Biocomposite design for food packaging

塑料垃圾对环境有着巨大的有害影响，工业面临着越来越大的压力，需要用可持续来源的聚合物取代传统的污染性石化聚合物。塑料薄膜食品包装虽然是一次性的，但在延长食品保质期和减少食物浪费方面发挥着重要作用，而食物浪费是温室气体的重要来源。虽然塑料薄膜通常由可回收聚合物制成，但由于食品污染，大多数塑料薄膜食品包装既不能生物降解也不能回收。因此，如果薄膜可以被设计成具有适当的性能，可持续来源和可生物降解，这些可持续的聚合物薄膜将是食品包装应用的更好选择，并导致大量塑料进入垃圾填埋场。有许多可持续来源和可生物降解的聚合物。然而，由于许多因素，转向可持续聚合物薄膜是具有挑战性的，其中最重要的是与石化聚合物相比，它们的性能较差。如果我们能够将可持续聚合物薄膜的性能提升到石化产品的水平，消费者和行业需求加上政府的激励措施将反过来推动大规模生产和低成本制造。因此，当务之急是提高可持续聚合物薄膜的性能，使其得到广泛应用。通过分别添加填充颗粒和增塑剂来形成复合材料，可以改善可持续聚合物薄膜的性能和可加工性。虽然在科学文献中有许多关于特定生物可降解聚合物复合材料（我们称之为生物复合材料）的研究，但由于缺乏合理的设计，进展缓慢。为了延长食品的保质期，复合包装薄膜必须起到气体和水分屏障的作用。薄膜还必须具有化学稳定性和热稳定性，具有足够的机械强度和柔韧性，以及透明度，从而使消费者在美学上感到愉悦。从制造角度看，薄膜必须易于加工。良好的阻隔性能通常需要高度的聚合物结晶度。然而，薄膜的柔韧性和透明度也是重要的属性，并且要求晶体不要太大，这可能会降低结晶度。填充颗粒的存在可以诱导或阻碍聚合物结晶度，这取决于颗粒与聚合物的相互作用。薄膜的微观结构是由其内部聚合物晶体的空间排列引起的，它决定了薄膜的大尺度特性，如柔韧性、透明度和气体阻隔性。我们提出通过界面性能和偶联剂控制结晶度，通过界面性能和加工控制微观结构，通过微观结构控制复合材料的性能。我们还希望设计指南可以转移到其他生物复合材料中。在这个项目中，我们将使用分子动力学模拟来模拟填料颗粒界面附近的聚合物结晶。中尺度（如有限元和蒙特卡罗）建模将用于模拟所得的微观结构。建模与实验准备、表征和性能测量相结合，将使界面特性和加工步骤与材料特性联系起来。该项目的成果将是：1)确定适合薄膜食品包装的生物复合材料，2)增加对填充颗粒如何影响聚合物结晶和微观结构的理解，3)加速生物复合材料开发的设计规则，以及4)建立工业吸收设计规则和新材料的途径。

Plastic waste has a hugely detrimental impact on the environment and there is mounting pressure on industry to replace traditional polluting petrochemical polymers with sustainably-sourced polymers. Plastic film food packaging, while single-use, plays an important role in extending the shelf life of food and reducing food waste that is a significant contributor to greenhouse gases. While plastic films are typically made from recyclable polymers most plastic film food packaging is neither biodegradable nor recyclable due to food contamination. Therefore, if films can be designed to have the appropriate properties, be sustainably-sourced and biodegradable, these sustainable polymer films would be a much better alternative for food packaging applications and result in a large reduction in the amount of plastic ending up in landfill. There are many sustainably-sourced and biodegradable polymers. Nevertheless, the switch to sustainable polymer films is challenging due to a number of factors, not least of which is their poor performance in comparison to petrochemical polymers. If we are able to drive the performance properties of the sustainable polymer films up to the levels of the petrochemicals, consumer and industry demand combined with government incentives will in turn drive large-scale production and lower cost manufacturing. It is, therefore, a matter of urgency to improve sustainable polymer film performance to enable its wide-spread uptake. The performance and processability of sustainable polymer films can be improved by the addition of filler particles and plasticisers, respectively, to form a composite material. While there are numerous studies of specific biodegradable polymer composites (which we name biocomposites) in the scientific literature, progress has been slow owing to a lack of rational design. To increase the shelf life of food, composite packaging films must act as a gas and moisture barrier. The films must also be chemically and thermally stable, have sufficient mechanical strength and flexibility, and transparency so they are aesthetically pleasing to the consumer. From the manufacturing perspective the films must be easily processible. Good barrier properties typically require a high degree of polymer crystallinity. Yet, film flexibility and transparency are also important attributes and require that the crystallites are not too large, potentially reducing crystallinity. The presence of filler particles can either induce or hinder polymer crystallinity, depending on the interaction of the particles with the polymer. The film's microstructure, caused by the spatial arrangement of the polymer crystallites within it, then dictates the large-scale properties such as flexibility, transparency and gas barrier.We propose that crystallinity can be controlled via the interfacial properties and coupling agent, that the microstructure can be controlled through interface properties and processing, and that the composite performance can be controlled through the microstructure. We also expect that the design guidelines will be transferable to other biocomposites. In this project, we will use molecular dynamics simulations to model polymer crystallisation near the filler particle interface. Mesoscale (e.g. finite element and Monte Carlo) modelling will be used to simulate the resulting microstructure. The modelling, combined with experimental preparation, characterisation, and performance measurements, will enable the interface properties and processing steps to be connected to the material properties. The project outcomes will be: 1) identification of biocomposites suitable for thin film food packaging, 2) increased understanding of how filler particles affect polymer crystallization and microstructure, 3) design rules for accelerated biocomposite development, and 4) establishing the pathway for the uptake of the design rules and new materials by industry.