Natural vs. Synthetic Rubber

I read this piece of news about the fate of natural rubber in this link:

https://www.thestar.com.my/business/business-news/2024/10/01/rubber-industry-embraces-green-growth

 Natural rubber is slowly being replaced by the synthetic analogue which is cheaper and easier to manufacture from petroleum similar to a lot of drugs now made from petroleum introduced by Rockefeller to “cure” lifestyle diseases here:

https://meridianhealthclinic.com/how-rockefeller-created-the-business-of-western-medicine/

 I have zero or almost zero knowledge about rubber or its chemistry. Here’s what I know about rubber.

Let me start with what I know by looking at the chemical composition and differences between natural and synthetic rubber. The source of natural rubber is primarily obtained from the sap (latex) of rubber trees (Hevea brasiliensis). The chemical structure and primary component of natural rubber is polyisoprene, which is an organic polymer made of repeating isoprene units (C₅H₈). The polymer has a cis configuration, making it highly elastic. The formula for polyisoprene is [C₅H₈]_n  where, n represents the number of repeating units in a polymer.

Compared with synthetic rubber, the source is made from petroleum-based products using chemical processes (e.g., polymerization of specific monomers). There are various types and compositions of synthetic rubber.

Here are some that I know. Styrene-butadiene rubber (SBR) is possibly commonly used and is made from styrene (C₈H₈) and butadiene (C₄H₆). Another is the nitrile rubber (NBR) made from acrylonitrile and butadiene. The third type I know is chloroprene rubber (CR or neoprene) made from chloroprene (C₄H₅Cl).

Other types of synthetic rubber include ethylene-propylene-diene monomer (EPDM) and silicone rubber.

As far as the differences between natural and synthetic rubber is concerned, it depends on the source. Natural rubber is harvested from trees, while synthetic rubber is derived from petrochemicals. In terms of properties, natural rubber has excellent elasticity, tensile strength, and resistance to wear and tear. It is more biodegradable but can degrade faster in extreme temperatures and with exposure to ozone or certain chemicals.

However, synthetic rubber is tailored for specific properties, such as better resistance to oil, chemicals, and temperature variations. Some synthetic rubbers, like SBR, are more durable under specific conditions but may lack the same elasticity or tensile strength as natural rubber.

As far as environmental impact is concerned, natural rubber is renewable and biodegradable, whereas synthetic rubber production relies on non-renewable fossil fuels. But which is better, natural or synthetic rubber?

As far as I know, natural rubber is better for applications where elasticity and tensile strength are important, such as tires and gloves. It performs well in shock absorption, whereas synthetic rubber is preferred in situations where resistance to chemicals, heat, and oils is crucial, like in automotive parts, industrial gaskets, and seals. That’s all I know on the chemistry and application of natural vs. its synthetic analogue.

However, I am more interested in physics than in chemistry. Thus, let me briefly talk a little about the tensile strength and elasticity of rubber.

Tensile strength is the maximum stress that a material can withstand while being stretched before breaking. The tensile strength is typically measured in megapascals (MPa). Elasticity of rubber is its ability of rubber to return to its original shape after being stretched. Elasticity is often quantified by Young’s modulus or the modulus of elasticity.

Let’s now have a look at the mathematics behind their measurements

The formulas for tensile strength and elasticity are:

Tensile Strength (σ) is

σ (sigma) = F / A​

Where:

F = Force applied (in newtons, N)

A = Cross-sectional area of the rubber (in square meters, m²)

Young's Modulus (E): (For elasticity)

E = Stress / Strain

Where:

Stress (σ): The force per unit area (N/m² or pascals)

Strain (ε): The relative deformation, calculated as the change in length divided by the original length:

 ε (epsilon) = ΔL / Lo​

 Where:

Lo = Original length

Δ (delta) L = Change in length

Additional parameters on the physics of rubber are its elongation at break point.  This indicates how much a rubber material can stretch before it breaks, expressed as a percentage of its original length. The modulus at 100% elongation (M100) is a value that measures the stress required to stretch the rubber to twice its original length.

This mathematics on rubber stretchability and elasticity is similar to what I wrote earlier about bungee jumping here:

https://scientificlogic.blogspot.com/2024/09/the-physics-in-bungee-jumping-without.html

 Both natural and synthetic rubber have their strengths and weaknesses, and the choice depends on the specific application.

jb lim