State of the Art of Coconut Coir Dust and Husk Utilization

State of the Art of Coconut Coir Dust and Husk Utilization

(General Overview)

by

E.A. Tejano[1]

Paper presented during the National Workshop on Waste Utilization, Coconut Husk

held on November 12, 1984 at the Philippine Coconut Authority, Diliman, Quezon City, PHILIPPINES.

© Philippine Journal of Coconut Studies, December 1985

The Philippines expects an average yearly output of 0.50 MMT of mixed fibers and 1.17 MMT of coir wastes. This assumes that all recoverable quantities of coconut husks are utilized in coir extraction activities.

The use of coconut husk in the coir extraction and processing activities although for the most part it is in the copra drying activities. Technologies such as dry milling and wet milling have made it possible to segregate coir from coir dust.

There is a wide scope of commercial utilization of coir and coir dust, either on their own or in combination with other raw materials, to make products like mat and matting, tawashi brush, twine and rope, particle board, fertilizer, rubberized coir and applications such as upholstery cushioning, pad and carpet underlay. There are hopeful commercial uses of coir and coir dust which are also described and discussed.

INTRODUCTION

The area planted to coconut in 1982 stood at 3.16 M ha. There was a total of 410 M trees planted of which only 345 M (84%) were fruit-bearing, having produced 13.9 B nuts. The remaining 65 M trees (16%) were either newly planted, old, diseased, senile, or otherwise past the productive stage.

The above figures give an indication of the volume of mixed fibers that could be derived from coconut husks. If the recoverable quantities would come from the wastes in copra making, which utilizes approximately 70% of the available coconut husk for fuel, the total nut production in 1982 could have yielded 501, 000 MT of mixed fibers and 1, 167, 00 MT of coir dust. These figures indicate the potential of coconut husk as another source of earnings for the industry.

To date however, relatively little attention has been given to the use of this coconut by-product. Several coconut-producing regions have sufficient supply of husks to support the profitable extraction of coir, yet less than 0.6 % of the total husk supply is utilized, the annual production of coir ranging between 2, 000t-3, 000 t.

Nature and composition of coconut husk

The coconut husk is that 5-10 cm thick fibrous covering of the coconut fruit which envelops the hard shell structure of 3.5 mm thickness. The external appearance of the husk varies from decidedly dull brown when fully ripe to bright green when immature. There are other varieties whose husks are golden yellow or yellow brown. The husk is full of long, coarse fibers, all running in one direction. The fibers are embedded in a matrix of material called coir dust. Since husks are porous, they absorb or retain water (Banzon and Velasco 1982).

According to the United Coconut Association of the Philippines (UCAP), the average weight of the husk of the coconut fruit is 0.4 kg. It has been established that 30% of the husk can be obtained as commercial coir fiber (Manas 1974). Of this extractible fiber, 40% is the coarse type usually referred to as bristle fiber and 60% is the finer material mattress fiber (Romualdez 1976).

The coir fiber dust constitutes the remaining 70%. The composition of coconut husk is illustrated in Tables 1 and 2.

Table 1

Composition of coconut huska

CONSTITUENT / PERCENT
Moisture
Lignin
Ash
Alkalinity of ash (as K2O) / 15.0
43.0
8.26
37.5

a Balce, S. (1956)

Coir is a fibrous material found between the leathery covering and the shell of a coconut. The natural color of coir varies from light brown to very dark brown, depending on the variety and maturity of the nut from which it was extracted, and the processing conditions. The fibers are stiff coarse, resilient, pliable and quite resistant to bacterial attack. They have very good water resistance being second only to the black fibers of the sugar palm, Arenga saccharifera (Copeland 1931).

The fibers consist mainly of lignin and cellulose. Cellulose which is water soluble pectins and hemicelluloses make up the bulk in the ground tissue of the husk. Lignin, the other main fiber constituent, is responsible for the stiffness of the coir. It is also responsible partly for the natural color of the fiber.

When viewed under the microscope in cross-section, the fiber is seen to be quite a simple vascular bundle surrounded by a sheath of thickened schlerenchymatous cells. The fibers are made up of elementary fiber cells with varied length of about 0.7 mm and thickness of 12mm-20 mm. The largest fiber may have a length of up to 35 cm and thickness from 0.3mm-1.5 mm, being thickest in the middle, as against abaca, which varies from 0.2 mm-1.0 mm (Child 1974a). In 1935 Hewitt and Thomas made an x-ray investigation of stretched and unstretched fibers of coir and found that the x-ray pattern is similar to that of cotton.

