A. El-Sabbagh

Low combustible polypropylene/flax/magnesium hydroxide composites: mechanical, flame retardation characterization and recycling effect

Natural fibre-reinforced polymer composites are nowadays receiving considerable attention, especially in the automobile and civil engineering industries. Reduction in flammability characteristics besides retention of their excellent mechanical properties will ensure wider market for these composites. Polypropylene matrix was reinforced with 30 and 50 wt% of flax fibres. Magnesium hydroxide was added at different levels of 0, 20 and 30 wt% in order to investigate the flammability resistance behaviour. Thermal and thermomechanical tests were carried out in order to evaluate new and recycled composites. Limited oxygen index was improved to more than 27 with 50 wt% flax/30% magnesium hydroxide, although very slow burning rate in the horizontal test condition was achieved with 30/30, 50/20 and 50/30 wt% for flax/magnesium hydroxides. Regarding the UL94 test, no sample passed vertical burn test. Recycling of these composites was investigated and showed 4 and 10% decrease in strength and stiffness, respectively. Recycling experiments on 50/30 system showed an effect of 5% limited oxygen index decrease after reprocessing for two cycles.

Thermal characterization of a series of lignin-based polypropylene blends

Polypropylene (PP), due to its chemical stability, is considered one of the main responsible of the increasing amount of plastic wastes on earth. To overcome this problem and to reduce the dependence of oil feedstocks, the use of lignocellulosics as fillers or reinforcements in thermoplastic materials has been increasing enormously in the last decades. In the present work, Liquid Wood (a mixture of cellulose, hemp, fax and lignin) was used to prepare, by mechanical mixing followed by thermal extrusion, blends of various PP/Liquid Wood ratios. Differential scanning calorimetry and thermogravimetric analysis experiments were performed in order to verify whether and how much the composition of the blends affects the thermal properties of the obtained compounds. Both calorimetric and thermogravimetric results indicate that the application of PP as a matrix does not limit the processing temperature of Liquid Wood, which may lead to a perfect marketable composite from these components. The addition of Liquid Wood also resulted in enhanced mechanical properties for the PP/Liquid Wood blends.

Modelling of Strength and Stiffness Behaviour of Natural Fibre Reinforced Polypropylene Composites

The mechanical behaviour (strength and stiffness) of natural fibre reinforced thermoplastics is investigated on the example of an injection moulded sisal-polypropylene system. An analytical model based on the rule of mixtures is developed to predict the mechanical behaviour of such composites. Considering interfacial characteristics this model accounts for the different modes of load transfer between matrix and fibre and their changeover. Close agreement between model and experimental results was achieved at low fibre contents (below 20 wt.%) as well as at higher contents (exceeding 40 wt.%). The model was finally verified against the experimental data and against available literature results.

Green Composites Based on Blends of Polypropylene with Liquid Wood Reinforced with Hemp Fibers: Thermomechanical Properties and the Effect of Recycling Cycles

Green composites from polypropylene and lignin-based natural material were manufactured using a melt extrusion process. The lignin-based material used was the so called “liquid wood”. The PP/“Liquid Wood” blends were extruded with “liquid wood” content varying from 20 wt % to 80 wt %. The blends were thoroughly characterized by flexural, impact, and dynamic mechanical testing. The addition of the Liquid Wood resulted in a great improvement in terms of both the flexural modulus and strength but, on the other hand, a reduction of the impact strength was observed. For one blend composition, the composites reinforced with hemp fibers were also studied. The addition of hemp allowed us to further improve the mechanical properties. The composite with 20 wt % of hemp, subjected to up to three recycling cycles, showed good mechanical property retention and thermal stability after recycling.

Prediction of Hypoeutectic Gray Iron Microstructure during Solidification and Solid Transformation Using Simple Fourier Model

Phases’ evolution during the solidification of a hypoeutectic 3.92% C-equivalence cast iron was modelled by considering the cooling history of the alloy from the melt, thus including both solidification and solid state transformations. Simple Fourier model was used to combine macroscopic heat flow and microscopic kinetics for phase evolution. Different cooling rates were obtained by casting cylinders and stepped plates. Measured number of primary austenitic nuclei, eutectic cells and volume fraction of phases during solidification (graphite, a-ferrite, pearlite and cementite), are correlated with the cooling rate. Growth rate constants for primary austenite, are found to be  = 8.7E-7, and n = 2.3. Growth rate constants for primary graphite (types A, B, and C), are found to be  =5.7E-7, and n = 2. The model matches with the experimental work where the error percent of modelling volume fractions of pearlite, graphite, ferrite and cementite ranges between 0.2 and 1.5%.

