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Journal articleMulakkal M, Castillo Castillo A, Taylor A, et al., 2021,
Advancing mechanical recycling of multilayer plastics through finite element modelling and environmental policy, Resources, Conservation and Recycling, Vol: 166, ISSN: 0921-3449
Plastics are attracting negative publicity due to the scale of current pollution levels, yet they are irreplaceable in several applications such as food packaging, where different types of plastics are combined in laminate form to produce multilayered packaging (MLP) materials which extend the life of food items packaged within them. Increased plastic recycling is urgently needed, however for MLP it is particularly difficult. For the first time, this study combines engineering tools with environmental policy towards developing solutions for current single use plastic packaging. This study investigates recycling challenges for MLP and emerging melt-blending based mechanical recycling solutions as this is the main current method for material recovery of conventional plastics. Melt-blending of MLP with compatibilisers is explored, and the current lack of models addressing the influence of compatibilisers is identified. This gap in knowledge is addressed using novel engineering models based on the finite element (FE) micromechanical modelling technique to estimate the mechanical properties of recycled blends. Our model output is compared with experimental data available in literature and the good agreement highlights its predictive ability, providing a fast and cost-effective novel method for optimising recycled plastics. The policy aspect proposes the introduction of twenty policies based on mission-oriented innovation strategy to enable deployment of the recycling technologies studied whilst improving the viability of recycling of material currently not recycled. Implementation of these measures by the stakeholders will enable adoption of new MLP recycling techniques, create demand for recycled materials from MLP and incentivise MLP collection to mitigate pollution.
Conference paperAurisicchio M, Zeeuw Van Der Laan A, Tennant M, 2021,
Material-Service Systems for Sustainable Resource Management, EcoDesign 2019
Journal articleLi-Mayer JYS, Lewis D, Connors S, et al., 2020,
Hierarchical multi-scale models for mechanical response prediction of highly filled elastic–plastic and viscoplastic particulate composites, Computational Materials Science, Vol: 181, Pages: 1-15, ISSN: 0927-0256
Though a vast amount of literature can be found on modelling particulate reinforced composites and suspensions, the treatment of such materials at very high volume fractions (>90%), typical of high performance energetic materials, remains a challenge. The latter is due to the very wide particle size distribution needed to reach such a high value of In order to meet this challenge, multiscale models that can treat the presence of particles at various scales are needed. This study presents a novel hierarchical multiscale method for predicting the effective properties of elasto-viscoplastic polymeric composites at high . Firstly, simulated microstructures with randomly packed spherical inclusions in a polymeric matrix were generated. Homogenised properties predicted using the finite element (FE) method were then iteratively passed in a hierarchical multi-scale manner as modified matrix properties until the desired filler was achieved. The validated hierarchical model was then applied to a real composite with microstructures reconstructed from image scan data, incorporating cohesive elements to predict debonding of the filler particles and subsequent catastrophic failure. The predicted behaviour was compared to data from uniaxial tensile tests. Our method is applicable to the prediction of mechanical behaviour of any highly filled composite with a non-linear matrix, arbitrary particle filler shape and a large particle size distribution, surpassing limitations of traditional analytical models and other published computational models.
ReportCastillo Castillo A, Mulakkal M, Bexis P, et al., 2020,
Journal articleSorce F, Lowe C, Ngo S, et al., 2019,
The effect of HMMM crosslinker Ccntent on the thermal-mechanical properties of polyester coil coatings, Progress in Organic Coatings, Vol: 137, ISSN: 0300-9440
The thermosetting polyester-based coatings crosslinked with hexa(methylmethoxy)melamine (HMMM) used for coil coating sheet metal experience large deformations when formed into architectural cladding and white goods. Cracking of the 20-μm-thick coatings must not occur during forming, to prevent corrosion of the steel substrate, so the relationship between the composition and the thermal-mechanical properties is critical to develop highly formable and durable coatings, and to choose suitable forming conditions. Free films of coatings with 5 % to 30 % crosslinker content have been analysed. Dynamic mechanical analysis (DMA) showed that the glass transition temperature (Tg) and crosslink density increase with crosslinker content. Differential scanning calorimetry (DSC) has been used to measure the Tg from the thermal response, based solely on the chemical structure, and agrees well with the DMA.Tensile tests were performed at temperatures as a function of DSC Tg (Tg - 40 °C to Tg + 50 °C). There was little variation in Young’s modulus and strain to failure in the glassy region where the intermolecular forces dominate, but in the rubbery region governed by the covalent bonds a lower crosslinker content gave lower values. This indicates that the failure mechanism undergoes a transition with increasing temperature from being controlled by the brittle fracture stress to the yield stress. The addition of TiO2 pigment increased the modulus and apparent yield stress at low temperatures in the glassy region, and increased the strain to failure and failure stress in the rubbery region. Failure envelopes, normalising the tensile data with the DSC Tg and the crosslink density, show the dependence on crosslinker content and pigmentation. This allows the behaviour of coatings to be predicted from their structure, and enhanced coatings to be developed based on the required mechanical properties.
