Updated: Jan 8, 2021
Sunn is a bast fiber which is obtained from the outer bark of the stem of sunn plant. It comes under the species crotalaria juncea and family of legume(fabaceae). It is also known as sunn hemp, Indian hemp, Bombay hemp, rattle pods and madras hemp. It grows to a height of 1 to 4 meter. It is originated from India and Pakistan. Largest producer of sunn fiber is India. It is grown in tropical and subtropical countries. It requires annual average temperature from 18 to 27 ͦ and average annual rainfall is as low as 200 mm.
Processing of sunn fiber:
sunn plants has to be harvested at the flowering stage i.e. 60-90 days after sowing so that fiber is thinner at this stage. It can be done by 2 ways i.e. By using hand or with a mechanical device. The stems are cut nearer to ground. Then they left for drying.
In the retting process, the bundles of sunn stems are immersed in water until the fibers separate from the stems. Then the bundles were taken out of the water and left to dry.
After retting, the stalks are crushed between two metal rollers so that the woody portion of the stalks can be removed. Removal of woody substance from the sunn stems is known as scutching.
Chemical composition of sunn fiber:
Fat and wax --------------------------- 0.5%
Nitrogenous matter ------------- 1.4%
ash ---------------------------------------------- 0.3%
Properties of sunn fiber:
Length: 5 to 20 mm
Breadth: 12-35 mm
Transverse swelling in water: 18-20%
Moisture regain at 65% RH: 10.5%
tenacity: 30-40 g/tex
extension at break: 2.5 -3.5%
flexural rigidity: 125-175 dynes cm-2
modules of torsional rigidity: 1-2×1010dynes cm-2
It has very good flexural properties.
The color of fiber is off-white.
It is fairly resistant to mildew.
It has high strength because it contains high cellulose content and low micro fibril angle.
It is used for making
Cordage, fishing nets, Soles of shoes, sandals, Ropes, tatpattis, sackimg, twines, canvas,
floor mats, rugs, carpets, webbing, table and bed linen, currency notes, cigarette paper,
tissue paper, carbon base paper, electrical condenser, handmade paper, airmail paper and wax impregnated paper.
It is a soil improving and green manure crop.
It is resistant to root-knot nematodes.
It will reduce soil erosion when it is used as a cover crop.
Polymer reinforcement is suitable with this fiber.