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Rosin

This topic provides information about Rosin, a solid form of resin obtained from pines and some other plants.

Rosin, also known as colophony, is the solid form of resin obtained from pines and some other plants, mostly conifers.
Local name : rosin
Plant Sources : Pinus roxburghii, Pinus wallichiana, Pinus keysia
Family : Pinaceae

Distribution : Extensive chir pine (Pinus roxburghii) forests are found in the Himalaya between an elevation of 1000m and 1900m. Chir pine yields commercially important oleo-resin which forms the raw material for rosin and turpentine oil industry in India. Blue pine (Pinus wallichiana) forests occur at elevation of over 2100m in the Himalaya. Khasi pine (Pinus keysia) is found in the Garo, Khasi and Naga hills whereas some exotic species of pines have been introduced at various places in India. Of the above species, only chir pine is widely tapped for resin on commercial basis, particularly in the hills of Jammu & Kashmir, Himachal Pradesh, Garhwal and Kumaun.

Production in India : 25,000 tons per annum (approximately)

Other producing countries : China, Indonesia, Portugal, Brazil and Russia.

Harvesting/Collection of Resin

Method of harvesting/tapping: For commercial purposes, resin is obtained by tapping standing pine trees i.e. by making a cut which exposes the surface of the wood. Resin canals are large and irregularly distributed in chir pine trees. The resin in the longitudinal ducts tends to reach the surface through transverse ones in the rays. Consequently, for tapping the trees only a shallow incision is necessary as the flow of resin from the transverse ducts stimulates of resin in large ones. The flow of resin is from top of the maximum incision, where both the horizontal and secretion vertical ducts are cut. On exposure to air, the volatile oil in the oleoresin (turpentine oil) gradually evaporates leaving clear, hard, glossy substance called rosin, which forms a protective coating over the incision and tends to stop further flow of resin.

In India two kinds of tapping are in vogue, viz.,

  • Light continuous tapping,
  • Heavy tapping.

Light continuous tapping : Light continuous tapping is done in trees above 0.9m in girth. Trees between 0.9 and 1.8 m in girth are tapped in one channel, and those above 1.8 m in girth in two channels each at a time. The first channel or each set of two channels is tapped for five years. At the end of five years, a new channel or a new set of two channels as the case maybe, is started leaving an inter space of 10 cm between the old and new channels. At the end of second five year period, another channel or set of two channels is again made leaving another inter space and so on till tapping has progressed channels,right round the tree. This is the common mode of tapping that is being practiced in India and the trees are regularly tapped without any rest.

Heavy tapping : In heavy tapping (also known as tapping to death), maximum possible out turn of the resin is derived before the trees are due for felling and it is achieved by cutting on the tree as many channels as it can bear, with a minimum inter space of 10 cm between the successive channels. It is generally started five year in advance of main felling in prospective regeneration areas and two years in advance of thinning in areas marked for thinning. The lowest girth prescribed for heavy tapping is 60 cm.

There are four methods of tapping pine trees i.e.

  • Box method
  • Cup and lip method
  • Rill method and
  • Bore hole method.
At present, three methods are commonly employed for tapping pine trees in India. These are (a) Box method, (b) Cup and lip method and (c) Rill method.

Box method : This is the oldest method of resin tapping. A cavity or box of 10cm x 10 cm and upto 12 cm deep is chopped at the base of the trees. It is meant to collect the resin as it exudes from the blaze or incision that is made just below the box, by chipping bark and outer layer of the sapwood. The resin oozes out of the blaze and is collected in the box.However, this method is very damaging and the trees tend to die within few years after resin tapping is started.

