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A novel green recyclable rubber polymer developed by Australian scientists can help to reduce the ever-growing environmental impact of the traditional non-reusable synthetic and mineral materials used in manufacturing and construction. The new material is composed of sulfur and canola oil and can be combined with fillers derived from recycled plastic waste to create reusable construction materials of the future.
作为减少合成塑料废物的环境影响的全球努力的一部分，可以在可持续的循环经济中很容易回收和重复使用的新型聚合物材料的开发正在从研究社区和行业中获得重大兴趣。亚博网站下载
Most recycled plastic waste is mechanically reprocessed into new source materials or melt-processed to manufacture new goods. This often leads to chemical and mechanical degradation of the recycled material, limiting its possible applications.
Industrial Waste as Source Material for Green Recyclable Polymers
Combining sustainable source materials, such as renewable biomass, agricultural, or industrial waste with newly developed processing methods, paves the way towards the next generation of green recyclable polymers, as it enables polymers to break down into reusable macromolecular building blocks
Elemental sulfur is an abundant and inexpensive by-product of the oil refining industry that is used for the manufacturing of a wide range of commodity chemicals and materials, such as sulfuric acid, fertilizers, and vulcanization of natural and synthetic rubbers. Sulfur supply (over 60 million tonnes produced each year) greatly exceeds demand, creating large stockpiles of unwanted raw material.
Under normal conditions, sulfur atoms predominantly form cyclic eight-atom molecules with a chemical formula S8. Upon heating, at a temperature of around 120 °C, sulfur melts into a clear yellow liquid and larger polyatomic rings, consisting of up to 35 atoms, can be formed.
Further heating of the sulfur melt (above 159 °C) initiates a ring-opening polymerization of the ring-shaped monomers into polymeric sulfur of high molecular weight. However, this process is reversible and sulfur polymers readily depolymerize back to the ring-shaped monomeric state.
具有高硫含量的橡胶聚合物作为常规橡胶的替代品
With the invention of the inverse vulcanization process in 2013, the synthesis of chemically stable and processable sulfur-based polymer materials (with a sulfur content of 50-80 wt%) became possible.
In the conventional vulcanization process, a small amount of sulfur is used to form crosslinks (bridges) between hydrocarbon polymer chains, converting the organic polymers into more durable and wear-resistant materials such as vulcanized rubber.
相反，反硫化过程使用大量的硫和少量的有机添加剂（通常是不饱和烃），该添加剂充当交联，并稳定聚合物硫，以抗聚合。
根据逆硫化过程，由澳大利亚弗林德斯大学副教授贾斯汀·夏尔（Justin Chalker）博士领导的研究小组合成了突破性的橡胶聚合物。该聚合物是通过菜籽油（一种不饱和脂肪含量很高的一种菜籽油）和50 wt％硫的菜籽油的随机共聚合制成的。
Structurally, the new polymer is very similar to natural or synthetic rubber, consisting of a network of crosslinked macromolecular chains, which makes it insoluble in most common organic solvents. It is also a highly sustainable material, as its synthesis does not require any organic solvents and uses only elemental sulfur (industrial by-product) and renewable plant oil.
Heat and Pressure Converts Rubber Powder into Versatile Material
弗林德斯的科学家与迪肯大学和西澳大利亚大学的合作者一起开发了一种名为“反应性压缩成型（RCM）”的创新方法，该方法可以使新橡胶聚合物的加工，回收和再利用。
Once the polymerization process is complete, the final product (a soft, brown rubber) is dried and ground into powder. The powdered rubber is then compressed in a hot press at a pressure of 10 MPa and a temperature of 110 °C. Within minutes, the material converts into a flexible rubber compound.
Although the temperature required for the RCM to take place is far lower than the temperature of the original inverse vulcanization process (180 °C), the combination of heat and pressure is sufficient to trigger sulfur-sulfur metathesis reaction (cleavage and reforming of the bonds between the sulfur atoms) at the interfaces between the compressed polymer particles. This leads to the formation of a continuous macromolecular network within the material.
