Secret of Rubber Band

We receive numerous questions from children and students about rubber band, but regret that we are unable to respond to all the questions. To solve this problem we have summarized them together with our answers. Please note that this information is confined to only rubber band made of natural rubber. We hope that this information is useful and informative to those who are curious or interested in the secret of rubber band.

 
Q1 : What is rubber band made of?
A1 :

Main material is "rubber", usually natural rubber, but some types of synthetic rubber are also used to obtain certain specific quality depending on the application. Besides, fillers such as calcium carbonate, carbon black, clay and additives like sulfur, stearic acid, zinc oxide, wax, oil, accelerators are mixed into rubber as ingredients.

Q2 : What is natural rubber?
A2 :

Natural rubber used for making rubber band is in block form made from latex emulsion collected from rubber tree called Hevea Brasiliensis planted in very large scale in tropical countries such as Thailand, Indonesia, Malaysia. Scientifically, natural rubber is "cis 1, 4-polyisoprene" with the chemical  structure of,
 

Q3 :

When natural rubber and its processing technology were discovered?
A3 : 1493 - 1496 :

Christopher Columbus discovered natural rubber in Haiti where he saw the natives there playing with ball made from the  exudation of a tree called "cau-uchu".
1736 :

Natural rubber was introduced to the western world by Charles de la Condamine.
1770 : John Priestly found that natural rubber could erase or rub away pencil mark, hence he called the material "rubber".
1820 :

Thomas Hancock invented a machine called "masticater" that allows the rubber to be softened, mixed and shaped.
1839 : Charles Goodyear discovered the process of vulcanization.
1876 :

H. Wickham collected the seeds and secretly carried over to London from Brazil. Later years, these rubber trees were planted in large scale in Ceylon and Singapore.


Q4 :

How was rubber band invented?
A4 :

It is believed that long-long ago, someone happened to cut an old bicycle inner tube for tying certain object, and then others found it very useful and convenient even though it was not as elastic as today's rubber band. Eventually commercial production commenced with right formulation by business minded people.

Q5 : Why rubber has to be vulcanized?
A5 :

Natural rubber itself is soft, less resilient, broken down easily when over stretched and not able to return to the original shape after being stretched. Moreover, it is easily damaged by heat, sunlight, oil, oxygen and solvent. During a process called vulcanization, the sulphur molecule becomes a bridge between rubber molecules and forms a three dimensional network with help of other ingredients (just like fishing net made of many lines of thread). This network improves the above weaknesses of natural rubber for practical use. Generally, the higher the rubber content, the higher the resilience and elasticity.

Q6 : What is happening inside rubber during vulcanization?
A6 :

At the vulcanizing temperature (practically, 140-200°C)., a complex chemical reaction starts to occur and leads to the formation of sulphur crosslink as shown schematically below,

a, b and c denote the number of sulphur molecules which range from 1-6. X denotes the residual of accelerator.

Q7 : How is rubber band produced?
A7 : Step 1:

Make so-called "compound" by mixing the necessary ingredients into rubber.
Step 2:

Feed the compound into a machine called "extruder" to make into tube form called "tubing", just like making Italian Macaroni.
Step 3:

Put a round pipe into each tubing, and heat up in pressurized steam tank. This pipe gives round shape to rubber band and this heating process is called "vulcanization".
Step 4:

Remove the pipe and cut the vulcanized tubing into "rings" using high speed cutter. These rings are "rubber bands".
Step 5:

Rubber bands are well washed and dried. After quality inspection, rubber bands are packed into bags or boxes for sales.

                                                                       

Q8 : How should rubber band be stored?
A8 :

Products made of natural rubber are, in general, aged faster by exposure to heat, air and sun light. Therefore, rubber bands should be packed, preferably in air tight bag or container, and stored in cool and dark place for securing longer life.


