The Different Types of Rubber

8 Different Types of Rubber Materials

The Right Material for Every Molded Product

Custom Rubber Corp. has the ability to use all the common rubber polymers when molding product, and a few very specialized rubber materials. These include:

Identifying Cost Savings
Custom Rubber Corp. has access to over thirty chemists through our network of strategic mixing partners, the majority of which are within a one hour drive from our facility. We are experts at identifying the best, most economical material source for any and every application or part.

A Beginner's Guide to Rubber : Organic Rubber VS. Synthetic Rubber

This is part one of our three-part series on rubber compound creation and rubber molding.

Organic Rubber VS. Synthetic Rubber

Organic rubber comes from natural or synthetic rubber polymers. Natural rubber comes from trees and plants, mainly in the form of latex, and is useful for its water resistance, high resilience, and large stretch ratio. Synthetic rubber comes from petroleum and is manufactured in chemical factories. Of approximately 15 billion kg of rubber produced annually, two-thirds is synthetic. Both natural and synthetic rubber is mixed with various quantities of carbon black and/or other non-black ingredients to create a rubber compound that meets various specifications. The actual rubber mixing with various ingredients is as much an art as it is a science. Parts per hundred of rubber (phr) is the measurement unit used to distribute various uncured rubber polymer, carbon black and non-black fillers, plasticizers, age resistors, vulcanizing ingredients, activators and other special purpose ingredients. The crude rubber is typically 100 phr of the formula and is not usable in its crude state. It usually needs to be vulcanized or cured (i.e. heated) to fasten chain molecules of monomers into cross-linked polymers in order to be usable after the rubber has been fully compounded. The crude rubber is typically mixed with approximately 50 phr of fillers. These fillers are grouped into carbon blacks and non-black fillers, typically in powder form. Carbon blacks play a part in determining the cure time and particle size of the rubber, which is marked by the American Society for Testing and Materials (ASTM) by N as normal cure time, or S as a slow-curing black filler. Non-black fillers, such as clays, calcium carbonate, silicates and silicas are added for economic or technical purposes. Some extend the product quantity, making it cheaper, while others reinforce the product and enhance tensile strength and tear and abrasion resistance. Fillers are divided into two large groups: reinforcing and non-reinforcing; but it's a hard distinction as many filler have intermediate properties.

Plasticizers & Age Resistors in Rubber Manufacturing

Plasticizers are usually added in small 2-20 phr increments to act as an extender to make the final product less expensive, or a processing aid to facilitate the manufacturing operations. It also acts as a modifier for certain vulcanizing properties. Petroleum oils are the most widely used as an extender and processing aid. These help in preventing misshapen molds and improving low temperature properties. Age resistors, or anti-degradants, are organic substances usually added in small amounts (1-4 phr) and retard deterioration caused by aging, extending the service life of the elastomeric product involved. They also serve to protect the rubber compound from oxygen, ozone, heat, sunlight, high energy radiation and high humidity. Age resistors come in two categories, the staining and nonstaining protectants. The latter does not discolor the rubber compound but is less effective than the staining protectant, which does exactly what its name implies.

Vulcanizing Ingredients in Rubber Creation

There are two types of vulcanizing ingredients classified by their functionality: accelerators and activators. Sulfur, or peroxide, are the main ingredients for vulcanization; however, these alone would take rubber compounds hours to cure. Accelerators increase the speed of vulcanization from hours down to minutes or even seconds. Accelerators range from Slow, to Moderately Fast, to Fast, and finally to Ultra Accelerators. Activators, added in small increments, increase the effectiveness of the accelerators. Special-purpose ingredients are not necessary in a majority of rubber compounds. However, they can be an added benefit by adding color, enhancing heat resistance, eliminating odors, or being anti-static agents. Coloring agents are divided into inorganic and organic pigments. Inorganic pigments are stable in heat and light and have little to no tendency to chalk or bloom; however, they do not produce bright colors, and large amounts are needed to create a certain intensity. They can also react with acids and alkalies. Organic pigments produce intense colors with relatively little pigment, but they have limited stability in the presence of heat and light. They also tend to bloom and chalk, react to many chemicals and can dissolve in many organic solvents and liquids. Flame retardants are chemicals added that reduce the flammability of the end product. Odorants can mask the characteristic odor of some rubber compounds, with vannilin frequently used to impart a pleasant scent. Anti-static agents are used to reduce the accumulation of dust or dirt on certain finished products and reduce the possibility of static discharge of accumulated static electricity. Blowing agents, retarders, and peptizers can also be added. Blowing agents are gas-generating chemicals that are necessary to create sponge or microporous rubber products. Retarders are substances used to reduce premature vulcanization during factory processing. Peptizers are added to facilitate the softening of crude rubber when being mixed, speeding up the mixing process. All these agents have different purposes and are added in exact proportions in an open mill or an internal mixer to create the final rubber compound. An open mill consists of two adjacent large steel rolls that roll in opposite directions to soften and mix the compound. Internal mixers can also be used and have a faster mixing time and tend to disperse the materials more efficiently. The finished compound is then sent to a rubber molding or extruding plant to make a finished rubber product. Stay tuned for part two to learn the basics of rubber molding, vulcanization, and finishing.