通过反应性压缩成型橡胶聚合物的回收
According to the Australian scientists, the reactive compression molding process is ideally suited for recycling and reusing of the rubber polymer. Their research shows that the new material can be ground up into a powder and remolded at elevated pressure and temperature many times without any degradation of its physical and chemical properties.
The relatively low temperature during the RCM process minimizes the thermal degradation of the material.
单击此处以了解有关塑料和橡胶测试设备的更多信息app亚博体育
Even after several RCM cycles, the remarkable material retains its strength and elasticity and can be shaped into tubing, insulation mats, coatings, and other products traditionally manufactured from conventional rubber.
Once these products have reached their end of life or are no longer needed, they can be ground up and recycled into something new.
Construction Materials with Tunable Properties
As stated by Ph.D. candidate Nic Lundquist, the leading author of the research, the most important advantage of the RCM method is the possibility to manufacture unique composite materials with tunable mechanical properties.
By using the rubber polymer as a moldable reactive matrix that can bind fillers such as plant fibers, sand, recycled plastic waste and carbon fiber, the researchers have created new composites that can be used as sustainable construction materials in the future.
了解有关材料表征设备的更多信息app亚博体育亚博网站下载
Two of the newly developed composite materials, one containing sand and the other plant fiber filler (50 wt% coconut coir), exhibited compression moduli of approximately 12 MPa (nearly double that of the rubber polymer alone) with much higher stiffness and elastic moduli.
植物纤维复合材料特别适合建造绝缘材料，而沙子复合材料可以代替不可回收的建筑材料，例如砖和混凝土。亚博网站下载后者的可能性特别令人感兴趣，因为水泥是一种不可再生的资源，具有重大的环境影响，导致空气污染，并贡献了超过8％的全球温室气体排放。
Multi-Use Rubber Polymers Boost Sustainability of Construction Industry
The versatility of the green recyclable rubber polymer was demonstrated in an experiment where the powdered material was first used to purify water contaminated with iron (due to the high sulfur content, the material can bind to metals like iron), removing more than 90% of the contaminant in 24 hours.
The iron-laden rubber was then subjected to RCM to manufacture insulation mats and other recyclable construction materials.
The newly-developed RCM process opens up the possibility for a new class of multi-purpose rubber polymers that can be efficiently recycled and reused to serve as a technological base for the manufacturing of future sustainable construction materials from recycled plastic waste.
参考和进一步阅读
N. Lundquistet al.(2020) Reactive compression molding post-inverse vulcanization: A method to assemble, recycle, and repurpose sulfur polymers and composites.化学欧元。J.，可用：https://doi.org/10.1002/chem.202001841
W. J. Chunget al.（2020）将元素硫作为聚合物材料的替代原料。亚博网站下载自然化学。, 5, 518–524. Available at:https://doi.org/10.1038/nchem.1624
Flinders University (2020)Revolutionary ‘Green’ Bricks Made from Recycled Plastic and Organic Waste.[Online]www.scitechdaily.com可用网址：https://scitechdaily.com/revolutionary-green-bricks-made-from-recycycled-plastic-and-comganic-waste/（于2020年6月20日访问）。
M. Irving（2020）“绿色”可回收橡胶为一次性建筑材料提供了新的生命。亚博网站下载[Online]www.newatlas.com可用网址：https://newatlas.com/亚博网站下载materials/recyclable-rubber-reuse-building-materials-plastic/（于2020年6月20日访问）。
Flinders University (2020)用塑料废物建造砖块。[Online]www.phys.org可用网址：https://phys.org/news/2020-05-bricks-plastic.html（于2020年6月20日访问）。
E. Turner (2020)研究人员发现了新的橡胶材料来创建绿色建筑材料。[Online]www.tmrblog.com可用网址：https://tmrblog.com/researchers-discover-new-rubber-material-to-to-greate-green-construction-material/（于2020年6月20日访问）。
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