INTRODUCTION:
Kenaf is a natural vegetable bast, lignocellulosic fiber which is obtained from the bast(bark) of the kenaf plant. “Hibiscus cannabinus”, “Malvaceae” is the genus and family of the kenaf fiber respectively. Kenaf is originated from Africa. It grows well in tropical and subtropical countries. It is cultivated in countries such as India, the US, Thailand, Malaysia, some parts of Africa and Vietnam countries. It produces 6 to 10 tones of fiber each year and grows up to 2.7 to 3.6 meters within 6 to 8 months of the plantation. Kenaf stem contains 2 types of fiber i.e.. Inner core fiber and outer bast fiber. Inner core contains 75 to 60% fiber which produces low-quality fiber and outer bast contains 25 to 40% fiber which produces high-quality pulp.
Processing of kenaf fiber:
Harvesting:
when the flowers are in bloom, harvesting can be done. so the fibers are of the best quality. When the plants are ready for harvesting, they can be cut by following two ways. Those are
By hand with a sickle or curved blade
By whole stalk harvesters
Retting:
There are 4 types of retting processes. Anyone process can be followed to separate the fibers from the stalks.
Biological retting:
Dew retting, water retting, and enzyme retting comes under biological getting.
In the dew retting, the stalks spread on the field and expose them to sun and rain for several weeks until the stalks begin to separate from the fiber naturally. But this method reduces the quality and strength of the fiber.
In the water retting process, the bundles of stalks are immersed in water of at least 60 cm in depth until the fibers separate from the stalks. This process takes around 2 weeks. Then the bundles were taken out of the water and left to dry.
In the enzyme retting process, fibers can be separated from the stalks by using enzymes like pectinase and xylanase. It is the safest and fastest process of retting.
Mechanical retting:
In this process, a decorticator is used to separate the bast and core fibers. Stalks will be fed by feeding mouth, then they will enter to beaters to crush the stalks. Then the crushed stalks which contain both bast fiber and core fiber will be pushed into the delivery plate and will be separated manually.
Chemical retting:
In this process, the stalks are boiled with acids and alkalies such as sodium hydroxide, sodium benzoate and hydrogen peroxide for several hours at a specific temperature and then washed with clean water. Compared to other retting methods the fiber which is obtained from this method is usually felt and rough.
Physical retting:
It requires low processing time. It involves 2 steps which start with modifying the surface by chemical treatment. Then the stalks will be subjected to a steam explosion. In this, the bast fibers will be separated from the core fibers by blowing apart. But this method only produces short fibers.
Drying:
After the retting process, the bast fibers are taken out from core fibers and wash them with clean water and allow them to dry.
Chemical Composition of kenaf fiber:
Properties of kenaf fiber:
Length: 2.6 to 4 mm.
Diameter: 17 to 21.9 micron.
Ultimate stress (Mpa): 350-600.
Strain%: 2.5 to 3.5.
Density: 1.45 g/cm3.
Tensile strength: 284 to 930 Mpa.
Young’s modulus: 21 to 60 Gpa.
Elongation to failure: 1.6%.
Moisture content: 6.2 to 20 %.
Cost: 1.58 RM/kg.
Can be dyed with Acid, basic, reactive, vat dyes.
Pale in color.
Lustrous.
Resistant to rotting.
Uses:
Kenaf fiber is used to make
Rope, twine and canvas.
Cordage, sacking.
Carpet materials.
Animal bedding and feed.
Packing material.
Used in paper production.
Automotive product.
Boat sails.