Journal articleZeeuw Van Der Laan A, Aurisicchio M, 2019,
After the depletion of their consumable components, Fast-Moving Consumer Goods (FMCGs) become obsolete. In an attempt to close the loop of resources (i.e. products, components or materials) FMCGs can be designed with revalorisation services. In these product-service systems (PSSs) consumers are assigned a key role in closing the loops of resource flows. To understand and define this role, we dissected eighteen examples of PSSs. From this analysis, four dimensions emerged that characterise distinct aspects of the PSSs: the form of obsolescence; the change of resources from obsolete to operative or recoverable; the prerequisite activities required of consumers for revalorisation; and the facilitators of activities (i.e. investments and incentives). These dimensions were used to model four data-driven archetypical roles of consumers named after the interaction between consumers and the resource in the obsolete state, namely keep, bring, consign or abandon obsolete components. The research concluded that revalorisation always takes place in designated locations. The roles that consumers fulfil in closed-loop PSSs involve carrying out activities to position resources in such locations. The roles always come at a cost, but PSSs can be designed to reduce it. PSSs can also be designed to induce a perceivable value of obsolete resources, which can be used to increase role fulfilment. This research presents a comprehensive understanding of the roles of consumers in the specific context of closed-loop FMCGs, identifies tactics to increase the fulfilment of these roles and suggests further research on behaviours and PSSs to understand the roles of other stakeholders in various type of PSSs.
Journal articleTsang WL, Taylor AC, 2019,
Fracture and toughening mechanisms of silica- and core–shell rubber-toughened epoxy at ambient and low temperature, Journal of Materials Science, Vol: 54, Pages: 13938-13958, ISSN: 0022-2461
The highly cross-linked thermosetting polymers used as adhesives and as the matrices of fibre composites for the construction of lightweight vehicles are very brittle, and finding effective toughening solutions for such engineering applications is a long-standing problem. An anhydride-cured thermosetting epoxy polymer has been modified by the addition of different wt% of silica nanoparticles, core–shell rubber particles and hybrids with equal wt% of both. The fracture energy was measured at ambient and low temperature (− 40 °C and − 80 °C) to understand the brittle fracture behaviour. The fracture and toughening mechanisms were identified by scanning electron microscopy of the fracture surfaces. Analytical models were used to predict the modulus and fracture energy; the predictions agreed very well with the measured values. Toughening using silica nanoparticles is especially efficient at low particle contents. This shows how epoxies can be toughened successfully for use in industrial and transport applications.
Journal articleGesslbauer S, Savela R, Chen Y, et al., 2019,
Exploiting noncovalent interactions for room-temperature heteroselective rac-lactide polymerization using aluminum catalysts, ACS Catalysis, Vol: 9, Pages: 7912-7920, ISSN: 2155-5435
Whereas harnessing noncovalent interactions (NCIs) has largely been applied to late-transition-metal complexes and to the corresponding catalytic reactions, there are very few examples showing the importance of NCIs in early-transition-metal and main-group-metal catalysis. Here, we report on the effects of hydrogen bond donors in the catalytic pocket to explain the high activity and stereoselectivity of a series of aluminum catam complexes in rac-lactide ring-opening polymerization (ROP). Four original aluminum catam catalysts have been synthesized and fully characterized. Structure–activity relationships and isotope effects show the importance of the NH moieties of the ligand in rac-lactide ROP. Computational studies highlight beneficial hydrogen bonds between the ligand and the monomer. Overall, structural characterization of the catalysts and mechanistic, kinetic, and computational studies support the benefits of noncovalent interactions in the catalytic pocket.
Journal articleTsai SN, Carolan D, Sprenger S, et al., 2019,
Fibre composites with thermoset polymer matrices are widely used. However, thermosets are very brittle, which can limit the applications of fibre composites. In this work, silica nanoparticles (SNPs) were used to modify two fibre sizings to improve the toughness of carbon fibre composites. Mode I interlaminar fracture and fatigue crack growth tests were conducted on the composites made using the silica nanoparticle-sized fibres. There was no significant change in the fatigue crack growth rate with the addition of SNPs. However, the addition of SNPs to either sizing increased the composite toughness. The fracture energy was significantly increased from 166 J/m 2 to 220 J/m 2 (increased by 33%) with only 0.89 wt% on fibre weight of SNPs. This is significantly more efficient than adding SNPs into the matrix, which can require addition of up to 20 wt% of SNPs , to achieve the same improvement in toughness.
Journal articleSorce F, Ngo S, Lowe C, et al., 2019,
Thermosetting polyester-based coatings are used to produce pre-painted metal in the coil coating industry. The coated steel sheet is formed into white goods and architectural cladding, which involves large deformations of the metal and results in large strains in the coating. The Erichsen cupping test is a standard method used to assess the formability, ductility and adhesion of coatings, which induces similar strains to those experienced during forming. It is a qualitative and robust quality control method, but the behaviour of coatings during the test has never been previously studied quantitatively. Failure of coatings on sheet metal during forming is a strain-governed process, so understanding the behaviour of a coating in the Erichsen cupping test will allow the formability, material properties and chemical structure of the polymer to be linked more closely, enabling the development of better coatings. A finite element model has been developed to calculate the coating surface strains for any level of indentation during the test, and has been validated using the surface strains during cupping measured by digital image correlation. A master curve of the maximum strain versus the indentation depth (Erichsen index) has been determined. This allows the strain to failure of the coating on a substrate, a critical material property which is otherwise difficult and laborious to obtain, to be simply determined from the Erichsen test for the first time. The relationship between the Erichsen index and maximum surface strain presented here enables users to obtain this material property both from future tests and from the results of historic tests (as many coating suppliers and users have extensive databases of Erichsen test results stretching back many years). This novel framework provides a quantitative method to analyse the performance of coatings used in the coil industry, redeveloping a century-old technique.
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