In a study on sulfate chemical pulping of coconut-coir pulp yield correspondingly decreased with the increase of active alkali from 15% to 25%. Screened pulp yields obtained were low and ranged from 36.2% for the high chemical charge with a corresponding permanganate number of 18.4 to a yield of 42.6% and permanganate number of 26.4 for the lower active alkali.

Using an active alkali of 15.6%, it was found that unbleached coconut-coir pulp had the highest strength properties among the coconut-coir pulps studied.

A comparative appraisal of the physical characteristics of pulp from the different pulping conditions showed a trend in the decrease of pulp strength with the increase of cooking liquor concentration. This indicated the prevalence of undesirable pulp degradation with the increase of active alkali.

Pure coconut-coir pulp has low potential physical properties while pure abaca pulp has high strength characteristic. Blending the low-strength pulps of coconut coir with the high-strength abaca and other long fiber pulps produced acceptable commercial grades of paper. Coconut-coir gave the experimental sheet a smooth finish and formation; this was complemented by abaca pulp for the strength properties necessary to meet acceptable standard values. Replacing 70% of the coconut coir pulp with abaca-stripping waste sulfate pulp improved the strength properties of the said paper considerably, but this remained inferior to the commercial kraft wrapping papers tested at Forest Products Research and Development Institute (FPRDI).

The experimental wrapping paper made from a blend of 40% unbleached coconut-coir pulp and 60% unbleached abaca-fiber-sulfate pulp complicated with the U.S. Federal Specifications for Grade B Kraft wrapping paper and also compared favorably with the quality of commercial wrapping papers tested at the FPRDI except for a slight deficiency in tearing resistance. Tests on experimental wrapping papers made from 100% coconut-coir sulfate pulp showed that it had low strength properties. The addition of 33% – 60% abaca fiber pulp improves considerably the strength of the experimental papers. The new samples were comparable to, if not better than, the commercial papers tested at FPRDI.

Table 2

Chemical composition of coconut husk fiber (in percent of dry weight)

FIBER
OLD NUT (%) / YOUNG NUT (%) / VERY YOUNG NUT (%)
Water soluble substances
Pectin, others soluble in boiling water
Hemicelluloses
Lignin
Cellulose / 26
14. 25
8.5
29.33
23.87 / 29
14.85
8.15
31.64
19.26 / 38.50
15.25
9.00
20.13
14.39

Source: G. N. Prabhu, Technologist, Coir Board, India

Experimental offset-book paper, which was produced from a stock furnish of a blend of 60% coconut-coir bleached pulp, complied with the strength and optical requirements of the U.S. Federal Specifications for offset-book paper. In quality, this experimental paper was superior to the commercial offset-book papers tested at the FPRDI (Escolano 1973; Tamolang 1976).

Nature and composition of coir dust

In the extraction of coir fiber from the coconut husk and in the production of finished materials from the extracted fiber, a large amount of coir dust is produced. The coir dust is about 70% of the weight of the coconut husk. It is described as that brown, spongy particle of low weight which falls out when the fiber is shredded from the husk. The composition of coir dust is given in Table 3.

Coir dust is rich in lignins and tannins. Under high pressure and temperature, these compounds soften and act as thermoplastic binding materials (Banzon and Velasco 1982).

The maximum water holding capacity of the dust is reported to be 82.3% and an addition of 2% of the dust to sandy soil is claimed to increase the moisture holding capacity of the latter by 40%. The observations of Croucher and Martinez in 1935 indicate that the coir dust ash is rich in sodium and potassium salts. The sodium chloride content of the ash decreases as the tree is grown further away from the sea. This also contains sodium oxide and sodium carbonate. The potassium oxide content is highest in ash produced at low temperatures and is also readily soluble in water.

Table 3

Composition of coir dust

PERCENT (DRY BASIS)
CONSTITUENT / a / b
Moisture
Ash
Cellulose
Pentosan
Furfural
Lignin
N
CaO
P2O5
K2O / 15.38
6.19
24.25
27.31
17.40
54.78 / 20.0
10.4
33.3
0.3
0.4
0.5
0.9

a/ Gonzales, B.P. (1970).

b/ Joachim, A.W.R. (1930).

