Alan Fernyhough

Hemp Fibre Reinforced Poly(Lactic Acid) Composites

The potential of hemp fibre as a reinforcing material for Poly(lactic acid) (PLA) was investigated. Good interaction between hemp fibre and PLA resulted in increases of 100% for Young’s modulus and 30% for tensile strength of composites containing 30 wt% fibre. Different predictive ‘rule of mixtures’ models (e.g. Parallel, Series and Hirsch) were assessed regarding the dependence of tensile properties on fibre loading. Limited agreement with models was observed. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) studies showed that hemp fibre increased the degree of crystallinity in PLA composites.

Expanded polylactic acid - an eco-friendly alternative to polystyrene foam

A commercially viable process to manufacture low-density expanded polylactic acid (E-PLA) products with environmental-friendly blowing agents such as carbon dioxide has been developed. The resulting material is a sustainable alternative to expanded polystyrene (EPS). The E-PLA has thermal conductivity and mechanical properties comparable to EPS and can be used in many similar applications. The process involves impregnation of PLA beads with carbon dioxide and fusing with heat, including steam heating. Gel permeation chromatography indicated that the PLA polymer molecular weight was not degraded by the foaming or steam heating process. Visual characterization showed that under some circumstances, PLA precursor beads exhibited voids, which disappeared during CO2 impregnation indicating some form of rearrangement or realignment of the polymer morphology or structure. Due to the effect of CO2 on the glass transition temperature of the PLA, a linear reduction of 5.5°C per wt% of absorbed CO2 was observed.

Analysis of mechanical properties of hemp fibre reinforced unsaturated polyester composites

Different chemically treated hemp fibre reinforced unsaturated polyester composites were investigated over a range of fibre content (0–60 wt%). Although Young’s modulus of all the short fibre reinforced unsaturated polyester composites was found to be higher than that of unreinforced unsaturated polyester; however, tensile strength of the composites exceeded that of the unsaturated polyester matrix only for the combined alkali- and silane-treated fibre composites at 40 wt% fibre content. The decrease in tensile strength of the composites could be attributed to stress concentrations caused by the fibres in conjunction with the brittle matrix. Impact strength of all the treated fibre composites was higher than that of the untreated fibre composites at all fibre contents. KIc and GIc of the composites decreased initially and then increased as the fibre content increased because more and more fibres being available to pull-out. The mechanical properties of the composites were increased further due to the alignment of long fibres.

Crystallinity effects in polylactic acid-based foams

The use of carbon dioxide for the production of polylactic acid foams has been increasingly studied recently. Much of the reported work has used supercritical carbon dioxide as a processing or foaming medium. However, a new foaming process which uses sub-critical liquid carbon dioxide conditions has been developed by the Biopolymer Network Limited. It is generally recognised that processing crystalline thermoplastics, including crystalline polylactic acid polymers, into foam products using carbon dioxide is difficult due to lower solubility of liquid carbon dioxide in polymers and the increased polymer rigidity hindering the expansion of the polymer matrix. However, fundamental studies, and the associated knowledge of the foaming mechanisms at play, have allowed some new approaches to be developed within sub-critical carbon dioxide conditions which overcome many of these difficulties in polylactic acid foams. In this study, several commercially available grades of polylactic acid, ranging from crystalline to amorphous, were processed using carbon dioxide via the Biopolymer Network Limited process (sub-critical carbon dioxide). By adequately adjusting the process parameters, different crystalline grades were successfully foamed to low density. The resulting foams exhibited low to high levels of crystallinity, and consequently displayed varying thermal or physical properties. Cellular structures were observed by scanning electron microscopy. Crystallinity and thermal behaviour of the foamed samples were characterised using differential scanning calorimetry. Mechanical properties and dimensional stability were also investigated. It was shown that the selection of polylactic acid feedstock, and its associated processing conditions, had a significant impact on the final quality and properties of the foams.

