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

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

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

The study of fibre/matrix bond strength in short hemp polypropylene composites from dynamic mechanical analysis

This paper presents results from an experimental study on the static and dynamic mechanical and viscoelastic properties of short hemp fibre polypropylene composites. Composites containing 10–60 wt.% short noil hemp fibre were injection moulded. The maleic anhydride grafted polypropylene (MAPP) and maleic anhydride grafted Poly(ethylene octane) (MAPOE) were used as coupling agents for modifying the matrices. Dynamic mechanical thermal analysis (DMTA) of the composites were performed over a temperature range of 25–150°C under frequency of 1 Hz. DMTA revealed no noticeable changes in α-transition temperature when the fibre content was 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 addition of MAPP coupling agent in comparison with addition of MAPOE coupling agent. This was also confirmed by tensile strength experiments and scanning electron microscope (SEM) observations

Injection molded noil hemp fiber composites: interfacial shear strength, fiber strength, and aspect ratio

Noil hemp fiber-reinforced polypropylene composites were fabricated using intermixer and injection molding machines. X-ray microtomography and Weibull statistical methods were employed to characterize the aspect ratio distributions of noil hemp fibers in the polypropylene matrices. The influence of fiber content (0–40 wt%) and compatibilizer addition (5 wt%) on IFSS (interfacial shear strengths) was evaluated by means of the modified Bowyer and Bader model. The evaluated IFSSs decreased from 9.7 to 7.2 MPa as the fiber content increased from 10 to 40 wt%. Also, the outcomes indicated increases to IFSSs for the maleic anhydride grafted polypropylene (MAPP)-coupled composites than uncoupled ones. They were used to predict theoretical tensile strength of the composites. A good agreement has been found between the theoretical and the experimental tensile strengths of composites indicating that the developed model has excellent capability to predict the tensile strength of noil hemp fiber reinforced polypropylene composites. Ultimately, the influences of interfacial shear strength; fiber strength and fiber aspect ratio were investigated using the developed model to predict composite tensile strengths

Predicting the flow stress behavior of Ni-42.5Ti-3Cu during hot deformation using constitutive equations

The hot deformation behavior of ternary Ni-42.5Ti-3Cu alloy was modeled. Hot compression tests were carried out at the temperatures from 800°C to 1000°C and at the strain rates of 0.001 s−1 to 1 s−1. The experimental results were then used to determine the constants for developing constitutive equations. There was an unacceptable fitting between the predicted and experimental results using Zener-Hollomon parameter in a hyperbolic sinusoidal equation form. The mismatches among the experimental and predicted results were observed almost for all tested conditions. By modifying the Zener-Hollomon parameter for the compensation of strain rate, a very good agreement was achieved between the predicted values and experimental ones. Both predicted and experimental stress-strain curves illustrate the occurrence of dynamic recrystallization. Also, in both cases, the peak and steady state stresses raised with decrease of temperature and increase of strain rate. The very good agreement between the measured and predicted results indicates the high accuracy of developed model and constitutive equations which can be used for predicting and analyzing the hot deformation behavior of Ni-42.5Ti-3Cu

A study on hot deformation behavior of Ni-42.5Ti-7.5Cu alloy

To investigate the hot deformation behavior of the Ni-42.5Ti-7.5Cu (wt%) alloy, hot compression tests were carried out at the temperatures from 800 C to 1000 C and at the strain rates of 0.001 s-1 to 1 s-1. The results show that the occurrence of dynamic recrystallization (DRX) is the dominate restoration mechanism during the hot deformation of this alloy. There is an increase in peak and steady state stresses with decreasing the deformation temperature and increasing the strain rate. The experimental results were then used to determine the constants of developed constitutive equations. There is a good agreement between the measured and predicted results indicating a high accuracy of developed model. Zenere-Hollomon (Z) parameter, calculated based on the developed model, indicates that DRX was postponed when the logarithm of the Zenere-Hollomon parameter fell around 33 at strain rate of 0.001 s-1 and temperature of 900 C. This phenomenon can be regarded as the interactions between solute atoms and mobile dislocations. The established constitutive equations can be used to predict and analyze the hot deformation behavior of Ni-42.5Ti-7.5Cu alloy