Accelerators

Types of vulcanizing accelerators

Sulphenamides:

They offer high scorch safety and cure rate. The more basic is attached amine, more is scorch safety and higher cure rate.Perhaps the most widely used sulphenamide is N-Cyclohexyl-2-Benzothiazole Sulphenamide (CBS) due to balance between scorch safety and cure rate. TBBS is another one which is used for more scorch safety. It produces vulcanizte of high modulus.

Figure 01: TBBS

 Thiazoles:

The most common accelerator related to this group is MBT. Later came MBTS. MBT provides medium vulcanization rate and vulcanizate of relatively low modulus. It can do scorching mainly in NR, during processing of green compound. For scorch safety, small amount of MBTS is added as replacement with MBT. It is common to use secondary accelerator or booster with MBT.

Figure 02: MBT

Guanidines:

The main accelerator is DPG. It has low vulcanization rate and relatively safe in processing. Their main use is as secondary accelerator with sulphenamides.

Thiurams:

The major member is TMTD. They give high vulcanization rate but are seldom used as primary accelerators.

Silicon Rubber

Advantages of Silicon Rubber

1.    Introduction:

Silicon rubber is usually classed as speciality elastomer due to its unique properties and higher price as compared to other common elastomers. There are two types of silicon elastomers. There are thermosetting rubbers that are vulcanized with heat and Room Temperature Vulcanizing (RTV) rubbers.

2.    Advantages:

·        Silicon rubber is resistant to;

Ø Ozone, oxygen, heat (up to 315^oC)

Ø UV light

Ø Moisture and general weathering effects.

·        High degree of flexibility.

·   By replacing minor amount of methyl substituents with phenyl groups, low    temperature flexibility (to low as -100^oC) is improved.

·     By replacing minor amount of methyl substituents with vinyl groups, compression set resistance is improved.

·      Compounded products give above properties plus;

Ø Superior resistant to compression set

Ø Excellent biocompatibility

Ø Vibration damping over wide temperature range

Ø Thermal ablative properties.

·    Long service life plus circuit integrity with no toxic gas generation, have secured placed of silicon rubber for appliance wiring.

·       Good chemical stability and flame retardancy.

·       Distinctive interfacial properties;

Ø Water repellency

Ø Releasability.

·        Good gas and vapor permeability.

·        Good transparency and coloring properties

3.    Conclusion:

Silicon rubbers give wide range of properties under extreme conditions of temperature. Liquid silicon rubbers (LSR) are processed through injection molding in industries.

There are developments in the optimization of LSR injection molding machines for ease to use, aren’t you curious now?