Electromagnetic shielding properties of iron oxide impregnated kenaf bast fiberboard

The electromagnetic shielding effectiveness of kenaf fiber based composites with different iron oxide impregnation levels was investigated. The kenaf fibers were retted for removing the lignin and extractives from the fibers and magnetized. Using the unsaturated polyester and the magnetized fibers, kenaf fiber based composites were manufactured by the compression molding process. The transmission energies of the composites were characterized when the composite samples were exposed under the irradiation of electromagnetic (EM) wave with a variable frequency from 9 GHz to 11 GHz. Using the Scanning Electron Microscope (SEM), the iron oxide nanoparticles were observed on the surfaces and inside the micropore structures of single fibers. As the Fe content increased from 0% to 6.8%, 15.9% and 18.0%, the total surface free energy of kenaf fibers with the magnetizing treatments increased from 44.8 mJ/m² to 46.1 mJ/m², 48.8 mJ/m² and 53.0 mJ/m², respectively, while the modulus of elasticity reduced from 2875 MPa to 2729 MPa, 2487 MPa and 2007 MPa, respectively. Meanwhile, the shielding effectiveness was increased from 30–50% to 60–70%, 65–75% and 70–80%, respectively.     

Polyamide-6/vegetal fiber composite prepared by extrusion and injection molding

The interest for the use of vegetal fibers as polymers reinforcement has recently increased because of their unique environmental and technological advantages. This work evaluated the use of Curauá fibers in polyamide-6 composites aiming at glass fiber replacement. Fiber content of 20, 30 or 40 wt% and fiber lengths of 0.1 or 10 mm were studied. Fibers were treated with N₂ plasma or washed with NaOH solution, to improve their adhesion to PA-6. Samples with 20 wt% of short or long fibers, with or without pre-treatment, were compounded in two different co-rotating intermeshing twin-screw extruders. These samples were submitted to mechanical and thermal tests. In conclusion, non-dried raw materials improved fiber/matrix interfacial adhesion. Tensile and flexural properties of this composite are better than unfilled, but lower than glass fiber reinforced polyamide-6. However, its impact resistance and heat deflection temperature are similar to the glass fiber reinforced polyamide-6 and its lower density, enable it to replace this latter in specific non-critical applications.     

Modifizierung des ABSE‐Polycarbosilazans mit Multi‐Walled Carbon Nanotubes zur Herstellung spinnfähiger Massen

Modification of the ABSE polycarbosilazane with multi‐walled carbon nanotubes for the creation of spinable masses An inexpensive method has been found to produce ceramic SiCN‐fibres via the precursor route consisting of five processing steps: synthesis of the polymer, preparation of the spinning mass, melt‐spinning, curing via electron beam and subsequent pyrolysis at 1100 °C in a nitrogen atmosphere. A special solid and meltable fibre polymer, the so‐called polycarbosilazane ABSE, has been developed in the last decade for this purpose. Due to its low molecular weight, an adequate catalytic and thermal aftertreatment was necessary to guarantee a stable melt‐spinning process. This article discusses an alternative way to prepare a qualified spinning mass, i.e. the addition of Multi‐Walled Carbon Nanotubes (MWCNTs) to the ABSE melt. For this purpose a homogeneous dispergation of the MWCNTs in the ABSE matrix is necessary. In this study, spinning masses were fabricated in different ways. By optical analysis and comparison of the level of dispergation in these spinning masses an optimized process for integration of the MWCNTs was identified. The influence of the addition of a dispersing agent is investigated as well. In using a dispersing agent, the level of homogeneous dispersion of the MWCNTs increases whereas the interactions between the particles and the precursor melt decrease. In first spinning experiments a good spinability of the masses were noticed. Thus the addition of MWCNTs represents a new way to modify the ABSE precursor for the melt‐spinning process.     

Modelling droplet motion and interfacial tension in filters collecting liquid aerosols

Extensive experimental investigations have shown some of the differences between the behaviours of the barrel and the clamshell shapes of droplets on filter fibres in flow fields. Realistic flow velocities (such as those used in many industrial filter systems) were utilised. The forces acting are air drag, interfacial tension and gravity. The properties of the interfacial restoring force are modelled, and show agreement with the experimental results, at least in the linear extension region before the onset of oscillatory behaviour of the droplets (induced by instability of the flow field). The model for the oscillatory behaviour is explored, and the natural frequencies of oscillation in the radial and transverse directions are shown to be the same, for the barrel shape. The clamshell shape also has the same natural frequencies, but they are different to those of the barrel shape. The coupling of the radial and transverse oscillation modes is explored for both the barrel and clamshell shape. Some contact angle results are given, both without airflow acting on the droplet and with increasing airflow.     

Mechanical properties of flax fibre/polypropylene composites. Influence of fibre/matrix modification and glass fibre hybridization

The effect of fibre treatments and matrix modification on mechanical properties of flax fibre bundle/polypropylene composites was investigated. Treatments using chemicals such as maleic anhydride, vinyltrimethoxy silane, maleic anhydride-polypropylene copolymer and also fibre alkalization were carried out in order to modify the interfacial bonding between fibre bundles and polymeric matrix. Composites were produced by employing two compounding ways: internal mixing and extrusion. Mechanical behaviour of both flax fibre bundle and hybrid glass/flax fibre bundle composites was studied. Fracture surfaces were investigated by scanning electron microscopy. Results suggest that matrix modification led to better mechanical performance than fibre surface modification. A relevant fact is that silanes or MA grafted onto PP matrix lead to mechanical properties of composites even better than those for MAPP modification, and close to those for glass fibre/PP.     

