Difference Between Vulcanized and Unvulcanized Rubber

Main Difference – Vulcanized vs Unvulcanized Rubber

Vulcanization is a chemical process which enhances the properties of most elastomers including natural and synthetic rubber products. It is considered as the most revolutionized invention in the polymer industry. Vulcanization was first discovered by Charles Goodyear. However, it was Thomas Hancock who first patented a commercial method for vulcanization. The rubbers that are not undergone the process of vulcanization are called unvulcanized rubbers. The main difference between vulcanized and unvulcanized rubber is that vulcanized rubber retracts to its original shape even after applying a large mechanical stress.

This article provides an overview of,

1. What is Vulcanized Rubber?
     – Definition, Properties, Process of Vulcanization

2. What is Unvulcanized Rubber?
     – Definition, Properties, Structure

3. What is the difference between Vulcanized and Unvulcanized Rubber? 

What is Vulcanized Rubber

Rubber that has undergone the process of vulcanization is called vulcanized rubber. During the process of vulcanization, chemical bonds are formed between the independent polymer chains of a particular rubber, resulting in a molecular network within the polymer matrix. These new chemical bonds are often called cross-links. Chains of sulfur atoms, single sulfur atoms, carbon-carbon atoms or polyvalent metal ions may form these cross-links. Vulcanized rubber becomes stiff and less sticky due to the formation of this molecular network. Most importantly, the vulcanized rubbers retract to their original shape upon the release of large mechanical stresses. Thus, the process of vulcanization reduces the amount of permanent deformation and increases the retroactive forces. In other words, the process of vulcanization decreases the plasticity, while increasing the elasticity.

There are four types of vulcanizing systems (curing systems);

– sulfur system,

– peroxide system,

– urethane crosslinkers,

– metal oxides.

The sulfur system is the most common and widely applying curing system in the world. It is a slow vulcanizing system that requires a large amount of sulfur, high temperatures and long heating periods. The most critical parameters of the process of vulcanization include the time elapsed before it starts (scorch time), the rate of vulcanization and the extent of vulcanization. An instrument called rheometer can be used to determine these parameters. 

Sulfur vulcanization system

What is Unvulcanized Rubber

The rubber that has not undergone the process of vulcanization is called unvulcanized rubber. Unvulcanized rubber is not strong and easily undergo permanent deformations when a large mechanical stress is applied. Unvulcanized rubbers are usually sticky.

Natural and Synthetic Precursors to Polyisoprene

Difference Between Vulcanized and Unvulcanized Rubber

Definition

Vulcanized Rubber: Vulcanized rubber is rubber that has undergone the process of vulcanization.

Unvulcanized Rubber: Unvulcanized rubber is rubber that has not undergone the process of vulcanization.

Structure of the Rubber

Vulcanized Rubber: Vulcanized rubber has an intermolecular system with highly cross-linked polymer chains.

Unvulcanized Rubber: Unvulcanized rubber only has polymer chains, doesn’t have cross-links or intermolecular networks.

Process

Vulcanized Rubber: The process is carried out by heating the rubber, mixed with a vulcanizing agent in a mold under pressure.

Unvulcanized Rubber: Such a process is not needed.

Deformation under a large mechanical stress

Vulcanized rubber: Vulcanized rubber forcibly retracts to its original shape without imposing deformations once the mechanical stress is released.

Unvulcanized rubber: Unvulcanized rubber imposes deformation when undergoing large mechanical stresses.

Chemical Composition of the Initial Polymer

Vulcanized rubber: Chemical composition is changed by the addition of curing agents.

Unvulcanized rubber: There is no such change in chemical composition.