 
Q9 :

What does "Latex Free" mean?
A9 :

Natural rubber contains a series of water soluble or extractable proteins (called "EP") which were reported to be a cause of allergy to the human body when contacted over a long period. Particular attention was bought up over the use of surgical and examination gloves. As these thin rubber gloves are commonly manufactured using liquid natural rubber (called "Latex") collected from rubber trees, they are called "Latex Gloves". 

Word "Latex Free" is often used to mean "Not made from natural rubber latex" or "Not contain natural rubber" in order to indicate indirectly "No risk of latex protein allergy".


 
Q10 :

What is CEC's "Latex Free Rubber Band"?
A10 :

CEC's Latex Free rubber band is made of a type of solid synthetic rubber which does not contain natural rubber just as gloves made from liquid synthetic rubber (called "Synthetic Latex" ) such as nitrile latex.


 
Q11 :

Can Natural Rubber be used for rubber products which may contact human body?
A11 :

Yes, it can be used.  Rubber products made from natural rubber latex used for medical treatment and examination are normally treated in an additional process of the production line in order to minimize the extractable protein content of the product. 

Rubber products made of solid (dry) natural rubber generally contains extremely low level of extractable protein as compared to the natural rubber latex products because of the many washing processes the latex has to go through before becoming solid (dry) rubber in the factory.  Therefore, rubber products made of solid (dry) natural rubber do not normally cause allergy problem in general, particularly when contact to human body is minimum. 

Natural rubber based products with lower natural rubber content have lower protein content inside naturally.


 
Q12 :

Can CEC natural rubber band be used for human contact?
A12 :

Yes,  CEC rubber bands are considered safe in term of protein allergy for non-medical application because they are made of solid (dry) natural rubber and are further washed in steam and fresh water at the final stage of rubber band production in CEC.


 
Q13 :

How much protein is contained in original liquid natural rubber (Field Latex)?  What about protein content in solid (dry) natural rubber made from the field latex?
A13 :

Original liquid natural rubber latex collected from rubber trees (called "Field Latex" or "Hevea Latex") contains  about 1 - 2 % of various proteins, extractable and non-extractable.  Some of these water soluble or extractable proteins are known to cause an allergic reaction. 

Liquid latex after the concentration is adjusted to 60% rubber content (called "Latex Concentrate") as a direct material to produce latex gloves still contains about 1/4 of the total proteins, but the rest, 3/4,  is removed during the concentration process. 

Solid natural (dry) rubber is made from field latex through coagulation, washing and drying processes, and the repeated washing with fresh water in the process makes the extractable protein to the level below 20 micro-gram  per gram of the solid (dry) rubber (mg/g).


 
Q14 :

How much  protein remains in natural rubber products like latex gloves and Rubber bands?
A14 :

Latex Gloves
Extractable protein  content (EP) of latex gloves varies from as low as less than 20 micro-gram per gram of gloves (mg/g) to as high as more than 1000 micro-gram (mg/g) depending on the manufacturing methods and processes.  Well leached powdered gloves and power-free gloves usually show low EP content below 100 mg/g. 

Rubber Band
Rubber band made of solid dry natural rubber contains the extractable protein below 20 micro-gram per gram of rubber band (mg/g) even for high rubber content rubber band. CEC rubber bands show even lower extractable protein (EP) content because of additional washing of the products in it's production process.


 
Q15 :

What is the allowable extractable protein (EP) content level for safety against latex allergy?
A15 :

Although no definite figure has been officially announced by any international organization yet, it is generally known that EP content lower than about 100 mg/g  does not cause allergy except for hypersensitive person.


 
Q16 :

Where such rubber proteins come from?
A16 :

The rubber trees cultured in farms could induce a large amount of various proteins in order to protect themselves from various stresses such as repeated tapping and treatment with plant hormone by changing their physiological conditions besides the proteins involved in rubber biosynthesis. 

These proteins are called "Defense-Related Proteins".  So far about nine of these extractable proteins are said to be possible causes of the allergic reaction.