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.
 
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 08/2017 
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