Enzymatic plastics depolymerization in moist-solid reaction mixtures

由于其耐用性、低重量、多功能性和低生产成本，塑料已在许多领域取代天然材料，并已成为现代技术和社会所必需的，最常见的塑料包括聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯（PET）、聚苯乙烯（PS）、聚碳酸酯（PC）、聚氯乙烯和聚氨酯（PUR）。全球塑料产量持续飙升，2015年达到3.17亿吨。在加拿大，不到9%的塑料被回收利用，约75%的塑料进入环境，危及海洋和陆地生态系统。而PET -一种广泛用于包装，瓶子和纺织品的塑料-是被认为可回收的罕见塑料之一，实际上它主要是作为低级产品重新使用的降级循环，例如从瓶子到地毯，之后它就不能再回收了。此外，将PET回收为食品级产品具有挑战性，需要使用苛刻的化学品、高温和高压。我们发明了一种环保工艺，该工艺基于自然界的酶而不是苛刻的化学品，用于分解PET塑料。已经报道了几种能够解聚低结晶度PET的酶;然而，它们对通常在消费品中发现的高度结晶形式的PET无活性。值得注意的是，我们的创新工艺不仅效率更高，而且还能够实现高结晶度PET的解聚。我们的技术包括在固体反应混合物中使用酶，而不是典型的水溶液或浆料。因为它不使用任何苛刻的化学品，有机或水性溶剂，并避免了对高温和高压的需要，我们的工艺最大限度地减少了废物的产生和能源消耗。我们的半固态反应混合物比粘稠溶液或悬浮液更容易处理，只需要温和的间歇机械混合。我们建议优化我们的PET解聚工艺，并使其适用于其他聚酯、PC、PS和PUR塑料。重要的是，拟议的研究将提供一种解决方案，将塑料废物直接回收到新塑料或其他商品化学品中。

Due to their durability, low weight, versatility and low production cost, plastics have replaced natural materials in many areas and have become essential to modern technology and society, with the most common plastics including polyethylene, polypropylene, polyethylene terephthalate (PET), polystyrene (PS), polycarbonate (PC), polyvinyl chloride, and polyurethane (PUR). The global production of plastics has continuously soared, reaching 317 M tonnes in 2015. In Canada, <9% of all plastics is recycled and ~75% finds its way in the environment, imperilling both marine and terrestrial ecosystems. Whereas PET - a plastic widely used in packaging, bottles and textile - is one of the rare plastics to be considered recyclable, in reality it is mostlydowncycled for re-use as lower-grade products, e.g. from bottles to carpets, after which it cannot be recycled anymore. Moreover, recycling PET back into food-grade products is challenging, requiring harsh chemicals, elevated temperatures and high pressures.We have invented an environment-friendly process, based on enzymes from nature instead of harsh chemicals, for the breakdown of PET plastics. Several enzymes capable of depolymerizing low crystallinity PET have been reported; however, they are inactive towards highly crystalline forms of PET typically found in consumerproducts. Remarkably, our innovative process is not only more efficient, but also enables the depolymerization of high crystallinity PET. Our technology consists of using enzymes in moist-solid reaction mixtures instead of the typical aqueous solutions or slurries. Because it does not use any harsh chemicals, organic or aqueous solvents, and avoids the need for high temperatures and pressures, our process minimizes the production of waste and energy consumption. Our moist-solid reaction mixtures are easier to handle than viscous solutions or suspensions, and only require gentle, intermittent mechanical mixing. We propose here to optimize our PETdepolymerization process and adapt it to other polyesters, PC, PS and PUR plastics. Importantly, the proposed research will offer a solution for recycling plastic waste directly to new plastics or other commodity chemicals.