Injection moulded short hemp fibre polypropylene composites

Natural fibre reinforced polymer composites are attracting the attention of various industrial fields due to both their environmental and economic advantages. Bio-composites, which refer to composites that combine natural fibres with either biodegradable or non-biodegradable, provide numerous benefits. The natural fibres in the bio-composites could be kenaf, jute, hemp or sisal. Investigations on the use of hemp fibres as reinforcement, to increase polypropylene performance, have introduced many applications for hemp fibre polypropylene composites in automotive and construction industries. The aim of this project was to utilise cheap waste hemp fibres (noil) to produce short fibre polypropylene composites and to carry out detailed investigations into the various parameters that contribute to composite performance characteristics. The microstructural, chemical and tensile characterizations of noil hemp fibre and normal hemp fibres were first studied using scanning electron microscopy (SEM), fourier transform infrared analysis (FTIR) and Dynamic Mechanical Analyser (DMA). Noil hemp fibre reinforced polypropylene composite samples with different noil fibre contents (10-60 wt%) were fabricated using an intermixer/extrusion and injection moulding machines. Maleic anhydride grafted polypropylene (MAPP) and maleic anhydride grafted polyethylene octane (MAPOE) were used as coupling agents for modifying the matrices. X-ray micro-tomography, image analysis and Weibull statistical methods were employed to characterise the size distributions of noil hemp fibres in the polypropylene matrices. X-ray micro-tomography provided direct observations and accurate measurements of length and width of noil hemp fibres within the hemp-polypropylene composites. The effects of the weight content of the noil hemp fibre and the addition of compatibilisers on the fibre breakage, due to the manufacturing process of the composites, were studied using X-ray micro-tomography in this project. Tensile, impact and flexural tests were carried out to study the mechanical properties of samples. Free vibration testing and dynamic mechanical analysis methods were also used to study the damping and thermo mechanical properties of the composites. Furthermore, the influence of fibre content and compatibiliser addition on interfacial shear strengths (IFSS) was evaluated by means of the modified Bowyer and Bader model. Finally, the influence of the type and initial length of the hemp fibre (0.2, 0.5, 1 and 2 mm) on mechanical properties of the composites was studied. The results indicated that the tensile strength of the noil hemp fibre reinforced composites without the coupling agents was lower than that of pure polypropylene. High noil hemp fibre content caused more fibre breakage due to the fibre-fibre interaction mechanism. The addition of coupling agents improved the tensile strength of the composites by the enhanced fibre/matrix interfacial adhesion. This was confirmed by SEM observations. It was also shown that the addition of MAPP reduced the fibre breakage due to the better dispersion of fibres. DMA revealed no noticeable changes in the α-transition temperature when the fibre content increased or coupling agents were added. The composites revealed better temperature resistance at higher fibre content. However, the increase in storage modulus was negligible in composites reinforced with more than 40 wt% hemp fibres due to the agglomeration of the fibres. The results of the damping ratio analysis revealed that higher interfacial bonding was achieved by the addition of MAPP coupling agent in comparison with the addition of MAPOE coupling agent. The storage modulus of the composites increased with the increase in hemp fibre content. However, the maximum damping ratio was obtained from the composite with 30 wt% noil hemp fibre. The addition of coupling agents reduced the damping capacity of all composites. However, 30 wt% noil hemp fibre reinforced polypropylene coupled with 2.5 wt% MAPOE revealed the highest damping ratio among coupled composites. Finally, the noil hemp fibre composites indicated slightly lower tensile properties than the alkali-treated ones. However, the difference was not significant. The analysis of the tensile, flexural and impact results indicated the optimum initial fibre length of 0.2 mm produced the ideal composites due to better dispersion of fibres (powders). This test methodology can be extended to different types of natural fibres

