THE VULCANIZATION OF RUBBER

The picture show a bowling ball that have undergo vulcanization process.Charles Goodyear (1800–1860) invented vulcanization of rubber when he was experimenting, and heated a mixture of rubber and sulfur.Vulcanization or vulcanisation is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur or other equivalent "curatives." These additives modify the polymer by forming crosslinks (bridges) between individual polymer chains.^[1] Vulcanized material is less sticky and has superior mechanical properties. A vast array of products are made with vulcanized rubber including tires, shoe soles, hoses, and hockey pucks. The process is named after Vulcan, Roman god of fire. Hard vulcanized rubber is sometimes sold under the brand names ebonite or vulcanite, and is used to make hard articles such as bowling balls and saxophone mouth pieces.

Process

Vulcanization is generally irreversible, similar to other thermosets and in contrast to thermoplastic processes (the melt-freeze process) that characterize the behavior of most modern polymers. The cross-linking is usually done with sulfur, but other technologies are known, including peroxide-based systems.
The main polymers subjected to vulcanization are polyisoprene (natural rubber) and styrene-butadiene rubber (SBR), which are used for most passenger tires. The "cure package" is adjusted specifically for the substrate and the application. The reactive sites—"cure sites"—are allylic hydrogen atoms. These C-H bonds are adjacent to carbon-carbon double bonds. During vulcanization, some of these C-H bonds are replaced by chains of sulfur atoms that link with a cure site of another polymer chain. These bridges contain between one and eight atoms. The number of sulfur atoms in the crosslink strongly influences the physical properties of the final rubber article. Short crosslinks give the rubber better heat resistance. Crosslinks with higher number of sulfur atoms give the rubber good dynamic properties but with lesser heat resistance. Dynamic properties are important for flexing movements of the rubber article, e.g., the movement of a side-wall of a running tire. Without good flexing properties these movements rapidly form cracks and, ultimately, make the rubber article fail.

 Vulcanization methods

A variety of methods exist for vulcanization. The economically most important method (vulcanization of tires) uses high pressure and temperature. A typical vulcanization temperature for a passenger tire is 10 minutes at 170 °C. This type of vulcanization is called compression molding. The rubber article is intended to adopt the shape of the mold. Other methods, for instance to make door profiles for cars, use hot air vulcanization or microwave heated vulcanization (both continuous processes).
Five types of curing systems are in common use. They are:

1. Sulfur systems
2. Peroxides
3. Urethane crosslinkers
4. Metallic oxides
5. Duece

   that how the vulcanization process conducted in industry scale.
   

THE UNIVERSE

can you imagine if there is no particle in our universe??our earth is made up from particle of death star.the stars made many kind of material such as iron,calcium,helium,carbon and etc.this particular star used up hydrogen gas with help of gravity to form new type of atom.Scientist have do many research about universe.I have some information about how universe exist.

According to the prevailing scientific model of the universe, known as the Big Bang, the universe expanded from an extremely hot, dense phase called the Planck epoch, in which all the matter and energy of the observable universe was concentrated. Since the Planck epoch, the universe has been expanding to its present form, possibly with a brief period (less than 10⁻³² seconds) of cosmic inflation. Several independent experimental measurements support this theoretical expansion and, more generally, the Big Bang theory. Recent observations indicate that this expansion is accelerating because of dark energy, and that most of the matter in the universe may be in a form which cannot be detected by present instruments, and so is not accounted for in the present models of the universe; this has been named dark matter. The imprecision of current observations has hindered predictions of the ultimate fate of the universe.
Current interpretations of astronomical observations indicate that the age of the universe is 13.75 ±0.17 billion years,and that the diameter of the observable universe is at least 93 billion light years or 8.80×1026 metres.According to general relativity, space can expand faster than the speed of light, although we can view only a small portion of the universe due to the limitation imposed by light speed. Since we cannot observe space beyond the limitations of light (or any electromagnetic radiation), it is uncertain whether the size of the universe is finite or infinite.Our universe now continue to expand.We have to thank to God because of His ultimate creation and allow us to live in this universe.

my pet

this is my sharky,

it is my favourite pet ever!!

walaupun pernah gigit saya dulu...

mungkin kurang kasih sayang kali...

hahaha...