DEVELOPMENT OF AN AGENT FOR TREATING SYNTHETIC AND NATURAL NETS

S. Takayama and Y. Shimozaki Tokai Regional Fisheries Research Laboratory, Tokyo, Japan.

ABSTRACT Specific gravity of a net of some synthetic , for instance 6 or vinylon, is not high enough to secure a quick or steady operation of the net for catching fish. Merits of the net treating agent under report are to increase 11 sinking force and velacity, 2) wear resistitnce, for both synthetic 6ber net as well as net, 3 1 to give better preservation to natural fiber net. When applied to nets of various kinds or natural fiber net, the agent has been found capable of improving fishing efficiency and durability of the nets. Particularly in cases of purse seines for tuna, skipjack or mackerel, and tuna longline, the function of gear treated with &is agent was proved excellent. Application of the agent is getting popular among trawl and set net fisheries.

INTRODUCTION The present research was commenced In some types of fisheries using such several years ago with an idea to prevent the synthetic fiber net as nylon 6 or vinylon with a disfiguxatian of set nets of synthetic fiber in tbe low specific gravity, it is particuIarlg importaat sea by increasing the specific gravity of net itself to find a means by which one may raise sinking rather than by modifying mustrnction of the net. force and velocity of net or rope from their normal The idea first proposed by Dr. Hideaki Miyamoto' levels: Purse seine bbermen who were accus- has been taken over by us in our experimental tomed to handling of tarred natural fiber net have work. Technical assistance and advice have often failed in encircling fisb with synthetic fiber been given to a commercial firm for producing a net because of its slow sinking speed. Attempts net treating material suitable for this purpose. to increase the sinking speed by use of additional Characteristics of net treated with the agent numbers of lead or by modification of the net were evaluated by the staff of the author's labo- structure bave ended in little success. When a ratory. manmade fiber net with a small sinking force The material thus formulated is no8 in a was used for set net fishery, drift of the net stage of commercial production by the name of currents prevented fish from entering the net, thus " Aritoku-Siricorn ". The main constituents are lowered fishing e6ciency. For that reason, net coal-tar and colloidal siIica with mixture of materials made of polyvinykdene chloride group various agents and liquid resins for stabilizing was found preferable for set net fishery, as they dica in tar, for facilitating quick drying on the bave a higher specific gravity than other types applied surface and slow drying among inner of synthetic fiber, even though their dynamic textures of net. resistance is not so high. Coal-tar is one of materials that has been usually tried with a view to covering up these demerits. Tarring a syn- EFFICIENCY OF THE TREATED NET thetic fiber net, however, could not increase With evidences on the merit established enough the sinking speed of the net, as the through a series of laboratory experiments coal-tar is stiIl lower in specific gravity than most ( Table 1 and 2 ), this treating agent has come to of the various kinds of synthetic fiber. Further- be widely adopted to various types of gear more, it retards the net from drying, and makes including trawl, set net, tuna longline, and purse it too adhesive- for. fishermen. - to handle. seine for tuna, skipjack- - and mackerel, As is * Present position : FAOIBTAP Fisheries Technologist, Central Pisheries TechnologicaI Station. Cochin, India. obvio~sinTable1,thewei~htofwebbingiaair r.p.rn.for3minutes. Despitethencarlyiden- which is increased by treatment has a large tical procedure of treatment,the absorbed amount influence upon the characteristics of the treated of the agents, as expressed by the weight increase webbing. The sample webbing was treated with in webbing measured in air, was found &fierent either one of agents, A, B, or C (cod-% Aritoku- from one kind of agent to another, natumllT due Sicorn Type PSI or Type S1) in a bath for 5 to different specific gravity among the agents minutes at 7VC, and then centrifuged at 3350 used (Table 11.

TABLE 1. itacrease in weight, specific gravity and sinking wlocity of webbings by various trcdmnts - - Treating Increase of net weight Speciic mavity Sinking Rate of increase webbings agents in air In water Treated Treating velocity in the velocity (%I (%) webbings agents ( cdsec ) (%I

