Performance enhancement of polymer nanocomposites via multi-scale modelling of processing and properties

计算机辅助数值模拟是材料研究的重要工具。它被用来预测材料在某些条件下的行为，这些条件可能难以用实验来复制，因为实验太昂贵或太困难。它还用于帮助理解材料的大尺度宏观特性（如强度）如何与分子水平上材料的纳米级结构（纳米=百万分之一毫米）相关。如果分子水平上的结构可以与材料在宏观水平上的行为相关联，那么就有可能设计出适合我们需要的材料，例如使它们更轻或更容易加工。聚合物，由于其特性和易于加工成复杂形状，是当今我们可用的最重要的材料之一，例如，在微芯片中使用聚合物将使低成本电子产品的下一次革命成为可能。聚合物纳米复合材料（NCs）是一种令人兴奋的新型材料，其纳米级颗粒分散在聚合物中。nc的好处主要来自于少量添加的颗粒（例如重量的5%）可以获得非常大的颗粒表面积。因此，它们显著改善了材料性能，显著提高了机械和气体阻隔性能。因此，使用这种材料的用户可以得到更有效的产品（或含有更少材料的产品）。该项目旨在开发计算机建模工具，以帮助材料生产者、产品设计师和制造商充分利用这些材料，比实验方法更快。在这个项目中，我们将创建计算机建模方法，将与任何聚合物矩阵NC工作。为了确保这项工作对工业有益，我们将集中精力应用这些方法来模拟nc在制造过程（拉伸吹塑和热成型）中的行为，这些过程涉及相对薄板的大应变双轴拉伸。这些过程用于制造包装，汽车和医疗设备行业的产品。设计和有效处理的nc提供了在这种情况下大幅减少所需聚合物数量的机会，因此有助于解决塑料废物的环境问题。因此，要模拟的材料将是在这些应用中最有希望的纳米材料：聚丙烯（PP）和聚对苯二甲酸乙二醇酯（PET），纳米颗粒将来自由硅酸盐材料层（血小板）组成的粘土。该项目的主要挑战将是找到能够在纳米尺度上描述粘土血小板（血小板大小、方向、血小板/聚合物相互作用）的材料的建模技术，然后将其与材料在加工成产品时的行为联系起来，并最终与产品在使用中的行为联系起来。这将涉及以下步骤：(1)使用透射电子显微镜（TEM）确定聚合物薄片的初始微观结构，以产生材料的高分辨率图像。然后使用图像分析软件对这些图像进行分析，以产生用于材料建模的数据。(2)根据(1)的数据构建板材的模型。(3)使用数学模型来模拟材料在成形过程中的行为方式，然后将该模型纳入用于制造塑料产品的实际过程的模拟中。(4)运行仿真，预测加工行为和最终零件性能。(5)通过实验验证模型结果。这项工作将由布拉德福德大学、牛津大学和贝尔法斯特女王大学的材料科学家、工程师和物理学家组成的多学科团队与工业界合作进行。

Computer aided numerical modelling is a valuable tool in materials research. It is used to predict the behaviour of materials under conditions that might be difficult to replicate experimentally either because experimentation is too costly or too difficult. It is also used to aid understanding of how the large scale, macroscopic properties of materials such as strength, are related to the nanoscale [nanometer = 1 millionth of a millimetre] structure of the material at the molecular level. If the structure at the molecular level can be related to the behaviour of the material at the macroscopic level then it becomes possible to design materials to suit our needs, e.g. to make them lighter or easier to process.Polymers, because of their properties and ease of processing into complex shapes are among the most important materials available to us today e.g. the next revolution in low cost electronics will be made possible by the use of polymers in microchips. An exciting new family of materials are the polymer nanocomposites (NCs), in which particles with nanoscale dimensions are dispersed in the polymer. The benefits of NCs derive primarily from the exceptionally large amounts of particle surface area that can be achieved for a small addition of particles (e.g. 5% by weight). Thus they offer dramatic improvement in material performance with significant increases in mechanical and gas barrier properties. The user of such a material therefore gets a more effective product (or one containing less material for the same effectiveness). This project is aimed at developing computer modelling tools to help producers of materials, and product designers and manufacturers exploit these materials to the full, much more quickly than could be done by experimental methods. In this project we will be creating computer modelling approaches that will work with any polymer matrix NC. To ensure the work is of benefit to industry we shall concentrate on applying the methods to modelling how NCs behave in manufacturing processes (stretch blow moulding and thermoforming) involving large-strain biaxial stretching of relatively thin sheets. These processes are used to make products for packaging, the automotive and medical device industry. NCs designed and processed effectively offer the chance to drastically reduce the amount of polymer needed in such cases, and therefore to help solve the environmental problem of plastics waste. The materials to be modelled will be therefore the most promising for NCs in such applications: polypropylene [PP] and polyethylene terephthalate [PET] and the nanoparticles will be derived from clays composed of layers of silicate material [platelets]. The main challenges in the project will be to find modelling techniques that will be capable of describing the material at the nanoscale level of the clay platelets [platelet size, orientation, platelet/polymer interaction] and then linking this to the behaviour of the material as it is processed into a product and finally to how the product behaves in use. This will involve the following steps (1) Determine the initial microstructure in a polymer sheet using Transmission Electron Microscopy [TEM] to produce a high resolution picture of the material. The images will then be analysed using image analysis software to produce data for material modelling. (2) Construct a model of the sheet based on the data from (1). (3) Use mathematical models to model the way in which the material will behave during forming and then incorporate this model into a simulation of the actual process used to manufacture the plastic products. (4) Run the simulation to predict processing behaviour and final part properties. (5) Validation of modelling results through experimentation. This work will be carried out by a multidisciplinary team consisting of material scientists, engineers and physicists from University of Bradford, Oxford and Queen's University Belfast, in collaboration with industry.