Fibres Guide

How to Identify the Synthetic Fibres Used In Rope Making

Many ropes look alike, especially with regard to material. Once a rope is removed from the reel or packing box or is otherwise separated from documentation, the material, and even the name of the manufacturer might not be easily determined.

Users frequently encounter ropes of unknown rope material. Some fibres are very similar in appearance. But important fibre rope properties such as strength, extension and durability are primarily functions of the material. Substitution of ropes of the wrong fibre material can have disastrous consequences in critical applications.

Simple observations and tests can be used to identify various fibres commonly used in ropes. Experts can distinguish some materials by appearance alone, but this is not generally reliable. Some tests can easily be performed in the field without special preparations and laboratory equipment. The burn test is the easiest to perform, but it may be impractical in some environments. Several appropriate tests should be performed for positive identification. Markings provided by manufacturers can also help in identification.

A thorough study of the techniques, practice with known fibre materials, and preparation of a few supplies will enable the user to identify most materials found in ropes. No single test should be relied upon for positive identification. Several appropriate tests should be used. When positive identification is very important, expert advice and laboratory testing should be relied on.

Further info

General information on Fibre Types

Identification by Appearance

Identification by Testing

General information on Fibre Types

A general knowledge of the various fibre types is helpful in identifying these fibres.

The three most common rope materials are nylon, polyester, and polypropylene. Polyethylene is sometimes encountered. Some ropes are made of combinations of several of these materials.

Some ropes are now made of new fibre materials which have higher strengths than the common materials discussed above. They are also significantly stiffer, and for this reason they are usually grouped together in a category called high modulus fibres.

Sometimes the fibre material is known by its trade name instead of its common name. Some rope manufacturer's trade names identify the material. The chemical abbreviation or an acronym are sometimes used.

Table 1 gives some general identifying characteristics of the various synthetic fibres used in rope making.

Table 2 gives a brief glossary of terminology and tradenames for fibre ropes and rope materials.

Further info

Common Rope Materials

High-Modulus Materials

Trade Names and Abbreviations

Common Rope Materials

The three most common rope materials are nylon, polyester, and polypropylene. Polyethylene is sometimes encountered. Some ropes are made of combinations of several of these materials.

Nylon is generally the strongest of these common materials when dry. However, some nylon ropes lose as much as 20% of their strength when wet. Two forms of nylon are used in ropes; nylon 6 and nylon 6.6. The properties of these fibres, and the ropes made from them, are not significantly different, except nylon 6 has a lower melt point temperature.

Polyester ropes are almost as strong as nylon when dry. Polyester retains its strength when wet, and thus polyester ropes are generally stronger than nylon ropes when wet.

Polypropylene is probably the most common material found in ropes used in the marine field. One reason is that it is lighter than water, and thus it floats.

Polyethylene is uncommon in large ropes. It used water-ski ropes and other small ropes used for utilitarian purposes. It is used extensively in the fishing industry.

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Comparison of Fibre Characteristics (Table 1)

High Modulus Rope Materials

Some ropes are now made of new fibre materials which have higher strengths than the common materials discussed above. They are also significantly stiffer, and for this reason they are usually grouped together in a category called high modulus fibres.

Aramid was the first such high modulus fibre. It is known by the tradenames Kevlar and Twaron.

High Modulus Polyethylene (HMPE) is a special form of the conventional polyethylene discussed above and it is much stronger and stiffer than conventional polyethylene. It is known by the tradenames Spectra and Dyneema.

Liquid Crystal Aromatic Polyester (LCAP) is know by the tradename Vectran.

Further info

Comparison of Fibre Characteristics (Table 1)

Trade Names and Other Terminology

Sometimes the fibre material is known by its trade name instead of its common name. Some rope manufacturer's trade names identify the material. The chemical abbreviation or an acronym are sometimes used.

For example, Dacron and Terylene are both trade names for polyester fibre. Some users call the rope by one of these names without knowing that it is actually polyester. The new high-modulus fibres, mentioned above, are usually referred to only by their respective trade names.