In the tarred webbing, the weigbt increase take, for example, skipjack purse seines operated measured in water remained nearly 100 per cent in the Pacific waters 100 to 400 miles off the of the non-treat4 one. In the samples treated northeast coast of Japan. Of the total 3eet by Aritoku-Siricorn (B and C in Table 11, engaging i~ that type of fishery, the number of however, it was 200 to 400 per cent over the boats using the seine treated by the agent oc- control. The weight increase in water is greater cupied 30 per cent in 1959, and 65 per cent in for the samples treated by B or C than that for 1960. It is estimated that their catches exceeded tarred ones I A 1. The fact is attributable to 25 to85 per cent over those harvested with tarred differences that have been introduced in the purse seines. specific gravity of the webbings by the treatments. Another advantage the agent has over the The weight increase resulting from the present coal-tar is that its portion applied on the surface treatment also raised the sinking velocity over of a net dries up quickly, while another portion that of the control to a higher rate than in the imbued into the texture of the net does so slowly. case of tarred samples (Table 1). This would In the present work the amount of tar to be enable a fishing net treated as under report to absorbed by the net was controlled centrifugally. remain steady against drift by current and to bold Yet it took two weeks or so for the tarred net a good shape for encircling fish schools. As the before its surface dried up (Table 2 1. This slow volume increase resultant from the treatment was drying of tar is perhaps the strongest reason that relatively small, hydraulic resistance of the net makes fishermen hesitate from re-treating their was small enough to permit easy up-hauling of nets with tar in a short intermission they have the net. As an evidence of these merits one may during a season. Furthermore, a tarred net kept A : Coal-tar. B : Aritoku-Siricurn Type PSI. C : Aritoh-Siricorn Type Sl. D :Won-treated. piled up one layef above tifiothet oil the deck, The net treated with Aritokn-Siricarn, on conglutinates together and is very often ripped the other hand, could dry up in one-third of the off in part at the time of paying it out. days needed for the tarred net. Stiffness measured for each sample with four mesh openings and five knots (Fig. 1) by a cantilever method was small in the treated samples, as the agent would not be readily hardened among fiber tissues. This secures for a &herman easy and efficient manipulation of his net. No wnglu- tination as is the case with tarred nets happens to the net treated in the present manner. This has greatly reduced chances of such an accident as the net being ripped ofE, at the heof paying out. Increase in dynamic resistance is another advantage the agent offers as in Table 2. Tes- ted with specimens prepared in the same man- ner as for stiffness, tensile strength was augmen- ted for the treated webbing 30 to 50 per cent over the control I D ). In wear resistance the treated webbings ( B and C 1 were 10 to 13 times Iin case of nylon 6 1, or 1.8 to 2 times ( in case of vinylon 1, stronger than the control (Dl. The increase in durability secured the treated net from the fear of being broken by the weight of catch at the time of hauling. The decrease in abrasion loss extended the service life of tuna longtine to almost twice as long than before. Increases in sinking veIocity and force made the Fig. 1. A specimen for determination of stiffness treated longline fairly free from the possibility and tensile strength. of forming kinks at the time of operation.