Coupled heat and fluid flow model and experimental verification of aluminium plate die casting

Abstract The present work aims to forecast mould filling, void shape, location and size as well as columnar to equiaxed transition (CET) in commercial pure aluminium casting. A model coupling the momentum equations of the fluid flow and heat transfer equations is presented, in which metallostatic pressure, air gap and oxide layer are considered. Different casting parameters were investigated such as casting configuration by varying the plate thickness from 5 to 20 mm, melt superheat from 40 to 120°C, mould preheat up to 200°C and different pouring heads ranging from 0·3 to 0·6 m. Regarding the microstructure and void formation, the approach based on the Niyama criterion, was considered. The experimental verification of the model was achieved by gravity die casting in the form of a rectangular cavity. Voids inside aluminium plate were investigated by X-ray imaging. Microstructure and CET was investigated microscopically. The supposed model proves its validity for mould filling and in detecting the void features and CET.

AN HYBRID GLASS/HEMP FIBERS SOLUTION FRP PIPES: TECHNICAL AND ECONOMIC ADVANTAGES OF HAND LAY UP VS LIGHT RTM

The aim of the present research was to investigate the replacement of glass fibers with hemp fibers for applications in the piping industry. The choice of hemp fibers was mainly related to the needs, expressed by some companies operating in this sector, for cost reduction without adversely reducing the performances of the pipes. Two processing techniques, namely hand lay up and light RTM, were evaluated. The pipe selected for the study was a curved fitting (90°) flanged at both ends. The fitting must withstand an internal pressure of 10 bar and the presence of acid aqueous solutions. The original lay‐up used to build the pipe is a sequence of C‐glass, glass mats and glass fabric. Commercial epoxy vinyl ester resin was used as thermoset matrix.Hemp fibers mats were selected as potential substitute of glass fibers mats because of their low cost and ready availability from different commercial sources. The data obtained from the mechanical characterization were used to define a favorable design of the pipe u...

Selection Chart of Flame Retardants for Natural Fiber Polymer Composites

Increasing the share of natural fiber thermoplastic composites NFTC in the market of engineering market demand to guarantee flame retardant properties. On the other side, addition of flame retardants FRs affects the mechanical properties negatively specially the whole tensile strength. Polypropylene PP reinforced with 30% natural fibers (flax, jute, hemp and sisal) are prepared using kneading and different FRs are mixed together. The effect of the different FRs on the flame retardance level, namely UL94, as well as the mechanical properties are studied. Hence, a selection chart for FRs is established. The studied FRs materials in this work are mineral, halogenated, halogen-free intumescent. Also, the effect of synergism with nanoclays and antimony tri oxide is considered. As a result of this experimental work regarding both the mechanical properties and the flame retardance levels, a material selection chart is built considering the tensile strength and flame retardance test UL94. This chart is enriched by other literature results. Also, the concept of this chart can be extended to deal with another mechanical property or another flame retardance test.

Flowability and fiber content homogeneity of natural fiber polypropylene composites in injection molding

As an index of viscosity, flowability of natural fiber polypropylene composites is assessed by spiral mold test using injection molding machine. The effect of the processing parameters like the injection temperature at 180-220°C, injection pressure at 500-1000 bar and the mold temperature of room temperature and 80°C on flowability is studied. The investigated parameters are the fiber shape (Non branched straight cellulose versus low flexural stiffness and branched hemp fibers), fiber length (0.5 versus 1.5 mm chopped cellulose fibers) and fiber content Wf (10 versus 30 wt%). The results show that the most significant parameters in a descending order are the pressure, temperature and the mold temperature. Another aspect of the product quality is the homogeneity of the fiber content through the whole injected spirals. Therefore samples are taken out at even distances along the spiral. The cut samples are dissolved to extract fibers and calculate the fiber content. Fiber content definition along the injecte...

Development of natural fiber/engineering plastics composites with flame retardance properties

Adding the natural fibre thermoplastic composites NFTC to engineering plastics represents a challenge due to the high temperature processing which in turn could result in the natural fibre damage. Finding applications for NFTC depends not only on the mechanical properties but also on the physical ones and the flame retardance property has an utmost importance. However; the implementation of flame retardants FRs materials has to counteract another challenge which is the drop of the corresponding mechanical properties. A comprehensive study is carried out for optimising the compounding process of the three constituents namely the thermoplastic, the natural fibre and the FR. A mixture of halogen-free phosphor based intumescent and inorganic hydrates is used as the FR system. FR mixture does not exceed 20% limit to allow enough binding effect of the thermoplastic with both fibres and FR. After conducting a screening study, it found out that Polybutylene terephthalate (PBT) and Polyamide (PA6) are good candida...