Dey Indranil, N Muhammed Ajnas, Rege Siddhesh Sadashiv, Islam Sk Safikul, Misra Ashok, Samanta Ketaki, Manna Kunal, Bose Suryasarathi
Department of Materials Engineering, Indian Institute of Science, Bengaluru - 560012, India.
ACS Appl Mater Interfaces. 2023 Nov 6. doi: 10.1021/acsami.3c13340.
According to current projections, of the 400 mega tons of plastic produced globally, 70% is waste and of that only 16% is recycled and the rest is incinerated. This is estimated to contribute to ca. 16% of the net carbon emission by 2050. Such a massive amount of unmanaged plastic waste and the associated huge carbon footprint sets a significant challenge to tackle in the coming decades. To achieve net-zero carbon emission, closed-loop circular economy in plastics is crucial but collection, sorting and processing the postconsumer recycled (PCR) plastics poses humongous challenge in achieving this circularity, unless an effective strategy is designed. In a first of its kind, a designer biobased molecule was synthesized (here maleated castor oil, mCO) that is steric and thermally stable and forms "homo-cross-linking" in the melt post grafting onto PCR-PP. This designer molecule, besides offering a transient network, helps bridge the fragmented PP chains which is usually not amenable from the traditional grafting (like maleic anhydride), thereby addressing a long-standing challenge of retaining the properties post grafting due to chain scission in the melt. The resulting maleated (m) PCR-PP now offers abundant functionality which helped us design single and dual covalent adaptable network (CANs) and evaluate their consequences on the structure-property correlation. The PCR-PP Vitrimers demonstrate a distinct rubbery plateau in the melt and reprocessability with >90% recovery in mechanical properties even after the fifth sequence of recycling. We propose here for the first time how the varying reactivity (single or dual) in the transient polymer network, through dynamic exchange, regulates the closed-loop circularity in PP Vitrimers. Our results begin to suggest that the varying reactivity should be taken into account as an additional design parameter, as it influences both the stress relaxation rates and the flow activation energy. We now understand that the topology reconfiguration is strongly dependent on this varying reactivity, which also controls the overall crystalline morphology and the structural properties in the Vitrimers. This study, in addition to opening new avenues for recycling PP, will help guide researchers working in this field from both academia and industry.
根据目前的预测，全球生产的4亿吨塑料中，70%是废弃物，其中只有16%被回收利用，其余的则被焚烧。据估计，到2050年，这将占净碳排放的约16%。如此大量的未管理塑料废弃物以及相关的巨大碳足迹给未来几十年带来了重大挑战。为了实现净零碳排放，塑料的闭环循环经济至关重要，但收集、分类和处理消费后回收（PCR）塑料在实现这种循环方面面临着巨大挑战，除非设计出有效的策略。首次合成了一种设计型生物基分子（此处为马来化蓖麻油，mCO），它具有空间和热稳定性，在接枝到PCR-PP上后在熔体中形成“均相交联”。这种设计型分子除了提供一个瞬态网络外，还有助于桥接通常难以通过传统接枝（如马来酸酐）实现的断裂PP链，从而解决了由于熔体中的链断裂而导致接枝后性能保持的长期挑战。所得的马来化（m）PCR-PP现在具有丰富的功能，这有助于我们设计单共价和双共价自适应网络（CANs），并评估它们对结构-性能相关性的影响。PCR-PP热致液晶聚合物在熔体中表现出明显的橡胶平台，并且即使在第五次回收序列后，机械性能仍能恢复>90%，具有可再加工性。我们在此首次提出，通过动态交换，瞬态聚合物网络中不同的反应性（单或双）如何调节PP热致液晶聚合物中的闭环循环。我们的结果开始表明，应将不同的反应性作为一个额外的设计参数加以考虑，因为它会影响应力松弛速率和流动活化能。我们现在明白，拓扑结构的重新配置强烈依赖于这种不同的反应性，它也控制着热致液晶聚合物中的整体结晶形态和结构性能。这项研究除了为PP的回收开辟新途径外，还将有助于指导学术界和工业界从事该领域研究的人员。