TABLE 2. Chmge in characteristics of the webbings by various treatments - Shrinkage Time to Stiffness Tensile Elongation Wear resistance** Webbings ~~~~~$gof webbings dry up strength (%I (day) (-1 (kg) (%) ( times 1 A 2 12 7.6 57.4 (1.3 263 222 (3.2 Nylon6 8 3 4 7.2 56.7 ( 1.3) 24.3 744 (10.8) (Amilan 1 C 3 4 6.4 56.4 ( 1.3) 24.8 946 ( 13.7) D - - 4.9 45.2 (1.01 27.0 69 (1.0) A 8 14 6.5 1 ( 4 39.2 127 ( 1.4 ) Vinylon 3 11 4 6.3 29.6 (1.5) 43.1 181 ( 2-01 Cremona) C 11 4 . 6.2 29.7 ( 1.5 ) 53.0 171 ( 1.8 ) D - - 4.9 20.0 ( 1.0) 31.5 93 ( 1.0 1 * See footnote of Table I for explanation. ** Determined by the use of the apparatus with a steel edge as in Fig. 3, Numerals in parentheses indicate ratio of tensile strength or wear resistance expressed on the basis of the non-treated samples. TABLE S Chctracterisbks of Manila mine treat& wish Arhka-Sirborn of other agents Tensile Knot Wear resistance* sinking Treating agwts Strength Strength Test A Test El velocity ' (kg) (kg) ( Number of abrasion ) cmlsec ) Non-treated f 5.4 11.3 -~Il.oO) 1313(1.00) 6.8 Cut& solution 15.9 11.3 112(1.67) 1194(1.36) 6.8 1% Kfiq after treamvnt with 3%Cutch solution 15.9 123 6 1455(1,11) 6.9 Copper naphtenate 15.1 11.4 A34 (2.00 1837 ( 1.43 ) 6.5 Coal-tar 14.4 11.1 462(6.90) -3172(2.41) 7.4 , Aritotu-Sirim PSI. 15.6 11.7 482(7.30) 469613.57) 8.9 Application of this agent to natural fiber CONDITIONS FOR THE TREATMENT net has proved effective in increasing not only In applying Aritoku-Siricorn, the more the wear resiswnce but preservation of the net as amount of the agent absorbed by the net, the well (Fig. 2 ). For this reason, expense for net greater will become the sinking force and material could be greatly saved for trawls which velocity. But on the other hand, this also ex- were operated along coast of the Japan sea. the tends the time needed for drying the treated net, and makes the net adhesive. Therefore, one has to determine an optimum amount of the agent to be absorbed by a nee. According to the experiments chedout so far, the optimum rate of the absorbed amount is, on the basis of the initial weight of net, W to 100 per cent for nets of nylon 6, and 100 to 14.0 per cent for vinylon nets. Where a centrifuge is not available, a net is often spread for drying after treating it with the present agent. In tbat case, the absorption rate was found 140 to 170 per cent for nylon nets, and 150 to 230 per cent for vinylon nets. As the mount absorbed by coal-tar treatment using no centrifllge is usually 90 to 120 per cent or 120 to 180 per cent for nylon or vinyl~nnets, respectively, the mount resulting from the un- controlled treatment with the present agent is 40 to 50 per cent higher than from uncontrolled tarring. If the absorbed amount is at a high Fig. 2. Change in tensile strength of natural fiber adhesiveness and conglutination twines treated with various preservatives level like this, and submerged in sea water. of the net would surely adversely afEect opera- 0...... Treated with K2Crp7 1% solution after tional efficiency and accidentally tear the net with cutch 3% solntion. asunder. Therefore, even in the absence of a A ...... Treated with cutch 3%solution. centrifuge, one should contrive a means to keep ...... Treated with coal-tar. @...... Treated with Aritoku-Siricorn. the absorbed amount, as close as possible, to an Solid lines show the change in tensile strength of optimum level. twine and dotted lines Manila twines. From the point of permeability and dye- T Tensile strength before immersion. .,..., ta TO ...... Tensile strength after immersion for fastness, it is generally desirous have a hinh some days. temwrature fir the treating bath. In case of &e in by us% in B. * The resistance was determined, test A, the of the a~naratasas in-- Fip. 3. test - * - .---- by another which had an oil stone with a ro&d ridge as in " The Modern Fishing Gear of the World " ( Fig. 8, p. 27. FAO, 1954 ). Numerals in parentheses are the ratios of the resistance erpresed on the basis'of the value of the non-treated twine. present agent, which boils at 80'C, and ignites product bas not yet been made to a satisfactory at 130°C,however, heating the bath above IOO'C level. In preliminary tests so far conducted, is dangerous. On the other hand, it is d&cult however, the rate at which the agent is washed to imbue the agent into texture of the net at a d a beated net is lower by 40 to 71) per cent than batb temperature Below 20eC, as is the case with the mte tarcoal shows, when compared on the -1-tar. In addition, shrinkage in webbing basis of the initial weight of each agent absorbed treated with this agent is somewhat higher than by a net. In skipjack and tuna fishing a tarred that resuhant from tarring (Table 2 ), as at the purse seine needs to be re-treated before every higher the bath temperature, the greater is the seasan and sometime inIthe middle of the season. shrinkwe. Taking these factors into account, Whereas, one treated with Aritoka-Siriemn can an optimum temperature for the present treat- be used in. succession, for two or three seasons ment was determined at 70' to 80°C for nets of with no need of re-treating during that interval. nylon 6 or vinylon, -50O to 60°C far polyvindi- In this regard, similar data have been obtained dene ( Saran acd to chloride Kurehalon 1, and 30- also from tune longline. Upon examining the 40°C for vinyl chloride ( Teviron and Envirron 1. durability of the agent which may vary from one The agent applied to a net at a temperature below these ranges is liable to be washed 03 kind of fiber to another, we have found that nets while in use. For nets of vinyl chlorideor ply- of nylon 6 or poly~in~lidenechloride separate vinylidene chloride, a batb temperature higher the agent faster than any other kind of fiber tes- than these specihed above may reduce dynamic ted. Next to them, vinyl chloride or Manila resistance of a net. hemp follow. Separation of the agent from cot- In regard to cases where an agent is ton or vinyIon nets was the least among the washed off a treated net, durability of the present variois kinds of fiber under report.