Session F34: Polymer Physics to Address the Dual Energy Challenge at Global Industrial Scale

A New Carbon Ontology: Hydrocarbons as Benign Material Resource for Civilizational-Scale Building

The talk will frame the macro scale of building and infrastructure development forecast for coming decades, especially in regions of population and economic growth, and highlight the startling environmental impact implicit in current building materials and methods as well as the in-use energy and maintenance footprints. Alternative materials that mitigate such impacts will be considered, such as mass timber, but the prime focus will be on emerging polymeric composite material-processing that has proved so successful in many other manufacturing sectors, especially in their remarkable structural capacity. A case will be made that adoption of polymeric composites offers potential for radical revision of building methods, with potential for civilizational-scale adoption in short timelines; and it will map out the environmental benefits that this might offer in both embodied and in-use impact. The challenges and impediments to broad uptake of hydrocarbon-derived buildings will be considered, and thoughts offered as to how these might be addressed effectively, with particular focus on fire retardancy and the economics of production. Emerging gas-deposition of carbon nanotube and graphene materials will be probed, which offer remarkable potential for poly-functional carbon dwellings that are suggestive of an elegant new carbon ontology: a carbon shroud for a carbon organism!



The talk will serve as a call for collaboration between upstream and downstream actors as vital to breaking into a highly entrenched and deeply conservative building “industry”. The need for radical new building technologies merits a purposeful mobilization (political, technical, logistical) that aims at nothing less than a massive re-orientation of hydrocarbon assets from prime use as fuel to prime use as building materials at a period of unprecedented urban development and against the backdrop of a mounting environmental crisis.   

Tools for polymer design: predicting rheology from molecular weight distribution and branching topology

Polymers make wonderful, useful materials! Yet, their success and ubiquity has itself caused problems, provoking examination of their sustainability and recyclability, and of the energy efficiency of their processing. In this context, the design and optimisation of new materials and processes requires tools with the ability to predict material properties and behaviour on the basis of their molecular structure. This talk will present our efforts to address the challenge of predicting the flow properties (rheology) of polymeric liquids, and discuss the physics underpinning the software we have developed. The potential design space is vast: practical polymers are polydisperse (broad and variable molecular weight distribution) and may contain branches (with potential to control the statistics of branch placement). These molecular variables affect the response of the polymers to flow: whether the strands align, or stretch, and by how much, in a given flow field. These dynamics in turn gives rise to relevant processing phenomena such as extension hardening, or shear thinning. We will focus on polydisperse linear polymers, for which we have developed a constitutive model ("Rolie-Double-Poly") embedded in software (https://reptate.readthedocs.io/) that quantitatively predicts non-linear rheology from molecular weight distribution. We will also discuss how chain branching affects the physics, as encoded within our "BoB" software (https://sourceforge.net/projects/bob-rheology/).   

Micromechanics of oriented semi-crystalline polymers: from structure to properties

The microstructure of semi-crystalline polymers, in terms of for example the degree of crystallinity, crystal type, size and orientation, may vary drastically depending on subtle details of the manner in which the polymer is shaped into the final product. For this material, often an oriented microstructure is formed, leading to anisotropic yield and failure kinetics.

To obtain a fundamental and quantitative understanding of how these anisotropic properties depend on the structure, a multiscale micromechanical model is developed. The modelling approach is based on a mean field framework, accounting for the crystalline phases, which are modelled by crystal plasticity and amorphous domains. The anisotropy of these amorphous regions is incorporated in the micromechanical model in the form of a pre-stretch of the amorphous network and anisotropic visco-plastic flow. Both aspects are found to be crucial for predicting the experimentally observed orientation dependence of the yield kinetics. With this combined experimental-modelling approach, new insight in the physical processes that govern the mechanics of semi-crystalline polymers are obtained.
  

A better future for fossil hydrocarbons and carbon nanomaterials

Every year we extract over 4.2 GT of oil, 2.5 GT of natural gas, and 3.4 GT of coal to sustain our economy. That’s equivalent to 8.7 GT of carbon and 1.3 GT of Hydrogen. Almost all of these resources are burned to generate energy, causing over 30 GT of CO2 to enter the atmosphere which is unsustainable in view of climate change—the only significant exception is polymers, which fix 0.35 GT/yr of hydrocarbon resources (~3% of the total production) into valuable solid materials. At the same time, every year we use over 12% of the world energy production (over 60 EJ) towards primary metals; most of this energy goes into mining, refining, and processing ~3 GT/yr of metal ores into usable metals, chiefly 1.6 GT/yr of steel, 50 MT/yr of Aluminum, and 20 MT/yr of Copper; it is accompanied by the generation of 3.7 GT of CO2 emissions, equivalent to ~20% of the emissions caused by burning oil and gas. This is the extent of our “materials-energy nexus”.

Can we break this inefficient cycle and replace metals with materials made directly from hydrocarbons? Carbon Nanomaterials—primarily CNTs and graphene—offer an opportunity. They can be made via pyrolysis of methane and other hydrocarbons, with concurrent production of hydrogen. In the past decade, methods have been developed to convert CNTs and graphene into macroscopic materials (fibers, sheets, 3D structures) that could displace metals based on their properties—strength, electrical and thermal conductivity. In this talk, I will discuss why carbon nanomaterials could be great candidates to utilize natural gas on a very large scale (GT/yr) to make materials with zero CO2 footprint and positive hydrogen production. I will outline the scientific problems that need to be solved to realize highly-efficient synthesis and conversion of these materials and will present an estimate of the potential benefits of such a transition in our use of fossil hydrocarbons.   

Quantifying tie-chain fraction and its impact on charge transport in model conjugated polymers

The presence of tie chains that connect between crystallites can critically impact the electrical properties of conjugated polymers. Yet, the community has not yet been able to directly visualize them, let alone quantify their content in conjugated polymers. We applied the Huang-Brown model, a framework commonly used to elucidate the structural origins of mechanical properties in polyolefins, to quantify the tie-chain contribution to charge transport in a series of model poly(3-hexylthiophene), P3HT, and its blends. Plotting field-effect mobility as a function of tie-chain fraction, as extracted from the Huang-Brown model, collapses the data on a single curve not previously seen when the charge transport property is plotted against molar mass. We find a threshold tie-chain fraction of 10^-3, below which intercrystallite connectivity limits macroscopic charge transport. Structural characterization via x-ray paracrystallinity analysis of these P3HT films suggests intracrystallite disorder to be the bottleneck that limits charge transport when crystallites are connected. Our study affirms the importance of connectivity between crystalline domains, with the Huang-Brown model implicating long polymer chains with rigid backbone to facilitate macroscopic charge transport.