differences between synthetic and natural rubber

2 ANSWERS

1. amomipais82
   

   HI,
   That's a great question, but kind of difficult to answer in an easy way.
   
   If you look at big tyres used on mining vehicles and heavy trucks, you'll find they have a higher percentage of natural rubber than synthetic.
   
   And in car  / light truck tyres, those tyres tend to have a higher percentage of synthetic rubber.
   
   But it's not really about whether natural or synthetic is better for "tyres" as such. It's about whether a particular type of material is better for the job it has to do.
   
   First, just in case you didn't know, there are a lot of different types of synthetic rubber. The ones most commonly used in tyres are
   
   * BR (butadiene rubber)
   * SBR (Styrene-butadiene rubber)
   * IIR (Butyl rubber -- or halo-butyl rubber)
   
   Second, when you build a tyre -- or any other rubber product -- you never use a pure elastomer, it is always mixed up into a compound and then cooked -- very much like baking a cake. You take 12 to 15 different ingredients, mix them up and then cook them. Before cooking, the rubber is called 'green' or uncured. During cooking a chemical reaction happens, which permanently changes the material (just like baking a cake).
   
   So the engineers select a base elastomer and a specific   compound or recipe for each of the seven to ten different  parts of a tyre. Each of those different components has to do a job, but in each case, the job is different and requires different characteristics.
   
   One part of the tyre is the inner-liner. It is the part of the tyre furthest away from the outside. It has one key job to do, and that is to keep the air inside the tyre, rather than letting it escape through the wall of the tyre. The inner-liner is made from a compound based on halo-butyl rubber, because that stuff is almost impermeable to gas.
   
   Another part of the tyre is the tread. That's the part which touches the road surface. In car tyres, that has a difficult job to perform. It has to do three main things:
   
   * Grip the road when cornering
   * Not wear too fast, to provide good life
   * Help with fuel ecnomy by not wasting too much energy.
   
   The best way to achieve that is to use a rubber compound based on synthetic rubber — often a mixture of a particular type of SBR called S-SBR mixed with BR. That is mixed together with a lot of silica and other ingredients to get a good combination of properties that deliver the three key benefits described above: good wear resistance, good grip and low rolling resistance.
   
   Other parts of the tyre such as the carcass, the sidewall, the under-tread and so on, need other properties. The tyre makers choose a compound that gives the best combination of properties for each of those different components. That compound might be based on SBR or BR or Natural rubber (NR) or something else entirely.
   
   Just in case you were wondering, it's not really a price thing. NR and SBR / BR cost  roughly the same amount, and the money you can save by selecting one material over another is not really enough to make a difference to the selling price. Besides, the cost differential changes with time and there is a cost associated with every change in the recipes and other process conditions. The end result is that the base elastomer tends to be chosen regardless of cost, and more on the specific performance benefits that one compound can offer over another.
   
   Well, not quite regardless of cost. Cost is certainly a big deal in tyre manufacture, but if cost is a problem, then the tyre makers try to save money in other areas, rather than switching between NR and SR.
   
   It is possible to cross substitute between natural and synthetic materials, but the  scope for cross-substitution is limited. Only about 5 to 10 percent of the material can be substituted. This means that for any given application -- tread in a truck tyre or carcass in a car tyre, for example -- the base material is fixed by the properties you need to make a good tyre.
   
   Big, heavy duty tyres tend to need different properties and characteristics from car tyres, so the combination of compounds chosen for each part of the tyre is different from  the combinations chosen for car tyres.
   
   In general -- but it's a huge over-simplification -- NR is used in tyres that need to deliver long life, good fuel economy and carry heavy loads.
   
   Hope this helps -- I'd be fascinated to find out why you're asking, though.

   Report (0) (1)  |   12 years, 7 month(s) ago  

2. Guest3261
   

   your full of s**t mate. you dont know what your on about.

   Report (2) (0)  |   12 years, 7 month(s) ago