Manufacturing and Recycling of Sisal-Polypropylene Composites

The current study focuses on manufacturing, recycling and mechanical testing of thin (1.5 mm) sisal-PP extruded composite sheets. An 3-factor two-level experimental design based on the Taguchi method was applied in the manufacturing of the composite sheets to maximise their mechanical properties. The sisal-PP composite sheets obtained by setting the factors predicted by the Taguchi analysis were mechanically recycled by pelletising the sheets and feeding through the extruder. The effects of recycling on crystallinity, fibre length, mechanical properties and stress-relaxation were evaluated. By selecting a fibre mass of 30%, polymer MFI of 1.3 g/10 min and 1% of lubricant, ~12%, ~20% and >100% increases in tensile strength, impact strength and tensile modulus respectively were observed. The fibre lengths dropped from 7 mm before extrusion to 6mm and under after extrusion, and under 5 mm after recycling. A marginal change (± 5%) in modulus values was observed in both directions after recycling, the ultimate tensile strength of the recycled sisal-PP specimens dropped down from 41.4 ± 2.5 to 36.4 ± 0.75 MPa along the machine direction, and increased from 19.2 ± 0.5 MPa to 21.4 ± 0.1 MPa transverse to the machine direction mainly due to the decrease in the reinforcing fibre lengths. The recycled composites exhibited greater relaxation compared to the sisal-PP composites; this is because, at higher temperatures, the polymer matrix is in a softened state and the bonding between the fibre and matrix is expected to be weaker and the short fibres behave like polymer rich areas and fail to share the imposed load, thus exhibiting greater relaxation at elevated temperatures.

Characterisation of hemp fibre reinforced Poly(Lactic Acid) composites

In this work, the mechanical properties including tensile strength, flexural strength, impact strength and fracture toughness of the PLA/hemp composites were investigated over a range of fibre content (0-30 wt.%). It was observed that, the tensile strength and Youngs modulus of the composites increased with increased fibre content. The flexural strength did not increase with fibre reinforcement, however, the flexural modulus of the composites increased significantly. Impact strength of the composites increased up to 20 wt. % fibre loading, however, further increased fibre loading caused a reduction of impact strength. KIc and GIc values decreased with increased fibre content.

Modelling Liquid Composite Moulding Processes Employing Wood Fibre Mat Reinforcements

Liquid Composite Moulding (LCM) processes are commonly used techniques for the manufacture of advanced composite structures. This study explores the potential of wood fibres as reinforcement for LCM preforms, considering mats produced using dry and wet methods. The compaction response of these mats has been investigated with and without the presence of a test fluid. Permeability of these mats was also measured as a function of fibre volume fraction. Reinforcement permeability and compaction response data were used to model two different LCM processes. The simulation results have been compared with experiments.

Environmentally Intelligent Biocomposites

Composites made from wood residues and biomasses, together with either conventional polymers such as polypropylene (PP) and their recyclate streams or with the new emerging biopolymers such as polylactic acid (PLA), were compounded and injection moulded. Mechanical properties and biodegradation analyses were undertaken. The addition of wood flour/sander dust (SD) and wood fibres (WF), to the PP, with suitable compatibilizer, increased the flexural and tensile modulus and strength, indicating a good bond between the fibres and matrix. The tensile and flexural strengths were decreased with the addition of wood fillers, additives and biomasses to a PLA biopolymer blend. Such biomasses and additives increased the biodegradation of the PLA blend, and some control over biodegradation rates was achievable.

Correlations Between the Physiochemical Characteristics of Plant Fibres and Their Mechanical Properties

Lignocellulosic fibres harvested from different plant types exhibit variations in mechanical properties that are associated with their chemical composition and physical features. This diversity indicates that plant fibres could be selected based on their physio-chemical properties for tailored applications such as enhanced vibration damping. In this study, bast, leaf, and mesocarp fibre bundles were investigated to understand correlations between their physiochemical characteristics and their mechanical properties with a particular focus on their vibrational damping ability. Due to the interrelations between the investigated variables such as cellulose content and microfibril angle, a multivariate analysis (principal component analysis) was applied to elucidate trends. The stiffness and strength of the fibre bundles were found to be positively correlated to high cellulose content and low microfibril angle while high toughness was correlated with fibre bundles of high lignin content and high microfibril angle. Conversely, the damping coefficient was found to be positively correlated to fibres containing high level of hemicelluloses, such as those extracted from leafy plants.