The Effect of Different Types of Rubber Softeners on the Regeneration Process of Reclaimed Rubber

Reclaimed rubber is obtained from the physical and chemical process of grinding, heating, vulcanizing which are applied to the old rubber scrap. It has a certain plasticity and viscosity. It can be reused and vulcanized again.

In the production of reclaimed rubber, rubber softener and activator are required to break part of the molecular chains and cross-linking points of the vulcanized rubber under the combined action of oxygen, heat and mechanical shearing force. And the rubber softener is very important for the production of reclaimed rubber.

The rubber softener is a low molecular substance, which easily enters the vulcanization network during the regeneration process of the vulcanized rubber, and acts as a swelling and plasticizing agent. The softener will relax the network structure of the vulcanized rubber and increase the oxidative penetration. This provides a convenient condition for the oxidative breaking of the crosslinked network structure and reduces the possibility of re-structuring of the rubber network structure in the vulcanized rubber, thereby accelerating the regeneration process of the reclaimed rubber.

The rubber softener itself has a certain viscosity and is soluble in rubber. After desulfurization at high temperature, it can be retained in the rubber compound to significantly increase the plasticity and viscosity of the finished reclaimed rubber. In the production of reclaimed rubber, the amount of softener should be controlled between 10-20%. Coal tar, pine tar, rosin, tall oil, dipentene, etc. are commonly used softeners. Different kinds of softeners can produce different reclaimed rubbers.

1.Coal Tar

The main components of coal tar are phenols, alkyl aromatic hydrocarbons, naphthalene, anthracene, pyridine, and asphalt. It is most commonly used in the production of reclaimed rubber in the early days. High-temperature coal tar is suitable for producing ordinary reclaimed rubber. Solid coal tar can be used in the production of high tensile strength reclaimed rubber. However, the reclaimed rubber produced by using coal tar as a softener is highly polluting with irritating odor, and has been banned by many countries.

2. Pine Tar

The main component of pine tar oil is resin acid, which is the product of pine root and trunk after retorting, which helps to improve the viscosity of rubber compound. It can improve the processing performance and physical machinery properties of reclaimed rubber during the regeneration process of vulcanized rubber and waste rubber products. Pine tar is mostly used to produce odorless reclaimed rubber.

3. Tall Oil

The resin acid and fatty acid in tall oil account for about 40% each. It is easy to separate the rosin during storage. As a softening agent, it needs to be heated during the reclaiming process of vulcanized rubber. Its pollution is less and mainly used to produce the environmentally friendly reclaimed rubber.

The rubber softener not only affects the quality of reclaimed rubber, but also affects the quality of rubber products containing reclaimed rubber. If the inferior softener or polluting softener is used in the production of reclaimed rubber, then the rubber products can have quality problems easily, including low mechanical strength, discoloration migration and failure to meet relevant environmental-friendly and odorless standard.