Effect of fibre treatments on mechanical properties of flax/tannin composites

Due to the inherent environmental benefits of using natural resin (tannin) and natural fibre (flax), flax/tannin composites could be potentially used for vehicle applications. One of the main limitations is the hydrophilic property of flax, resulting in the poor fibre/hydrophobic matrix interface quality. Alkali, acetylation, silane treatment and enzymatic treatment were selected to modify non-woven flax mats to prepare the composites. The fibre morphology was studied through scanning electronic microscopes (SEM). The effects of fibre pre-treatments on dynamic and static mechanical properties of composites were investigated through adequate experiments, such as dynamic mechanical analysis (DMA) and static tensile testing. The modified rougher fibre surface broadened the glass transition peaks of composites due to the improved surface adhesion. However, there is no big improvement of tensile strength after modifications. The pure NaOH (sodium hydroxide) treated composites remain the tensile properties and offer good flax/tannin wettability

Mechanical properties of three-phase polyamide 6 nanocomposites

This work focus on the mechanical properties of three-phase nanocomposites using multiscale reinforcements. The influence of the nano-fillers content, as well as the temperature were studied. Polyamide-6 reinforced with short glass fibre 30 wt.% and with an addition of nanoclay (montmorillonite) and/or nanosilica (SiO2) were tested in order to characterise their tensile properties at room temperature and at 65oC just above the polyamide 6 glass transition temperature. SEM analysis were conducted on the fracture surface of the tensile bars. SEM investigations showed the importance of the interaction matrix/filler for the material behaviour. Our study also shows that the increase of OMMT percentage in polyamide-6/glass fibre composite made the material more brittle and had a negative effect on the tensile properties. Further, for the silica-based nanocomposites, an optimum was found for a nanofillers content of 1wt.%

Mechanisms of thermoplastics to metal adhesion for applications in electronics manufacture

The Substrateless Packaging process was developed at Loughborough University as an alternative method of manufacturing electronics with an improved end-of-life materials recovery profile. The process involves injection moulding to overmould electronic components in thermoplastic polymers. Initial prototype samples manufactured in previous work exhibited undesirable small gaps around the embedded components after solidification and which were thought to be the result of adhesion problems between the thermoplastic overmould and components. The study reported here had the aims of determining quantitatively what factors affect adhesion, and to identify which thermoplastic polymers are most suitable for the process. Following a literature survey, six engineering thermoplastics, PC, PBT, PS, ABS, PA 6 and PMMA were chosen for study as overmoulding materials, and tin as the solid adherend. The literature survey also identified the mechanisms contributing to adhesion at the metal-thermoplastic interface in insert moulding as material properties, interfacial forces between the materials, wetting at the interface, temperature of the insert (consequently temperature at the interface) and insert moulding parameters. A methodology was designed to allow investigation of all these factors, with Atomic Force Microscopy (AFM) force-distance measurements being used to measure room temperature interfacial forces, high temperature contact angle for wetting, and pull-out strength tests on overmoulded tin-coated wire for overall system adhesion. Excellent repeatability was seen in the measurements obtained with all three experimental methods. Moldflow finite element simulations of the insert moulding process were also undertaken. For the AFM measurements tin particles were adhered to the probe with the aid of a Focused Ion Beam (FIB) apparatus. PA and PMMA interatomic interactions with tin were found to be noticeably stronger than the other polymers. From consideration of the different possible contributions to the measured forces, it was concluded that the trend of interatomic interactions obtained is due to a combination of electrostatic forces, capillary forces and dispersion forces acting between the materials tested. In the high temperature contact angle measurements it was observed that the contact angles for all the materials producing drops in equilibrium reduce monotonically with rise in temperature at the interface. The work of adhesion was calculated from the contact angles for PMMA using the Young-Dupre equation and values of surface tension from the literature. It was found that it does not increase monotonically with temperature as might be expected from the contact angles. The works of adhesion at 240°C for all the materials were also calculated and it was found that the materials ranking for expected adhesive strength changed significantly from that expected from consideration of contact angle alone. In the pull out tests, except for PC, the breaking loads for the materials tested rise then fall with rise in temperature of the insert. It was observed that peak breaking load for the amorphous polymers ABS, PS and PMMA occurred for insert temperature just below Tg of the polymer, and for semi-crystalline polymers PA 6 and PBT it was just above Tg. The ranking of materials by maximum pull out strength was found to be consistent with the ranking by mechanical strength (tensile strength at yield) of the thermoplastics. The Moldflow simulations yielded the significant results that the thermoplastic melt comes in contact with the insert at relatively low pressure (less than 0.6 MPa), and that the temperature of the melt near the insert drops to the temperature of the insert almost instantaneously on contact. Therefore it was concluded that the efficacy of holding pressure on assisting wetting of the insert by the thermoplastic melt may depend on the temperature of the insert interface. The results in terms of material rankings from both the material level tests (AFM force distance experiment and wetting at high temperature) did not correspond to the mechanical strength test results. It was therefore concluded that the choice of material for thermoplastic overmould cannot be made purely based on the material interactions at interface between tin and thermoplastics in solid or melt phase. It was also concluded that the observed variation in the pull-out strengths with temperature of the insert maintained during overmoulding, must be largely due to the thermo-mechanical properties of the material at the interface. Based on the results of the study, PC, PBT and PMMA were recommended as being likely to give superior performance to the ABS which was used in early trials of the substrateless packaging process. Of these, from a process economics point of view, PBT would be the most suitable.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Improving mechanical properties of novel flax/tannin composites through different chemical treatments

