All About Rope Construction

Rope seems so simple yet the construction and fibers used in a rope can have a huge impact. Understanding what the difference is in the different fibers is key to choosing the right product for your individual application. We look at the options by identifying the three groups of fibers and then looking at seven different materials used to manufacture the fibers.

Fibers used in a rope can have a huge impact.Monofilaments

As the name implies this is a single strand about 1/100th of an inch thick that are fed in parallel into the braiding process. Each strand is fed on its own.

Multifilaments

Exceptionally thin (about 1/10,000th of an inch) stands are bundled together when fed into the weaving process. This is the most common type of stand found in ropes as production costs are reduced.

Textured fibers

These are shorter fibers that are bundled together to create a strand. The finished product is typically less uniform and rougher to the touch.

Science has played a significant part in creating fibers for rope production. What makes this complex is where companies have trademark names for a fiber that has become a catch phrase for the product, in many cases arguments over what is the best product for an application boils down to two brand names for the same product. They all have their positive and negative aspects.

Polyethylene = Dyneema®Dyneema is a material that exhibits increased breaking loads and reduced stretch.

DSM, the Dutch chemical corporation, changes polyethylene on a molecular basis and turns the fibers in one direction the result is Dyneema®, a material that exhibits increased breaking loads and reduced stretch. It’s Polyethylene base means thatDyneema® has a very low specific weight making it float. It also has  good abrasion strength and a resistance to sunlight. The only downside of Dyneema® is that it creeps, meaning that over time and under load the fibers 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. The fiber has an exceptionally high breaking load with zero stretch and exceptional temperature resistance but does not like sharp bends and can be sensitive to long exposure of sunlight.

Polyester (PET or PES)

Polyester is the workhorse of the rope industry as the fiber offers a great number of chemical and physical advantages. It hasdecent breaking loads and low stretch as well as good abrasion resistance in both dry and wet conditions, and good resistance to sunlight. 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.

Polyamide (PA)

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 in time PA can become stiff. Longer exposure to sunlight is not recommended.

Polypropylene (PP) = XLF

PP is extremely lightweight and very abrasion resistant make it the ideal choice for an all round rope. The product has a high stretch factor which needs to be kept in mind when choosing for any application.

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 highest breaking loads with minimal stretch and high temperature resistance. Its only weakness, however, is its extremely low resistance to sunlight. PBO is an emerging fiber in the rope industry offering significant improvements over all other options.

The many properties of each fiber means the correct rope for your application should be based on what you specific needs are. As is true in most things compromises may need to be made for longevity of the product or for higher strength. Keep in mind too that modern rope companies do combine materials using high strength core with protective outer covers.

  Dyneema® Vectran® Technora® Polyester Polyamide Polypropylene Polybenzoxazole
Strength              
Breaking Tenacity – Dry (G/den) 6 23.0 26.5 9.5 10.4 6.5 41.9
Wet strength vs. Dry strength 100% 99% 95% 100% 90% 100% 100%
Shock – Load Absorption Ability Fair Average Poor Very Good Excellent Very Good Average
Weight              
Specific Gravity 0.95 1.40 1.44 1.38 1.14 0.91 1.54
Floats Yes No No No No Yes No
Elongation              
Percent at break 15-25 3.8 1.5 – 3.6 12 – 15 20-34 15-25 25-35
Creep High Low Very Low Low Moderate High Very Low
Effects of Moisture              
Water Absorption None 2.5 – 5.0 3.5–7.0  1 8 None None
Dielectric Properties Excellent Poor Poor Good Poor Excellent Excellent
Degradation              
Resistance to UV Fair Poor Fair Excellent Good Poor Poor
Resistance to Mildew Excellent Excellent Excellent Excellent Excellent Excellent Excellent
Storage requirements Wet / Dry Wet / Dry Wet / Dry Wet /Dry Wet / Dry Wet / Dry Wet / Dry
Abrasion Resistance              
Surface Good Fair Fair Excellent Very Good Good Fair
Internal Good Fair Fair Excellent Excellent Good Fair
Thermal Properties              
Melting point or char point Moderate Moderate High High High Moderate High
Resistance              
Acid Excellent Excellent Fair Good Fair Excellent Fair
Alkalis Excellent Excellent Fair Fair Very Good Excellent Fair
Oil and Gas Very Good Very Good Very Good Very Good Very Good Very Good Fair

 

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