Molecular modelling of flow-induced crystallisation in polymers
Lead Research Organisation:
University of Nottingham
Department Name: Sch of Mathematical Sciences
Abstract
Products made of semi-crystalline plastics are found everywhere in our everyday lives. From food and drinks containers to high performance plastic components, semi-crystalline plastics comprise the largest group of commercially useful plastics. The crystallisation of plastic is strongly affected by its molecular shape. This is because plastics are made-up of long-chain molecules, or polymers. The connected nature of polymer molecules forces them to crystallise into a mixture of ordered crystalline regions, which are interspersed with regions where the chains are more randomly arranged. The proportion of amorphous and crystalline material, along with the arrangement and orientation of the crystals, is collectively known as the morphology. The crystal morphology strongly influences strength, toughness, permeability, surface texture, transparency and almost any other property of practical interest. It is known that morphology can be determined by the flow conditions that a plastic experiences as it crystallises. Typically, these flows occur during the process that shapes a plastic product. For example, flows occurring while injecting a plastic into a mould or blowing it into a film. Thus, by understanding how flow affects crystallisation it is possible, in principle, to enhance the final properties of a product by careful control of how it is processed. Unfortunately, a detailed understanding of polymer crystallisation at a molecular level, particularly under flow has been difficult to acquire. This is because flow-induced crystallisation in polymers depends on the subtle interplay of several complicating factors. Firstly, polymer crystallisation during flow is controlled by the shapes that flow forces the molecules to form, and precise theories for how polymers move under strong flow have, until recently, not been sufficiently accurate. Secondly, crystallisation is polymers is always incomplete; the connected nature of polymer molecules frustrates the materials efforts to reach the lowest energy state so equilibrium concepts cannot be applied. In fact the final state is controlled by the crystallisation kinetics. In this project we take a new approach to flow induced crystallisation to overcome these two problems. Recently derived molecular flow models have been shown to reliably predict the configuration of polymer molecules under flow, and we use these as the starting point of our model. To capture the crystallisation kinetics we employ an efficient kinetic Monte Carlo simulation technique to simulate the early stages of crystal formation. Influence over these early stages, experiments suggest, are the primary method by which flow controls crystallisation. Results from these simulations will improve our understanding of flow-induced crystallisation and will provide a template for us to derive more simple differential equation based models, which will be suitable for flow modelling of plastic processing.
Publications
Graham R
(2010)
Molecular modelling of flow-induced crystallisation in polymers
in Journal of Engineering Mathematics
Graham RS
(2014)
Modelling flow-induced crystallisation in polymers.
in Chemical communications (Cambridge, England)
Graham RS
(2010)
Kinetic Monte Carlo simulations of flow-induced nucleation in polymer melts.
in Faraday discussions
Hamer M
(2010)
Analytic calculation of nucleation rates from a kinetic Monte Carlo simulation of flow induced crystallization in polymers
in Journal of Non-Newtonian Fluid Mechanics
Hamer M
(2012)
A method to project the rate kinetics of high dimensional barrier crossing problems onto a tractable 1D system
in Soft Matter
Jolley K
(2011)
A fast algorithm for simulating flow-induced nucleation in polymers.
in The Journal of chemical physics
Jolley K
(2012)
Flow-induced nucleation in polymer melts: a study of the GO model for pure and bimodal blends, under shear and extensional flow
in Rheologica Acta
McLeish T
(2009)
Neutron flow-mapping: Multiscale modelling opens a new experimental window
in Soft Matter
Mykhaylyk O
(2011)
Monodisperse macromolecules - A stepping stone to understanding industrial polymers
in European Polymer Journal
Description | We have developed a model for how flow changes crystallisation in polymers. We have also developed tools to allow us to compute with this model much faster and in some cases we can solve the model without needing a computer. Both of these make the model easier and more effective to apply. We have shown that the model can describe experimental data and can thus be used to draw conclusions about how polymer molecules behave when crystallising under flow. |
Exploitation Route | Our model can be used by industrial scientists to predict how flow will change the final properties of plastic products. Two examples are plastics processing (eg injection moulding) and 3D printing with plastics. |
Sectors | Chemicals,Manufacturing, including Industrial Biotechology |
Description | We have been assisting polymer producers Dow and SCG in understanding of flow-induced crystallisation in polymers. This has informed their ability to meet the processing requirements of their customers. We have secured ongoing ESPRC support for a joint project with these partners (and Autodesk) to continue to develop modelling and experiments in this area. |
First Year Of Impact | 2016 |
Sector | Manufacturing, including Industrial Biotechology |
Impact Types | Economic |
Description | EP/P005403/1 Flow induced crystallisation in polymers: from molecules to processing: Design by Science |
Amount | £937,655 (GBP) |
Funding ID | EP/P005403/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 11/2016 |
End | 11/2019 |
Description | Semi-crystalline Materials in Additive Manufacturing: fellowship for Claire McIlroy |
Amount | £150,000 (GBP) |
Organisation | Royal Commission for the Exhibition of 1851 |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 09/2017 |
End | 09/2020 |
Description | Collaboration with Prof. Roberto Pantani, Chemical and Food Engineering Dept., University of Salerno, Itlay |
Organisation | University of Salento |
Country | Italy |
Sector | Academic/University |
PI Contribution | This collaboration resulting in the exchange of ideas and the sharing of experimental data prior to publication. This enabled the project team to analyse these data and submit a publication during the lifespan of the project |
Start Year | 2010 |
Description | Collaboration with Professor Paula Wood-Adams of Concordia University |
Organisation | Concordia University |
Country | Canada |
Sector | Academic/University |
PI Contribution | I have initiated a collaboration with Professor Paula Wood-Adams of Concordia University. This has involved project members exchanging ideas with Prof Wood-Adam's group and modelling their experimental data. This collaboration led to a joint conference paper at the Society of Rheology meeting in 2010. |
Start Year | 2010 |