Since the first factories began manufacturing polyester (聚酯) in the 1950s, humans have produced about 9. 1 billion tons of plastic. And about 12 percent has been burnt, releasing harmful gases into the air. Most of the rest has ended up in landfills and in the natural environment. Plastic inhabits the oceans, cities and national parks, in large or tiny pieces.

Carbios is among the companies that are attempting to commercialize a type of chemical recycling, which breaks down polymers into their fundamental moleculars, called monomers (单体). Those monomers can then be recombined into polymers that are as good as new.

But some experts warn that chemical recycling may face many of the same issues that already plague the recycling industry, including competition from cheap plastics made from the raw materials. For the past several years, Carbios has been improving a method that uses an enzyme (酶) found in a microorganism to convert polyethylene terephthalate (PET), a common ingredient in plastic bottles, into its monomers.

Enzymatic recycling’s promise isn’t limited to PET: the approach can be applied to other plastics. In early experiments, it took weeks for enzymes to process just a part of a batch of PET. In 2020, Alain Marty, chief science officer at Carbios, announced they’d developed an enzyme that could stand warmer temperatures and change nearly an entire batch of PET into monomers in a matter of hours.

Most PET produced globally is used for textile fibers, which, because they often contain mixed materials, are rarely recycled. Mats Linder, leader of Stena Recycling in Sweden, said he’d like to see recycling technologies focus on these and other parts of the recycling industry where conventional recycling is coming up short.

As it happens, Carbios is working to do just that. Gregg Beckham, a senior research fellow at the National Renewable Energy Laboratory, believes the global plastic problem will call for a diverse mix of technological solutions. He thinks enzymatic recycling and other recycling technologies are advancing rapidly, and he’s optimistic that they’ll have a role to play.

The world’s biggest electric vehicle — a 45-ton mining dump truck named the eDumper — may have to give up its throne. The newcomer, powered with both electricity and a reserve of hydrogen fuel, is going to steal that title as the largest electric mining truck.

London-based Anglo American is developing the beast of a machine — it weighs 290 tons — as part of its sustainable mining vision. The conceptual work is done, but U.K-based Williams Advanced Engineering will bring the truck to life. The idea is to replace the vehicle’s diesel engine (柴油机) with a high-power modular lithium-ion battery (锂电池). “We are delighted to be involved in this innovative and exciting project which shows the potential of battery technology that can adapt to increased demands, from automotive and motorsport to ‘heavy duty’ industrial applications,” Craig Wilson, managing director of Williams Advanced Engineering, said.

While the eDumper — a mining truck used to move stones from the sides of mountains in Switzerland — relies entirely on pure electricity and pure physics for power, the Anglo American truck will use both a lithium-ion battery and a hydrogen fuel cell (电池) module. Altogether, the new truck will have over 1,000 Kilowatt hours of energy storage.

Hydrogen fuel is a clear fuel that produces only water as a by-product when consumed in a fuel cell. It’s typically produced from natural gas, nuclear power, or renewable wind and solar power. Adding hydrogen fuel cells to the vehicle’s battery will allow the truck to run for longer periods of time without recharging.

There’s also a third type of power that comes into play with the Anglo American truck: kinetic (动力的) energy created through the process of regenerative braking (再生制动系统). When an electric vehicle — be it the Anglo American truck, or the eDumper — rolls down a hill, that movement creates electrical energy for the battery as you brake. The electric motors power the car through the battery’s stored energy, but can also become mini generators that return some energy back to the battery.

After Anglo American finishes test trials with the truck, the firm will conduct studies to understand how the truck’s power units can be used to provide energy storage in other applications.

Chalk used in school classrooms comes in thin sticks. Lessons are often presented to entire classes on chalkboards (or blackboards, as they were originally called) using sticks of chalk. 【小题1】

As found in nature, chalk has been used for drawing since prehistoric times. And it helped to create some of the earliest cave drawings. Later, artists of different countries and styles used chalk mainly for sketches(素描),and some such drawings have survived. 【小题2】The method was to grind(碾碎)natural chalk to a fine powder, then add water, clay, and various dry colors. It was then rolled into stick shape and dried.

【小题3】 Class sizes began to increase at that time. Therefore, teachers needed a convenient way of conveying information to many students at one time. Not only did instructors use large blackboards, but students also worked with personal chalkboards, completing with chalk sticks and a sponge or cloth to use as an eraser. These small chalkboards were used for practice, especially among the younger students.

An important change in the nature of classroom chalk brought was in chalkboards. Blackboards used to be black, because they were made from true slate(石板).While some experts advocated a change to yellow chalkboards and dark blue or purple chalk to copy writing on paper, when makers began to shape chalkboards from synthetic(合成的)materials during the 20th century, they chose the color green, arguing that it was easier on the eyes. 【小题4】

Almost all chalk produced today is dustless. Earlier, softer chalk tended to produce a cloud of dust that some feared might contribute to breathing problems.【小题5】 It's just that the dust settles faster.