Rubber as a fuel
Dr S.S. Verma
Today most tyres, especially those fitted to motor vehicles, are manufactured from synthetic rubber. Rubber is an elastic hydrocarbon polymer which occurs as a milky emulsion (known as latex) in the sap of several varieties of plants. Synthetic rubber is made through the polymerisation of a variety of monomers to produce polymers.

Healing wounds with current
The idea of deliberately subjecting yourself to a session of electric shocks may make you cringe, but as a new study has found, it just may be worthwhile if you’re injured, for it speeds up the healing process.

Prof Yash Pal

Rubber as a fuel
Dr S.S. Verma

Today most tyres, especially those fitted to motor vehicles, are manufactured from synthetic rubber. Rubber is an elastic hydrocarbon polymer which occurs as a milky emulsion (known as latex) in the sap of several varieties of plants. Synthetic rubber is made through the polymerisation of a variety of monomers to produce polymers.

As the number of vehicles is increasing so are the heaps of discarded rubber tyres. Though every vehicle owner makes efforts to use tyres up to their maximum life but ultimately tyres are removed from service and heaps of discarded tyres can be seen everywhere and at auto-repair shops in particular.

Old tyres are an environmental nuisance around the globe. Although tyres themselves are not considered hazardous waste, these dumps sometimes catch fire and may burn for months before they can finally be extinguished, creating enormous volumes of toxic air pollution, oil, and heavy metals.

Ironically, those same characteristics which make waste tyres such a problem also make them one of the most re-used waste materials, as the rubber is very resilient and can be re-used in other products; it also yields much energy when burned under controlled conditions.

According to the Rubber Manufacturers Association, the average passenger-car tyre is estimated to produce more than two gallons of oil when burned which represent plenty of energy but also plenty of volatile waste. Thus, single biggest use of scrap tyres in the world, however, is as fuel. Environmentally or even economically speaking, so far, it is not the best method of reclaiming scrap tyres, but it beats the alternative of disposing or dumping unused tyres. In 2000, approximately 47 per cent of the scraped tyres in USA were burned for fuel.

So, industries have to set out a national wave of tyre-derived fuel (TDF) development in more environmental friendly way. While it may seem counterintuitive to anyone who’s seen an uncontrolled tyre fire, there actually can be environmental benefits to controlled burning of scrap tyres or TDF chips for energy.

TDF produces slightly more heating value than coal with similar emissions. Experts say that coal mixed with TDF produces less ash, greenhouse gases and metal emissions than burning coal alone.

Cement kilns are considered good places to use TDF because the ash is incorporated into the final product and there is no waste to dispose of. Energy-intensive pulp and paper mills and metal foundries are also strong candidates for using TDF, in part because TDF is often cheaper than coal. Such industrial users of TDF can often burn whole tyres, a practice that cuts down the expense of shredding tyres.

Unregulated or under-regulated, tyre burning can be an environmental disaster and a health menace. Effectively regulated, it can be an answer to fuel problems. The controlled and environmental damage from burning discarded tyres needs the wisdom of an experimental tyre burn that could demonstrate an effective way of disposing of old tyres.

It would be very interesting to have a scrap rubber fuelled stove for the use of common people. By burning of rubber under pressure with optimum conditions of fuel-air ratio, there will be no black smoke or any visible smoke.

The pyrolysis of rubber needs the secondary air to be increased to keep pace with higher rates of fuel volatisation. If conditions are not properly controlled the stove would roar like a rocket for a few minutes before returning to its pellet fuelled calm.

The forced air helps a lot. Carbonised rubber will be left over which might make an interesting briquette. It may be a more suitable fuel for other purposes.

Recently, the SpaceDev (US company) has developed a hybrid propulsion system which is safe, low-cost and the largest of its kind in the world, burns a combination of rubber and laughing gas. This highly innovative hybrid rocket motor technology uses nitrous oxide (N2O) or laughing gas, as an oxidizer, and hydroxy-terminated polybutadiene (HTPB), or rubber, as the fuel. Both of these are inexpensive and can be safely transported and stored without special precautions, and will not explode when combined, thus making the ideal propulsion system for manned space vehicles.

Though, the company’s aim is to make space travel safe, frequent and affordable for the general public but this technology can show a new way for the use of discarded rubber as fuel for a scarp rubber stove in times to come.

