Listen and read 34: Recycling - Thấm Tâm Vy

Nội dung text: Listen and read 34: Recycling - Thấm Tâm Vy

1. octane. When solidified glue containing these bubbles is heated appropriately the LISTEN AND READ 34 hydrocarbon expands, inflates the bubbles and, as happens with expandable RECYCLING graphite, cracks the glue. The crucial phrase in all this is “heated appropriately”. Crackle, pop, snap Dr Broughton and his colleagues have had to pick substances that do their stuff at a temperature sufficiently high as not to be encountered during a machine’s SELF-DESTRUCTING GLUE SOLVES normal operation, but sufficiently low that it will not damage the components to A STICKY ENVIRONMENTAL PROBLEM be disbonded when they are heated up to disbond them—which may be done either in an oven or by using a hot-air gun that resembles a souped-up hair GLUE THAT deliberately comes unstuck sounds like a joke. But it is useful to dryer. In this context, having two approaches provides flexibility. Expandable be able to take things to pieces for recycling once their lives are over, so graphite’s disruptive effect is triggered at a slightly higher temperature (160°C) adhesive that becomes unadhesive on command could be valuable. James than the 125°-150°C which causes the microspheres to inflate. (The exact Broughton, a chemist at Oxford Brookes University, in Britain, thinks he has just behaviour of a microsphere depends on which hydrocarbon is inside it.) This the things. The inventions he and his colleagues have come up with are not new process is, moreover, surprisingly quick. Dr Broughton’s colleague Lucy glues, per se, but rather “disbonding” agents that can be put into existing glues Eggleston, who works at the National Composites Centre, in Bristol, says that to break their grip when after a mere six seconds of heating, “the components just pop apart”. Disbonding it is no longer needed. In of this sort might have wide application. But one particular prize the team have the past, when the in sight is the wind-turbine market. Turbine blades typically have glass-fibre components of machines skins, balsa-wood cores and metal or carbon-fibre spars. That makes them ideal like cars and aircraft candidates for disbonding at the ends of their lives. In Europe alone, 14,000 were made mainly of wind-turbine blades will be decommissioned over the next five years. For these, metal, welding and disbonding comes too late. They will, though, need to be replaced—and the soldering were the green credentials of wind-farm operators would certainly be burnished further if principal ways of joining those replacements were designed for easy recycling.■ The Economist 30.05.2020 them together. But the Notes: spread of plastics—and - per se: [< Latin] = by itself - microsphere: chất làm mềm hóa chất khác particularly of - souped-up: được nâng cấp composites like glass - decommission: hủy nhiệm; cho dừng hoạt động (lò phản ứng ) fibre and carbon fibre—means that glued joints are much more common than - balsa wood: a soft, lightweight wood used in model airplane kits and other projects. Balsa sticks, they used to be. Effective recycling requires materials to be sorted and processed balsa blocks, balsa planks, and balsa sheets. [gỗ bấc; gỗ bần, làm nút chai ) separately. Taking an object to pieces is the first stage of doing that. Recycling things that have been glued thus involves disbonding the glue. Dr Broughton’s disbonding agents are called expandable graphite and thermally expandable microspheres. Expandable graphite is a powdery substance in which graphite’s famously flat and slippery carbon sheets are interspersed with sulphuric acid. When an adhesive containing this additive is heated appropriately, the acid decomposes into three gases: sulphur dioxide, sulphur trioxide and steam. That forces the graphite layers apart. This expansion, Dr Broughton observes, acts as a crack initiator. It breaks up the glue and frees the joined components. Cây Chân thỏ hay gỗ bấc Thành phẩm gỗ balsa Thermally expandable microspheres, by contrast, are plastic bubbles, ten (tên khoa học: Ochroma pyramidale) microns across, that are filled with a hydrocarbon such as butane, pentane or Thẩm Tâm Vy LISTEN AND READ 34