Experimental study on RC beams with FRP strips bonded with rubber modified resins

This paper presents the effects of adhesive properties on structural performance of reinforced concrete (RC) beams strengthened with carbon fiber reinforced plastic (CFRP) strips. The epoxy adhesives modified with liquid rubber of different content were used to bond the CFRP strips, and four point bending experiments were carried out on RC beams. The experimental results show that different CFRP strip thickness of 0.22 and 0.44 mm resulted in a transition of failure mechanism from interfacial debonding along the CFRP-concrete interface to concrete cover separation starting from the end of CFRP strips in the concrete. Moreover, it is suggested that no matter interfacial debonding or concrete cover separation, the rubber modifier enhanced the structural performance by increasing the maximum load-carrying capacity and the corresponding ductility, compared with the beams bonded with a neat epoxy resin. The improvement of structural performance due to modified adhesive was associated with the modification of stress profiles along the CFRP-concrete interface especially the stress concentration at the end of FRP, and the enhanced interlaminar fracture toughness. Rubber modified epoxy therefore is worth further studying in practical repair applications.     

External CFRP tendon members: Secondary reactions and moment redistribution

The response of prestress secondary reactions in the post-elastic range has been a topic of much controversy. Due to the brittleness of FRP (fiber reinforced polymer) composites, external FRP tendon members may have different moment redistribution characteristics compared to conventional concrete members. This paper presents a numerical investigation into the secondary reactions and moment redistribution in prestressed concrete continuous members with external CFRP tendons. The investigation parameters include the initial prestress level and the pattern of loading. The secondary reactions are computed using a newly developed method based on the linear transformation concept combined with a nonlinear finite element analysis. The results indicate that the secondary reactions increase quicker after concrete cracking and nonprestressed steel yielding. As a consequence, the secondary moment should be included in the design moment. The moment redistribution behavior for symmetrical loading is shown to be quite different from that for unsymmetrical loading. The study also shows that the effect of initial prestress on the moment redistribution is rather important.     

Influence of refiner fibre quality and fibre modification treatments on properties of injection-moulded beech wood–plastic composites

Thermo-mechanical pulp (TMP) fibres made from beech wood were produced using increasing refiner gap widths and thus with increasing fibre length and coarseness. Fibres (60% by weight) were compounded in an internal kneading mixer using high-density polyethylene as the matrix and injection-moulded. Fibre lengths and length/width ratios were determined (a) before processing and (b) after injection-moulding and Soxhlet extraction using the optical FibreShape system. An increase in fibre length resulted in a decrease in water absorption and an improvement in flexural strength and modulus of elasticity of the wood–plastic composites (WPC). However, flexural strength of the WPC with TMP fibres was not improved compared to WPC with wood flour when maleic anhydride-grafted polyethylene (MAPE) was used as a coupling agent. After injection-moulding, differences in length of the various TMP fibre types were minor. Fibre geometry before processing strongly influences the water absorption and flexural properties of the composite. Fibre treatment with emulsified methylene diphenyl diisocyanate (EMDI) resin before compounding was shown to be equally efficient in reducing water absorption and improving flexural strength as the addition of MAPE during the compounding step.     

On the effect of geometrical designs and failure modes in composite axial crushing: A literature review

Composite materials have been known for its low density, ease in fabrication, high structural rigidity, and wide range applications, i.e. aeronautic applications and automotive industry. Due to this, extensive studies had been conducted to evaluate its axial crushing ability to replace metallic materials. In this paper, it reviewed the usage of fibre reinforced plastic composite (FRP) as an energy absorption application device. Failure modes and geometrical designs such as shapes, geometry and triggering effect have been studied where these factors affected on peak load and specific energy absorption significantly. Accordingly, numerical analysis for axial crushing of affected factors had been simulated to predict the failure mechanisms of FRP composites.     

The effect of CuO coatings on the electrokinetic properties of stone wool fibres determined by streaming potential measurements

Commercial stone wool fibres were modified with copper(II) oxide coatings. This oxide is widely used in processes of surface modification for filter materials to improve its bacterial retention. The microorganisms are already susceptible to low concentrations of copper in contrast to humans for which copper is an inert material in the concentration range. Additionally, the coatings changed the electrokinetic properties of the fibres. As a result, the isoelectric point (IEP) of the untreated fibres was shifted from acidic towards a more basic pH range. A positive or no charge on the surface of the fibres allows them to be a substrate for the positively charged adsorbents of negatively charged waterborne contaminants with the use of electrostatic adsorption. The coatings were prepared by dip coating with the use of two different coating precursors: the aqueous suspension of CuO nanoparticles and aqueous solutions of copper(II) nitrate trihydrate or copper(II) acetate or a mixture of thereof. The zeta potential of the modified fibres was determined by a streaming potential method. The adhesion of the coatings was tested by flushing and ultrasonication of the modified fibres. The isoelectric point of the fibres was shifted towards a more basic pH range for all precursors with the largest impact of the copper(II) nitrate trihydrate precursor. This coating changed the IEP of the fibres from 4.1 to 8.3 pH value. The highest calculated coverage of the coatings was in the range of 54% and was obtained by using copper(II) nitrate trihydrate/CuO nanoparticles precursor. Although, we do not predict such modified fibres to act as a standalone water filter, we believe they have the potential to be an excellent support material for active adsorbents.