Due to the inherent environmental benefits of using renewable materials, mimosa tannin resin (a natural phenolic resin) reinforced by flax fibres could offer desirable characteristics (lightweight, economic and low environmental impact) aiming at reducing carbon footprint of superlight electric vehicles. The non-woven flax mats were chemically treated (alkali, acetylation, silane and enzymatic treatment) to prepare tannin composites through compression moulding (130 °C/35 min/1.5 MPa). The change in fibre morphology was seen in SEM (scanning electronic microscope) images. The treatments (except enzymatic) showed significant improvement in tensile properties, along with enhancement (acetylation) in flexural properties, but little effect on impact resistance for all treatments. APS (aminopropyl triethoxy siloxane) treated composites showed highest tensile strength of 60 MPa and modulus of 7.5 GPa. BTCA (butanetetracarboxylic acid) treatment led to the highest flexural strength of up to 70 MPa. NaOH treatment retained the impact failure force of about 0.5 kN and sustained the saturation energy (4.86 J) compared to untreated composites (4.80 J)

Measurement of Nanoparticles Release during Drilling of Polymer Nanocomposites

Nanomaterials are one of the promising technologies of this century. The Project on Emerging Nanotechnologies [1] reports more than 1600 consumer products based on nanotechnology that are currently on the market and advantages link to the reinforcement of polymeric materials using nano-fillers are not to demonstrate anymore. However, the concerns about safety and its consumer perception can slow down the acceptance of nanocomposites. Indeed, during its life-cycle, a nanotechnology-based product can release nano-sized particles exposing workers, consumers and environment and the risk involved in the use and disposal of such particles is not well known. The current legislation concerning chemicals and environment protection doesn’t explicitly cover nanomaterials and changes undergone by nanoparticles during the products’ life cycle. Also, the possible physio-chemical changes that the nanoparticles may undergo during its life cycle are unknown. Industries need a standard method to evaluate nanoparticles release during products’ life cycle in order to improve the knowledge in nanomaterials risk assessment and the legislation, and to inform customers about the safety of nanomaterials and nanoproducts. This work aims to propose a replicable method in order to assess the release of nanoparticles during the machining of nanocomposites in a controlled environment. For this purpose, a new experimental set-up was implemented and issues observed in previous methods (background noise due to uncontrolled ambient environment and the process itself, unrepeatable machining parameters) were solved. A characterisation and validation of the chamber used is presented in this paper. Also, preliminary testing on drilling of polymer-based nanocomposites (Polyamide-6/Glass Fibre reinforced with nano-SiO2) manufactured by extrusion and injection moulding were achieved

