Jute

We work with a jute grower and mill, a national jute laboratory, environmental laboratory, and specialist natural fibre rope makers. With their expert advice, we refine the specifications for the production of plants, yarn and rope for the precise application of prolonged human skin contact for erotic, sadomasochistic bondage.

Jute may be the nicest rope material to work with, but it is not the strongest. If you use jute, you must pay strict attention to factors giving the best strength, and know how to maintain its integrity. Many will absorb the styles of others at workshops, etc., but how many of us know that much about our main tool?

Everything begins with jute filament quality; where these filaments are taken from the plant; how long they are; how fine; how free of impurities. Coarse fibres limit the cross–sectional integrity. Fine, long fibres are more flexible and pliable – ideal for rope, and are more effectively spun into yarn. The very highest grade of jute should be used to make rope with the aim of supporting a person safely.

There are different yarns for weaving and twisting. Yarn grades such as CRM, CRT, CRX, etc., are all made for Van de Wiele looms for carpet backing applications. These yarns are of a lower grade material, with significantly shorter filaments and different twist dynamics specific for weaving, and not for twisting into rope.

Like all plants, jute is highly dependent on the weather during its growth, the timing of cropping, and various processes before spinning into yarn. Therefore, measuring the final strength when it has been made into rope is variable.

We could take an average, measure n pieces and apply the lowest result as a specification. This is okay until the next piece comes in under specification. As advised by The International Standards Organization and the Deutsches Institut für Normung, the variables do not permit any logical measurement.

Growing years matter; temperature, sunlight, rainfall and humidity all have an effect. The best jute is grown in a season where the temperature stays within 24 to 37˚C and has long periods at 34˚C. Pre–monsoon low rainfall will affect the quality. A bad season will produce a lower quality fibre.

Jute is a fertility exhausting plant requiring fresh alluvial soil. Clay or sandy soils produce sticky and coarse fibres respectively, and these need fertilizers; chemicals that will end up in the rope. Jute plants need to be cropped at a peak moment and only the best selected for processing.

Jute fibres are softened by retting in slow moving, clear water at an even–temperature of 34˚C. The process is completed within 8 days before bacteria or acidity compromise the filaments. If the temperature varies by just 2˚C, the time may double, and bacteria may be present. If the water quality is impaired, the fibres will suffer and pick up contaminants.

After drying naturally, the loose jute fibre is baled and transported to the mill, where separation begins with manual hackling. The first task is to segregate the best material. With jute, this is the longest, strongest, supple fibre from the centre, known as High–Grade, Clean–Batch. Further hackling will sort decreasing grades down to Sack–Quality, until only the dust is left.

Grading sets the level of impurities that will have significant repercussions on the longitudinal strength of a rope, and the amount of hairiness. The latter is also affected by other stages of the process. Individual fibres are separated by carding, where they are drawn parallel ready for spinning. Excessive carding can break and shorten filaments, increasing final hairiness. Fibre strength is also influenced by this stage. Lower grades of jute are more prone to breakage, and more likely to tangle into Habijabi clusters.

Between the grading and the carding stages the jute fibres are still in a loose state. Additional cleaning can be made, including washing and drying without stress. After drawing, the batching medium is applied at spinning to help the fibres coalesce as they twist. Jute yarns intended for industrial applications use Jute Batching Oil (JBO) because it is cheap. However, it is not advised for prolonged human skin contact.

When making yarn, the filament twist is critical to strength. The aim is an optimum between coherence and obliquity. A low yarn twist is weaker, not necessarily due to fibre breakage, but because of slippage leading to catastrophic tear. High yarn twist compromises linear orientation, causing shear. For soft, strong rope, the optimum yarn twist should not be compromised in production.

All yarn is single–ply unless it is twisted with other single–ply yarns. If a rope strand is 12 single–ply yarns counter–twisted together, 6 x 2–ply or 4 x 3–ply of the same yarn, it is the same mass. It is just constructed differently. Uniformity and softness can be lost in multiple–ply yarn construction as the twist dynamics oppose, making it knurl. Tighter multiple–ply twisting produces castellation and stress.

Natural plant fibres contract when wet as the filaments swell. With tension applied, as rope dries, it returns to roughly the same length. But it won’t shrink so much after the first time, as filaments become unstable, compromised by this action.

To understand the hygroscopic behaviour of plant fibres, we must explain the variability of properties depending on the batch, variety and the location they have come from within the plant. Fibre absorbs moisture. There is a direct link between this hydrophilic behaviour, weakening of the microstructure, and the reduction of shrink and expansion over the first cycles, especially after yarn and rope has been formed and is twisted under tension.

With finished rope, this means that it should not be made fully wet. Shrinkage and expansion of the first cycle is the most aggressive, and will compromise overall strength. The liquid will reduce the binding oil used in spinning the yarn.

Oil and wax can be used in rope conditioning. They should not go rancid, or penetrate too much to make the rope greasy and heavy. Plant fibre is like human hair; dry and brittle can be easily broken and damaged. A little softening can make the rope pliant and flexible, and help to maintain its core strength.

Jute is naturally hairy. This can only be reduced, but not eliminated. Jute of the highest grade and long filament orientation is straightened in carding to make the fibre parallel to the axis of the sliver. Drawing produces a regular filament overlap. After batching and spinning, a coating can also reduce hairiness.

Inspect your rope meticulously. Take a length, check the outside, then unwind the strands and yarns. You may find complete breaks, dark bark and waste, specks, long ruddy cuttings from the weaker root base, and Habijabi tangles. Together with short fibre loss, these will compromise strength, i.e. any imperfection is a weak point.

Jute rope is light and soft to work with, but it requires knowledge, not only about how to use it, but how to maintain it, and if necessary, when to discard it and renew it.

©AMATSUNAWA 2019