The process of hardening rubber is known as vulcanization. This method was discovered accidentally in the early 19th century and then developed in order to find some way to make latex, the natural excretion of rubber trees, more rigid and resistant to abrasion. After heat is applied, sulfur and other chemicals are added to natural rubber. The order in which the chemicals are added, as well as their amount and nature, are crucial to the success of the vulcanization process. While still hot, the vulcanized rubber is placed in a mold. Upon cooling, a shaped and hardened rubber remains.
Wear gloves since the rubber vulcanization molding machine will have to heat up to at least 140 degrees Celsius. The machinery will get hot and the molds may still be warm when you remove them. Also, natural rubber is adhesive and will stick to your bare hands.
Mix sulfur into the desired quantity of latex. The amount of sulfur added is determined using a ratio known as parts by weight per hundred parts of rubber (pphr). The standard amount used in industry today is 2.5 pphr. This ratio can be altered to create vulcanized rubber with different properties, but 2.5 pphr ensures the highest level of durability.
Add 1 pphr of zinc oxide to the mixture. This compound activates the vulcanization process and helps the sulfur make better molecular links with the natural rubber. This increases durability in the final product.
Add one of many possible accelerators to the latex mixture. Thiazole and sulfenamide are common choices. The ratio can vary from 1 to 3 pphr.
Add 1 pphr of an anti-oxidant to the mixture. Anti-oxidants will prevent deterioration of the finished product's exterior due to oxidation from molecular oxygen or ozone in the air.
Heat the mixture to somewhere between 140 degrees and 180 degrees Celsius. The temperature maintained throughout the vulcanization will affect the way the sulfur forms a polymer, or chain of molecules, with the natural rubber.
Pour the liquid vulcanized rubber into a mold of your choice. Allow it to cool. The finished product will be durable, resistant to abrasion and oxidation and much harder than the natural latex with which you began the process.
Things You'll Need
- Latex, or natural rubber
- Rubber Vulcanization Molding Machine
- Gloves
- Sulfur
- Zinc oxide
- Stearic acid
- Accelerant (Sulfenamide or Thiazole)
FAQs
Rubber can be hardened through vulcanization, thermal hardening, chemical hardening, radiation hardening and other processes. These processes cross-link the rubber molecules, making it stronger and more durable. The specific hardening method will be selected according to the actual needs of the rubber product.
What is the process of hardening of rubber? ›
Vulcanization (British English: Vulcanisation) is a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to include the hardening of other (synthetic) rubbers via various means.
How to increase the hardness of rubber? ›
Inorder to increase the strength and hardness, they are heated with sulphur for few hours by the process of vulcanisation. Vulcanised rubber is hard, durable and less elastic.
What makes rubber stiff? ›
If the chemistry of the chain is suitable, an atom belonging to one chain can form a chemical bond with an atom from another chain. This bond is called a cross-link. The nature of the cross-linking bonds is covalent. The cross-links inhibit the motion of the polymer chains and so increase the stiffness of the rubber.
How to make rubber stronger? ›
Exposure to heat and sulfur creates new cross-links in the rubber that, ultimately, makes the rubber stronger and more elastic.
What is added to rubber to make it hard? ›
Detailed Solution
The correct answer is Sulphur. Sulphur is used to make natural rubber more strong and bouncy by the process of Vulcanization. Vulcanization of rubber is a process that improves the elasticity of rubber and strength of rubber by heating it in the presence of Sulphur.
What chemical will harden rubber? ›
Vulcanization. A chemical process in which rubber is heated with sulfur to form cross-links between long rubber molecules to improve the hardness, elasticity, and other material properties when needed, such as tensile strength and weather resistance (see Curing above).
How do you increase the stiffness of rubber? ›
Adding carbon black to rubber will increase its stiffness. There are two effects: Firstly, when a composite is made of any two non-reacting materials, the stiffness is the weighted average of the two materials. Therefore, adding any stiffer phase to a material will make it stiffer.
Can rubber go hard? ›
Oxidative rubber degradation can cause hardening or softening, depending on the structure of the elastomer. Hardening is more common because free radicals produced due to heat, oxygen and light combine to form new crosslinks, which reduces the flexibility of the rubber.
What causes rubber to harden? ›
Exposure to oxygen can often cause the rubber to harden, reducing its flexibility and causing cracking. Oxidation and ozone attack occur when oxygen atoms react with the polymer chains within a rubber. Rubbers with double bonds in the polymer chain are particularly susceptible to degradation by oxygen.
The hardening of rubber at low temperatures is one of the well-known physical characteristics of rubber. The loss of elasticity of raw rubber by hardening at 0° to 10° C., its turning to the consistency of glass, and its fragility at −19° C.
How do you increase the tensile strength of rubber? ›
For improving the tensile strength and quality of natural rubber, it is heated with sulphur.
Is there a way to harden rubber? ›
Vulcanization is a chemical treatment process that involves the application of chemicals — usually sulfur — to alter the physical properties of rubber.
What is the process of hardening rubber? ›
Inorder to make the rubber stronger, and more flexible, it is heated with sulphur for few hours. This process is called vulcanisation. Vulcanised rubber is more resistant to heat, and other environmental conditions.
How to stop rubber from drying out? ›
- Store rubber at room temperature.
- Avoid exposure to UV light.
- Wash rubber with gentle cleaners.
- Keep conditioning to a minimum to restore softness.
- Store rubber objects in airtight containers.
Synthetic motor oil or transmission oil will not damage rubber, or other types of o-rings or gaskets.