In 1980, Wilson reported his results in experiments on the calorific value of coir (both dust and fiber), using the Darroch bomb calorimeter, and found that the average calorific value of these materials was 4.192 calories per gram.

Coconut Coir-Dust Tannin. Tannin was extracted from coconut-coir dust by leaching with hot water at a temperature of 60°C. The tannin liquor extract concentrated, then spray dried. Tannin analysis of the extract by the hide-powder method gave 28.47% tannin and 50.72% non-tannin. This gave a tannin to non-tannin ratio of 0.5 which is lower than of that mimosa extract (2.6), commercial imported tannin extract.

In cooperative study with the Bureau of Animal Industry, using coconut coir-dust tannin extract, FPRDI found that the cowhide and goatskin leather produced was inferior in all aspects to that of hide tanned with mimosa tannin extract (Tamolang 1976).

Tanpowderflourdust. An invention patent, Patent No. 1592, was granted to Lauro A. Ynalvez of FPRDI on August 20, 1964 for his new product. Tanpowderflourdust is a good binder for particleboard and adhesive for plywood manufacture. This binder is phenolic in nature and, therefore, is moisture-resistant (Tamolang 1976).

Fiberboard. Coconut coir and coconut petiole were pulped separately in a laboratory Asplund Defibrator. Medium-density hardboard was made from coconut-coir pulp. The dimensional stability of the fiberboard coconut-coir was excellent. Based on its specific gravity, the coir fiberboards would be classified as semi-hardboard or medium-density hardboard according to the trade definition. (0.40 – 0.80).

Except for water absorption, the thickness swelling and modulus of rupture characteristics of the 100% coir boards meet the requirements of service hardboards or medium-density hardboards. Contrary to previous experience with wood hardboard, water absorption and thickness swelling were not much favorable reduced significantly by the heat treatment (Semana 1975).

Table 4 shows that the carbonization of coir dust and wood gives about the same yields of charcoal and pyroligneous liquor. The coir dust gives a higher gas yield and lower tar yield than wood. The coir dust gas is high in hydrogen and low in methane and carbon monoxide. The total heat content, as shown in Table 5, of coir dust gas is higher than that of wood due to its high non-condensable gas content (Festin and Jose 1979).

Table 4

A comparison of yields of carbonization of coir dust and wood

COIR DUST (%) / WOOD (%)
Charcoal
Pyroligneous liquor
Non-condensable gas
Tar / 40
28.0
27.0
3.5 / 41.3
31.7
17.0
10.0

According to a study by Ricafrente (1980), 1.0 kwh of electrical energy was produced from 8 kg of coconut husk. One liter of diesel oil-fuel is considered equivalent to 8.0 kg of coconut husk. Up to 78% of the diesel fuel oil requirement of a diesel engine driven generator can be replaced by coco husk gas (Ricafrente 1980).

A comparative analysis of the husk, coir and coir dust shows that the dust and coir are similar to Philippine hardwoods in holocellulose, lignin, alcohol-benzene, hot water and 1% NaOH extractives. The lignin, ash, silica, and extractives are mostly contained in the coir dust. These are the principal undesirable components for pulp and paper products. Hence, their removal improves the quality of coir as a pulp and paper raw material (Francia etal. 1973).

Utilization of coconut husk

Coconut husks are generally removed from whole coconuts at the farmsite in close proximity to the trees from which they are harvested. After dehusking, the husks are piled and left to rot in the fields or normally burned as waste. A greater portion however, is used as fuel in farmsite copra making. To a certain extent, husks are utilized in handicrafts, floor polishers and other minor applications.

To some degree also, coconut husk is used for coir fiber extraction. Fiber extraction activities are mainly concentrated in Southern Tagalog and Misamis Occidental in Mindanao. The number of extraction plants operating has fallen from 6 in 1980 to 3 in 1983.

There are two (2) methods of processing the coconut husk: namely, the manual and the mechanical processes. The manual process is simple and no investment for equipment is needed. The coconut husks are gathered and retted in a creek or waterhole for several weeks to loosen the fibers from the pith. The retted husks are then removed and pounded in a round rod to crush and separate the fiber from the pith. The product is a mixture of bristle and mattress fiber. This process is the most widely used in the Philippines because it is very efficient and needs shorter retting periods for the husk prior to debriefing process.