Novel hybrid flax reinforced supersap composites in automotive applications

Flax fibre bio-epoxy composites have not found many commercial uses in structural applications on account of their lack of cost efficiency and high susceptibility to environmental changes. Non-woven flax mats were subjected to alkali, acetylation, silane and enzymatic treatment, and then combined with untreated unidirectional (UD) flax fabrics to make hybrid flax bio-epoxy composites. Mechanical and environmental resistance (aging) tests were performed on the treated flax fibres. The glass transition temperature was detected at about 75 °C with little effect of treatments. Untreated composites were found to have a tensile strength of 180 MPa while no significant improvement was observed for any of the treatments, which are also not environmentally friendly. The amiopropyltriethoxysilane (APS) composites after Xenon aging, retained the tensile strength of 175 MPa and a modulus of 11.5 GPa, while untreated composites showed 35% reduction in elastic modulus

The effect of temperature changes on to quasi-static tensile and flexural performance of glass fibre reinforced PA66 composites

A significant method of reducing CO2 emissions in road vehicles is to reduce the vehicle mass. One means in which this can be achieved is to adopt lightweight materials such as thermoplastic composites. Thermoplastics offer advantages in term of weight when compared to conventional steel and aluminium casting. In this study thermal mechanical testing has been conducted on two types of commercial polyamide 66 (PA66) with 35 wt.% short glass fibre reinforcement. One of the materials was impact modified with an elastomer to increase material toughness. Experimental results showed both the reinforced PA66 materials to be temperature dependent. All test results demonstrated the trade-off in the mechanical properties of the two materials especially the impact modified. PA66 with 35 wt.% short glass fibre exhibits the best tensile strength, flexural strength and modulus for each temperature tested. Whereas the impact modified PA66 with 35 wt.% short glass fibre exhibits the higher strain and toughness for each temperature tested

Mechanical and impact performance of three-phase polyamide 6 nanocomposites.

In this work, three-phase nanocomposites using multiscale reinforcements were studied to evaluate the influence of nanofillers on static and dynamic mechanical properties at varying temperature conditions. In particular, short-fibres reinforced polyamide 6 (30wt.%) composites with various weight fractions of montmorillonite (OMMT) and nanosilica (SiO2), manufactured and investigated. Quasi-static tensile properties were investigated at room temperature and also at 65°C just above the polyamide 6 (PA6) glass transition temperature. The low velocity impact tests were conducted on the manufactured cone-shaped structures to evaluate the crash behaviour and energy absorption capability. The study results shows that the increase of the weight percentage level of OMMT in PA6/glass fibre (30wt.%) composite made the nanocomposites more brittle and simultaneously deteriorated the tensile properties. SiO2 nanofiller at 1wt.% was found to be the optimum ratio for improving tensile properties in silica-based nanocomposites studied. It was further noted that for both types of nanofillers, the crashing behaviour and energy absorption in dynamic properties were improved with increase in nanofillers weight percentage in the composites. The study also shows that the brittleness behaviour of the nanocomposites investigated is associated to the fibre/matrix interaction which is dependent on the nanofiller type and has significant effect on crash modes observed

Aerogel/epoxy thermal coatings for carbon fibre reinforced plastic substrates

The present work studies an aerogel/epoxy composite that was dip coated onto a carbon fibre substrate by adding the aerogel at the 1 h and the 1.5 mark of the epoxy cure. Both coatings show decrease in thermal conductivity values (39% and 47% respectively) when compared to a pure epoxy coating. The coatings’ reflectance spectra also provided further evidence for the existence of the nano-pores within the aerogel particles. The aerogel coating was modelled using material properties from literature and solved using finite element methods. The model, which validated using experimental data, was then used to predict the coating’s performance in cyclic thermal loads. Additionally, coatings on a single surface- top and bottom; were also modelled and compared with the double coating system wherein it was seen that the double coating system had the lowest rate of temperature change and fluctuations at steady-state in contrast to the bottom coating which, showed the fastest drop in temperature as well as the highest fluctuations at steady state conditions. The performance of the top coating was in the middle

Non-isothermal cure kinetics of aerogel/epoxy composites using differential scanning calorimetry

The present work determines the non-isothermal cure parameters of aerogel/epoxy samples along with the effect of a wetting agent. The cure parameters were calculated using Kissinger and isoconversional methods after which the reaction was modeled with the Sestak–Berggren equation. It is seen that the composites had higher activation energy and frequency factor values compared to the pure resin, and similarities in cure parameters between the aerogel/epoxy composites with and without the wetting agent were seen. Hence, the former’s use is advocated due to its positive influence on the resin–aerogel interface without sacrificing the cure parameters