine bleached fibers were prepared and shred with 1/3 and 2/3 of diglyme, in order to avoid the formation of hydrogen bonds between the cellulose fibers. Afterwards, the composites materials have been obtained through kinetic mixing and injected into the shape of standard specimens in order to submit them to tensile and flexural test. The results show that the addition of diglyme helps the formation of hydrogen bonds between the reinforcement and the PLA. This is achieved by avoiding the generation of hydrogen bonds between the cellulose fibers. Only the fiber treated with 2/3 of diglyme followed a lineal and positive dependence of the tensile strength when increasing reinforcement content was added. The same composite materials also showed a linear behavior of the flexural strength against the fiber content. The intrinsic tensile and flexural strength of the fibers were also modeled. Although the obtained tensile and flexural strength were promising, more research is needed to ensure good results for higher than 30% fiber contents.

Approaching a new generation of fiberboards taking advantage of self lignin as green adhesive

This study describes the use of lignin as natural adhesive for the production high density fiberboards (HDF) made from wheat straw. In the present work, this agricultural residue was used to produce thermomechanical pulp and the used lignin was obtained from the spent liquors generated in the same process. A hot pressing process was conducted to manufacture these fiberboards and different percentages of this green adhesive were targeted. The wheat straw raw material and its pulp were characterized. Apart from that, the chemical composition and the thermal properties of the lignin sample were evaluated. Physical and mechanical properties were assessed and the results revealed that the panels made only with wheat straw fibers had a flexural strength value (52.79MPa) even above the value corresponding to the commercial HDF (41.70MPa). Also, results showed that the incorporation of soda-lignin lead to lignocellulosic composites that, as lignin content was increased (from 0 to 15%), mechanical properties were enhanced. The highest mechanical performance was reached for fiberboards at 15% of lignin with a flexural strength of 96.81MPa, a flexural modulus of 3.55GPa, and finally an internal bond of 1.46MPa.

Towards More Sustainable Material Formulations: A Comparative Assessment of PA11-SGW Flexural Performance versus Oil-Based Composites

The replacement of commodity polyolefin, reinforced with glass fiber (GF), by greener alternatives has been a topic of research in recent years. Cellulose fibers have shown, under certain conditions, enough tensile capacities to replace GF, achieving competitive mechanical properties. However, if the objective is the production of environmentally friendlier composites, it is necessary to replace oil-derived polymer matrices by bio-based or biodegradable ones, depending on the application. Polyamide 11 (PA11) is a totally bio-based polyamide that can be reinforced with cellulosic fibers. Composites based on this polymer have demonstrated enough tensile strength, as well as stiffness, to replace GF-reinforced polypropylene (PP). However, flexural properties are of high interest for engineering applications. Due to the specific character of short-fiber-reinforced composites, significant differences are expected between the tensile and flexural properties. These differences encourage the study of the flexural properties of a material prior to the design or development of a new product. Despite the importance of the flexural strength, there are few works devoted to its study in the case of PA11-based composites. In this work, an in-depth study of the flexural strength of PA11 composites, reinforced with Stoneground wood (SGW) from softwood, is presented. Additionally, the results are compared with those of PP-based composites. The results showed that the SGW fibers had lower strengthening capacity reinforcing PA11 than PP. Moreover, the flexural strength of PA11-SGW composites was similar to that of PP-GF composites.

Bleached Kraft Eucalyptus Fibers as Reinforcement of Poly(Lactic Acid) for the Development of High-Performance Biocomposites

Poly(lactic acid) (PLA) is one of the most well-known biopolymers. PLA is bio-based, biocompatible, biodegradable, and easy to produce. This polymer has been used to create natural fiber reinforced composites. However, to produce high-performance and presumably biodegradable composites, the interphase between PLA and natural fibers still requires further study. As such, we aimed to produce PLA-based composites reinforced with a commercial bleached kraft eucalyptus pulp. To become a real alternative, fully biodegradable composites must have similar properties to commercial materials. The results found in this research support the competence of wood fiber reinforced PLA composites to replace other glass fiber reinforced polypropylene composites from a tensile property point of view. Furthermore, the micromechanics analysis showed that obtaining strong interphases between the PLA and the reinforcement is possible without using any coupling agent. This work shows the ability of totally bio-based composites that fulfill the principles of green chemistry to replace composites based on polyolefin and high contents of glass fiber. To the best knowledge of the authors, previous studies obtaining such properties or lower ones involved the use of reagents or the modification of the fiber surfaces.

Recycling dyed cotton textile byproduct fibers as polypropylene reinforcement

The textile industry generates a large amount of byproducts that must be treated before being recycled or disposed of. The treatments to extract the dyeing agents are mandatory, and involve costs and interaction with toxic reagents. A relevant amount of such byproducts are short cotton dyed fibers. Cotton fibers are high-quality cellulosic fibers and can be used as composite reinforcement. In this paper, dyed cotton fibers were used to formulate, obtain and tensile test composite materials. The impact of the presence of dyes was studied and such dyes enhanced the interphase between the matrix and the reinforcement. On the other hand, when a coupling agent was incorporated to the formulation of the composites, the dyes hindered the chemical interactions between the maleic acid and the OH groups of the cellulosic fibers. Nonetheless, the composite materials showed competitive mechanical properties that were better than other natural fiber-reinforced composites and comparable to some glass fiber-based ones. Dyed cotton fibers can be used as reinforcement without further treatment, increasing the value chain of the textile industry and decreasing the chemical treatments necessary to recycle or dispose of dyed textile fibers.