Table 2 lists some frequently used rope material trade names and chemical abbreviations. It also gives other common terms used for synthetic fibre rope products. This is not a complete list of trade names, and is not intended as an endorsement of the products listed. Fibre producers' and rope manufacturers' literature may be consulted for other trade names associated with a particular fibre material.

Identification by appearance

Preliminary identification can sometimes be made by the fibre appearance. This is seldom a reliable way of determining the fibre identity, but it is helpful in narrowing the number of possible fibres. Then only a few tests may be required to positively identify the particular fibre material.

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Fibre Appearance

Colored Marker Yarns

Rope Color Markings

Internal Marker Tapes

Fibre Appearance

Polyester fibres and almost all nylon fibres are very fine and hair like, typically about 0.023 mm dia. These fibres are almost always white. It is virtually impossible to distinguish between nylon and polyester by appearance alone. HMPE and the multifilament form of polypropylene are very similar to nylon and polyester in appearance.

AA monofilament form of nylon (tradename Perlon), 3 to 6 mm dia., is found in some European ropes. This Atlas fibre is round, stiff, and larger in diameter than heavy pencil lead. It is usually mixed with the multifilament form of nylon in rope making.

Polypropylene is encountered in several different forms in ropes. It is sometimes a thin multifilament fibre, similar to but slightly thicker than polyester and nylon. It is sometimes a thicker monofilament, resembling straw or bristles, typically 0.1 to 0.15 mm dia. In this form it may either be a continuous fibre, or it may be cut into short lengths and then processed like natural fibres to form staple yarn. Another form of polypropylene resembles a thin tape, typically 0.06 to 0.1 mm thick. The tape is sometimes twisted so it appears to be a circular fibre. This tape may be fibrillated or split so it appears to be a collection of small flat fibres which cling to each other.

Ropes made of monofilament polypropylene are frequently black, orange or yellow. The dye helps to prevent UV degradation. White monofilament polypropylene fibres with some other form of UV protection are also common.

Multifilament polypropylene fibres are usually white. They are almost indistinguishable from nylon and polyester fibres by appearance, except they are usually slightly thicker and thus stiffer. This contrast may be evident in mixed fibre ropes.

Polyethylene fibres typically are bristle-like, in the range of 0.2 to 0.4 mm dia., and are thus similar to the monofilament form of polypropylene. Polyethylene is not damaged by ultraviolet effects, need not be dyed, and is usually natural white. However, colored polyethylene is common, especially yellow and orange. Thus it is difficult to distinguish polyethylene from monofilament polypropylene by appearance.

Aramid is a very fine straw-colored fibre. Almost all large aramid ropes have a braided jacket of nylon or polyester or are covered by an extruded polyurethane coating. Also, the individual strands are usually jacketed.

HMPE is a very fine, very slippery fibre. Some HMPE ropes are jacketed, but others are unjacketed. Sometimes a light dull-blue coating is processed onto the unjacketed HMPE rope.

LCAP, at least in the Vectran form, is a very fine tan or dirty yellow colored fibre similar to, but not as yellow as aramid. LCAP is very uncommon in rope products at the time this paper was written. Most LCP ropes will probably be jacketed.

Many modern ropes are a blend or mixture of several of the above fibres. Combinations of polyester and polypropylene fibres in ropes are common. Some, but not all composite ropes made of polypropylene and polyester are essentially as strong as ordinary polyester ropes.

Another form of mixing fibre is in the fibre extrusion process. One example is Karat, a copolymer consisting of polyester and polyethylene. This particular fibre is straw-colored.

Colored Marker Yarns

Table 3 shows the marker yarn color code specified by the International Standards Organization (ISO) and the British Standards Institute (BS) for identifying fibres in ropes. This code is also called for in the Oil Companies International Marine Forum (OCIMF) Guidelines for Large Marine Hawsers. Unfortunately, this material color code is not commonly followed.

Some rope manufacturers identify their ropes by various color marker yarns, and some of these manufacturer's markers also identify the rope material. A few of these marker color codes are shown in Table 2.

As can be seen from Table 2, the international "standard" marker yarn material code colors duplicate those used by some rope makers for other purposes. Thus caution should be taken in using such marks as a means of identifying rope materials.

