A. Hodzic

Development of recycled polymer composites for structural applications

Abstract This paper is concerned with the formulation of composite materials for structural or semistructural applications using thermoplastic polymer waste. The mechanical and thermal properties of a proprietary blend of recycled polymers with a range of different fillers were investigated. The effect varied with the aspect ratio of the filler and the mode of loading. Spherical calcium carbonate gave a marginal improvement in modulus. Plate-like mica produced a significant increase in modulus without reduction in strength. Glass fibres caused a significant increase in modulus and strength while decreasing the linear coefficient of thermal expansion. Hybrid systems containing glass fibre and a lower aspect ratio filler were also investigated to obtain a material system which combines high properties and reasonably low cost. It was found that addition of small quantities of mica to glass fibre reinforced blends exhibited a significant synergy in tensile strength and modulus.

Plastics recycling: insights into life cycle impact assessment methods

Abstract The increased consumption of plastics in day to day life has a significant impact on the environment. Life cycle assessment (LCA) is widely used to select a sustainable alternative in plastic waste management. The LCA studies on mechanical recycling and energy recovery scenarios showed that recycling resulted in lower emissions and provided benefits to the environment. These results are valid only if the performance of the recycled plastic is equivalent to those of the virgin materials. Many LCA studies have been focused on individual impact categories rather than aggregated single score. The decision making process becomes complex if individual impact categories are used. This research is focused on the comparison of LCA results between individual and aggregated impacts and integration of performance of recycled plastics in LCA. The results indicated that recycling was the preferred option if it could replace a minimum of 70–80% of virgin plastics.

Compressive behaviour of nanoclay modified aerospace grade epoxy polymer

Abstract The effect of nanoclay on the compressive response of an aerospace grade epoxy polymer was studied. The resin was modified with montmorillonite clay type nanomer I.30, and compressive tests were performed on the optimised specimen geometry. A series of nanocomposite with 1–5 wt-% nanoclay content was fabricated using mechanical stirring and three-roll mill methods. The degree of dispersion of the clay nanoplatelets was examined using TEM. Static uniaxial compression tests were conducted. The compressive stress–strain curves showed that the presence of nanoclay improved the compressive strength and stiffness, promoted higher plastic hardening behaviour after yielding and enhanced the fracture toughness (area under σ–ϵ curve) of the epoxy polymer. The fracture surfaces of the broken specimens were observed using SEM with the aim to identify critical failure mechanisms that contributed to the polymer toughening. Rule of mixtures, Halpin–Tsai and modified Halpin–Tsai models were employed to estimate the compressive modulus of the clay–epoxy nanocomposite system.

Blast Resistance and Damage Modelling of Fibre Metal Laminates to Blast Loads

A robust and efficient computational model has been developed which is capable of modelling the dynamic non-linear behaviour of GLARE panels subjected to blast loadings. Numerical model validation have been performed considering case studies of GLARE panels subjected to a blast-type pressure pulse for which experimental data on the back-face deflection and post-damage observations were available. Excellent agreement of mid-point deflections and evidence of severe yield line deformation were shown and discussed against the performed blast tests. A further parametric study identified GLARE as a potential blast attenuating structure, exhibiting superior blast potential against monolithic aluminium plates. It was concluded that further work needed to be carried out to take into account the influence of geometry (cylindrical structures), pre-pressurisation effects and boundary conditions

Fabrication of patterned thermoplastic microphases between composite plies by inkjet printing

We report on the pioneering application of inkjet printing in depositing patterned thermoplastic microphases between composite plies and the beneficial effect of the printed thermoplastic on the interlaminar fracture toughness of carbon fibre-reinforced polymer laminates. Double-cantilever beam test and short-beam shear test were employed to investigate the mechanical performances of the engineered composites. The results from this work revealed that by printing thermoplastic poly(ethylene glycol) and poly(methyl methacrylate) between the carbon fibre-reinforced polymer plies, mode I interlaminar fracture toughness (GIc) is noticeably enhanced, whilst the shear strength has also been preserved. Scanning electron microscopy was used to investigate the fracture surfaces generated during the double-cantilever beam test. The microscopic addition of the thermoplastic polymers (approximately 0.015 wt%) did not increase the weight of the composites significantly, which compares favourably to other conventional toughening methods.