Then the environmental pollution from the rubber burning will be controlled and discarded rubber tyres can be put to common man’s use as a rubber fuel and above all heaps of discarded/wasted tyres will be put to an effective use.

The writer is from Department of Physics, Sant Longowal Institute of Engineering and Technology, Longowal

Healing wounds with current

The idea of deliberately subjecting yourself to a session of electric shocks may make you cringe, but as a new study has found, it just may be worthwhile if you’re injured, for it speeds up the healing process.

Though first suggested by German physiologist Emil Du Bois-Reymond 150 years ago, this healing method had been ignored. Now, Josef Penninger of the Austrian Institute of Molecular Biotechnology in Vienna and Min Zhao of the University of Aberdeen, UK, have added their support to the theory by demonstrating that natural electric fields and currents in tissue play a vital role in organising the healing process by attracting repair cells to damaged areas.

As a part of the experiment, researchers grew layers of mouse cells and larger tissues, such as corneas, in the lab. They found that by applying varying electric fields to “wounded” parts of the tissues they could accelerate or completely halt the healing process, depending on the orientation and strength of the field.

They then identified which genes were involved in controlling the process. The gene expression of several types of repair cells was affected, including neutrophils and fibroblasts.

“We have not reinvented the cells’ genetic migration machinery. We have simply shown that electric fields switch them on too. We were originally sceptical, but then we realised it was a real effect and looked for the genes responsible. It’s not homeopathy, it’s biophysics,” the New Scientist quoted Penninger as saying.

Mark Ferguson, a wound-healing specialist at the University of Manchester, UK, said that the study proved that heat could heal wounds faster.

“For many years there have been anecdotal reports of the effects of electrical currents on wound healing. This paper not only demonstrates the effects of electrical currents on cellular migration to wound defects, it also provides a mechanistic understanding of how such signals alter cell behaviour,” he said.

Cells and tissues essentially function as chemical batteries, with positively charged potassium ions and negatively charged chloride ions flowing across membranes. This creates electric field patterns all over the body. When tissue is wounded this disrupts the battery, effectively short-circuiting it. The resulting altered fields that attract and guide repair cells to the damaged area. — ANI

THIS UNIVERSE
PROF YASH PAL

We cannot extinguish a petrol fire easily by pouring water on it. Why?

I started thinking about this only after I received your question. I believe the reason for the difference might be the following. A fire flame is produced when the vapour of a combustible gas mixes with oxygen at high temperature. In the case of coal, wood or a candle the combustible gas is produced through the heating of coal, wood or the wax of the candle. If I cool down the coal, wood or the wick of the candle by pouring water, the source of the combustible gas gets throttled and the fire is extinguished.

However, the case of petrol fire is different. Petrol is volatile and you can smell its vapour even at normal room temperature. Petrol is also lighter than water. Pouring water on petrol does not bottle up the vapour, which then continues to feed the fire above.

Oxygen is always available. Therefore one has to find ways of cutting off the oxygen supply. We have to choke the fire. Some times this is done by setting off explosions, which suck out a lot of oxygen from the vicinity of the fire! For ordinary sized fires simpler ways of choking might be used, for example covering the fire with a thick blanket.

Why does a heated glass tube crack when we throw a few drops of water on it?

Ordinary glass expands when heated. This happens to most materials. Glass is a poor conductor of heat. It is also brittle, meaning it would rather break than bend. When we throw some water on the hot glass tube, the portion of the tube on which the water droplet falls is suddenly cooled and wants to contract. This produces larges stresses and breaks the glass. If glass were a good conductor of heat, the spot where the water droplet falls would not cool that much because heat from the neighbouring areas would quickly flow in. If it were not brittle it would only have a dent and a break would be avoided.

It should be pointed out that special varieties of glass have been prepared that have a low coefficient of thermal expansion. Many pieces of equipment and instruments made of such low thermal expansion glass are needed in several scientific and technological applications. They are specially needed for making mirrors of large astronomical telescopes. A telescope mirror made of glass, being rather thick, may not break due to slight differential heating, but it would certainly deform. This would seriously impair the telescope performance. The basic starting point in glass making is usually limestone, sodium carbonate and sand — heated together to a high temperature.

Normal glass is a mixture of calcium and sodium silicates. Special very low expansion materials are sometimes prepared using combinations of lithium, aluminum and silicon oxides.