Numerical simulation of a three-stage Stirling-type pulse-tube refrigerator

The pulse-tube refrigerator (PTR) is a rather new device for cooling down to extremely low temperatures, i.e. below 4 K. The PTR works by the cyclic compression and expansion of helium that flows through a regenerator made of porous material, a cold heat exchanger, a tube, a hot heat exchanger and an orifice, in series. In a Stirling-type PTR compression and expansion are generated by a piston. The compression increases the temperature of the helium in the tube and makes it flow towards the orifice; the expansion decreases the temperature and makes the helium flow backwards to the regenerator. The net effect of warmer helium flowing in one direction and colder helium in the opposite direction is that of cooling power at the cold heat exchanger. Three PTRs are inter-connected aiming to obtain the desired 4 K lowest temperature. The conservation laws of mass, momentum and energy, and an equation of state, are simplified using asymptotic analysis based on low Mach-numbers. The regenerator is modelled one-dimensionally with Darcy’s law for flow resistance. The tube is modelled either one-dimensionally without resistance or two-dimensionally with axisymmetric laminar viscous flow. The heat transfer in the porous medium of the regenerator and in the solid tube wall is taken into account. The gas can be either ideal or real. All the material properties, including viscosity and conductivity, are taken temperature and pressure dependent. Three single-stage PTRs are connected with the regenerators in series and the tubes in parallel and six flow possibilities at the junctions are considered. Three by-passes (double-inlets) are used to enhance and tune the performance. The governing equations are numerically solved with a finite-difference method of nominally second-order accuracy in space and time. Pressure correction, flux limiter, 1D-2D connections and domain decomposition are the keywords here. Special attention is paid to suitable initial conditions, high resolution in the boundary layers and to the correct calculation of the three-way junctions in multi-stage PTRs. The model describes the fluid dynamics and thermodynamics of the pulse tubes and regenerators. The heat exchangers are assumed to be ideal in the whole analysis. The equation of state for real gas and other real properties of gas and regenerator material, which are temperature and/or pressure dependent, are applied in the three-stage PTR which works with extreme low temperatures, where the ideal gas law does not hold. The numerical methods require special attention. Typically for flow problems we deal with various length scales. Straight forward discretisation will result in unnecessary fine grids and therefore unacceptable computational time. We developed robust and efficient algorithms to deal with boundary layer problems. The employed domain decomposition technique allows for using coarse grids in areas where the solution does not change significantly. It also decouples a larger system into smaller ones, leading to smaller complexities. The objective of computing accurately and efficiently the steady oscillatory flow and heat transfer in a PTR has been achieved. In particular the tiny viscous and thermal boundary layers of a PTR operating at high frequency (20 Hz) could be resolved. The simulated three-stage PTR was able to cool down close to 5 K. The developed software is intended for use in design and optimisation of multi-stage PTRs

Learning Representations from Persian Handwriting for Offline Signature Verification, a Deep Transfer Learning Approach

Offline Signature Verification (OSV) is a challenging pattern recognition task, especially when it is expected to generalize well on the skilled forgeries that are not available during the training. Its challenges also include small training sample and large intra-class variations. Considering the limitations, we suggest a novel transfer learning approach from Persian handwriting domain to multi-language OSV domain. We train two Residual CNNs on the source domain separately based on two different tasks of word classification and writer identification. Since identifying a person signature resembles identifying ones handwriting, it seems perfectly convenient to use handwriting for the feature learning phase. The learned representation on the more varied and plentiful handwriting dataset can compensate for the lack of training data in the original task, i.e. OSV, without sacrificing the generalizability. Our proposed OSV system includes two steps: learning representation and verification of the input signature. For the first step, the signature images are fed into the trained Residual CNNs. The output representations are then used to train SVMs for the verification. We test our OSV system on three different signature datasets, including MCYT (a Spanish signature dataset), UTSig (a Persian one) and GPDS-Synthetic (an artificial dataset). On UT-SIG, we achieved 9.80% Equal Error Rate (EER) which showed substantial improvement over the best EER in the literature, 17.45%. Our proposed method surpassed state-of-the-arts by 6% on GPDS-Synthetic, achieving 6.81%. On MCYT, EER of 3.98% was obtained which is comparable to the best previously reported results

Sharpening the sword and rounding the shield: online jokes and the vernacular response to political reform in Iran

This thesis is an ethnographic study of Iranian political jokes: a hybridized genre of folklore which intersects in both online and oral spheres where it is created and shared. It specifically explores the emergence and growth of politicized humorous cellphonelore, which I term “electionlore”, during and after the 2016 February elections in Iran. Analysing different joke sub-cycles in this electionlore, I argue that these jokes serve as a powerful tool for my informants to construct their own “newslore” (Frank 2011) and make manifest what I term and define “vernacular politics” through which they were mobilized and unified in their political activism. I diverge from the theory of “resistance jokes” (Powell and Paton 1988; Bryant 2006; Davies 2011) and propose a new framework for studying political jokes in countries in suspense between democracy and dictatorship: jokes as an effective and strategic form of reform and unquiet protest

