Understanding the Limitations of Natural Rubber in Product Design
How much do you know about the material limitations of natural rubber in product design? Most product designers and engineers are well aware of the advantages of natural rubber – high elasticity, high tensile strength, excellent compression set, high stretch recovery, good resistance to alcohols, ketones, and organic acids. These properties make natural rubber an optimal material for a variety of applications that require repeated stretch and recovery or compression and recovery. Natural rubber is a versatile material but there are applications where it is not the optimal material. Product designers will often focus on all of the advantages of natural rubber and forget to take into account the limitations of this natural material. It’s important to have an understanding of the advantages and limitations of natural rubber early in the design process before costly errors are made.
One of the biggest limitations of natural rubber is its poor resistance to hydrocarbons, fats, oils, and greases. Contact with these substances can cause swelling, softening, or complete dissolution of the rubber part resulting in partial or complete failure. This is the primary reason natural rubber is not an optimal material choice for certain industrial sealing or gasketing applications that involve any of these substances. At The Hygenic Corporation, we once received a request for rubber tubing as part of a new product design in which the rubber tube would house oils. The designer opted for natural rubber in his design due to its elastic properties; however, he failed to account for the fact that natural rubber cannot withstand exposure to oils without degrading. He was in final design stages and assumed he would be able to easily source all of his desired parts, including the rubber tube. This was perhaps a costly mistake because his product was designed around a stock rubber tube that would not be able to withstand the effects of the oil. If he were earlier in his design process, the team at the Hygenic Corporation could have guided him to a better choice, or custom formulated a rubber tube that may have worked. Unfortunately, he was too far along in his design process to allow any time for customization. Stories like this are why we strongly encourage designers and engineers to speak with us early in their design process to allow time for customization and testing.
A rubber manufacturer can usually optimize the rubber part for the intended application by enhancing or diminishing certain material properties in the compound. It’s also important to note that when customizing formulations, compromises on other properties will likely be required If a property, like ozone resistance, is enhanced there will be another property, such as elasticity, that will be slightly compromised. It’s important to speak with an expert to understand what customization is possible and any tradeoffs that may occur.
Another limitation of natural rubber is the vulnerability it has to ozone and weather elements, especially if there are no anti-ozonants added to the compound. However, there are instances where a product design requires the elastic properties of natural rubber and biodegradability; in this case it is an optimal material choice. Even with the addition of anti-ozonants, designers and sourcing engineers must evaluate how long the enhanced natural rubber part can last in their product design and any effects degradation will have on the product. At Hygenic, we once received a request for rubber sheeting with a 20-25 year life expectancy as part of a design that would indirectly expose the rubber sheeting to UV rays and weather elements. Unfortunately, even if the rubber part was stored in ideal conditions and not repeatedly used, it would still degrade over time because it is a natural product. So, by exposing the rubber part to elements, like UV rays or weather, it will degrade even quicker, much sooner than 20-25 years. The life expectancy of a rubber part will vary depending on many factors and it’s imperative that the designer conducts feasibility studies to confirm whether or not natural rubber is the optimal choice for their intended application.
Another concern with natural rubber is that it may contain latex proteins that are known to incite allergic reactions in those who have a latex allergy. While the presence of rubber proteins can be reduced to near or below detectable levels, an allergic individual may still react to the part. This is the main reason that many medical applications no longer use natural rubber as a material n their product designs. Many companies have opted for synthetic rubber because it does not contain the latex proteins but still exhibits properties similar to natural rubber. About 30 years ago, Hygenic accepted the challenge from one of their medical customers to create a disposable tourniquet strap that was made of synthetic rubber. As a result, a synthetic rubber formulation was created that very closely mimics the properties of natural rubber latex but does not contain the latex proteins and is now widely used in many of our medical applications.
Using synthetic rubber to protect people from latex proteins is just one example of the viable natural rubber alternatives that are available. In addition to synthetic rubber, there are special thermoplastic elastomers (TPEs) that can also be an alternative. The suitability of each material will have to be evaluated separately because each material has their own set of advantages and limitations. For example, TPEs typically are not a good material choice in applications where heat is a factor because the material will soften as it’s not crosslinked like a vulcanized rubber material.
Understanding the limitations of natural rubber, or any of the design’s intended materials, is crucial for a successful product design. As for rubber, it’s also important to be aware that there is a certain amount of formulation customization that can happen to tailor the properties of the material to a specific application. This is why product prototyping is so highly recommended before a final material is selected. It is also typically helpful to speak with a rubber manufacturer or custom compounder early in your design process to learn what is possible.If you are working on a product design or are sourcing a new part and have a prototyping or material formulation question, please fill out our contact us form to have a technical expert contact you.
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