Cup and lip method : In this method, the outer bark of the tree is scraped off with the adze to a reasonably smooth surface of 60 cm long, 15 cm wide and 25 cm above the point where the lip is fixed. In light tapping.channels are initially located on south or south-west face of the tree as better yields are obtained from the warmer aspects.Subsequent channels are made in an anti-clockwise direction. A cut of about 15 cm broad and slightly slanting outwards is made with a curved chisel and mallet about 25 cm below the lower edge of the blaze. The lip, a rectangular piece of galvanized iron (15 cm X 5 cm), is driven into the cut to collect resin into a pot kept below. The pot is partially covered to prevent pieces of bark, dirt etc.from falling into the cone, and  also to minimize the evaporation of resins that accumulate into it. In order to open up the clogged resin ducts and aid in the smooth and continuous flow of resin, the channels are freshened at definite intervals.

The cup and lip method of tapping has number of disadvantages. Even though a channel depth of 2.5 cm has been prescribed for the blazes, very often the depth exceeds the prescribed limit. The inherent hacking action involved in case of adze, makes it very difficult to control the depth of the blazes.Also the tapper makes much deeper blazes in the hope of getting more resin. Deep cuts around the hole results in loss of timber and make the trees less resistant to wind storms. Moreover, after covering the circumference of he tree, a second cycle of tapping is not possible because of the slow healing of deeper blazes. This generally results in abrupt fall in resin production.

Rill method: This is an improved method, standardized at Forest Research Institute, Dehradun to overcome the disadvantages of the cup and lip method. In rill method, the bark of the tree over a surface area of about 45 cm in height and 30 cm in width is removed with the help of a bark shaver. The surface is made very smooth and the thickness of the bark left should not be more than 2 mm to facilitate freshening of the blaze. The blaze frame is kept on the stem in the vertical portion, 15 cm above the ground level and the position of the blaze is marked with a marking gauge. The control groove is cut with a grove cutter by drawing it from top to bottom. The lip is then fixed in the tree with nails.

For freshening of the blaze, the tapper stands near the tree on one side of the blaze and holds the freshening knife at the lowest point of the control groove. The knife is then pulled up by the tapper along with blaze line marked on the tree. The depth of the rill is about 2mm into the wood. After making a freshening on both arms of the blaze a 1:1 mixture of dilute sulphuric acid (20%) and dilute nitric acid (20%) is sprayed on the freshly cut rill with the help of spray bottle. Exudation of oleoresin starts soon after the rills are made.The pot containing the oleoresin is emptied into a collection can. The resin adhering to the pot is removed with the help of a scraper.The control groove is also increased to avoid accumulation of resin in it

Bore hole method : Forest Research Institute, Dehradun has developed a new tapping technique known as bore hole technique of resin extraction from Pinus roxburghii. In this method holes are made near the ground level with the help of a machine into tree's sapwood to open the resin ducts and exudating resin is collected in a closed container. The hole in each tree is done approximately 10 cm above the ground. It has been found from the studies that holes of 15cm depth and 2.5 cm diameter are suitable for obtaining maximum resin yield. The holes are drilled straight into the tree stem with a slight slope towards the opening so that resin drains freely.

Immediately after making the hole the stimulants/ chemicals (mixture of sulphuric acid and ethephon i.e., 2-chloro-ethyl phosphonic acid) are sprayed inside each freshly made hole. Spray volume of 1 to 2 ml are applied to each hole. Chemical treatment is done once only, immediately after boring holes. After treatment a spout is installed inside the hole by gently hammering with a small mallet or pushing with palm of the hand to achieve compression fitting in the hole. The spout is meant for joining the collection container (polybag made up of high density poly ethylene, HDPE, 35.3 x l2 cm) tightened to each spout.

Once the polybag is filled with resin, it is removed from the tree and poured into a collection can and immediately a new polybag is tied for future collection of resin. Some of the advantages of bore hole method of resin extraction are as follows

  • There is less stress due to small size (2.5 cm diameter) of the hole. The hole heals fast.
  • The technique is very suitable for the protection of tree against fire, insect, pest and diseases.
  • Prolong resin flow can be obtained from bore hole for a period of several months without wounding the stem.
  • The holes are made with the help of a machine, therefore the labour productivity of the technique is several folds greater than other method.
  • The technique could be very effective in conservation and management of pine resources.