One-dimensional analytical and numerical models of the pulse-tube cooler

Three one-dimensional models describing the fluid dynamics and thermodynamics in the tube section of a pulse-tube refrigerator have been developed: numerical, analytical and harmonic. The numerical model concerns a finite-difference scheme that is second-order accurate in space and time. The analytical model is exact and based on the method of characteristics. The harmonic model is approximate and assumes sinusoidal variations of all variables. Some typical results for a single-stage Stirling type pulse-tube refrigerator are presented

One-dimensional analytical and numerical models of the pulse-tube cooler

Three one-dimensional models describing the fluid dynamics and thermodynamics in the tube section of a pulse-tube refrigerator have been developed: numerical, analytical and harmonic. The numerical model concerns a finite-difference scheme that is second-order accurate in space and time. The analytical model is exact and based on the method of characteristics. The harmonic model is approximate and assumes sinusoidal variations of all variables. Some typical results for a single-stage Stirling type pulse-tube refrigerator are presented

Ground hemp fibers as filler/reinforcement for thermoplastic biocomposites

Mechanical properties (tensile, flexural, and impact) of ground hemp fibre polypropylene composites were investigated. Ground alkali-treated hemp fibre and noil hemp fibres with various initial fibre lengths were utilized to reinforce polypropylene matrix. Firstly, the microstructural and tensile characterizations of the two types of fibres were characterized using scanning electron microscope (SEM), Fourier transform infrared analysis (FTIR), and Dynamic Mechanical Analyser (DMA). Then, the fibres were ground into different lengths of 0.2, 0.5, 1, and 2 mm; composites containing 40 wt% short hemp fibre and 5 wt% maleic anhydride grafted polypropylene (MAPP) were fabricated by means of a twin screw extruder and an injection moulding machine. Finally, influence of hemp fibre type and initial hemp fibre length on tensile property of the composites were investigated. The results revealed that addition of either noil hemp fibre or normal treated hemp fibre into the pure polypropylene matrix increased the tensile strength almost twice and stiffness of the composites more than three times. Although noil hemp fibre composite indicated slightly lower mechanical properties than the normal alkali-treated fibre composites, the difference was not significant. The analysis of the results provided the optimum initial fibre length (powder) of 0.2 mm hemp polypropylene composite. The results can be extended to different types of natural fibres

One-Dimensional Simulation of a Stirling Three-Stage Pulse-Tube Refrigerator

A one-dimensional mathematical model is derived for a three-stage pulse-tube refrigerator (PTR) that is based on the conservation laws and the ideal gas law. The three-stage PTR is regarded as three separate single-stage PTRs that are coupled via proper junction conditions. At the junctions there are six fluid flow possibilities each defining its own boundary conditions for the adjacent domains. Each single stage cools down the gas in the regenerator to a lower temperature such that the system reaches its lowest temperature at the cold end of the third stage. The velocity and pressure amplitudes are decreasing towards the higher stages and there is an essential phase difference between them at different positions. The system of coupled PTRs is solved simultaneously first for the temperatures and then for the velocities and the regenerator pressures. The final result is a robust and accurate simulation tool for the analysis of multi-stage PTR performance

Development and characterization of green composites from bio-based polyethylene and peanut shell