Table 5

Comparison of carbonization gas of coir and wood

GAS / COIR DUST / WOOD
CO2
CO
H
Other hydrocarbons
Fuel value MJ/m3 / 32
16
4
4
9.97 / 54
28
1
2
10.80

A summary of the uses of the fibers produced, their origin and the method of their extraction, is highlighted by Romualdez (1976) in the following list:

EXTRACTION METHOD:

I. Wet Milling Process

Raw Material: Matured Husks

Type of fiber extracted and end uses:

1.0 Bristle Fiber

1.1 Unarranged Bristle

Yarn for Nori Netting

For twisting and rubberizing into bed and upholstery cushioning, car seats, carpets underlays, air filters and gym mats

1.2 Arranged or Straight Bristle

Tawashi brushes

Brush mats

Coir tufted carpet

2.0 Mattress Fiber

Needle pads

Filtration pads

Caulking materials for boats

Upholstery stuffing

EXTRACTION METHOD:

II. Dry Milling Process

Raw Material: Green Husks

Type of fiber extracted and end uses:

Mixed Bristle and Mattress Fiber

Yarn material for carpet and rugs

Yarn material for various mats:

rod mats

corridor mats

ribbed mats

creel mats

bit mats

sinnet mats

III. Other Uses:

Rubberized Fiber

Felting or rigid board of interplaced fibers

Particle boards with coconut husk particle core

Water soluble extract from CH and its application in leather technology

Coconut husk fertilizer

Water reservoir during summer months

Charcoal production

Utilization of coir dust

While a great deal has already been learned about the solid parts of the coconut, coir dust has, up to now, the least use and is still considered waste and nuisance. It is known to have no commercial importance except, maybe, in applications where sawdust is used in a very limited amount.

In an effort to find immediate solution to the perennial problem of coir dust disposal, several product development activities where undertaken that may bring about the large scale utilization of this waste material. The products that showed market potential in the various field of utilization are enumerated as follows:

1. Building Materials

Slabs and hardboard

Composite flooring, ceiling board, roofing and walling materials

Sound and thermal insulation

Sand-replacer in CHB making

Filler in fabricated cement articles

Coirlite (good strength & electrical resistant)

Water resistant board

2. Chemicals

Tanpowder Flourdust,

adhesive for plywood manufacturing

binder for particle board

filler in plastic industry

Activated carbon for absorbent purposes

Tar and pyroligneous acid

Potassium oxide

3. Agricultural Value

Cocopeat

Growth medium

Reclamation of backwater areas

Fertilizer

4. Fuel and Energy

Charcoal briquette

Coco gas

Light oil

Boiler Fuel

5. Novelties and Others

Writing board

Slates

Container items

Lollowares

Glazed board

The non-utilization of coir dust represents a cost to extraction plants both through the neglect of a potentially valuable product and because of storage costs of this waste. In terms of phytosanitary aspect the heaps of coir dust accumulated would also become attractive breeding places for destructive insects and diseases that may destroy the still standing and healthy coconut trees.

REFERENCES

BALCE, S. 1956. A Survey of Potential Industrial products of the Coconut. Paper read at the Symposium on Problem of Coconut Plantation and Industry, Eight Pacific Science Congress, November 1953, Quezon City, p. 23.

BANZON and VELASCO. Coconut Production and Utilization. p. 277 (1982).

CHILD, R. 1974. Coconuts. Tropical Agriculture Series 2nd ed., Longman Group Ltd., London.

COPELAND, E.B. 1911. Philippine Agriculture Forester; 1:44-50.

CROUCHER and MARTINEZ. 1935. Cocohusk Ash As Fertilizer, Chemical Abstracts. 29 1976

ESCOLANO, J.O. 1973. Prospects of Blends of Coconut Coir and Abaca Pulps in Papermaking. FORPRIDE Digest 2(2):43.

FRANCIA, P.C., ESCOLANO, E.U. and SEMANA, J.A. 1973. Proximate Chemical Composition of the Coconut Palm. The Philippine Lumberman 19(7).

FESTIN, T.F. and W.I. JOSE. 1979. Utilization of Waste Coir Dust as a Source of Fuel. Paper presented at the 2nd Recycling World Congress. Manila, March 20-22, 1979.

GONZALES, B.P. 1970. Analysis and Pulping of Coir Dust. Emata, R. (Ed.) 1970. Coconut Research and Development. V.3, UCAP, Manila p. 163-173.