The boom in natural fibers – vegetable before animal
As a result of sustainability, environmental protection, and, not least of all, legal requirements, industry has focused increasingly on natural fibers over the past few years, whereby nowadays cotton, jute, hemp and flax represent the most frequently processed of them. In 2013, around 30 million tons of natural fibers were produced. Cotton made up the largest share at 79%, followed by the fiber groups flax, hemp, jute and ramie, which together accounted for 13% of the total volume. Wool was in third place with 4%.
Organic or inorganic – the bandwidth is large
In general, the term "natural fibers" refers to all textile fibers and fiber materials which can be obtained without chemical changes from plant and animal material and readily converted into textile fabrics. Bamboo viscose and lyocell are not termed natural fibers but regenerative ones. Wood fibers are generally considered as a separate group of materials.
Natural fibers can be subdivided as follows:
- Bast fibers
- (wood and bamboo are considered separately, however)
- Alfa grass
- Rabbit fur
- Sheep's wool
- Silk waste
Natural fibers can also be simply divided according to their processability into hard and soft fibers:
- Hard fibers (sisal, coconut)
- Soft fibers (cotton, hemp, flax, jute)
Natural fibers can be found in numerous everyday products. The most famous natural fibers are probably cotton, linen/flax, wool, and silk. Cotton is mainly used for the manufacture of clothing, or household textiles such as sheets and towels. Hemp and flax fibers are used alongside cotton and wool for padding upholstery in the automotive sector, and also for the production of composite materials, e.g. press-molded parts for the automotive industry. Natural fibers are also experiencing a boom in the construction sector because of their insulating properties, good compatibility and biodegradability, and find ever newer areas of application.
Ever more applications for the old classics
The potential applications for natural fibers have become almost limitless thanks to new processing methods and treatment options over past decades. Here are general application examples of the most commonly processed natural fibers:
- Underwear, sleepwear, outerwear, workwear
- Handkerchiefs, umbrellas, laces
- Kitchen towels, hand towels, bath towels
- Summer clothing, suits, skirts, shirts, blouses
- Bags, cases
- Bed linen, table linen, furnishing fabrics
- Cordage, sewing threads
- Sweaters, vests, coats, winter blouses
- Stockings, socks
- Blankets, carpets
- Fire protection textiles, technical felts
- Elegant lingerie, formal dress
- Ties, scarves
- Furnishing fabrics, bed linen
- Fire protection textiles, buttonhole silk
The right needle facilitates processing
For the needling industry, the organic natural fibers, jute, hemp, sisal, coir and wool form the lion's share, whereby needled felts are mainly used for mattress pads, doormats, floor coverings, carpet backings, and also, increasingly, numerous applications in the automotive sector (needled molded parts, usually in invisible locations).
In the field of inorganic natural fibers, rock wool and basalt wool are mainly used for insulating and absorbent products. Here, the following applications are worthy of mention:
- Insulation material for various types of furnaces
- Insulation for general construction
- Exhaust systems and sound-absorbent nonwoven coverings for the automotive industry
Mechanical processing via the needling of natural fibers can be difficult, because on the one hand natural fibers – as opposed to man-made ones – are relatively irregular in their structure, and on the other, sometimes only very short fiber lengths can be produced.
Generally, when needling, it is advantageous to use conical needles or needles with graded barb sizes. The different sizes enable use of a sufficient number of fibers of different sizes or diameters. In addition, smaller barbs near the needle tip enable reduced penetration force, which helps to protect the needle from overloading and also prevents increased load on the needling machine.
GEBECON® – the first choice for abrasive natural fibers
Because of their stability, conical needles in particular cause less needle breakage and thus have a longer lifespan, which is especially important where abrasive natural fibers (kenaf, coir, linen) are concerned. Here, the GEBECON® from Groz-Beckert combines especially good stability with acceptable surface quality. Generally, the shelf life of the needles can be improved by special coatings, for example with partial chromium plating or GEBEDUR® treatment.
Where higher weights are processed, needle breakage primarily occurs in the first rows. This problem can be reduced or even avoided by using shorter needles. A shorter needle is used for stabilization, and prevents a chain reaction. A one-sided needling is usually enough to produce the required product properties. With very high product weights, however, double-sided needling is advantageous. Experience has shown that suitable conical needles for processing of natural fibers lie in the gauge ranges from 32 to 36gg. When choosing needles for wool (cotton, fine sheep wool) there is a tendency toward very fine gauges such as 40 to 42gg. In contrast, with coconut fibers especially, the common practice is to use Grob gauge needles in 16 or 18gg, with specially reinforced shanks with 12 or 13gg.
The right barb protects against breakage
During the processing of inorganic fibers it is also very important to ensure that the fibers are not too badly damaged, as these kinds of fibers generally display very low elongation and can consequently break easily. Here, it is advantageous to use needles that have been given special metallurgical treatment, and which also have barbs with an increased projection or a large barb depth. Generally, for products where inorganic fibers are processed, needles with RF barbs are preferable to conventional barbs. If there are particularly high demands on protection of the fiber, the use of an HL barb is recommended.
For bulky insulation webs, needle combinations are sometimes used that are graduated in length, in order to achieve smooth and continuous needling. With these fibers, production is generally run with very low needle densities and low needle strokes, to prevent damage or even destruction of the fibers.
Coordination is everything – a practical example
In practice, the processing of natural fibers requires good coordination for an economically efficient production process, with good needle life and adequate machine speeds. Selecting the right needles in the manufacturing process is crucial here. Here is an example from practice:
Needling a mattress pad
- Fiber type: Hemp
- Product weight: 1.000 gsm
Pre-needling: 15 x 16 x 36 x 3 1/2 M332 G 53037 (614481)
- Penetration depth: 14 mm
- Penetration density: 50 E/sq cm(S/sq cm)
Main needling: 15 x 16 x 25 x 3 1/2 M333 G 83012 (608761)
- Penetration depth: 12 mm
- Penetration density: 140 E/sq cm (S/sq cm)