A review on composite materials based on recycled thermoplastics and glass fibres

Abstract The purpose of this paper is to review recent work on composite materials based on recycled thermoplastics and glass fibres (GFs). The high collection and separation cost of plastics waste, and the legislative push to increase recycling rates, require the inclusion of increasing proportions of low‐quality plastic waste into recycled products. A robust method for upgrading mixed plastics recyclates is the incorporation of fillers and reinforcements. In particular, addition of chopped GF can lead to material systems with more favourable and consistent sets of mechanical properties. Provided a good interfacial adhesion is achieved, the key structural properties of the composite (stiffness and strength) are mainly dictated by the reinforcement. Therefore, a wide range of polymers, including blends, are accessible for recycling into semistructural products. Glass fibres are one of the most cost‐effective ways of reinforcing recycled polymers, as testified by several patents and commercial products which appeared in the last decade.

Influence of additives on recycled polymer blends

Polymer systems based on polymer waste offer promising way to increase recycling in the society. Since fillers play a major role in determining the properties and behavior of polymer composites, recycled polymers can also be combined with fillers to enhance the stiffness and thermal stability. In this study, blends of recycled polyethylene and recycled polypropylene with mica and glass fiber were prepared by melt blending technique. The effect of the particle loading, filler type, and filler–matrix interaction on thermal degradation and thermal transition of processed systems were investigated. Thermogravimetric analysis, differential thermogravimetric analysis, and differential scanning calorimetry were used in this investigation. Comparative analysis shows that both fillers produced different effects on thermal properties of the processed systems. These results were confirmed by calculating the activation energy for thermal degradation and thermal transition using Kissinger and Flynn–Wall expressions.

The Applicability of Taylor’s Model to the Drilling of CFRP Using Uncoated WC-Co Tools: The Influence of Cutting Speed on Tool Wear

This work investigates the applicability of Taylor’s model on the drilling of CFRP using uncoated WC-Co tools, by assessing the influence of cutting speed (Vc) on tool wear. Two different resins, possessing low and high glass transition temperatures (Tg), and two different reinforcements, high strength and high modulus woven fabrics, were combined into three different systems. Flank wear rate gradient exhibited to be more reinforcement dependent, while the actual flank wear rate showed to be sensible also to the type of resin. In terms of tool life, all CFRP systems adjusted into a power-type tool life vs. cutting speed curve through the full range of cutting speeds (1,000 RPM to 18,000 RPM). Therefore, Taylor’s model can be applied to estimate the tool life in the drilling of CFRP using uncoated WC-Co tools with good accuracy.

Review of life cycle assessment on polyolefins and related materials

Abstract Life cycle assessment (LCA) is a sustainability measurement tool that identifies the environmental impacts of a product. The uniqueness of the LCA lies in its methodology, which aggregates all environmental burdens throughout the product’s life cycle, providing many variables for optimisation of the product (or process). Having occupied a major market share, the environmental impacts associated with the manufacturing and disposal of polyolefins are quite high. The main theme of this paper is to review the reported LCA studies on polyethylenes and polypropylenes including recycled plastics, biobased materials, which are competing with polyolefins, and polyolefin composites. The widely claimed green product ‘recycled plastic’ is analysed in detail from an LCA perspective, and key points, which determine its sustainability, are discussed. The environmental impacts associated with the manufacturing of polyolefins and their bioalternatives are highlighted. The few published studies of polyolefin composites on different applications are also discussed.

Learning from each other: engaging engineering students through their cultural capital

Abstract This paper presents work carried out during the past four years by teaching staff at the University of Sheffield with classes of over 250 Engineering Management students. The cohort is varied, with students from different disciplines of engineering, countries of origin, previous educational backgrounds and levels of work experience. For the past four years, students have been asked to fill in a two-part survey investigating their perceptions of their native culture, based upon the factors that would be required to run a successful engineering project in their country of origin and the Kluckhohn-Strodtbeck Cross Cultural Analysis Framework. This paper builds on previous work and suggests that students’ cultural perceptions are highly complex and that using an interactive and student-centred pedagogical method in order to recognise and value their cultural capital not only enhances their cross-cultural knowledge and skills but also potentially leads to enhanced student engagement.