Period of harvesting/collection

Rosin from chir pine forests are tapped from April to November each year. Most of the forest trees are owned by Government while a small yield is also obtained from private or community forest.

Yield

Experiments conducted on trees growing at the Forest Research Institute, Dehradun, have shown that a maximum yield of 5.13 kg/blaze/year of resin can be obtained by rill method, while the corresponding yields by the other two traditional methods are 1.5 kg/blaze and 3.1 kg/blaze per year respectively (Chaudhari et al.,1990).

Processing and Value Addition

Resin is collected in bucket and brought to central places from where it is taken to the factory. Resin obtained from Chir pine trees is distilled into turpentine oil and rosin. The crude resin is processed in the following manner:

Crude resin is in a very impure state when it reaches the factory. It contains water, bark,needles,dirt and even insects, They are stored in a suitable shed after being brought to the factory. Before processing the top of the tin bucket is cut and the dirt that is floating on the top of the resin is removed manually.

During winter, resin is a bit hard to work, so some amount of turpentine oil is mixed to dilute the resin. The screw elevator lifts this resin along with the impurities to the mixing vats which are large vessels made of mild stee1.They have V-shaped bottoms that are provided with steam jackets for heating the resin. The resin is heated indirectly in this vat by passing steam through copper coils for 4 to 6 hours to melt the resin in it.The is maintained up to 95℃. The temperature molten resin is t hen stirred with iron arms mechanically and passed through 40.mesh stainless steel wire net to remove bigger impurities like pine needles, bark pieces etc.and then pumped by centrifugal pump into a rest vat.The resin is allowed to rest in the rest vat for about 18 to 20 hours. During this rest period, the impurities and dust if present, settle down by gravity. The dust/impurities are removed through a bottom valve and sent for processing separately as inferior grades of rosin. Resin from rest vat is carried to the compression chamber, from which it is carried to distillation kettle by steam pressure.

In the distillation kettle, the resin is cooked for 1-2 hours by indirect steam. The molten resin remains inside the copper tubes and steam remains in the outside. In this process the turpentine oil and moisture present in the resin get evaporated and condense in the condenser. Turpentine oil is collected in a Separator.

The rosin left in the distillation kettle is taken out at 165℃ and collected in trolleys, wherein about 100-200 grams of oxalic acid (depending on the quality of resin) is mixed to increase the transparency,/ shine of rosin.

Storage : Rosin is packed in Tin Patra Barrels of  200 kg of capacity and stored in cool condition under shed.

Quality control : Both rosin and turpentine oil find wide use in various industries. They are graded into various categories for commercial use. There are 12 grades of rosin which are in vogue in trade circle and are also recognized by the ISI (1955), as given in Table.1

Properties

  • Rosin is brittle solid and consists mainly of free organic acids called rosin/resin acid of the formula C19H29COOH and related neutral materials like resin acid esters, anhydrides, aldehydes, hydrocarbons, unsaponifiable matter and fatty acids.
  • lts colour varies from light yellow to red,brown, blue, or black.
  • Its specific gravity is 1.08 and melting point is from 100 to 140℃.

Industrial Applications

  • Rosin is used in making cement varnishes, paints, sealing wax, adhesives,inks and some soaps.
  • It is used as a dressing for machine belts and bows of violins and cellos.
  • It is used in the preparation of certain metals for soldering.
  • Rosin gives a stiff coated surface to certain kinds of paper. This is needed for printing and writing.
  • In pharmacy, rosin is used in some plasters, and similar ointments,preparations.
  • Athletes rub it upon their hands or the soles of their shoes to prevent slipping. It is also extensively used for its friction increasing capacity in stringed instruments.
  • The tin lead solder commonly used in electronics has about 1% of rosin as a flux.
  • It is also used in the manufacture of linolium, sealing wax, oil, cloth, special flooring compounds and coverings. lubricating compounds and disinfectants.

Source: Indian Institute of Natural Resins & GUMS

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