Internal Marker Tapes

Some ropes have a marker tape buried within a strand. These marker tapes generally bear the name of the manufacturer, the type of material, and the year of manufacturer.

Marker tapes are required in most ropes procured by the U.S. Military in various MIL Standards. It is also required by the OCIMF Guidelines for large ropes used as SPM mooring hawsers. Some rope manufacturers include such markers in most of their rope products.

In double braid rope, the tape may be in the center of the core or between the core and the cover. In other ropes, this tape is usually within the strand which has the colored marker yarn.

The marker tape is a conclusive way of identifying a rope material, when it can be found. In an unspliced rope, the marker tape can be found by untwisting the end of a strand. In broken rope, it may be found by careful disassembly of the rope.

It may be difficult to find and examine the marker tape in a spliced rope in service. The tape usually cannot be found and removed for examination without disturbing the rope structure. However, a piece of the tape might be found and examined in the end of a splice tuck.

Identification by Testing

Simple test methods used in combination can conclusively identify most rope fibres. The following brief instructions, together with the tables, may be sufficient to conduct most of the tests.

Further info

Burn Tests

Burning Characteristics of Synthetic Fibres (Table 4)

Specific Gravity Test

Melt Test

Stain Test

Burn Tests

Burn testing is a generally reliable way of identifying fibres. Table 3 provides a listing of burn test characteristics. The burn test method should be used with proper precautions.

Hold a specimen of the fibre or yarn by clean forceps over a clean flame, such as a gas burner or wooden match. While the specimen is in the flame, observe the reaction of the specimen and the nature of the smoke. The smoke should be sniffed with care to determine its smell.

Remove the specimen from the flame. Observe the reaction of the specimen and its smoke and again sniffed the smoke. Any flame on the specimen should then be extinguished.

Observe the nature of the melted end of the specimen, taking care to avoid touching hot residue. Use a metal or wooden stick instead of a finger to draw out or crush the residue.

Smell alone should not be used for identification. It is influenced by coatings on the fibres, and pollutants to which the rope has been exposed. The sense of smell is not be very precise.

Further info

Burning Characteristics of Synthetic Fibres (Table 4)

Specific Gravity Test

Some fibres can be distinguished by differences in specific gravities, which are listed in Table 4. Make sure that all air is removed from the yarn or fibre bundle before making a determination. Polyethylene, polypropylene, and HMPE will float. The other fibres sink in water.

A more detailed method, using a density gradient tube, is described in ASTM D276. That method might be useful to distinguish between nylon and other materials.

Melt Test

The melting point is a reliable means of distinguishing some common forms of fibres. Melt temperatures for the various fibres are given in Table 4. This test can be conducted using a calibrated melting point apparatus. The method is described in ASTM D276.

An alternate method is to place the fibre on a metal sheet, together with known fibres. Place the metal sheet on a hot plate or other controlled source of heat. Slowly raise the temperature until the unknown material begins to melt, presumably at the same time as one of the known materials.

Melt point determination is the only reliable way, other than stain or chemical testing, to distinguish between nylon 6 and nylon 6.6. It is generally not accurate enough to distinguish between materials with melt points closer than about 10°C. Thus it is not capable of distinguishing between nylon 6.6 and polyester.

Stain Test

Stain testing can be conducted with several commercially available test kits. This method can be useful in environments where burn testing is not allowed, such as on the deck of a tanker or drilling platform.

Black Rit dye is available in many stores. It can be used to distinguish between nylon and polyester. Nylon will take the dye while the polyester will remain white.

"duPont Fibre Identification Stain No. 4" is available from Pylam Products Co., 1001 Stewart Ave., Garden City, NY 11530. It can distinguishing between polyester (yellow), nylon (red), and the polyolefins (white). However, it cannot distinguish between nylon 6 and 6.6 or between polyethylene and polypropylene.

"Shirlastain A" is available from Shirley Developments Ltd., Didsbury, Manchester, M20 8SA, UK. It can distinguish between nylon 6 (pale yellow) and nylon 6.6 (dark yellow), and distinguish these from polyester (unstained).