Catalysis for Compatibilizers: Upcycling Plastic Waste into Value-Added Materials

塑料对环境的影响是一个Jekyll和Hyde难题。虽然塑料污染对环境造成了真实的危害，但塑料也使整个欧洲的二氧化碳排放量减少了5-9倍，部分原因是它们被用作运输车辆的轻质部件和建筑绝缘材料。塑料还通过减少20%的食物浪费来应对全球粮食安全挑战。然而，目前的生产方式是不可持续的。到2015年，全球生产的8300吨塑料中，有4900吨被丢弃。从线性塑料生产模式向循环经济转变具有迫切的重要性，需要创新的科学技术。目前，超过99%的塑料是由原油生产的。到2050年，预计年生产将使用全球石油储量的20%，产生的二氧化碳是航空业的两倍。为了节约石油储备并避免能源密集型裂化过程，必须找到替代原料。废弃的塑料废物提供了一种有吸引力的替代原料，通过将这种废物材料升级为有用的增值产品。然而，目前只有10%的塑料被回收利用。这部分是因为“回收”材料通常是降级循环的，材料性能（如强度和柔韧性）的降低导致价值逐渐降低，直到回收很快不再具有成本效益。使这一复杂过程进一步复杂化的是，塑料产品通常含有多种类型的塑料。例如，牛奶盒由聚乙烯（PE）制成，但盖子和标签由聚丙烯（PP）组成;这些塑料需要分离并随后作为单独的组件回收。创造性的科学解决方案对于解决这些问题至关重要。过去两年出现了一种改变游戏规则的技术。“化学拉链”的发明使得PE和PP的组合能够有效地回收，从而避免了分离这两种材料的需要。“拉链”是一种设计有不同和交替的“牙齿”的分子;一组牙齿与PE相互作用，而另一组牙齿与PP相互作用，将这两种塑料缝合在一起。值得注意的是，通过结合PE，PP和“拉链”生产的新混合塑料提供了比任何单个组件都更坚固的升级循环材料。这些“拉链”的工业化商业化将彻底改变PE和PP的报废处理。然而，迄今为止开发的技术是有限的。虽然已经开发了用于PE和PP的化学拉链，但用于聚酯的类似系统尚未开发。将这一概念转化为聚酯是一个令人兴奋的目标，因为可降解聚酯（如聚乳酸（PLA））的使用在过去四年中翻了一番。商业PLA产品包括一次性饮用杯、薄膜和食品包装，并且一些PLA产品涉及混合塑料系统，例如PLA食品托盘与PE薄膜。回收公司报告称，回收物流中PLA的污染越来越严重，这是一个问题，因为目前的分离技术不如传统塑料发达，而且这一挑战将越来越大。生产新的化学拉链，将PLA与PE，PP或聚苯乙烯（PS）混合，将彻底改变目前的回收工艺，并从废物中创造一系列新的升级回收塑料材料，然而，这些系统的发展受到生产这种拉链的重大科学挑战的阻碍。该项目将通过设计一种催化剂，可以在两种不同的化学反应之间切换，一次一个牙齿地建立这些拉链，从而为PLA生产定制的化学拉链。这些变革性的拉链将被应用于PLA与PE、PP和PS的结合，从塑料废物中创造出一种新的理想的、多样化的和有价值的材料，为社会带来重要的经济、环境和能源效益。

The environmental impact of plastics is a Jekyll-and-Hyde conundrum. While plastic pollution poses a very real environmental danger, plastics have also reduced CO2 emissions across Europe by a factor of 5-9, partly through their use as lightweight components in transport vehicles and as building insulation materials. Plastics also address the global challenge of food security by reducing food waste by 20%. However, current production methods are unsustainable. Of the 8300 Mt of plastic produced globally by 2015, 4900 Mt has been discarded. Moving from a linear plastic production model to a circular economy is of urgent importance and requires innovative scientific technologies.Over 99% of plastics are currently produced from crude oil. By 2050, annual production is predicted to use 20% of global oil reserves and generate twice as much CO2 as the aviation industry. To conserve oil stocks and avoid energy intensive cracking processes, it is essential to find alternative feedstocks. Discarded plastic waste offers an attractive alternative feedstock, by upcycling this waste material into useful value-added products. Yet only 10% of plastics are currently recycled. This is partly because "recycled" materials are generally downcycled, with a reduction in material properties such as strength and flexibility leading to progressively lower value applications until recycling is rapidly no longer cost effective. Further complicating this complex process, plastic products often contain multiple types of plastic. For example, milk cartons are made of polyethylene (PE) but the lids and labels consist of polypropylene (PP); these plastics require separation and subsequent recycling as individual components. Creative scientific solutions are crucial to address these problems.A game-changing technology has emerged in the past two years. The creation of "chemical zips" has enabled efficient recycling of a combination of PE and PP, avoiding the need for separation of these two materials. The "zip" is a molecule designed with different and alternating "teeth"; one set of teeth interacts with PE while the other set interacts with PP to stitch these two plastics together. Remarkably, the new hybrid plastics produced by combining PE, PP and the "zip" give upcycled materials that are stronger than any of the individual components. The industrial commercialisation of these "zips" is set to revolutionise the end-of-life treatment of PE and PP. However, the technology developed to date is limited.While chemical zips have been developed for PE and PP, analogous systems for polyesters remain unexplored. Translating this concept to polyesters is an exciting target, as the use of degradable polyesters such as polylactic acid (PLA) has doubled in the past four years. Commercial PLA products include disposable drinking cups, films and food packaging, and some PLA products involve mixed plastic systems such as PLA food trays with a PE film. Recycling companies have reported increasing contamination of recycling streams with PLA, which is problematic as the current separation technologies are less well developed than for conventional plastics, and this challenge is set to grow.The production of new chemical zips that could amalgamate PLA with PE, PP or polystyrene (PS) would revolutionise current recycling processes and create a range of new upcycled plastic materials from waste, yet the development of these systems has been hindered by the significant scientific challenge of producing such zips. This project will enable the production of bespoke chemical zips for PLA by designing a catalyst that can switch between two different chemical reactions to build up these zips one tooth at a time. These transformative zips will then be applied to the combination of PLA with PE, PP and PS to create a new class of desirable, diverse and valuable materials from plastic waste, with important economic, environmental and energy benefits for society.