How is sisal fiber made?
The steps in sisal fiber processing are as follows:
Sisal plantlets come from either suckers or bulbils which are collected from a mature sisal field. Then these sisal plantlets are planted in single or double rows and to reduce shading between plants, they are oriented north-south. Around 4,000 and 5,000 sisal plants per hectare are planted so that enough space is left to maneuver between the rows. In Brazil, very low or almost no irrigation is done. Commercial fertilizers or pesticides are also not used during the cultivation of sisal plants.
Since, sisal plants grow all year and have a very fast growth hence, after two years of the plantation, the sisal plants are ready to harvest. The plants can remain productive for 10 to 12 years. Around 180 to 240 leaves are produced by each plant which results in yielding 1 to 4 tonnes of fiber per hectare. Sisal is a labor-intensive crop. The leaves are cut manually, usually once a year every few weeks to allow sufficient photosynthesis and moisture capture. For cutting the leaves cutters called cortadoras are used. The heavy leaves are deposited at the end of rows from where they are taken to a central processing unit. The leaves must be processed as soon as possible to avoid deterioration.
• Fiber Extraction
Fiber from sisal leaves is extracted by a dry decortication process. In the decortication process, to separate the fibers from leaves, the leaves are crushed, beaten, and brushed away by a rotating wheelset with blunt knives. For large scale production, leaves are transported to a central decortication plant where this process is done using a machine called a decorticator. Then leaf tissue is removed from the machine, bound together, and weighted.
Then fibers are washed in water tanks to remove mucilage, chlorophyll, and the waste parts of the leaf. But sometimes due to water scarcity, this process is usually skipped.
• Fiber Drying
The wet fiber is then dried in a drying yard where they are hung over-drying wires. The drying process should be done for approximately 72 hours to reduce the moisture content to around 13%.
• Brushing and Bailing
The dried sisal fiber is transported to the brushing and baling facility. To remove the last impurities and make the fibers soft and shiny, sisal fiber is brushed using a large brushing machine. Then the fibers are sorted by quality and are baled using a baling press. These baled sisal fibers are stored and then sent to other facilities for further processing or export.
• Fiber grading
The grading process of sisal fibers is done based on both the quality and length of fibers. The four-length classes of sisal fiber are extra-long (length over 1.10 m), long (length between 0.90 and 1.10 m), medium (length between 0.70 and 0.90 m), and short (length between 0.60 and 0.70 m).
The quality of the sisal fibers is graded based on the following categories:
• Type 1 (Dry and well-brushed fiber): they are cream or clear yellowish in color. They are soft, shiny, have normal strength, and are free from impurities.
• Type 2 (Dry and brushed fiber): They are yellowish to brownish in color. They have average shine and are slightly rough.
• Type 3 (Dry and brushed fiber): They are either yellowish, brownish or greenish in color. They have average shine, rough and some color differences are allowed.
Sisal fiber that does not meet the above quality levels or is shorter than 0.60 m, is graded as type 4 or refugo (scrap).
• Spinning process
After cleaning and drying, sisal fiber bale is sent to the sisal yarn factory. There before using, the fiber is sprayed with certain moisture and sesame oil in order to make sure the process goes smoothly. Then to comb fiber, a sisal combing machine is used. This makes the sisal sliver to be average size and straight. After the combing process, the sisal fiber is sent to the drawing machine for drawing processing. There the sisal sliver is passed through a series of rollers, resulting in straightening the individual fibers and making them more parallel. And finally, for making yarns the fibers are then sent to the spinning machine.