Background on Rubber
Natural rubber comes from rubber producing plants, wherein a milky white fluid, called latex, is extracted from the tree. Though there are numerous plants that can provide latex, historically the most notable one has been the Hevea Brasiliensis tree found in South America, and more recently from a commercial viability standpoint in Indonesia, Sri Lanka, and on the Malay Penninsula, where current estimates are that approximately 90% of all natural rubber originates.
The rubber trees are “tapped” by making a diagonal cut in the bark of the tree, where the latex then slowly escapes via dripping, and is collected. The average annual output per tree is approximately 5.5 pounds of the liquid. Being that latex consists of approximately 30-40% rubber particles, 55-65% water, and then minor amounts of protein, sterol glycosides, resins, ash, and sugars, in order to extract the rubber from the latex it must be done through mechanical separation. The latex is strained, mixed with water, and then treated with an acid to force the suspended rubber particles to congeal. The congealed rubber is then pressed into thin sheets, and left to dry for further use and/or processing.
HISTORY OF RUBBER DEVELOPMENT
The first known use of rubber is hard to trace back, but it is recognized that the first use dates back to the 11th century when in Central and South America rubber was used to coat fabric to increase its’ water resistance. Later in the 1700’s, a French scientist and traveler brought back rubber, from South America, to Europe, where the development of rubber really started to take off commercially. In 1770 a British chemist by the name of Joseph Priestley coined the term Rubber. In 1818, the first real commercial use of applying rubber to fabric was done, which was subsequently later patented by Charles Macintosh in 1823. Also during this period in early 1820’s, a method to shape rubber was developed, and then in around 1850, Charles Goodyear discovered the process of vulcanization, where you heat rubber with sulfur, which crosslinks the rubber, decreasing it tackiness, as well as decreasing rubbers’ sensitivity to hot and cold. In 1882, John Boyd Dunlop patented the pneumatic tire, bringing rubber to significant prominence. This influx of demand for rubber, through the tire development, depleted the supply, leading the British to import rubber trees from South America to begin plantation growth, first in Singapore, Malaysia, and Sri Lanka. In the early 1900’s, much more scientific and chemical development was done on rubber to try to improve its’ properties. This proved critical for Germany when during WWI their rubber supplier were cut off, and they had to begin developing synthetic rubber. Then in WWII, the US was faced with a similar reality when Japan cut gained control of the majority of the Asian rubber supply destined for the US market. In response, the US focused on its’ development of Synthetic rubber. In 3 years, from 1941 to 1944, the US increased its own synthetic rubber production capacity by 10,000%. After the war, many countries followed suit, developing their own synthetic rubber production facilities, to remove the reliance on others.
PRODUCTION OF NATURAL RUBBER
Growing natural rubber involves many steps, and numerous scientific disciplines to be merged together to provide a cohesive operation and plan.
- Planting – Seeds are planted and grow for between 12-18 months before being suitable for grafting, after which they are removed from a nursery environment and planted on a plantation. The bud quickly grows but the tree must be left to mature for between 6-7 years.
- Tapping – Harvesters shave off a bit of bark, and then notch a line in the revealed bark to a depth of about 1/3” deep. The milky white liquid, latex, drips from the cut vessels, and then flows down the barkless patch, where it is collected, typically in a cut mounted to the tree. This tapping continues on alternating days, with new patches being cut just below the prior one, until the tapping is about a foot from the base of the tree. Once that side of the tree is tapped out, a repeat effort is done on the other side of the tree. Each tapping produces less than 8 ounces of latex before the barkless spot is covered with coagulated latex (much like a scab on a cut).
- Liquid Processing – Once transported to the processing facility, the latex mixture is further processed into a concentrated liquid by removing water, effectively increasing the rubber content (to approx. 60%), which is then supplied to factories for the use mainly in the adhesive and coating industries.
- Dry Processing – Once the concentrated liquid is removed, the remaining rubber and latex mixture is treated with acid to congeal and coagulate, before be forced through a large extrusion dryer to remove all the remaining water, leaving just dry crumb rubber. The crumb can be used as it is, or be further processed into sheets, slabs, placed into a mold, or can then be joined with other components/chemicals to further expand the potential uses (examples being steel reinforced tires, or latex surgical gloves).
Synthetic rubber is made from two petroleum based unsaturated hydrocarbons, styrene and butadiene. Due to the relative difficulty in the production of natural rubber (due to time and geographic presence of the plantations), synthetic rubber has reigned king for many decades. Typically, synthetic rubber is developed for specific applications, and is specifically for those applications due to the process used to make them, and the resulting properties.
The production of natural rubber has failed to meet the growing demand for rubber, and today two-thirds of the world’s rubber is synthetic. Manufacturing developments, such as the invention of epoxidized natural rubber, may reverse this growing synthetic rubber trend, but at the same time synthetic rubber is benefiting from manufacturing developments that make the production more efficient, less costly, and with lower polluting effects to the environment. Time will tell what happens within the rubber industry, but for sure, one main focus will be recycling rubber and finding new applications with the old material.
Though there are as many as 2,500 other plants that produce rubber, it is not made fast enough to be profitable. United States Department of Agriculture researchers are looking at ways to speed up the process by genetically engineering a plant to make larger initiator molecules. These molecules start the rubber-making process, and if such molecules were larger, rubber could be produced up to six times faster.