All About Rope Construction
Rope seems so simple, yet the construction and fibers used can have a huge impact. Understanding the characteristics of different fibers is key to choosing the right product for your individual application. Let’s start by identifying three types of fibers and seven common materials used to make them.
As the name implies, this is comprised of a few individual strands about 1/100th of an inch thick that are fed in parallel into the braiding process.
Exceptionally thin (about 1/10,000th of an inch) strands are bundled together when fed into the weaving process. This is the most common type of strand found in ropes as production costs are reduced.
These are shorter fibers that are bundled together to create a strand. The finished product is typically less uniform and rougher to the touch.
The intricacies of fiber composition have sometimes led companies to trademark names for a fiber. The trademarked name then can become a catch phrase for the product. A common example of this in the fiber world is Dyneema® and Spectra®, which on a molecular level are the exact same product (UHMWPE) made in different factories.
ULTRA HIGH MOLECULAR WEIGHT POLYETHYLENE (UHMWPE) = DYNEEMA®
The Dutch chemical corporation DSM changes polyethylene on a molecular basis, turning the fibers in one direction to make Dyneema®. The result is a material that exhibits increased breaking loads and reduced stretch. The polyethylene base means that it has a very low specific weight making it float. It also has good abrasion and UV resistance. The primary weakness of Dyneema® is that it creeps, meaning that over time and under load the fibers permanently elongate or stretch.
LIQUID CRYSTAL POLYMER (LCP) = VECTRAN®
Hoechst Celanese, the U.S.-based corporation, produces liquid crystal polymers (LCP) under the Vectran®. These are highly complex, modified polyester chains producing a fiber with minimal stretch, highest breaking loads, high temperature resistance, and low sensitivity to bending and sharp edges. What is more, unlike Dyneema® it does not creep. However, its big shortcomings are its low UV resistance and the high price of its raw materials. Therefore, it is indispensable to surround a Vectran® core with a protective cover in order to counteract its UV instability.
ARAMID = KEVLAR®, TWARON® OR TECHNORA®
Japan-based Teijin produces Twaron® and Technora® fibers, while U.S.-based DuPont produces Kevlar®. Each of these products is a para-aramid fiber made of co-polymers. This fiber has an exceptionally high breaking load with zero stretch and exceptional temperature resistance, but weakens significantly around sharp bends and can be sensitive to long exposure of sunlight.
POLYESTER (PET OR PES)
Polyester is the workhorse of the rope industry and offers a great number of chemical and physical advantages. While the breaking loads and stretch characteristics are weaker than UHMWPE, LCP, or Aramid, it has great abrasion resistance in both dry and wet conditions, good UV resistance, and a much lower cost. You will find PES used as the primary material in cost effective line or used as a cover for high tech fibers to improve abrasion resistance or protect the core from sunlight exposure.
Some applications require higher stretch qualities combined with high load capacity. PA offers this combination as well as the ability to withstand wet and dry conditions. One downside is that when submerged for longer periods of time, PA can become stiff. Extended exposure to sunlight is also not recommended.
Polypropylene (PP) = XLF
PP is extremely lightweight, floats, and has great resistance to abrasion. The product has a high stretch factor compared to the other fibers we have covered and a lower breaking strength, which should be taken into consideration when specifying the fiber for an application. Sometimes the stretchiness can be advantageous, you will commonly see this used as a towline for small boats.
POLYBENZOXAZOLE CRYSTAL POLYMER (PBO) - ZYLON
The Japan-based Toyobo corporation produces polybenzoxazole crystal polymer under the name PBO. PBO is a high-tech fiber that combines the highest breaking loads with minimal stretch and high temperature resistance. Its only weakness is its extremely low resistance to sunlight. PBO is an emerging fiber in the rope industry offering significant improvements over all other options, but the high price and rapid degradation when exposed to UV rays limits the number of practical applications.
Each fiber’s unique properties need to be considered when choosing the correct rope for your application. Different applications might require maximum abrasion resistance, or the highest breaking strength, or perhaps whatever option is the cheapest. Commonly you will find modern rope companies combining fibers in a blend or a double braid, for example a UHMWPE core surrounded by a protective polyester cover.
For more information or for fiber selection advice, please contact us at [email protected]
Ronstan is the proud national distributor of Robline Ropes in the United States and Australasia.