Flow induced crystallisation in polymers: from molecules to processing

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Polymer processing is a multi-billion pound, world-wide industry, manufacturing products used by virtually every person in the developed world (and beyond) on a daily basis. This vital sector of the UK economy will gain a significant competitive advantage from a molecular understanding of how polymers crystallise during processing, as it will enable stronger, lighter, more durable and more easily recycled plastic products. In this proposal we will overcome the key experimental, simulation and numerical issues in understanding polymer crystallisation to deliver a molecular based, predictive platform for the processing of semi-crystalline polymers. We will tightly integrate a family of progressively coarse-grained simulations and models, covering all relevant lengthscales within a single project. This will displace the current sub-optimal semi-empirical approaches in polymer processing and enable molecular design of polymer products, through choice of processing conditions. By facilitating the manufacture of polymer products with tailored properties this program will provide a critical competitive advantage to this important industry.Polymers are long-chain molecules, formed from connecting together a large number of simple molecules. These long-chain molecules are at the heart of the multi-billion pound plastics industry. Semi-crystalline polymers make up a very significant fraction of the worlds production of synthetic polymers. Unlike simple molecules, the connectivity of polymer molecules means they crystallise into a composite structure of crystalline and amorphous regions. 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, capacity to be recycled and almost any other property of practical interest. Furthermore, polymer crystallisation is radically influenced by the flows that are ubiquitous in polymer processing. Flow drastically enhances the rate at which polymers crystallise and has a profound effect on their morphology. Flow distorts the configuration of polymer chains and this distortion breaks down the kinetic barriers to crystallisation and directs the resulting morphology.Understanding polymer crystallisation is a formidable problem. The huge range of relevant lengthscales ranges from the size of a monomer (nm) up to near macroscopic crystals (micro-metres). The range of timescales is even wider, ranging from the monomer relaxation time (ns) to nucleation (hours at low under-cooling). Our project will involve extensive multiscale modelling, supported at each level by experiments specifically designed to address key modelling issues. Our experiments will involve controlled flow geometries, the systematic variation of molecular weight and the probes of both nucleation and overall crystallisation. Close integration of experiments and all levels of modelling is a key feature.We will develop an interrelated hierarchical family of multiscale models, spanning all relevant lengthscales and delivering results where piecewise approaches have been ineffective. Each technique will be tightly integrated with its neighbours, retaining the molecular basis of the models while progressively addressing increasingly challenging systems. This will cumulate with the low-undercooling and high-molecular weights that are characteristic of polymer processing. Each simulation will use a rare event algorithm to dramatically increase the nucleation rate, the cause of the very long timescales. Insight from the most detailed models will guide the development of faster modelling. At the highest coarse-graining, the program will derive models suitable for computational modelling of polymer processing. Using these models in cutting-edge finite element code, we will compute FIC behaviour in polymer processing geometries.