This is the accepted version of the following article: Garcia-Garcia, D., Carbonell-Verdu, A., Jordá-Vilaplana, A., Balart, R. and Garcia-Sanoguera, D. (2016), Development and characterization of green composites from bio-based polyethylene and peanut shell. J. Appl. Polym. Sci. 43940 doi: 10.1002/app.43940, which has been published in final form at http://dx.doi.org/10.1002/app.43940[EN] In the present work, different compatibilizers, namely polyethylene-graft-maleic anhydride (PE-g-MA), polypropylene-graftmaleic anhydride (PP-g-MA), and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene-graft-maleic anhydride (SEBS-g-MA) were used on green composites derived from biobased polyethylene and peanut shell (PNS) flour to improve particle polymer interaction. Composites of high-density polyethylene/peanut shell powder (HDPE/PNS) with 10 wt % PNS flour were compatibilized with 3 wt % of the abovementioned compatibilizers. As per the results, PP-g-MA copolymer lead to best optimized properties as evidenced by mechanical characterization. In addition, best particle matrix interface interactions with PP-g-MA were observed by scanning electron microscopy (SEM). Subsequently HDPE/PNS composites with varying PNS flour content in the 5 30 wt % range with PP-g-MA compatibilizer were obtained by melt extrusion and compounding followed by injection molding and were characterized by mechanical, thermal, and morphological techniques. The results showed that PNS powder, leads to an increase in mechanical resistant properties (mainly, flexural modulus, and strength) while a decrease in mechanical ductile properties, that is, elongation at break and impact absorbed energy is observed with increasing PNS flour content. Furthermore, PNS flour provides an increase in thermal stability due to the natural antioxidant properties of PNS. In particular, composites containing 30 wt % PNS powder present a flexural strength 24% and a flexural modulus 72% higher than the unfilled polyethylene and the thermo-oxidative onset degradation temperature is increased from 232 8C up to 2548C thus indicating a marked thermal stabilization effect. Resultant composites can show a great deal of potential as base materials for wood plastic composites.This research was supported by the Ministry of Economy and Competitiveness -MINECO, Ref: MAT2014-59242-C2-1-R. Authors also thank to "Conselleria d'Educacio, Cultura i Esport" - Generalitat Valenciana, Ref: GV/2014/008 for financial support. A. Carbonell-Verdu wants to thank Universitat Politecnica de Valencia for financial support through an FPI grant. D. Garcia-Garcia wants to thanks the Spanish Ministry of Education, Culture and Sports for the financial support through an FPU grant (FPU13/06011).García García, D.; Carbonell Verdú, A.; Jorda-Vilaplana, A.; Balart Gimeno, RA.; García Sanoguera, D. (2016). Development and characterization of green composites from bio-based polyethylene and peanut shell. Journal of Applied Polymer Science. 133(37):1-12. https://doi.org/10.1002/APP.43940S1121333

Processing and characterization of high environmental efficiency composites based on PLA and hazelnut shell flour (HSF) with biobased plasticizers derived from epoxidized linseed oil (ELO)

[EN] Different amounts of epoxidized linseed oil (ELO) have been added to poly(lactic acid)-PLA composites with hazelnut shell flour (HSF) to provide a plasticizing effect and improve the low intrinsic ductile properties of PLA/HSF composites. Mechanical, thermal, thermo-mechanical and dynamic mechanical properties have been studied in terms of the weight percentage ELO. Mechanical resistant properties in both tensile and flexural tests decrease with wt.% ELO while a remarkable increase with wt.% ELO is obtained. These results reveal a clear plasticization effect of ELO but, in addition, internal structure of PLA/HSF/ELO composites shows good PLA-HSF (matrix-particle) interactions so that indicating that ELO also provides a coupling effect between PLA matrix and HSF filler. ELO addition leads to a decrease in storage modulus (G ) obtained by dynamic mechanical thermal analysis (DMTA) in torsion mode thus giving clear evidence of the plasticization effect of ELO. Overall, the use of ELO in PLA/HSF composites is an attracting way to improve the low intrinsic fragility of these green composites; furthermore, ELO provides an improvement on thermal stability and a coupling effect between the polymer matrix and the surrounding lignocellulosic filler.This research was supported by the Ministry of Economy and Competitiveness - MINECO, Grant Number: MAT2014-59242-C2-1-R. Authors also thank to "Conselleria d'Educacio, Cultura i Esport" - Generalitat Valenciana, Grant Number: GV/2014/008 for financial support.Balart Gimeno, JF.; Fombuena Borrás, V.; Fenollar Gimeno, OÁ.; Boronat Vitoria, T.; Sánchez Nacher, L. (2016). Processing and characterization of high environmental efficiency composites based on PLA and hazelnut shell flour (HSF) with biobased plasticizers derived from epoxidized linseed oil (ELO). Composites Part B: Engineering. 86:168-177. https://doi.org/10.1016/j.compositesb.2015.09.063S1681778